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Discussion Starter #1 (Edited)
Don't get me started on the better prospects for tire wear...but there is a whole world of tire performance waiting for your discovery just by squaring up your rear wheels to the road (0 deg camber). The stock and standard "pass" specs can be anywhere from -.5 to -1 deg in the rear, and it will stay like that even if you get an alignment. What you need is eccentric camber bushings installed. The thing I didn't know is that, while the camber change is fixed on such a part, they can be installed in such a way to give you any number in between the fixed +/- spec. I'm guessing the mechanic installs them at a certain angular position to increase or decrease the effect of the camber bushing. The caveat...once the part is pressed in, the setting is permanent. There is no "adjustment" after that, aside from removing them.

Now with that out of the way, my behind the wheel feedback...

You will immediately notice the improvement in grip in the back, naturally because you are finally using the entire contact patch of the tire, instead of the just the inner half of the tread doing all the work as it would in stock config. From the seat of the pants, I would say my cold weather traction with the new rear camber (i.e., no camber) is as good as my warm weather traction with the stock rear camber.

On launch, I can still break them loose with enough throttle, but it takes a decent amount of throttle, now. When you take off with full rolling contact, you are going forward with great urgency (like you are about to take the virginity of the space-time matrix right in front of you). When you take-off with some wheel slip, you are still going forward with great urgency. You will hear the engine note is dealing with a good amount of load while it is slipping (instead of the more usual free revving, like the tires just gave up entirely). The take-off while slipping is a bit squirmy, too, so pilot that steering wheel. ;) Though, I don't know if that is more about my nearly worn tires being shaped to the previous camber condition, or if it is just a natural artifact of running 0 deg camber. Could be some of both, too. If you figure, a slipping launch with full tire contact means you are using 100% of traction just for thrust. So any lateral control is pretty well out the window...there's no traction headroom left at that point for anything else.

On hard cornering, the rear-oriented powerslides are less readily graceful (maybe you want this or not). Either the rear tires are hooked or they are not. If you have power-on at the moment, then they will surely hook with less power, which halts the lateral motion in the rear. The rear will hook into your turning line as if you gently nudged a tire against a curb. ;) If you weren't power-on and the rear is sliding, you are going to keep sliding, because there is no "emergency" traction that is going to show-up to save you...so better hope you didn't overcook it too much, or you have plenty of clearance to accommodate your slide. That's what I think the stock rear camber is about on these cars. The rear will break away early, but it still has more traction to harness as the body leans and the camber gain aligns more of the tire to the pavement. So at some later point, it will take a lock after the initial slide. It's safer, but also less intuitive about where your real limit is.

U'ees with some flamboyant powerslide are raw and aggressive. You keep the power on to continue the rotation, but all along, the tires are very determined to regain a lock with rolling traction. When they do, you are going to go forward whether you have completed your U'ee or not...again, the rear will tell you so as if you just nudged the tire against a curb.

This car is more raw and brutal than ever, and I'm just rolling on all-season performance tires. ;) If you have stagger in your tires widths, you may need less after this mod. ;)

There was one other guy on here that also has the mod (for the same objective of 0 camber), and he is on a manual, as well. I don't recall what his username was, though. I invite all who have done so to share their observations, of course. For the new owners in the crowd, you may want to consider this even before you start playing around with different tire brands. ;)

One totally unintended benefit...I suspect my fuel economy got a little bump, too. I was expecting a small hit from rolling resistance of a full contact patch, but by the meter numbers (which may or may not represent the true value), I am effortlessly hitting 30 mpg on instantaneous readings while in mds mode. I'm not saying I'm actually hitting 30 mpg, but whatever number it really is, it will surely be better than the numbers I was hitting before. I was never just effortlessly dancing on the the number 30, previously, so "something" must have got better.
 
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Discussion Starter #3
Actually, I don't know anything about the parts. They were provided by the shop. I can find out, if you like, but I just got the impression they were generic parts for the job that any shop could order. They certainly weren't pricey as far as part cost on the service ticket...about $100 for the pair.
 

