msindi

Ok - got those height numbers...Center of wheel from ground to arch (I was surprised - gonna drop it more next week)..
Front - 25.625
Rear - 26.375
Heights are same as John D II (we use the same tech!!)
I think I will lower 0.25 inches front and rear...

KPV

Mansoor,
That means your rear height is essentially unchanged from the stock value.

Chris Y.

I believe Mansour's height might be a little higher due to his 295/30-19" rear tire. I found this to be the case when using the 295/30 and my car dropped about 20mm after switching to the 315/25-19's.

Mansour... Are your struts on the highest setting, or is there still some threading left for adjustment? Just wondering since I have the H&R (old single spring design) and there isn't enough front clearance to get up my driveway. So I ordered the RUF kit to be installed next week.

Thanks!

msindi

My rear was dropped about 22mm from stock...It is definitely lower than stock height but I realize I am the highest lowered car along with John D II!!
I have to go back for a re-alignmnet and so I will drop another 0.25 inch all aorund....at least until I get my Techart front...

Christer

As a fellow 911 owner, albeit the very much older sibling of all your cars - the above results worry me. On the 964, there is a particullar stance that all cars when corner-weighted and aligned should conform to. In the case of the 964, the car should slope at 1 degree angle from rear to front. This is the case no matter how high or low you set your car up at.

Obviously, I have no idea what the 996 TT angle-of-attack should be, but by the looks of it neither do your mechanics. The factory USA Turbo is pretty even front/rear when measuring fender to ground (obviously this does not necessarily mean that the car is pointing up at the front, the fenders are not a good measurement for this). Msindi's car seems to have what I would describe as a hotrod attitude, something out of a Pontiac GTO or Chevelle SS. Other cars are more even at whatever height they are at. Have all your cars been corner balanced? The AOA is quite important for any 911 I would have thought, if your car is too low at the front, the corner weights will be out and may cause handling issues.

As I said, I am no expert on 996TT suspension mods, but it seems to me very strange that the results can differ to this degree. Can someone explain?

msindi

Dont forget that the factory height data point uses 18" wheels whereas most users here have 19" wheels instead!!

Christer

msindi

Normally, if one uses bigger wheels the aspect ratio of the tyre (i.e. a lower profile tyre) is reduced leaving the overall diameter of the wheel/tyre combo the same. We can get back to this later. Did you corner-balance your car? What are the specs as far as AOA from Porsche? Maybe you did not use the Porsche specs, maybe the PSS9's came with instructions on how to do it and which figures to use? I'd really like to learn more from all of you if you have the time.

Bob M

Actually Mansour, not all of us have 19" wheels. The general consensus as I believe to be true is that from a performance stand point, 18" wheels are the better choice. I am considering going to the Kinesis 18R wheels, which have centers that give the wheel the "look" of the 19" wheels, but still have the performance the 18" wheels provide. At the moment, there are more choices of tires in this size too. Someday anyway ...

Christer, I originally had my ride height set even at all four corners. When I showed a picture of it to one of the well-respected members of this board, he made the same comment you did regarding the one-degree height difference between back and front, so I changed my ride height to where it is now. Maybe it's too high now, I don't know. I did have it aligned and corner balanced. I found that when either I myself or especially when carrying a passenger, the rear compresses slightly from the added weight, so the rear ends up being about .750 higher than the front. I like my current front height, so what I might do is lower the rear so that it is at the same relationship to the front as per GT2 specs.

And ... I wasn't able to do my shock setting experiments yesterday, so it will have to wait a bit. I'll post my impressions when I finally do it.

Bob

KPV

Christer,
I have done a lot of research into this prior to purchasing and prior to advising my alignment shop what I wanted from the ride height characteristics. The 911 Turbo comes in three models, the USA turbo, the ROW (Rest of World) turbo and the GT2. Each of these cars is lower than the one prior. Porsche has specific ride height criteria for each of the cars. The ride height is measured from the ground to specific points on the chassis in the front and in the rear.

The reference measurement in the front is:
"From the road surface to the lower edge of the hexagon-head bolt (a/f 18) of the tension-strut screww connection to the body"

The reference measurement in the rear is:
"From the wheel contact surface to the locating bore in the rear-axle side section (between toe and camber eccentricitics).

