jthwan22

If you only have garage floor to use, can you take measurements with the car nose in then nose out? Average the difference?

pete917

Im running Bridgestone S01's:

- front tyres 215x55x16
- rear tyres 245x45x16
- front tyre pressure 31 psi
- rear tyre pressure 34 psi

rusnak

Concrete is very wavy, especially the stuff we've been getting recently in our area. And since it's usually screeded off to drain, it is not even meant to be even. It's meant to flow water out to a driveway.

We had a garage alignment thread last year, and I showed some pics of a 6' level that I use, on top of washers to compensate for wavy concrete. You place the washers next to the tire contact patch, and get an angle reading with the digital level. This allows you to calibrate the floor angle in the calculation, so that your angle reading on the door sill is somewhat accurate.

g-50cab

How old? We have not been able to get S01's in the states (at 245/45/16 sizes) for years!

pete917

The tyres are almost new. They were hard to get and I think will be impossible to get in the future. (I'll have to think of alternatives when the time comes).

I have ordered a dig inclinometer, so Ill have the ability to take some measurements as soon as it arrives.

I know it's not the correct way to measure ride height, but people often refer to the distance from the wheel arch to the ground. Im not going to use this method, but I was wondering if anyone knew their heights when measured this way?

theiceman

24 3/4 rings a bell

I will double check when i go to the garage

pete917

thanks iceman. Would you mind doing front and back, then I can check mine as a comparison while im waiting for the new gadget to arrive :-)

theiceman

. damn .. i have to put my bunny slippers on now and go out to the garage ..

front 25 3/4 from the floor to fender lip through centre of wheel.
Rear 25 1/2 from floor to fender lip through centre of wheel.

Mine is not tracked or lowered I don't think , but it might at least give you a refence point

pete917

thanks Ice. Those slippers sound good.

Mine is 24 3/8 rear, and
25 1/8 front.

So, using this a reference point, looks like the front might be raised a little high and not giving the 1 degree down angle needed.

Time will tell when the inclinometer arrives.

Thanks alot, I appreciate you making a special trip to the garage with the slippers on

theiceman

must of been where i got confused about the angle . Obviously the wheel arches aren't the same distance from the ground. so must be in slightly different heights on the car . I have a 1/4 difference front to back , you have 3/4 so you may be right . would be good to hear some other guys chime in though .. especially those who track their cars and have corner balanced.

pete917

I agree, they must be different heights. Once I get that inclinometer we'll for sure....


as you say, it would be interesting to here others and what heights and differences they have.

pete917

OK, some progress. I have managed to get a consistent reading on the inclination of my car.

I placed a block adjacent to the centre of the wheel on both front and back. Both blocks being the same thickness;

I then ran a straight edge from one block to the other. The top of the straight edge now represents the angle of the car at the tyre contact points.

Next I zeroed my inclinometer on the straight edge

Then I transfered the inclinometer to to the centre point of the door sill.

I measure an inclination of 0.4 degrees (down at the front)

So, the distance between wheel centres on my car is approx 231.5cm. Over that distance at 0.4 degrees there should be a difference of 1.61cm. Looking at my original readings of rear 61.9cm and front 63.5cm thats a difference of 1.6cm.

So, Porsche recommend a 1 degree gradient. This means I need a further 0.6 degrees or 2.42cm less onfront. This would make my ride heights as follows:

Rear 61.9cm
front 61.08cm.

So I have some adjusting to do

Just for reference. A 1 degree slope over 231.5cm is 4cm. So the front of the car needs to be 4cm lower than the rear. So clearly the height of the arches at the front and rear of the car are not the same....

More progress anon..

whalebird

The change in rake front/rear will result in a change in caster to the same degree.

pete917

I hadnt thought of that. So does that mean my castor will reduce as the nose goes down?

whalebird

yep. sure does. I think you will be happy once you get a good set up on your car. I risk repeating myself, but I think a good corner balance and alignment will do wonders. Get the rear-toe balanced out (if this is a street car)as well. I will not give hard numbers off the top of my head, but many uni-body cars cannot be caster adjusted including a 911, although you can move the struts around at the top mount a little. Furthermore, the caster is not even from side to side. I cannot say for sure about the various 911 models, but the body of many cars have a bit more caster on one side than the other to compensate for the "crown" in the road. It's opposite for the RHD cars from the LHD cars and is built into the body/chassis of the car. Regardless, you should be able to achieve the proper specs for your car if it has no collision damage.