Topic: Tire question

[2wheels]

See link
https://www.canadasmotorcycle.ca/dunlop-k81-universal-tire.html

They call this tire 4.25/85 -18
It seems this number is half the old style and half new.
Can someone explain for me?

I was thinking of getting a 4.10 -18 for my K0 CB750 rear .  And was wondering if the above tire is close enough.

[Powderman]

Obviously it is the next size bigger, should be okay. They are just showing the number in the old way and the new way to make correlating easier.

[HondaMan]

If the number is a non 0.25" number, the tire is probably a clone copy of the old trigonometric "TT100" tires. Those came in sizes like 4.10", which was equal to 3.25" round profile, or 4.25", which was equal to 3.50" round profile. To get one that is the same size as the 4.00-18 rear tire you need, the trigonometric number is 5.10x18, which is equal to 4.00" height.

This numbering is related, in the trigo-shaped tires, to the vee-profile shape of the tread. The tread is taller and thicker in the center than on the round-profile tires, so the number is bigger, while the tire itself is not. Today's trigo-tires, unless your are buying racing Dunlops or Bridgestones, are actually built on round-profile metric carcass bases, so they do not perform like trigo tires. They just LOOK like them.

Sad, but true...the true trigonometric tire on the CB750 was the very best way to go for 1-up riding, IMHO...they disappeared in 2002, though.

[2wheels]

Thanks guys.