Cross Bike -> Mountain Bike

Four years ago, I decided to buy a new bicycle. After having had only relatively cheap mountain bikes (which cool kids needed back then :P), and using it only for regular day to day driving, usually on roads and some unpaved dirt roads, I figured something more street oriented would be more useful. So I got a cross bike, to have the best of both worlds.

Lately, I found myself riding more and more beyond roads, around the local chines and forest trails, and my crosser really got to its limits (and I over the handlebar more than wanted :). So a mountain bike made more and more sense to me. Still, I really like my current bike and it held up really well over the past years, even tough I took it to much harsher terrain than it was made for - and I really couldn't get myself to buy yet another bike.

The solution was obvious: get a pair of MTB tires.

After looking into it, I realized that it wasn't that easy. While there are MTB tires for my 622 mm rims, they are really narrow in profile, and neither the rims nor the frame could support wider tires (it's a road bike after all). The other solution was to by a new set of smaller rims with wider tires. The most obvious choice was a 559 mm rim (aka 26"), but it would really look awkward on the road frame and probably not handle quite as it should. Luckily the intermediate size of 584 mm (aka 27,5" aka 650B) is becoming increasingly popular and parts reasonably priced. I figured it would, once again, make a good compromise.

Unexpectedly it doesn't really seem like the common thing to do, I really could find no proper information on the topic, and as I'm not a bike expert, I wasn't really sure if everything would fit. There seem to be only few people who ever tried to convert a road bike to a MTB - much more common is the reverse - and I only found one who actually did and wrote a few lines about it. This person (who owns the same bike than I do, which really isn't a very common model!) however went with his 622 mm rims and the one, narrow, tire choice.

Long story short, I decided to give it a go and just try it out.

As I had to get new rims anyway, I figured I might as well keep my current wheels and have to sets to chose from (one for the road, one for everything besides). I carefully measured my frame to find out if things would fit, and picked the following components:

  • Veltec ETR Race 584 mm wheels
  • 180 mm discs for my brakes
  • Shimano CS-HG80 Cassette (the same as on the current set)
  • Schwalbe Nobby Nick 60 mm for the front
  • Schwalbe Racing Ralph 57 mm for the rear

The wheels weren't exactly cheap, but they do seem reasonably priced for the specs. The tires seem to be a popular combo for my use case, so I figured it would be a decent choice. I went with the wider front tire because I could :) and it seemed to make physical sense. The Racing Ralph for the rear is only available up to 57 mm, and my measurements indicated that this was as wide as could possibly fit in the frame - after putting the wheels in, this turned out to be true, 3 mm wider and the outer blocks would touch the frame.

Lastly, I also read about tubeless setups in my research - and having had a couple of flats that would be eliminated by one - which seemed to be a good idea.

I've learned some lessons though: If a rim is markted as "Tubeless Ready", it doesn't mean that it is air tight, nor does it mean it would come with an air tight rim strip. Instead it just means the rim has a bed which makes it easier to install a tubless kit. Also, getting the tires to pop into the bead was harder than I expected. Even with the valve cores removed and a strong compressor, they just wouldn't pop. The trick to use soapy water to make it easier turned out to be a really good one. It still took me a while (longer than I care to admit), but in the end both tires popped and it seems to hold. It probably really isn't worth to go for expensive fitting fluid, but if you're having trouble, soapy water really seems to do the trick.

So in the end, everything fits, the two sets of wheels really give me a lot of flexibility without having to own two bikes and thanks to the quick releas I can exchange them within a minute. The tubeless setup seems to hold so far, though some testing remains to be done. I haven't tried it in heavy terrain yet, but the wheels seem to be really good and roll off easy, and the whole setup seems to be quite OK. The bike still handles nice, and off road, the wide tires really feel and handle much more comfortably.

If you decide to convert your (cross) road bike to a MTB, I think this setup is a good way to do it, and if you do the necessary measuring, you too will be successfull.

All in all, the new wheels cost me about EUR 450 - not cheap, but certainly cheaper than a new bike. If it was worth it? Time will tell.

Last but not least, a before and after picture: Old 622 mm wheels New 584 mm wheels

A few closeups are in my gallery.