bunjeeman

That would be a great mod before I advance onto an adjustable rear beam. I've run Yokohama ADVAN AD07, A048 Dunlop D02G all new tires. They all have their subtle differences but the wondering around still exists.......

Thanks!

Mike Rainbird

iTrader: (3)

What pressure are you running them at?

bunjeeman

30-32 PSI when hot........

G1EN

The pressure of a tyre would not cause this issue, nor type of tyre to be fair.
I am aiming to get my new Steering rack fitted to see if that makes things any better or anything is ntoice upon taking bits and bobs off.

Mike Rainbird

iTrader: (3)

Er, yes it does .

Some (as an example the Yokohama AVS's) are prone to tramlining when the tread gets near the wear indicators .

Mike Rainbird

iTrader: (3)

What sizes are you using?

What wheels, size and offset?

bunjeeman

Have to agree with you Mike, the pressures do affect the handling quite a lot. But the problems I'm experiencing is much more severe.

I'm currently using Compomotive MO's 17x8 ET33 with 10mm spacers, 235/45/17.

I've used 225/45/17 also and 18x8.5 wheels with 225/40/18 tires.

Although each configuration have their differences, the wandering is the same. Kind of like constant tramlining front and rear.

Mike Rainbird

iTrader: (3)

Have you had the geomtry checked RECENTLY? As the problem with the standard car is that the geometry has to be adjusted with the front ARB bush retaining bolts undone fractionally, to prevent these from binding when you carry out the adjustments. Otherwise as soon as you drive a few miles down the road, the bushes settle and the geometry goes to rat shit.

bunjeeman

The geometry was set with the bolts undone, as I also had the corner weights checked and adjusted at the same time.

Mike Rainbird

iTrader: (3)

This is a tricky one! Have you checked the tyre pressures recently? What are they cold?

Did you have to adjust the ride height drastically at all to move the weight around the car?

Measure the height at each corner and report back, ground to centre of wheel arch.

What angle are the drive shafts sitting at static ride height - could you be experiencing excessive bump steer (which will increase the lower the car is?).

bunjeeman

Thanks for your efforts Mike, this is indeed a tricky one. I've run a tuning business here in Hong Kong and also manage a race team running Porsche Cup cars...... We do all the set ups for these cars with great results, yet my own car baffles me!

I've never run the car low as I know the inherent geometry issues with these cars unlike my Porsche Cup cars which are fully adjustable. As I used the Grp. N Tarmac Spec as a reference for the set up in the past, I believe the ride heights were close to the followng:

Front:

160mm measured from center line from the T.C.A joint to ground

Rear:
170mm from steady plate mounting plate to ground

The car was surprisingly balanced and cross weight percentages very pretty close, we only had to make 1-2 mm changes side to side. Close enough for road use. We even did it as per our race cars with half tank fuel, sand bagged to replicate my Cheeseburger loving frame and even took off the ARB mounts (for real side to side weights)

As I said earlier, the only thing that looked to be out of place was the rear toe out. Let me know when you get the shims in so I can get some off you. By the way if you need some made over here in China then let me know also as we have great fabricators we use for our race team.

The tires can be as low as 23-25 psi when cold, because we have pretty high ambient temperature and very high road surface temps during the day.

As the drive shafts are not really that far off horizontal as the car is not riding very low. But I never actually measured.

Sorry that I can't get you the exact numbers right now as I am traveling in China for work and not in Hong Kong where the car is.

The car is actually schedule to be in for a major overhaul, fresh engine, new bushes etc. So will inspect all the major components for wear and tear, will also be rebuilding the steering rack with new tie rods, and also the steering column. Hope I will find something then........

There just doesn't seem to be much I can check for anymore when the car is static, it seems to be the geometry is going wrong it's dynamic. We measured /set up put the car down, rolled it and jumped around on it to make sure the suspension was settled and pit it back on our corner weights and nothing seemed to have changed....... I think you can understand my frustration!!! We can set up a championship willing Porsche but can't get my own Cossie to driver normally!

