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      03-15-2013, 04:13 PM   #1
Jonjt
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Square setups. Why?

What's the deal with square setups? I could never understand why anyone wouldnt want to maximize the amount of rubber under their fenders. Sure, auto makers tend to design cars to understeer and square setups can help negate that. However, there are many ways to change a cars limit and transient behavior. Front/rear tire size ratio is only one of them.

So, square advocates, what gives?
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      03-15-2013, 04:58 PM   #2
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What's the deal with square setups? I could never understand why anyone wouldnt want to maximize the amount of rubber under their fenders. Sure, auto makers tend to design cars to understeer and square setups can help negate that. However, there are many ways to change a cars limit and transient behavior. Front/rear tire size ratio is only one of them.

So, square advocates, what gives?
You already sited a big reason (understeer). The other reason is to allow tire rotation. The rears tend to wear faster than the fronts; a square setup allows the user to maximize the tire's life by rotating front to rear.
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      03-15-2013, 05:04 PM   #3
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You already sited a big reason (understeer). The other reason is to allow tire rotation. The rears tend to wear faster than the fronts; a square setup allows the user to maximize the tire's life by rotating front to rear.
The tire rotation thing is a big deal, I suppose.

Understeer can be taken care of with prober anti-roll bars, tire pressures and spring wreights.
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      03-15-2013, 05:43 PM   #4
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Winter setup. Works better in snow
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      03-15-2013, 05:48 PM   #5
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I chose square setup for the reasons previously discussed (minus snow), but I also found a better deal on 4x 275/35/18 tires than I did on 2x 265/35/18 and 2x 285/35/18. I forget what the price difference was, but I was planning on going 275 square anyways so the difference in price was just an added plus for me, not a deal breaker.
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      03-15-2013, 06:50 PM   #6
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Quote:
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The tire rotation thing is a big deal, I suppose.

Understeer can be taken care of with prober anti-roll bars, tire pressures and spring wreights.
Are you implying that changing anti-roll bars and determining correct spring rates (likely requiring the expense and time of experimenting with differnt variations) to tune out under steer are easier than buying a set of wheels and tires...? You may not know that swapping the anti-roll bars on an M3 is not a trivial install. IIRC the rear bar requires dropping the subframe. I'm all for modifying cars to realize the best performance possible but sometimes there are easier ways to do the same thing.
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      03-15-2013, 08:00 PM   #7
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Neutralize balance and tire rotation for me.

I run 275s all around. Up front that's basically max rubber. Room for more in the rear, but then you're potentially dialing understeer back in.

Yes, there are other ways decrease understeer, but none quite as simple and effective. Square setup and RS3s transformed the car for me, improved track performance drastically.

And for those that track, the ability to rotate is seriously valuable. Potential savings of thousands annually.
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      03-16-2013, 01:28 PM   #8
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Quote:
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However, there are many ways to change a cars limit and transient behavior. Front/rear tire size ratio is only one of them.
Starting with a square setup starts with a balanced platform. Dialing out under steer on a staggered platform means the suspension settings are biased towards one side of their usable range, effectively reducing the useful range of adjustment.

Upgrading to adjustable shocks, setting up drop links for tuning roll bars, installing thicker roll bars, and so on ... are all much more complicated and invasive projects than changing to a square wheel setup.
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      03-16-2013, 09:28 PM   #9
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Quote:
Originally Posted by MikeBlaszczak View Post
Starting with a square setup starts with a balanced platform. Dialing out under steer on a staggered platform means the suspension settings are biased towards one side of their usable range, effectively reducing the useful range of adjustment.

Upgrading to adjustable shocks, setting up drop links for tuning roll bars, installing thicker roll bars, and so on ... are all much more complicated and invasive projects than changing to a square wheel setup.
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      03-17-2013, 08:40 PM   #10
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Quote:
Originally Posted by slicer View Post
Are you implying that changing anti-roll bars and determining correct spring rates (likely requiring the expense and time of experimenting with differnt variations) to tune out under steer are easier than buying a set of wheels and tires...? You may not know that swapping the anti-roll bars on an M3 is not a trivial install. IIRC the rear bar requires dropping the subframe. I'm all for modifying cars to realize the best performance possible but sometimes there are easier ways to do the same thing.
No, I wasn't implying that at all. I'm more interested in understanding the technical particulars of a one setup over another.

