NoVector

At the 3rd Coast Get Together, Herman spent a lot of time discussing ride height--and that it was more about balancing the car's weight. Alignment aside, if a person wants to lower the car, wouldn't the goal be to have the load balance be close to stock? After putsing around with my car up on all 4 corner this week, I see where he's coming from--if the height is too high in the back, it would increase load on the front and vice versa. Be interesting to see what the scales would say...

Personally, I'm not going to 2nd guess the 50 lb brains at Porsche--my GTS is going back to factory height.

/ Bruce

dr bob

Again. you reinforce my point. You are exactly WRONG about lowering helping in all areas. I can give you the whole geometry lesson if you'd like. And I have spent a few days in front of a classroom.

Put something sacrificial on the bottom of the front if you want it to look lower, maybe some of that plastic garden edging or something. Use cheap, easy-to-replace fasteners. Maybe hide a couple casters in the front splitter, but make little skid ramps in front of them for driveways.



Meanwhile, for those following along at home, do a little Renn research and see all the testimonials from 928 owners who have ripped stuff off the bottom of the engine, torn spoilers off on casual road hazards, and those discovered that the car drives a lot better when the sag is finally adjusted out. The car is designed to drive with the lower control arms and the tie rods level at speed. Even Mark's calibrated eyeball can see that this is not the case with the car at 160mm, sitting still.


The farther the height is from design, the greater the toe change will be with any suspension movement. That little depression in the road from truck abuse will cause the toe to change, trying to steer the car. As the front and rear wheels go into and out of these depressions separated by the length of the car, it will steer one way then the other, forcing the driver to take continuous corrective action. Better tires make the situation worse. Good shocks make the situation worse. Wider wheel with insufficient negative offset make the situation worse. Softer rear springs make it worse. Good news is that getting the geometry correct eliminates all of those "make it worse" factors.


Mark, if you HAVE to lower your car, use offset wheel bearings and caliper bolts.

mark kibort

no, ride height does very little for balance (talking front to rear only). corner balancing is a way for racers to get balance on 4 corners so that handling is the same, for turns in either direction, and to increase handling when at the limit. I align my car with cross weights near perfect. It is almost impossible to tell the difference when they are WAY off on the street. the nice thing about our cars is that when the ride hight is visually right, the balance and cross weights are not that bad.

mark kibort

Wally,

Just because you are in front of a classroom, doesnt mean you are projecting the correct message. Sure, the geometry of the 928 in front is such that there is a big arc if you plot the toe change (and camber) with suspension movement. the amount of movement, with sport shocks and springs is almost nothing on street driving. even in spirited driving, the weigth transfer is enough to negate most of the "bad effects of a toe change". Now, on a stock car, the toe difference wheel to wheel is HUGE. one tire could be at full droop and the other fully compressed, realizing the max limit of the problem!

Ive race the car for many years now, in most all configurations and have experienced the differences with right hight changes, good and bad. The only bad is that if you HAVE a stock suspension, you can get more movement with pot holes, and big weight transfer. This is a reason to have a higher ride hight. I too have a friend that experienced the block hit due to much to low of a car setting. In LA, he hit a pot hole and killed his alternator. BUT, his ride hight was near 140, maybe lower. would 1" have helped ? hard to say.

The benifts of lowering the car are known. better handling all the way around. I run 110mm. trust me, you are not going to catch me with the same car set at 170mm, for sure. Anderson, Fan, Doty, Kao, etc etc. I drove for 2 hours in an enduro with a car set up like scots, and scots as well, with ride hights of near 160mm. they drove like crap. when lowered to 135ish, there was a huge benifit in handling. Dont take my word for it, go to a skid pad, track, autocross, etc and see the diffference.

Now, with stock suspension components, expecially tired ones, and at stock weights, the problem with the geometry settings are going to be worse, not better with higher ride hight. If you did your homework, you would see that under extreme suspension travel, due to extreme weight transfer, the horizontal tie rod setting (stock ride hight) will induce more weight transfer under load and give more disparate movemet side to side. this over shadows the geometry curve you are refering too.

Its complicated and involved, but if you dig into the trade offs, its better to lower the car from stock. In europe, Porsche did this with all models and if you at least, lower the car by 1" from stock, you will be happy with the looks and it wont be in danger of having handling issues or hitting anything.

