Question about center bore sizes

[tom3]

I have seen that on older Chevys the hub is a bit bigger than later models. Say up though early/mid 90s larger, then in the 2000s it was smaller.

 

[Alex_M]

Whatever it is, you want hub centric wheels, wheels that mount securely to your hub, this is what keeps them in place, not the lug nuts. Guys who run lug centric wheels usually pick them up off the side of the road at some point.

That's more than a little bit of an exaggeration. There's nothing wrong with lug centric wheels as long as no wheel spacers are used, your studs and lug nuts are in good shape, and as long as you are staying within the load rating of the studs.

 

[Alex_M]

Hey btw, just spoke to Lenny from Motorsport-tech.com (they make Bora spacers for 30yrs and measure everything precisely). He said that although the specs all over the Internet do say 78.1 or 78.3, if you use a micrometer to measure the actual GM hubs… They are exactly 77.8!

Apparently most online sites simply upload data sets when making these databases, which creates and echo chamber, sometimes resulting in proliferation of inaccuracy.

This all makes sense since my blasphemous Ram wheels are literally spec’d at 77.8, and fit my GM hubs like a glove… Perfectly tight. And come to think of it, likely wouldn’t even fit at all if the hub was indeed .5mm too big.

Either way, I’m shocked… I’m going to measure the center bore on some GM rims next and see what that comes to.

You're talking about a .013" difference between measurements in standard imperial measurements. I'd guess that the wheels are probably machined .005" larger than the hubs to avoid stacking tolerances making a press fit, and a used set may have a bit of wear from install/removal. That spec was probably taken from a measurement someone took from a used set. May have also been measured with a bore gauge that wasn't straight in the hub bore, or slightly out of spec.

I'd be curious to see a picture of the Mopar wheels on your GM.

 

[Rayyy]

I haven’t measured the center bore of these rims yet, but will do so when I take them off to install the spacers I ordered (which is what sent me down this rabbit hole to begin with). I’ll measure my center bore of the hub too.

I would prefer everything sits extra tight, especially if adding spacers.

In any case, here are the wheels in case you are wondering which ones they are.