How much rear neg camber can we get and how?

[911st]

What is the most rear neg camber we can get our of a 3.2 Carrera at close to Euro Height?

Any tricks other than elongating the rear bottom hole on the spring plates?

Looks like -2.5 to -3 deg if one is lucky of camber is about it.

[Jack Olsen]

This isn't an answer to your question, but usually the limiting factor is the front -- with the restriction being that you don't want too big a difference (more than a degree) between the front and rear.

[TT Oversteer]

I think Elephant sells an item called "camber max" that lets you dial in as much as you want.

[Peter Zimmermann]

The pyrometer tells all. Set the car at about 1.5 degrees negative (if you have big torsion bars), after a hot lap at your next DE "shoot" the rear contact patch. When your camber is right the inner tread rib will be about 25-30F hotter than the outside tread rib. If the tires measure the same across the contact patch you can add a bit more negative; if the tire is hotter on the outside you definitely need more neg. camber.

[911st]

Peter, I though you wanted equal temps across the tire. Help me under stand wanting hotter inner tread?

TT, I suspect the Camber Max makes adjustment easier but I seem to think it will not allow any more than -3 deg neg camber with out modifying the toe concentric and lower slot but do not know this for sure.

Jack, Thx. One other knowledgeable noted a .5 deg max delta so it is good to hear 1 deg. I wonder why' when I hear generally accepted rules like that. I wonder if one can get -3 out rear, and only -1 in the front, dose it make sense to give up the rear camber in the name of balance. Dose not seem valid to sacrifice the solid rear traction just because the front is a bit weak.

My car is stock suspension built to 86 specs where the rear was stiffened up relative to the front. Currently at -1.25 and -2.5.

All good stuff the weigh.

[Peter Zimmermann]

Originally Posted by 911st

Peter, I though you wanted equal temps across the tire. Help me under stand wanting hotter inner tread?

Personal experience! I ran 31mm rear T-bars in my PCA Club Race car, and that is the method that I discovered generated the best lap times. Set to generate equal temps across the contact patch, the car wasn't as drivable in high speed corners (for instance, turn 8 at Willow Springs Raceway - which is done at full throttle in top gear). I would imagine that different drivers have different preferences regarding how the car reacts, it all comes down to how smooth you want the car. I don't like abrupt twitches at the apex, so the hotter inside temps gave me just a bit more control.

[Dan (almaden)]

Peter just mentioned the biggest factor and I had mentioned it in another thread by 911st earlier.
Everyone likes their car set up differently. While the ideas we give you are valid for our purposes, they may not be to your liking.
Look at any race series and the drivers take the exact same car and set it up differently for their tastes.

I like my cars slightly loose. Others like tight...
Have you developed enough track time and your "buttometer" to tell what you want in your cars handling?

I still think you have too much delta front to rear camber and that is causing your tire wear...also going to even more rear camber is only going to exacerbate the situation.
You need to get more camber up front if you want to keep the rear where it currently is.

[Jack Olsen]

Originally Posted by 911st

Jack, Thx. One other knowledgeable noted a .5 deg max delta so it is good to hear 1 deg. I wonder why' when I hear generally accepted rules like that. I wonder if one can get -3 out rear, and only -1 in the front, dose it make sense to give up the rear camber in the name of balance. Does not seem valid to sacrifice the solid rear traction just because the front is a bit weak.

So long as all four wheels are touching the ground, you really can't deal with the front and rear as separate systems. My F/R difference might not be a good example, since so little of my suspension geometry is stock. But in your shoes, I'd look into the Elephant offset camber plates or decambered ball joints or some other scheme to get more negative in front, and probably dial back the rears to 1/2 or 3/4 degrees of that. But (again, if I were in your shoes), I'd also defer to a good setup guy. It's not my area of expertise by a long shot.

[aston@ultrasw.c]

Front camber. I have 2+ deg negative using stock parts and a strut brace. To get this I loosened everything up then put a ratchet strap around the top of the struts. I used a couple of rope loops at each end so the force would be applied right were the strut pokes through the tower.

Then I tightened the strap and cinched everything down. Over 2 deg easy!

I then took it to a laser alignment jig to double check my measurement.

[arbita1]

Originally Posted by 911st

Peter, I though you wanted equal temps across the tire. Help me under stand wanting hotter inner tread?

Here is some info on that topic if you're interested:

http://www.hankooktireusa.com/motor/motor_techinfo_temperature.asp

[Peter Zimmermann]

Originally Posted by Peter Zimmermann

I don't like abrupt twitches at the apex, so the hotter inside temps gave me just a bit more control.

Just so I don't mislead you, a lot more than negative camber went into the setup that I liked the best, getting a 911 to handle per its driver's needs is a lot of work, and the front and back must be set to complement each other.

[69911e]

Yes, you can get more by slotting the adjustment eccentric bolts and welding onto the other side. I posted pics quite a few years ago. The Elephant product may do even better.
I made a system 15 years ago which monitored the temp pattern across the tire in 1/10 second intervals for all 4 tires and recorded the data for the race duration. For even heat delta in a corner (best approximation to normal force) you will end up with a hotter inside temp when measured in the pits.

[911st]

Originally Posted by arbita1

Here is some info on that topic if you're interested:

http://www.hankooktireusa.com/motor/motor_techinfo_temperature.asp

A little bit of gold here, thank you!

First I need a tire probe instead of my inferred temp gauge. However, my tires do seem to look like I have tire slag from hot rubber near the outside half but not the inner.

My fronts have been running closer to 180 when I get near 200 on the rear. Per the article this may confirm that I am not pushing or understating. It did not feel like it but I am still learning.

The article also confirms what Peter says about hotter inner temps in the 10 to 20 deg area. If the inner is more than about 20 deg hotter there needs to be less camber. I will look for this. I suspect however, that with the body roll I get with stock suspension and the loss of camber with stock rubber bushings, I can use all the neg camber I can get.

Also, on another page they say target air pressure for a DOT race tire is 40 lbs hot plus or minus. While my Dunlop Z1's are actually such a tire, they are very close. I think I will use this as a target starting point. I know this is for a different tire but again, it is just a starting point and is near what others have recommended.

I am not a big fan of general rulls for some reasion. However, I can get my head around looking at the front and rear as separate systems. My car is stock and lowered. Different camber curves, the rear pushing 50% more weight, and the front carring much of the braking are all factors that may play off against each other. Front tires with less neg camber stop faster. If one pushes, more camber makes them bit more.

Having said that, I am going to try for more front neg camber but I am going to concentrate on getting the rears to work as well as they can as a prioriaty. They have to do 50% more work than the fronts.

Again, thank you all for putting up with a novices questions that may enjoy knowing how things work a bit to much.

I love these cars.