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      03-22-2012, 12:38 PM   #23
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I respectfully disagree. setup of 275/275. My understeer has gone away because I have increased traction in the front axle, not because I have decreased it in the rear. I have not decreased overall traction at all. Quite the contrary. Now I can feel a neutral slide (4-wheel drift) through mid-to higher-speed sweepers, while before it was all push, and can now rotate the car into lower speed corners with trail brake, an aggressive turn-in and appropriate throttle use much more easily than with the staggered setup I had before.
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      03-22-2012, 12:55 PM   #24
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Yep!Chumpcar & Lemons are great leading edge technical hotbeds to help guide your track day preparation
FYI, tires are a free upgrade for Chumpcar, as long as we run street tires. So we can spend as much $$ as we want. We cannot find a better lap-grip/$$ tire out there. They are great tires.
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      03-22-2012, 01:12 PM   #25
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FYI, tires are a free upgrade for Chumpcar, as long as we run street tires. So we can spend as much $$ as we want. We cannot find a better lap-grip/$$ tire out there. They are great tires.
We are not exposed to them up here as Dunlop does not sell them here in Canada or at least the last time I checked.
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      03-22-2012, 01:28 PM   #26
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We are not exposed to them up here as Dunlop does not sell them here in Canada or at least the last time I checked.
You can't buy from Tire Rack?
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      03-22-2012, 01:41 PM   #27
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You can't buy from Tire Rack?
Sure can but with shipping it works out to $387.50 + 7% duties & installation.I paid $330 last year for installed NT05's.My local tire guy is also checking this out for me.

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      03-22-2012, 07:57 PM   #28
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I respectfully disagree. I went from a street (PS2) setup of 255/275 F/R to a square track (NT-01) setup of 275/275. My understeer has gone away because I have increased traction in the front axle, not because I have decreased it in the rear. I have not decreased overall traction at all. Quite the contrary. Now I can feel a neutral slide (4-wheel drift) through mid-to higher-speed sweepers, while before it was all push, and can now rotate the car into lower speed corners with trail brake, an aggressive turn-in and appropriate throttle use much more easily than with the staggered setup I had before.
Agreed. Did the exact same transformation and got same result, very satisfied!
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      03-22-2012, 08:33 PM   #29
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All good points, although you must've got the last set of AD08s in 275, SehrSchnell, because I only see 265 and below left in a 35/18. Looks like my options are NT05's for eight eighty-eight, Star Specs for two bills more, and AD08s for a bill more than that (sorry if that's confusing, dunno if this forum censors prices outside the classifieds). Since the Star Specs would also be usable if we get a summer storm that soaks the track, it sounds like they would be the best bang for my buck.
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      03-23-2012, 02:49 PM   #30
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Sure can but with shipping it works out to $387.50 + 7% duties & installation.I paid $330 last year for installed NT05's.My local tire guy is also checking this out for me.
Not available in Canada as of yet with no ETA according to Goodyear Canada(Dunlop).They are available according to the website.Now I on a mission!
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      04-15-2012, 01:06 AM   #31
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Not available in Canada as of yet with no ETA according to Goodyear Canada(Dunlop).They are available according to the website.Now I on a mission!
I would stay away from the Dunlop SS...had a friend with a terrible experience using them on his car. Long story, but I know i am never going to use them myself!
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      04-15-2012, 02:43 AM   #32
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I would stay away from the Dunlop SS...had a friend with a terrible experience using them on his car. Long story, but I know i am never going to use them myself!
Post link, pls!

Or at least say what the issue was. Was it wear-related? Maybe grip decreased when they got hot?

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      04-15-2012, 02:49 AM   #33
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Originally Posted by Sleeper519 View Post
... My understeer has gone away because I have increased traction in the front axle, not because I have decreased it in the rear. I have not decreased overall traction at all. Quite the contrary. Now I can feel a neutral slide (4-wheel drift) through mid-to higher-speed sweepers ...
This comment got me thinking... It seems natural to me that F/R grip should be equal, if F/R weight is equal. Maybe not, since front & rear do different things... interesting to contemplate.
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      04-15-2012, 10:14 PM   #34
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Originally Posted by Drifty// View Post
This comment got me thinking... It seems natural to me that F/R grip should be equal, if F/R weight is equal. Maybe not, since front & rear do different things... interesting to contemplate.
For the same weight and inflation pressure, by putting a wider tire you make the contact patch wider and shorter. This increases lateral grip but reduces longitudinal traction.

