IRC M5B - Anyone use it? Will a 140 fit my KDX?


Oct 7, 1999
I have a '00 KDX-220 / w/ drilled airbox / Fredette porting / milled head / bored carb / rev pipe / stiff fork springs and gold valves / IMS wide footpegs / tall seat foam / gripper seat cover / tall Renthal bars / JVC solid bar clamp.

I ride with an '98 RMX-250, '98 XR-400 and a '00 WR-400 and they are all convinced that the IRC M5B is the best tire ever made (especially for mud) and each guy uses it on his bike.

On a wet, muddy day at the Buffalo Range (in Ottawa, IL), I was having trouble getting up small hills on my '00 KDX-220 while the RMX-250 was going up them with ease. This was a really muddy day and the park has a lot of slimey greasy clay.

My RMX buddy swore it was his IRC M5B tire getting him up the hills and I swore it was his bikes VERY smooth power delivery and his riding ability. We swapped bikes and it was the same story... my KDX was spinning the rear tire and his RMX (under my butt) was hooking up and climbing easily. So it wasn't riding ability... the RMX DOES have a smooth power delivery, but so DOES my KDX... so it sure FELT like the tire...

I have a set of Michelin Cross Competition S12's on my KDX-220 right now. Back = 130/80/18 - Front = 90/90/21. I run 10-14 PSI depending on conditions. They only have 3 or 4 rides on them and still looks like NEW tires. I have more than a half inch of space on each side of the tire to the swingarm, so it looks like a 140 will fit!

Will a 140 fit the KDX?
Have you ever used the IRC M5B on a KDX-220?
Did you like it?
How was it in MUD?
Did it last very long?
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Aug 7, 2001
140 M5B on a KDX

here in the great state of oh-ree-gone..., M5B's tend to be pretty popular. they work great in the extended wet, muddy, winters; work pretty well during those days in the dunes or on the beach; and are at least passable in the hard. they're relatively cheap, and last well. i got a buddy who's absolutely sold on 'em & runs 140's on his KDX220, with plenty of clearance for the chain. having been thoroughly roosted by M5B's on several occasions, i can vouch for their ability to drive. i ran 'em on my recently departed RMX, and have used them on my KDX. and..., contrary to popular belief (they are "directional"), you can reverse them pretty well when the knobs round off. their big hard knobs hold studs well, too. like i said, they drive well, but i think S-12's drive at least as well, and hook up better on their side's (a particularly slick side-hill comes to mind). i'll probably start with S-12's again this winter & see how they hold up from start to finish. i wouldn't be at all hesitant to run M5B's, and may do so late spring for the transition between muddy-soft and clay-hard. ride hard!


Nov 18, 2000
Ditto the above positive comments for the M5-B. If you do a search you'll find more threads on tire preferences than you'll ever want to read.

If your running a 130/80-18 it's probably a michelin.

Also, check your tire pressure. Too much air pressure can be a problem.


Jun 25, 1999
I run the 140 Irc M5b on my 500 and wont even think about trying any other tire unless IRC quits making that tire for some reason. It wears extremely well and as to hardpack, mine lasted a week in Colorado (rocky mountains for sure) and provided decent traction even when the rocks were a little wet. I had to re-learn how to ride my 500 with this tire due to the awesome hook-up provided. I now have 3 other riding buddies that are using this tire with excellent results. I would probably lean towards something smaller than the 140 for your kdx though. I would start with the 120 and go from there.


dirtbike riding roadracer
Mar 28, 2001
Not to be the only negative one here, but I killed one in a 50mi hare scramble and two trail rides, three of my customers did almost the same thing. (YZ125, YZ25 & YZ426F). I think its too rocky here, tires don't last long on this side of the mountain as compared to the other guy in oregon.

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