Motorcycle Tire Size

[mbuk]

Building a Kawasaki KR1S (250 production) for Bonneville and i am having trouble getting the original tyre size in V rating which is 140/60/18, but i can get 140/70/18. Will the higher profile tire be good or bad or not make much differance?.

   140/60-18   140/70-18   Difference
Diameter inches (mm)   24.61 (625.2)   25.72 (653.2)   1.1 (28) 4.5%
Width inches (mm)   5.51 (140)   5.51 (140)   0 (0) 0%
Circum. inches (mm)   77.33 (1964.12)   80.79 (2052.09)   3.46 (87.96) 4.5%
Sidewall Height inches (mm)   3.31 (84)   3.86 (98)   0.55 (14) 16.7%
Revolutions per mile (km)   819.37 (509.13)   784.25 (487.31)   -35.12 (-21.82) -4.3%

Thanks

Andrew Lewis

[sabat]

Hard to know exactly, but I would guess it won't make much difference, the speed rating is certainly more important in this case. Be sure to include an accurate circumference measure in your gearing calculation. good luck, Dean

[donpearsall]

Which Bonneville are you attending? Speedweek? BUB?

If BUB I asked the same question of Drew, the head AMA/FIM inspector and was told that with a production bike, it is allowed to change tire size if it is required to meet the speed requirements.

Don

[mbuk]

Hi, i will be attending Speedweek. i don't think there's an tech issue. It's more a performance question.

Andrew

[JonAmo]

Well I guess if you use the 140/60/18 "V" you can't race.... Use the 140/70/18 and in this case it doesn't matter what it does, because you now can race... Doesn't seem like too much of an decision to me?

[edinlr]

The 70 series tire should be slightly taller than the 60 series, so it will raise your gearing slightly (lower numerically).  I have found there is often as much as a half inch height difference between the same size tires, but it is probably less than a one tooth change on your rear sprocket.  Enjoy the safety of your new tire.