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Wheels | Tires | Spacers | Hub -- Sponsored by The Tire Rack Specific topics relating to wheels and tires.


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Old 04-17-2018, 06:47 PM   #155
mrg666
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Originally Posted by why? View Post
and yet that is absolutely what the wider tire is always better crowd is arguing. Of course it is absurd.
I am not aware, did anybody say that? I think the "crowd", as you call them, mainly thinks that wider looks better. I haven't seen anybody looking at those skinny tires with admiration and telling each other how smart their owners should be and they should know something that everybody else missed. You guys are not that smart, "crowd" is not that stupid. Just install those wide tires and you will feel better, I promise.
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Old 04-17-2018, 07:45 PM   #156
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Because there are other factors. It is all about balance. You can have too much mechanical grip for a car to overcome. And that will absolutely slow a car down. Because grip=friction. Now if the car has a massive engine and can never get enough grip, that is one thing. But out cars have 200 hp, if that, to the wheels. And every bit of extra grip means the engine has to work harder to do everything.

Now maybe that is just a regurgitation of what you meant. It just felt like you were arguing that no matter what the wider the better, and all track cars should run as wide a tire as possible and the most aggressive aero they can possibly create.
Please donít put words in my mouth because you lack reading comprehension.
I suggest you re-read all my posts. Especially my last. No where did I say that you should slap on 305ís on a stock twin and youíll turn better lap times. Does the 305 provide more lateral grip? Absolutely. Hell if you have a twin capable making use of 305ís on the track then hats off.

I was merely trying to clarify why wider tires are better on a road course. But along with every statement I qualified it with all things being equal and that there is a point of diminishing returns on each individual vehicle/setup.
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Old 04-17-2018, 08:35 PM   #157
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Pressure is defined as force per unit area (lbs/in^2 or N/m^2). You're describing 2800 lbs of force to the ground, not pressure. Saying "pressure per square inch" is like saying (lbs/in^2)/in^2 or lbs/in^4 which is not a unit of pressure.

Pressure is inversely proportional to the area so if you apply the same amount of force (2800 lbs) to a smaller area, pressure goes up:
2800 lbs/area (in^2) = some pressure (psi)
2800 lbs/smaller area (in^2) = some bigger pressure (psi)
sorry for my gross misuse of terms. i guess my question is, why does that matter unless you are normalizing tire performance to how many air particles are in the tire. like, i get that for a certain volume (provided all else is equal) the larger tire will have lower pressure. i just dont get why that matters.
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Old 04-18-2018, 01:12 AM   #158
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fatoni: pressure also affects contact patch (see eg. wear for overinflated or underinflated tires). So if wider tires due more volume need less pressure for same weight load and you overinflate reusing pressure from skinny tires, you may slightly reduce grip from sides of tire. If more grip (ok, lateral grip for transitions) was reason for wider tire install, why not maximize it? 2.4 was for stock tiresize. Why do you think people pass some air out when they heat a lot tires on track? I guess in similar fashion one can slightly squeeze out extra grip if running more optimal pressure in wider ones.
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Old 04-18-2018, 09:40 AM   #159
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Please donít put words in my mouth because you lack reading comprehension.
I suggest you re-read all my posts. Especially my last. No where did I say that you should slap on 305ís on a stock twin and youíll turn better lap times. Does the 305 provide more lateral grip? Absolutely. Hell if you have a twin capable making use of 305ís on the track then hats off.

I was merely trying to clarify why wider tires are better on a road course. But along with every statement I qualified it with all things being equal and that there is a point of diminishing returns on each individual vehicle/setup.
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Old 04-18-2018, 09:47 AM   #160
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All else equal, within a reasonable range, wider tires will generally give more lateral grip for reasons of contact patch shape, how it deforms under lateral load, and how that affects grip vs. load curve. Additional grip *by itself* would make you faster. The only question is where is the point of diminishing returns vs. heavier wheels/tires, aero drag, and rolling resistance. Here's what I think:

Additional aero drag from wider tires is going to be pretty damn small. Difference in vehicle frontal area with 245s vs. 215s at stock ride height is about +0.005 or one half of 1%, nothing. Coefficient of drag will be slightly different as well, but considering that the 245s will put the outside surfaces of the wheel/tire closer to the profile of the body it's possible that wider wheels/tires on stockish wheel offsets might actually reduce Cd, but either way it's going to be a small difference within a reasonable range of widths.

