Changing camber in your front wheels is pretty straight forward, right? There are some things that are inadvertently altered when we change our cambers. Let’s go through the process and see that we might need to consider the overall effect of making camber changes.
Why Change? – The reasons why we might want to change cambers include the following. We might see where the tire temperatures are not ideal in our view for the type of car, type of tire and design of race track we are running at. We also might want to experiment with camber to see if the tire could use more and provide us with more traction. The tire temperatures might look good to us, but hey, what the heck, let’s see if more is better.
Tire temperatures are not really the final determining factor in judging whether we have the best camber in our front tires. In some suspension designs, the tire can roll through camber changes such that temperatures rise across the tread, but the tire is never at the ideal camber. The temperatures lie to us sometimes. I’ve personally seen this happen.
An example of this is the NE pavement Modifieds, being the SK division as well as the Tour Modifieds. Some teams run very little right upper control arm angle, close to 5 degrees or so. With that angle, the tire runs the straightaways on the inside edge, the transition on entry on the middle of the tire and the mid-turn on the outside. When the team checks the tire temperatures, they might look OK. But the tire never has the best tire contact patch.
You can get a clue this is happening by simply observing the car going through mid-turn. I once visited with the late and great Teddy Christopher and went with him to Stafford for an SK race several years ago. I watched him in practice through turns one and two and noticed that the RF tire was going into positive camber.
Back at the pits he asked me what I thought. I said it looked pretty bad, not really in those words. I talked to his crew chief, a seasoned veteran, and we found out where he had gone wrong. He had been fooled as well. When he made changes to the control arm angles on the car that next week, Teddy went out and won two or three in a row, not that it was unusual for him to do that. But the team had been struggling as of late and that change helped them a lot.
The moral of the story is, when your car goes out, look at the tires and see if they look like they have the camber you think they need on the race track. Visuals can tell us a lot.
Basic camber knowledge tells us that on a circle track, turning left, we need positive camber in the left front tire and negative camber in the right front tire. When the chassis travels in dive and roll, these cambers will change. How much depends on the control arm angles, especially the upper angles.
Ride Height – When we decide we need to change the cambers, we need to know what else we are changing when we do that. A quick camber change on pit road does not just represent the “one change at a time” edict like we, and others, have preached for years.
On the left front, the spindle inclination, or angle of the ball joints from a front view, is usually less than at the right front. I’m used to 5-7 degrees of angle. This puts a lot of the tire outside the intersecting line that passes through the ball joint centers.
As such, when we add positive camber to the left front, we essentially jack up the chassis. In other words, we load the LF and RR more so which unloads the RF and LR corners. This de-wedges the car (reduces cross weight for you new guys) and can make the car looser.
If the car turned better after the change, we might think that the added camber did the trick when in reality it was the drop in cross weight that made the car turn better by making it looser.
At the RF corner, if we take away negative camber, we add to the wedge, or cross weight, of the car. Since that spindle has a higher degree of inclination, the intersecting point falls closer to the tires center of contact patch. So, the effect is less than at the LF.
If the LF addition of positive camber de-wedges the car and taking away of negative camber at the RF adds to the wedge in the car, then they might cancel each other out, right? No, because for each degree of change in camber, the LF changes the wedge more than the RF does. The net is still a looser car, but how much is dependent on the amount of camber change and the overall design of the suspension.
If we add positive camber to the LF and also add negative camber to the RF, we have really loosened up the car because both of those actions took wedge out of the car. Boy, she’s turning now, Jack. But not necessarily because the camber change caused the tires to work harder.
The bottom line here is this, when you change the camber in one wheel, bring the ride height back to normal, or what it was before the change. Then you wouldn’t have changed the cross weight percent and loading on the four tires. At least not statically.
Bump Setup Camber Change – With the advent of the bump setups in circle track racing, camber change of any significant amount while on the bumps is a thing of the past. But we’re not out of the woods yet. There is still a lot of camber change going on from when the car is on the grid to when it is going through the turns.
So what, we might say. The tires are loving it because our cambers are staying very close to ideal due to very little vertical chassis movement. And you’d be right, but what about the transition onto the bumps? What happens during that process? Few teams consider what happens then. Let’s see.
As we have discussed above for a more conventional car, when we change the cambers, we are also changing the corner heights and along with that, the distribution of loading on the four tires. If the chassis travels some three or three and a half inches down onto the bumps, where does the wedge, or cross weight, go to then? It has to change, we have already discussed that little tidbit.
Weight change due to the jacking effect of camber change (and that is essentially what it is, the tire jacks up, or down depending on the change) also changes the loading on the four tires.
We already know that the extreme travel associated with bump setups, from ride height to on-track height will most times load the sway bar. This adds cross weight to the setup. If the camber change from all of that travel changes the cross weight too, then where do we end up? Good question.
Finding Loaded Cross Weight – The major point made here in this piece is that camber change will change the loading on the tires and we have to know this in order to plan for it in our preparation of the race car.
If we know how much the cross weight will change due to chassis travel, then we can adjust our cross weight percent with the car at ride height. Say we gain 2% of cross weight at full travel, then all we need to do is set 2% less cross weight in the car at normal ride height.
Put the car on the bumps only with the bar loaded and see what the cross weight goes to. Then adjust your cross weight percent with the car at ride height. It’s as simple as that.
Or, you can adjust the bump spacing to the shock body to bring the cross weight percent back to what you want while on the bumps. That will compensate for the sway bar and the camber change that happens due to the high amount of travel.
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