I’ve been dreaming of doing a Tangent Ascent build ever since I first read about it in Karl Gesslein’s excellent review of the unit late last year. The more I researched this mid-drive, the more interested I was. Ron (spinningmagnets) wrote a great overview of the drive here on electricbike.com shortly after it was introduced in late 2015, and I’ve probably read every word written about the unit on the Tangent Motors web site at least 10 times. After I got over the initial shock of the package’s $2300 price, I realized this drive system used the highest-quality components available, and was quite a marvel of engineering by its creator, Dave DuBose. While some huge hub motor systems exceed it in raw power, the Ascent seemed to be the ultimate compact and high-powered mid drive.
The road leading to my dream build
I own the Kuberg FreeRider e-dirt bike that I reviewed here a few months ago. I really enjoy the bike, and it’s very powerful, but…it does have some drawbacks. First, being designed mainly for teenagers, it’s a bit small if you’re much over 5’8″. And, it looks like a motorcycle – which could potentially be a problem with other trails users if you are riding on mixed-use trails that are shared by non-powered cyclists and hikers.
While I always rode responsibly and never had any problem encounters with other trail users, I always dreamed of similar power and performance, in a dual-suspension mountain bike. Being able to keep all the advantages of a bicycle – light weight, being able to pedal as well as operate under power, and to fly more ‘under the radar’ when riding on mixed-use trails – was really appealing. A great dual-suspension bike powered by the Ascent seemed to be the perfect solution.
Indeed, in Part 2 of my Crazy e-Bike Pricing article, I described my ultimate off-road e-bike dream build – the Canyon Sender DH bike, powered by the Tangent Ascent. Finally, after several months of planning, work, saving, and pulling parts together from across the globe, I’ve been able to make my dream build come to fruition. I chose the Canyon Strive AL 6.0 Race – an Enduro bike – rather than their sleek Sender DH bike, for one main reason. Even though the Sender is great – the ultimate off-road bike, in my opinion – it has no room for a frame-mounted battery inside the triangle. When I thought about the design for this build, I wanted a bike that could use 2 different battery packs: a smaller, inside triangle-mounted pack on the bike for convenience, and a larger pack that would be kept in a backpack, to unleash the full 6kW potential of the Ascent. As the Sender DH had no room for a triangle-mounted pack, I chose the Strive and immediately got to work on designing a custom battery pack that would put as many cells as possible inside the tight space.
I should also mention: I paid for the Tangent Ascent system reviewed here with my own money. It was not a freebie, nor a review sample provided on loan. Now that I’ve owned the Ascent for over a month, and have abused it (and the bike) relentlessly during that time, I can say that it’s all I was hoping it would be, and more. Many times while riding I found myself not only smiling, but breaking into spontaneous, out-loud laughter. To me, this is the best proof of amazing performance: something is performing so far above expectations, so far above the usual for that type of thing, that you can’t help but laugh in joy and amazement. I have found this ‘spontaneous laughter’ test also works in the case of A/V gear, as well as high-performance cars. Back when I was reviewing home theater equipment, occasionally an audio system or a projected image would be so spectacular, so amazing, so above what everything else could provide, that you couldn’t help but laugh out loud at how amazing it was. Same thing happened to me, many times, while riding my Tangent Ascent bike.
The mid-drive, with its internal cycloidal gear reduction, is an engineering masterpiece
Let’s do this a little differently and get immediately into the pros & cons of this unique mid-drive system. These will serve as an ‘executive summary’ and outline for the review, and I’ll expand upon each point below.
Immediate, strong, neck-snapping power
Can’t handle a 14S (52V) battery pack when it is fully-charged to 58.8V
Great power/responsiveness even at lower amps (e.g., 50A)
Requires a very strong battery – 120A – to make full use of the Ascent’s 6kW power
Light weight, very compact
Some bike frames can’t accommodate the battery needed inside the frame triangle, meaning a backpack battery must be used
Can be mounted on modern, swoopy downtube frames or inside the frame triangle
Bike drivetrain will likely require upgrading
Can use as a surprisingly effective PAS system – even though not designed for this
Needs some maintenance – grease must be injected into the drive every 100 miles
Incredible build quality & engineering
All components are top-notch
Included Domino throttle is by far best in the industry
Great freewheel, you can easily pedal and ride like it as a non-powered bike
New, updated Ascent version uses revised windings in Astro motor to reduce heat and increase RPM
More fun than should be possible on a bicycle
Adapting RC gear into high-performance e-bikes
First, if you aren’t familiar with the history of the Tangent Ascent, I won’t repeat it here. Read the excellent articles by Karl and Ron, linked above, for more background on the drive. To summarize, the Ascent uses the US-built and very powerful Astro 3220 motor in its 6kW version, and the smaller but still powerful Astro 3210 in the 3 kW Ascent. The Astro motors come from the RC world, where they are famous for powering large-scale RC airplanes. Astro motors have been of interest to high-performance electric bike builders for a long time – Matt Shumaker from Recumpence has been building some crazily high-powered Astro-based drive units for a few years now – some even with three 3220s powering them. And electricbike.com founder (and Luna Cycle owner) Eric Hicks has also experimented with various powerplants based on the 3220.
