robbed666

Hi All,

I'm still sorting out my handling "issues". Any turbo (wide) body/conversions that had problems with "bumpsteer"? If so how did you cure/reduce it ?
I notice the front top mounts are fitted 180 degrees out on a turbo cars, would this help? Also on other (marques) cars that are lowered. The steering rack track rod ends are moved up (with additional hardware), so the steering arm are as horizontal as possible in a neutral state. Is there a kit/similar conversion for a 964 ? Sorry for all the questions, but the handling of my car really spoils the driving experience.

Wachuko

This is more of a friendly bump than anything else... I have a wide bodied coversion but it is a C4... so not much help I can give...

SonnyV

I believe there are kits for 964, or at least pre 964 911s. I had it put on my 911SC years ago. It was just 2 thick washers that you install under the steering rack to bring the geometry up to almost parallel to the ground.

Do a search for bump steer kit.

Good luck,

Sonny

Dr. Dynamics

Couple of things that you may whant to check:
- Verify the rim offset and tire width. If you change the stock's tire centerline location (tipically more outwards of the car with wifer tires), this may create more torque around the cars scrub radius (imaginary line crossing the upright pivot points to the tire centerline on the ground), therefore creating more or less feedback to the driver.

- How are the roads in the UK? At least in PR they are pretty bumpy! If I put tires with a pretty high cornering stiffness (hard sidewall), and also with good grip, they tend to kick my steering everytime I brake or susp droop occurs on top of a bad road since the tires grip will tend to follow the damaged road surface. This feels like bumpsteering, but what is happening is that the harder sidewalls will not allow the tire to absorb or disort (having less slip angle).

I used to have Yokohamas A520 for daily driving but I switched to to 712 khumos since they are softer, last longer, pretty good for often autoxxing, and most importantly...less $$$$.

Just some things to have in mind...let me know what changes did you do to the suspension, if any...hope it helps...

robbed666

Hi
My suspension is still set as a "normal" C2, should I change the top mount as per the drawing below for a "turbo" set up ? as I'm running 225 18's up front with spacers. As I understand it I now have a very large positive scrub radius, and the "turbo" setting applies less "positive" to allow for wider tyres and spacers.



SCRUB RADIUS:
Definition: The distance between the extended centerline of the steering axis and the centerline of the tire where the tread contacts the road. If the steering centerline is inboard of the tire centerline, the scrub radius is positive. If the steering centerline is outboard of the tire centerline, the scrub radius is negative. Rear-wheel drive cars and trucks generally have a positive scrub radius while FWD cars usually have zero or a negative scrub radius because they have a higher SAI angle. Using wheels with different offset than stock can alter the scrub radius.

Wachuko

That is how mine is set up (see photo). but again a C4 WB conversion. It is as your diagram shows (#2 setting).

robbed666

Hi Jaime,
I think yours is set to #1, the drawing is the driver's side (LHD), and your photograph is the passenger's side. If the top mount is offset towards the centre of the vehicle then it is #1.

Computamedic

Rob,

I'll say up front that I haven't looked into this in any detail so there's every chance what I say is wrong, but surely moving the top mount of the strut isn't going to do anything for the wheel/axle position since it's position is located by the bottom end, i.e. the wishbone.

I suspect the factory turbo bodied cars use a different stub axle/wishbone setup which requires the suspension strut to be mounted more outboard to accomodate the wider track. The rear suspension is similarly wider for the same reason.

You can immediately see the difference if you get a turbo bodied car next to a converted NB car and look at the position of the brake calipers. When I last put my TB conversion next to a factory TB my front calipers were a good 2 inches further inboard - even more at the back.

Changing the full suspension setup to the same as a factory TB car is likely to be horrendously expensive since there are so many parts to change- both front and back.

Regards


Dave

tafkai

lots of turbo owners are fitting n/a gear at the back , so you'll get a cheap used set ??
try the 965 bored

Wachuko

You are correct... my mistake. I failed to see the strut mount location

robbed666

I spent this morming, front wheels in the air, suspension loaded, and unloaded, to check if my problem is due to worn steering/suspension components. All appears to be OK. So the next thing to try is 4 wheel alignment. What I need is some settings to dial in. Can any one suggest a good road compliant set? I not interested in fast "track" settings, just "easy driving" settings for a lowered, after market wide body converted C2 running 18's (225 F & 265 R).

Computamedic

Rob,

Although my car is a C4 it also has the wide body conversion and 18" wheels. I had my car aligned by JZM last August and there's a link to the before and after alignment here

The print out shows the range of adjustment and the actual figure settled on by JZM.

Hope it helps.


Regards

Dave

robbed666

Hi Dave, Thanks for the link.
How does your car "feel" now?

Computamedic

Rob,

It's difficult to draw too much of a conclusion. Without doubt the car is MUCH more stable than it was before - but that doesn't say a lot since, as you can see from the "before" figures, the settings were way off.

I've never driven another 964 so don't have anything to compare it to. If I had to be critical I'd say the front end is not "direct" as, say, our BMW 330 but that's probably the inherrent understeer nature of the C4. Being 4WD the C4 handles better on power through a corner so it's directional ability depends on how much you are pushing on.

Overall I'd say a 1000% improvement so the settings I gave you must be a good starting point at least.

Regards


Dave