Lastly, the design of the 928, especially the S models , causes much risk when parking, due to its long and low nose and components. so, its not a jeep or caddy. its a sports car. if you cant be careful with it, you deserve to have the nose ripped off. (or buy a Vet with the 2" rubber strip for the front air dam.

In summary, the 928 has a geometry movment curve for good reason It trys to keep the tire flat under hard cornering, and undulations of the road. For anyone trying to get a little more performance out of their cars, lowering the car is the first, and best thing you can do. Coupled with a slightly stiffer suspension, you will notice less wheel movement and better tire wear, if aligned properly. Bigger tires and wheel help with handling, regardless of offsets, however it can basically change settings by effectively changing the levers that the tires operate from. (e.g. wide tires and wheels make the suspension softer, but lower the CG which will lower weight transfer, so there are trade offs). So, the real considerations should ONLY be the type of driving and clearance for the obsticals you might be encountering. If you live in NY city, yes, a little higher would better. in San Jose Ca, not so much.
DE plus street duty and you are careful, go lower!

Anytime you want to have a ride hight clinic at the track, let me know. you can take your 4x4 settings vs mine and experience the trade offs.

Here is a video of my car doing some very fast 50mph S turns to see suspension travel. notice, there is none! (or none really to speak of)
this is why what I am advoacting works. Its the reality.

PS: by the way, at 135mm in the rear, the rear CV axles are at horizontal. at 170mm, they are angled.

HERE ARE THE VIDEOS OF THE SUSPENSION IN ACTION:
on the track
http://www.youtube.com/watch?v=tZy4HEerwmo
on the street
http://www.youtube.com/watch?v=V2nmzFeWB0c
in the mountains
http://www.youtube.com/watch?v=shNwdGBorlk


Mk

WallyP

I'm Wally, not dr. bob, but like dr. bob, I have spent time in front of a classroom.

I disagree. Street driving is better with the car at close to spec height.

I hope that newbies reading this will take time to investigate and decide for themselves...

mark kibort

Sorry, i was responding to both of you .

Hey, I too wish the newbies to do some research and make their own decisions. BUT, what I have is both street and race experience here with tire wear and handling, and I can say that the lowered 928 doesnt wear the tires any faster at all, and will handle quite a bit better This is from somone that had had a BAD alignement back in the late 80s and found out about the lifting the car thing! once I found out about that, my 928 world was good again.

after watching the video, it is very clear to see that ther is not much movement in a sport suspension set up. One thing to think about, is the drooping side has extreme toe changes as well when the ride hight is to spec. This is because it is starting at near parallel . If you think about it, when the tie rods are angled, the compressed wheel will have a greater toe and camber change. (toe will create a desensitization of the steering input in theory, while camber will be greater, actually BETTER for a car that is being race or with soft springs, because it will need more camber to prevent wear.) The drooping side will do the opposite. in extreme handling, the lifting tire will be scrubbing the inside edge, due to toe-in, while he compressed side toes out. calculate the movement based on a certain amount of spring compression. Do this starting at parallel tie rods (stock height) and then do it again at lower than stock height (say 110 to 135mm "very low"). You will see that it isnt as bad as the fear mongers are alerting us to see. Again, we are splitting hairs here, as usual, there are many trade offs.

I was on a drive today, as I am on all weekend days, doing some spirited running around town. It is solid as a rock. no "tramlining", no darting, no nothing, even when I hit a sigle wheel depression, or a dip in roads. I also run DOT race rubber on the street and have for 15 years. Ive never seen any unusual tire wear. they always go bald, pretty even across the tire.

Now, the reason for most handling issues is alignment, set up or worn parts

I think the larger tires also makes the car drive much better, but we had the lemons racer which is set around 115mm in front and drives very stable, even on its small 245 tires.

I do worry about a newbie taking out his air dam, but I dont think that 1/2 to 1" lower than stock will make a hill a beans difference in ANYTHING that you could measure, besides the car driving better! . Ill get up in front of a classroom to discuss and white board why this is true, anytime!