Rolling resistance is theoretically *less* with wider tires, as a wider/shorter contact patch undergoes less hysteresis. Tires with a narrower/longer contact patch have to have more deformation in the middle of the tread and hence lose more energy while rolling. On the other hand, wider tires with a greater mass of rubber being deformed could tilt the advantage in the other direction... In practice for a reasonable range of tire widths this effect is going to also be very small.

Additional rolling resistance due to *adhesion* (sticky rubber not wanting to let go of tarmac) is not really going to be a factor on the street on street-compound tires as in those conditions the tires don't get hot and sticky. At the track it could be a factor in lap times for low power/weight cars like the FT86 and Miata, but due to the nature of how the tire deforms I'm not sure it wouldn't be *worse* for narrower tires vs. wider. The narrower tire with longer contact patch is having to be "unpeeled" from the ground over a longer circumferential distance vs. wider tire with shorter contact patch.

The biggie in terms of how going too wide on wheels/tires can hurt you in terms of performance has got to be WEIGHT. More rotational mass will hurt acceleration of a modest power/weight car, and at some point this will hurt lap times more than increased lateral grip from wider tires helps.

In reality *other factors* have a MUCH greater impact on performance, to the point that it's difficult to isolate the effects of *only* going wider on wheels/tires without changing tire diameter and/or the stretch/pooch of the tire on the wheel (inherently an issue as tire widths are in 10mm millimeter increments and wheel widths are in 1/2" increments!).

I'm on the verge of deciding between running 225/45-17 on 17x8 or 245/40-17 on 17x9 for track events this year, and honestly I doubt that there's more than a tenth or two difference, all else equal. But I might go 245s based on vanity...

My 0.02, FWIW...
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Old 04-18-2018, 10:01 AM   #161
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All else equal, within a reasonable range, wider tires will generally give more lateral grip for reasons of contact patch shape, how it deforms under lateral load, and how that affects grip vs. load curve. Additional grip *by itself* would make you faster. The only question is where is the point of diminishing returns vs. heavier wheels/tires, aero drag, and rolling resistance. Here's what I think:

Additional aero drag from wider tires is going to be pretty damn small. Difference in vehicle frontal area with 245s vs. 215s at stock ride height is about +0.005 or one half of 1%, nothing. Coefficient of drag will be slightly different as well, but considering that the 245s will put the outside surfaces of the wheel/tire closer to the profile of the body it's possible that wider wheels/tires on stockish wheel offsets might actually reduce Cd, but either way it's going to be a small difference within a reasonable range of widths.

Rolling resistance is theoretically *less* with wider tires, as a wider/shorter contact patch undergoes less hysteresis. Tires with a narrower/longer contact patch have to have more deformation in the middle of the tread and hence lose more energy while rolling. On the other hand, wider tires with a greater mass of rubber being deformed could tilt the advantage in the other direction... In practice for a reasonable range of tire widths this effect is going to also be very small.

Additional rolling resistance due to *adhesion* (sticky rubber not wanting to let go of tarmac) is not really going to be a factor on the street on street-compound tires as in those conditions the tires don't get hot and sticky. At the track it could be a factor in lap times for low power/weight cars like the FT86 and Miata, but due to the nature of how the tire deforms I'm not sure it wouldn't be *worse* for narrower tires vs. wider. The narrower tire with longer contact patch is having to be "unpeeled" from the ground over a longer circumferential distance vs. wider tire with shorter contact patch.

