Did I buy the wrong trailing arms?

CHILI · CHILI's Garage

I have an RSR (widebody) clone. I recently bought aluminum trailing arms and adjustable springplates. But, after reading a few posts, I've noticed guys with widebody conversions are using 930 trailing arms.

Is that what I should get? And, more importantly, what's the difference? I don't see how they could be wider since they still have to meet up with the springplate.

TIA,
Chad

jluetjen · jluetjen's Garage

There's a geometry change using the "Turbo" trailing arms that raises the rear roll center (which stiffens the rear end in roll and helps to keep the inside front tire on the ground) and increases the camber gain in roll (which tends to keep the outside rear tire square to the road under extreme cornering forces).

In order to convert to these arms, you'll also need to update the inner trailing arm mounting points.

MichiganMat · MichiganMat's Garage

Wait for JackO to chime in, he's running standard arms, not Turbos.

The 930 arms are more burly for those super-wide 11-inch rims, but they cost about 5x the 911 price. Where do you want to spend your money?

CHILI · CHILI's Garage

So, I can run the regular control arms with no issues? It's just that 930 arms are better for the above reasons.

That's right, right?

Wil Ferch · 03-09-2006, 11:53 AM

Others more knowledgeable will chime in...but I don't think it's a "burly" issue..it's that the pivot points / pick up points that determine the geometry of motion are slightly different for the Turbo...as jluetjen described.

- Wil

klaucke · 03-09-2006, 11:53 AM

Yes, you can run normal 911 trailing arms. It's common on a lot of widebody conversions, I'd say more popular than swapping them for 930 units. While they offer some advantages over normal arms, there are a lot of other factors impacting suspension performance that you can exploit. You need wheels or spacers set up for a widebody (i.e. rims w/ proper offset to push the tire out to near the fender lip).

len911 · 03-09-2006, 12:26 PM

You can run standard 911 Al suspension arms. Might want to upgrade to rear monoballs at the pivot point to control toe changes. As others have said, either spacers or custom offset wheels will work. Here's my car with 8.5 & 10 x17 CCWs. Car is a 74 with steel flares and 74 suspension using front monoballs and polybronze bushings all around. Lou

Bill Verburg · Bill Verburg's Garage

You can use either n/a or turbo trailing arms, but in addition to the geometry changes and installation issues that have been mentioned, the 930 arms have 3.5" brake mounts, you need turbo calipers or better, M will not fit

Tyson Schmidt · 03-09-2006, 12:57 PM

If you run the 930 trailing arms, you have to weld in new inner pick-up points, since the 930 arms are shorter.

The wider track was achieved on the 930 arms by widening the bearing area outside the spring plate mounting points. They still used a 1" spacer in addition to the wider arms.

On Jack Olsen's car, we went with 911 arms because they are easier to find and cheaper in the event of an incident. It also keeps the camber change to a minimum.

We used the camber boxes for the inner pick-up points so we could raise outer pick-up points as well with the 935 spring plates. This raises the rear roll-center height, and brings the camber curve back in range with lowering, and gives some anti-squat geometry.

tom1394racing · 03-09-2006, 01:46 PM

I am running standard 911 aluminum trailing arms with the stock pick-up points on my RSR clone. I am using 16X11 rear wheels with 275X16 tires. This required 1'' spacers to center the tires in the wheel wells.

Bill Verburg · Bill Verburg's Garage

The o/s of the wheel is also relevant and needed

tom1394racing · 03-09-2006, 01:52 PM

Bill

I'll check and post the offset later

len911 · 03-09-2006, 01:57 PM

As a reference point, my 3 piece CCWs are as follows... 8.5s have 5.25" backspace and +0.5 offset. 10s have 4.5" backspace and -1" offset. No spacers needed, no clearance issues. Lou

CHILI · CHILI's Garage

Thanks guys. I'm glad to hear that. More importantly, my wallet is glad to hear that!

Tom and Lou, very nice cars!

Grady Clay · 03-09-2006, 03:42 PM

There are several other “minor” (expensive) issues with stub axles, tapered rear wheel bearings, hubs, looong wheel studs and such.

It takes deep pockets for parts and engineering to use the 930 parts. The 911 set-up works great and is more easily serviceable. I think one of the issues with the (desirable) M491 is the cost of a curb contact.

Best,
Grady

tom1394racing · 03-09-2006, 05:17 PM

[QUOTE]Originally posted by tom1394racing
[B]I am running standard 911 aluminum trailing arms with the stock pick-up points on my RSR clone. I am using 16X11 rear wheels with 275X16 tires. This required 1'' spacers to center the tires in the wheel wells.

I just measured my rear wheels and tires.

http://members.rennlist.com/1976c38/index.html

I get the following:

Section width=31cm
Backspace=12.5cm
Offset=backspace-section width/2=-2cm

Porsche Doc · Porsche Doc's Garage

Hey Chad,
The trailing arm stuff you have will do just fine.
We do it with regular Alum arms all the time.
The only time we use the turbo arms is on some race cars.
Or if the customer just wants them.
Keep what ya have Man!