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Discussion Starter #5
Those figures are probably fine for focus on cornering, but not for rabbit outta the gate launches. ;) You want those wide rear tires to do something for you with all that engine torque, you better square them up with the pavement. :D
 

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0 deg camber on an alignment rack doesn't equate to 0 deg camber under acceleration. As the car's weight transfers towards the rear, the IRS allows the tire camber to change.

The only way to keep camber consistent is to switch to a solid rear axle.
 
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Interestingly, I'm at around -1.6 in the rear, have no problems with uneven wear, the grip is progressive and isn't there then gone.

Adjusting the camber out while running the stock height and suspension isn't likely to really do much in the grand scheme of things, what you need to do is lower the car and run springs with a higher spring rate along with stiffer shocks. This lowers the center of gravity and reduces squat on launch, both of which will help with hooking up. Good tires make a big difference, too.

All else being equal, having a larger contact patch doesn't increase traction or friction, BTW.
 
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0 deg camber on an alignment rack doesn't equate to 0 deg camber under acceleration. As the car's weight transfers towards the rear, the IRS allows the tire camber to change.

The only way to keep camber consistent is to switch to a solid rear axle.


>>>>Now that is a true muscle car lol solid rear axle!!!
 

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Actually, for the 1/4 mile it's best to set up the car with softer springs. Weight transfer towards the rear can dramatically increase traction in rear wheel drive cars.

For road courses, I agree with having a stiffer/lower suspension set up.
 
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Actually, for the 1/4 mile it's best to set up the car with softer springs. Weight transfer towards the rear can dramatically increase traction in rear wheel drive cars.
There are lots of different trains of thought on this subject, but a soft suspension that squats results in quite a bit of lost energy. A more compliant suspension will work better on rough track surfaces, but with a good, clean track you want to be able to get more power to the ground faster and a firmer suspension does that.

Ultimately, adjustable suspension will help the most so that you can adjust it to the track you're at. There is no one-setup-works-best for all strips.
 

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Too much negative camber to begin with or change in camber angle on hard launch due to weight transfer to the rear may also be a contributor to wheel hop. For drag racing I definitely agree locking the camber angle at 0 degrees should be ideal.
 

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Discussion Starter #12
0 deg camber on an alignment rack doesn't equate to 0 deg camber under acceleration. As the car's weight transfers towards the rear, the IRS allows the tire camber to change.

The only way to keep camber consistent is to switch to a solid rear axle.
Well, I can certainly agree with that. If for nothing, the sra is the king of consistent camber. That is the whole point of getting the camber fixed on these cars...to better simulate the 0 camber behavior of a sra. I realize it cannot be duplicated exactly, but squaring up the wheel alignment is definitely a step in the right direction. You are correct that weight transfer will throw off the 0 camber, but wherever it drifts to, it will still be better starting from a value of 0 deg, than starting at -.5 deg, eh? I can attest to that the feel of extra traction is occurring. It's not a subtle thing, here. There's more traction available because the tires are in better contact with the road, now. That's entirely the whole point of keeping your wheel alignment up to date in the first place...unless it was just a big lie all along. ;)

If I had these camber bushings installed and felt nothing spectacular, I would be the first one here to say the experiment was a bust...trust me on that. :)
 

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There's more traction available because the tires are in better contact with the road, now.
Nope, there is exactly no more traction available now compared to before, it doesn't matter if the contact patch is bigger. All else being equal/the same, you have the same amount of traction as before. It may be able to maintain the same amount of traction for longer before breaking loose, but you don't have MORE traction now. It's a physical impossibility.





Sent from a cool, little device from the future.
 

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Discussion Starter #14 (Edited)
Interestingly, I'm at around -1.6 in the rear, have no problems with uneven wear, the grip is progressive and isn't there then gone.
You are working in a drastically different use case than I or most regular driving people are, in the first place. I doubt you can recommend everybody start running -1.6 deg rear camber because you do, and nobody will have problems with that.

Adjusting the camber out while running the stock height and suspension isn't likely to really do much in the grand scheme of things, what you need to do is lower the car and run springs with a higher spring rate along with stiffer shocks. This lowers the center of gravity and reduces squat on launch, both of which will help with hooking up. Good tires make a big difference, too.
Many ways to skin the same cat. I just chose 2 camber bushings to do the trick. I may not have achieved the ultimate benefits that you did, but I certainly got a big bump over the way it was stock. I would say lowering the car with a springs kit, all new shocks, having to employ camber bushings anyway to back off the resulting camber, expensive rims to fit wider and pricier tires, sacrifice to ride quality just to get better traction is pretty well beyond what I would ever consider doing on my car.

