911 Rod

Seeing that I am pulling out most of my suspension I might as well lower the car to Euro specs. If life was so simple.
I had the car corner balanced last year so I figure it needs all 4 corners to come down the same amount. Right?
My understanding is that it should be 25 1/2" to the top of the inside front quarters and 25" in the rear. Right?
I measure the fronts and they are already around 25" and the rears are around 26".
If I only lower the rear, it will make it rear heavy. If I lower the front as well (to keep it balanced) the front will be too low.
Is my car twisted?
I plan to have the car balanced afterwards and I want to be in the ball park before I get there.
Thanks

Edward

Assuming the CB was done properly last year, your car will, theoretically, be fine if you lower the rears equally. A CB is a comparison of diagonal weights expressed in percentages. So if the rear end is lowered, it changes the actual numbers sure, but the ratio can stilll be, again theoretically, at 50% diagonal wts.

Remember, too, that measuring at the fenders is not the most accurate measurement of ride height as there are significant variances in body panels from car to car, especially over the decades of road use. Get a baseline measurement from fixed suspension points, then lower the rear accordingly. If you lower the rear equally on the L and R as measured from a suspension point (in reference to your original numbers before you adjusted anything), then your CB should remain close. And even though you are adding weight bias to the rear, you are also reducing cg and roll center of the rear.

Edward

911 Rod

Thanks for your input Edward.
The person I did the CB with is very knowledgable. I believe it is 59/41 or 61/39?
I understand what you are saying about the fenders. I measured both sides and they are quite a bit different. My theory is that the distance between the fenders and fixed suspension points will stay the same.
Does the car have to be lowered to a precise height?
Should the eccentric height adjustments in the rear be in the middle of the adjustability for tweaking latter during CB?
Thanks
Rod

Peter Zimmermann

Rod: Fender measurements can be made, but only after you ascertain that your floor is level. Even then there might be a little bit of difference, but as a rule of thumb it's a good place to start. Nothing beats a good alignment rack. The measurements you state are really way off, a result of someone thinking that if they spent 5 minutes "lowering" the front that they had lowered the car. With your settings 911s just don't work. The key to ride height is to measure your rear radius arms, when you get them where they need to be (resulting with an approx height, floor to quarter panel, of about 25"). At that point the front can be set to about 25.5", which gives you an excellent platform to align and corner balance. But, when lowering a 911, everything is keyed off of those rear radius arms, and the angle that they hang at (with the shocks & trailing arms disconnected) after the torsion bars are turned. There is definitely some trial & error involved, but when you get them the same and put the car back together, measurements from the floor, using Edward's way or to the fenders, only serve as a verification that you're at where you want to be. Have fun with it!
Pete

911 Rod

Peter: Does the floor need to be level if I place the car in the same spot to check my lowering?
Remember I will be taking it in for a CB and alignment after.
I'm hoping to put in the ER bushings, ball-joints, mono-*****, truss brace this weekend. Any tips? Looks pretty clear. Bentley etc.
Next weekend the rear. I'm sure I'll have more questions.
Thanks for your help.
Rod

Edward

You're welcome, Rod.

Caution: long-winded response alert ...

A "precise" height is really up to you and how sensitive you are to the dynamics of your car. Barring a complete hatchet job, anything close will yield a good "feel" when cornering. Of course, if the car feels different cornering L vs R, or doesn't stop straight under hard braking (but brake system is good and seems to stop straight under light braking loads), then you are a good candidate for a CB. Or if you just want to be assured that your car is properly balanced, then a CB is the way to go, especially under track conditions where you are probing the limits and you're focusing on learning how to drive the car well, not wasting time/energy trying to compensate for a whacked chassis setup.

The "optimal" height is as low as is practical for you given certain limits ...slam the car down and driveways become a problem, not to mention you are reducing susp travel. With stock front spindles, I understand that the rule of thumb is that the inner pivot point of the A-arms should be no lower than the outer point of the A-arm. So looking at the front of the car, the arms can be parallel to the ground, or the inner points of the arms higher than the outer points ...if inners are lower than outers, then your chassis is too low and prob will not have much travel left in them thar struts.

