If you want to rock a ton of amps in a hot-rod hubmotor street monster for the kind of sweet hard acceleration that can embarrass an expensive sports car, the latest trend is to mount the hubbie into a rear wheel that uses Moped rims and tires. This article will show you why you want this, and what parts are being used right now by garage builders to make this happen.
Isn’t a moped just a light motorcycle?
There aren’t many mopeds in North America, but…in the rest of the world? there are tens of millions of them. The classic moped has a 50cc single-cylinder gasoline engine, but it is also light enough that if the engine stops running, it also has pedals that can propel the moped (pedaling first is also used to get the engine started).
Moped tire sizes are measured at the inside-diameter (ID) of the tire (just like motorcycles), but bicycle tires are measured by the average outside-diameters (OD) from years ago. This is why for several years now, hot rod non-hub ebikes put 16-inch Pirelli moped tires on wide 20-inch bicycle rims (they fit!). The best selection in moped tires is for the 17-inch and 19-inch sizes, and visually…a 17-inch moped interface is very similar to a bicycle 20-inch, and the 19-inch moped interface is very similar to a 24-inch bicycle interface.
Why moped…instead of small motorcycle tires and rims? The answer is the speeds they are designed for. A small motorcycle might be expected to have a top-speed of 55-MPH (85-km/h), and possibly carry two adults. Mopeds in the sizes I am talking about here typically carry one person and top out near 40-MPH (72-km/h), since they are intended for city streets, instead of major highways.
As a result, moped rims can be found in aluminum, to reduce the mass of weight that is spinning (the flywheel effect). Most small motorcycle rims in these sizes are steel, for added strength (but of course, heavier). Another key reason is that motorcycle rims use thicker spokes and larger spoke nipples. Moped rims can be found with smaller nipple mounting holes, which allow us to use thinner spokes than a motorcycle.
The main reason that moped rims are useful for hot rod ebikes is…the extreme spoke angles that are required, because mounting a large diameter direct drive (DD) hubmotor into a smaller diameter rim. A bicycle rim manufacturer doesn’t know if the end user will use a single-cross spoke pattern, or maybe a 2-cross, or 3-cross pattern (plus pedal-only bicycle hub spoke-flanges are small diameter). As a result, bicycle rim spoke-nipple holes are usually designed with a radial orientation, and a very limited range of angle to either side.
Moped and motorcycle rims both have holes that are designed from the factory at a steep angle. Moped wheels often used a large-diameter drum brake (similar in size to a small hubmotor), and also use a one-cross or two-cross spoke pattern instead of a 3 or a 4-cross (which is good news for us), but…whether they are using a 1-cross or 2-cross pattern, these rims all use the same pre-determined nipple angles.
All the information below is for large REAR hubmotors, with all of them using DISC brakes (no rim brakes, but…might also have regen as a magnetic brake, using the motor)
Big DD hubmotors in smaller diameter rims
The trend for off-road this year is to get the motor out of the rear wheel, and to mount it to either the forward part of the swingarm, or onto the bicycle frame. However…for whatever reason, when someone wants a high-powered E-bike for the street?… the large rear Direct-Drive (DD) hubmotors remain popular (Cromotor, MXUS, Crown, 35mm-40mm width stator hubs that have been ventilated or oil-cooled, etc).
[Side note: front wheels can be laced up with a variety of spoke arrangements, with whatever works for you, but…large rear hubmotors use a standard 36 holes (36H) in their spoke-flanges and rims]
These big DD hub motors are heavy, so…trying to save a few ounces by using a bicycle rim is being seen less and less. (I also recommend full-suspension at any speeds over 30-MPH / 48 kph, due to unexpected pothole hits).
There are performance benefits to using a higher voltage or a faster Kv of motor, and then mounting that hub in a smaller diameter rim. Due to the way that bicycle vs moped tires (and rims) are measured, a 17-inch moped tire/rim is very similar to a 20-inch bicycle tire/rim (2.25 – 17 moped tire has a 21.5″ OD). A 19-inch moped rim/tire is similar to a 24-inch bicycle.
Department Of Transportation rated (DOT) moped tires are very durable and flat-resistant, where bicycle tires are usually lighter for a given width of tire.