Two main issues always seemed to come up with Astro-based builds: gear reduction and heat. The 3210 & 3220 love to spin fast – up to 10,000 RPM – and reducing that high RPM to a 150RPM maximum to match human pedal cadence has proven to be a difficult task. To do this extreme reduction in a very compact size package has been even more difficult. The second issue some builders encountered was overheating – since the Astro motors are designed to be put into RC planes, with a constant stream of forced-air cooling, they can get pretty hot under the constant high load and reduced passive cooling of an e-bike environment.
Dave DuBose, founder of Tangent Motors, has developed his ingenious mid-drive system based on the Astro motors that seems to overcome these problems. He designed an extremely compact cycloidal gear reduction system that provides a 40:1 reduction ratio, in a package only a few inches long and barely larger in diameter than the Astro motor itself. In his own machine shop, he produces the gearbox and components for the drive. Gears for the cycloidal reduction are chro-moly steel, and the housing and mounting brackets are milled from aluminum. To address overheating, the entire enclosure acts as one huge finned heatsink. And the newly updated version of the Ascent uses a new motor winding that Dave says increases efficiency and RPM, while reducing heat.
For e-bike or engineering geeks, these gears are pure porn
Since the entire mid-drive is so compact, it allows some very useful mounting options. First, the drive can be mounted inside the frame triangle on some bikes, which could be very useful depending on your application. Also, many modern high-performance Enduro and Downhill bikes (dual suspension, off-road type) use a long, swoopy downtube design rather than a straight tube going up from the bottom bracket. Like on my Canyon Strive, this design not only looks great, it’s one of the key elements for the bike’s great handling. The problem with this is that for traditional mid-drives like the BBSHD, the motor must hang straight down – like a cow udder – from the bottom bracket. This gives your bike frighteningly little ground clearance and makes it unusable for serious off-roading.
Before installing the Ascent on my Strive, I installed a BBSHD/Ludicrous mid-drive to test and see how it fit the bike. Technically the motor did fit the bike – I was able to get it installed easily and the bike did run under power. But I was so afraid to hit the motor housing or controller when going over a bump, curb, or hill, I couldn’t enjoy riding it. I kept this configuration for about a week before deciding it was best for the health of my BBSHD, and my sanity, to take it off. Much like a thong in size 24, just because something’s technically possible doesn’t mean it should be done.
With swoopy, modern frame designs, the BBSHD hangs down dangerously low
Looks pretty, but not good for trail riding
Unpacking & Installation
One area where you can tell that Dave DuBose is an engineering genius, and not a marketing guy, is in the packaging of the Ascent. To me, something with this level of engineering brilliance should be packaged like the fine jewelry that it is – in a beautiful custom-designed box that opens to reveal each component, perfectly coddled in custom-cut foam, on display for gawking and appreciation before undertaking the build process. Instead, my dear (and I mean this in both the affectionate, and the expensive way) Tangent Ascent came in a surprisingly small, nondescript brown box with each part wrapped in brown Kraft paper. Well, the main thing is that it came undamaged, and that the drive rocks.
The system comes complete with everything you need – drive, mounting brackets, Cycle Analyst v3 and cables, drive chain, spider, cranks, White Industries HD freewheel, Truvativ Giga Pipe ISIS bottom bracket, chain, Domino throttle, and beautifully-built power cables. But definitely, the packaging could use some work to live up to the quality of everything else in the kit. This thing deserves to be packaged like the fine jewelry that it is.
It was a very good day when this package arrived at my door – just needs a better box
Installing the Ascent was fairly easy and straightforward. The kit can include mounting brackets of different lengths to best accommodate your frame. Tangent’s site has drive bracket templates you can download and print out, to see how the drive will fit for your particular application. For my medium size Strive, the 220mm bracket proved to be the best match – it puts the drive high up and out of the way of obstacles. My ground clearance after the drive was mounted was barely less than it had been sans drive! The Ascent is available in 68mm BB width, as I used for the Strive, as well as 100mm and 120mm versions for fat bikes.
Drive template helps you imagine how the TA can be mounted
The scariest, and most butt cheek-puckering part of the entire install, was the very beginning. The Ascent uses a threaded ISIS bottom bracket, which luckily matched the threaded BB on my Strive. But I was so worried about stripping one, or both, of these, that I probably test-fitted the threading 10 times before really starting to thread it in. I greased the outer threads on the BB and very carefully started threading it into the BB. Thankfully, the Truvativ BB went in OK and nothing got stripped, but I was really worried there for a while. Currently, the Ascent is only compatible with threaded bottom brackets, but Dave says that versions which accommodate PF (press-fit) BBs will be available in the near future.
Once the Truvativ ISIS bottom bracket was in, rest of installation was easy
Once that was in, everything else was easy. Various length mounting straps are included for securing the drive to your downtube. I attached my 32T RaceFace narrow-wide chainring, cranks, pedals, and both chains. Then I wired up and mounted the CA3, connected my frame battery, and powered her up. That was when I first hear “The Sound” in person, and I have to say, I really liked it. This being my first build using the Cycle Analyst, it took me a while to figure out how to get into all the menus and set up all parameters as I wanted. Yes, the CA3 looks like something from 1983, and is in bad need of both a case and a display makeover, but at least it’s functional. Besides being easy to read in all different kinds of outdoor light, the coolest feature that I liked about the CA3 is its ability to program and remember 3 different power level settings, which can be accessed at the touch of a button.
