what is the biggest size, back tire that will fit on a 99wr400

I want to get the biggest size on the back but some are 120 100's others 140 80's..

what is the difference...


A lesson I learned: Be careful how large you go. Too much traction may just be bad for your engine. Kind of like putting it on a dyno, ALL DAY.

In the old days, the open bikes could use 150/80 X 18 (Metzler) or the giant Terraflex Knobbies. Those things were monsterous. And those open bikes use to put out 45hp. todays open bikes are approaching 60hp.

Now, the open bikes go with 120/80 X 18. There is a reason for that.

I think, now that is I think mind you, that you may be able to get away with a 130 size tire. Wheelspin is not a bad thing, since these bikes are so tractable.

[This message has been edited by NH Kevin (edited 12-28-2000).]

Another thing you should keep in mind is I don’t think all the brands are sized in an identical manner. A 130/100-18 Pirelli at my local shop is dwarfed by an IRC of the same size.

For what it’s worth I have been running a Dunlop 120/90-19 on my YZ ever since I wore out the original. It clears the silencer, but my fender and mud flap are taking some abuse (a 120/100-18 will be almost exactly the same height/width, about ¾” taller than stock). I’ve got a standard length chain and currently a 47 tooth rear.

any tire will fit, if my terraflex fits (it clears everything when you have an extra link or two in the chain), any tire will fit the wr400 I have one, and I decided to go with the terraflex.

I run the Teraflex in rocks and it just fits in the swingarm on my 450! The tire is so damn heavy. I think it is twice as heavy as my S12 rear for sand and mud. :cry:

I want to get the biggest size on the back but some are 120 100's others 140 80's..

what is the difference...

I had a 130/80-18 on the back of my WR426. It was the IRC M5B or something like that, so I know it will fit. Keep in mind if you go to a wider tire and keep the aspect ratio the same, the tire will be taller and it will change the gearing enough to easily feel it (feels like as much as 2-3 teeth on the rear sprocket). If you run a stock 110/100-18, this means the width is 110mm wide, while the sidewall is 100% of the width. Means its also 110mm's high. So each time you go up a notch like a 120 from a 110, drop the aspect ratio down 10%. So a 120/90-18 will keep it about the same, while the 130/80-18 would be the same also. When I say the same, I mean the total circumference compared to stock. Measure your original tire with a tape around the outside edge and then compare it with the wider replacement. This will also keep your tire from getting too tall, affecting handling, changing gearing and rubbing the rear of the swingarm on the inside towards the front. Disadvantage to having a low profile tire or small apect ratio it the ability for the tires sidwalls to absorb impact. But I found riding home on a flat was easier when there was less sidewall to flex and also a little tougher to change tires too. So for every advantage, it seems you get a disadvantage. I know a 130/80-18 will work, anything past that... :cry::cry:

:cry: you can actually get a 160 section tyre in no problem...but I havent found one yet with knobbles on....just kinda smooth ! :cry:

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