Fogey1

OK, I'm confused. The factory Technical Specifications books say:
Front 190 -20mm
Rear 173 +10mm

So, Mark, are you telling us the factory says to set a ride height that causes the car "to not handle as it was designed?" And that the factory didn't follow it's own tech specs for cars it sold it Europe, but lowered them?

Conceded that YMMV, and race cars might be different.

Has anybody ever seen the ride height specs for a Club Sport or a factory campaigned or supported 928?

mark kibort

Dear confused, (kidding, it a valid question)

the technical spec does say 190mm, minus 10mm is 180mm and plus for the rear is 180mm. thats where I got that ball park number from. Have you seen a car at 190mm and 183mm? It looks like a 4x4

Look the factory does a lot of things that are not optimal. The have these specs not for best performane, but for best all around safety, and performace as trade offs, because they can be liable for most ANYTHING you can do with a car. Think about it, if you owned a rent a car company, would you set the cars up for handling for missing the curbs at Safeway for ANY type or age driver?
Ever go 150mph on the autobaun in a stock car with stock OLD springs and shocks? I was going 120mph one night on the bayarea local mountain 4lane hyway with my car set at 110mm and hit a major depression, and almost took out my oil pan! (at 150mm,that wouldnt have been a problem) but at 150 to 180mm it would have been, with stock stuff on the car.

Anyway, the point here, you have to make the decision based on your driving style, roads you frequent and your ability or capability to drive acording to all the mentioned limitations. BUT, if you do, the car will handle better, be safer, and look better at much lower than factory ride specs. I dont know about the 928, but in europe the 911s are 1" lower than their US counterparts. why would they do that. less gravitatioal pull of the moon on that side of the earth??
They do it, because the germans are much more descriminating about performance and have fasterer roads to drive the cars on legaly.

To answer you last question, if the geometry didnt work as I say, why would the factory CAMPANGED, SUPPORTED AND SET UP 928 race car, set at 115mm and 130mm rear for ride height? (yes, it was near this setting) Now, Bob and Walt will go on saying thats a race car and they dont care about tire wear, but thats not it. Ive already proved that on the street for 100s of thousands of miles, i have seen NO adverse handling or wear issues vs a stock set up, nor do extreme offset of the wheels hurt anything and Ive actively changed that factor at the track by near 1" with no difference.

Bob and Walts concern is purely conjector based on the geometry characteristics of the system. (I wish I still had that plot that Devek did 5 years ago). Ive tried to explain why its not really a factor that you need to worry about.

mk

ew928

How well does a lowered 928 handle when it's dragging it's front air dam under the car. (BTDT)
How much weight is lost off the heavy front nose of a 928 when the A/C compressor is knocked off the block?

The S4 front air dam makes a heck of a racket being dragged under the car.

mark kibort

So, what was all that "time" spent doing at the 3rd coast event? after all that, I hope you understand that you cant change the weight balance by raising and lowering the car, front to worry, so no need to worry. As I mentioned before, it ony can change your CG height, for weight transfer changes during braking and acceleration.

Why dont you start by doing an outline of your "geometry" lesson. Dont forget to include all of the factors such as spring rates, shocks, duration and extent of "toe change" if you hit a pot hole and then base this "lesson " on real world performance based on someothing like the Video I posted which shows the extreme of what our cars can see (including a pot hole or major depression as was seen on the video, but not the curbs or pot holes seen while driving in Chicago, or on a dirt road in texas)

Bottomline, the car will handle better a little lower than the factory spec. If you are at all cocerned with looks, as most of us are, you will see that the most common ride height is around 150mm-160mm. Sure, you have to be somewhat careful with our air dams . anyone that has owned a 928 has broken one, no matter what the ride height. Is a sport car, not a Ford Taurus.

dr bob

Mark, there's no doubt that the car will have a lower CG and roll center with the car lowered. In fact it would be a lot better if there wasn't that darn ground in the way under the middle of the car, the part that rides between the tires.

You preach about stuff like this, without bothering to share the fact that your results and methods do not apply to 99+% of the 928's on the road. Your car may feel like it handles better when you get the car lower, mostly becaus ethe shocks are below their normal travel range. If you've had shocks apart before, you know how the metering rods and tbe inertia parts work to stiffen the travel at motion extremes. But the rest of the world cn't drive there cars that way, because they want the tires to last, they do drive over imperfections in the road, and they don't want to have to swerve to avoid cigarette butt-sized debris that will damage the car. Your daily drive is not a 928. Yes you generally drive the car to the track, but that hardly makes it a street car.