You are right about front and rear tires doing different things. Remember the friction circle, the rear tires also have to propel the car, so less lateral grip is available when you are on the throttle (maybe not on your quattro though )
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      04-16-2012, 08:53 PM   #35
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For the same weight and inflation pressure, by putting a wider tire you make the contact patch wider and shorter. This increases lateral grip but reduces longitudinal traction.

You are right about front and rear tires doing different things. Remember the friction circle, the rear tires also have to propel the car, so less lateral grip is available when you are on the throttle (maybe not on your quattro though )

Wider, yes. Shorter??

Your contact patch will have more total surface area contacting the pavement, which will increase both lateral and longitudinal grip. One of the best things about having the wider rubber up front is the increase in the braking ability of the car (longitudinal grip).
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      04-16-2012, 09:07 PM   #36
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Quote:
Originally Posted by Sleeper519 View Post
Wider, yes. Shorter??

Your contact patch will have more total surface area contacting the pavement, which will increase both lateral and longitudinal grip. One of the best things about having the wider rubber up front is the increase in the braking ability of the car (longitudinal grip).
I believe your statement is not entirely accurate, unless you reduce tire pressure that is.

As I mentioned before, for a given load and tire pressure, the contact patch area remains essentially the same regardless of tire size (with the exception of the effect of sidewall stiffness naturally). The math behind this is quite simple: contact patch area (sq in) = load (lb) / tire pressure (psi).

So a narrower tire will provide better longitudinal grip and a wider tire will provide better lateral grip. Everything in life is a compromise .

When we talk about the famous friction circle, it is not an actual circle but more of an ovoid shape that is dependent of tire size.

Last edited by CanAutM3; 04-17-2012 at 06:39 AM.
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      04-16-2012, 10:25 PM   #37
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I believe your statement is not accurate, unless you reduce tire pressure that is.
...implies the contact patch of a 195 mm tire has the same area as that of a 305 mm tire, assuming all else is equal.

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So a narrower tire will provide better longitudinal grip and a wider tire will provide better lateral grip.
...implies the same 195 mm tire will out-brake the 305 mm tire.

Supporting evidence would be appreciated.

BTW, I also don't see why the shape of the contact patch should relate much to lateral vs. longitudinal grip. In fact, it seems to me that the narrower tire would be better setup to transfer force to the sidewalls & wheel, in the case of lateral acceleration.
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      04-16-2012, 10:45 PM   #38
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...implies the contact patch of a 195 mm tire has the same area as that of a 305 mm tire, assuming all else is equal.
Yessir (well sort of, assuming all else is equal: tire structural stiffness does have a significant impact though, especially with drastic size differences like your example)

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...implies the same 195 mm tire will out-brake the 305 mm tire.

Supporting evidence would be appreciated.
In theory yes, but there are many other factors involved. With good performance tires, the brakes ability to dissipate heat is one of the important limiting factors.

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Originally Posted by Drifty// View Post
BTW, I also don't see why the shape of the contact patch should relate much to lateral vs. longitudinal grip. In fact, it seems to me that the narrower tire would be better setup to transfer force to the sidewalls & wheel, in the case of lateral acceleration.
I don't want to get too technical, already got for it .

From what I remember it all has to do with slip angle. Essentially how tire elements deform as they enter contact with the road surface and eventually slip as they are being unloaded during a rotation. The more the tire elements stay in contact with the surface, the more grip is generated. So the longer the contact patch is in the direction of the load, the greater the grip in that direction.

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      04-17-2012, 12:39 PM   #39
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Yessir (well sort of, assuming all else is equal: tire structural stiffness does have a significant impact though, especially with drastic size differences like your example)



In theory yes, but there are many other factors involved. With good performance tires, the brakes ability to dissipate heat is one of the important limiting factors.



I don't want to get too technical, already got for it .

From what I remember it all has to do with slip angle. Essentially how tire elements deform as they enter contact with the road surface and eventually slip as they are being unloaded during a rotation. The more the tire elements stay in contact with the surface, the more grip is generated. So the longer the contact patch is in the direction of the load, the greater the grip in that direction.
No worries, no flame here.

But, I don't see how a 195mm tire can have the same contact patch area as a 305mm. That was your original inference, that a wider tire has less longitudinal dimension ("shorter") than a narrower tire. The longitudinal dimension should be exactly the same, while width obviously increases, and therefore area increases.

We area assuming car weight and tire pressure are static for this math problem. And sidewall characteristics and slip angles, etc. shouldn't enter into it.
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      04-17-2012, 04:38 PM   #40
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Originally Posted by Sleeper519 View Post
No worries, no flame here.

