How to convert motorcycle tire sizes?

[Fordiesel69]

I was hesitant to post in the motorcycle section as its gear more towards lubes. I have a 90/90-18 front and a 110/90-18 rear. Would like to put dual sport tires on and cannot get these sizes. Duro has some tires that look like the tread I want, but I dont know how to convert properly.

Example the front tire is the important one for the speedometer accuracy. 90/90-18 converts to a 2.75/3.00x18. So what one do I buy? A 2.75 or a 3.00? I am just not understanding.

 

[mrsilv04]

Are there any on-line owner's groups for your make/model of motorcycle? You surely aren't the first to run into this problem, and likely they already have the answers for you.

 

[Reggaemon]

The 2.75 will keep your speedometer the closest to what you have now, that said I would go with the 3.00.
I've found motorcycle speedometers to be very inaccurate, usually reading higher than the actual speed.
I always up size if I can, never downsize.

 

[DriveHard]

The 2.75 will keep your speedometer the closest to what you have now, that said I would go with the 3.00.
I've found motorcycle speedometers to be very inaccurate, usually reading higher than the actual speed.
I always up size if I can, never downsize.

agree here...nice post

 

[02SE]

What motorcycle is it? I have a bike that gets it's speed and odometer signal from the countershaft sprocket. Others which use the ABS/wheel-speed sensors, and some of the old ones I've had have the speedo/odo drive from the front hub.

 

[Fordiesel69]

TU250x. Driven off front sproket.

 

[OILJUNKIE]

Honey, I think i bumped the curb.

 

[Ranger83]

The 2.75 will keep your speedometer the closest to what you have now, that said I would go with the 3.00.
I've found motorcycle speedometers to be very inaccurate, usually reading higher than the actual speed.
I always up size if I can, never downsize.

Believe if you test them you will find they read 8% or so high. But the odometer is exact.

“ECE Regulation No. 39, which is a 14-page document detailing speedometer accuracy for vehicles sold in EU countries. According to this law, a speedometer can read high by as much as 10 percent plus 4 km/h at a specified test speed, but under no circumstances can the speedometer read low.”

 

[Dadillac]

There are 25.4 mm in an inch. So 90 mm would be 3.54 inches. The second 90 is the sidewall height as related to the width in percentage. So a 90 height would be 3.54 times 90 percent or 3.2 roughly. And the 19 is the rim diameter. Hope this helps

Don