Corner balance expectations vs. results

B.Green · 03-16-2015, 09:33 PM

After resto of all suspension bushings (ER stuff) and changing to aggressive street torsion bars, I painstakingly researched and set to Euro height for 88 Carrera and was level side to side. Car was immediately delivered to local Porsche specialty shop for alignment and corner balance. When I got the car back, it was noticeably higher on the passenger side than the driver side and was lower than Euro spec on driver side - difference being over 1/4 inch at fender arch (I know that is not the place to measure, but it is a quick reference after taking proper measurements and knowing the relationship).

I guess I expected the car to be level with driver weight, but without experience, figured it must be right.

Fast forward to last weekend at an autoX event, I experienced tire damage to driver front tire due to fender interference. Tires are popular size 205's on the front so I did not expect to have problems, but realize now that the lower driver front corner is too low.

So, I have to go up, but before I do, I wanted to post this to see if sounds normal to end up with a car so much lower on one side after corner balancing, The car is original and stock other than T-bars.

Thanks for any comments / suggestions. Bob

michael lang · michael lang's Garage

Bob, you started going down the slope when you changed the bushings and the slope got a little steeper when you went with new t-bars. Now you're gaining some momentum with ride height and corner balance adjustments. Do you see a pattern starting to form here?
Forget about the way the car looks for just a minute, what is the weight balance difference? When I had my car last done, the tech was able to get dialed in to 51/49 % difference between left and right sides with the alignment specs that I wanted the car set to. Yes, the ride height that I had originally did change and it looked odd at first but as soon as I drove it...it was like magic.
Based on your post, I would start with looking at the spec sheet that you should have been given when you had the alignment and corner balance. If you're getting l/f tire rub, there may not be enough negative camber in that corner, maybe the caster needs to be adjusted a little more forward or back. Maybe you will need to roll the fender to eliminate that. Maybe you will need to raise the l/f corner of the car slightly. Can post a copy of the alignment and corner balance sheets that the tech gave you for the car? If the shop did not supply you with them, that's okay, the computer systems nowadays can retrieve data based on VIN so they should be able to supply you with that.
There are a lot of very knowledgeable people on this board that can help you figure this out and you may not be that far away from having this figured out. Please keep us updated.

DanielDudley · 03-17-2015, 02:03 AM

I had to do a slight roll on the fender lip at 10 and 2 o'clock. But I would think it could be possible to corner balance the car and raise up that entire side a bit. Sometimes that involves messing with the rear torsion bars, or special adjustable swing arms.

FWIW, all my 911s have been lowered, and I am pretty sure that they all had a slight roll at 10 and 2. One that didn't wound up pulling the front inner lip down slightly after a hard run. A lot of people will tell you that clearances are worse on one side of their car than the other. I never really noticed that myself, but several of my cars have had adjustable rear arms.

I'm a big guy, so I would naturally like it if the driver's side was a little higher.

Lyle O · Lyle O's Garage

As Mike mentions above, if you post your spec sheet we can see what the cross balance ratio is and specific corner weights. A couple of things, though...
The car should be balanced with a full tank of gas, and the approx weight of you in the drivers seat (sand bags or something). With that, it's hard to think it ends up with the drivers side LOWER without you in it. Remember that all 4 corners of the car adjust, but it's a lot easier to adjust the front than the rear, especially depending on the index setting of the torsion bars (those need to be pretty close to start with). That may be what happened in your case (shop didn't want to mess with reindexing). I've never had a balanced car with driver side front lower than the rest. Also, I've run 205's on a very lowered car, and never had rubbing, so that's not typical either. If the car is balanced properly, and aligned properly, there will be a noticeable improvement in driving behavior.

javadog · 03-17-2015, 04:57 AM

Porsche specifies a maximum height difference of 5mm from side to side on the front axle and plus or minus 5mm on the rear. They also like to see the weights within 20 pounds, per axle. Some technicians will get things within specs and quit, others will try and get them as close to optimum as they can. Others will anticipate the added weight of a driver, etc.

