Crepitus

I am preping a 84 for DEs and a few AXs. I need to use a wheel that will clear C5 brakes. I want to use Z06 fronts (square). Can I safely use a set of 4 wheel adapters to correct the offset? These are the usual 6061 billet adapters, 1" thick. The car will weigh about 3000# and use DOT 100 street tires, 275 40 17. About 375hp

Thanks!

CHJ In Virginia

I personally would never use adaptors. Check the regulations of the group that you want to run with, many do not allow their use. The best way to go is to get a set of ARP extended length studs and a set of wheels with the proper back spacing for the brakes you want to use. There are quite a few folks running C5 Brakes on the front of C4 cars. Check old threads for what wheels they used.

vettehardt

Adapters are Ok to use. Large spacers are not! I have been using 3" adapters on my '73 to run C4 16X9.5 wheels for nearly 15 years now on the original studs. I know many people who run the adapters with no problems. That includes a guy who runs 18" C5 wheels on his '85 and '95. I have seen those using spacers, but don't use longer studs have wheels come loose.

Crepitus

I would prefer to run a set of correct offset wheels. The problem is 1 proper set of wheels like CCW or Kodiak's well take over 3000$ out of the budget. I have 2 sets of 17" Z06 wheels that cost well under a grand for all 8. That is a strong motivation to consider adapters.
Checking with the sectioning bodies and tracks is a very good idea. (Vette club, PCA)

Thanks for the replies guys
Dave

GettReal

Run with longer ARP studs so the lug nuts will be well threaded... and do the usual of torquing in between sessions.

c4cruiser

Are you to the point where you can test-fit the C5 wheels and tires on the car with the C5 brakes in place?

The front C5 wheels will clear the brakes and these wheels have a 56mm offset. The 84-87 cars used a wheel with a 38mm offset (the 9.5x16 wheel). That difference is only 3/4". The C5 wheel should bolt on with no adapter needed but you need to check for any potential rubbing of the edge of the tire against the wheelwell or frame rail.

I have a C5 front brake setup on my 87 and I use AFS 17x9.5" wheels with the proper offset built in so I don't need adapters. I have no problems with clearances. There is very little difference in the outside dimensions (like diameter and tread width) of the 275/40-17 tire and the old 255/50-16 tire.

If there is no interference at full lock, you should be OK. The wheel/tire combo will look a little strange because the 3/4" difference will be noticeable.

Crepitus

Cruiser, Thank you for your advice.
I consider you one of the top half dozen or so authority's on C4 track prep.
I had not considered bolting the Z wheels to the hub face because I don't want to give up 3/4" of track. I bought a set of 86 spindles to assemble with the C5 brake set. As long as the adapters position the caliper the same distance from the hub center I expect to be OK because the wheel and brake combo is a stock C5 setup with the exception that the wheel spokes will be spaced 1" away from the caliper. This will add 1/4 of track on each side. Some of that will be lost at the top of the tire by adding a little camber (2 - 2 1/2*)
Unless I am missing something my main concern is if the adapters will hold up. I went with the 1" thick instead of 3/4" for 3 reasons. There is a little more mechanical strength, more clearance between the stock studs and the wheel hub face, and the extra 1/4" track could help grip a little. I dint think the reduction in wheel rate will be a big problem with the 84 Z51 springs. A little cosmetic rubbing doesn't bother me.
My biggest concern is if there is a significant chance that they will loosen or break.

c4cruiser

I guess that the final decision would be based on what the tech inspectors or sanctioning bodies say about use of adapters. At our autocross events, we have a few people running C4 wheels on C3 cars and the large adapters don't seem to be an issue.

In any event, go with a high quality set of adapters and you should be OK. While using ARP studs would be a good idea for the adapters, using the longer ARP studs on the wheel hubs may cause problems when you go to install the wheels over the adapters. ARP studs are typically a good 1/2" longer and if these studs stick out too far beyond the face of the adapter, you may not get the wheel mounting flange to sit up against the adapter face.

Consider using hardened lug nuts for both the adapter and the wheels. And a good idea about going with later spindles! IIRC, the 84 spindle has less "meat" around the holes where the caliper bracket attaches.

0Motorsport Tech

Hey guys,
As a forum sponsor and producer of custom spacers and adapters since 1996, I thought I would throw my experience into this thread.

1) ALWAYS check with the governing body/track officials if you intend on racing with any modified parts.

2) We have built adapters for all kinds of track cars, stock cars, rally cars, baja trucks, even Le Mans.
We've built them for military vehicles taking IED's in combat. We've built them for Chrysler, Ford, and Goodyear among others.
We've never had them sent back. We've never had one fail since 1996.

We're here to answer any questions you may have on the subject, and we're glad to help out in any way.

USAsOnlyWay

I called ARP and asked a while back which would be better:

1) Putting ARP/hardened stock length studs in both the hub and the adapter (1") so that you bolt the adapter on and then bolt the wheel to the adapter.
OR
2) Putting elongated ARP studs in the hub and not bolting on the adapter but just passing through the adapter and bolting the wheel on.

They said it was better to run ARPs through to the wheel and then make sure I had enough threads to go through the lug nut.

I've used the first method up until now with no problems but I guess the second option is better?

0Motorsport Tech

We can build the adapters to accomodate any thickness. Sometimes they're flat without the studs, sometimes they have studs built in, sometimes they have lug bolts instead.
A minimum of 15mm is required to build a spacer with studs sticking out. You may need to cut your stock studs down to ensure the wheel sits flush on the adapter.
If you want to go between 7 and 14mm, you may need to get extended studs to replace your stock studs to ensure they'll safely fit.
We can usually figure out the situation over the course of a short phone call.