Front Tire Size - Handling Changes?

Hi All,

I recently bought an 07 YZ450F that I really like. A nice change from the CRF450R and YZ250 2T I previously had. The bike has a Pirelli Scorpion 90/90-21 MC 54rr front tire which the last owner raved about. I have always run a 756 on the front of my bikes. The bike handles different than what I was expecting in the front. It turns quick enough but seems to lack stability under hard front braking. Also, it is not very stable in sandy areas, again not what I was expecting from this bike. Both my CRF and YZ with a 756 up front were much more stable in the sand than the YZF is. The stock front tire size is an 80/100. I am going to switch to either an MX31 or 51 (not decided yet), but should I stick to the stock 80/100 size? What effect is the 90/90 size having on the handling of the bike compared to the stock 80/100? Here in Idaho the riding is a mix of everything.

Thanks for the help, this forum is great,


Dave, what part of Idaho are you in? I am in Rathdrum. I also have an '07. I currently am running the stock 742FA and don't like it much. I don't know how the sizing will change handling, but before you do any tire changes, try moving the forks up in the clamps a few mm.

I did this and it did wonders for how the front end bit in and stayed there.

Like I said the stock tire is not my favorite, because when muddy they seem to want to slide out from under the bike no matter what I am trying to do.(turn, go straight, or whatever.)

Good luck, and happy riding.

P.S., PM me if you are close by and we can set up a ride together.

As far as size goes, I've had good experiences with switching from a 80/100-21 to a 90/100-21. I feel the bike stays planted over rocks better and provides a better overall ride. I've heard that using the larger front tire can keep a bike from flowing into ruts easily, as in a motocross track, but I have not experiences this.

I've used two different 90/100x21's, and I find them more effective as a hard surface tire than soft, although the point regarding stones and roots would be applicable simply because you can run them at a lower pressure, just as you can an 18" rear vs. a 19.

You can see this with flat trackers. On a hard surface, sticking to the surface, rather than into the surface, becomes more important, so a larger section tire with more contact area works better. But overall, for anything softer than hard pack, I prefer the handling of a suitable tread design in an 80/100.

Thanks to all for the tips. I'm going to try the Geomax 51 in the stock tire sizes front and rear. The local shop said that in the Boise area that's the best setup.


Fantastic tire. You'll love it.

Thats the combo I'am running on my 08 yz450f, I love it, works good at the track, and out the trails.

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