All of that said, the Porsche specs for ride height measurements for each of the three cars are:

USA:
F158(+/-10), R158(+/-10)

ROW:
F138(+/-10), R148(+/-10)

GT2:
F118(-10), R133(+10)

Note the tolerance difference with the GT2 in that they only allow a -10 in the front and a +10 in the rear.

All of these measurements are based on 18 inch wheels with spec tires. Now, when I embarked on this journey I did two things, I solicited the info from fellow Rennlisters for ride height previously posted AND made a comparison of the USA turbo ride height to the GT2. I wanted my car set up for GT2 specs. So, if you look at the difference between the two (USA turbo vs GT2) you end up with a delta of 40mm (1.5748 in) drop in front and 25mm (.9843 in) drop in the rear. Realizing the overall diameter of my 19 inch tire and wheel setup was very close to the factory 18 setup, I simply measured from the ground to the 12:00 position of the wheel well for my own piece of mind and had the shop use the chassis measurements previously mentioned for setting it up. The stock car measured 26.6875"F and 26.25"R. If you subtract the 1.5746F and the .9843R, you end up with 25.11F and 25.26R. This has an almost imperceptible nose down attitude and in agreement with the Porsche specs except for the very minor error of the difference in overall tire diameters between the 19 and 18 inch wheel setup.
My car was corner balanced.

Christer

Ken I realise that in this case, the adjustments you have made are not for performance so that's fine. Everyone likes the look of a lowered car (within reason) and HUGE wheels.

As there was such a difference in not only heights, but differences between the heights front and rear between all of you it just looked a little like someone had calculated the ride heights by 'wetting their finger and holding it up in the air'. This could be detrimental to performance and having read a post some weeks ago where someone was saying their TT was scary above 120mph etc. and most of the comments were to throw money at it, I just thought I would bring this up. A lot of the time, performance problems such as instability and crap tyre wear can be tracked back to 23" wheels, ultra low ride heights or just plain wrong setups. Judging by the different setups here, someone has it wrong from a performance point of view anyway. Cosmetic reasons are subjective.

KPV

Christer,
I am not sure I follow your reasoning. And I am ONLY referring to my specific ride height setup with regard to my following comments. I know that 19 inch wheels are almost universally thought to be a performance degradation over 18's. Although the side wall height is shorter on 19's, equating to stiffer response characteristics, the wheels themselves are generally heavier. It is this unsprung weight that is the cause for the degradation as far as I know.

Regarding ride heights, the only difference between my setup and a GT2 is the difference in the overall tire diameter between the factory 18's and the aftermarket 19's.

msindi

I had to go 19s because my brakes do not clear with 18s....

cobra06

Is this after corner balancing, or was that not done ?

Christer

yes, I understand what you are saying. What I meant to say was (and I actually wrote it but deleted it in my last post as I realised that it had no relevance to cosmetic changes but here we go) that the GT2 has a different weight distribution to your car. Therefore I would assume that if your car is at GT2 heights front and rear exactly, that your corner balance is out of spec. Presumably at the front where you have extra weight.

Anyway, this might not make any difference to you specifically but others here might want to check things over to make sure they are within the correct specs as the differences here are quite big.

End of subject for me - just an observation.

KPV

Christer,
I am still not sure I follow your reasoning. Again, pertaining to my specific setup, the car was dropped to GT2 specs and it was corner balanced. Physics are physics and you can only change the corner weights on a car a certain amount before the geometry (left-right list, nose up, rear up) becomes too pronounced. The concept of corner balancing is meant to approach a perfect 50/50 left right bias. The front-rear bias is a different matter. Due to the fact that the wheelbase is spaced farther apart than the track, and since the engine represents a large part of the overall weight of the car, modifying the front-rear bias is less efficient without appreciably modifying the ride height (jacked up or nose up).

Some go so far as to account for the weight of a driver in the driver's seat and a 1/2 tank of gas (good average) just to be as precise as possible. I went into a long dissertation about the contribution of these weights to the actual wheel weights using basic engineering statics (physics) in a previous post to show how much a driver and a tank of gas will impact the corner weights on a car.