Dynod BUT couldnt get traction even in 5th so only made 404bhp lol

Texx

Super Moderator
Guys after doing some research maybe this is something to consider. Have a read through this and see what you think. I dont think its as simple as what your saying Texx. Seems like there is alot more to it.

And dont get me wrong i really value your views here im just throwing this out there, Im no expert. And your obviously very knowledgeable.

http://www.performancesimulations.com/fact-or-fiction-tires-1.htm


Just had a quick skim through that (couldn't bring myself to read the whole lot word for word).

The data suggests to me that the contact patch area may deviate slightly between a wide/narrow tyre when looking at various loads and tyre pressures, however I would imagine some of that is to do with the design of the tyre carcass to cope with racing conditions. After all the tyre would need to maintain most of it's shape when the car is thrown hard into a corner.

Though the data does suggest that with at the extreme increase in load a wider tyre may in fact have a slightly larger contact patch area, at the same time there is a reduction in the amount of pressure that larger contact patch is putting onto the ground.


All of this won't add up to more grip from a tyre anyway. The weight of the car is the force pressing the tyre onto the road, the area of the tyres contact patch just spreads that weight out. Why do football players have studs on the bottom of their boots rather than playing in smooth bottom flip flops? The higher contact patch pressure due to the lower contact patch area (the same weight acting down on small studs rather than the whole surface of a flip flop) provides them with better 'grip'.


This can be demonstrated by putting the open palm of your hand flat onto a table, push your body weight down onto the table through your hand and then try to slide your hand across the table. Then do the same but use the tip of your index finger rather than the palm of your hand (i.e. a smaller contact patch area but higher contact patch pressure). You should find it more difficult to slide your finger across the table than you did with the palm of your hand, however if you did this quickly you would find that your finger would start to burn (overheat) where as the palm of your hand would remain at relatively the same temperature.

Now go back to your 'palm of the hand' exercise but give a heavy exhale of breath onto your hand first, this will increase the coefficient of friction of the surface of your skin and suddenly the amount of 'grip' or resistance to sliding across the table should be increased.
 

Paul_JJ

Member +
Good info here, that explains why the tyre pressure must remain the same no matter what's the size of the rim or width, as the car weight remain the same.
 

AdamB

Member +
Very good read here lads.

But :haha:
I can't help but throw it in there... how can the tyre on my dads skyline (285) provide the same grip as my 195 tyre? A wider tyre will have a larger patch across the ground like you demonstrated Texx with your paint skills. Surely a patch stretched wider across the width of the tyre will provide better traction since its not being "point loaded"? Where as with a 195 tyre the loading point will remain within a smaller section of the contact patch, therefore being easier to "break" traction since the loading has been concentrated over a smaller surface area.
 

Texx

Super Moderator
how can the tyre on my dads skyline (285) provide the same grip as my 195 tyre?

I'm not saying it would. Your 195 tyre would probably be too narrow for the Skyline to begin with, however the 285 probably wouldn't provide the Starlet with any additional grip over the 195. The 285 might appear to prevent wheel spin in the Starlet, but that would be more to do with the additional drag from the increase in unsprung weight. The tyre size needs to be sensible and suited to the size and weight of the car, also you need to take into account the intended use and the prolonged periods of speed the car is going to achieve most often.

Let's put it this way, if you could fit a 195 tyre with a softer compound without it over heating, why would you want to add more unsprung weight to the car by fitting wider tyres? Seems like a backwards way to go in terms of gaining performance.