It sounds like yours needs a little more tweaking.

JR

DRACO A5OG · DRACO A5OG's Garage

That is the down side of the corner balancing, you sacrifice looks for performance but that seems very off skew. I would take it back and have them corner balance with you in the car and 3/4 tank of gas.

When you replaced the rear T-bars and re-indexed, were the plates at equal angles. You may need to raise the driver rear to compensate for the passenger front.

Adjusting just the fronts will throw you corner balance off, but re-indexing the rears will require a new corner balance in any case.

You did not indicate what the camber settings were from the alignment, do you have a read out?

my 2 cents

B.Green · 03-17-2015, 11:34 AM

Thanks for the replies. All appreciated. I did get a printout but am away from it. I will try to comply.

As for driving / braking versus "looks", I am ok with the results - just surprised that I could see the car noticeably low on the driver side even WITHOUT me in it. Replies here would seem to support that curiosity - though I did not supply enough data.

Car was aligned and corner balanced with about 1/2 fuel and my weight in the car. Spring plates were very equal and started with the angle calculator results found on the site (thank you!). However, assembly ride height was done at stock conditions with little fuel and no driver weight.

As the car is driven on the street, I know it needs to be high enough for mostly stress free driving and am happy to compromise there and I would prefer to be high enough so as not to have to roll fenders even with common sized tires.

I also know that this is a starting point and that I brought this on myself once I started "playing". I believe that even at my level of experience (low), the car handled and stopped better than it did previously so would like to do what it takes to maintain that and gain some clearance.

I value your responses and help every time I ask. Bob

msterling · msterling's Garage

Is the tire rubbing on the fender lip near the top or elsewhere? You said 205 width tires, but what rim diameter, width and ET? Porsche fronts are usually ET 23.3 and 205 width rarely interferes with 15" or 16" rims. More negative camber and rolling the fender lips is commonly the cure.

I ran into rubbing with 17" 225/45-17 tires and 17x7 ET 23.3. Mine rubs on the right side and snags the inner fender near the top. I am adding negative camber and rolling the fender lips.

tshebib · tshebib's Garage

You can also rub on the inside if you're not careful.

B.Green · 03-18-2015, 11:30 AM

Bridgestone RE-11 205-55-16 on 7" Fuch fronts. So would not have expected issues.

I will get up inside well and look for rubbing signatures on the inside too. Thanks.

I too expect that rolling the fender would take care of it but am trying to sort out the reason for the big difference (+.25") between left and right when it started out level. There seems to be consensus here that much difference is suspect.

I know that shocks are not part of the "listing" stance, but would they be any part of keeping the rubbing from occurring. I left some old Koni adjustables in after the suspension work because they seemed to cycle the same off of the car. The driver's side is not adjustable any more - as the adjusting shaft is frozen and I could not break it free. Otherwise I would have cranked them up to see if there was any difference in the rubbing.

LARRY SHARP · LARRY SHARP's Garage

The factory ride height is set by comparing the centerline of the torsion bars compared to the centerline of the wheels. This keeps the error of a bad fender reading (body repair) to a minimum. It also gets rid of the affect of tire diameter differences

JAR0023 · JAR0023's Garage

Single data point. I have 205/55r16 RE-11s on 7" Fuchs. They are noticeably larger than the Toyo 205s that came off the car. I bet the measure closer to 225.

B.Green · 03-18-2015, 03:32 PM

If I did not make it clear in first post, I set the resto height and level using the proper TB measurements. I ended up with good fender comparisons enough that I could use them for rough "before and after" corner balance comparison to verify the visibly low driver side.

I will crawl under to get the proper measurements.

Good point. I agree that the Bridgestone RE-11 appear wide but don't have anything to compare to.

I do have a work associate that has a true Euro 85 with the same tires (but on 6" wheels) with no issues. His appears quite low (but level) but I have only done fender measurement. Has done some track time without wheel / fender rubbing.

