akrott1

My friend (fellow track day'er) and I were discussing suspension set up the other day. I told him that everyone on the site here was recommending the 35mm bar upgrade. We were trying to understand from a vehicle dynamics standpoint why that would help turn in, or help eliminate push. Is it simply because it does a better job of transferring the weight over to the outside front tire, creating a larger contact patch = More Grip?

Please explain....

Aaron

O-taka

actually, swaybars work by pushing down the inside tire
keeping both planted

Sam Strano

Helping turn-in isn't the same as eliminating push, fwiw.....

The car responds more crisply for a couple of reasons. The first is simply because the bar is stiffer. The car doesn't roll as much, and you have to basically get through the roll before the car really changes directions. Secondly, in transition a bigger swaybar acts like more shock rebound.

As for eliminating push. Sometimes yes, sometimes no. This depends on the other parts on the car. The reason it works on a lot of cars is due again to less roll. You lose negative camber when the car leans. the more it leans, the more you lose. If you keep the car more flat, you don't lose as much camber, helping the contact patch and trumping the increased wheel rate. Now, on cars that are say very stiff with 600+ pound springs type setups you might get more push. the car is already more flat, and adding more bar will simply give too much wheel rate without a pay off of better camber control. Also, the rear setup (and tires, and sizes, and shocks, and about 14 other things) effect the way bars work on individual cars as well.

mitchntx

Sam, help me understand something ...

As I understand it it, the reason behind more static negative camber is to compensate for the loss of camber when the suspension compresses. True?

In your mind, what is the tire contact patch target? Is it 100% possible contact patch with even weight distribution across the contact area when car is at full lean?

Is this measureable? How does one know? What do you use to find the optimum?

I've been doing a lot of reading the last couple of weeks, trying to visualize the dynamics of what is happening while making a corner. Trying to grasp a lot of information that folks have posted concerning a specific setup and their personal results. Finally, attempting to understand the dynamics of how one chassis component or measuremnet can have suck a profound effect (either positive or negative) and another will have little or no affect.

Sam Strano

Ok, I'll try.

The reason behind more static negative camber is compensate for the loss of camber, but it's due mostly to the car's rolling than the suspension compressing. As the suspension compresses it gains camber, it doesn't lose it. Note how much more negative camber you got when you lowered the car. When the car leans, the upper a-arms tilt out along with the shock tower, and that results in a loss of camber.

The tire contact patch target is 100%. It is possible, and you know you're there when you have nice equal tire temps. However, taking good temps is something that most folks are lazy about. One has to use a probe type pyrometer, not an IR one. You have to take them IMMEDIATELY after working the tire hard (like on a skidpad), taking them after running a cool-down lap isn't going to work as the inside will read hot due to the camber and that you'll be rolling on the inside only back to the pits.

mitchntx

OK ... that makes sense ...

It's not the suspension compressing rather the relative angle of the body to the pavement (where the tire is). That makes perfect sense.

A probe pyrometer is more acurate, granted. But wouldn't an IR pyrometer, if used consistantly, give you temps that could be used to measure changes? While the actual temp might not be accurate, if a change in suspension gave you a delta of 20* at some point on the tire, that data could be used to quantify the change ... right?

lincmarkv

In part. Radial tires also prefer a static negative camber, period. The cornering force increases for them this way. Hence, for instance, Nitto's reommendation of 5 degrees of negative camber for their 555RII.

Dan

5.0THIS

going along with a point Sam made....... I race in the NASCAR Weekly racing series here in colorado, and when we are setting up our chassis, which varies week to week with varying weather and track conditions, the pyrometer is one of our best friends to find out what we need to do to the car, with the suspension angles and pressures, to maximize the contact patch. On some tracks and road coarses it may be beneficial to set the car up where it turns better in one direction, if that track has an abundance of right or left turns, so not always in road racing or autocross are cars set up exactly equal side to side. just my .02$

Sam Strano

Nope. First you are only reading the surface of the tire and not seeing what's going on inside. Hell, the sun will effect that, which easily could make the outside much hotter on the gun than it really is since the middle and inside are in the shade of the wheel-well. I suppose it's better than nothing, but no substitute for a real pyrometer.

Sam Strano

Wow, that's them covering their asses....... I guess they don't want to have anyone bitching about outside tire wear.

Each tire does "need" or want different camber based on the construction. 5 degrees is excessive IMO, and indicates a tire that deforms an awful lot.

What you looking for is to stand the tire straight up under the hardest cornering you see. If you go to www.racerpix.com and into the 2001 season, then Street Prepared, then E-Street Prepared, and then find my name (sorry, can't link it) you'll see a pic of a '99 Firebird I used to run that illustrates this well. Notice the loaded front tire is using all the contact patch, just look at how the rim is sitting nice and straight. Now, that was 3 years ago and I've done some tweaking since then, but that was very close and a good example of what we are talking about.

5.0THIS

We use a probe type pyrometer in our racing, as do most people out there. the only thing some people use IR pyrometers for is to measure the racing surface temperature.