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[mozilla]

Wider rims are easier to spin in a straightline

[CrazyG]

.....Wider rims are easier to spin in a straightline

Do whaaa ? ! ?   
Skinny wheels n tyres will always spin up more easily on dry roads
as they have less contact area to grip with...straightline or otherwise....
that is unless you are using ultra cheap tyres with rubbish compound.

[mozilla]

Ok imagine 2 wheels with identical sidewall height but different widths. Such as a 205/45/17 and 225/35/17. For arguments sake assume weight is the same too.  Both are at the same psi therefore they are both putting out the same footprint area (physics of neumatic tyres). Now the difference in the footprint is the 205 has a longer but thinner shape 225 has a more boxier short and wide contact with the ground. The long and thin contact patch really digs into the ground as its forced to flex more. The wider wheel's contact patch is stretched sideways which makes it easier to skip when accelersting. This is the same reason why wider rims are faster round corners as they dont skip/lose traction when turning as much as skinnier rims. Pretty much all road and track racing prefer wider rims. However have a look at drag racing and the wheels a lot taller than wider. They dont care about lateral grip its just max grip for straightline acceleration.

[CrazyG]

NOTE:  Split this off from an orignal post as it was starting to go off topic.

[CrazyG]

Contrary to your argument, before I had my CDi remapped
it ran on 195/50R15's......and it was virtually impossible to
spin the wheels no matter how hard I tried.

After the remap the car 'danced' and 'dashed' here n there
across the road as the tyres could not put the power down...
they span up as easy as pie.

Solution...bigger n wider wheels n tyres.
Spin ups were much much harder to induce. And it no longer
'danced n dashed' across the road.

Oh, and dragsters are not road cars, so they're not really a good
comparison to make, but as you have, there are other reasons
as to why dragster tyres are tall...but not that narrow.
1/ they have no suspension, so the tyres are the suspension.
2/ they run them at low pressure...so less tall tyres wouldn't
    have any 'give' so be no good acting as suspension
3/ the low pressure and large diameter (tallness) allows the hub
    inside the tyre to 'wind up' the sidewalls so they can put the
    power down. 

[Problemchild]

Only way it would be easier is if the wheels were a smaller size so that the frictional force x the moment arm (wheel radius) becomes less.

I think .... It's been a while

JJ

[mozilla]

What size are wolfraces you have now CrazyG? They're probably a fair bit heavier than the 195/50/15 and if 205/40/17 the outer diameters almost an inch bigger (22.7 vs 23.5 inches). Anyways there are too many other factors to consider such as grippy tyres and was the psi the same.

A similar discussion has been had on the forum before I think, hopefully Alex will be along shortly to back me up 😊

[Alex]

Yes, that's the physics of it, a narrower tire will have a longer contact patch that favors straight line grip, while a wider tire will have a shorter patch, but because the contact patch is the same area (same car, same PSI) it will be wider, favoring lateral grip.

That being said, wider tires have to deflect less at each turn to create that contact patch, so they heat up less, so they are made from a softer compound, that's more grippy.

So if all things were equal (same car, same PSI, same rubber compound) then the narrower tire would have more grip. 

So wider tires don't necessarily mean more grip, it's down to the compound of the rubber.

[CrazyG]

What size are wolfraces you have now CrazyG ? They're probably a fair bit heavier than the 195/50/15 and if 205/40/17 the outer diameters almost an inch bigger (22.7 vs 23.5 inches). Anyways there are too many other factors to consider such as grippy tyres and was the psi the same.

Not Wolfie's but Fox....17x7
outer dia is actually 0.75" larger...giving a +1.44" extra rolling
circumference, negligable difference in 'real' terms, and psi -2.

But I fail to see the reasoning as to why a wider tyre will have a
shorter patch (as Alex puts it) than a skinny tyre but have
the same contact area ?
The contact patch is wider on a 205 than a 195.....so why should
it be any shorter...unless the 205 is over-inflated. If the psi were
the same then there is a 'possibility'.....very slim mind. However,
any decent tyre specialists will tell you that you should decrease
the psi by 1 or 2 lb when you increase the profile width + decrease
the profile height (as in change from 195/50 to 205/40). Why, to
retain the ride quality as the shoulders of the 40 profile are shorter
and would give a harder ride. So if anything, the contact area due
to the reduction in psi will allow more tyre to be in contact wtith the
road.
And again...if the wider tyre as you say is heavier, then it will be even
load for the engine to spin up than a skinnhy lighter one.

Putting those 2 things together the arguement you put forward just
doesn't make any sense. That's not to say that what you say may not
be true or the case, just that logically to me it doesn't appear to.

Now if you were to point me in the direction of the writings of someone
well known, giving actual test data+details on the subject, then I'd have
no option other than to believe what you are saying, otherwise I agree
with JJ....

Only way it would be easier is if the wheels were a smaller size, so that the frictional force x the moment arm (wheel radius) becomes less.

[Alex]

Because the surface area of the contact patch is only influenced by the weight of the car and the pressure in the tire.

So tire width has no importance in the theory of it.

In practice, the tire sidewall stiffness also has an impact on the surface area of the contact patch.

[mozilla]

Because the surface area of the contact patch is only influenced by the weight of the car and the pressure in the tire.

So tire width has no importance in the theory of it.

In practice, the tire sidewall stiffness also has an impact on the surface area of the contact patch.

I suppose lower profile tyres (which are inevitable when going wider) use much more grippier rubber compounds which becomes the deciding factor. Probably improving grip over the thinner, higher profile variety and making the theory irrelevant in the real world

[stoatsngroats]

Pardon my noobness!, does a wider tyre produce a greater weight distribution of a given load, compared to a slimmer tyre, thereby reducing the effective 'weight' per sq inch of contact...?   If correct, isn't the 'grip' easier to over come...?    So for a given power/torque, the grip can be exceeded earlier f the 'weight' is lower... 

I'm wrong no doubt, but that appears to make sense to my understanding of physics, albeit, a limited understanding!!

[Problemchild]

Yeah - the pressure is less

Same car weight / 4 wheels = force on each contact spot

Pressure = force/area

So as the area gets bigger the pressure reduces (hence why an elephant produces less pressure than a ballerina on tip toes and why tanks can travel across quite soft ground)

Friction isn't dependent on area though - only the force and the coefficient of friction between the 2 surfaces. So narrow or wide tyres don't make a difference.

Can't remember how this relates to lateral grip though.

JJ

[CrazyG]

Ah...now I'm beginning to uderstand.....sort of   

[Alex]

Here is a clip I though I'd share with you, not really relevant or instructive, just fun

http://www.youtube.com/watch?v=HPh90yNX-mY