Tire size comparison calculator.

[leighd42]

I found this handy calculator yesterday at Tacomaworld.com. Perhaps you have already seen it but I thought I would share anyway. With this calculator you get a visual comparison with overlay and all the ratio information for your front and rear tire size choices. I entered the info for the factory std tire size 90/90-19 and 110/90-18 then played with the tire sizes to see what combination tires would fit on our stock std rims while trying to keep the ratio of tire diameter the same as stock. It seems that a 100/90-19 and 120/90-18 combination is almost identical diameter ratio as 90/90-19 and 110/90-18 but you will ride about 3/4" larger in diameter. I was considering a 100/90-19 with 110/90-18 since 90/90-19 is harder to find but this combination results in a taller front than rear wheel which I think will slow down steering.The page quickly shows how your chosen combinations will affect rollout with a handy speedometer correction chart too.... Anyway I will be running Pirelli Sport Demons on my cafe this spring. Since I can't get a 90/90-19 in the Pirelli ,I will get (F:100/90-19 and R:120/90-18) to replace my center groove split Avon Roadriders.

DL

 

[pamcopete]

When calculating RPM's vs MPH with a motorcycle tire, you must use the rolling distance rather than the diameter or circumference of the tire as a motorcycle tire has a circular cross section which means it has an infinite number of circumferences and only the rolling distance will yield the effective circumference. The rolling distance is the distance that the motorcycle travels for one revolution of the rear tire. Rolling distance various from tire to tire due to factors such as the brand of tire, the tread depth, the composition of the rubber, the inflation pressure, the temperature of the tire and the weight of the motorcycle and rider. Here is a Excell spreadsheet that yields RPM vs MPH using rolling distance:

http://www.amckayltd.com/xs650revs.xls

 

[leighd42]

I never would have known that but it makes sense. I know the site is for Toyota trucks but the size calculator seems to work for motorcycle tire sizing from what I can tell. I will bookmark the xs650revs.xls.

Thanks again PamcoPete!
DL