Hey Folks – First time poster here. ’86 Corvette owner. I'd like to bounce something off you experts.

Ok, my “current” setup for wheels is 5-spoke C5 wheels with 1” adapters, which bring the wheels pretty much flush with the fender well lips.

I’ve purchased C7 Z06 style replica wheels (17” DIA x 9.5”W w/ 275/45’s). With my 1” adapters the Z06 replicas sit a little “proud” (outward) of the fender well lips due to the offset difference. I’m not crazy about this look. Without the adapters, the wheels are a little too recessed for my liking as well.

To make a short story long:

These wheels are advertised as fitting 88-96 C4’s. Knowing the 84-87 track width is 1” narrower overall than the 88-96’s, I purchased ¾” adapters, where the factory wheel studs protrude slightly. This would put me ¼” wider on each side than the 88-96 factory hub-to-hub width. The replica wheels have recesses between the lug holes, but the factory studs still interfere with installation. The reason for ¾” adapters was due to no ½” adapters available (only spacers).

Therefore, if I want these wheels to fit the way they’re intended, I need to space them ½” with spacers, which is perhaps frowned upon.

Looking for input from you guys, here are my perceived options:

- Utilize ½” hub-centric spacers and install ½” longer wheel studs

- Utilize ¾” hub-centric adapters and install shorter wheel studs (I’m not crazy about this, as I worry if factory wheels would have sufficient thread engagement if the adapters were removed).

- Install with no spacers/adapters and live with the slightly recessed look

What say y’all? Thanks for your time.

 

A lot depends on how you drive the car. I have 3/4" adapters on my '90 with C5 wheels. The previous owner cut the studs to make them fit. While I don't love the idea, they haven't given me any trouble, but I drive pretty tame most of the time. They are not something I would be comfortable on a road course with. The safest option is long studs and spacers, but installing them will not be fun.

 

Thanks for the info, jv. Likewise, I'm hesitant to cut my studs. Researched replacing the studs a little. Curious if longer studs can be installed without removing hubs, etc.

 

I don't think you should have to live with wheels sitting too far inward. I hate that look, and from a performance perspective it's not ideal either. So...
Like jv9999, I recommend the first of these two options. This will have by far the most safety and structural integrity. You really don't need hubcentric anything. That doesn't help hold the wheel on - it just makes it a little easier to mount the spacer and wheel while you tighten the lug nuts. All the force holding the wheel in place comes from the friction of the interface between the hub face and wheel mounting surfaces. The force for that just comes from the tension the lug nuts apply to the studs. The wheel must not rely on the center bore to center itself! You cannot get more simple or secure than sandwiching a solid piece of metal between the hub and wheel: there is literally nothing to fail here and no reduction in the friction. The only thing you have to do is ensure your studs are long enough to get adequate threads captures by the lug nuts, as you clearly already know. The only thing that sucks about this is replacing the studs in the rear hubs (from what I understand - never done it on an early C4 like yours). The fronts aren't even hard.

I'm not a fan of thinner adapters. The reason 3/4" is the thinnest they make is because any less doesn't leave enough "meat" to support 10 holes and 5 wheel studs safely, and because it's on the ragged edge of not allowing enough threads for safe lug nut capture of the hub's original studs. With 12mm studs (is that what an early C4 also has?), you need about 12mm (1/2") of threads available to the lug nuts (that's 8 turns of the nut). But with a 3/4 thickness, 1/2" is going to be the very most you can probably get - maybe less. If you can pull one wheel and install one of your adapters, count the turns you can get for the lug nut holding the adapter to the hub. Then see how much you'd have to cut off and estimate how many fewer turns that would entail. If you can get the eight turns, and you think you can cut the studs and still be able to start the lug nuts on them properly, then it's okay to use them. This has the added advantage of not costing you any money!

 

Thanks for the thorough response, Matthew. I agree with you on the clamping force of the wheel mounting surface. I've had non hub-centric adapters and installing wheels on them makes me cringe when sliding them over the wheel stud threads. The hub "lip" aids with removal and installation.

I'll mock up the 3/4" adapters one more time before returning them to measure how much of the factory studs would need to be removed.

 

Oh, if you can still return the adapters for a refund, then I'd do that and go the spacer-and-longer-stud route. The one piece of research you should do beforehand is to look up the procedure for replacing the rear wheel studs on your car. Just make sure you can do that job. My factory service manual for my 96 won't cover the procedure on your early C4.

Addendum:
Here's a thread on getting to those rear studs.

 

I actually read that thread recently. I've found several threads on removing the studs from early C4's but seemingly no conclusive consensus. Guess I'll yank the wheel off and have a look.