The biggie in terms of how going too wide on wheels/tires can hurt you in terms of performance has got to be WEIGHT. More rotational mass will hurt acceleration of a modest power/weight car, and at some point this will hurt lap times more than increased lateral grip from wider tires helps.

In reality *other factors* have a MUCH greater impact on performance, to the point that it's difficult to isolate the effects of *only* going wider on wheels/tires without changing tire diameter and/or the stretch/pooch of the tire on the wheel (inherently an issue as tire widths are in 10mm millimeter increments and wheel widths are in 1/2" increments!).

I'm on the verge of deciding between running 225/45-17 on 17x8 or 245/40-17 on 17x9 for track events this year, and honestly I doubt that there's more than a tenth or two difference, all else equal. But I might go 245s based on vanity...

My 0.02, FWIW...
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Old 04-18-2018, 10:25 AM   #162
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fatoni: pressure also affects contact patch (see eg. wear for overinflated or underinflated tires). So if wider tires due more volume need less pressure for same weight load and you overinflate reusing pressure from skinny tires, you may slightly reduce grip from sides of tire. If more grip (ok, lateral grip for transitions) was reason for wider tire install, why not maximize it? 2.4 was for stock tiresize. Why do you think people pass some air out when they heat a lot tires on track? I guess in similar fashion one can slightly squeeze out extra grip if running more optimal pressure in wider ones.
My confusion comes from The fact that he's using this to make a case for a smaller wheel and tire and that's the part that is confusing me.
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Old 04-18-2018, 11:11 AM   #163
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I donít like to bring up cars at parties.
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Old 04-18-2018, 11:16 AM   #164
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TL;DR

I seriously cannot believe what people try to pass off as "knowledge" while using words they dont even understand.

For the people trying to actually share knowledge, give it up. Those with the wrong ideas are not here to learn, they are here to prove they "know things". Anyways, I laugh a bit, then I cry in a corner when I read half the things that are being said here.
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Old 04-18-2018, 11:26 AM   #165
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I'm on the verge of deciding between running 225/45-17 on 17x8 or 245/40-17 on 17x9 for track events this year, and honestly I doubt that there's more than a tenth or two difference, all else equal. But I might go 245s based on vanity...

My 0.02, FWIW...
I currently track on 225 with a light wheel and while I could get a little bit more grip out of them with more camber and a wider wheel, I don't think it'd be much. I'd like to have more mechanical grip when cornering, but I do like the benefit of a light wheel/tire combo...light steering, better reaction over bumps, cheaper tires, etc. The only time I think running 225 is to my advantage would be on the straights at Thompson or Palmer, but then also keep in mind I'm trying to dump slightly more speed at the end with a smaller tire.... If you could find a sticky 245 or 255 tire and wheel combo that was within 2-3 pounds of a similar 225 setup, I'd say go for the bigger combo.
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Old 04-18-2018, 11:35 AM   #166
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I donít like to bring up cars at parties.
Lol. I've had people tell me I'm obsessed with cars.. my car specifically.
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Old 04-18-2018, 12:03 PM   #167
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Here....everyone read:

Part 1 – Tyre as a vertical spring
Part 2 – Road Interaction & Contact Patch Grip
Part 3 – Longitudinal Forces
Part 4 - Lateral Forces
Part 5 – Load Sensitivity
Part 6 – Combined Tyre Forces
Part 7 - Set Effects

- Andrew
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Old 04-18-2018, 12:36 PM   #168
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Here....everyone read:
Part 4 - Lateral Forces
I was just glancing at this one, and they've misdefined "slip angle"! Slip angle is the angle between the direction the wheel is pointed in (parallel to the ground) and the direction the wheel's velocity vector, i.e. the direction it is actually traveling in. It is NOT the angle they show, between the "contact patch thread" and the wheel, that angle is going to be very small and does not account for the tire *slipping* laterally relative to the ground.

Consider a wheel/tire traveling/sliding parallel to the wheel's axis, 90į to the direction the wheel is pointing in. Slip angle is 90į. Their definition would say that slip angle is 0į!
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