# 101 MPH on a 2007 YZ450F

I personally have not. However, a friend of the family had a YZ450 with a Scotts and a KTM 450 EXC with a GPR and he said the Scotts was superior. I have dealt with the staff at Scotts for many years and their customer service is great. Once, my damper had a little bit of black grease near the top of the armature, nothing major at all. I called them up and they rebuilt it for me at no charge.

I think I will go for the scotts bolt on kit(above the handlebars) then. I have only heard great things about scotts products and customer service.

On their website they only show kits for the 06-07 bike. Will these fit the 08 with the shorter headtube? Or is there a special kit for the 08?

Thanks again.

They should fit, but the definitive answer will come from Scotts themselves. Call them. They have great people in telephone service as well.

They should fit, but the definitive answer will come from Scotts themselves. Call them. They have great people in telephone service as well.

I will give them a call and see what they have to say.

So how fast should a stock crf250r with 13/51 gearing go top speed? Just wondering, thats what I have, also how do you figure it out guys? Some kinda formula?

my brother has got his KTM 525EXC up to 104 on the highway with stock gearing. He geared it down now so it goes about 85.

... how do you figure it out guys? Some kinda formula?

You need to know the peak RPM the engine is limited to, or can reach in high gear, the loaded diameter of the rear tire, the primary reduction ratio, the transmission ratio in high gear, and the final drive ratio (external sprockets).

Then:

First calculate the overall reduction ratio:

(Rear Sprocket/Front Sprocket)*Primary Ratio*Transmission Ratio = Overall Ratio

Then:

[(RPM/Overall Ratio)*Tire Diameter*3.1416]/1056 = speed at rpm in given gear.

Then reduce the answer by 9-12% for dirt, or 4-8% for pavement to allow for tire slippage (this will vary wildly based on the tire, the surface, and in particular, gets greater with speed)

Gray, I enjoy TT mainly because of your extensive knowledge....and I only see your posts regarding the YZ..... Thanks.

Gray, I enjoy TT mainly because of your extensive knowledge....and I only see your posts regarding the YZ..... Thanks.

It's almost like I wouldn't buy anything else besides a YZ because I can get so much extensive info from Gray. You should work out a deal w/Yamaha (and TT for that matter)! Thanks again!

You need to know the peak RPM the engine is limited to, or can reach in high gear, the loaded diameter of the rear tire, the primary reduction ratio, the transmission ratio in high gear, and the final drive ratio (external sprockets).

Then:

First calculate the overall reduction ratio:

(Rear Sprocket/Front Sprocket)*Primary Ratio*Transmission Ratio = Overall Ratio

Then:

[(RPM/Overall Ratio)*Tire Diameter*3.1416]/1056 = speed at rpm in given gear.

Then reduce the answer by 9-12% for dirt, or 4-8% for pavement to allow for tire slippage (this will vary wildly based on the tire, the surface, and in particular, gets greater with speed)