Help settle an argument please

Entai

Entai

Entai

Caporegime
Joined
28 Feb 2004
Posts
74,822
Hi all, here is a good one for you, a guy at work, wants to get wider wheels and tyres so that at traffic light races he will get better traction, and a better launch, with less wheel spin.

I said, most likely that will not happen, if anything you will be worse off I said. As the friction is still the same between the tyres and the road surface, no matter how big the tyres.

My reasoning is, that surely the size of the surface area of a contact patch between tyre and road, has no bearing on the friction coefficient of that contact.
The friction coefficient is only determined by the types of material that the friction is occuring between, (tyre rubber and road tarmac) and to some extent the load applied to those materials.

So in this example, the contact patch is still between the same two materials, and if anything, the load on the contact patch will be less than he already has (he is changing from steelies to alloys as well, so lighter wheels), and getting wider tyres so the contact patch is larger spreading the load more. Therefore by my reckoning in a straight line he will possibly have less traction than before, but in cornering he will be much better off.

He still insits that bigger tyres equals more rubber on the road so it has to be more grip.

So who is right??
 
Last edited:
Raymond Lin said:
Surely bigger surface area = more grip ?
Click to expand...

But the friction coefficient is constant between the two materials so surface area does not come into it.

The friction coefficient between metal and glass is the same wether the glass is 2 cm squared or 200cm squared.
 
Similar to what Fox has already said. Why do you think race cars have slick tyres?
More contact area = better grip

Further, if what you say is true, why does 4 wheel drive = better traction?
 
Entai said:
But the friction coefficient is constant between the two materials so surface area does not come into it.

The friction coefficient between metal and glass is the same wether the glass is 2 cm squared or 200cm squared.
Click to expand...

I see what you are saying but what if.

A car with

scenario A - Wheels that is 1mm wide

vs

scenario B - Wheels that is 500mm wide

I would say B would get off the mark faster won't you ?
 
Friction is simply the power of interlocking particles. If you have more of those, then there's more friction.

It's quite simple.
 
If the rolling radius is the same the grip will be worse from a standing start. A thinner tyre will have approx the same contact patch to a wider tyre with the same rolling radius. The thinner tyre will have a higher aspect ratio so when the car squats the tyre will squish enlarging the contact patch (just realising Im talking about RWD here and dont know what type of drive his car has). A wider tyre with a smaller aspect ratio will resist that squishing.

A thin tyre will have a long contact patch, good for going forwards, a wide tyre will have a wide contact patch, good for going round corners.
 
Last edited:
Bear said:
If the rolling radius is the same the grip will be worse from a standing start. A thinner tyre will have approx the same contact patch to a wider tyre with the same rolling radius. The thinner tyre will have a higher aspect ratio so when the car squats the tyre will squish enlarging the contact patch (just realising Im talking about RWD here and dont know what type of drive his car has). A wider tyre with a smaller aspect ratio will resist that squishing.
Click to expand...

Exactly what I was thinking.

He has an Astra GSi Turbo, but don't let that put you off him, he is a decent enough bloke really.;)

Again he is FWD so the weight transfer will also diminish the squish of front tyres.
 
[TW]Fox said:
If you are correct, why do dragsters have such large tyres?
Click to expand...

Dragsters have wide tall soft tyres so that on launch they rise and form a very long thin contact patch to launch the car off the start line.
 
Entai said:
Dragsters have wide tall soft tyres so that on launch they rise and form a very long thin contact patch to launch the car off the start line.
Click to expand...

Fox was talking about width not height.

Anyway, at actual launch point the tyres dont stretch tall, that happens after launch. At launch the tyre squidge down and spread over the road surface.
 
merlin said:
Fox was talking about width not height.

Anyway, at actual launch point the tyres dont stretch tall, that happens after launch. At launch the tyre squidge down and spread over the road surface.
Click to expand...

The initial width helps create the height once power is applied, because the sidewalls are so soft, that is why one rotation of a tyre gives a distance travelled of over 12 feet.
 
Entai said:
The initial width helps create the height once power is applied, because the sidewalls are so soft, that is why one rotation of a tyre gives a distance travelled of over 12 feet.
Click to expand...

Great, but not actually relevant to the point. :p

You said the tyres are high and wide so they stretch up to give the launch.

I said that imo the tyre doesn't go tall untill the initial launch has happened.

Point is the tyre going tall has nothing to do with the actual bite once torque is applied to the tyre in the very first instance.
 
Raymond Lin said:
I see what you are saying but what if.

A car with

scenario A - Wheels that is 1mm wide

vs

scenario B - Wheels that is 500mm wide

I would say B would get off the mark faster won't you ?
Click to expand...

you would have more downforce on the tyre with Scenario A, just like a woman wearing Stelleto heels has the downforce of an elephant :eek:
 
You must log in or register to reply here.
Back
Top Bottom