MN80Vette

I really like the gray 18x8 BOSS 338 wheels I have on my '80:



The center of stock wheels have the same inside diameter (ID) as the outside diameter (OD) of the hubs. The inside of the wheels centers them on the hub - hub centric.

What I don't like about the BOSS 338's is that they are not hub centric like the original aluminum alloy wheels. The lug nuts hold the wheels in place on the vertical plane, not the inside of the wheel. The ID of the wheels is 3.25"



The OD of the rear hub is 2.75":



I thought I was having problems balancing the wheels, but the out-of-balance feel on the highway was caused by the wheels not being centered on the hub, not the wheels/tires being out of balance. A guy at the tire store explained that if you put the wheels on and tighten them up part way, lower the car, and finish tightening the lug nuts, the wheels can be moved off center by the weight of the car before the lug nuts are completely tight, thus causing the out-of-balance feel on the highway.

Well, I had our machinist son make me some hub centric adaptor rings to make up the difference between the hub OD and the wheel ID.



Here is a picture of how they fit inside the wheel:



And here is a picture of how they fit on the hub:



They work great!!!

Next, I am going to have him make a new hub centric adaptor that includes an integrated spacer to get some of the 1/2" of backspacing I lost with the BOSS 338's.

Mako72

Excellent! I've been wanting to check this on my TT2's as well. I know they're not hubcentric.

MN80Vette

Do you have a caliper that can measure the ID of your TT2s? If so, I'm curious what it is.

I don't know whether the 3.25" is "standard" for after market wheels or unique to BOSS and maybe a few other wheels.

BTW, I found out that the OD of the front hub is not the same as the OD of the rea hub. I had to tap the rings on the rear hub but they don't fit the front hubs.

Front hubs are 2.80 OD yet the original wheels fit front or rear. I don't have any stock wheels to measure, but the ID must be at least 2.80" I guess wheel ID to hub OD tolerance doesn't have to be exact.

Can anybody post the ID of stock aluminum wheels?

chevymans 77

The lug nuts should center the wheels not the hubs.

I would check that you have the correct lug nuts.

What style lug nuts do these wheels take?

Neal

Billysvette

I have the Boss 338 wheels and i have no problems,mine are centered perfectly.You might have a problem.

MN80Vette

Original Corvette wheels are hub centric. Almost all aftermarket wheels are lug centric to be universal, but hub centric adaptors are available for some cars.

Like most aftermarket wheels, BOSS 338's take standard 7/16-20 cone lug nuts. With lug centric wheels, 100% of forces on the wheels go to the lugs. Hub centric wheels limit the stress on the lugs because the hub helps keep the wheel centered.

That's not a problem for normal driving, but forces are higher in autocrossing. Hub centric rings reduce the risk of sheered lugs.

Billysvette

I dont think you are racing those wheels ,are you?these wheels are not race wheels,they are just good for the street,and cheap.thats probably why they are not hub centric.

RobbSalzmann

I have these exact wheels in chrome. Any chance you could make a set of those for me? How much would that cost?

chevymans 77

the shear strength of a 7/16-20 grade 8 bolt is around 13500 psi.

there are five studs on each wheel, add the clamping forces of the lug nuts and consider that is on a 3300 lb car with close to a 50/50 balance so divide the total weight by 4 and that is what each wheel is carrying.

the five studs aren't anywhere near there limits no matter what you do with the car.

now I'm no engineer so I could be way off on this one.

I did talk with a group of engineers at work prior to putting the adapters and Z06 wheels on my car. Once they looked everything over I was convinced there was nothing to be concerned with.

I do agree with you that the hub centric wheels will limit the stress on the studs.

Neal

MN80Vette

There's racing, and there's racing. I don't do any serious racing. Some events don't even require a helmet. I am sure my "racing" is well within the limits of these wheels.

Most aftermarket wheels are not hub centric because hub size varies so much. The variety of bolt patterns is bad enough for manufacturers to match without adding hub size inventory too.

MN80Vette

Of course lug centric wheels are within some bench measured threshold, otherwise they wouldn't be on the market. However, the effects of stress are cumulative. The lugs on my car are 32 years old and have gone through an unknown number of tightening cycles, improper torque, potholes, etc. with the POs. As CO, I am going to limit the additional stress I put on these lugs.

GM engineers who know this stuff better than I do designed my Corvette with hub centric wheels. Lug centric wheels are not better, so I am sticking with hub centric.

RobbSalzmann

When I bought these wheels on my car (a 77), I was only able to get a few turns on the factory studs so I replaced all the studs with longer ARP bolts. The wheels do center just fine, but I like the idea of the ring thing you have. I held the 3/8" spacer centered in place with a bit of green tape around the edge.

Did you have to replace your studs to install these wheels on your car?

MN80Vette

No, I did not need to replace the studs for these wheels. The rule of thumb I heard is that the threads the lug nuts grab need to be at least the diameter of the lug (7/16"). I had that many threads with standard conical lug nuts and the BOSS wheels.

I tried 3/8" spacers to get some of the 1/2" backspacing of BOSS wheels, but they weren't hub centric and the lug holes were too big to accurately center the spacers on the hub. I switched conical lug nuts with an extended shank that fit inside the lug holes of the wheels. They grab more threads than standard conical lug nuts.



I just sketched out a hub centric 3/8" spacer yesterday and gave it to our son to make.



These are going to be more expensive to make than the adaptor rings alone because the stock needs to be 6.25" in diameter vs. 3.25" and the metal outside the ring needs to be machined from 3/4" to 3/8".

noonie

MN80Vette

You may want to use some antisieze on the hub and alum ring.
My wife's Caravan has alloy hub centric wheels and I had one hell of a time getting them broken loose from the hub due to corrosion. Very tight fit. On my 1 ton, I had to loosen the nuts a bit, lower the truck back down on the ground and shake it from side to side to break it loose. Use antisieze on all the rims on all vehicles now.

I made a set for an old set of rims and made the rings enough of an interference fit on the rim that I had to chill the ring and warm the rim a bit.

MN80Vette

That is a good suggestion. Thanks!

I thought about that last week. When I put them on a few days ago, I was "just going to try one" and putting the lug nuts on lightly finger tight so I could try to wiggle them. THEN I decided to tighten them up for a test drive. One thing led to another, and now it's going to make more time to do the job right with anti-seize.