I own a 2007 CRF250X. It's a woods bike and has a 18" rear wheel. The CRF250R has a 19" rear wheel. What's the rationale behind a motocross bike having a larger rear wheel than a woods bike. It doesn't make sense to me (yet). I thought that a larger rear wheel would roll over obstacles better (for woods) and a smaller rear wheel would accelerate faster (for the track). Could someone enlighten me, please?

Compare tire over all diameter. They are almost the same.

A 19" wheel is a little lighter than a 18" but a 18" has a bit more sidewall and therefore more forgiving in rocky terrain. So on a race bike, (tracks are rarely rocky) the lighter wheel is an advantage. On a woods bike, the larger sidewall reduces rock induced pinch flats.

Ahhh!!! Now THAT makes sense! :)
Thanks! :thumbsup:

Also a 19" tire has shorter sidewalls and less sidewall flex which supposedly helps in cornering feel.

19" give a better feel over the whoops...Lots of us run 19s in the woods, but the 18 offers better flat/rim protection because of the taller side wall...

If you decide to run a trials tire in the woods, they are only available in 18 inch.

cxcmoto said:

That's exactly what I'ma gonna do :)

Keep in mind nearly all trials tires are 100 series and have comparably tall sidewalls.