Spider, cranks, and drive chain mounted
This is very handy for uses in cases like this build, where I’ll be using the drive with three different battery packs. You can set a maximum power (watts, amps, or both) limit for each power setting to best match the battery that you’re using. On my bike, I set up Lo/Med/High power settings for my 52v packs, with the amps limited at 40A, 80A, and 110A respectively. One strange thing about the CA3, at least for those used to BBSHD builds, is that the speed sensor mounts on the front wheel rather than the back. It took me some thinking to decide how to run the cable so it wouldn’t interfere with the Stive’s 160mm front suspension travel.
Test-fitting my homemade 14S / 5P frame pack for the bike
One thing you must consider carefully when deciding to build a TA-powered system, right from the start of designing your build, is what battery you will use and how it’ll be mounted. Many bikes shown on the Tangent site are super-sleek DH bikes with no room within the frame triangle for a battery. These builds require using a backpack battery; no other battery mounting option is possible (except maybe for a Mighty Mini under the seat – a bad idea as I’ll explain below). I hate backpack batteries. But I knew that for my build, in order to reap the maximum 6kW power from the Ascent, a backpack battery would be needed. As mentioned earlier, I chose the Strive because it has just barely enough room inside the frame triangle to mount a compact but powerful triangle pack. I build all my own battery packs now, and I knew that a custom-built pack would be necessary to fit inside the unusual shape of the Strive’s frame triangle.
My custom pack, almost ready to mount in the frame
When designing this build, I knew I’d be using 2 different packs (3, actually) to power the bike. The smaller, 14S / 5P triangle pack would be mounted inside the frame and be used for convenience for those times I didn’t want to lug around a backpack battery (almost always). But since the pack was built with very high-output Samsung 25R cells, it’d still be capable of providing plenty of amps to the hungry Ascent. In the CA3 program, I limited the pack’s amp draw to 80A to preserve the pack, but this compact pack is capable of 100A maximum.
I also built a larger, very beefy 14S / 8P pack based on the same 25R cells, with a massive 150A continuous BMS, for use as my backpack battery. This pack would be used when you need to get the full 6kW potential from the Ascent, or when extra-long range was needed. Besides these two packs, I also built a ‘mini cube’ 14S / 2P battery pack that can be mounted under the seat, for use as an emergency extra power supply, or to try riding the bike in its lightest form possible.
Just keep in mind, if you’re planning a Tangent Ascent build, what battery you use with it and where you’ll mount it. The Ascent loves amps – I’d recommend at minimum a triangle pack that can deliver 50A continuous. Interestingly, I did a couple entire test rides with the bike set to a 50A limit, to mimic the 2500w maximum power of the BBSHD/Ludicrous combination (or the power of using a 50A max continuous battery pack). I found that even limited to 50A, the Ascent still ripped – it had strong acceleration and immediate responsiveness, and was still a joy to ride. So if you get the Ascent but think you’re missing out because your battery ‘only’ provides 50A max – don’t worry, the Ascent is still hella fun when limited to 50 amps.
If your mind is set on a backpack battery as an easy solution for a bike with no space in the frame triangle, no problem – but do a test first. Load a backpack with 10-12lbs. of dense weight, then attach an umbilical cord from the pack to your bike’s frame. Do a couple full rides (1-2 hours) like this and see if it bothers you or not. Being an old motocross guy, I ride mostly off-road, and stand a lot. For my riding style, the weight of the backpack battery and the way the power cord inhibits standing while riding really make backpack battery usage unappealing to me. In the time that I’ve been testing the Ascent, I’ve probably put 15 charge cycles on the smaller frame-mounted pack, and 2 cycles on my backpack battery. This brings me to the next point, and the first real problem area to discuss about the Ascent – the voltage limit due to its controller.
The 58.8V Problem
The Tangent Ascent kit is advertised on Tangent’s site as working great with Luna 14S (52V) triangle battery packs – this isn’t completely correct. At issue is the drive’s Castle Creations Talon HV120 controller. While this RC-based unit is small, light, and super-powerful – all great attributes to have in a high-powered mid-drive – it does have a limitation when it comes to e-bikes. This other main component of the drive system also comes from the RC world – Talon controllers are made for high-powered RC helicopter applications. Dave fills the controller with potting compound to help it be more water-resistant for e-bike usage.
But there is a problem: the Talon HV120 is designed for a maximum 12S LiPo battery pack – that’s 50.4V max, as shown on the company’s site here. In the e-bike world, we like to use 14S packs, which are 52V nominal. These have several advantages over using 48V packs (discussed in previous electricbike.com articles). But the problem when using these with the Ascent is that, fully charged, 14S packs put out 58.8V – way above the controller’s 50.4 maximum design spec. After completing the build, I first test-drove my Strive with a half-charged pack (about 50V), and everything worked perfectly. Then, I fully charged the pack for a full off-road test drive the next day.
