Rim size vs tyre size calculator?

**prvoke** · 15th August 2007, 08:26

Aside from clearnace issues etc does anyone have a calcualtor or table that shows what sizes fit what widths?
Or can anyone tell me that a 110/70 will fit ok on a 2.5" front rim

thanks

**Grub** · 15th August 2007, 09:02

Originally Posted by prvoke

Aside from clearnace issues etc does anyone have a calcualtor or table that shows what sizes fit what widths?
Or can anyone tell me that a 110/70 will fit ok on a 2.5" front rim

I learned a Great Wisdom a few months ago when going for new tyres on the '90 CBR. And that is that the tyre that goes on that rim is the one the manufacturer recommended when that rim was on that bike. The manufacturer's riders and engineers spent hundreds of hours on the test circuits working on the best combination of tyres for that bike to get it to work right.

The problem is that everyone thinks new bikes with big fat sexy tyres look cool - and they do. But the same tyre on a 1989 bike might just turn it into a killer. It might not roll onto corners at all, it's steering may be weird, the whole geometry of the frame, camber, head angle and swing arm will probably stop working as one - certainly as they were designed to do.

So just have a good think about this first ... figure out if you can do better than Honda's supercomputers, riders and test rigs did in speccing your bike. The '90 CBR we have is one of the sweetest handling things on it's daily commute over Paikak hill, it's the whole original spec package that makes it that good.

Also be aware that tyres are made for specific width rims and if you deviate from that you get tyres that are curved into a funny shape and they stop operating as they were designed to, no matter what bike they're on.

**prvoke** · 15th August 2007, 09:52

fair enuf thats the sorta info i was after, trouble is i cant seem to find a decent tyre in 100/80/17 ?

**Grub** · 15th August 2007, 10:05

Originally Posted by prvoke

fair enuf thats the sorta info i was after, trouble is i cant seem to find a decent tyre in 100/80/17 ?

Talk to a good bike shop, they'll order one in. They have direct access to the manufacturers data. The tyre on your bike is likely a crossply as it is on mine. You can't sub a radial 70 series and make it work but TSS got the 80 series for me. Their advice was spot on and they supplied the goods.

**prvoke** · 15th August 2007, 10:09

What are you running at the moment? Ive got worn bridgestone battleax bt45s. i could jst replace with new but thought i may as well step up ?

**bimotabob** · 15th August 2007, 22:29

Originally Posted by prvoke

Aside from clearnace issues etc does anyone have a calcualtor or table that shows what sizes fit what widths?
Or can anyone tell me that a 110/70 will fit ok on a 2.5" front rim

thanks

Yeh watch out mixing radials with cross plys it's a no no.
Also the rim is too narrow as that tyre is for a 3 inch like RGV

Tyre manufacturers like Pirelli put out cool booklets with rim widths with the IDEAL tyres and also the ACCEPTABLE tyres.

Eg 4.5 inch can take 150, IDEAL 160, 170 or 5.5 inch 170, IDEAL 180,190.
This is by memory but you get the idea - but the bikes geometry etc alters the right choice also and is why some bikes don't always have the seemingly best choice

Don't go super wide for looks like has been said.

Regards