Early Trailing Arm Geometry for Widebody

[Ferrino]

I have it in my notes that the 930 trailing arms extend each side by 22mm. My source was this post.

[Bill Verburg]

Originally Posted by Ferrino

I have it in my notes that the 930 trailing arms extend each side by 22mm. My source was this post.

The pick up points were moved outboard 22mm, the 930 arm needed to be shorter to compensate, but when I looked into this I found the wheel mounting face was 33mm outboard.

Ill look through the source documents to try to find where that # came from. It was all soooo long ago.

[BRAIDusa]

Originally Posted by Bill Verburg

Yes, each side of the rear 930 pushes it's wheel out 1.3"(33mm) more than a 911.

Then they added 28mm spacers to that so that they could use the same wheels as were used on the 911.

in the front of a 930 they use a 21mm spacer, till '80 it was a removable spacer, from '80 they increased the hub o/s 21mm

Thanks Bill. That's great. I had the spacer thing down but the arms were throwing me off.

[Bill Verburg]

Originally Posted by Bill Verburg

The pick up points were moved outboard 22mm, the 930 arm needed to be shorter to compensate, but when I looked into this I found the wheel mounting face was 33mm outboard.

Ill look through the source documents to try to find where that # came from. It was all soooo long ago.

I can't find the source material but another way to find that # is to start w/ the factory rear track #s

This isn't 100% accurate because track changes w/ height change but starting w/ stock height rear track for a 911 & 930 in mm
1380 1501
spacers
0 56(2x28mm)
subtract
1380 1445
measuring wheel ET x2 911 has 7ET 23.3 930 has 8ET 10.6
46.6 21.2
subtract
1333.4 1423.8

result 90.4mm difference in wheel mounting face
divide by 2
45.2mm /side

My guess is that is comprised of 33mm wider trailing arm + 22mm wider pickup points

[BRAIDusa]

Originally Posted by Bill Verburg

I can't find the source material but another way to find that # is to start w/ the factory rear track #s

This isn't 100% accurate because track changes w/ height change but starting w/ stock height rear track for a 911 & 930 in mm
1380 1501
spacers
0 56(2x28mm)
subtract
1380 1445
measuring wheel ET x2 911 has 7ET 23.3 930 has 8ET 10.6
46.6 21.2
subtract
1333.4 1423.8

result 90.4mm difference in wheel mounting face
divide by 2
45.2mm /side

My guess is that is comprised of 33mm wider trailing arm + 22mm wider pickup points

45mm seems like a lot.

I'm thinking of installing the same naked wheel on my 84 Carrera and my friend's 88 930 and measuring back to the inner wheel well wall. That should be fairly definitive don't you think?

[porsche930dude]

Bruce Andersons book has info about the diffrent pickup points

[Bill Verburg]

Originally Posted by BRAIDusa

45mm seems like a lot.

I'm thinking of installing the same naked wheel on my 84 Carrera and my friend's 88 930 and measuring back to the inner wheel well wall. That should be fairly definitive don't you think?

I'm still looking for the original source material

It's clear that there are several causes for the wider track,

I rethought the process of using the rear track
911 930
1380 1501 rear track in mm at std ride height
690 750.5 1/2 so we are only dealing w/ one side
0 28 spacers
690 722.5 subtract the spacers to get to the wheel mounting face
23.3 10.6 7" & 8" wheel ET, these are positive(ie move the wheel ctr line inboard) and need to be added to the above to eliminate them
713.3 733.1 this is the distance from the center line of the car to the wheel mounting face
the difference is 19.8mm/side, i.e. the 930 wheel mounting face is 19.8mm further out board

This makes sense because the fenders were extended 2"/side, the 19.8 + a 28mm spacer moves the 8" wheel 1.95" outboard to fit the 930 fender

[BRAIDusa]

Originally Posted by Bill Verburg

I'm still looking for the original source material

It's clear that there are several causes for the wider track,

I rethought the process of using the rear track
911 930
1380 1501 rear track in mm at std ride height
690 750.5 1/2 so we are only dealing w/ one side
0 28 spacers
690 722.5 subtract the spacers to get to the wheel mounting face
23.3 10.6 7" & 8" wheel ET, these are positive(ie move the wheel ctr line inboard) and need to be added to the above to eliminate them
713.3 733.1 this is the distance from the center line of the car to the wheel mounting face
the difference is 19.8mm/side, i.e. the 930 wheel mounting face is 19.8mm further out board

This makes sense because the fenders were extended 2"/side, the 19.8 + a 28mm spacer moves the 8" wheel 1.95" outboard to fit the 930 fender

I like that more. I'm still going to measure when I get my hands on a 930 again.

Thanks Bill.

[Bill Verburg]

Originally Posted by BRAIDusa

I like that more. I'm still going to measure when I get my hands on a 930 again.

Thanks Bill.

Always best to measure

It will be interesting to see the actual measurements from a 930, please let us know

[BRAIDusa]

Originally Posted by Bill Verburg

Always best to measure

It will be interesting to see the actual measurements from a 930, please let us know

Well, I think I did this right.

88 930:





84 Carrera:




Using the same wheel on both cars I measured back to the inner fender wall. 930 is 88mm, Carrera 67mm. Difference is 21mm. Less than I expected. Perhaps I should have used the same tape measure.

[Bill Verburg]

Originally Posted by BRAIDusa

Well, I think I did this right.

88 930:





84 Carrera:




Using the same wheel on both cars I measured back to the inner fender wall. 930 is 88mm, Carrera 67mm. Difference is 21mm. Less than I expected. Perhaps I should have used the same tape measure.

That's darn good agreement w/ the 19.8mm that I came up w/ by comparing the track difference.

Thanks for settling this!

[BRAIDusa]

Originally Posted by Bill Verburg

That's darn good agreement w/ the 19.8mm that I came up w/ by comparing the track difference.

Thanks for settling this!

Shall we declare it "so"?