G1EN

Ok yes, if you do let your tyres get to the wear indicator it can, but would wonder why they are risking pretty much running on slicks as in this country you never know when rain is coming. lol

But im pretty sure this issue is the same as what i have...

Somtime when i break too, the heavilly steers to the left.

I have standard rims with brand new tyres on at 32 psi, though needs checking when i drive it again and only lowered 25mm on Koni;s.

Have put adjustable TCA's on very recently, but that hasnt cured anything.

Mike Rainbird

iTrader: (3)

Check the CV joint on the steering column for play and report back (the one located near the exhaust - this has a propensity to be damaged from the heat of the exhaust and might be an issue)?

The only other thing I can suggest is to temporarily get the car to toe IN on the rear with some washers on the back two bolts of the hub and see what effect that has on the handling?

Is the handling worse when the tyre pressures are cold compared to when they warm up? Have you tried running them with a few more psi in to see what effect this has?

Have you checked the engine mount under the exhaust manifold? Does the car pull in any particular direction under braking, or does it tug from left to right, tramlining even worse under braking?

What make poly bushes are you using - it sounds like you might have some that are simply not up to the job?

bunjeeman

Hi Mike, just checked the CV joint and there doesn't seem to be any play. But I'm having the column taken out and reconditioned with new joint and all the bushes along the column.

Also rebuilding the PAS rack and having new tie rods put in.

As with any tire, when they are cold and not up to temp they handle differently, a little worse I think. I've had them up to 34PSI as i know some molded slick types don't like low pressures due to their tyre wall construction. But the core problem is still there.......

I have Vibra-Techinic engine and gearbox mounts, I had an orginal gearbox mount failure a couple of years ago which made the car handle weird too, the momentum of the engine wanted to go straight when trying to turn, but like the feeling I'm having now.

The tramlining doesn't get better or worse when braking hard and I have Powerflex bushes up front.

Mike Rainbird

iTrader: (3)

Have you got a friend who you can swap wheels with, just to eliminate this? As I hate spacers, unless they are the proper hub-centric ones?

I also think that 235/45 is an odd size maybe not suited to the car? Have you tried a 235/40?

bunjeeman

Yep, tried many wheels and tire combinations..... no Joy!

I've run 225/45/17, 235/45/17, 235/40/18...... with and without spacers

Mike Rainbird

iTrader: (3)

Only further thing I can suggest is to put two small spacers on the back two bolts of the rear hub to get the rear to toe-in, to see if it is the back end that is wandering (the tail wagging the dog)?

bunjeeman

Thanks Mike for all your suggestions, I will try this mod too..... when will you get some more of your shims in?

Cheers!

Mike Rainbird

iTrader: (3)

They're on back order from the States, so unfortunately I can't give an exact date....

bunjeeman

Ok Mike, please let me know and keep a set for me..... you can email me at benau@yahoo.com when you have them in......

Cheers!

G1EN

Just a stab in the dark..

Was thinking this last night.

It wouldnt be the Centre Diff (Transfer Box) to cause these issue would, as i know mine is fook and i know you get RWD and FWD and 4WD, but if the Transfer is fook like 80:20, 80:30 90:10 instead of 100% RWD, 100% 4WD etc, would that upset this upset the handling??

bunjeeman

How could I test the transfer box?

Disabled Account

No it wont be the transfer box........but it could be a worn front diff, or the oil within the front diff is too thin or even wrong grade (too thin).

bunjeeman

No it wont be the transfer box........but it could be a worn front diff, or the oil within the front diff is too thin or even wrong grade (too thin).[/quote]

Thanks for the advice, I'll make sure the correct oil is put in when the new engine and transfer box is put in........

G1EN

Only way of know if the Transfer Box is Knackered is putting the car on a set of rollers, isnt possible to see on the road as all wheels would be truning at the same time.
But as L8 ECU said, that it couldnt be that...

bunjeeman

Thanks for the info.......