930 vs Carrera rear hub spacing question

[Geneman]

hi peeps,
can anyone tell me if the 930 alum trailing arms on a late 80s car.. are a wider track than just normal car carrera trailing arms? meaning, do the 930 hubs project the wheel farther out into the wheel well ?

i am trying to find out if it is proper to size wheels for 930 flares, by using 930 specs ( which include the turbo trailing arms)

my car has regular carrera trailing arms....

does this make sense?

thanks frank

[Peter Bull]

To the best of my knowledge, the answer to your first question is yes. The 930 has a wider track than a Carrera from the same period of time.

A friend of mine had an SC with 930 trailing arms. AFAIK the SC and the Carrera has similar trailing arms. He used 9" wheels with an offset of about 50 mm in order to get the wheels inside the wheel arches. For comparison, a 9" Ruf wheel that fits the rear axle of a Carrera has an offset of 17 mm.

/Peter

[winders]

This post will probably answer your question:

Early Trailing Arm Geometry for Widebody

If not, the rest of the thread may.

[chris_seven]

There are two main differences.

The Turbo Trailing Arm is shorter than the SC Trailing arm which affects the manner in which it pivots with respect to the spring plate.

This means that if you are fitting Turbo Arms you will have to modify the brackets on the Torsion Bar Tubes by welding on the extension pieces.

These extension pieces move the mounting centres apart and compensate for the shorter arms.

The Turbo arms won't fit without these brackets as the wheelbase would be wrong and the spring plate will be in completely the wrong place.

These is a difference in width of the hub between the flange for mounting the brake rotor and the spring plate which is one of the important measurements.

The Turbo Arm is about 35mm wider in this area (I have only measured this crudely) and there is also a spacer fitted to the Turbo between the wheel and the brake rotor on the rear and I don't have an Arm that is built up at the moment.

I would like to see measurement made from a fully set up car as I think that the difference with the spacers is more like 63mm per side (28mm spacer + 35mm on hub position)

The track measurements will also take the wheel offset into account and this will also need to be considered.

[winders]

Chris,

Did you look at the post I provided the link to? 21mm is the answer....

[Geneman]

Thanks Scott , Chris and Peter ..perfect answers... (Great link also Scott!) Hugely Helpful happy mothers day to all. I will be a in mancave all day assembling BBS wheels to new specs.. Thanks Frank

[chris_seven]

Scott I did read this thread and to me it doesn't seem right.

The dimension that controls the wheel mounting face must be the distance between the spring plate mounting face, the hub flange, the brake rotor thickness and any spacers fitted.

As the Turbo is fitted with a 28mm spacer it is hard to understand how the overall width change is only 21mm.

This would mean that the distance from the spring plate mounting position to the hub flange would have to 7mm narrower which isn't the case.

As the spring plate position is controlled by the body shell whatever happens inboard of this has no effect. As far as I know

If 21mm is the distance to the hub face and doesn't include the spacer than that would seem better and I could be 10mm adrift in the crappy measurements I made by eye earlier but by using this number the wheel position would still be incorrect as the spacer needs to be considered when Turbo Arches are being fitted.

I will dig out the rotors and the spacers of the Turbo Arms later in the week and measure the distances from the spring plate mounting to the end of the spacer.


We fitted some 9" wide rims from Rota Fox that had an offset to suit a stock SC to an SC that had Turbo Flares welded on at the rear and we needed 55mm spacers to make them remotely fit and we still didn't completely fill the arch.

[winders]

Originally Posted by chris_seven

If 21mm is the distance to the hub face and doesn't include the spacer than that would seem better and I could be 10mm adrift in the crappy measurements I made by eye earlier but by using this number the wheel position would still be incorrect as the spacer needs to be considered when Turbo Arches are being fitted.

The question really is what is the difference to the hub face. Spacers should be considered separately and that is where the 21mm number comes from. There are even pictures showing the the actual measurements.

[chris_seven]

Originally Posted by Geneman

hi peeps,
can anyone tell me if the 930 alum trailing arms on a late 80s car.. are a wider track than just normal car carrera trailing arms? meaning, do the 930 hubs project the wheel farther out into the wheel well ?

i am trying to find out if it is proper to size wheels for 930 flares, by using 930 specs ( which include the turbo trailing arms)

my car has regular carrera trailing arms....

does this make sense?

thanks frank

I thought that the original question was concerned with wheel position and as the spacer is standard it must be part of the answer

[winders]

Originally Posted by chris_seven

I thought that the original question was concerned with wheel position and as the spacer is standard it must be part of the answer

I never said the spacer width wasn't part of the answer.

The way to do this is figure out the 911 vs 930 difference hub face to hub face. That is the real difference between the a 911 and 930. Spacer width is variable. Then one factors in the spacer used on the 930, whatever width it might be, to determine the effective hub face difference.

If were having custom wheels made for my 911 or 930, I would adjust the offset to eliminate the need for spacers.