Alfa 33 - Bloody body roll and tyre sidewall wear

[AlfaCorseChris]

In short, my 33 is the occasional track day car with friends, where I cant use my racing Sprint.

It HAD, OMP springs, koni yellows front and red rears set to 3/4 stiffness, 17" wheels with straightened camber and tow out running on extra load michellin tyres 205/40/17.
Bodyroll was too much for the track so I changed some stuff.
In now has, Eibach springs, Koni yellows front AND rear, fronts set to full stiff rears set to 1click before full stiff, camber total 2 degrees negative and tow out total 1 degree. Also now running on powerflex bushes all round.

Handling-wise it's a lot better, body roll is much less but I still get some.
I still have a rear sway bar to install and thinking of replacing my front sway bar to a thicker one, maybe out of a sud.

But WHY ON EARTH does it keep understeering and WHY OH WHY does it keep running excessively the sidewalls of my tyres, even with a 3bar tyre pressure ? This doesnt make sense to me... :/


Any advice ?

[Veesix75]

What are the spring rates .

I set my konis to 1/4 turn from max stiffness, but equally have springs that would make your teeth fall out on a normal road.

I got rid of roll and understeer by using stiffer springs front and rear, the rear stiffer than the front. No anti rollbars fitted.

[PETROLHEAD]

In short, something i learnt a fair bit about just this weekend really, i thinks its not the lack of equipment, its the art of "Roll Centres" thats at play here.

all the lowering and stiffening in the world, alone, doesn't make a race car, and neither does budget.

Tom from BLS gave me a masterclass whilst we were at Silverstone racing this weekend, and that gave me plenty of extra work to consider for the 16v Sud, on setting things correctly via the panhard rod etc to reset the correct roll centre line through the length of the car.

springs, dampers, height adjusters, etc etc are all vital parts, but can also upset things notably until fully set up with the whole car in mind.

you're heading in the right direction Chris, you've got your tow and camber set up, but there's still more to do yet mate.


which part of the tyres is getting scrubbed off, the inside or outside edge?

[KevJTD]

3 BAR tyre pressure!!!!

bloody hell mate, that's near 45psi.

guessing from what i've been told in the past by tom/bryan/ted that that is probably double what you need to be running

but as shrew says, the car as a whole needs considering rather than one magical bolt on part.

or we'd all buy one

[PETROLHEAD]

I'll have two!

[AlfaCorseChris]

Its the outer sides of the tyres mate. Where it USED to say "Michellin SCRApilot"

Spring rates are stiff although I dont know what the stiffness actually is.
They are definately stiffer than my old OMP's and for sure stiffer than H&R's.
I've put my Eibach Pros now on, which I tested on the ground with my own weight and they are definitely stiffer.

Now, regarding the centre of roll, I still havent adjusted the panhard rod but would it really make that much difference ?
My left tyre wears the side wall more than the right one, but I was under the impression that this was due to tighter right cornering.

I've also removed lots of excess weight from the front (a/c compressor, hoses and condessing units as well as the damping material on the floor panels).

Body roll has improved A LOT from last time, but still, I get no grip from the front end on tight cornering.
Tried braking with my left and throttle with my right at the same time, which seemed to help a bit, got a faster exit, but cornering was still the same, so it wasnt a matter of too much momentum.

[PETROLHEAD]

the outside edge!

not what i was expecting to hear Chris, not with you just having your camber and set up.

Just to clarify, make sure we didn't lose anything in translation, the front camber adjustment has meant that the tops of the front wheels are now closer together than the bottom of the front wheels,

so apart from a couple of degrees, that your 33 looks along these lines

If thats the case, i can only guess that it is indeed the roll centres at play here.


I suspect what it happening is that the rear of the car is sufficiently higher enough to be tipping the body roll centre line down at an angle towards the fronts, and your stiff rear springs are forcing the fronts down at the opposite corner, sufficiently that its pushing the tyre over towards its outer edge.


thats one theory anyway, make any sense?

[AlfaCorseChris]

Makes sense but not the case :/ Car is flat ... oh hang on...

my rear konis arent set to full stiff ! they are a click off ! So thats actually allowing my rear end to raise on harsh braking !
But hang on... that cant be it ! Can it ? I mean... from the pictures some people posted of my car, the front end raises quite a bit anyway

[CJY]

When I did my track day in my 33 I was looking for 30 psi hot this translates to cold psi fronts 24 and rears 26. The car handled very well I'm running 185/60 r14. I hope that helps!

[PETROLHEAD]

Hi Chris, good to hear from you buddy


yep that would be a lot more along the lines of a track set up.

what was the rest of your 33 set up like? did you keep it awd?

[Veesix75]

CJY - what tyres were you using.

The Dunlop and toyo track day tyres are optimal at approx 36psi fully warmed up according to what I've always been advised.

I set my toyo r888 at 26 front and 28 rear cold, when I check them after coming off track the fronts are 34 to 36, the rears are 32 to 34 . Air and track temps obviously make a difference. On a really hot day I go down a lb on the cold figures.

Used the above settings on 33, sud and Clio on 15 inch wheels.

