02TransAm/Batmobile

iTrader: (32)

I've been having a heck of a time figuring out appropriate ARP studs to pair with an undetermined wheel spacer that'll place my wheel flush with the fender that I thought I'd throw this out there for anyone else having similar troubles.

First off, I could not find a true stock stud length on the forums - some were saying 2", 1.5" and 2 1/8". I know ARP 100-7708's are 2.5" and their 100-7713's are 3.25" but those lengths are listed as UHL's - under head lengths - and I didn't know how to compare these lengths to stock's. I had my stock studs replaced by the 100-7708's previously and measured them to give a better apple-to-apple comparison between the two to ascertain the max allowable spacer thickness with ARP's studs. Based from the information I was reading here, if stock studs were 2 1/8" and ARP's were 2.5" then a 3/8" (9.525mm) spacer would offset the increase in stud length but that's incorrect.






Using ARP's measurement diagram of wheel studs I was able to measure the stock studs and provide some numbers:










Stock Studs:

Total Length: 2.073"
UHL: 1.903"
Knurl Dia.: 0.509"
Knurl Length: 0.300"
Nose Length: 0.326"


ARP 100-7708

UHL: 2.500"
Knurl Dia.: 0.509"
Knurl Length: 0.315"
Nose Length: none


ARP 100-7713

UHL: 3.250"
Knurl Dia.: 0.509"
Knurl Length: 0.315"
Nose Length: none


ARP 100-7726 - For those wanting stock length in ARP form, this is it.

UHL: 2.000"
Knurl Dia.: 0.509"
Knurl Length: 0.315"
Nose Length: 0.200"


ARP 100-7725

UHL: 2.500"
Knurl Dia.: 0.509"
Knurl Length: 0.315"
Nose Length: 0.200"


The difference between ARP's UHL and stock's UHL will give you the max spacer thickness that offsets the increased stud length. Therefore a 15 mm spacer with ARP 7708's places you around "OE spec."

ARP 7708 UHL - Stock Stud UHL = 0.591" (15.16 mm)
ARP 7713 UHL - Stock Stud UHL = 1.347" (34.21 mm)


My next question for those more knowledgeable, because the stock stud has a nose with no threads as opposed to ARP's which is threaded to the end, would a more accurate comparison involve subtracting the nose length too? The nose length on stock studs eats up more than 8 mm of allowable thread.