DRACO A5OG · DRACO A5OG's Garage

So your rears, are the even or does driver side dip down a bit?

You see height adjustments affects diagonally as well as front to side.

B.Green · 03-18-2015, 04:40 PM

Drivers rear is 1/4" lower (by fender arch - I know - bad, but will also also crawl under to get real numbers).

Driver's front is 5/16" lower.

Car started out level side to side before corner balance.

Standing behind the car (no driver), or even driving behind it (with driver), it is clearly low on driver side. I'm only 165 lbs.

HarryD · 04:41 PM

When I had my 73 911 lowers aligned and corner balanced by a very respectable race shop, the heights were noticeably different side to side. The weights were right on so I was happy. I did develop a rubbing issue and had to roll my front lips (205/55-16 tires on 6 x 16 wheels) and I have a slight inside inside rub I choose to ignore.

If the car works, make the adjustments to the body and move on. Raise it only as a last resort.

911pcars · 03-18-2015, 05:28 PM

Quote:

Originally Posted by B.Green

After resto of all suspension bushings (ER stuff) and changing to aggressive street torsion bars, I painstakingly researched and set to Euro height for 88 Carrera and was level side to side. Car was immediately delivered to local Porsche specialty shop for alignment and corner balance. When I got the car back, it was noticeably higher on the passenger side than the driver side and was lower than Euro spec on driver side - difference being over 1/4 inch at fender arch (I know that is not the place to measure, but it is a quick reference after taking proper measurements and knowing the relationship).

I guess I expected the car to be level with driver weight, but without experience, figured it must be right.

Fast forward to last weekend at an autoX event, I experienced tire damage to driver front tire due to fender interference. Tires are popular size 205's on the front so I did not expect to have problems, but realize now that the lower driver front corner is too low.

So, I have to go up, but before I do, I wanted to post this to see if sounds normal to end up with a car so much lower on one side after corner balancing, The car is original and stock other than T-bars.

Thanks for any comments / suggestions. Bob

I would return the car to the shop who did the work and ask why.

IMHO, the shop should have alerted you to an obvious ride height difference and given you the option of favoring even ride heights over exact corner balance. Maybe there's a chassis alignment issue. They also should have road-tested your car and perhaps discovered the rubbing tire issue. Suspension usually settles after alignment adjustments. It seems like they skipped this part.

Factory sway bars? If so, corner balancing is a compromise unless there are adjustable drop links on the sway bars to compensate for slight height settings on each corner. Otherwise, fixed-length drop links pre-load the chassis and negate true corner balance.

Sherwood

Sherwood

Driven97 · 03-18-2015, 06:23 PM

Is that even common practice to raise a side of a car significantly to try to get L & R percentages similar? Seems like you'd really have to lean a car over to affect that.

I do mine in competition trim (no spare, low fuel, driver weight,) and aim to get the cross percentages equal. That eliminates the effect of one leg of your table being longer / shorter. Don't worry about the L to R difference unless you have movable ballast.

Also, don't forget to disconnect your swaybars before measuring as preload in those can totally throw off your measurments, and roll / shake /shimmy the car after each adjustment to re-settle.

javadog · 03-18-2015, 11:16 PM

The shop could get the left side higher, and still keep the weights within spec, if they wanted to.

7" wheels on the front have been known to rub on a lot of cars.

JR

911pcars · 03-18-2015, 11:45 PM

Quote:

Originally Posted by javadog

The shop could get the left side higher, and still keep the weights within spec, if they wanted to.

7" wheels on the front have been known to rub on a lot of cars.

JR

Raising one corner adds weight to that corner. Raising one side adds weight to that side. The weight thus transferred makes other corners support less weight.

Thus, at a specified ride height, unless one physically moves, deletes or adds weight within the chassis (e.g. move battery, delete pass. seat, add ballest, etc. the scales speak for themselves.

Sherwood