Camber effects - what to expect

dfink · 07-25-2009, 01:37 PM

Well in an effort to squeak out just a but more from the poor little p-car I increased the fromt camber from about .5* in front to around 2.4* degrees in the front. The rear already was already around 3. This not done lightly. It requires shaving the shock mounts, removal of the shock tube and notching of the adjustment holes and center hole. By shaving I mean removing a 1/2 inch from the inboard side.

Do you think I can expect a bit less push. No testing till next weekend. Partial track day and auto-cross on sunday.

Just stuffed 225-45-16 up front on 7" rims and 275-45-16 on the rear with 8" rims. Looks like an off road car crusher but still a lot of meat. Initial street tests can't push real hard appears as though the front is finally going to grab hold a bit.

175K911 · 07-25-2009, 01:55 PM

I run similar camber specs on my '86, but also have a lot of other suspension mods too. If your car is reasonably stock, you should find you have better front end bite once you've gotten into the turn and can get the outside front tire pretty flat on the ground. Especially if you've been running -3 in the rear with only -0.5 up front.

Question though- what are you running for toe? If you're still running toe-in up front that will also contribute to your push. You want to have a touch of toe-out for steering response though that can cause instability at high speeds.

The one downside to the -2.5 camber up front is under braking. In a straight line you've gone from probably having 90% of the tire contact patch on the ground to something less since the tire's no longer flat to the road in a straight line. I'd be careful at first and work up to threshhold braking.

One other comment is on your tire choice- the front tire is shorter than the 225/50-16 that most run on the track which will lower the front end a bit. And a 275/45-16 on the back? Is that a misprint? The tire should be a 245/45, so your rear tire is way taller than stock. So your front tire is too short and the back tires are too tall, this must really jack the rear of the car in the air. Another thing that's going to cause understeer. And how do you squeeze a 275 on an 8" rim? Most who run a 245/45 mount them on a 9" wheel, including the factory.

So you asked if the camber will get rid of the push. It will help, but there are other things to work on too if you want to get the car to be more neutral.

dfink · 07-25-2009, 03:01 PM

Quote:

Originally Posted by 175K911

I run similar camber specs on my '86, but also have a lot of other suspension mods too. If your car is reasonably stock, you should find you have better front end bite once you've gotten into the turn and can get the outside front tire pretty flat on the ground. Especially if you've been running -3 in the rear with only -0.5 up front.

Question though- what are you running for toe? If you're still running toe-in up front that will also contribute to your push. You want to have a touch of toe-out for steering response though that can cause instability at high speeds.

The one downside to the -2.5 camber up front is under braking. In a straight line you've gone from probably having 90% of the tire contact patch on the ground to something less since the tire's no longer flat to the road in a straight line. I'd be careful at first and work up to threshhold braking.

One other comment is on your tire choice- the front tire is shorter than the 225/50-16 that most run on the track which will lower the front end a bit. And a 275/45-16 on the back? Is that a misprint? The tire should be a 245/45, so your rear tire is way taller than stock. So your front tire is too short and the back tires are too tall, this must really jack the rear of the car in the air. Another thing that's going to cause understeer. And how do you squeeze a 275 on an 8" rim? Most who run a 245/45 mount them on a 9" wheel, including the factory.

So you asked if the camber will get rid of the push. It will help, but there are other things to work on too if you want to get the car to be more neutral.

This is just one of many attempts. Car is in no way stock anymore. 22-30 torsions, 22mm sways front and rear, 8 point welded cage, 2350 with a hundred pounds of lead in the right front to balance the car. Fronts are within 10 lbs and so are the rears, the cross is balanced with me in the car the total balanced weight is 2500. The front / rear ratio is 44%F - 56%R.

Tire sizes are not misprint other than the 225 is 50 not 45.
Front is 225-50-16 24.7" on 16"x7"
Rear is 275-45-16 25.6" ON 16"x8"

So correct there is a 1" difference in the height which is noticable in the rake of the car. The 8" rim is actually the min for the 275-45 if it was a 275-30 then it would probably need a 10" rim which I don't have. The tires fit very nicely on the rear. Note the oil lines have been relocated and the 3.6 camber is needed to get them in there.

I do run some toe-in. I tried toe-out and intial turn in was OK but it seemed to increase the tendancy to push. The Toe-in has added some stability at speed and seems to be beter through the turn though turn in takes a bit more effort.

rfloz · 07-25-2009, 03:09 PM

A little toe out will definitely help on initial turn-in and your revised camber looks a lot better balanced.

If you are still having understeer mid-corner, you might want to try an adsuctable rear anti-roll bar. Thse are great for balancing the car. I suggest rear only (or at least first) if you don't already have a through the body front bar as the rear is a lot simpler and cheaper to install.

If you don't already use one, a probe type pyrometer will really help you get your setup close and can diagnose a lot of different problems.

911st · 07-25-2009, 06:54 PM

The extra camber should make the front bite better and get you close to max hold. Your springs and sways should take you from about 4 deg lean stock to about 2.5. Thus, your front tires should be close to squre to the track as long as you are not lifting the inside front tire to much.

8" front rims up front sould help.

Are you running a welded dif or limited slip and how is it set up?

What brand and type of tires are you using?

What is your front lip to the ground and front tire diamter spec?

