Taller Tire Means higher Top End, Right?

[Hatter]

Ok, so ever since my tire fiasco at the VMOA rally in Eureka Springs, I have been running a Metz 140/90/15 ( all I could get at the time). I have noticed that my top end speed has dropped 5 or 6 mph (GPSed) due to the shorter tire.

Now I am going to replace both front and rear tires, and am thinking about a 170/90/15 rear.

How much will that increase my top end, if any?

hat

 

[naughtyG]

I haven't seen a rear tire in 170/90-15. Which one are you looking at?

Usually the only 90 profile rear is the 150/90-15, and the 170 comes as 170/80-15.

I went from 150/90 to 170/80 and did not notice a difference in speed. Remember that as you go faster, the tires grow taller and narrower so a 170/80 should get about the same circumference at speed than a 150/90.

 

[one2dmax]

The profile (aspect ratio) is the second number and is a percentage of height to width (the first number). So 80% of 170 = 136mm side walls (keep in mind these are approx numbers). 90% of 150 = 135mm so you should not see any noticeable difference.

90% of 140 = 126mm (9mm shorter on top sidewall and again on the bottom sidewall) so it's a noticeable difference.

The popular aftermarket wheels can be harder to estimate. So you would take a 190/50/17 which would have 85mm sidewalls but have 2 inch taller wheel. You'll still be significantly shorter if you do the math.

The shorter setup would give you quicker acceleration (like changing to a larger rear sprocket) but hurt top end performance. And the opposite is true for larger diameter combinations.

Sean