Wider is better?

[RichardP]

The phrase “Wider is Better” has a connotation of being a bit of a joke since it was used as a cheesy advertising catch phrase for a vehicle few people thought was “better” regardless of it’s real or perceived wide stance. Regardless of the connotation, it still poses a real question: Is wider better?

Chris and I attended a recent Driver’s Edge event at Texas World Speedway with my American Iron car. On hand with us was a Race Technology DL1 data acquisition system, a fresh set of shaved Toyos and some new 1” thick spacers that would get the front track width of my car right to the new 73” width allowed by the 2008 AI rules. Since I have gotten some questions lately about the effect of track width on lap times, the conditions seemed ripe for a bit of testing.

Saturday morning at the track started out a bit foggy but once it cleared I went out for a session to scrub in the tires and get them up to temp so the hot tire pressures could be more accurately set.

I sent Chris out for a similar reconnaissance run and he came back reporting a setup not to his liking. The last tuning done on the car was with very worn tires and it’s not surprising the car was reacting differently on the fresh rubber. After a few adjustments to the car, it was ready for some testing.

I told Chris that we were going to do some back to back comparison testing but I didn’t tell him what changes I was going to make to the car. In an effort to keep the testing consistent between runs Chris made it his quest to line up several like sized passengers. He somehow managed an amazing run of short and petite females for the task despite some complaints by them of being considered control “ballast.” Actually, David Love managed to sneak into the passenger seat on one run. While he didn’t upset the weight factor too badly, he blew the attractiveness ratio all to hell.

The baseline run was with 1” thick spacers in front and no spacers in the rear. The narrow test run was with no spacers front or rear (2” narrower in front). On the subjective front, Chris thought the handling was pretty good for the baseline run but came in raving about how much better the handling was with the narrow setup. Really??? That wasn’t what I was thinking his reaction was going to be. Chris was also pretty shocked when I told him what I had done to the car. Subsequent test runs were with the 1” spacers in the front and ¼” or ½” spacers in the rear trying to get closer to the same front/rear width ratios that made the car “handle” so well. I would have liked to add more to the rear but fender rub prevented it.

So the narrow setup made the car “handle” better but did it make it “faster?” The data acquisition would have to answer that question.

Unlike my previous aerodynamic analysis where the differences in the data were significant enough that I used detailed data specifically from representative corners, the data from this analysis was subtle enough that the differences tended to fall into the noise. Only by accumulating full lap data did a pattern between the different setups emerge.

By looking at the best lap time from each representative session we find that the best lap time from the narrow setup was a 1:58.16 while the wider setups had best session lap times of 1:57.64, 1:57.59, and 1:57.67. This shows about a half second gain by going a full 2” wider.

Looking at the lap spreads from above might lead one to believe that Chris really isn’t human. Looking closer at the data, however, shows that there is more variability between the different laps than the above numbers tend to show. It’s about impossible (even for Chris) to get everything just right for a complete lap. There is always going to be a lap where one section was done really well while another lap excelled in a different section. The cool part about data acquisition is that you can break up the track into several different parts to gain insight into these kinds of things. From this, you can calculate a theoretical best lap time using all the sections that you got just right. I’ve attached a picture of the track showing the different sections I used for this analysis.

To validate the above data, we can take a more restrictive look at the data by only using Saturday’s valid sessions and try to reduce driver variability by looking only at theoretical best lap times for each session. For the narrow setup we get a best theoretical lap time of 1:57.17. The wider track width Saturday sessions have best theoretical session times of 1:56.58 and 1:56.44. Again, we find a variance in the ½ second range.

Anyway, a 2” difference in track is pretty significant. Even with that, the data shows the benefit of a wider track is small but real. Fortunately, for this modification, it’s a lot easier and cheaper for the reader to test on their own than the aero stuff I posted earlier. That’s assuming fender clearance issues aren’t precluding you from adding spacers…


Richard P.

[AI#97]

Thanks Richard! Again Great Data and makes me wish I had a DAQ setup. What did you have to do to get the tires covered at 73"? I know you were saying the fenders needed some work to do that on a fox...?

