In my motocross and desert racing days my bikes all had 21”/18” wheels. Since the bike’s OEM wheels are both 19ers I wanted to find a 21” front wheel. Well after researching they are almost impossible to find. Because the bike is a hybrid between a mountain bike and moped the hubs on the Sur Ron are MTB, but the rims are motorcycle. A lot of guys on the Facebook group have used 26” MTB rims on the front. The overall diameter of a 26” MTB rim/tire is the same as a 21” moto rim tire.
But what dissuaded me from going that route are the tire choices for a 26er. They are almost all exclusively MTB tires. 21 inch motorcycle tires are the defacto size so guess what? TONS of tire choices. And MTB rims/spokes are designed for bikes that weigh about 40 pounds. The Sur Ron weighs 110 pounds in OEM trim…. So I researched a few places and decided on using a guy out of NYC to build my wheel.
I had mentioned to a private Facebook group about my purchase of the 21er and in typical forum fashion ALL OF THEM PooPoo’ed the idea. “Too heavy” was their consensus. Yet when I asked them what they didn’t like about the handling of the 21 inch rim, NONE OF THEM had ridden a Sur Ron with a 21!
When I mentioned that to my well builder, here’s what he said:
” Okay the extra weight thing;;;;
#1 yes it’s more weight but when you ride it you’ll see how much better your bike is “planted” on the trail/road!
#2 lighter mtb wheel is a much more of a loose feeling front end that at speeds will want to drift off of your line! Really bad on fast dirt roads!
#3 mtb tires don’t work on a 130+ lbs motobike! Motoped community has all ready tried to
I’ve tried the moto wheel in the back & MTB front for about 3 months.. trying many many 26” tires and at the end,they just don’t werk well because of the extra weight of the bike…
I had to run 45-50 psi on mtb front so it wouldn’t get pinch flats on rocks and roots. That much psi the tire doesn’t work that well or ride well!
Motorcycle tires I use 22 psi or so and grip the road/trails awesome”
So after mounting and trying the 21er all I can say is WOW. It has transformed the bike into a very capable off-road bike. Rutted downhills are not scary now, holding a line in a turn is just like it should be, planted. Bumps are smoother than before. All in all I would never go back to the 19 inch rim. What are the downsides? The OEM front brake on the Sur Ron is overwhelmed by the added weight of the 21 inch tire rotation. In the past I could do stoppies with the 19s. Not so with the 21s. So I have ordered a 224mm (9”) rotor to replace my 203 in hopes that solves the issue. If not then I will upgrade my front brake to a Magura MT5s. I love those brakes and have experience with them. Of course if Brembo made MTB brakes I’d be SO THERE!
Update: I mounted a 225mm Hope floating rotor and the bike stops on a dime. You can read about it in my section on Brakes.