308 lug bolts | FerrariChat

308 lug bolts

Discussion in 'Technical Q&A' started by juanito308, Jan 21, 2004.

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  1. juanito308

    juanito308 Karting

    Mar 7, 2003
    Littleton, Colorado
    Full Name:
    Tried looking this issue up in both archives with little success. When I bought my '79 308 GTB over a year ago, I liked the black lug bolts against the OEM 14" wheels. Little did I know. Found out recently from my mechanic that they are aftermarket lug bolts that are all 5mm too short! I have had numerous "spirited" runs with the car and he said that the wheels could have easily come off! ARGG, not for the faint of heart. I have now ordered replacements from Hill Engineering.

    My question, how critical is 5mm anyway? My mechanic sounds desperate but I have put over 1,500 miles on the car since purchasing with no ill effects. I appreciate all technical input.
  2. Mike C

    Mike C F1 Veteran
    Lifetime Rossa Owner

    Aug 3, 2002
    Southeast USA
    Full Name:
    Mike Charness
    5mm is about 1/5 of an inch (almost .2 inch). Considering you generally only have 3/8 to 1/2 inch of threaded surface in contact with the hub, you're potentially cutting that contact area by around 50%. Certainly not optimal, potentially dangerous, but probably ok for cautious street speeds. But would *I* personally continue driving it until I got the new bolts? Not me, except for maybe a very occasional very short trip. There's no reason to push your luck.
  3. ronr

    ronr Formula Junior

    Oct 30, 2002
    DFW, TX
    Full Name:
    How many threads are in 0.2 inches? Probably not more than 3 or 5? Compare that to how many threads WERE engaged when the lug nut is torqued down (just for the sake of comparison as to how much engagement you're missing out on). If you've got plenty (define plenty...) of thread engagement, and the bolts are torqued down properly, then the lug studs should be properly loaded in tension. Doesn't sound that awful to me, but wouldn't hurt to get the correct length lugs installed.

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