The answer to this isn't to go with the train of thought where by you fit the widest tyres you can physically get on the car, the obvious way is to fit the narrowest tyres possible that are made of the softest compound you can use without them over heating, tune your tyre pressures to get the temperature across the contact patch as even as possible and most of all ensure that the suspension/steering geometry is suitable for your intended use and setup correctly. The ambient/road surface temperature will also play a big part in tyre selection, for example a cold winters day vs a hot summers day wouldn't see the same performance from the same tyre, the tyre that performed well in the winter would over heat in the summer, like wise the tyre that performed well in the summer would struggle to maintain it's temperature during the winter. In this respect you could either use tyres made of a softer/harder compound, or use the same compound but use a wider/narrower variant of that tyre. But, lets not forget tyre pressure in this scenario. Temperature is a measurement of the speed at which molecules and atoms move around in a gas, as temperature increases the atoms and molecules move faster, in an air tight container (such as a inflated tyre) this results in an increase in the gas pressure. So it's clear to say that as the temperature of the tyre increases so does the air pressure inside the tyre. Hang on, doesn't tyre pressure affect the contact patch??! It seems now we realise the tyre pressure increases with tyre temperature, our contact patch is shrinking as the tyre heats up. What can we do now, well either we drop the initial tyre pressure to achieve our desired contact patch under driving conditions, or we use a wider tyre to control the heat more effectively. Both of these solutions have their advantages and disadvantages.

There's no perfect single tyre size and compound for every car, it's trial and error but based more on physics than guess work.


I suppose if we want to simplify this as much as possible, assuming the weight of the car remains the same we can say that:

Tyre compound provides the level of grip
Tyre pressure controls the area of rubber touching the ground
Tyre width controls the operating temperature of the tyre compound

A mixture of all three factors ultimately dictates the traction available under all conditions. A tyre that provides the most traction off the line will no doubt over heat after several hard laps around a race track. Like wise a tyre that provides maximum grip under hard track driving will not provide a great deal of traction when launching off the line.

The idea of 'wider tyres, more grip, fuck yeah!' is very much flawed.
 

AdamB

Member +
I'm not saying it would. Your 195 tyre would probably be too narrow for the Skyline to begin with, however the 285 probably wouldn't provide the Starlet with any additional grip over the 195. The 285 might appear to prevent wheel spin in the Starlet, but that would be more to do with the additional drag from the increase in unsprung weight.

Getting confused here lol, but in the first post you stated the width and height of the tyre has no effect on grip level, so in esscence all be it a 285 tyre or a 195 tyre, if they are both of the same compound, same pressure and under the same load the larger tyre would not provide any more grip?
 

Texx

Super Moderator
By adding additional mass to the wheel (i.e. a larger tyre) it'll require a greater deal of force to get it moving, so using this method to reduce wheel spin would be no different to reducing the power output of the engine when using the lighter wheel/tyre combo. You might see less wheel spin but it'll not result in any additional force accelerating the car.
 

AdamB

Member +
Agreed, which is why to me anyway, its obvious that a drag car would use the smallest tyre it could get away with because its linear acceleration will be faster than that of a wide tyre?

However would it not need to be carefully considered what the car was going to be used for as to what size tyre to go for?
As a track car will want a wide tyre to dissipate heat, yet a drag car will want acceleration?
 

Texx

Super Moderator
a track car will want a wide tyre to dissipate heat

That depends as to whether the tyre compound being used is over heating. If the narrower tyre in use isn't getting too hot there's no reason to fit a wider tyre. However, if your narrower tyre is doing fine, you could switch to a wider tyre made of a softer compound to increase the available grip, but bear in mind that the wider tyre will weigh more and also have an impact on the way the car drives.


However would it not need to be carefully considered what the car was going to be used for as to what size tyre to go for?
As a track car will want a wide tyre to dissipate heat, yet a drag car will want acceleration?

Exactly! My original point was that you won't see an increase in traction just from fitting wider tyres to the car, there is far more at play than that.
 

AdamB

Member +
That depends as to whether the tyre compound being used is over heating. If the narrower tyre in use isn't getting too hot there's no reason to fit a wider tyre. However, if your narrower tyre is doing fine, you could switch to a wider tyre made of a softer compound to increase the available grip, but bear in mind that the wider tyre will weigh more and also have an impact on the way the car drives.

Is there anyway to tell what tyre would be best to go for then? How can you tell how soft the compound is? Just thinking because if say its a road car, and you run say yoko ad08's on a 195 yet you find them overheating, how can you increase size and get a softer compound when the ad08's could be the softest compound you can buy?
 