In the pic above, the builder wanted the absolute smallest diameter tire on the recently popular MXUS 3000W hubmotor. He used a 20-inch bicycle tire, and mounted it to a 16-inch moped rim. The moped tire selection for 16-inch rims is nowhere as good when compared to the selection of choices for 17-inch rims. I’m only posting this pic to show what’s possible.
Moped tires can be easily and cheaply found in width/height as narrow as 2.0 inches, to over 3.0…and here is a link with a lot of info on moped tires/rims
Rims and Nipples
Once you start looking, you will find moped rim widths in 1.4, 1.6, and 1.85 inches wide (along with 16, 18, and 21-inch diameter rims). And, although you can find them in both aluminum alloy and steel, I recommend focusing on the aluminum 17 and 19-inch rims, using a width of 1.6-inches, because…that will allow you to take advantage of the experience and collected data of the experimenters who have pioneered this. They have already identified the best value options in the optimum sizes that work best.
The lighter 1.4-inch wide moped rims have a nipple hole that is 6mm in diameter, so manufacturers have an infrastructure in place to mass-produce 6mm holes in these rims. The 1.6 and 1.85-inch wide rims typically have 8mm holes to handle very thick 10ga and 9ga spokes.
The 1.6-inch wide rims allow a proper fit of tires that are wider than the lighter 1.4-inch rims, but the typical 9ga/10ga spokes used on actual mopeds are heavier and less springy than what we want for a powerful E-bike. So…how do we resolve these conflicting desires?
John Rob Holmes (JRH from Holmes Hobbies, in Columbia Missouri, USA) has ordered and stocks aluminum 17 and 19-inch moped rims under his Medium MoPed / MMP brand. Since he was special-ordering them to his specs, he was able to get the 1.6-inch width that hot-rod E-bike customers wanted, but…have them using the smaller 6mm holes. Then, he special-ordered nipples to be made that had a fairly large 6.0mm OD normally found on 9ga/10ga spoke nipples, but had their threads drilled and tapped for the smaller 12ga, 13ga, and 14ga spokes.
John is a respected vendor and has been a member of the endless-sphere.com forum since July of 2008.
If you don’t want to order rims and spokes from Holmes Hobbies to build your own wheel, the next best option is to add stainless steel washers to Holmes Moped 6mm nipples. This allows you to fit the affordable Sapim stainless steel 12ga spokes that are recommended into the 8mm holes found on common 1.6-inch wide moped rims.
You will need to dish these washers into a shallow bowl shape, which is easily done with a cheap 3/8-inch hydraulic tubing flare tool. Standard 12ga bicycle nipples will require washers when used on any moped rims. Common 12ga nipples have a 4.6mm body, and a 5mm washer works well. For Holmes moped nipples (6mm 10ga body with a 12ga hole), an SAE #12 washer has a 6.4mm ID.
Standard nipple gauge / diameters:
14 gauge = 4.1mm body, 6.2mm head (common bicycle size)
13 gauge = 4.1mm body, 6.2mm head
12 gauge = 4.6mm body, 7.5mm head
11 gauge = 4.6mm body, 7.5mm head
10 gauge = 6.0mm body, 9.4mm head
The two situations where stainless steel washers have been used is…Qulbix Raptor owners seem to like the 19-inch Prowheel brand rim in the 1.85-inch width (shown in the pic above), which allows the mounting of very fat “dirt bike” knobby tires, but…that rim has 8mm nipple holes. By ordering Holmes Hobbies 6mm moped nipples and adding washers, you can use 12ga spokes on the 1.85-inch wide Prowheel.
[note: why not just use 10ga spokes with NO washers to put a big hubmotor on a Prowheel? The highly respected Buchanan 10ga spokes are $3 each! plus they have no flex at all, and are heavier than 12ga spokes.]
The second situation where you might see these washers is: when using common 4.8mm body-diameter 12ga nipples, and using them on any random 17/19-inch diameter and 1.4-inch width moped rim…which normally have a 6mm nipple hole.
It is not recommended to use common 4.8mm diameter 12ga nipples on the large 8.0mm holes found on common 1.6-inch wide rims (even with washers), and this is why Holmes Hobbies stocks his special order 12ga/6.0mm “moped” nipples.