But, I don't see how a 195mm tire can have the same contact patch area as a 305mm. That was your original inference, that a wider tire has less longitudinal dimension ("shorter") than a narrower tire. The longitudinal dimension should be exactly the same, while width obviously increases, and therefore area increases.

We area assuming car weight and tire pressure are static for this math problem. And sidewall characteristics and slip angles, etc. shouldn't enter into it.
My understanding:

There are two elements of a tire that support the weight of car: the tire structure and the air pressure inside the tire, with the latter carrying most of the load. Just think of it, if you totally deflate your tire, the tire by itself is not able to support the weight of the car (except for run-flats).

The tire does not stay perfectly round, it deforms to create a flat section where it contacts the pavement (imagine an under-inflated tire as an extreme example). The length of this flat section times the tire width is the contact patch area (assuming a rectangular contact patch). Pressure needs to be applied to a surface area to be able to exercise force. Hence the equation I stated: contact patch area = load / pressure.

However, this equation does not factor in the load that is carried by the tire structure. It can be used to compare a given type of tire of similar sizes, where the tire structure is fairly similar. For example comparing a 245 NT01 to a 275 NT01 (which was the original point of the discussion ). But if you compare different types of tires or tires of very different sizes, the tire structures will have a greater impact.

The general principle still applies though, but not necessarily in a linear fashion.

So yes, the area of the contact patches of a 195 tire and a 305 tire will most likely be similar; but not exactly the same, as the load carried by the tire structure will be different for both tires (most likely with the 305 structure designed to generate a slightly larger contact patch). And yes, a 195 tire will have a narrower and longer contact patch than a 305 tire

Hope this was of some help .

Last edited by CanAutM3; 04-18-2012 at 07:26 AM.
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      04-18-2012, 10:04 PM   #41
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So, what's the point of wide tires? Is it just down to a weaker structure yielding a slightly larger contact patch? Is it to have a larger air volume to resist heating from the brakes?

I guess you were saying it's to have a wider-shaped contact patch for better lateral grip, but is that really all?

Anyway, now I don't feel so bad about going only 275mm. I was thinking I maybe should have pushed for 285, but wanted to play it safe.
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      04-19-2012, 08:31 AM   #42
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So, what's the point of wide tires? Is it just down to a weaker structure yielding a slightly larger contact patch? Is it to have a larger air volume to resist heating from the brakes?

I guess you were saying it's to have a wider-shaped contact patch for better lateral grip, but is that really all?

Anyway, now I don't feel so bad about going only 275mm. I was thinking I maybe should have pushed for 285, but wanted to play it safe.
^^This is the main reason.


However, there are other important benefits. But we need to go deeper in tire dynamics to understand them. So far, we have pretty much considered most parameters as constants. To consider the load on the tire and the impact of the tire structure as variables, the equation needs become: contact patch area = (total load – load carried by tire structure) / inflation pressure.

The more a tire needs to deform to create the contact patch, the greater the proportion of the load is carried by the tire structure (think of a spring, the more you want to deform it, the more load is required). So from our equation, the contact patch area does not increase proportionally with the total load.

Further, there are two basic components of tire grip: the normal friction of rubber against tarmac and the interlocking of the tire rubber to the tarmac imperfections. The first component depends mostly on the load but the second is a factor of both load and contact patch area. So the bigger the contact patch area, the greater the grip the tire can provide. It is not a linear correlation though, if you double the contact patch area you will not double the grip.

Combine both of these parameters, and it become clear that a tire's grip does not increase linearly with the load that it carries.

To put all this in application, consider a car that is cornering. There is a weight transfer from the inside wheels to the outside wheels, thus reducing the total grip that was available. This is the main reason why it is so important to lower the center of gravity of a car to improve handling.

So why is a wider tire better? A wider tire needs less structure deformation than a narrow tire to create the same contact patch area, so it is less sensitive to changes in load. An obvious benefit while cornering.

It is also a reason that sometimes braking performance can be improved with wider tires, with the wider tire reacting better to the rear to front weight transfer. However there is a sweet spot to be found between the shape of the contact patch (wide vs narrow) and the change of contact patch area due to the load transfer.

There is also the impact of how the shape of the contact patch changes with varying loads (from rectangular to round to triangle), but I’ll stop here…

Last edited by CanAutM3; 04-19-2012 at 01:25 PM.
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      04-20-2012, 12:14 AM   #43
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It seems to me that a larger tire will require less deformation to support the same load. Less deformation -> less heat -> more stable tire pressures & longer tire life.
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