Alignment changes as car is lowered

[awdbandito]

When lowering a car using the adjustment screw on the control arms.

Does it generate toe-in and negative camber

or

Toe-out and negative camber?

[Flieger]

Depends on where you are currently. Can you post a photo showing the angle of your A-arms and tie-rods?

[awdbandito]

A arms are above horizontal.
They were at horizontal, and then I adjusted the screws to lower the car. This brought the arms above horizontal and increased camber. I'm trying to find out what this does to my toe.

[Trackrash]

You can get a general idea of your toe using a tape measure. Or you could set up some strings and get a more accurate measurement.

[dad911]

Originally Posted by awdbandito

.....They were at horizontal, and then I adjusted the screws to lower the car. ......

You may be happier (better handling) with the old heights. I assume car was not corner balanced after lowering. Did you turn adjustments equal amounts?

Did you lower rear also?

If you increased the angle away from horizontal, that effectively shortened the toe arms.

[FinallyGotOne]

I had a reputable shop lower my 911SC (1979) front and back. Afterwards it handled terribly. Then I went and had a full alignment by a shop that the 1st shop recommended, and it felt loads better!

[Porsche84]

Look at the tie rods. If they are to the rear of the spindle and they also angle up like the A arms, then you are adding toe out. If the tie rod is in front of the spindle, and the same change is made, you are adding toe in.

[Zeke]

Originally Posted by Porsche84

Look at the tie rods. If they are to the rear of the spindle and they also angle up like the A arms, then you are adding toe out. If the tie rod is in front of the spindle, and the same change is made, you are adding toe in.

Not sure there was ever a 911 that had the front steer set up.

When a 911 is lowered past the tie rods being level, you are adding to toe out. This is why a steering rack spacer is used to reduce bump steer at the lower height.

[911st]

I belive lowering increases neg camber and toe in untill the A arms are 90 deg to the strut which would have to be really, really, really low.

[rnln]

neg camber but I think toe out, because the tie rods are pulling in the rear of the wheels.

[Flieger]

Originally Posted by 911st

I belive lowering increases neg camber and toe in untill the A arms are 90 deg to the strut which would have to be really, really, really low.

Yes, the critical angle is relative to the strut. The tie rod is a different length and pivots at a different point than the A-arm, though, so the camber and toe curves do not match.

Usually, you get more camber and more toe-out.

[Les Paul]

I got my 930 25 years ago next week. It was in perfect shape inside and out. On my backroad course it would go over 150 easily but was squirelly no matter alignment or tire. I had a turbo s spoiler and a Ruf front installed, went to 17 inch turbo twists, lowered front, and the one they said helped the most, corner balanced. The reputable shop said that it was pretty effed up. The car had only had one owner and the front right fender replaced in the prior 9 years. Cutting back to the chase it was as planted at 150 as it was at 90.

[Tyson Schmidt]

You will get more negative camber and it will toe-out.

[awdbandito]

thanks for the info. I am pretty sure as I lowered the car I ended up with toe out and additional negative camber. I was just trying to make sure.

[911st]

Got it, as the car gets lower the bottoms of the struts push wider because of the A arm effect adds neg camber.

However, I believe the tie rods push out until they get to square to the ground . After that they then get shorter as they start to angle upward toward the struts.

So I suspect lowering most always increases neg camber. However when lowering from stock height, at first it toes in, then at some point past "euro heigh look" can start to toe out.

[Tyson Schmidt]

Originally Posted by 911st

Got it, as the car gets lower the bottoms of the struts push wider because of the A arm effect adds neg camber.

However, I believe the tie rods push out until they get to square to the ground . After that they then get shorter as they start to angle upward toward the struts.

So I suspect lowering most always increases neg camber. However when lowering from stock height, at first it toes in, then at some point past "euro heigh look" can start to toe out.

No, actually it toes out the whole way, just in a curve.

This was designed in from the factory. Not only are the control arm and tie-rod not parallel, they are also different lengths. Plus the tie-rod is moving in a uniform arc, while the steering arm is not. Makes things a little more complicated than meets the eye.

[Flieger]

Originally Posted by 911st

Got it, as the car gets lower the bottoms of the struts push wider because of the A arm effect adds neg camber.

However, I believe the tie rods push out until they get to square to the ground . After that they then get shorter as they start to angle upward toward the struts.

So I suspect lowering most always increases neg camber. However when lowering from stock height, at first it toes in, then at some point past "euro heigh look" can start to toe out.

The tie-rod connects to the steering arm on the strut and the toe is controlled by the length between the steering arm and tie-rod pivot. Therefore, the tie-rod does not car what the ground is doing, just where the strut is. The toe will be more outward as the strut moves away (gaining negative camber). If the strut moved in, over the top of the camber curve, it would toe-in. I do not think you can get that low without some effort.

[911st]

This is in interesting puzzle.

Spit balling, it seems the A arm and tie rods move over two different arches. This is why a lowered 911 is subject to bump steer.

I believe struts mostly widen with compression or lowering unless one goes extremely low. If any thing the rate slows quickly. Think of a flattening camber curve.

The tie rods however move over an arch where there attachment points gets wider at first and part way through compression they narrow increasingly.

I believe that going from stock height the rate the struts move apart is slower than the rate the steering arms move apart.

Then the rate the steering arms move apart slows as the struts continue to move apart.

Finally the rate the struts spreed apart starts to slow but the rate the steering arms are pulled together starts to steepen.

Thus, I suspect with lowering at first there is a slow increase in toe in, then a range where toe change is more or less stable. Then as the car gets low, we start getting in increase in toe out. This is where we start being very aware of bump steer.

[Flieger]

Someone needs to take out the torsion bar and make a video of the suspension moving throughout its travel. Any volunteers?

[Tyson Schmidt]

Originally Posted by 911st

This is in interesting puzzle.

Spit balling, it seems the A arm and tie rods move over two different arches. This is why a lowered 911 is subject to bump steer.

I believe struts mostly widen with compression or lowering unless one goes extremely low. If any thing the rate slows quickly. Think of a flattening camber curve.

The tie rods however move over an arch where there attachment points gets wider at first and part way through compression they narrow increasingly.

I believe that going from stock height the rate the struts move apart is slower than the rate the steering arms move apart.

Then the rate the steering arms move apart slows as the struts continue to move apart.

Finally the rate the struts spreed apart starts to slow but the rate the steering arms are pulled together starts to steepen.

Thus, I suspect with lowering at first there is a slow increase in toe in, then a range where toe change is more or less stable. Then as the car gets low, we start getting in increase in toe out. This is where we start being very aware of bump steer.

You have to remember that Porsche designed in the toe-out on bump even at stock U.S. ride height. The lower you go, the more a given amount of compression makes it toe out. That's why it gets more severe the lower you go.

I've measured bump steer on a lot of cars and can tell you that you'd have to raise the car pretty high to have the bump-steer curve you are talking about.