However, when I tried to test the bike on the stand, I found that the motor would apply power for a fraction of a second, then cut out. Let off the throttle, then apply throttle again, and it’d do the same thing. Power would apply for a fraction of a second, then cut off. I thought something was seriously wrong with my kit – I didn’t know about the HV120s voltage limit. After readying up on the controller, I realized that I was probably over the max voltage the controller can handle. An e-mail to Dave DuBose confirmed my intuition, that a 14S lithium pack hot off the charger is just above the voltage limitation for the HV120.
Castle Creations Talon HV120 controller is compact & powerful – but can’t handle 58.8v
The next days were filled with extensive testing, to learn just where the controller’s high voltage limit lies. I found that you can reliably feed 57.4V to the HV120 and it’ll work perfectly – which is pretty amazing, considering the unit is designed for 50.4V maximum. The HV120 gives status beeps upon power-up that indicate any error condition, as well as telling you how many series cells are in the battery pack you have connected. In the case of my 14S pack at 57.4V, it always gives you 12 beeps – indicating a 12S pack. But this makes sense, as the unit is designed for a 12S pack maximum. If you feed it 58.8V, the controller just beeps twice upon startup. Anyway, 57.4V is the max.
The positive side to this is that 57.4V is also (coincidentally) the exact voltage of a 14S pack charged to 90% – so you could implement a regimen of charging your pack to only 90%, which will greatly extend the life of the pack. The downside to this is that sometimes the pack still needs to be fully charged, to balance the cells. Also, you’ll need to purchase a charger that can charge to 90% – either the Luna Advanced Chargers can do this, or the Cycle Satiator from Grin Technologies.
The problem is that none of this is mentioned on the Tangent Motors site – from reading the site, you’d think that everything will be hunky-dory using a 52V triangle pack from Luna, with no issues at all, but this simply isn’t the case. The Ascent is not fully compatible with 14S lithium battery packs. 57.4V is the max the HV120 can reliably take, and that means either you need to use a 13S (48V) battery pack and not worry about it, or use a 52V pack and charge it to 90%. After much practice, I did find a ‘kludgy’ way to get the Ascent to work with a fully-charged 14S pack, hot off the charger. But it’s pretty abusive to your drivetrain, and requires some huge open area, so I can’t recommend it as a practical fix or workaround.
From a dead stop, if you blip the throttle, then let off, the bike will lunge forward a bit. Do this 3-4 times to get the pack below its full 58.8V charge. Next, make sure you have LOTS of open space ahead of you (think airport runway), and it’s preferably really flat terrain. Because you’re going to go forward at a pretty rapid pace and have to stay on the gas. Quickly twist the Domino throttle to 50-60%, make sure your weight is forward so as to not wheelie off the bike, creating your very own “and you know the bike is dangerous” video moment. The bike will lunge forward and the power will not cut off, as long as you stay on the throttle.
I figured out that this is because the instant heavy load on the pack causes the voltage to drop below the controller’s 57.4V limitation. As long as you keep the motor under heavy load, the voltage will stay below this limit and the power won’t cut off. But it feels very abusive to the drivetrain, as well as being pretty damn scary unless you are in a wide, wide open area. Anyway, I learned to live with the Ascent’s voltage limitation and found it to be only a minor negative. With my big backpack battery, I normally charge it to only 90% anyway, to maximize the lifespan of the pack. With my frame pack, I charge it to 100% in order to get the most watt-hours/riding time from this smaller pack. Using the kluge described above, I’m still able to use the bike even on a full charge. But this limitation should be clearly stated on Tangent’s site.
The Tangent Ascent oozes quality – build quality of the drive, and all the related components, is awesome. As I said before, it’s like engineering jewelry. Tolerances are tight, everything fits perfectly, and it feels solid and high-quality. All the components feel solid and quality – the freehub, spider, sprockets, and mounting brackets all look and feel great.. The drive unit is solid, but not too heavy at 9 lbs., and it’s surprisingly compact. With the long 220mm bracket, the drive fit my Canyon Strive perfectly.
The Ascent oozes quality – even the chain tensioner is a work of art
I finished the build in the evening, so I decided to just take it around the block for a quick test-drive, before a full trail ride the next day. Using my 14S / 5P frame pack, I chose the 80A medium power setting on the CA3. At my pack’s 57V charge, this meant an effective maximum power of about 4560 watts. That’s 6.1 horsepower. Not bad for a 50 lb. bicycle.
I twisted the silky-smooth Domino throttle. My first thought – holy, holy crap. The bike leaps forward urgently with each throttle application, like it’d just been rear-ended by a KAMAZ truck. With my BBSHD builds (including those with the Ludicrous), when you hit the gas, it’s like your request for instant acceleration goes through a Bafang committee inside the controller. They say, “OK, we got your request for acceleration. You’re asking for quite a lot. Here’s your acceleration, you can gain speed at an enjoyable, but prudent and reasonable rate.” Then you get some nice, smooth, fully-loaded-747-taking-off-like, gradually building acceleration. Nothing that really gets the adrenal glands pumping, but it’s pleasant nonetheless.
Not so with the Tangent. Your request is sent directly from the Domino throttle to the electrons just waiting to get out of those 25R cells, and the controller sends a bunch of those sombitches to the Astro 3220, like RIGHT NOW. No committee here to approve your request for instant acceleration. It just hauls ass. Ask it to do the same thing again, no problem. And again. And again. To the point of doing it so many times that, to bystanders, this must look really childish. Wheelies? No problem. Donuts on dirt? Easy. On cement? Even more fun. So, yeah: nice, smooth gradual power is fun. But instant, hard-hitting power is awesome. There is a big, big difference in the riding experience.
