# How fast is the 08 450f

Just woundering the top end speed on the 08 yz450f is.

Don't know for sure, but we had a paved airstrip that was part of a hare scramble course last summer and there was a radar display board towards the end. With my bike geared at 14/48 I clocked four times at 88mph but I was still accelerating (barely) for about 100 yds past the radar before having to get on the brakes for the corner. That was helmet on the bar pad and with my left arm tucked down on the gas tank. It felt like I could have sqeezed 95mph out of it with a little more room.

I think with the stock 13/49 gearing I would have maxxed out my speed before the radar around (and this is pure speculation) 80 mph.

I did some calcs. If anyone sees an error, please let me know and I'll correct it. I used the stock rear wheel but different tire size as I run a 120/100. If you want to know a specific top speed for a scenario I don't have, just reply or PM me and I'll plug it in. I didn't know how to post the excel file directly.

A simpler, and often more accurate, calculation can be done by simply measuring the rolling radius of the rear wheel. My numbers vary from yours by 4%, but I usually use an arbitrary 27" for the rear wheel diameter.

A couple of points about calculated speeds are that it is very difficult for a YZF to pull high gear past about 10K because the power drops off fairly hard at that RPM, and such calculations don't take into account the slippage of the rear tire. On pavement, at that kind of speed, a knobby will loose at least 5% of the calculated speed. On a dirt track, using half-mile tires, it's closer to 10%, and on most off-road surfaces, tire slippage accounts for 10-20% or more.

Im not sure how the 07 matches up to the 08, but i clocked my 07 yz450 at 86.7mph. Completely stock bike on pavement measured by a handheld gps. I didnt hit the revlimiter, and there was no elevation change(flat road).

MY 06 YZ with 13/50 tops out at 83mph on a hard pack dirt road.

The chart looks pretty close:thumbsup:

I've got completely stock 06 and I also ran 86 with a hand held GPS on a dry lake bed at 2,000 ft altitude.

My YZ250 went 73.

A simpler, and often more accurate, calculation can be done by simply measuring the rolling radius of the rear wheel. My numbers vary from yours by 4%, but I usually use an arbitrary 27" for the rear wheel diameter.

A couple of points about calculated speeds are that it is very difficult for a YZF to pull high gear past about 10K because the power drops off fairly hard at that RPM, and such calculations don't take into account the slippage of the rear tire. On pavement, at that kind of speed, a knobby will loose at least 5% of the calculated speed. On a dirt track, using half-mile tires, it's closer to 10%, and on most off-road surfaces, tire slippage accounts for 10-20% or more.

I'm with ya 110% grayracer. Rear Wheel dia is ~28.5", there is your 4% to 5.25%. After looking at some dyno sheets last night and found that the peak HP is at about 9000 rpm, 11000 was too high of an estimate, so I split the difference, kinda. I have found that on pavement these calcs are within about 5mph. In dirt it is about 10-12mph slower than the chart.

lets just say that it's faster than you need it to be while riding on dirt.

Is it ok to hold my bike wide open for minutes at a time, like on a dry lake bed?

I always think the thing is going to explode or something:jawdrop:

Is it ok to hold my bike wide open for minutes at a time, like on a dry lake bed?

I always think the thing is going to explode or something:jawdrop:

It can take it as long as you have the jetting right.