Wheel change 16" to 15" what's best?

[Silvia]

I guess that depends on what you mean by "better"
As I understand it, lower profiles mean less sidewall to flex and so sharper steering response.
Less sidewall flex could mean less to absorb road shocks too and a rougher ride...
Some popular sedans have low profile tyres from new, indicating that steering response is more important and that they have found ways for the suspension to absorb the additional road shocks....
Tyre pressures can be important too....

[sailaholic]

Yah but most race cars have pretty decent sidewall heights... And sidewall flex can be controlled with tire design.

I think styling and perception have more to do with rims / sidewall Size. I remember top gear fitted "standard ss" tires to a hsv and got better lap times from it.

I think what your saying is correct, but a 60 series Tyre was once considered low profile. So I just wonder where the advantage stops?

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[hks_kansei]

I think what your saying is correct, but a 60 series Tyre was once considered low profile. So I just wonder where the advantage stops?

Maybe we're heading back to when the rubber was vulcanised onto the rim itself

[Silvia]

This is the best article I've seen on the subject and debunks many myths ,like bigger contact patch means better grip etc. You can learn a lot from this....

http://autospeed.com.au/cms/title_Tyres ... ticle.html

Summarizing, what factors are important in terms of tyre grip? Tyre width has no direct relation to the amount of grip generated; it is a secondary factor, and the width basically relates to cooling potential and so the tyre compound that can be used. The size of the contact patch has no bearing on the amount of grip generated at all, apart from the extreme of where the compound is getting so hot that it no longer acts as a solid (and therefore doesn't follow Amonton's Law). The tyre pressure has no direct bearing on the level of grip (apart from aquaplaning), but it does have a bearing on the heating and cooling characteristics of the tyre. Having a lower tyre profile gives improved handling through reduced sidewall stress and improved contact patch shape stability.

[project.r.racing]

If you wanna turn corners, then don't bother with that article.

[sailaholic]

They had a few things they skipped over, but I don't know it well enough to explain it. Any chance you can project r?

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[Silvia]

Project r?
The article is certainly food for thought in the light of "fatter is better" thinking.
But when it says a lower profile means "lower sidewall stress", I can't help thinking it means more sidewall stress ,because the distortion of a higher sidewall profile is being reduced by less flexing - there is less sidewall to allow flexing so it's taking more lateral stress in staying rigid.

[sailaholic]

Stress will remain the same for the same loading condition, strain (deformation) will change. ;-)

So sorter sidewall equals smaller strain in tire.

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[Silvia]

I'd see it more as lower sidewall = same stress on smaller area. But smaller area = less deformation.
Then you would also have to consider shorter sidewall = less bump absorbtion
so rougher ride.
....the trick is to balance these out for max steering response while still acceptible ride quality

[NitroDann]

This is the best article I've seen on the subject and debunks many myths ,like bigger contact patch means better grip etc. You can learn a lot from this....

http://autospeed.com.au/cms/title_Tyres ... ticle.html

Summarizing, what factors are important in terms of tyre grip? Tyre width has no direct relation to the amount of grip generated; it is a secondary factor, and the width basically relates to cooling potential and so the tyre compound that can be used. The size of the contact patch has no bearing on the amount of grip generated at all, apart from the extreme of where the compound is getting so hot that it no longer acts as a solid (and therefore doesn't follow Amonton's Law). The tyre pressure has no direct bearing on the level of grip (apart from aquaplaning), but it does have a bearing on the heating and cooling characteristics of the tyre. Having a lower tyre profile gives improved handling through reduced sidewall stress and improved contact patch shape stability.

Was going to write a long post, but its not worth my time....

Tyres dont ONLY work under the principles of friction, ever seen tyres leave marks on the road? YES? well if a tyre is leaving itself on the road its not only friction working, its also adhesion. This is why tyres can produce cornering forces over 1G, which is not possible with friction alone (and no downforce).

Google physics.

Dann

[93_Clubman]

...max steering response while still acceptible ride quality

And what's acceptable in terms of steering & ride differs from person to person depending on their priority.

[deviant]

This is the best article I've seen on the subject and debunks many myths ,like bigger contact patch means better grip etc. You can learn a lot from this....

http://autospeed.com.au/cms/title_Tyres ... ticle.html

Summarizing, what factors are important in terms of tyre grip? Tyre width has no direct relation to the amount of grip generated; it is a secondary factor, and the width basically relates to cooling potential and so the tyre compound that can be used. The size of the contact patch has no bearing on the amount of grip generated at all, apart from the extreme of where the compound is getting so hot that it no longer acts as a solid (and therefore doesn't follow Amonton's Law). The tyre pressure has no direct bearing on the level of grip (apart from aquaplaning), but it does have a bearing on the heating and cooling characteristics of the tyre. Having a lower tyre profile gives improved handling through reduced sidewall stress and improved contact patch shape stability.

Was going to write a long post, but its not worth my time....

Tyres dont ONLY work under the principles of friction, ever seen tyres leave marks on the road? YES? well if a tyre is leaving itself on the road its not only friction working, its also adhesion. This is why tyres can produce cornering forces over 1G, which is not possible with friction alone (and no downforce).

Google physics.

Dann

Something like 10% slip under acceleration and cornering is the point you achieve maximum 'grip' and 8% slip under braking? Might be the other way around...basically a tyre is performing at its best when it is juuusssstttt losing grip.

You feel it when you get a nice 4 wheel drift going or hear the tyres howling under brakes without locking up...fun stuff

[Silvia]

And what's acceptable in terms of steering & ride differs from person to person depending on their priority.[/quote]

Perhaps so....but for road use, never met anyone who likes a banging hard suspension and everyone seems to like a good response to steering input..

[93_Clubman]

And what's acceptable in terms of steering & ride differs from person to person depending on their priority.

Perhaps so...but for road use, never met anyone who likes a banging hard suspension and everyone seems to like a good response to steering input...

We're not talking suspension, we're talking tyres. And just because you haven't met them doesn't mean they don't exist, i.e. absence of evidence, isn't evidence of absence. Again, what's a good ride & good steering varies from driver to driver. A variation on the fast, reliable or cheap, you can only have two, rule applies.

[sailaholic]

Yes but, what people consider hard and good changes., people at work think their rodeo rides nice. I think
Its so bouncy that its just as likely to put you in a tree.

Fyi, you think about stress in the wrong way, but I don't have time to explain. Basically stress is force on area. You also need a clearer view of which sizes you are looking at.


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