My car is already at 72.5" in the front and pushed the rear to a little over 73" at the last event. Car reacted very strangely but lap times saturday morning at Houston were also a weird read. I dropped from 45.2's from the previous event to 44.2's and .3's.....on a front left tire that had only 10lbs of air in it. Don't know if it was the playing with the track width, the camber/caster changes or the new track config...? CMC times seemed a little slower on the new config and with Frank and Kirsh getting signficantly faster, it's hard to tell if the track config and new paving made the biggest difference. I do know that this year, I have been off track more times than I have in the previous 3 years of doing this so I might just be FINALLY driving harder!! :lol:

I think this DAQ stuff is going to prove to be the tool I personally need to map changes/improvements to the car. Your information and having talked to Daron about the ones they are using at Apex tells me this might be my next purchase. I just have to get my laptop working again!! ops:

Can you post details on the different units you have used and your thoughts on user friendliness?

Thanks!

[Todd Covini]

Thanks Richard!
Cool stuff and, as always, written in a succinct NASA (the space guys, not the race guys), SAE kinda way.
I have a set of wheels that require me to run spacers up front for caliper clearance...as well as wider front track. Always liked that setup.

-=- T

[RichardP]

What did you have to do to get the tires covered at 73"? I know you were saying the fenders needed some work to do that on a fox...?

Stretching Fox fenders to fit over the current AI width is well beyond my skills. I've done every thing I know to do but when that's done, you just basically cut away whatever would rub at full bump. It leaves a bit of tire out in the open. It sure would be cool to have the much wider SN95 fenders. Or maybe some of the flares that Donovan now has...

Richard P.

[donovan]

Fender flare envy...


Good stuff RP!!

That reminds me... I still have your fender lip roller...

DD

[GlennCMC70]

well who am I to argue w/ a "rocket scientist", right? well you guys know me well enough to know that won't stop me.
lets start by saying I'm in no way saying Richard is wrong, but rather my questioning is along the lines of - are you sure and teach me why I'm wrong. w/ that said, lets move on.
I read Richards findings and I understand the intent of the testing. I remember Richard saying they only put spacers on the front or they put more on the front than the rear. adding spacers will add more leverage on the spring thus making it act softer - or so I've been lead to think so.
if the car was balanced when they started and more spacer was added to one end than the other, it would seem to me the car would now be not as balanced as it was before. in my eyes, adding the same amount of spacer to each wheel will not really change the balance, but make the car "feel" like its on a softer rate spring (which is not what was done here). so by that logic (right or wrong) adding more (spacer) to the front than the rear would make the front more "softer" than the rear thus making the rear more loose than before (or the front less tight to use a NASCAR term). so is it possible that the car was faster because the set-up was "better" w/ the "softer" set-up on front more than it was faster because the track width was wider?
its been Mitch's and my findings (backed up by a few other 4th gen CMC guys) that a overall softer rate set-up (still balanced) is just a tick slower, but just as fast anywhere on the track line wise. and that a stiffer set-up is faster, but must be kept on the "line" more so that the previous set-up.

let me have it Richard.

[AI#97]

To use Glenn's theory, let's use this info as a test...

Mustang lower control arms are roughly 18" from pivot to ball joint...I think. If you move the Wheel (lever arm) out 1 full inch, would this effectively lower your wheel rate by 6%...? Is that a big amount? Front springs at 475 lbs/in would be like taking a 28.5# softer spring???

I know maximum has a wheel rate formula for stangs but what wheel offset does that formula take into account? 17x8 with stock offset or a 17x9 with additional offset..? Not that I really would be able to cognitively do anything with this information but hey, it's fun!

So, widening the rear track on my softened the rear springs by 25# and the car turned better at mid corner, but pushed on exit at the carousel as usual. Now what?!!! :lol:

[mitchntx]

If you move the Wheel (lever arm) out 1 full inch, would this effectively lower your wheel rate by 6%...? Is that a big amount? Front springs at 475 lbs/in would be like taking a 28.5# softer spring???

Are you serious?

If you CAN'T tell a 28# difference in spring rate, then that kind of confirms what we were discussing several weeks ago about testing, prep and data collection.

Also, effective spring rate, taking EVERYTHING into account (springs, shocks, sways, chassis bind, etc.) can be changed in yet smaller increments by air pressures.

And being as Glenn has let the cat out of the bag ...

In the 4th gen F-Body world, a stiff set-up is a faster set-up. But it requires precise air pressures and precise driving technique. You have to be on "the line" with little room for error.

Soften the set-up, and you will lose a few ticks on the stop watch, but the car is a lot more forgiving.

I won't explain that that is a qual set up and a race set up.

There are several ways in which to quantify results from track width by adding wheel spacers. In order to keep EVERYTHING in perspective and relative, we have chosen to measure wheel spacer effect in terms of spring rate.

