How much thread on wheel bolts?

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E55BOF

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Good afternoon all. I'm beginning to wonder about the length of the wheel bolts on my (probably - don't ask...) R129. As a general principle, about what length of wheel bolt on a car would you expect to actually engage with the threads in the hub?
 
The 55k bolts stick out 20mm past the centre of the wheel that touches the hub. I would ask a fellow member with a R129 to measure the same for you. The engaging part is meaningless as it is the thickness of the hub which is only a few mm thick.
 
Pretty much all of the thread depth in the hub.
 
As said the hubs aren't that thick, probably ~1D (1 x bolt diameter) of thread? Given the bolts (and torque value) are class 10.9 (stronger/tougher than 'standard' high tensile class 8.8) i'd want full thread engagement which ideally means a couple of threads worth sticking out the back as the first couple of threads aren't full depth due to thread lead in. Factor in the thickness of the disc 'top hat' that sits over the hub and (very roughly) you're up around 20mm of bolt sticking out of the back of the wheel. Obviously if they're too short the chances of thread damage increases and too long can result in the excess interfering with handbrake mechanisms etc

Assuming the wheels are MB/AMG somewhere like alloywheelsdirect will give the bolt specs for example 16" Mercedes Alamak wheels in Standard Silver - Alloy Wheels Direct (57715) bolt pack 1L which you can then look up Packs of Wheel Nuts and Wheel Bolts from Alloy Wheels Direct to find they're 39mm long which'll be the same for all MB/AMG wheels and probably most other brands
 
Roughly 20mm will do me fine; thank you. I'll take a look at Alloy Wheels Direct as well.
 
Thanks again guys. The front bolts on the R129 I bought recently with Carlsson wheels were 5mm too short! The muppet who fitted them used 10mm front spacers, but only 5mm longer bolts than standard. Two or three turns of thread in the hub was all that was holding them on, and a couple had started to strip...

It's a good job I hadn't done any even moderately spirited driving; a front wheel coming off as I hammered round a corner could have spoiled my whole day...

Sorted now, retapped the threads in the hub, new longer bolts, and all is well. Thanks again.
 

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