964 instability at speed?
02-04-2002, 04:35 PM
#31
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Nah.. you're absolutely right.. the Speedlines really make the car. 
I also think I've finally decided that the polished centre Speedlines are over the top - just too shiny (particularly with Speed Yellow), so there's no point in buying a new set of wheels. I'll just get the damaged rear refurbished and save the money for other things, like tyres, suspension work, rebalancing, bump stops etc etc
I also think I've finally decided that the polished centre Speedlines are over the top - just too shiny (particularly with Speed Yellow), so there's no point in buying a new set of wheels. I'll just get the damaged rear refurbished and save the money for other things, like tyres, suspension work, rebalancing, bump stops etc etc
02-04-2002, 09:13 PM
#32
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Greg,
I aso felt my 89 C4 felt unstable,especially at high speed...I had a four wheel alignment(to Euro specks) and corner balance done and it has fixed the problem...
Your car looks great....
George
89 C4
71 914
Member#001017-2219
I aso felt my 89 C4 felt unstable,especially at high speed...I had a four wheel alignment(to Euro specks) and corner balance done and it has fixed the problem...
Your car looks great....
George
89 C4
71 914
Member#001017-2219
02-05-2002, 05:49 AM
#33
I had the same problem as George above. I had the standard 16" design 90's on the car, and anything above 110-120mph got a little 'skiddish'. This weekend I fitted 17" Boxter S wheels, and got the 4 wheel alignment done. They found that at the front the camber was all wrong - I don't know whether it was negative or whatever but the inside of the tyres were being worn down badly. After this, I took it up to an indicated 140mph, and as George says would feel happy to take my hands off the wheel.
It must be something to do with the suspension/alignment - I can't believe that a Turbo would handle like this when my 'bog standard' C2 doesn't!!
It must be something to do with the suspension/alignment - I can't believe that a Turbo would handle like this when my 'bog standard' C2 doesn't!!
02-05-2002, 03:09 PM
#34
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Well.
I took the car out again today to give it another chance, and although initially it felt OK, on one veeery gentle high-speed left-hander which I took at 100mph (I'm sure an experienced driver with a good car could take it at 150) I suddenly thought "I'm not going to make it - the car's going to leave the road". So I'm certain there's something wrong. I cannot believe the car should handle like that.
So I took it round to the dealer and asked them to drive it and give me their opinion. Although they didn't think anything serious was wrong, the guy who drove it did admit that there was a little something funny about the way the car set itself up for bends. He suggested a full wheel alignment be done.
Anyone still reading this topic will remember me insisting they had already done one, since I asked for it to be done and was promised it would be. Well it turns out - they never did do the wheel alignment before selling me the car!!
Let's call it an oversight or a misunderstanding or something neutral. Anyway the upshot of it is that the car is now booked in for the wheel alignment it should have had before I bought it, and we'll see what difference it makes. The only other thing we noticed was that the left front shock absorber feels softer than the right front. I'm not sure how much this would contribute but I'm guessing it's not ideal...
Anyway at least someone's doing something about it...
I took the car out again today to give it another chance, and although initially it felt OK, on one veeery gentle high-speed left-hander which I took at 100mph (I'm sure an experienced driver with a good car could take it at 150) I suddenly thought "I'm not going to make it - the car's going to leave the road". So I'm certain there's something wrong. I cannot believe the car should handle like that.
So I took it round to the dealer and asked them to drive it and give me their opinion. Although they didn't think anything serious was wrong, the guy who drove it did admit that there was a little something funny about the way the car set itself up for bends. He suggested a full wheel alignment be done.
Anyone still reading this topic will remember me insisting they had already done one, since I asked for it to be done and was promised it would be. Well it turns out - they never did do the wheel alignment before selling me the car!!
Let's call it an oversight or a misunderstanding or something neutral. Anyway the upshot of it is that the car is now booked in for the wheel alignment it should have had before I bought it, and we'll see what difference it makes. The only other thing we noticed was that the left front shock absorber feels softer than the right front. I'm not sure how much this would contribute but I'm guessing it's not ideal...
Anyway at least someone's doing something about it...
02-05-2002, 07:17 PM
#35
Drifting
Interesting discussion. I came from a 1989 944 Turbo S that was rock solid at speeds up to 285km/h. When I jumped into the 1991 911 Turbo, I backed out of the throttle at 170km/h because it felt scary.
Subsequently to that, I installed a RUF suspension, 18" wheels and tires and aligned/cornerweighted the car. The suspension made the biggest difference. From my vantage point, it felt like one of the front factory shock absorbers had a leaking seal allowing excessive movement. Also, the nose up attitude likely contributed to the instability.
In addition to that, the alignment plays a huge part in driver confidence. I have the C2 Turbo setup to be very agile as I auto-x and intend on tracking the car. I use a very aggressive street alignment:
Front
Camber: -1d30m
Caster: 3d15m
Toe: 0d (actual was 8m total toe-in)
Rear:
Camber: -1d30m
Toe: 0d (actual was 5m total toe-in)
Even with these settings, the car now drives wonderful and is stable. The front goes a bit light in really high speed driving, but I think that is fairly normal for these cars. To counter that, I'm installing a front splitter from FVD and we'll see if that makes it even more stable.
Adjust your ride height for a slight nose down attitude and then corner weight it. Align it, then you're done.
Farzaan
Subsequently to that, I installed a RUF suspension, 18" wheels and tires and aligned/cornerweighted the car. The suspension made the biggest difference. From my vantage point, it felt like one of the front factory shock absorbers had a leaking seal allowing excessive movement. Also, the nose up attitude likely contributed to the instability.