All else being equal, having a larger contact patch doesn't increase traction or friction, BTW.
Well of course it does in real practice...maybe not linearly, but there is a corresponding trend. Plus things are rarely "equal" in comparison in real practice, anyway. When talking about real tire dynamics, we're not just talking about pressure and friction. That's kind of a newbie mistake. It's more about adhesion and surface area...but that is all kind of baiting me to go off-topic. The topic here still remains...better tire contact to pavement is naturally going to yield better utilization of what the tire can achieve.

We aren't riding on infinitely rigid cylinders on an infinitely rigid plane, hence the friction and pressure model pretty well goes out the window. It's good for a basic physics class, but it is the wrong model for actual tires on actual road.
 

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I have a good amount of experience in setting cars up for various customers, and just want to add/re-enforce a couple things here

There are non adjustable camber bushings, (SPC) and there are adjustable camber bushings, (Whiteline)

You can install rear camber bushings in both the camber link and the tension link to gain more adjustment if needed, this is how i have my charger setup. The thing that you need to keep in mind is that you have to be sure the tension link bushings are adjusted equally since they will effect rear caster which can't be measured with an alignment machine.

Adjusting the camber to 0 or just a hair positive will help the car launch for drag racing, however the tires will tend to 'roll' much easier in the corners.

In a car with IRS you want to prevent the rear of the car from compressing to much, if it does compress to much the rear will gain to much neg camber, and you will spin the tires much more easy. (Cars with solid rear axles follow a different set of rules)

Tires with lower profiles (the middle number in the size) are less compliant to less than perfect camber.

If you want to turn, then 0 camber is not your friend.
 

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Discussion Starter #16 (Edited)
Yes, that is how the tech configured my rear camber...just a hair over 0 deg. On the hard cornering, I have more lateral traction than I can use, anyway. So can't really chalk it up to a loss. If I were ever in a position to use all of it, the watchful eye of the police would give me more cause for worry than how much the tire rolls onto the shoulder. I got camber gain working for me there, anyway. So can't really say there is too little camber available, for my uses. When it was stock camber, the outer shoulders in the rear went virtually unused. That sort of hinted the direction I needed to go, imo.

If I do see more wear on the outer shoulder after a true long term evaluation, I'll certainly let you all know.
 

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You are working in a drastically different use case than I or most regular driving people are, in the first place. I doubt you can recommend everybody start running -1.6 deg rear camber because you do, and nobody will have problems with that.
I think you may be making some assumptions about how I use my car that may be incorrect. I do about 4 track days per year, each one is probably 100-125 miles of track time for a total of 400-500 miles on the track. The rest of the time is spent on the street. That means with my previous set of tires (Nitto NT05) there was 500 miles of track and at least 7,500 miles on the street. Tire wear was even across the tread. If anything I should've seen excessive wear on the inside of the tires, especially because of track time, but I didn't. Setting 0 camber doesn't guarantee even wear nor is it the only way to achieve even wear, that's my point.

Many ways to skin the same cat. I just chose 2 camber bushings to do the trick. I may not have achieved the ultimate benefits that you did, but I certainly got a big bump over the way it was stock.
Oh, I have camber bushings as well. If I didn't then I'd be at -3.00 in the rear. :D

Well of course it does in real practice...maybe not linearly, but there is a corresponding trend. Plus things are rarely "equal" in comparison in real practice, anyway. When talking about real tire dynamics, we're not just talking about pressure and friction. That's kind of a newbie mistake. It's more about adhesion and surface area...but that is all kind of baiting me to go off-topic. The topic here still remains...better tire contact to pavement is naturally going to yield better utilization of what the tire can achieve.

We aren't riding on infinitely rigid cylinders on an infinitely rigid plane, hence the friction and pressure model pretty well goes out the window. It's good for a basic physics class, but it is the wrong model for actual tires on actual road.
This has been discussed in another thread already, but might as well reiterate it here.

