I'm after some info about motorcycle tyres (and more specifically the tyres on my vespa scooter) but I presume the ideas and theories would apply to any bike tyres. Any MotoGp tyre genius's on board?

I recently switched from Michelin to Bridgestone tyres, I've been using the michelin for a long time and fancied a change as the Michelin S1 is a very old tyre design (been around since the early 90's if not before) they are both a 'sports' type tread with a nice rounded profile (not like the old traditional 'wheelbarrow' type scooter tyre) but after switching I noticed something about the profiles of the tyres, the michelin has a profile (radius?) that looks like it's been cut out of a circle (single radius profile??) and the tread depth is the same at the edge as it is in the middle... but my new bridgestones have a profile as if it's been cut out of a slightly more oval type shape (more 'pointy' on the middle) and the tread depth gets shallower towards the edge of the tyre.

I was wondering what the advantages are of both designs and why a tyre manufacturer would do one or the other, for what it's worth I prefer the brighestone's they feel less 'squirly' when traveling over white lines and patches in the road but that might be nothing to do with the shape of the profile??

for reference here's what the look like

Bridgestone
http://ssl.delti.com/tyre-pictures/Brid ... oopB01.jpg
Michelin
http://pictures.universal-tyres.co.uk/t ... s1-600.jpg

and here's a bad 'paint' picture showing what I'm trying to describe..

Assuming they are the same profile, say 300X10, and speed marking (from J to ZR) the more arched one will have a belt made from different material to the belt in the more rounded one. The 'footprint' or contact patch is probably the same on both but, but the sharper one will 'squish' more as it gets it the ground. Contrary to what you would assume, the more 'pointed' tyre will probably take slightly more force to steer due to this, which if you have a single side fork you will be glad of as there is less steering deflection on ripples (road markings etc)

As we are all different body weights, and like different feels, experiment with your tyre pressure for a better set up. (not too much, +- 5psi at most

cheers Moby, yeah that's my experience so far that the bridgestone (the pointy ones) feel a bit more stable and much nicer over the ripples like you say, I'm glad it wasn't my imagination but I wasn't sure if it was the shape that was helping with it, good to know .. thanks. As long as they keep making them I'll stick with the bridgestone in future.

Can I weigh in with a completely non-expert opinion based only on intuition (the tyres' behaviour might be counter intuitive - or I might)?

You say the tread depth is shallower towards the edge of the tyre. I would have thought this was a disaster waiting to happen when you lean it over into a bend on a wet road? Sounds great in the dry, loads more contact patch in a corner than on a straight, but in wet conditions, don't you want more tread (more grip) when you're cornering than when you're going in a straight line?

To me this tyre sounds like it gives you great acceleration from standstill in a drag race and makes the bike really unstable through corners (both in wet conditions).

Plenty of motorcycle tyres have this tread setup, I always assumed it is to give more even wear across the tread surface, since you spend (generally) more time riding on the centre of the tyre than the edges.

_________________
"Guys I'm coming in, I'm having too much grip"
- Chanoch Nissany

right, whatever the reasons that is certainly a product of it and a positive for me, unless you are getting your knee down round corners on a regular basis (which I'm not!!) you aren't going to wear the outside cm of the tyre down at all.

I don't really know enough (anything!) about tread patterns to comment on this but it's only a couple of mil shallower. To get over on that part of the tread I would have to be leaning at a pretty extreme angle though anyway, I think my stand/exhaust/floorboards would be scraping the ground.... like this!


so as a 'wet race' tyre, I'd agree but for everyday road use I don't think it's a problem.

Due to the shape, and the 'squish' mentioned above, the tread gaps close up when the machine is upright so is close to the same displacement in actual fact.
The other, more important part is that tyre material is flexible, so the smaller and stiffer the blocks are at the edges the better it feels. If you have ever ridden a bike with off road tyres on you would feel the flex of the big chunks of rubber when the bike is leaning over and it is err, attention grabbing to say the least. You want the wheel to feel as if it is staying in a constant curve (for the same steering input. bars and/or lean) not a sort of wobble every time a rubber block flexes.

I dont know if I have conveyed what I mean here, but that is the reason, along with you spend less time on one bank or the other that on the center section or center and part of one side, so it conveniently evens our wear.