Certainly, the reasons you've cited for going with a square setup are not trivial. Thanks!
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      03-17-2013, 08:48 PM   #11
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Which specific technical details are you asking about, Jonjt ?
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      03-18-2013, 10:49 AM   #12
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Quote:
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Which specific technical details are you asking about, Jonjt ?
Well, I was looking to understand all of them. I wanted to have a full understanding of why someone would choose a square setup over a non-square setup, considering the limitations on traction you run into with a square setup. I see now that the considerations are largely practical on most cars, not technical.
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      03-18-2013, 11:35 AM   #13
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Well, the technical issues sort of cause the practical issues.

Suspensions are quite complicated, so you've got quite a journey ahead. Books like Racing Chassis and Suspension Design and Race Car Vehicle Dynamics are great places to start. Understanding tyres is also helpful, and a copy of The Racing and High-Performance Tire Handbook is a must have, too.
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      03-18-2013, 12:29 PM   #14
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Quote:
Originally Posted by MikeBlaszczak View Post
Well, the technical issues sort of cause the practical issues.

Suspensions are quite complicated, so you've got quite a journey ahead. Books like Racing Chassis and Suspension Design and Race Car Vehicle Dynamics are great places to start. Understanding tyres is also helpful, and a copy of The Racing and High-Performance Tire Handbook is a must have, too.
I'm familiar with the techincal particulars of suspension design. At least, with double wishbone and multi-link. I did design work on them for a few years, while studying in college. That's kinda why I was curious why so many people recommend square setups, when a properly designed and tuned chassis will be able to overcome any understeer tendencies a non-square setup might introduce.

I have a copy of RCVD sitting on my bookshelf at home. Pacejka's work is somewhere on my computer.

Since it's more of a practical issue than one of technical superiority, I understand why some people choose to go square.

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      03-18-2013, 01:15 PM   #15
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Any issues with steering weight/feel by moving to a wider front tire? Is turn in affected? I can't say that I have the ability to sense these small changes but I am interested none the less.
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      03-18-2013, 01:29 PM   #16
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So all things being equal (driver expertise as well)....will a car with the standard 275/18 square set up get around the track faster than a car with the standard staggered set up, either 18 or 19? I have a new square set up waiting to go on soon.
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      03-18-2013, 01:29 PM   #17
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Any issues with steering weight/feel by moving to a wider front tire? Is turn in affected? I can't say that I have the ability to sense these small changes but I am interested none the less.
There might be. It will depend on a lot of things, like offset, tire size, diameter, tire compound, camber angle, and, of course, something called slip angle.

On most cars, the axis about which the front wheel turns isn't vertical, nor does it intersect the tire through the center of it's contact patch. The wheel will tend to roll around the rotation axis when the wheel is turned. The radius between this axis and the wheel center is called the scrub radius. The specific wheel you pick can affect the length of this radius and therefore, the torque needed to turn the wheel, at speed. A similar effect occurs in because of something called caster. The wheel will tend to lean left or right/scrub across the pavement. This is what causes the car to move slightly when you turn full lock to full lock. Its the reason wheels tend to look as though they are leaning out when the car is turning. It also has a huge effect on steering effort and by extention, feel/turn in, because the vehicle will tend to heave a bit (You are fighting the vehicles weight, as well as the firction between the tire and the road). For that reason, you will find that heavier vehicles tend to have less caster and camber than smaller, more sporty vehicles. But, having less of both tends to make the vehicle less stable at speed, up to a point.


Know that this mechanism is the only mechanism the driver has to receive feedback through the steering system. The amount of restoring force that is working to return the car to 0 degrees of steer tells the driver a huge amount about how much traction he has left.

So yeah, different tires can have a huge effect upon feel and turn-in, technically speaking, anyway. Whether or not a driver cna feel those effects is another matter. (although, i'd say that many drivers can feel a difference but, might not be able to understand what is changing and how to take advantage of it).



About the slip angle bit, this angle increases to a max value, at which point, the tire losses traction and you eat shit. That max value varies per tire. But, suffice to say that each tire behaves very differently as it approaches this limit. Some are linear, some are progressive, some are regressive. You have to know how your tires behave at this limit because, you don't want surprises.

God, I miss chassis design.