Have you tried playing with the sway bar settings--softening the front?

dfink · 07-25-2009, 08:07 PM

Quote:

Originally Posted by 911st

The extra camber should make the front bite better and get you close to max hold. Your springs and sways should take you from about 4 deg lean stock to about 2.5. Thus, your front tires should be close to squre to the track as long as you are not lifting the inside front tire to much.

8" front rims up front sould help.

Are you running a welded dif or limited slip and how is it set up?

What brand and type of tires are you using?

What is your front lip to the ground and front tire diamter spec?

Have you tried playing with the sway bar settings--softening the front?

My plan is to eventually get 17" 10 & 12 or put 10s all around.
The sway bars front and rear are adjustable at this point I am into the big items. Once I get things closer to what I think is acceptable I will try to tune a bit with the sway bars. The basic alignment being the subject as at this point some adjustments can make a 2 or 3 second difference on an autocross. I know the tire setup I have is not ideal. I would like the 17" with a low profile and a diameter of around 24.5 but just can't afford the new wheels right now. I am going for max rubber with the wheels I have. The front camber increases took a bit of a commitment to cut the shock towers. Again couldn't affort the $675 adjustable camber plates. I don't think even those would have given me as much front camber as I have now.
As for tires they are hoosier A6s
Ground clearance in front I don't know. I did have a fender ride height of 23.5" rear and 24" front when I had on 23X9X15 goodyears cantilever slicks. Add in the height of the new tires at 24.7 and 25.6 and I am probably pretty close to a stock ride height.
The diff is a factory limited slip with gaurd transmission plates. Its probably only a 40% and that is on a good day but it will spin both tires on a hard launch.
This is an XP class autocross car that sometimes see the track. At the track it is pretty well behaved. At 2350 and 275RWHP it scoots along pretty good. Autocross however takes any ugly habit and multiplys it. I am hopeing the camber adjustments in the front fall into the large adjustment category. I will know next weekend.

stlrj · 07-26-2009, 07:31 AM

[QUOTE=dfink;4798381 Do you think I can expect a bit less push. No testing till next weekend. Partial track day and auto-cross on sunday.[/QUOTE]

I think you are expecting less push with the additional negative front camber. My guess is that your front end will have less bite due to the reduced contact patch, just as your braking will have suffered too.

As soon as you apply the brakes coming into an auto-cross corner, your car will have a tendency to push more even before you turned your wheel. Turning in the corner will only make it worse.

I hope for your sake I'm wrong.

Cheers,

Joe

175K911 · 07-26-2009, 07:58 AM

dfink-
Sounds like you've got a fairly good start on curing your push. Just a couple more thoughts (from close to 30 years of modding and tracking 911's):

With that much rear tire compared to the front, you're still going to get push in the tighter turns. Just to much of a difference front to rear.

Toe out will most definitely help your push, but as mentioned, at the sacrifice of some high speed stability. I run toe out everywhere but VIR, then I run zero toe. But never toe-in, the car would plow like crazy in tighter turns.

When I went from open diff to my Guard set at 50/80, I had to completely change my suspension setup to get rid of the push in the tighter 2nd and 3rd gear turns. Went from 31 to 33 rear torsion bars (23 front) and changed the valving on my front Bilsteins.

How does the car feel in the higher speed 4th gear type of turns? Is it neutral or does it still push?

dfink · 07-26-2009, 10:01 AM

Hard to say on the track only had it out one day but if felt pretty stable I never really felt out of control other than some instability at high speeds which I lessened with a quick track side toe-in. Increase.
Dang it now I have confused myself. I guess for the autocross I had it setup with toe-out to make it turn. Then it was unstable at the track so I had to put some toe-in on the front. I have not take the front toe-in back out. I will need to do that track side as there is a track day just before the next autocross. I just use 1/2 turn which is easy to do with the turbo tie rods. Not so easy with the stock ones.
I really think the front camber is going to make a significant difference. The debris pattern on the front tire after a couple of test drives looks much better than before.
I have koni adjustable sports on the front and rear. I just set the rears to the #2 position from the #3 position. I don't think #3 was letting the car transition properly in the slaloms. Fully adjustable coil overs would be nice but probably not going to happen.

911st · 07-26-2009, 05:57 PM

I am not an expert but have some thoughts.

I did not know you were talking about AutoX.

Front camber and toe out are important in autoX for front bite.

You get front camber from several things. One is tilting the strut as you did (or lengthening the A arm). Another is setting the ride height and or A arm to achive effective gain camber as the Arm advances (camber curve), caster also adds to camber as the wheel is turned, and last is how much you let the front of the car tilt / sway (spring rates and suspension geometry).

With a normal stager on a 911 there is not much difference between front and rear tire sizes however, the rear has to support 50% more weight than the front. Thus, it only takes one good front tire to hold the front but it takes more than one rear tire to hold the back's weight. Setting the car up front stiff transfers some weight to the inside rear tire to maintain balance in a corner.

If you are running a 225/275 stagger you no longer need to run that type of set up. To get the front to do as much work as possible you will have to transfer some weight back to the inside front wheel. If you have an agressive limited slip, even more so.

With AutoX it is more of a benefit to have the rear be able to rotate. Thus, setting the rear stiff and the front soft may help you better achieve your needs in two ways.

Different types of tires do need different camber settings. I think the best is to watch for wear patterns over time. Tire temps are of course the accepted way.