Texx

Super Moderator
if say its a road car, and you run say yoko ad08's on a 195 yet you find them overheating, how can you increase size and get a softer compound when the ad08's could be the softest compound you can buy?

First thing to do is check the tyre pressure when the tyre is hot, you may get some improvement from dropping the cold pressure, also look at camber and toe settings, if the tyre is running on the edge of the side wall too often the heat generated will be concentrated into a smaller section of the tyre. If that's not enough then your left with either switching to a 205 AD08 (assuming we're talking 15" wheels) and hope the additional 10mm width will drop the tyre temperature enough, or switch to a 195 tyre with a harder compound than the AD08. Failing that you'd have to look at a different diameter wheel that will accommodate different tyre width/compound combinations.

Again, there's no single tyre size/compound/pressure combination that will provide the best results under all conditions. It's also quite possible that the tyre is overheating because your pushing the car beyond the limits of what is reasonable, more often than not learning to drive the car quick whilst looking after your tyres is a challenge in itself.
 

Topher-EP82

Member +
Texx - loving the knowledge on tires :D great fun to read.

OP - Man this car is powerful.. I can't imagine 450Bhp in a starlet... jeeeez lousie that must be one fast car . good luck with your next Dyno session buddy, i'll be watching out for the thread titled 500Hp at last ;P
 

Dan3SGTE

Member +
Texx - loving the knowledge on tires :D great fun to read.

OP - Man this car is powerful.. I can't imagine 450Bhp in a starlet... jeeeez lousie that must be one fast car . good luck with your next Dyno session buddy, i'll be watching out for the thread titled 500Hp at last ;P


Thanks mate :) Its quite hard to imagine the kind of acceleration, its just stupidly fast, a constant hard pin you back in your seat till the top speed.. And just savage around the roads with torque steer to easily send you in a bush lol. Its a good experience.
 

AdamB

Member +
First thing to do is check the tyre pressure when the tyre is hot, you may get some improvement from dropping the cold pressure, also look at camber and toe settings, if the tyre is running on the edge of the side wall too often the heat generated will be concentrated into a smaller section of the tyre. If that's not enough then your left with either switching to a 205 AD08 (assuming we're talking 15" wheels) and hope the additional 10mm width will drop the tyre temperature enough, or switch to a 195 tyre with a harder compound than the AD08. Failing that you'd have to look at a different diameter wheel that will accommodate different tyre width/compound combinations.

Again, there's no single tyre size/compound/pressure combination that will provide the best results under all conditions. It's also quite possible that the tyre is overheating because your pushing the car beyond the limits of what is reasonable, more often than not learning to drive the car quick whilst looking after your tyres is a challenge in itself.


Thanks for that mate.
Is there a reason why other cars use such wide tyres from the factory? Like Range rovers, is it just due to the weight of the vehicle they will need a wider tyre?
What about like a small lotus, surely they have tyres wider than the starlet? Yet most are used on the road so the wide tyre you would find isn't suitable unless its on track?
 

Dan3SGTE

Member +
Thanks for that mate.
Is there a reason why other cars use such wide tyres from the factory? Like Range rovers, is it just due to the weight of the vehicle they will need a wider tyre?
What about like a small lotus, surely they have tyres wider than the starlet? Yet most are used on the road so the wide tyre you would find isn't suitable unless its on track?

It cant be just weight as you get corvettes that only weigh like 1400KG and they are using 300's on alot of them! And porches they arent heavy but they use massive rear tires and these cars have incredible traction...

I get the whole theory behind all this now thanks to texx... However, i will still be going for a larger 16's wheel for more gearing(which in effect wiill spread the power giving more traction anyway but also i will try a 215 tire and see how i get on... I do love a theory but until i personally put things into practice sometimes i just cant accept things and this is one of those things...
 

Rev

Member +
Just a simple thought, although contact patch area can equate to grip the shape of the patch will mean grip varies in corners . I guess with strong sideways movement say the tyre lifts 1 inch of tread it will be lifting more of the square patch contact area than the wider tyre contact area which has a thinner patch at the edge.
 

