250-500cc tire help.....

just picked up a 2011 wr300 yesterday and she needs a tire asap.. it has a 120-90-18 dunlop on it now and it looks super tight. from what i see the bike calls for a 140-80-18. has anyone run into an issue with fitment with the 140? any help would be great!

correct

FIM? So the 120/90- 18 is the better tire to stick with?

I run a Dunlop 110/90-18 on the WR 250

Can someone highlight benefit for thinner rear tire on dirt bike? Sorry if that's dumb question..

That's what im trying to figure out... I ride single track in the sand. Would a wider rear help the bike track better?

I ran an IRC m5b rear size 140/80-18 and really liked all the traction I had. It would tractor up, over, and through anything! I ran the same tire in a 130/80 and it was good and have also ran 120/80's but they seemed to break loose quite a bit more than the larger tires.
Some guys swear by skinny tires and some guys like me swear by wider tires. I ride in good Iowa dirt rarely any rocks and typically some kind of hill climb at every race. I am really digging that IRC for my conditions.
With my new 350 it came with 110/100-18 Dunlop mx51 and it came off right away, just didn't hook very well for me. I have a pirelli xcms 120/80-18 on now and it go's OK but I don't like the lack of breaking. I just got a full set of Kenda Washougal sticky as well as a kenda Millville 2 rear but have not tried either yet. With the taller 100 side wall ratio it does seem to take the hits better but typically the shorter side wall tires corner better without a springy or mushy feel.
It seems like for rocky conditions I've heard guys running Dunlop or kenda or maxis desert tires with tubliss at 3-5 psi in rear and 5-8 in front with great success. My 2 cents...

Sorry for the dumb question what is a FIM tire?

I think Federation of International Motocross. They limit the knobby height in hopes of churning less trail during enduro events. Mostly a Euro governing body.

Out here most guys run 110 or sometimes 120 on 300 2-strokes for woods/enduro. I am running a 110/100-18 AT81 on mine right now.

Stock Michelin is a 140, but Michelin measures their tires in an odd fashion so it's not as wide as it sounds. I would not want to run a true 140 on the WR, too heavy.

I agree with the IRC M5B. It's a monster, no slippage pretty much ever. Between the rekluse, long swingarm, and tire, my bike climbs anything.

How much have you extended your swingarm? Does it turn in good still? I run a long chain and all the way back to help keep the front down.


I run a M5B as well in a 120. Seams good traction except at a snail speed in rocks, I seam to spin alot. Not sure if a Trials would do any better in that small loose shell situation, I love the tire and have a hard time giving it up. Alot of guys I ride with use 140 M5B and like them as well.

Use UHD tubes and low air pressure when speeds are slow.

Small width tires stay in ruts
The larger 140 climb out quite well
If your inteferance is with the swing arm try looking for a lower profile percentage
Ie. 120/90/18 will be dam near the same radius as 140/80/18
The 90 is a percentage if the width.

Oh your chain maybe too short did you know if its been cut?

I've run nothing but a 140 on my 250 * I like the extra big tire. Better traction.

Ill have to give a 140 a try on my next tire. I run a Tubblis system at like 4-5# air. It does good for the most part, just the occasional steep uphill, almost have to stop at a switchback, then try to take off again in rock. that when it kicks my butt.

The tubliss guys told me the desert tires at real low psi are totally different tires and they related it to a trials tire with good brakes when you ride the rocky stuff....

Not extended, just longer than everyone else's KTM/Husaberg swingarms.

I ran a 120x100x18 and loved the traction, but it ate the mud flap. (shock protector) I was running 14X48 gearing, (1 larger on countershaft) so shortened wheelbase because of stock chain.