For anyone who is interested, a friend of mine clocked a 04 yfz and a 2000 model 400ex with his radar gun. (he works in law enforcement)


The YFZ was stock except for the cam mod and the airbox lid removed. He may have been running a k&n. He did re-jet. The rider weighs between 140 and 150 lbs. He was clocked at 75 mph on level ground.


The 400ex was stock except for a k&n filter. It was probably running stock jetting but I'm not sure. The rider was a bit over 200 lbs. The rear tires were 22" mud grips. I can't remember what kind though. The 400 was clocked at 70 mph on level ground.


The 400 was pretty impressive to be stock.


Anyway, there ya go.


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Its imazing how much speed can be gained by the 22 inch tires on the 400ex!

The yfz is gear limited at 79mph. Anyone with stock gearing, stock tires, and stock cdi, that says they go faster than 79 is lying!

With a 15 tooth front sprocket, 20inch tires, and a +500 cdi, the yfz is capable of hitting 89mph. You just have to have the horse power to get you up there to utilize the full potential of the gearing.

I can bounce of the rev limiter all day in 5th, with the above mods done and obviously enough horse to carry me up to the 11,250rpm limiter in 5th!

 

how come the bigger tires make you go faster. i always figured that it would make you go slower just cuz it takes more RPMs to rotate the tires, but i dont know very much about that stuff, can someone explain.

 

Changing tire size does the same thing as changing a sprocket size. If you go up in rear tire size you will run slightly more top end/less low end and if go down it will give more low end power but less top end speed

 

The taller tires change the gear ratio. The taller tires actually take less rpm per tire rotation. Taller tires do rob horsepower though.

 

oh, i see. thanks

 

Taller tires (generally) do rob power, due to the added weight. However, that isnt true all the time.
Everything above is correct. Taller tires give you topspeed at the expence of slower accel. Oppisite happens when you go down to say an 18, more a mx track.
Putting 22 inch tires on a quad that usually runs 20's is almost like going up one tooth on the counter sprocket.

 

taller tires= more top end
shorter tires = more acceleration

it takes more to get the big tires goin than it does to get the little ones goin... but once there goin it takes less to get the big ones goin faster than it does little ones.