In terms of front-rear height relationship, most shops like to go with the 1 degree of rake rule of thumb, while some are more aggressive than that.

As for your rear eccentrics, hopefully the springplate is nearly centered in its travel on the whole arm. Otherwise, your alignment guy will run out of adjustment room when he raises/lowers that corner, and is then going to have to re-index the torsionbar and start again ...more labor cost. So if you want to save money, get it as close to your desired heights as possible, trying to get the springplate as centered on the arm as possible. Just a couple mm of movement on the plate translates to about a 1/4" of height change so you've got "some" room here, unless you're already close to maxed out now.

Post back if you've got any more questions. FWIW, I setup my SC (full-time Tracmeister ) and ended up getting a perfect 50% CB. While that may not translate exactly from car to car, it'll probably get you close, or at least give you an idea of how far you can go; I have those ride heights if you're interested. If you are using your car for street duty, however, it may be a bit lower than you'd like. I hope all that made sense.

Edward

Edward

Edit:

Rod,
I just read your post that you're doing bushings, etc. Take good, careful measurments as Pete said BEFORE you do anything, and also of the springplate angle with the sways disconnected. This way you can get her back pretty close, minimizing that trial and error. And when you finish the installation and are fine-tuning ride heights, be certain to actually drive the car a few minutes, loading up the suspension (don't go crazy though ) to settle her out, then park in the same spot in your garage to recheck heights (rolling the car and bouncing on the bumpers does nothing ...I know

And the best advice yet: listen to Peter!

Edward

911 Rod

I understand what you are saying.
The car sees about 10,000 miles of street every year and 2 or 3 weekends at Mosport.
I want the car to be all it can be so that anything else can be attributed to driver's skill.
I'm pushing the car very hard. I'm at the limitations of my street tires (SO3's)
A radical drop is not necessary. I would like to keep the components stock other than the suspension points.
I thought that the weight was to be closer to 60/40 so that under braking it became 50/50. No?

911 Rod

I'll supply the beer and BBQ if you guys want to make the trip to the great white north!
Taking note of the spring plate angle the car is obviously in the air with the trailing-arm disconnected. With no weight on it is their an angle should aim for?
Will this be the difference between before and after?
Thanks
Rod

imcarthur

Yes, it should be. Use plywood or old panelling 'platforms' & a water level or a string level & very careful careful measurements. The stiffness of the chassis makes it important.

Also mark the springplate's adjustment position along with it's angle relative to the body when unloaded. If you change the adjustment position it will confuse your springplate angle.

Ian

Peter Zimmermann

Edward: I never realized how important being precise left to right was, until I spun my SCCA E/P 914 a few times - only during right turns. After Riverside got me in turn #6 I started thinking about why the car spun. Sure, I was at the edge of adhesion, but I couldn't for the life of me figure out why I couldn't feel the car get away. Until I took the car back to the shop and spent an entire weekend learning how to "string" the car. Guess what? The trusted, highly experienced, well-known alignment facility that I'd been using had given me a parallelogram, instead of a rectangle. We re-set everything by hand, using basic camber and weight tools, towed the car to Phoenix Firebird and won both ends of a double regional, including two poles. What a difference!

