If you had a 90mm high 16" tire that runs 3000rpm @70MPH
what would be the reading with a 85mm high 16" tire?

5mm (0.19685") smaller circumference per revolution

Thanks
Zeroroadkill
'00 FLHRI

A little history about this question:
The Metzler ME880 140/90B16 rear tire is 90mm high and I run 3000rpm @70MPH. The new Metzler ME888 is not offered in a 140/90B16, but instead in a MU85B16 which is 5mm smaller in heigth than the ME880 140/90B16. I'm considering the newer ME888 tires, but need to know how the lower profile tire will effect RPM to MPH readings.

 

Assuming the 'reading' you are wanting is speed = 68.8MPH
Cheers

Edit: assumed you wanted the new speed @3000RPM .. if what you want is RPMs for 70MPH w/lower profile tire it's 3052

 

65mph would be 63.5 so you would be going slower with 85 vs 90. To do actual 65 your rpm's will be increased.
Clif

 

You might want to consider.... 5mm is not much. Think about it this way. Old 90mm vs new 90mm. There's going to be at least 5mm difference.... more than likely, more than 5mm. Now throw tire pressure into the mix. A difference of 5 lbs in the trie is going to change the tire footprint on the pavement.... probably 5mm or more.

You are not going to notice a change

 

Taking into account...

That our speedometer is set at the factory 2-5% higher than actual speed, does it really matter?

 

Do we know what the diameter of the MU85-16 tire is?Can't figure it out without that info.

 

Cant be accurately figured untill you compare the "actual" tires. I have seen a very large difference in the same size tires from different makers.

 

Check it on a gps once you install. At 70mph my speedometer runs about 73.

 

If you could measure it.....when you are going 69.44mph,your speedometer will read 70mph and your tach will read 3000rpm...I think.

 

I'm just a simple Coon *** from south Louisiana, but I would have my buddy measure the 90mm tire from the rim to the ground. Then I would let air out until the rim gets 5mm closer to the ground which I would now put me at 85mm. I'm going to guess the tire pressure close to 28-30lbs and I think that would be safe enough for a 2 mile ride. I would go test ride it and have my answer. When I get home I would put air pressure back to normal. I wonder how much the gear ratio has changed?