It's actually not the wrong model, it just doesn't take into account all of the variables to give a truly scientific answer because there are more forces than just static friction at work. However, it still very much applies and to ignore the basic laws of physics and friction is a newbie mistake. ;)

A given tire compound is going to have a specific CoF. Adhesion is a part of the total traction/friction equation when it comes to tires, you can't say "We're not just talking about friction" and say it's about adhesion. Adhesion IS part of traction/friction when it comes to tires.

As I said before, all else being equal (as in unchanged), a larger contact patch does not increase the friction/traction. It just doesn't. Why? Because when you made the contact patch larger you then reduced the pressure being applied per square inch/mm/whatever you want to measure. So larger contact patch = same pressure applied across a larger area = less pressure applied to each quadrant. The only way to get MORE traction is by changing the tire compound to increase the CoF or to add more weight.

If your tires were able to hold, say, 0.92g of force with the smaller contact patch then how much force do you think they would be able to hold with the larger contact patch?

0.92g.

The only difference the larger contact patch makes is that the forces are spread across a larger area, this means more of the tire's tread is able to do work which translates into the tread lasting longer before overheating. More area doing work means that the tire can MAINTAIN grip longer before the tire heats up enough to reduce the CoF to the point where the tire breaks loose.

Hope you get what I'm saying. Basically, the larger contact patch means the tire can run at the limit of traction/friction for longer before the friction causes the tire to get too hot and lose traction. The larger contact patch does not increase that limit to provide more traction/friction/adhesion because you haven't done anything to actually do so.
 

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Discussion Starter #18 (Edited)
Well, that's part of it...more of the tire tread is at work, hence more surface, hence more adhesion effect (like how strips of ziploc mesh). If you just have a corner of the tire making contact, you have less area, and that part of the tire is working harder, too. So it will wear away, and it is easier to shear material from that confined area of the tire, as well (all of that will be happening before you even get to melting effects...if you got melting effects, then you are just plainly overloading the material, altogether). That implies less force, hence less traction. So while you may have higher surface pressure over a smaller area, the material in that confined region is going to get sheared away more easily. That doesn't equate to more force, just more wear. At best it is a wash, but in reality, there is inefficiency when you work something harder. So in more realistic terms, you lose some fraction of the ideal case. That's why the friction and pressure model goes faulty relatively quickly. It's great if you have an infinitely rigid cylinder (zero deformation) mating to an infinitely rigid planar surface. However, that just does not describe a real life tire on a real life pavement surface. They deform from their native shape on load, tread material squirms around on load, the material surfaces interlock on the microscopic level of peaks and valleys, and material strength creates a limiting factor under extreme loads when it no longer pulls between 2 objects (but stays intact), rather it separates from its matrix in shear.

There's a whole lot going on than just friction and pressure, for sure. For a low-tech approach, you are just better off employing suitably soft material (to exploit adhesion) but with much larger surface area so it doesn't get overloaded so easily. The material that stays intact will generate more force over that area, hence better real traction.

We don't see top-fuel dragsters with skinny rear tires because the surface pressure will be higher, right? There's a point where you are just overloading the material, so you get less in the end. That's why we see them approach it with brute amounts of surface area. True it is also softer material, but in the end, the shear force is distributed over a larger amount of material, so the overall force will be higher than the skinny tire approach (or if you just cambered that super wide slick to ride on the inner corner). The material has to survive for it to generate the force. That won't happen if you overload it with too small an area of contact patch. It survives because you have a wide span of material doing only moderate work (relative to their failure point).

If the friction/pressure model had (much) validity, we would all just be equally fine on 235 wide tires on these cars, right? You could just tweak traction by changing material softness, right? I think it is fairly obvious nobody would buy that theory that 235 is theoretically all you need and all you can ever use. ;)
 

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I think you may be making some assumptions about how I use my car that may be incorrect. I do about 4 track days per year, each one is probably 100-125 miles of track time for a total of 400-500 miles on the track. The rest of the time is spent on the street. That means with my previous set of tires (Nitto NT05) there was 500 miles of track and at least 7,500 miles on the street. Tire wear was even across the tread. If anything I should've seen excessive wear on the inside of the tires, especially because of track time, but I didn't. Setting 0 camber doesn't guarantee even wear nor is it the only way to achieve even wear, that's my point.