Rod: Going by your measurement of 26" I think it's safe to assume that your car is set at USA height in the rear. Before you start the job, raise the back wheels off the floor and study the rear wheels, and how they hang. Use a long straight edge on both vertical and horizontal planes. (After you've re-set everything you'll find this info helpful in order to do a preliminary setup before taking the car to the alignment shop). When you get everything disconnected from the radius arm (also know as a springplate) measure it from horizontal. In other words, put a protractor on the car's threshhold (door open) and a second protractor on the radius arm. The two readings will give you the number that you need. Do this BEFORE you disconnect the radius arm at the torsion bar cover, but AFTER you remove the rear lower of the four bolts holding the bushing cover in place. If you don't take out that bolt it will interfere with the free angle (drop) of the radius arm. I think that your resulting measurement will be about 41 - 42 degrees. (Of course, for any number of reasons, your car may be lower than USA height, and might be set at about 37 degrees, which means that your change will be a little less radical). If you're going to run Bilsteins you want about 34 degrees (35 degrees with Boges), which is the reading for a "typical" Euro ride height result. Euro height is about as low as you want to go with the car and still hope to achieve the necessary rear squat in order to get the car out of a corner using the maximum possible throttle. Do the rear of the car first, that's where everything is that matters. As Edward stated, you have to put the whole thing together and take it for a short drive to get everything settled in, especially after doing bushings. When your car is at the height that most people consider "right," you should be able to see a gap between the top of the rear tire and the closest part of the quarter panel lip. My '82 measures 24 7/8" on a vertical plane through the center of the wheel, and shows about a 1/2" gap (225/50x16s on 7" wheels). When you're all done, and you've raised your front a bit you'll have leeway to set your corner balance. You can use your radius arm bolts for minimal change (hopefully they're in their original, stock positions), and you can use the front height adjusters to do the same. When you're all done, and you find an alignment spec that suits your driving style you'll swear that you're in a different car. Have fun with it.
Pete

Edward

Rod,
What Pete said.
It's not hard at all, just labor intensive. Take your time and take good measurements. I'd like to give you angles, but they would be meaningless as I have 31mm torsion bars in the rear, so my arm's angle will be significantly smaller than a car suspended with a softer bar. BTW, you're doing all this work and inevitably popping some serious $$ for the eventual alignment and CB, have you replaced the Torsion bars? Make sure you've got the springrate you want, or you'll find yourself doing this again.

Pete,
I've heard of such stories as yours!! Even worse that you took it one of those "trusted shops"!! I've never experienced the L-R imbalance myself, but figured it's a whole lot easier (and in some cases, safer) to heed good advice than to find out the hard way myself. When I did up my Trackmeister, I setup my heights and alignment to the "really-damn-close" settings, then got a trusted local shop (of which you know, I'm certain) do the final alignment and CB. The car is amazing! Just flat out planted and stable. And best of all, predictable and readable, which makes her a very confidence-inspiring platform ...can't wait to burn up the street rubber and get some Rs on there. I can't say enough about what a good alignment and CB can do to transform a car. Thanks for sharing!

Edward

911 Rod

Thanks for all of the info guys.
I'll start tackling the front this weekend.
The back ............... after that.
I'm sticking with the stock torsion bars for now.
Do you suggest moving up to the little bit larger Turbo ones?
I'm off the the used Porsche parts supplier this afternoon.
It's an 86 911 if you didn't know.
Rod

Edward

Rod,

Suspension compliance and what is "acceptable" is obviously so subjective, so what you want is largely up to you. But given the suspension upgrades you are already are planning, and the fact that you are track minded, I would go with 22/29 torsions. While the turbo bars are a bit stiffer, it's a very, very mild increase in spring rate, almost not worth doing, IMHO. I had 22/28s and did not at all feel they were too stiff or jarring for street duty, and mine is gutted so is prob quite a bit lighter than your 86. If you are interested in a bit more compliance, go with 21/27 or 28.

And for matching your new springrate with shocks, you can always replace the rears later. But the front struts will require an alignment so you should do that now, as well, and don't cost that much more (yeah, I know it's adding up ...BTDT ). Not that I am trying to spend your money. It's just that you are doing so much in work and fine upgrades, and spending good dough on an alignment and CB, it'd be a shame to not go one step further "while you're in there." You'll not only save yourself the cost of align/CB later, but you'll have a much more satisfying street/track performer in the end. Of course, all IMHO. Best of luck to you

Edward

Peter Zimmermann

Edward is correct, do the T-Bars now. Also, I agree with his size choice - 22F/29R. Many posters/enthusiasts prefer the 22/28 combo, but I found that I had more flexibility with sway bar adjustments and tire pressures with the 29s. With Bilstein Sport-valved (custom) shocks all the way around it was pretty stiff for street use - I definitely could not get close to potholes!
Pete