Manufacturers use different measuring systems (Helpfull).
It doesn't really make a lot of odds if you're stuck; something around 4" or 100mm ish will sort the rear.
I run 110/100-18 road legal MX tyre for snotty trail riding.
The recommended size for an MT21 would be 120/90 and for a Mitas E09 130/80. You'll notice that as the width goes up, the aspect ratio goes down so the actual running diameter of the tyre is about the same.
This is from Trelleborg's website.
Trelleborg motorcycle tyres are produced in standard inch sizes and in metric sizes in compliance with ISO standards. Other manufacturers including Mitas, Michelin, Pirelli use metric designation according to ETRTO standards.
The difference between the two systems is that the ISO designation is the width of the sidewall (SW), while the ETRTO designation states this width as the width of the overall Tread pattern (OW). The following conversion table can be used as a rough calculation:
ISO DESIGNATION . . . . . ETRTO DESIGNATION
TRELLEBORG . . . . . . . . . MITAS, MICHELIN
80/100-21 .........................90/90-21
110/100-18 ......................120/90-18
120/90-18........................ 140/80-18
100/100-19 ......................110/90-19
110/90-19........................ 120/80-19
120/90-19 ........................130/80-19
Last edited by Big Yellow Tractor; 15 Mar 2012 at 09:11.
Reason: formatting
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