AdamB

Member +
Just a simple thought, although contact patch area can equate to grip the shape of the patch will mean grip varies in corners.

This is what I was trying to get my head around, a narrower tyre will have its weight loaded onto a a more compact area of the contact patch, where as a wider tyre will spread the weight out over the width better than what a narrower tyre could, thinking that the wider tyre will provide better traction.
But as has been pointed out it will depend on what the car is going to be used for as to what tyres and area of contact patch would be best suited, as for a track car surely a wider tyre with a wider contact patch would provide better traction through corners.

I do agree with Dan, its hard to get your head around this, its one of those that needs to be put into practice to see the results.
 

AdDaMan

Member +
The reinforcement in a tyre carcass transmits force to a wider area inside the tyre than just the contact patch. Plus the sidewall also supports some of the road load, more so with lower profiles. But as the tread blocks cover less than 100% of the contact patch, the ground pressure under them can actually be much higher than the inflation pressure, just to add to the confusion.
Also the overall equation changes as the tyre heats up, and as speed changes too.
Mathematical models are becoming increasingly complex as more is discovered about tyre behaviour.

In summary, wider tyres DO have more contact area, but a tyre twice as wide does not have twice the area!
 

Dan3SGTE

Member +
The reinforcement in a tyre carcass transmits force to a wider area inside the tyre than just the contact patch. Plus the sidewall also supports some of the road load, more so with lower profiles. But as the tread blocks cover less than 100% of the contact patch, the ground pressure under them can actually be much higher than the inflation pressure, just to add to the confusion.
Also the overall equation changes as the tyre heats up, and as speed changes too.
Mathematical models are becoming increasingly complex as more is discovered about tyre behaviour.

In summary, wider tyres DO have more contact area, but a tyre twice as wide does not have twice the area!

Alright Ad, jeez where did that come from lol! Nice bit of info
 

Paul_JJ

Member +
It cant be just weight as you get corvettes that only weigh like 1400KG and they are using 300's on alot of them! And porches they arent heavy but they use massive rear tires and these cars have incredible traction...

I get the whole theory behind all this now thanks to texx... However, i will still be going for a larger 16's wheel for more gearing(which in effect wiill spread the power giving more traction anyway but also i will try a 215 tire and see how i get on... I do love a theory but until i personally put things into practice sometimes i just cant accept things and this is one of those things...

Porsche have the engine above the wheels at the rear of the car, that pushes a lot weight on them during the hard acceleration and helps with breaking as well. Also lets not forget how much electronics these cars are currently using...
Cars like Range Rover are really heavy which means that during the hard acceleration or cornering almost 3 tonne will go just on 2 wheels, they have to be big to withstand the pressure in my opinion.

I have 2 sets of different alloy wheels one is 195/50R15 and the other is 185/60R14 - this is talking on my own experience - I used to have Dunlop Tyres on both 15 inch and 14 inch - so here we have exactly the same compound - but different:
1) Wheel weight 13 kg vs 15kg (Fully inflated)
2) 10mm width difference
3) 1 inch wheel difference but the profile is 50 vs 60 - so the actual height is almost the same.

What are the pros and cons here:

15 inch Pros
1) Better grip under hard acceleration in dry - reduced wheel spin
2) Better braking in dry
3) Better handling in dry

15 inch Cons compared to 185/60R14:
1)Bad comfort
2)Wet/snow grip (Acceleration/Braking) is not brilliant, but OK
3)The Handling in Wet is not as good

The 14 Inch results would be the opposite of the 15 inch.

So based on my own experience the conclusion would be:
For bigger power in dry the profile has to be as low as possible and the width of the tyre should be increased, but that would ruin the comfort/driving in the wet or snow, so it would be ideal for the summer or for those who live in a hot climate. However for those who live in a cold climate a smaller tyre width and a bigger profile would be recommended. And this is exactly what I do - I use 15 inch in most of the year and in the Winter I use 14 inch wheels with snow tyres.

I hope this helps.
 
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