Alan Herod

Ride Height question came up in another forum and led to some discussion.

I get confused whenever I read the Bruce Anderson book, 'Porsche 911 Peformance Handbook'.

From the book - Measure ride height as the difference between center of axle/wheel and center of T-bar. Euro Front 108mm +/- 5mm. Rear 12mm +/- 5mm. Quote concerning rear from BA book 'We have found that for lowered cars the center line of the tosion bar can go as far as 1 1/2 inch below the center line of the axle and that 1 1/4 inch works very well.'

There is no clear indication in the book on what to do with the front once you have lowered the back to achieve the 1.25 T-bar lower then axle.

The good thing about using the relationship between centerline of T-bar and axle is that it is independent of tire diameter.

The book suggest a 1 degree slope toward the front which 'results in 0.5 inch higher ar front fender lip then the rear'. I have no idea if this relationship should be maintained when the back is lowered to BA's suggested 1.25 measurement. The solution might be as easy to solve as observing that the factory raised the front spindle 18mm for the RSR struts to avoid lowering the roll center excessively. I suspect when BA lowers to the 48+mm lower then Euro, that he is using raised spindles in front. Is there a definitive answer?

Peter Zimmermann

Alan: Ride height is much easier than that explanation! I assume we're talking about your SC, so put the car on a level floor. Measure through the center of each wheel from the floor to the closest painted part of the front fender or rear quarter panel. If you get about 24.75 - 25" rear, and about 25.25 - 25.5" front, rejoice. Your car is at Euro ride height. Be sure that your tire pressures are set to 29F/34R cold before you measure!
Pete

Alan Herod

Pete, Thank you -- you are quite right about air pressure as well, but unfortunately it has been a long time since I have used the stock size tires. I have pondered this for some time and prefer not to measure that way since I generally use 15 inch wheels for the track, primarily for the positive change in gearing. Tire dimensions or inflation variances do not affect the relationship when using the T-bar to axle centerline difference. Based on the specs given in the book you can lower the rear 16mm + 31.25mm from Euro spec with good results with no mention of what you do with the front.

I replied to this thread http://www.dorkiphus.com/porsche/viewtopic.php?t=2720

CrossT

I've tried to lower my car [86 cpe] and the lowest it will go in the rear is about 25.5 in. So, I set the fronts to 26 in. I have been told that to go lower in the rear, the t-bars need to be 're-indexed' or set to a different position on the end spline. Is it a major PITA to 're-index' the t-bars in the rear to accomodate going down to Euro?

todd
86 coupe

Alan Herod

Todd - there is a fine procedure for reindexing that addresses taking measurements to arrive at your desired settings. The procedure is based on using the same T-bars. Since I changed T-bars, the procedure did not work that well and it ended up being a trial and error process. I did it in a parking lot, then had a race shop do four wheel alignment. It is really not that difficult, just tedious. Wayne's book has good directions.

CrossT

Thank you Alan. I have the 101 Projects book and I didn't think of looking there.

todd
86 Coupe

JBO

This amy be a dumb question- when you pull out the TB to reindex, would you turn it to the right to raise or lower the height?

Peter Zimmermann

JBO: Before removing the spring plate (after it's completely disconnected and you have removed the rear, lower bolt from the bushing cover) you measure its drop angle with a gauge (magnetic base protractor). Then remove the spring plate, and turn the torsion bar as needed, using inner and outer splines, to achieve the measurement that you want. There really is no guess work involved. Then, while corner-balancing the car (if you have two-piece spring plates) you can loosen the two large bolts on them and make fine adjustments only.
Pete

Edward

JBO,

Remember, too, that the number of inner splines is fewer than the number of outer splines (40 and 44, IIRC) which, if you move either one or both, will get your spring plates in the ballpark for your desired setting. And definitely get the angle finder ...without it you will be forever guessing. I borrowed a friend's and with it, it still took a couple of tries to get it right where I wanted ...couldn't imagine how many more tries if I didn't have it. Note the angle before you loosen anything to get a base reference, then adjust accordingly. I think 1degree of springplate change is 7-9mm of height, or something to that effect.

Edward