Special mention has to go to the Italian-made Domino throttle that’s included with the kit – this is by far the best EV throttle that I’ve ever used. Besides how great it just feels mechanically, it has a smooth, progressive, linear voltage ramping that makes it very easy to control the exact amount of power you want to apply, with complete confidence. Plus, in the CA3 you can program the throttle mapping to exactly match your taste and riding style. I love this throttle so much, I want to get one for all my electric bikes and scooters. It’s a $100 throttle, but…it is worth every penny.
The next day, with a fully charged pack (and backpack battery charged to 90%), I took the bike to my local mountain trails for some real off-road testing. It was a weekday, mid-morning, so the trails were almost totally devoid of hikers and cyclists. There are some very big, long uphill sections in these mountains, as you can see in this video I shot – note that the sound seems louder on the video than it does to bystanders. Also I had the throttle pegged during much of the video:
The most noticeable improvement, and change, compared to the BBSHD, is on large uphill sections of the trails. On big hills, which I previously trundled up at 12mph maximum with the BBSHD, the TA fairly flew up those same hills at 25-27mph without even getting out of breath. With my solid 190+lb. butt and 50lb. bike, it was really pretty amazing. All this, with my compact frame pack limited to 80A max – I wasn’t even using the Ascent’s full 6kW potential.
Then, I tested the bike out with my two other self-built packs. First was the massive 14S / 8P, 150A-capable backpack battery. I set the CA3 to its high power setting of 110A (120A is technically the max the Ascent can handle, but I decided to limit it to 110A as I was afraid for my drivetrain). Surprisingly, for about 90% of the trail riding, the greater power potential was not noticed or needed. It was only in a very few cases that I needed more than the 80A that my smaller pack could provide. 110A at 52V is a LOT of power, and I really only pulled that much when I tried a couple high-gear top speed runs. Of course, I noticed much greater range with this pack – with this 20Ah pack I got in over 2.5 hours of mountain trail riding before I was exhausted – and the battery was not even down to LVC yet. With my 12.5Ah frame pack, I was able to trail ride about 80-90 minutes before the pack reached LVC.
My huge 14S8P, 20Ah backpack battery provided long range and 120A power – but wasn’t comfortable to carry
But, I found that I enjoyed using the bike much more with the smaller frame pack, even thought it had less power. This was because I could ride and move freely without the burden of a backpack or umbilical cord, and the reduction in power running at 80A was barely noticeable. As mentioned above, for fun I also tried a few rides limiting the Ascent to 50A, to simulate what it’d feel like with a 50A max pack (and to match the power level of a BBSHD/Ludicrous combo). Again, the TA still provided great power, and great fun, even limited to 50A, or about 2800w at a full 57v charge.
Finally, I tried the bike with my tiny 14S 2P 25R mini cube battery, mounted under the seat. It was pretty incredible to have such a light bike (about 43#, with this pack) that could still take off and fly up hills. Even though this pack can provide 40A continuous, I set the power limit on the CA3 to 30A, to preserve my little pack. The small pack works fine as an emergency power supply, or for light PAS duty, but the Ascent really demands too many amps to be compatible with such a tiny pack. 25Rs have very little voltage drop – they’re one of the best cells out there when it comes to not dropping voltage under high load. But even with the strong 25Rs, I saw pretty significant voltage drop under power, even just off a full charge. I rode the bike for about 40 minutes on the trails with my mini cube, using a very light touch on the throttle along with some PAS (more about this below), and decided that had been enough torture for my poor little pack.
CA3 looks ancient, but allows 3 power/amp presets. Domino throttle is amazing
Each of the 3 packs I made for the bike provided a different experience, but one thing was consistent while riding the bike off-road – it was incredibly fun. I must’ve smiled hundreds of times, and laughed out loud at least a dozen times, during the first week of test-riding the Strive/TA combo. It was simply awesome fun to ride, and it felt like it was more fun that you should be allowed to have on a bicycle.
Any Overheating Problems?
I was pleasantly surprised: even beating on the Tangent Ascent through huge mountain trails, riding for over an hour at a time, it didn’t get too hot. The Ascent has an internal temperature sensor that is connected to the CA3, and provides the rider with constant feedback of the motor’s temp. My trail rides would start with the motor at about 28 degrees C. Then, after about 80-90 minutes of hard off-roading, the highest temps I saw were only 62-64C. When riding flatter trails or on the road, the Ascent rarely rose above 54C. In the world of high-performance electric motors, these temps are very cool indeed.
After my trail rides, I checked the temps with an IR thermometer which showed the TA to be even cooler than what was shown on the display. The motor case, and gearbox housing, rarely showed over 50C. Since Astro rates the motor and its windings to handle up to 200C, the fact that the Ascent stayed below about 64C in all my thrashing on it is pretty incredible. I think passive cooling could even be further improved for the TA, though: on the 6kW version, with the 3220 motor, the butt of the Astro hangs out pretty far from the aluminum housing. Currently it has no heatsinking on it, however, the cool radial heatsink that Dave designed for the housing could be extended to cover the rest of the motor housing. While not providing the effect that active cooling would, this extra heatsinking would surely help passive cooling and keep temps even lower.
