froggy47

I have some used rims coming (thanks Bob M.) 18's with a 10" front & 12" rear. The front has good backspace for my c5z but the rear will require a spacer to move it out away from the tub.

My stock 18x10.5 rear is 58mm backspace and the new rim will be 18x12 with 79mm backspace.

I have run a 1/4" or a 3/8" rear spacer to clear the 335x30x18 a6s using stock lugs and lug nuts with an extended threaded shank (plenty of thread engagement, more than original).

I clear the outer fender fine with my ride height & suspension set up.

So I am familiar & comfortable with the use of spacers.

Will run that same rear tire on the 12" rim.

Now this new setup will need about a 3/4 inch spacer I think.

So do I a) put some arp longer lugs on use the 3/4 inch spacer

or

b) try some adapters.

I have never used adapters, I guess you nut the adapter on, like it's a wheel & then nut the wheel to the adapter?

Anyway do you figure 3/4 inch is right for what I need & any comments on adapter vs spacer?

If you have never used either, please don't post, and also don't post about "should have bought the wheel with the right backspace".

Crepitus

I dont think anybody really likes the idea. But it will allow me to run 100$ Z06 wheels instead of 750$ CCWs. So I have been looking in to them to. A couple things I have found; Thicker spacers have more cross section. The C3 guys use them and they seem to hold up for them. VP&B says they will be fine. My plan is tork them with blue lock tight, check run out with a dial indicator, check often. I am going to use GM lugs on inside and outer studs. On the inside the OD will need to be turned down a little. I think it is very important to be sure the lug contacts the full width of the seat.

greendot

you lucky dog, getting that deal on those wheels. I was late seeing them.

Anyway, I have used adapters as thick as 1.25" on my C3 and C4 cars with no issues. You can get hub centric adapters when they are that think so that's a good idea. Never had an issue with them loosening.

Big spacers are a bad idea. The extra bolt length gives more bolt stretch IMO.

froggy47

Thanks guys,

My setup now with the stock lugs / extended threaded nut / and the 3/8 SPACER has worked flawlessly for many years. I take out the spacer for street use in between events and for high speed track days.

The lugs are original (2004) and I am switching rims a lot as I guess I am sort of a rim collector, so they get torqued/retorqued 2x a month or more.

The wear occurs mostly to the nut threads (which are replaced yearly)

The 3/4 inch spacer (if that's what I need) is only 3/8 more than what I have used for years. I am not sure that will introduce any significant additional lug stretch than what I may already have been seeing.

So my thinking is with an upgrade to a longer ARP lug and with the careful inspection 2+ times a month, that this "simpler" setup may be preferable to introducing 5 more nuts on each corner to use an adapter.

I really have never seen a "scholarly" discussion on spacer vs. adapter and why use one vs the other. If anyone has a link to that kind of info I'd be interested in reading it.

BTW I am talking of high quality billet alum spacers/adapters not the cast junk.



I wonder if the adapter is mostly for when you want to change a bolt size/pattern?

Crepitus

Might find a little more info here.

http://forums.corvetteforum.com/auto...for-track.html

froggy47

Thanks, I read the whole web site & seems like a good vendor. Nothing about whether to use a spacer or adapter.

http://www.motorsport-tech.com/wheel_adapters.html

A spacer seems to have more "contact area" than an adapter, since the adapter has those big "counter sunk" holes for the first set of lug nuts to go into.

The contact area is important IMO because while the side of the spacer/adapter facing the car sits against a flat surface (the brake rotor actually) the side of the spacer/adapter facing AWAY from the car is in contact with the backside of the WHEEL which (more often than not) is NOT a flat surface, it usually has some machined out areas in the wheel center that may or may not match up with the machined out areas of an adapter.

You want as much contact area flat to flat as possible in all cases.

Here is a thread on a Porsche forum that mentions the use of spacers (20-50mm) from the factory on the wide body versions

http://forums.pelicanparts.com/porsc...-question.html

Don't understand why it would be fine for the Porsche engineers to use them, but many on CF think it's a bad idea?

The thread does mention that adapters are verboten as the tech inspector cannot verify the torque on the adaper easily, which does make total sense.

vettehardt

For anything over 1/2" I would use an adapter. A lot less stress on lugs and studs. I run 3" adapters on my 73 and 76 vettes to allow me to run 9.5"x16" or 9.5"x17" C4 style wheels. My dad and I have been running these adapters since about 1999 with no issues. Believe me, we autox the crap out of the 73!!!! I have never broke a lug or stud and am still using the original lugs that came with the adapters from VBP. I also know of several others running 1-1.5" adapters on their C4s to run 18" wheels. The only one I know had a problem is a guy who left his lugs loose and the wheel came off. Adapter wasn't damaged.

The adapters you just bolt on and torque just like a wheel. Then bolt on and torque the wheels.

vettehardt

If you think about it, where are "most" wheels milled out on the back side? Between the holes. That is exactly where the lugs of the adapter are so there wasn't going to be any contact in that area anyways. The only areas doing the holding are those around the lug area anyways, even if both surfaces were completely flat. With a good quality adapter it will be true on both sides. Unless you get something caught between the adapter and rotor or adapter and wheel, the wheels will run as true as if you bolted them directly on the car.

Also remember it isn't so much about the stretching of the lug. It's more about the shear forces exerted on the lug. The longer the lug and wider the spacer, the mroe shear forces and torque can be exerted on that lug.

USAsOnlyWay

I posted in the thread linked by Crepitus.

I have an early C4, it requires 3/4"-1" adapters to run late C4-C5 offsets. I've accomplished this until now using a 1" adapter with studs pressed in. No problems and when you switch to race tires, I would always check to make sure they were torqued properly.

I also picked up a different set of lightweight race rims and wanted to get more thread-nut engagment so I either needed to:
1) Replace the adapter studs with ARP slightly longer ones
2) Replace the wheel studs with ARP-7713 3" long studs and use a spacer

I called ARP, and they said option 2, no adapter, just a spacer. Didn't seem to think it was an issue. I mean, why would they make a 3" stud if it was only good till 2" out?

I've decided to do that but haven't run it yet. I would suggest buying wheel centric spacers with the shoulder (or even buying wheel centric adapters and knock out the studs if you need to). Mine have a nice close tolerance and sometimes the spacer/adapter will come off with the wheel, which gives me some piece of mind that there is no play and once bolted down it is a solid fit.

Let us know what you find.