Grumpy and Confused about Ride Height Settings
04-12-2005, 02:11 AM
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Grumpy and Confused about Ride Height Settings
Well... the car goes in for an alignment on Thursday, so I'm mussing about with ride height settings on my '99 C4 with PSS-9's. I want to get this dialed in so the shop does not have to deal with setting ride height, and no, I don't really care about corner balancing the car... just getting a good, even, height.
Right now the car measures 120mm in front and 130mm in back, as per the measurement points in the manual. With this setup the car has a very slight forward rake... when measured on the frame bottom (just in front of the back wheel and just behind the front) there is about a 5mm rake from front to back.
Now, X74 spec with 18" wheels is 118±10mm front and 133±10mm rear - so by going by those specs I'm right there, 2mm high in front and 3mm low in back, but I'm still pointing nose down.
I guess my main question is, does the factory mean to have the nose pointing at the ground??? It would seem if I want level ride I'd want to go up about 5mm in front, so then I'd be 125 in front and 130 in the rear - pushing the limits of the spec, but level for my car. I'm hoping this would not be too low for the PSS-9's - I've been reading all the who-ha about hitting the internal bump stops if one goes too low and I don't want to deal with this... but I still want the car at around that X-74 lowered height.
What do you guys think ???
Also... I'm going back and forth between X74 and GT3 alignment settings.. the main difference seems to be .5 deg neg camber in front (x73) vs. 1 deg neg (GT3) and again in the rear, except only about 10' more neg camber for the GT3 back there.
I do a handful of driver ed and auto x every year.. so an aggrssive alignment would be nice, but I don't want to wear out the inside of the tires too much either with day-to-day driving. Would the GT-3 alignment be going too far ?
trev
Right now the car measures 120mm in front and 130mm in back, as per the measurement points in the manual. With this setup the car has a very slight forward rake... when measured on the frame bottom (just in front of the back wheel and just behind the front) there is about a 5mm rake from front to back.
Now, X74 spec with 18" wheels is 118±10mm front and 133±10mm rear - so by going by those specs I'm right there, 2mm high in front and 3mm low in back, but I'm still pointing nose down.
I guess my main question is, does the factory mean to have the nose pointing at the ground??? It would seem if I want level ride I'd want to go up about 5mm in front, so then I'd be 125 in front and 130 in the rear - pushing the limits of the spec, but level for my car. I'm hoping this would not be too low for the PSS-9's - I've been reading all the who-ha about hitting the internal bump stops if one goes too low and I don't want to deal with this... but I still want the car at around that X-74 lowered height.
What do you guys think ???
Also... I'm going back and forth between X74 and GT3 alignment settings.. the main difference seems to be .5 deg neg camber in front (x73) vs. 1 deg neg (GT3) and again in the rear, except only about 10' more neg camber for the GT3 back there.
I do a handful of driver ed and auto x every year.. so an aggrssive alignment would be nice, but I don't want to wear out the inside of the tires too much either with day-to-day driving. Would the GT-3 alignment be going too far ?
trev
04-12-2005, 02:48 AM
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Since you have a C4, are you susceptible to the same issues the guys w/the PSS9s on the Turbos are having? Turns out that they are riding on the bump stops when running at X74 height (IIRC). they had to raise them near stock in order to restore decent handling.
Just thought I'd throw it out there. IIRC the C4 has more in common w/the Turbo suspension-wise, than the c2, especially up front. I believe the bulk of the threads are on 6speedonline in the Turbo section. Worth a search.
Just thought I'd throw it out there. IIRC the C4 has more in common w/the Turbo suspension-wise, than the c2, especially up front. I believe the bulk of the threads are on 6speedonline in the Turbo section. Worth a search.
04-12-2005, 03:27 AM
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Well.. I do know that the C2, C4, and turbo PSS9 sets are all different part numbers..... so I'm hoping that I'm not affected.
If I am... I'm a little upset that I paid 2 large for a set of coilovers that bottom out if adjusted lower than stock - if this is the case Bilstein will be hearing from me !
Anyway, I'm thinking of going up 4-5 mm in front, so the fronts will be at 124-5mm high and the rears 130mm high, with a GT-3 alignment.
trev
If I am... I'm a little upset that I paid 2 large for a set of coilovers that bottom out if adjusted lower than stock - if this is the case Bilstein will be hearing from me !
Anyway, I'm thinking of going up 4-5 mm in front, so the fronts will be at 124-5mm high and the rears 130mm high, with a GT-3 alignment.
trev
04-12-2005, 02:47 PM
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FWIW
I recently had PSS9's installed on my TT by Perfect Power in Libertyville, IL. Sol Snyderman took the time to explain to me the ins and out, ups and downs of lowering with PSS9's. The bottomline is to follow the Bilstein recommendation that comes with the kit, and check it against the Porsche spec. You'll find that the Bilstein spec gets you very close to the ROW settings.
More importantly, due to the 996 suspension geometry, as you lower the car you will gain negative camber. This phenomena is the same as that which occurs as the wheel hits a bump and is driven up into the chassis. The negative camber increases. Sol said that it's just about impossible to achieve the Porsche spec for camber at the ride heights listed in the shop manual.
While everyone talks about bump steer when going VERY low, a more important issue is that you have altered the front stearing geometry and are affecting the ackerman. This will lead to some squirrelly steering response.
My advice is to find a shop that has installed the system on several cars, and use their advice regarding ride height, corner weight, and alignment. They've been there, done that.
Cheers,
I recently had PSS9's installed on my TT by Perfect Power in Libertyville, IL. Sol Snyderman took the time to explain to me the ins and out, ups and downs of lowering with PSS9's. The bottomline is to follow the Bilstein recommendation that comes with the kit, and check it against the Porsche spec. You'll find that the Bilstein spec gets you very close to the ROW settings.
More importantly, due to the 996 suspension geometry, as you lower the car you will gain negative camber. This phenomena is the same as that which occurs as the wheel hits a bump and is driven up into the chassis. The negative camber increases. Sol said that it's just about impossible to achieve the Porsche spec for camber at the ride heights listed in the shop manual.
While everyone talks about bump steer when going VERY low, a more important issue is that you have altered the front stearing geometry and are affecting the ackerman. This will lead to some squirrelly steering response.
My advice is to find a shop that has installed the system on several cars, and use their advice regarding ride height, corner weight, and alignment. They've been there, done that.
Cheers,
