How to setup a chassis for track use | Pro tips from BimmerWorld's James Clay

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By Guest Writer
Jul 11, 2022 | BimmerWorld, Chassis | Posted in Shop Work , Suspension & Handling | From the May 2022 issue | Never miss an article

Photography by Kevin Adolf

Story by James Clay

How do you set up a car, whether it’s a new build or one that you’ve been running for years? At the end of the day, it’s about keeping those tires happy. James Clay, pro driver, president of BimmerWorld and graduate of Virginia Tech, walks us through his team’s progress, whether it’s BMW’s latest GT3-class racer or BimmerWorld’s own ChampCar effort. 

It’s very rare that we get a fully new car, but when we do, it’s usually a similar configuration–given our BMW focus–to something we have done before. 

The E46 was just an iteration of the E36 suspension design, for example. The E9X was a new 3 Series with a similar front strut layout but with the addition of a multi-link rear, so we could at least apply the same front basics to that car. And the F8X and G8X platforms that followed were very similar to the E9X

But most new car models are developed in pro racing, and by the time most people are converting or using them for race use, businesses like ours have a good bit of pro experience and knowledge available. 

This info can then translate to customer cars. We do all the expensive development and heavy lifting and develop packages and individual setups for customer needs.

But whether the car’s a familiar chassis or new to us, how do we actually get it ready for the track?

Setting an Early Baseline

I really want the car to be ready to hit the track when it leaves the shop. So if it’s a new chassis, we do the development work to determine our alignment specs: toe curves, camber curves, etc.

We also have defined spring rates, and thus wheel rates, that put us in the box we like to work in. Shock choice is core. 

[How To Calculate Spring Rate–and How to Understand Cutting Coils | Handling Basics]

This way we can have the right baseline parts on the car and base static alignment settings. This early work also shows us how that static alignment will translate to a dynamic alignment once on the track and under load.

This is, of course, assuming that we are working on a race car with racing parts. When you’re working on a street car, almost by definition you’re on the soft side of what would be considered optimum–and when I say “race car,” I’m translating that to “optimized.” 

Somewhere out there exists the perfect balance of performance and stiffness. A good alignment before leaving home should get you in the ballpark. 

For example, if I have a street car with some racing parts on it, I know that I almost always want to make it even stiffer because the base car is too soft. Optimum performance is a curve with a zenith–too soft and you aren’t optimum, and too stiff and you are not optimized on the other side of that perfect point. 

We anticipate the optimum point on a race car, but I’m aware we may need to stiffen or soften the setup to nail it. But on a street car, we are working on the front side of the curve, and we almost always see benefits from stiffening as we climb toward optimum. That same curve concept applies to anything in setup: tire pressures, spring rates, shock settings, etc.

[How to set tire pressure, align your chassis and shop smart]

Trackside Setup

The initial run at the track is always used to determine overall balance of the car. Is it coupled, meaning the front stiffness is balanced with the rear stiffness? Or in long, sweeping, high-load curves, do we need more or less front or rear stiffness? This is defined by spring rate and, to a lesser degree, anti-roll bar stiffness. 

Then we start working on more dynamic situations that further bring in the bars and shocks. I separate a corner into four sections: braking, turn entry, mid-turn and power-down. 

Aero adds some complexity, and the driver needs to be able to differentiate an aero balance from the car’s platform balance. And when you start working on transitions between linked turns and longer connected sections of track, that adds another layer.

After sorting out car balance, we look for the biggest problem: What’s the one thing that is keeping the car from going faster? 

But we also have to look at that part of the track. If there’s a significant mid-corner issue, for example, we need to make sure the problem isn’t caused by braking and turn entry. 

Tuning a suspension properly is really a balancing act and an art form. One adjustment to address a specific problem in a specific place on track or section of a turn often has an effect, desired or not, in other places as well. It’s a matter of being aware of all the potential cause-effect relationships and moving forward methodically.

Data vs. the Driver’s Feedback

The driver is absolutely critical to the tuning process. We can use tire wear (which takes time to develop) and data (although it takes a higher-level engineer to get past the minutiae and into the real root of what the data is telling you), but the driver is by far the best tool. 

That being said, it takes a driver with specific development experience to quickly move the process forward. So many drivers are accustomed to driving whatever they’re given, so it takes skill to recognize when you’re driving around a problem and when you should instead make the car better so you don’t have to. 

But with that task comes responsibility: You have to make sure you’re addressing the real or right problem. Otherwise, even with an experienced engineer guiding the process, you can end up in a no man’s land because changes are made on incorrect feedback that will move you outside of the box that you really want to be in. 

Once at the track, listen to the driver but keep a close eye on the numbers. While driver confidence matters, does the data say one setup outperforms another?

A couple of key things will help guide you here. First, always use the stopwatch. How a driver feels matters, and some drivers will go faster because they’re more comfortable with a certain setup, but always know when you’re making that decision and sacrificing ultimate speed for comfort. 

Likewise, just because something feels fast doesn’t meant it is. Use the data and stopwatch to evaluate. Tire wear and some other things matter, but always be mindful of the clock. 

Second, and most important, remember that when you have a methodical and documented approach (you documented everything, right?), you can always go back if you were wrong. Don’t be afraid to turn knobs and change things. If you get it wrong and you don’t like it and you are slower, change it back. Even with an experienced driver, we can sometimes not know what side of the curve we’re on from that optimum point, so adjusting one thing a notable amount and then going the other direction from the baseline will give great insight.

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Comments
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AndyHess
AndyHess New Reader
4/4/22 1:38 p.m.

As part of chassis setup, one helpful article would be how to accurately align wheels at a home shop, with a less than level floor.  Toe-in is relatively easy using string setup similar to the one in the articles image.  But three things: what are reasonably priced camber measurement tools.  How can such tools measure accurately if the floor is not perfectly level (Making an assumption that there are no reasonably priced laser measuring tools for camber).  And three, how do you get under the car to adjust without raising it - and if you do raise it to make a camber/caster adjustment, making an educated guess on adjustment, then setting the car back down back in the exact spot and the exact same ride height in order to replicate an accurate re-measure?  Thanks GRM.

Colin Wood
Colin Wood Associate Editor
4/4/22 2:04 p.m.

In reply to AndyHess :

Really good questions. Let me take a look and see if we have anything related to what you're asking about. And if we don't, I'll be sure to pass it on.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
4/4/22 2:46 p.m.

In reply to AndyHess :

The way to deal with a floor that's not level is shims. Put down some sort of platform for each wheel and then shim them all to be level.

Your cellphone is a camber measuring tool, especially when combined with a length of metal that goes from lip to lip on your wheel. You can also buy fairly inexpensive angle gauges.

The way to get underneath without raising it is to use a set of hub stands. If you're having to lift to make adjustments, you're probably just lifting one corner at a time. That makes it easy to drop back in the same location because the other three wheels won't have moved. Really, if your car is moving laterally when it's in the air you have another much more serious problem.

BimmerMaven
BimmerMaven New Reader
4/5/22 6:11 a.m.

Alternatively, drive up on 4 ramps . Shim the ramps.

Mark the ramps, shims, floor for next time.  Being consistent and repeatable is more important than the actual measurement .

DWNSHFT
DWNSHFT Dork
4/5/22 12:30 p.m.

My method was the tried-and-true floor tiles method.  After I got four stacks in the right place and leveled, I spray-painted the outline of each stack on the floor and wrote down how many tiles in each stack.  So after that it was easily and quickly repeatable.

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