Even after hard trail riding, the Ascent didn’t overheat – but more heatsink area on the Astro 3220 motor would be welcome
I did have one situation where it got pretty warm, though. I needed to get the voltage of one pack down before putting the pack into storage, and didn’t have the time for a long ride. I don’t have a load tester on hand, so I put the bike on a stand, locked the throttle to about 70%, and let the rear wheel spin in 8th gear. This was only draining about 300-400W, but I had planned to let it run a couple hours this way until the pack was down to 52V for storage. I was doing other things in the house while it was running, then after about 45 minutes I walked by the bike and noticed an unusual (and not good) smell. Something was definitely getting really hot. I looked at the CA3 and was shocked to see the internal temperature reading at 120C! I immediately shut the bike off and let it cool down.
Nothing was damaged, it ran fine after cooling, but I was pretty shocked to see the motor get so hot running under almost no load for a long time. I don’t know if this means that after very long constant running time, the Astro always gets very hot, or if this would be an issue for long-distance commuter bike applications. The motor was still well under its 200C design spec maximum, and was not damaged, but it was still pretty surprising to see it reach 120C while just spinning on the stand for a long time.
My unit used for this test is Serial #1 for the newly updated version of the Ascent which is designed to dissipate heat better. Dave has spec’d different windings from Astro, which he says allow the motor to create less heat and also spin faster at the same time. Since the motor spins faster than the previous version, all TA kits now come with the 40:1 gear reduction (previously the 6kW kit was available in either 20:1 or 40:1 reduction). Proper final gearing is achieved by changing gears on the motor and spider.
A Surprise Bonus – PAS!
The 6kW TA is marketed as a throttle-only system without PAS. Tangent has recently released a lower-powered version of the Ascent designed for PAS, which should be shown soon on the company’s site. But – I was pleasantly surprised to learn that my 6kW brute also works as a great, intuitive, responsive, and comfortable PAS system as well. Not in the traditional way, of course – there’s no torque or cadence sensor in the system. But with that great Domino throttle, you can use the TA as an amazingly effective PAS system just the same.
I learned this when I encountered hikers or non-powered cyclists on the mountain trails I ride. At first I would just pedal by unpowered to not shock them with the Ascent’s angry bees sound (more on this below). Then I decided to try upshifting a couple gears and just feathering in a tiny bit of throttle while pedaling. The Domino allows such precise throttle control that you can perfectly dial in just the right amount of power to assist your pedaling efforts. After a few times trying this – voila’ – I had turned the 6kW TA into a perfect PAS system! With practice it became second nature. Not only that, I found that I liked using the Ascent in ‘PAS Mode’ much more than using PAS with the BBSHD.
As my experience with the Ascent increased, I found myself using a combination of all three power methods on each ride – pedaling only (because the Ascent has such a great freehub, pedaling feels great), PAS with a little throttle, then full-on throttle only. The great thing was that it felt like I hadn’t lost what a great unpowered bike the Strive is – I could still ride it as an unpowered bike and enjoy how it rode before motorizing it. With the Ascent, I still had 3 bikes in one – unpowered, PAS, and throttle.
6kW Ascent worked surprisingly well as a PAS system
More about unpowered riding – the Ascent has such a great freehub I need to give it special mention. You can pedal this TA-equipped Strive like a normal bike, and it still feels exactly like a normal, unpowered bike. The motor/gearbox disengages when you pedal, and you feel almost no additional resistance. It feels stunningly close to a normal unpowered bike, which is amazing. This is in stark contrast to my BBSHD-equipped bikes. When trying to ride them unpowered, in comparison they feel like pigs, not comfortable and with much more weight and resistance than the bike had before it got motorized. This TA bike felt great to pedal without power, almost like the motor was never there – and I found myself doing this often with the bike while trail riding. Besides having amazing power, the TA makes pedaling so enjoyable that you actually want to also get a good workout while enjoying the bike’s awesome power.
Negatives – Let’s Address Those Cons
So as I’d hoped and expected, the Tangent Ascent is great. Awesome. I never want to give it up. In fact, I wish I could buy a few more right now. Just because it feels like something this fun, this powerful, is bound to be made illegal by some regulatory agency and I want to hoard TAs while you can still get them. But all can’t be perfect in TA land, right? There have to be some negatives, yes? Why yes, there are. Let’s address what I found to be the cons of this amazing, powerful little mid-drive.
Of course, this is an obvious one for most of us. At $2300, the 6kW kit costs more than some good complete e-bikes. When I designed my off-road dream build in this article, I realized that it cost more than my Kuberg FreeRider e-motorcycle, and more even than some cars. But, very few exceptionally great things come cheap. And when you add up the cost of all the high-quality components in this package – the Astro 3220 motor, Talon HV120 controller, amazing Domino throttle, CA3, freehub, spider – PLUS the cost of the gearbox components, PLUS the cost of the aluminum housing parts, PLUS Dave’s time to build it all, PLUS his amazing engineering feat to design it, you realize that the Ascent is actually really inexpensive for what you are getting.
