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I’m in the process of fitting new wheels. After reading here and on other sites that the 1988 IROC have 70.3 mm hubs I ordered hub centric spacers for the front wheels. I was a little surprised when they didn’t fit. My car appently have 70.5 mm hubs both front and rear. Is there anybody else that have had this issue?
It's good that somebody brought this up. Scott at Big Brake Upgrade and I discussed this situation awhile back, emailed pictures and measurements of actual hubs, rotor bores and wheel bores. Turns out, there's a wide range of inconsistencies.
Hub size is commonly spec'd as 70.3, but more often than not it will be 70.5 or in the 70.3-70.5 range.
Center bores in wheels and brake rotors tend to be in the 70.6-70.7 range. That's not an accident or a mistake. They have to fit over 70.3 (70.5) hubs, whether it's a front hub or an axle hub. Therefore, the bore in spacers and adapters should also be in the 70.6-70.7 range to fit like wheels and rotors do.
Such tolerances are supposed to factored into the bores of spacers/adapters, but that doesn't always happen, and a bore will actually be 70.3, which doesn't fit over a 70.3 hub (that's probably larger than 70.3 anyway).
There might also be a "step" within the bore of an adapter, instead of the adapter being bored consistently through, and that "step" can prevent a long hub from fitting all the way through.
Anymore, it seems that the best way to be sure the fitment will be correct for our older style hubs is to go over these factors directly with the manufacturer, otherwise there's likely to be a problem. Or buy "off-the-shelf" and use centric rings.
I was here looking for one of Tim M`s pictures when I ran across this. I just wanted state why that 70.3 exists. Usually you will see "corvette" along with that number and thats no mistake. The corvette C5 -C7 had a hub bearing, the hub itself had a register for the rotor at 70.6 MM, above where the rotor sat the register was smaller at 70.3 Not that they would direct fit a 3rd gen but let's say you try to fit C5-C7 wheels on a 4th gen or something with a straight 70.6 mm hub they are a tight fit (.3 interference actually) So the corvette had a 70.6 and a 70.3 register...I am assuming the corvette wheels are along the line of a 70.4 pilot at minimum
12-20-2022, 07:43 PM