[Spacenut]

Hi Chris - ARBs are probably the key component here. From your description it seems that you have ARBs front and rear, with the front being the thicker/stiffer ot the two. From what I understand of chassis dynamics that would promote understeer in a FWD car - you make the end that you want to slide more stiffer. So to kill understeer on a FWD you make the REAR ARB stiffer than the front; this promotes more weight transfer onto the outside front wheel, which grips harder, while the stiffer back end tends to slide more.

I've heard of double rear ARBs being fitted with only a thin front ARB, and some cars running a rear ARB but no front. Also worth remembering that the Watts linkage/beam axle at the back acts like an ARB anyway.

Tyre pressure is the simplest form of chassis tuning. You increase the pressure at the end you want to slide more. So going 3 Bar at the front will tend to promote understeer, which is probably not what you want...

Something to think about at your next track day perhaps?

Lauren

[AlfaCorseChris]

Hi Lauren,

what you say makes perfect sense. I have tried and played a lot with my tyre pressures, going from as low as 1.2 bar gradually up to 2.5.
Yes there is difference is sliding, but I was under the impression that my fronts kept folding the sidewall and thats why they kept wearing off the writing on the sidewalls instead of the thread of the tyre.
Thats why I got pissed last time and said, ok, I'm going Full Monty on this ! 3 bar pressure to see if they keep folding in. The tyres themselves are supposed to be the Michellin EXTRA LOAD ones with additional strength on the side walls, and they are just 40 in profile - 205/40R17.

I agree that the panhard rod does act like a rear ARB but thats in the same way the DeDion of the 75 acts like the same.

The rear ARB hasnt been installed yet and wasnt on at the track day as I run out of time.
By what you are saying though you got me thinking....

I will install the rear, grabbing it from as further out as I can on the rear axle (side to side, and mounting it on the body of the car instead of the suspension arms.
Then I will keep my front one as it is and not change it to the Sud one

I would remove the front as well, but then I'm afraid bodyroll might increase dramatically and cause other issues

How about that ?

[Spacenut]

Sounds logical to me. Its a weird one and no mistake, but if an ARB at the back is the only thing you haven't tried, then its worth a go.

If you increase the roll stiffness at the rear and decrease at the front by the same amount, the overall body roll should remain about the same. But if you can persuade the back end to slide first, the front tyres should have a chance!

It still seems counter-intuitive that the high front roll stiffness should promote so much grip in the front tyres - they ought to be skittering off the road, not gripping!

Lauren

[PETROLHEAD]

It still seems counter-intuitive that the high front roll stiffness should promote so much grip in the front tyres - they ought to be skittering off the road, not gripping!

Lauren

Its a strange dark art eh!

Interested to hear some results Chris, hopefully positive of course, so get cracking!

[AlfaCorseChris]

Well the adjustable panhard rod is ready so will be throwing that on next week, as I got the car last night and discovered that I developed a fuel leak from the top of my fuel tank - probably the stupid aftermarket fuel hoses again.

My 16" wheels arrive tomorrow as well, so might be worth doing the rear sway bar along with those.

[PETROLHEAD]

16's?

What tyres Chris, 205 45 16's?

[AlfaCorseChris]

Well I've got 205/40 17's now, and I believe the correct size for 16's would be 205/50/16 but I dont know yet

[PETROLHEAD]

Depends what you mean by "correct" chris?


205 45 16 has an almost identical rolling radius at a 205 40 17 you currently run.

and 205 50 16 would be a difference in diameter of +15.5mm over your current tyres.



i would have thought the 45 profile would be better, and easier/cheaper to source Chris, would be here anyway i think, particularly in a sporty tyrec choice.

[BS25]

Chris - I'm sure you'll find a rear anti-roll bar helps as per the responses above. Do you have any smaller diameter wheels with suitable tyres? Other than cars on slicks with stiffer springs, most Suds/33's have run happily on track with 14" wheels, I always felt anything more than a 14" diameter and a 195 section was too big for a road spec car, even on track.

For reference, on my road going Sud back in the day we used to run -20mm ride height springs, 350lb front, 300lb rear springs, Konis all round and sticky Yoko's (185 wide and 60 section A001HFR's) on 14" diameter wheels. Geometry was reset to account for the lowered ride height and a little negative camber added at the front. Front roll bar was standard, no rear bar was fitted. This was essentially the BLS 'fast road' spec of the 80's/90's. No excessive roll on track days and really good fun - quick too for the day considering it was a standard 95bhp engine! I'll go as far as saying that the springs made a big difference but sticky tyres really made it come alive (set 32F, 28R cold). I did try it with a set of decent but not track biased road tyres and it was much less fun!

Hope your mods show you some positive progress.

[AlfaCorseChris]

Thanks for the tips Bryan, I'm in the process of finishing off these mods, and 16's is the smallest I can go at the moment with those front calipers.

Sticky tyres for sure, thinking semi slicks though so it can drive on the road as well.
The owner of the one and only track in Cyprus is a friend of mine, and told me not to go for the Yokohama's as they are too hard for that track.
He suggested the Falken semi slicks which is what he uses on his own cars as well.

I get what you mean about fun. I'll try to sort these out before I come to UK so I can have a good comparison and let you know of my findings