Yes, it’s expensive – but quality of all components is top-notch
There are some other high-powered options out there for less money: the big Cyclone, which can do 7500w, the Mini Cyclone that can do 3000w (both of these I have not tested), and the BBSHD running at 72/84v with an external controller (which I have tested, full review coming soon). While each of these provides more power, and is more responsive, than the stock BBSHD, none of them have the raw power or beauty of the complete Tangent Ascent kit. And none of them yet come as a complete package like the Ascent does.
The next negative for me is the effective chainline you get with the Ascent. By design, the drive has the motor gears on the inboard side of the spider, while your chainring is mounted to the outside. Dave DuBose designed an excellent spider that brings your chosen chainring close to the inside drive chain. But it’s still pretty damn far away from the frame, especially when compared to the BBSHD with an offset chainring like the Luna Eclipse. When I first built this bike using the BBSHD, I was able to position the Eclipse chainring so close to the frame that it was almost touching – the teeth were about half a mm away from the swingarm. This gave me a great chainline that allowed me to use all 11 gears of the Strive’s wide-ratio cassette. The TA puts the chainring a good 12-14mm away from the swingarm.
Chainline is pretty far away from frame, because chainring is on outboard side of dual-gear spider
To put that into perspective, it’s not as bad as what you get when using the 30T Luna Mighty Mini on the BBSHD – that puts the chain even farther away from the frame. But it’s still so far from the frame that my 1st and 2nd gears in the cassette were unusable – the chain was simply bent too far over to use those gears. 3rd gear was my effective first gear. Still, it matched well with the small 32T RaceFace narrow wide chainring that I used for trail riding – even 3rd gear provided great hill-climbing torque, and the motor never bogged down up big inclines.
Chain is bent inward a bit, on 6th gear – straight line is around 8th gear
The easiest solution for this: first, replace the 11S aluminum cassette with a heavy, strong, steel 10S cassette. Then remove the smallest 2 cogs (or gears 8 & 10) and put them on the inside of the cassette, inboard of 1st gear. Now, your 1st gear is in the same place that 3rd was before. Adjust the derailleur limits and you’re good to go. But a better solution would be if Tangent (or Luna) made an offset chainring for the TA – a’ la Luna Eclipse – that moved the chain outside the spider and even closer to the drive chain. That still wouldn’t bring the chain tight to the frame, however – the only way to do that would be to switch positions of the chainring and motor drive chain, putting the motor drive gears on the outside. I don’t know if this is even possible, so for now, my chainring hack seems to be the best option.
Most likely, you will need to upgrade your drivetrain (chain & cassette) if you install the TA on your bike. My Strive 6.0 has a light, delicate, 11-speed drivetrain with a wide ratio aluminum cassette. The Ascent pumps about 10X more power through these components than they were ever designed to handle. To be honest, I was expecting the bike’s drivetrain to blow up less than 10 minutes into the first ride. That it made it over 200 miles before failing is incredible.
How to make your delicate drivetrain not explode with such huge power? You need to ride smart, with lots of mechanical sympathy. First, I used the throttle very gingerly, keeping in mind I was putting over 10 times the load on the drivetrain than it was intended to handle. It’s not that I didn’t use full throttle – I did, many times. I was just ginger in rolling on the gas – doing it gradually, and making sure I was in the lowest gear possible for the speed I needed at that moment. Also, I would often pedal to get going from a dead stop, then once I was up to about 12mph, gently start rolling on the throttle. But, there were many times during my month of test-riding that the full 6kW of the Ascent was going through that aluminum cassette and thin 11 speed chain, and they didn’t immediately disintegrate.
It was only after about 200 miles of off-roading that my drivetrain started to show signs of failure. Nothing catastrophic, but the cassette started showing wear, and from this the chain began slipping under heavy load (usually uphill). Also about the same time this started happening, I had a few instances of the chain coming off the chainring. Twice it came off inboard, which was easy to put back on. But once it came off outboard and got lodged between the nuts on the spider and the right crank, which couldn’t be fixed in the field. I had to walk the bike back to my car. I will replace the bike’s drivetrain with a heavy-duty 10 speed steel cassette and strong 10-speed chain, and I’ll update in the future to keep tabs on how they hold up.
This should be self-evident, but here’s exactly what NOT to do with your TA bike: Come to a dead stop on a huge incline. In 8th gear (or higher), pin the throttle. If anyone does try this with their 6kW TA, mated with a 120A battery, please post some photos of the result.
Regarding IGHs (internally geared hubs), I know that some Ascent users have mated their drive with an IGH. However I have no experience with IGHs yet so I can’t speak to which, if any, of them can handle the massive torque of the Ascent. I have read in several forum posts that the King of all IGHs – the Rohloff – is not able to handle such huge power that the Ascent provides.
Finally – the elephant in the room – that SOUND!
I left this point for last, as it’s both a pro and a con for me – but mostly a con. First – I like the Ascent’s angry sound. A lot. There has been so much discussion in online forums about the “Tangent Sound” – it seems either people love it or hate it. Some have described it like a metallic can full of angry bees, others say it sounds like a 2-stroke dirt bike. To me it sounds a bit like an R/C plane engine – not the tiny ones, but the really, really big scale R/C motors, running at full tilt. Whatever you think it sounds like, one thing everybody can agree on – the Tangent Ascent is not silent.