[note: it is possible to use the lighter aluminum 1.4-inch wide moped rims on the front of an ebike (instead of 1.6), whether off-road or for the street, but…it is completely un-necessary, since the affordable, light, and strong downhill (DH) bicycle rims and tires are readily available everywhere. I have only seen that done to get an anodized color-scheme that matches the rear. When shopping and comparing, 1.4-inches is 35mm wide…If you DO use a 1.4 moped rim on the front, the thickest gauge spoke you should use on the shaft is a 13ga, and even 14ga is acceptable (12ga is too stiff for a light front wheel). If you have a choice, always chose “butted” spokes, which have a thicker head by the L-bend]
You may be wondering why we are recommending a 12ga spoke (a gauge that is heavy for a bicycle, but light for a motorcycle) on a rear hub, instead of a thicker 10ga/9ga spoke…which is what these rims were actually designed for from the factory. The answer is that a true moped would be about twice as heavy as an electric bicycle, plus a moped would be expected to be able to run at 45-MPH, where an electric bike would more commonly travel with a 30-ish MPH top speed.
Tires narrower than 2.75-inch are considered to be moped tires and will not be listed in motorcycle tire sizing charts. Also, be aware that 2-ply tires are much lighter than 4-ply, and 2-ply is still plenty tough by E-bike standards.
“….17 x 2.5 tire is my favorite all around…Shinko SR241 19 x 2.75 is my favorite tall tire, It comes in about 24.5″ OD…I would suggest between 2.5 and 3.0 width tire on a 1.6″ wide rim, but you could get away with others…The alloy rims will be 1.6″ wide, those take 3” tires very well…16 and 18-inch moped rims and tires do exist, but 17 and 19-inch have a much better selection of tire choices (whether street or off-road)…Some sizes I know are common, and from memory:
17 X 2.25, 2.5, 2.75, 3.0
19 X 2.0, 2.25, 2.5, 2.75, 3.5
…Treatland.tv (San Francisco, USA) has a lot of moped tire options…17 x 2.5 is going to be 21″ ish in OD…MTB tires are pretty expensive compared to moped tires. Maybe it is the size of the molds, or lower volume, or whatever. Rubber for Rubber a DOT tire is generally a lot better value…”
Alan B: …M62 Gazelle 2.5-17 measures 21-3/4″ diameter unmounted and just over 9-1/2 pounds a pair. The tubes are just over a pound each…
Rix: …I keep going back to the Shinko 241. I now I have a 19 on the front like yours with an SR241 2.75-19 and have eliminated the need for any MTB tire inventory. Rear is a 3.00-17 SR241…
Kent: …For those considering 19″ but find you don’t have enough frame width for a 2.75 or 3″, there still is the 19″x 2.50. It fits nicely on a 1.4 or 1.6 rim…
Spokes and Nipples
“…We saw a great need for thicker spokes to mate up to modern electric bike and classic moped hubs. What we didn’t want was something too thick for your hub strength! Enter the Holmes Custom Moped Spoke, our butted 11/12ga swaged spoke that is as comfortable on your Puch or Derbi as it is on your MXUS or CroMotor hub. Beefy where it is needed, yet thin enough to give the wheel flex and prevent premature breakages. Perfect for alloy, steel, moped, and light motorcycle rims mated up to your lightweight electric or gas bike.
We typically use our 11/12 butted moped spokes on the rear, with 12ga, 13ga, or 14ga Sapim Stainless on front depending on the bike. A perfect balance of strength and flex for your not-so-common bike! Spoke orders are not returnable or exchangeable. Spoke includes matching nipple. Max spoke length 243mm, Min spoke length 65mm.
Nipple body is 6mm diameter, head is 9.4mm diameter, length is 16mm. Nipple uses a 5mm Allen wrench.
Our 11/12 butted “moped” spoke diameter at the hub end is 2.9mm (11ga). Spoke diameter on the shaft and at the thread end is 2.6mm (12ga). Spoke head diameter is 5.7mm.
We also carry “standard” bicycle Sapim 12ga nipples. Brass with nickel plate, 4.8mm diameter body, 7mm head diameter Uses a 4mm Allen wrench.
The custom moped nipples I had made are threaded for 14, 13, and 12ga spokes. They are for 6mm spoke holes (10ga), which are found on most 1.4″ wide rims, and also our 1.6″ wide MMP rims.
