Too Fat or not too Fat, that is the question

December 15, 2019
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When trying to figure out what to buy or build one of the biggest choices you will have to make is what width tires you want. Ebike tires can be anywhere from tiny < 1-inch skinny road tires all the way up to 5 inch wide fat tires. Different widths of tires will have a massive difference in the performance of your ebike in a variety of different conditions. This article will help clear up some of the confusion around tire width and help you to make informed purchasing decisions for your next ebike.

A decision tree for tire size, click to enlarge, recommendations in bold

Defining tire widths

For the purposes of this article:

  • < 1″ wide is a skinny or ‘road’ tire
  • 1 – 2.4″ wide is a ‘normal’ tire
  • 2.4 – 3.5″ wide is a plus-sized tire
  • 3.5 – 4.5″ wide is a fat tire
  • 4.5 – 5″ wide is a 5″ fat tire

The tire widths on these charts are for the tire mounted on an appropriate sized rim, which for the > 4″ tires can be 90-110mm wide. They are also the ‘actual’ tire widths not the ‘advertised’ tire widths. Typically whatever size the tire is sold as is a bit wider than the tire will actually be. For example, the Snowshoe 2XL is sold as a 5.5″ tire, but the actual width on a 100mm rim is closer to 5″. I’m not sure why fat tire manufacturers do this, but they do.

This custom-built ebike, the Christini AWD Fat-E 5 (review here) is the newest addition to my fleet, you won’t find anything fatter than this

A fatter tire means more resistance

So the reason that all those screaming fast road bikes have skinny tires that are pumped up to 110PSI is that the bigger your tire is, the more resistance it will have. Because the contact patch is much larger, you have more road friction. Fat tires also tend to be run at lower PSI’s so that means that they also have much more resistance, thus eating up more battery power, thus requiring a bigger battery and more power to go the same distance. In snow conditions, it is not uncommon for me to run my fat bikes with 10PSI in the rear and 5PSI in the front. Although this makes riding in the snow awesome, it creates a tremendous amount of drag and it means that I have to go out riding with a huge battery on my back and often if the battery dies I end up walking the bike because it’s less effort than riding.

The 27.5 Plus-sized tires on the 2000W Luna Ludicrous X-1 (review here) is close to ideal for singletrack trail riding

Fatter tires mean more suspension

When you ride with a bigger tire the tire gives you quite a bit of cushion when rolling over obstacles. A lot of ebikes with large fat tires can get away without even having a suspension at all, and are still safe at speeds <30mph. Let me be perfectly clear though, that when you are going super fast on a fat-tired ebike and you hit something huge like a speed bump things can quickly escalate out of control. When I test drove Curt’s 72v Cyclone cargo bike build and hit a speed bump going about 35mph the bike jumped very high in the air, then bounced when it came down. I thought I was going to lose control of the bike, but I didn’t. When you jump with a fat-tired bike without any suspension it will bounce and when it bounces it often feels like the bike is unpredictable (because it is). Fat tired ebikes are great, but not for jumping.

3″ Duro tires on 100mm rims look awesome, check out my 3000W Soul Stomper

Weight weenies tend to lean toward skinnier tired ebikes

I am a weight weenie, and to me it makes sense to tend to lean toward the skinnier sized tires to ebikes. The problem is that it’s a tradeoff between ebike range and safety. With skinnier tires you can go longer distances faster with less power, but road debris and potholes pose more of a risk. With a fat tire ebike you can relax and ride in comfort and spend less effort focused on road debris and potholes, but you also lose range. Being more casual in your riding might be counterproductive since when on an ebike in the city it often feels like everyone is trying to run my ass over.

The Luna Fixed is a stealthy skinny tired ebike that can go long distances despite its small battery because of its efficient design

You can offset some of the disadvantages of fat tires by pumping them up as high as you can

Any bike tire will have a MAX PSI listed on the outside. With fat bike tires it tends to be around 20PSI. Don’t ever pump up a fat bike tire higher than that number, even to seat the tire. It will deform and become useless. By pumping up fat bike tires to their max PSI you create the lowest amount of rolling resistance you can.

