I picked up at 95' TRX90 for my daughter for 400$ since it didn't Idle and needed a seat cover and chain. Fixed the idle as the idle fuel/air screw was turned all the way in, reset it to 1 3/8 turns out, and installed a new chain and it runs and drives perfect. Its has a nice set of Douglas wheels and Fast Trekker tires but the rear tires are too short for my needs and the bike only has 2" of ground clearance under the chain guard. The 90 is just going to be used on our wooded property for now and needs some more clearance to clear small rocks and stumps. The Tires are 18x9.5x8 Trekkers that measure VERY short at only 16" tall @ 3psi. I found a set of 20x10x8 trekkers cheap and I think they would fit fine but I'm wondering if a set of 22x11x8 tires would fit on the back since these douglas wheels have a larger offset then the stock wheels. I don't mind a loss of power, my daughter is only 50# an in currently moves my 210# butt with ease up any hill I have around me.

 

if the tires fit that would be fine and if it has 18 inch tires on it and the gearing is still stock which i think is 13/50 you can get something around 10/47 to get you about the same power it has now and a little more clearance. the 22 inch tires will only get you 2 more inches of clearance but hey its two inches you didn't have before. also remember because of the taller tires it will have a higher center of gravity which makes it more prone to flipping or over turning.

 

My experience with the little 90 has been that the stock tires/rims are very good for technical terrain. The fronts are 20" and the rear 19", and while the ground clearance isn't spectacular it works pretty well.

Back in the day, my kids could ride their 90's everywhere I went on my 4X4 Rancher. If they got hung up, it was simple to just go pick up the light little 90 and carry it through the rock crawling sections.

I would look for some stock tires and rims on ebay.