308 GT4 Camber question?

Hi Everyone.
I am currently setting up the front alignment of my 78 RHD 308 GT4 (euro). I have oversized wheels and tyres all round.
225/40 ZR 18 on the front and 235/40 ZR 18 on the rear - been on car around 3 years.
Ever since I have owned the car the front camber has been out, having it checked a month or so ago I found that the rhd side is 7mm negative and the lhd side 8mm positive (top to bottom on the rim.

The manual says it should be between 1 and 3.25 mm positive camber.

I have read all the posts on this site about GT4s and camber and noticed that some owners with larger tyres run -ve camber.
1. Is there a reason for this?
2. What is the best value for the camber?
3. Should I just set it to the manual default?

Thanks in advance..

Cheers
Nick

 

Hi Nick,

The first thing you need to do is have the camber measured in degrees, not mm. The reason, the owners manual quotes camber in mm for the stock 14" wheels, not 18" wheels. You have a very assymetric car there, either all the shims are missing from one side or something is bent. I would have a good look at this first. The poor old thing must have driven like a pig.

Back to your camber. Negative camber allows more of the tyre to remain in contact with the road during hard cornering. Have you ever noticed how the outside of many cars tyres wear after a track day? That's because the outside of the tyre "Rolls" under.

The reason why Ferrari suggest zero or positive camber on the front is because they want you to fly off the road into the trees frontwards. Dialling in understeer makes the car safer for the average motorist but if you can put a degree of so of negative camber on the front, that will make the car turn in a little nicer and give you more front end grip.

There is no best value for the camber. It is a compromise. if you drive the car agressively, Then I would run as much negative camber on the front as possible, you are limited by the front lower suspension forks, it will be somewhere around 1 to 1 1/2 degree negative. If you drive the car quietly, I would be happy with the stock setting.

As a data point, if you are running stock spring rates on your GT/4, your car will have too much compliance in the suspension to take advantage of the 40 profile rubber. I would suggest no less than a 50 series and certianly do not run a 225 on the front (A 360 runs a 215, this preserves the nice turn in for example).


Let us know how you get on.

Regards,

Carl.

 

Hi Carl
My car is an ex track car, where it went round and round a track (castle Donnington) for some 20 years. Everything was out, tracking the lot! I have set the tracking as near as, but want to leave the final adjustment until the camber is sorted out. I have used some basic trig to work out what the stock mm values should be on the rims with the 18" wheels on - that equates to between 1.3mm and 4.2mm (as opposed to 1mm and 3.25mm).
You are right it does handle like a pig, although having both wheels pointing roughly in the same direction it is better than before!
Would .75 degrees (0deg 45') (which is what I have on the rhd side) be OK? Or should I go for more?
I take what you say about the tyres, but I trieds to find the closest match to the stock rolling circum (on the rear) and then chose a narrower tyres for the front. As they have plenty of life left in them I and kind of stuck with what i have got for now..

Regards
Nick

 

Hi Nick,

Well, it would have been faster round LH bends with that set up!

When you alter camber, you also alter toe, so there is no point not doing the whole lot at once. (This is the same for the front and the rear)

3/4 a degree negative is a fine place to start. Seriously, once it's sorted, it will be so much better than it is before I'm sure that's where you'll leave it! With the 40 aspect tyres, go for zero toe and stock caster (4 degrees) and the stock toe and camber settings on the rear. You have checked the rear as well right?

Just out of curiosity, what is your caster value on the front? I bet it is highly asymmetric and this is critical, especially for a car with a positive scrub radius.

There are some good wheel alignment explanations here:

http://www.familycar.com/Alignment.htm

Regards,

Carl.

 

Thanls Carl,
The rear is spot on, I have had it checked.
So if i go for .75 degree -ve camber, 4deg caster, and 0 toe in?

It is funny because when i bought the car 4- 5 years ago i let a mate drive it and he said it felt like it was fighting you all the time round bends. That was with the 15" split rims and P7s it had on. I just assumed it was normal!

Just another question - How do you set /check the caster, the manual just says use a suitable tool.

Cheers
Nick

 

Hi does anyone know whether there should be shims on the top of the stub axle where it meets the top suspension arm on a 78 GT4?
I know there are shims on the lower arm that is where the caster is adjusted. I have 6 on both arms, on the os they were towards the back and the caster was spot on 4degs, on the other side they were in the front and the caster was way off. I swapped them round and now the caster is spot, but I can't see anything about shims at the top only the bottom