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Dirt Tire Size Range

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I have a Honda CRF450X 2007.
The bike specs for this bike are Front: 80/100-21 Rear: 110/100-18
I wanted to find out if there is any play with these dimensions.
If it would work with the tires a bit smaller or larger?

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Yes. My personal off-road choice for my '05 450X is to go a bit wider front and rear with Dunlop AT81s. I've been running a 90/90-21 and a 120/90-18 with no issues.

For more durability on rocks, I've been using the Maxxis Desert 120/100-18 on the rear. The AT81 is an amazing all-condition off-road tire, but wears quickly.


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oh okay, my tires are supposed to be Front: 80/100-21
Rear: 110/100-18
the tires I want to buy are Front Tire80/100M-21
Rear Tire120/90-18
do you think this will work?

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And if this helps

The first # is the width.

The second # is the aspect ratio.

The third # is obviously the diameter.

IMO the ###M is most likely the load/speed rating BUT I might be mistaken.

This gives some pretty good pics of tire measurements BUT the width/aspect ratio is (much like tire choice) a subject thing and really depends on the actual tire and where/how you ride.


I ride mostly tight/hard/technical and the trails can get really wet/snotty in the PNW and I like a 120/90 rear on my 250R but thats just me


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One consideration thought is that sizes can vary between different tire brands

as there is no industry standard exactly where to measure.

As an example, say a Kenda 110/100-18 may actually be smaller than a Maxxis of the same posted size.


For rough rocky trails, I've been running quite a large 90/100-21 on the front of my CRF250X.

No doubt it's heavier to steer around but I find it soaks up square edged hits much better.

Edited by mlatour

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oh okay gotcha will note that.
thanks for the help with the tires man if u have any idea about draining a carb i would to know how.
i just drained my fuel out of my tank and if possible would like to get the fuel mabye left in the carb out so it isnt sitting in there.
If anyone know how or best way to do this please let me know.
Definitely not comfortable taking out the carb.


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Like most variants of the popular Keihin FCR carburetor

it should have a drain screw on the bottom left hand side which allows the bowl to drain via one of the rubber lines


Link to parts microfichehttp://www.partspitstop.com/oemparts/a/hon/5053fee9f870021c54beac2f/carburetor

the screw pictured next to #48 in the above diagram should be it.

Another option is loosening the bowl bottom drain plug, usually takes a 17mm wrench.


As for the tire size variance between brands, from recent personal experience :

although both were marked as 100/100-18, a Kenda Washougal II was smaller overall (height and width) versus a Maxxis Maxxcross IT.

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if your looking at michelins.....

Michelin size 120/80x19 = 100/90x19 Conventional sizing
Michelin size 120/90x18 = 100/100x18 Conventional sizing
Michelin size 130/70x19 = 110/90x19 Conventional sizing
Michelin size 130/80x18 = 110/100x18 Conventional sizing
Michelin size 90/90x21 = 80/100x21 Conventional sizing

100/100x18 = 120/90x18 Michelin M18
110-120/100x18 = 140/80x18 Michelin M14
100/90x19 = 120/80x19 Michelin M12
110/90x19 = 130/70x19 Michelin M199
140/90x18 = Michelin M02
80/100x21 = 90/90x21 Michelin M15

Edited by highmarker

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