Last edited by Jonjt; 03-18-2013 at 01:48 PM.
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      03-18-2013, 01:34 PM   #18
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So all things being equal (driver expertise as well)....will a car with the standard 275/18 square set up get around the track faster than a car with the standard staggered set up, either 18 or 19? I have a new square set up waiting to go on soon.
If the staggered setup causes the car to understeer, possibly. Assuming both drivers are good, the guy with the understeering car may be able to compensate with a different line.


Your question is predicated upon "....all else being equal". And, that is something that is nearly impossible to achieve and, not very relevant for a single car. I would choose a tire setup that is most practical for you and tweek the chassis to tune out any undesirable behaviors. If you end up with rear axle traction issues, you may need to go staggered and then reevaluate your position. But, that will certainly be more expensive and less practical. If that happens, I'd either focus on driving technique to launch the car better or, just stop launching it. hahaha

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      03-18-2013, 01:43 PM   #19
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If the staggered setup causes the car to understeer, possibly. Assuming both drivers are good, the guy with the understeering car may be able to compensate with a different line.


Your question is predicated upon "....all else being equal". And, that is something that is nearly impossible to achieve and, not very relivent for a single car. I would choose a tire setup that is most practical for you and tweek the chassis to turn out any undesirable behaviors. If you end up with rear axle traction issues, you may need to go staggered and then reevaluate your position. But, that will certainly be more expensive and less practical.
Maybe this is for another thread but there seems to be a large enough sample of people on this forum that have switched from staggered to square set ups. I'm curious to know if the lap times increased or decreased solely because of this change.
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      03-18-2013, 01:53 PM   #20
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Maybe this is for another thread but there seems to be a large enough sample of people on this forum that have switched from staggered to square set ups. I'm curious to know if the lap times increased or decreased solely because of this change.
It's an interesting question. But, I'm not confident you'd be able to determine this because the wide variance in driving skill and consistency would introduce a lot of noise into your study. This kind of thing is best investigated by trained and experienced race drivers on a single closed track, under consistent conditions and with the same car, every time.


I totally understand your intellectual curiosity but, if you are doing this as justification for going with one setup over another, I think you will get lost, fast. Just go with whatever is convenient for you.


*I'd do the staggeed myself but, I also see HDPEs as technical exercises in addition to being fun. I like to spend time setting up the chassis, to the best of my ability. Whether or not that makes me faster is another matter because, I don't really have the resources to really understand if my changes are actually making me faster. I can only make educated guesses and have fun while doing it.
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      03-18-2013, 04:39 PM   #21
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Quote:
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It's an interesting question. But, I'm not confident you'd be able to determine this because the wide variance in driving skill and consistency would introduce a lot of noise into your study. This kind of thing is best investigated by trained and experienced race drivers on a single closed track, under consistent conditions and with the same car, every time.


I totally understand your intellectual curiosity but, if you are doing this as justification for going with one setup over another, I think you will get lost, fast. Just go with whatever is convenient for you.


*I'd do the staggeed myself but, I also see HDPEs as technical exercises in addition to being fun. I like to spend time setting up the chassis, to the best of my ability. Whether or not that makes me faster is another matter because, I don't really have the resources to really understand if my changes are actually making me faster. I can only make educated guesses and have fun while doing it.
Yes. Ideally you would want an experienced driver on a familiar track in the same car.
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      03-18-2013, 04:42 PM   #22
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Quote:
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Maybe this is for another thread but there seems to be a large enough sample of people on this forum that have switched from staggered to square set ups. I'm curious to know if the lap times increased or decreased solely because of this change.
When I tracked my previous car, I went from staggered with Yokohama AD08s to square with Continental slicks then back to staggered when the slicks corded. Obviously the square slicks setup was much much faster. Once I got used to them, I was about 6 sec faster on a roughly 3-mile course.

For me, the staggered setup results in too much understeer. The car plows through turns, and that's not because of tire pressure. Maybe it's my technique, and certainly the slicks are more awesome anyway, but my experience was that even with camber plates, the E92 M3 has plenty of plant in the rear but too much understeer up front, and going with a square setup gives the car much better rotation through turns. You're not so much sacrificing grip in the rear, you're adding more grip up front. And given the 50/50 balance of BMWs, square is a more balanced result, no?

On my E36 M3 racecar, I've run only square on the track (as does everyone else). I can't imagine going with narrower front tires just to emulate a staggered setup.
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