Looking to purchase new tires for MX and I am curious wheater to get 18" or 20". I know all the pros use 18" but why?

 

For mx 18 on an 8" wheel is the ticket because of the low profile. This helps in the turns. The 8 inch wheels are stronger and while still giving you enough rubber to protect the rim, it also allows you to run a lower air pressure for more grip.

I was running 18" tire on a 10" wheels. They looked cool and slid good but you had to keep them pumped hard to keep from bashing the wheel so they spun too much.

 

Why not the 18" on a 9" rim. There was a article in one of the rags a few months ago saying this was a good tire for the in between, it slides well with good cushion.

 

The 9" wheel is probably fine but if you look at your 18" tire options you will find that you can choose from more different tires if you go with an 8" wheel. Not all 18" mx tires can be bought for 9"wheels and all of them can be for 8" wheels.

 

Yes, I think only holeshots are avaliable in 9 inch wheels. Still you will find that you could run lower pressure on the 8" wheels without dinging the rim. I learned this the hard way.

 

I am planning on racing next year, I was planning on getting 18 inch tires but have not made up my mind yet either. The track I will be racing on is very sandy and gets very deep ruts. Alot of riders during the last race were getting hung up and actually stuck because of their ground clearance. What do you guys think, might I benfit by running 20 inch?

 

the track i run is sand and we race after the bikes so the ruts get deep i have yet to get stuck.
i run 18 inch cut turfs at 5 pounds work good the people that get stuck just are not going fast enuff.