 

Well the verdict is with the 3/4" adapters installed, the factory studs protrude approximately 1/4" (see picture below). Based on Matthew's 8 turns = 1/2" thread engagement mentioned above, cutting the factory studs would prohibit installing wheels without adapters. Currently the wheels require exactly 8 full lug nut revolutions to seat without adapters. This is based on Matthew's suggestion above and recommendations to have thread engagement equal to or greater than the stud diameter.

Approximately 12 revolutions is required to seat the nuts of the adapter to the factory hub. Therefore, cutting the studs gives me enough thread engagement for 3/4" adapters, but not enough to install wheels without adapters. If I were keeping the car forever I wouldn't mind this. But I think the longer stud route is the best, as future owners of the car may want to install factory wheels.

There's a thread by Raidmagic from 2013 illustrating that the rear wheel studs can be replaced without removing the hub: https://www.corvetteforum.com/forums...al-1987-a.html. I am hoping this is correct for an early C4.

I think my best solution is to install 1/2" longer studs with 1/2" spacers to achieve the 88-96 track width these wheels were intended for. I'm trying to research what the factory stud length is so that I can find studs 1/2" longer, or as close to 1/2" longer as possible while still using my chrome acorn lug nuts. Can anyone verify the factory stud length? 12mm DIA X 1.5 X length?




Thanks again.

 

Multiple sources including Dorman, Wagner, and Raybestos all say it is 41.5mm in length. Here are the full specs per Dorman. This appears to be the same stud in all C4, C5, and C6 Corvettes.

 

It is possible to change rear studs without removing the bearing. I’ve done it. I made some tools to do it with. I’ll try to find them tomorrow and take a pic. I use ARP longer studs with 1/2” spacers and have never had a problem while tracking the car. I’ll take a pic of the package for part number.

 

You guys are awesome!

 

It appears approximately 2" length is what I would need. Anyone familiar with ARP's 100-7726, and does that sound correct? Any other brands to look for?

There's a Dorman stud on Summit's website: https://www.summitracing.com/parts/rnb-610-323

And here's the ARP: https://www.summitracing.com/parts/arp-100-7726

The knurl diameter is different by a few thousandths. ARP has .509" dia (12.93 mm), and the Dorman has a .504" dia (12.8 mm). The factory studs appear to have a .501" (12.73 mm) knurl diameter.

 

I had longer ARPs on my C4, and no complaints at all. They are generally considered the gold standard, but they are spendy. I just bought some Dormans for my Camaro, so I'm not elitist about it! I don't think those teeny differences in knurl diameter matter at all, especially since they are erring on the side of being slightly larger.

 

You da bomb Matthew. I sincerely appreciate your help man.

 

OP - you've most everything required except maybe 'good advice'. To determine wheel stud lengths required you measure first what you've got and confirm all 20 are same! You could easily end up with another maybe larger 'parts bucket'.

Measure exposed stud length of what's there now! 'rotor hub face to tip'!

I wouldn't say MM is 'da bomb' but he is for sure opinionated! Me too!

It actually wouldn't hurt since you've got wheels already to post the width/offset info from the 'back-side'! Measure what the wheel will actually require for stud length using your capped wheel nuts if you want to retain them. Get your hands on a wheel stud 'locally' for comparisons. No WAG for ordering!

Compare what you measure to the Dorman 610-323 that was mentioned in the thread you referenced. A wheel stud with 'dog point' is generally preferred but not always possible. You're concerned with thread length and under-head dimension vs a generic thread length from Dorman.

If the studs in your hubs currently were 'dog point' you likely wouldn't be here!! Correct 'dog-point' fabricated studs and use what you've already bought? Might be an interesting thought!

 

Wheels are 17x9.5 w/ 54mm offset & 7.38" backspacing. All 20 studs are indeed the same, but need to verify they're factory length.

 

Sorry just saw your edited post. The current studs do not feature a dog point.

 

I knew that and I saw your snapshot. You might consider a visit to a dealer and compare to GM product. A 9595682 might be an interesting comparison. Glue a nut to a stud bore and measure depth required.

 

I measured the wheel studs from hub to end, and got approximately 1 5/16". The hub thickness appears to be approximately 3/8". With these two combined I get 1 11/16" (1.6875"), which is close to the advertised factory length of 41.5mm, or 1.634" according to my back of the envelope math.

With the caliper & rotor off, it appears I can remove the studs without removing the hub assembly if I remove the parking brake shoes. We'll see..... I sprayed the studs with PB Blaster. Once I order & receive new studs I'm hoping they won't put up a fight.

 

I personally run 3/4" (actually 20mm) spacers with 1" longer ARP studs. (85 cradle in 88 car)

I knocked the China studs out of the hub-centric hub adapters and now they are just thick spacers.

I run the car on the street, used to do autocross, and now run top speed events. I have confidence in the longer stronger studs holding everything together.