A forum for owners of Yamaha TTR250 trail and enduro bikes!

ttrpaul · Member

Metric tyres sizes on TTR250 4GJ

Cubber · Super Guru

Welcome, Paul.

The choice of tyres is really down to personal choice, price and availability with a pinch of "where do you ride?" thrown in.

For the East Devon lanes, which can be muddy but usually semi-hard, rutted with the occasional stones I've chosen:-

Rear = Pirelli MT43, 400x18 it says on the tyre

Front = Michelin Enduro Competition IV, 90/90-21 it says on the tyre

I've found them to be very rewarding and confidence building. They give good grip in the majority of situations but if I'm in very deep, sticky, gloopy mud then the rear tyre can be a bit overcome. cry

In such conditions (South Devon) the rear choice is something knobblier, like Mitass CO2.

Ask the question in Yorkshire, Scotland and Norfolk and you'll get three more different replies at least. biggrin

Martyn

ttrpaul · Member

Thanks very much Martyn,

I can appreciate that tyres are a very personal thing - it's just the basics of the size that's got me confused, as I'm not used to tyres being measured in inches, the rear being a 4.60-18.

I've done some googling but get lots of suggestions from 100/100-18 to 130/80-18? 4.60 x 25.4mm = 117mm wide, so a 120 is nearer the mark but what profile was a 4.60-18 originally?

Confused.com !

Thanks for any pointers and I'm looking for road legal knobblies such as the Michelin AC10 or Maxxis M7304/5.

Paul

Haggis Hunter · Veteran Member

Have a look at THIS Paul.

I have had the problem of which tyre. The AC10 is good in muddy conditions but most of my riding is on rocky/sandy ground. I found the AC10's a little vague at times on the hard stuff.

I got a newer TTR which has got Dunlop D605 tyres fitted which I have found to be much better on this type of ground.

BTW my old raid, fitted with the AC10's, tyre sizes are 90/90-21 front and 120/90-18 rear.

Hope this helps

Peter

ttrpaul · Member

Cheers Peter, that's great.

Paul

brindabella · Senior Member

tyre sizing is a nightmare, but to partly answer the original question...

4.60-18 is a ridiculous (and now out of favour) method of saying that the NOMINAL tyre width is actually 4.50 INCHES.
don't laugh - the Americans confusingly decided to add 0.10 to the nominal width to indicate a "low profile" tyre.
the profile indicated by this is ROUGHLY 82% in contrast to about 90% or so for an actual 4.50 width tyre.
so 4.00 and 4.50 are standard profiles with their low profile variants designated 4.10 and 4.60.

sensible people use the metric system eg 110/100-18 where the first number is width in mm.
but sadly even this leads to problems - the manufacturers (eg European vs Japanese) cannot agree on HOW to measure the width.

one crowd measure across the tyre excluding the knobs, the other including the knobs. this matters a lot!
and anyway it is still just a nominal width, and rounded - not an actual width.

ideally you want it designed to fit the rim width (yet another dimension) and have the same circumference. as the original.
that would mean it would fit and not give a speedometer error.

I personally think it is wise NOT to go the "bigger must be better" path because bigger tyres are harder to fit, often foul the fender, fork gaiters, chainguard etc, and can lead to worse handling, as well as being more expensive and heavier.

of course the ideal has to be cheap, available, high traction, easy to fit, puncture proof, good looking, well balanced, and last forever..
...your mileage may vary

["if the shoe fits, wear it" - cinderella?]