Okay everyone, I have a a FMF Power Core IV-2 silencer, 11:1 Wiseco piston, and XR400 cam. I am wondering if I went with 18" Turf Tamers in the rear, if I would need to change the gearing to get back lost top end?[img]i/expressions/face-icon-small-confused.gif[/img]

 

Assuming you are running 20 inch tires now, a change to tires that are really 18 inches tall, and not just close to that size, you will lose 10 percent of your top speed if you can't rev the engine any higher. In other words, if your top speed was 60 when hitting the rev limiter, your top speed with the new tires will be 60mph-10%= 54 mph. All gears, including first will also be 10 percent lower, which gives you a great climbing gear if you can stand the loss of top speed. If you go up on tooth on the front sprocket you will gain about 8% of your gearing back, which you put back close to where you started before changing tires.

Good luck,
Lorrin

 

Wow. Thanks a lot for your help Lorrin. Much appreciated.

 

Does your equation (sp?) work for going up to say a 23" rear tires??

SoCalQuads