[RichardP]

OK. Lets start with the math. First of all, it’s very cool that Matt ran the numbers to try and quantify the changes that were made. Excellent stuff. Well except for the part about the math being wrong. The math for this situation is much more interesting than that. We’ll stick with the front suspension. The rear is a whole different set of math but the end results would be about the same.

Matt mentions the Mustang control arm length and does his math from there. Since the effective control arm length is from the inner pivot axis to the center of the outer ball joint, adding wheel spacers does nothing to the control arm length. Since the control arm length doesn’t change and neither does its relation to the spring, then the wheel rate (the effective spring rate at the wheel) doesn’t change either. The important distinction here is that the wheel rate is a calculation that applies to “bump” only. Spacing the wheels out doesn’t affect this.

Similarly, on a Mustang equipped with coil-overs, changing the length of the control arm wouldn’t change the wheel rate either since the correlation between wheel travel and spring compression wouldn’t change. On a Mustang with the spring in a pocket on the lower control arm, changing the length of the control arm does change the wheel rate but it’s not a linear function like Matt’s math would imply. Not only does the control arm have a different leverage advantage on the spring, this leverage change also changes the effective amount that the spring is compressed. It becomes a squared function.

So, beyond that, does adding or subtracting wheel spacers alter the “roll rate” of the suspension? Yes, but that lever arm is based around the roll center of the suspension and has little to do with the actual length of the control arm. For this roll rate (the stiffness of the suspension in roll) we have not only the resistance from the springs but also the sway bar.

For roll, the forcing function lever arm is the vertical distance between the roll center and the center of gravity of the car. The force applied is the mass about the CG times the G-force the car is seeing. The resistive force lever arm is the distance between the roll center and the effective contact patch of the tire. The resistive force is applied by the spring and the sway bar along this lever arm.

For my car, the lever arm that was changed by adding the wheel spacer is on the order of 32” long. That means that an additional inch isn’t all that much of a percentage change. The math here isn’t all that challenging but I’m not going to bother with it 1) because I don’t have good numbers for all the relevant parameters, and 2) because the simple math would only apply right as the car started to roll. As the car rolls, the roll center migrates both vertically (altering the forcing lever arm) and horizontally (altering the resistive lever arm). The latter is especially important since the roll center can often migrate several feet away from the center of the car.

I’ll agree with Mitch that I can certainly feel a 28# difference in spring rate but I don’t think this change was nearly that much.


OK, away from the math and on to the realities of testing. So yes, I did add 1” spacers to the front but was only able to add ¼” and ½” spacers to the rear. If it had been possible to run full 1” spacers in the rear, I would have done it and it would have been a better test.

Within the testing that we were able to do, we did find some interesting results, however. While Chris did note slight differences in “handling” and “balance” (more handling than balance, btw) between the different rear spacer configurations, the data shows that the differences between the lap times were negligible. This is in contrast to the differences between the wide and narrow front setups where there was a small but noticeable change in lap times. The front was the dominant change and the rear was more of a subtle tuning thing.

I would love to repeat the test with the ability to control the rear spacing better. Actually, it would be more interesting to see what the effects would be on a CMC level suspension. Unfortunately, everyone I know that would want to do the testing on their car has a Fox Mustang. You can put a narrow setup on a SN95 Mustang but you can’t put the wide setup on a Fox without doing illegal and irreversible modifications to it’s fenders.

It’s not hard to set up the basic data acquisition tool in a race car if someone else wants to try it at an event I’m attending. We were planning on putting it in Daron’s car at TWS before they ripped a shock apart to end their weekend. It’s a shame, too, since I really wanted to see how they were accomplishing the great 1.5x:xx lap times there…


Richard P.

[AI#97]

Are you serious?

Yes! I have no friggin' clue how to tune a race car suspension. There I have said it. I also don't do well at anything more than simple trig when it comes to math, although I somehow slept my way through 4 semesters of structures with A's....

Richard, you have done WAY more investigation into the "physics" of suspension geometry and have probably forgotten 10x more than I know. You got this stuff down.

I just wish I knew why my setup seems to be fast? Dumb Luck? Imagine if I actually figured out how to make the car really work?!!! :lol: I am running a stock rear sway bar, no adjustable brake proportioning valve and some Hotchkis front bar that I have no idea how it compares to the stock ones that you guys run and basically have a car that is just a bunch of catalog parts bolted onto it that are no different than any other MM equipped car in the US.

Personally, I just like getting in and driving the piss out of the car and not stressing about all the math! Think I will keep doing that for now. Maybe that's why my desire for a street car has been growing?!