The Ascent’s sound is a necessary byproduct of the metal gears’ movement within its cycloidal gearbox. And remember, at full tilt, that Astro motor is spinning at 10K RPM – almost any metal gears turning that fast are going to make some sound. As I mentioned, with a month of hard riding, for me the sound was both a pro and a con.
Pros: if you’re an ex-MX rider like me, the Ascent’s sound will bring back pleasant memories of your gas bike riding days. Riding my Ascent-powered Strive, with its angry sound, feels a little bit like riding my old 1996 YZ250. Only if the YZ250 weighed just 50 lbs., didn’t smoke, and could be easily pedaled like a bicycle. Also, because it’s not silent, the sound lets bystanders (hikers, cyclists, pedestrians) ahead of you know something is coming behind them. With the BBSHD, I’ve had to yell many times to let people know I was coming up behind them. Not the case with the Ascent. This truly is helpful, and I can see that for commuter usage the Ascent’s sound could really help avoid collisions with pedestrians, as they can now hear you coming behind them.
Another pro: psychologically, the Ascent’s sound makes it feel like you are going faster. Because it sounds angry and aggressive, you must be going fast! I call this the “Ferrari 360 Effect” – for many years, I’ve owned a Ferrari 360 with a loud Tubi exhaust system, that sounds like an angry, menacing, beautiful symphony behind you while driving. At 400bhp, the car is really not very fast. But driving at 40mph up a curvy mountain pass, it feels like you are flying at 90mph due to that incredible sound. Same thing with the Ascent – at any given speed, it feels like you are going twice as fast as a BBSHD bike, due to that wonderful, angry sound.
Loved by some, despised by others: the Ascent’s ‘angry bees in a metal can’ sound is definitely controversial
Cons: So if I like it, why is the Ascent’s sound a con? There are several reasons. First, to some, the sound can get irritating after a while. There were some times during my rides that I just wished for silent, relaxing riding… to glide along the trails in perfect peace and silence. For that, luckily, I have my BBSHD bikes. Also, with that sound comes vibration (actually, it’s the other way around – the vibration is what’s causing the sound). You do feel a bit of vibration from the gearbox up through the grips. On a few longer rides, I had to stop and rest a bit because my hands had fallen asleep from the constant slight vibration. You may not experience this, maybe it’s because I’m old now, but it did happen a few times where I had to stop and wake my hands up due to this. It’s not a strong vibration, you just feel it a little bit, but it is more pronounced when the Ascent is running at max RPMs.
But the main negative I experienced regarding the sound is the reaction it causes in bystanders and other trail users. People are understandably very confused when they hear and see you riding up to them – they think at first, it must be a gas bike due to the sound. Then as you get closer they see it’s not a motorcycle, it’s a bicycle. And there’s no smoke coming out. So it sounds a bit like a gas bike (which is a big no-no on these mixed-use trails) but it’s obviously electric, obviously powered – people are just confused. While I did get the occasional smile and thumbs-up from bystanders, mostly the looks I got ranged from confused to angry.
This is in huge contrast to riding the same trails with my silent BBSHD bikes. Riding slowly and silently by hikers and cyclists, I got tons of smiles, questions, and thumbs-up. As described above, I learned to use the PAS method with my Ascent, where I would slow way down, upshift, and pedal by others with the motor turning very slowly. This way, it sounds much less menacing and helps keep harmony with other trail users. But the positive side to this is that people do hear you coming, and aren’t as shocked as when you come up silently behind them.
The main takeaway: you just need to ride smart, and responsibly, when using the Ascent. Don’t buzz by hikers or cyclists at 30mph using full throttle. Don’t be that douchebag who does this just because you can. With great power comes great responsibility – ride your TA bike responsibly, especially near others, and you’ll find the sound doesn’t really create any problems with other trail users or pedestrians. Just be prepared for lots of really, really confused looks from people.
But for me, and other performance freaks, the sound the TA produces is a small compromise to make for its amazing performance. And many – like me – think its sound is actually a cool feature that makes this system unique. I understand the gearbox does get slightly quieter with usage, so I’ll report on that in the future. And a last-minute update: Dave DuBose told me he’s testing out a new gearbox that is quieter than the current one. I hope to test it out in the coming months and will post here when I do.
Conclusion – Tangent Ascent is the ultimate mid-drive
Despite the minor negatives described above, I love the Tangent Ascent. It’s awesome: a super-powerful, compact, light, technically advanced, complete, high-quality system. It’s enabled me to have fun off-roading a bicycle that I never knew was possible. Yes it’s expensive, but the quality and love that goes into this low-volume, hand-made drive makes it well worth the price. Mine will never be for sale. The Tangent Ascent is an engineering masterpiece, and the state of the art in e-bike mid drives. Get yours before somebody makes having this much fun illegal.
About the Author:
Patrick M. is a A former coupon-book entrepreneur and travel agency owner, and Patrick developed one of the first consumer-review web sites way back in 1996. In the early 2000s, he worked as a journalist, serving as contributing editor for two home theater magazines. Now, Patrick splits his time between producing documentary movies and renovating homes – but his true passion has always been anything with wheels and ultra-high performance.
Written by Patrick M, May 2017