The Luna Banana is a mad fun urban mini-bike runabout that you can squeeze 2 people on (review here)

Plus-sized tires are the bomb for singletrack riding (without snow)

I’ve been riding trails for 15 years now on bikes and I have moved to 29 plus tires for my main trail bikes. I love the large diameter tires and the plus-size allows me to run lower tire pressures without worrying about pinch flats. Plus-sized tires are all the rage, and once you start riding on them, it’s really hard to go back to a standard-sized tire. When I trail ride with a ‘standard’ tire I feel like my teeth are going to rattle out of my head. It really is that bad.

The drool-worthy 2500W Ludicrous Apollo (review here) has a huge battery and 3″ trail tires on it

For deep snow, the fatter the better

Any amount of snow that is more than 1″, you are better served riding a fat tired ebike with big lugs. The lugs will create a lot of drag, but also create a lot of traction. The bigger tires you can get to fit in your frame, the happier you will be. There are only a few frames I know of that will fit a Snowshoe 2XL in the rear and they are:

Nice clearance on 100mm rims:
-RSD Mayor V3/V4
-Pole Taiga
-Salsa Blackborow
-Christini AWD Fat-E 5 (Review here)
-Carver custom-built Titanium frames

Just enough clearance on a 80/90mm rim:
-Fatback Corvus/Skookum
-Trek Farley (aluminum 2016+)
-Norco Bigfoot
-Surly ICT
-Bikesdirect Lurch (build thread here)
-Bikesdirect FB5 2.0 (build thread here)

I’ve also found that for snow riding the PSC skunk striped tires are the way to go. Also for deep snow you’re going to want the most powerful drive unit you can find. I only ride with the Ludicrous BBSHD running at 50 Amps (2500 Watts).

My KHS 3000 didn’t fit Snowshoe 2XL’s in the rear but it did fit the Snowshoe XL tires, available here in XL frame size only for $3230 (get the Ludicrous version)

Just how much more efficient are skinny tires?

In my experience going one step down in tire size will generally get you about 15-20% more range (if you ride at the same speed under the exact same conditions). The least noticeable bump in range happens between the normal-sized tires and the plus tires. A plus-sized tire pumped up to its max PSI will perform pretty well when it comes to how much resistance it has. Another huge factor is the size tread that is on the tire. Tires like the Surly Bud and Lou have a huge amount of rolling resistance that is immediately noticeable. In general, if you want more efficient tires, get ones with smaller lugs or no lugs at all. Be aware that slick tires like the Duro Beach Bum tire just won’t work in the snow or very well on trails at all. Where slick fat bike tires like this really shine is on taco bikes like the Luna Banana available for $2600 here (get the ludicrous version). Fat tires on cruisers and taco bikes look awesome and ride well which is why people buy them.

The Sur-Ron Light Bee can fit a 3.5″ trials tire, but only just barely

The best width tire to use depends on what you’re using the ebike for and the amount of clearance you have for the front and rear wheels. Most ebikes do not allow you to increase the tire sizes very much, so make the decision about what width tires you want before you buy an ebike, because once you have an ebike, it’s often difficult or impossible to dramatically change the tire sizes. Although you can go down in tires sizes, like how I mounted a 29″ plus wheelset on a 4″ tired fatty, you just can’t go up. It’s conceivable you could copy my setup and get a front suspension fat bike and then get a 29 plus set of tires for spring, summer & fall trail riding. That setup would give you the best of both worlds, with only a few hundred dollars squandered on an extra wheelset and tires. How you approach tire width is up to you, but be smart and do your homework before you buy.

Ride on.

Karl Gesslein is a degenerate hooligan of the highest caliber living in upstate NY. His passion for e-bikes and all things sustainable causes him to be obsessed with climate change and finding solutions that will keep humanity from becoming extinct from our own hubris. His personal blogs include electricbike-blog.com, awaken-spirit.org & chestnutparadise.com.


1 Comments

  1. As a weight weenie, (originally a road bike rider…cervelo R3), my first ebike rig was a cannondale F700 on 26×1.5 tires and a BBs02. the Rig weighed 43 lbs, I weigh 135. With some work, I could move around at 35 mph. I have since upgraded to a plush Giant Anthem with a BBSHD…same 35ish mph top end, same paved commute. I’ve stepped up to Schwalbe MotoX 2.4×27.5 tires. I was concerned about resistence, but they roll very nicely, they also take a wonderful set when I lean into a turn at speed, and they absorb a lot of the higher frequency noise on the ride.

    I’d recommend them to anyone that’s on the fence about skinny tires. They support all rim sizes, providing the benefits of wider tires without losing speed as far as I can sense.

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