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Stretched Tyres

mitch33
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Russman Grand Master

Russman

Posted
Posted
contactpatch1hk3.gif

"Imagine driving on to a glass road and looking up underneath your tyres. This is the example contact patch (in red) for the situation I explained above. The narrower tyre has a longer, thinner contact patch. The fatter tyre has a shorter, wider contact patch, but the area is the same on both."

Because you now have more space the weight is less per cm so the contact patch decreases. Of course all sorts of factors change this, eg tyre pressure, how much its stretched etc.

Stolen from http://www.chris-longhurst.com/carbibles/tyre_bible_pg2.html

They might stretch them but its not ridiculous stretch eg a 195 on a 9.5" rim.

I don't get this. Sorry to get all technical but it's been done already. I read the the wheel and tyre bible. pretty good info.

So what they're saying is that the contact patch on the road is determined by the weight of the car and tyre pressures already and if you get wider tyres then the contact patch front to back is less because it has more left to right.

Sure but why do race cars have wide tyres then. Don't wide tyres still give more grip?

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adam-__- Grand Master

adam-__-

Posted
Posted (edited)
I don't get this. Sorry to get all technical but it's been done already. I read the the wheel and tyre bible. pretty good info.

So what they're saying is that the contact patch on the road is determined by the weight of the car and tyre pressures already and if you get wider tyres then the contact patch front to back is less because it has more left to right.

Sure but why do race cars have wide tyres then. Don't wide tyres still give more grip?

Okay I'm kind of confused now.

When they compare wider tyres to thinner tyres, is this when they put these tyres onto a wheel that's the same width? For example, they put some 205 tyres onto a 6.5" wheel, you get more of front to back grip, but if you put 225 tyres onto the 6.5" wheel you'll get more of a side to side. Is that what they're trying to say?

But lets say if you put these 225 tyres onto a wider rim, like a 7" or even 7.7", would this be more grip than the other because the shaped of the tyre on the ground won't be a rounded shape?

I hope some can understand what I'm trying to say and can explain it better. :rolleyes:

Edited by adam-__-
Russman Grand Master

Russman

Posted
Posted
Okay I'm kind of confused now.

When they compare wider tyres to thinner tyres, is this when they put these tyres onto a wheel that's the same width? For example, they put some 205 tyres onto a 6.5" wheel, you get more of front to back grip, but if you put 225 tyres onto the 6.5" wheel you'll get more of a side to side. Is that what they're trying to say?

But lets say if you put these 225 tyres onto a wider rim, like a 7" or even 7.7", would this be more grip than the other because the shaped of the tyre on the ground won't be a rounded shape?

I hope some can understand what I'm trying to say and can explain it better. :rolleyes:

Yeah ok.

In my head I still think that a 225 on a 7in rim will have the same contact area as a 225 on a 8in rim when the car is standing still.

Even comparing a 205 to a 225 on the same rim, they have almost the same rolling radius and circumference so there is not much change in front to back contact patch. Maybe this small amount is what they are refering to.

Ahh who cares. Wider tyres are better almost all the time. haha...

scathing Grand Master

scathing

Posted
Posted
Sure but why do race cars have wide tyres then. Don't wide tyres still give more grip?

Wider tyres give you a wider contact patch. So when you're cornering and the tyre flexes, you don't get as much shrinking in the contact patch.

For drag racers, since they run their tyres super deflated, it means you can have more surface area because the tyre doesn't even have to be remotely close to resembling a circle anymore.

scathing Grand Master

scathing

Posted
Posted
Because you now have more space the weight is less per cm so the contact patch decreases. Of course all sorts of factors change this, eg tyre pressure, how much its stretched etc.

That last bit is why, in context, I was wrong. :laugh:

But that's a really good, succinct, graph for what I was thinking of.

~Hypnotik~ Rising Star

~Hypnotik~

Posted
Posted
anyone know if 234/45/17 can be stretched onto the rear 8.5 inch wide rims?

Stretched?? Are you serious?? A 235 on a 8.5" rim won't even be REMOTELY stretched, it'll still be bulging a bit. Personally I wouldn't use anything more than a 235 on a 8.5 rim. I'd be using a 215.

To SAFELY stretch a tyre and be safe for road use, these are the minimum sizes:

7inch 175/60

7.5inch 185/55

8inch 195/50

8.5inch 205/50

9inch 215/45

9.5inch 225/40

10inch 235/40

10.5inch 245/40

11inch 255/40

11.5inch 265/35

12inch 275/35

You WILL be able to fit smaller tyres, but may not be safe...

Here's a good thread on tyre stretching-

What tyre to fit on a 18x10" rim??

  • 2 weeks later...
ISC-Performance Veteran

ISC-Performance

Posted
Posted

Going through this same sort of dilemma at the moment. I have "x" amount of money to spend on tyres and seeing if its going to give me better grip to run a 255/265 size tyre that is of a cheaper brand or to run a very common sized 235 tyre and buy a decent grippy tyre. If I was to run the 235 stretched I would also be looking at running some "decent" spacers to increase track and therefore one would think increase handling at the same time. The tyres are going onto 9.5" rims on a R32 GTR.

Ryan

  • 1 month later...
Mr_G Mentor

Mr_G

Posted
Posted
probably much of the same thing here but thought I'd see if anyone have ran the following sizes..

I've got 17x8 front and 17x9 rear buddy club P1's

Looking at running 215/45 on the 8" rim and 225/45 on the 9" rim

Who had those sizes?

On my current car, i run 225/40/18 on a 9" rim. We tried stretching a 215/40/18 on there but it was a no-go as it popped off. Needed to be a 45 profile for it to work.

The 215/45 will fit easily on a 8"

nisskid Grand Master

nisskid

Posted
Posted
anyone know if 234/45/17 can be stretched onto the rear 8.5 inch wide rims?

lol

thats not stretching, u can run a 235 on a 9.5" rim comfortably.

stretching has its advantages, but none of which have anything to do with making the tire work properly. stretching makes the tire very stiff and means less side wall flex as road tires have weak as piss sidewalls which has been mentioned, this is preferential to a lot of drifters, hence why it became popular in japan. having less sidewall flex means the tire acts more predictably and responsively, which means its often good to fit the the rear on drift cars to allow that response and predictability when flicking the rear around. im currently using a 225/45 on 9.5" wheel for drift, it does make it very predictable, but its pretty shit traction and not really good for anything but drift.

its also a lot about looks, just ask the boys over on ns, it can look tough used right but in the end its not really practical.

ansch: 225 of a 9" wheel will be fine, 235's are probably a better option tho.

nisskid Grand Master

nisskid

Posted
Posted
Stretched?? Are you serious?? A 235 on a 8.5" rim won't even be REMOTELY stretched, it'll still be bulging a bit. Personally I wouldn't use anything more than a 235 on a 8.5 rim. I'd be using a 215.

To SAFELY stretch a tyre and be safe for road use, these are the minimum sizes:

7inch 175/60

7.5inch 185/55

8inch 195/50

8.5inch 205/50

9inch 215/45

9.5inch 225/40

10inch 235/40

10.5inch 245/40

11inch 255/40

11.5inch 265/35

12inch 275/35

You WILL be able to fit smaller tyres, but may not be safe...

Here's a good thread on tyre stretching-

What tyre to fit on a 18x10" rim??

yep spot on.

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