In addition to that, the alignment plays a huge part in driver confidence. I have the C2 Turbo setup to be very agile as I auto-x and intend on tracking the car. I use a very aggressive street alignment:
Front
Camber: -1d30m
Caster: 3d15m
Toe: 0d (actual was 8m total toe-in)
Rear:
Camber: -1d30m
Toe: 0d (actual was 5m total toe-in)
Even with these settings, the car now drives wonderful and is stable. The front goes a bit light in really high speed driving, but I think that is fairly normal for these cars. To counter that, I'm installing a front splitter from FVD and we'll see if that makes it even more stable.
Adjust your ride height for a slight nose down attitude and then corner weight it. Align it, then you're done.
Farzaan
02-06-2002, 12:01 AM
#37
Instructor
Horst -
Sorry for just getting back to you. I have Yokohama AVS tires on my baby on OZ 17" Racing wheels. I really like the combo. They are a little soft - but great on grip and fairly cheap from the Tire Rack.
- Jeremy
Sorry for just getting back to you. I have Yokohama AVS tires on my baby on OZ 17" Racing wheels. I really like the combo. They are a little soft - but great on grip and fairly cheap from the Tire Rack.
- Jeremy
02-06-2002, 12:03 AM
#38
Instructor
Horst -
Sorry for just getting back to you. I have Yokohama AVS tires on my baby on OZ 17" Racing wheels. I really like the combo. They are a little soft - but great on grip and fairly cheap from the Tire Rack.
- Jeremy
Sorry for just getting back to you. I have Yokohama AVS tires on my baby on OZ 17" Racing wheels. I really like the combo. They are a little soft - but great on grip and fairly cheap from the Tire Rack.
- Jeremy
02-06-2002, 06:57 AM
#40
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Arthur
Not a stupid question, corner weights are critical to how a car handles. The 968 club sport has always regarded as an excellent handling car because of it's 50/50 weight distribution.
let me try and explain using the example below
The front of the car weighs 1250 lbs divide 1250 lbs by 2 = 625 Lb’s each side.
The rear weighs 750 lbs which equals 375 lbs each side.
These are called the corner weights.
You subtract the unsprung weights from the corner weights.
Front 625 lbs minus 50 lbs equals 575 lbs.
Rear 375 lbs minus 75 lbs equals 300 lbs.
We know all four springs need to be compressed by 2" to achieve the ride height.
So the front springs are 575 divided by 2 (equal to the 2" compression) which equals 287.5 lbs/inch.
and the rear 300 divided by 2 (equal to the 2" compression which equals 150 lbs/inch.
Not a stupid question, corner weights are critical to how a car handles. The 968 club sport has always regarded as an excellent handling car because of it's 50/50 weight distribution.
let me try and explain using the example below
The front of the car weighs 1250 lbs divide 1250 lbs by 2 = 625 Lb’s each side.
The rear weighs 750 lbs which equals 375 lbs each side.
These are called the corner weights.
You subtract the unsprung weights from the corner weights.
Front 625 lbs minus 50 lbs equals 575 lbs.
Rear 375 lbs minus 75 lbs equals 300 lbs.
We know all four springs need to be compressed by 2" to achieve the ride height.
So the front springs are 575 divided by 2 (equal to the 2" compression) which equals 287.5 lbs/inch.
and the rear 300 divided by 2 (equal to the 2" compression which equals 150 lbs/inch.
02-06-2002, 07:16 AM
#41
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Arthur
I've found a great web page which really explains it all in plain English (unlike my explanation above)
It also reveals why cars that have collapsed front suspension cones understeer so badly
<a href="http://www.grmotorsports.com/cornerweight.html" target="_blank">Corner Weights</a>
I've found a great web page which really explains it all in plain English (unlike my explanation above)
It also reveals why cars that have collapsed front suspension cones understeer so badly
<a href="http://www.grmotorsports.com/cornerweight.html" target="_blank">Corner Weights</a>
02-06-2002, 07:42 AM
#42
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Thanks for the explanation, George. So, corner weights are basically prestress levels in the springs, right? I would imagine the car needs a certain prestress in the springs, and Porsche has numbers for these to be optimal - possibly depending on all kinds of parameters such as springtype, unsprung mass (i.e. wheel-tire combo), etc.
What are these numbers and how can it be checked for correctness, and possibly adjusted. I have to bring my car in for alignment, so they may have a look at the corner weights at the same time.
What are these numbers and how can it be checked for correctness, and possibly adjusted. I have to bring my car in for alignment, so they may have a look at the corner weights at the same time.
02-06-2002, 07:50 PM
#43
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George, I read the article concerning cornerweights and it seems to me that is't not necessarily something needed for a car that's only used on the street under differing circumstances. It's interesting though - I could have thought of this myself being an engineer, but it never came to mind really.
02-06-2002, 09:09 PM
#44
My NA cab has 18x10's and 18x8's...Kinesis 3.6 Turbo wheels...gorgeous replicas....about $2700 USD for the set from Wheel Enhancement. At 135mph the car is rock solid and smooth as glass. Hi-speed balanced on the car.
Haven't read all the posts but it's possible you have a bad tire...belt separation or the like. Also, maybe a bad wheel or a missing/damaged front spoiler. Most likely it is alignment/wheel/tire related IMO.
Haven't read all the posts but it's possible you have a bad tire...belt separation or the like. Also, maybe a bad wheel or a missing/damaged front spoiler. Most likely it is alignment/wheel/tire related IMO.