Please, in the future, when you make a recommendation, remind readers that the advice you share does not actually apply to them unless they are seting up a car for the same duty that yours enjoys. People do actually believe some of the things you write, so it's important that you share the context of your recommendations and advice so they don't go down the wrong path, thinking the advice applies to their street cars. maybe something in your signature line so it's always there.

mark kibort

Here is the car recently jacked up and let down for a picture of very low ride height, but looks cool. this is 135mm front at this point. This is what your car will look like at 135mm (when it settles its 112mm and the fender is over the tire) . you can see, this is "one finger" with the screwdriver stuck between the tire and the fender.

the next picture is the tie rod angle with a screwdriver that is 135mm long showing ride height.

the rear is 145mm and the fender is about half way over the tire.

last picture is the car totally settled at 113mm and 135mm F/R.

this , i consider to be the lowest street setting. It would be dangerous with any driving on unknown roads or having a funky driveway to climb. however, at the front up in the 150 to 160mm range, you would still have good looks, better handling and be one inch out of danger.

all in the effort to help.

mk

FredR

I recommend a lift because they are usually flat and levelled and easy to work from if you have one locally. I tried to do it on the deck and gave up- I thought it was a waste of time for anyone taller than 12 inches

If a 928 was on stock springs at 130mm up front then it is a wonder the car even got out of the car park- it must have looked like a sniffer dog in action.

Some interesting points in this thread but I still maintain that if you want to lower the car, do not try it unless you have stiffer springs and if you do, go to the bottom end of the WSM range or slightly lower and consider dropping the rear slightly more than the front and you will have a good performance compromise for the street. This is how I have my 928 set up and it works just fine for my purposes with the big wheels on [and stock for that matter].

I also run with about 2 degrees of front camber and Carl's lower brace plus a very strong top brace. The front tire differential wear is barely noticeable after about 5k miles.

I would dearly like to have access to corner balance scales but like most, I do not and neither do the local agents but if the springs are accurate then not much of a prolbem I reckon .

If you are a track junkie like Mark you can go lower. I believe the front suspension geometry is very cleverly designed and permits this without too much in the way of deleterious effect but clearly it is not something you just pluck out of the air so to speak- you need to know what you are doing set up wise.

Not a good idea if you go Wadi bashing- as Mark says get a 4x4 for that [I have-2 of them]!

Regards

Fred R

mark kibort

Your avitar looks like a pretty lowered 928, and looks great.

I dont know what you are recomending as far as a lift or deck, but you can see checking the ride hight, is easy just on the ground. adjusting, you will have to take the tires off and lift the car anyway. adjusting toe is easy if you loosen the securing nuts and drive around to settle and then adjust by reaching in with a 15mm wrench, but i usually just jack the car up and to a couple of half turns when I am close. (i.e. 1/8toe out moving to 1/8" toe in, or in other words, fine tuning)

if the ride hight is 130mm, it looks like my picture before settling. I dont know where the "dog sniffing" comment comes from.

If you are running 2 degrees of camber, thats a lot for the street, even at the track, i only run about 1.7 degrees and thats a good compromise. if I was only street and some track, I would probably run about 1.2 to 1.5 degrees.

having set up many 928s by cornerbalancing, you can get pretty darn close by just getting the car ride hight where you want it. lower the driver side front a couple of turns, as that corner is usually heavy vs the other side.

Yes, the suspension is very ingenious. It can have camber and toe changes that allow for moderate street setting, but effective track performance. unusual in the sports car world.

Yes, I also agree, if you are going to lower the car, usually you need to change springs anyway, as you cant lower the stock spring set up to well. sagging springs can help. . cutting the springs are an option as well. (usually 1 coil will work, even with old springs) the springs might not be as lively when old.

rluvsporsche

Mark
I'm definitely confused as well. My factory manual has two pages of height adjustment values. 190 -20mm and the other page states 180 -20mm front.
Which one should be followed for MY87?
If I drop the car 1" or / both replace my upper A-arm will it require alignment?