Oh, I have camber bushings as well. If I didn't then I'd be at -3.00 in the rear. :D



This has been discussed in another thread already, but might as well reiterate it here.

It's actually not the wrong model, it just doesn't take into account all of the variables to give a truly scientific answer because there are more forces than just static friction at work. However, it still very much applies and to ignore the basic laws of physics and friction is a newbie mistake. ;)

A given tire compound is going to have a specific CoF. Adhesion is a part of the total traction/friction equation when it comes to tires, you can't say "We're not just talking about friction" and say it's about adhesion. Adhesion IS part of traction/friction when it comes to tires.

As I said before, all else being equal (as in unchanged), a larger contact patch does not increase the friction/traction. It just doesn't. Why? Because when you made the contact patch larger you then reduced the pressure being applied per square inch/mm/whatever you want to measure. So larger contact patch = same pressure applied across a larger area = less pressure applied to each quadrant. The only way to get MORE traction is by changing the tire compound to increase the CoF or to add more weight.

If your tires were able to hold, say, 0.92g of force with the smaller contact patch then how much force do you think they would be able to hold with the larger contact patch?

0.92g.

The only difference the larger contact patch makes is that the forces are spread across a larger area, this means more of the tire's tread is able to do work which translates into the tread lasting longer before overheating. More area doing work means that the tire can MAINTAIN grip longer before the tire heats up enough to reduce the CoF to the point where the tire breaks loose.

Hope you get what I'm saying. Basically, the larger contact patch means the tire can run at the limit of traction/friction for longer before the friction causes the tire to get too hot and lose traction. The larger contact patch does not increase that limit to provide more traction/friction/adhesion because you haven't done anything to actually do so.
Good post.

The larger contact patch of a drag tire, when combined with heating the tire compound by purposefully spinning before a run, creates a glue like adhesion between the tire and the rubber on the track. That glue like adhesion begins to change the whole pressure per square inch rule of thumb. When you begin to calculate just how quick Top Fuel cars accelerate for instance, the laws of physics pertaining to everything mentioned above are being bent.
 

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Discussion Starter #20 (Edited)
The most basic reason that the friction/pressure model is insufficient to describe a real tire/pavement scenario is because it oversimplifies the behavior of coefficient of friction. It assumes it is constant, when in reality, the effective value also varies with load. Granted it is a bit of a leap to think it just "varies" with load, but that is why just looking at it as normal force acting with a simple coefficient of friction is too simplistic. The relationship is more complex than reducing the behavior down to a simple constant.

What Yahooligan is trying to say here is that the net traction of a tire doesn't change even when you vary the amount of surface area that supports the tire (as in different degrees of camber). Reduce the area, and the surface pressure increases on the smaller footprint...net normal force remains the same. Increase the area, and the surface pressure decreases over a larger footprint...net normal force remains the same. That part is all fine.

The problem in the model arises with the idea that if you concentrate the force over a smaller area of the tire, will you get an equal amount of traction out of the tire?...the answer is you won't. There's an "inefficiency" involved. You work the tire twice as hard, you only get 80% back (just to pick a number to illustrate the point). That is why it is you are usually better off employing greater surface area with a wider tire. Yes, the surface pressure will be lower, but the material in the tire will be operating in a more linear range for traction. Start angling the tire (as in increasing camber), the contact surface area decreases, contact surface pressure increases, but the tire capability is dropping off (sort of like a torque curve at higher rpm).

The more classic way to we observe this is if we just imagine the tire in simple contact with the road (0 deg camber). If the initial load is x, then we can count on y amount of traction force. If we double the load, we don't automatically get double the traction force. Maybe we get only 150% traction, rather than 200%. Quadruple the load, maybe we get only 170% traction, rather than 400%. You see the trend? As the load increases, the tire performance is leveling-out, instead of increasing proportionally. There is a rising inefficiency as you make it work harder. This works the same as the scenario of making the tire material work harder over a smaller contact patch. What you get back isn't 1:1.
 
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