Using a direct drive hub motor with steel flanges you could go up to 9ga spokes.
Prowheel rims are made for a 9/10 gauge spoke, and require washers to use a thinner spoke…”
Spoke gauges / shaft-diameters:
14 gauge = 2.0mm (common bicycle spokes)
13 gauge = 2.3mm
12 gauge = 2.6mm (max thickness recommended for hubmotors on E-bikes)
11 gauge = 2.8mm
10 gauge = 3.1mm (1/8-inch)
9 gauge = 3.5mm
Nipple gauge / diameters:
14 gauge = 4.1mm body, 6.2mm head (common bicycle size)
13 guage = 4.1mm body, 6.2mm head
12 gauge = 4.6mm body, 7.5mm head
11 gauge = 4.6mm body, 7.5mm head
10 gauge = 6.0mm body, 9.4mm head
“…Some sizes I know are common and, from memory. 17 x 2.5 tire is my favorite all around. I would suggest between 2.5 and 3.0 on a 1.6″ wide rim, but you could get away with others…The alloy rims will be 1.6″ wide, those take 3” tires very well.
16 and 18-inch moped rims and tires do exist, but 17 and 19-inch (both 1.6-inch wide) have a much better selection of tire choices (whether street or off-road).
Tires narrower than 2.75 are considered to be moped tires and will not be listed in motorcycle tire sizing charts.
17 x 2.25, 2.5, 2.75, 3.0
19 x 2.0, 2.25, 2.5, 2.75, 3.5
Treatland.tv has a lot of moped tire options…Shinko SR241 19 x 2.75 is my favorite tall tire, It comes in about 24.5″ OD.
17 x 2.5 is going to be 21″ ish in OD, MTB tires are pretty expensive compared to moped tires. Maybe it is the size of the molds, or lower volume, or whatever. Rubber for Rubber a DOT tire is generally a lot better value….”
Alan B: M62 Gazelle 2.5-17 measures 21-3/4″ diameter unmounted and just over 9-1/2 pounds a pair. The tubes are just over a pound each.
Rix: I keep going back to the Shinko 241. I now I have a 19 on the front like yours with a SR241 2.75×19 and have eliminated the need for any MTB tire inventory. Rear is a 3.00×17 SR241
Kent: For those considering 19″ but find there isn’t enough frame width for a 2.75 or 3″, there still is the 19″x 2.50. It fits nicely on a 1.4 rim
Conclusion, so…whats the hot set-up?
You ordered a Monster Cromotor from Zelena Vozila, an ebikes.ca “The Crown“, or the new MXUS 3000W to rock 72V X 80A = 6,000W, and you’ve got money burning a hole in your pocket. You don’t have time to screw around, so…you contact Holmes Hobbies:
19-inch diameter for off-road (with a lower Kv motor), 17-inch for the street (with a higher Kv motor). 1.6-inch wide “MMP” aluminum moped rims with special-order 6mm spoke holes, which allow tires from 2.0 to 3.0 wide. Their special order moped nipples that he stocks don’t require washers on his rims (fatter 10ga body, 12ga hole and threads)
You want affordable Sapim stainless steel 12ga spokes (not listed on Sapims’ web-catalog, but JRH has them). Much stronger than 14ga bicycle spokes, but still light enough to have some springiness, flexibility, and stretch. Holmes Hobbies special orders butted 11/12ga, which means the shaft and threads are 12ga, but the end that hooks onto the hub flange is a slightly thicker 11ga…right at the point where other spokes might break. The hub spoke flange on big hubmotors is steel, so you never have to sweat spokes breaking there.
A one-cross pattern uses shorter spokes than a two-cross, so one-cross is lighter.
Too many models to list only one of them as “best”. A 4-ply construction is common, but heavier.
For the street, look for DOT-rated moped 2-ply, which is stronger than bicycle tires, but still reasonably light. Gazelle M62, Pirelli ML75, and Hutchinson GP1 are popular brands with good price/performance ratios.
For off-road, Shinko SR241 is a popular 4-ply, it has a “dual use” tread pattern that is adequate on the street, but knobby enough to provide good grip in loose of-road tracks….
Written by Ron/spinningmagnets, May 2015