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Hello,
I have a 2005 C55 AMG (W203 with a W209 front end).
I currently have this really scary problem of the rear lug bolts cracking over time while driving. I have aftermarket Forgestar F14 wheels that are made hub centric with a 66.6mm ring and have had them for over 6 years. However, it now seems my car wants to eat lug bolts. When this happened twice before I thought it might have been because I was using low quality lug bolts, so I installed Otis LA lug bolts which have always been trouble free for my other cars that used them. I have been checking the torque on my lugs once a month just to make sure things were OK again. (80 ft lbs in a star pattern) Today, I was checking it again and on my right rear wheel, 3 of the lugs started turning when I applied torque with a torque wrench. I pulled one of those lugs out and it had cracks in the threads!
I am thinking that it might be a problem with the wheel hub/flange. Maybe the bolt holes have wallowed out, causing the lug to move around in the hole. (Loose lugs turn into cracked lugs, based on what I read) Has anyone had an issue with rear lug bolts cracking?
I am nervous as hell to drive my car right now. I don't want my wheel to come off!
Last edited by Rahulio1975280C; 01-01-2023 at 06:10 PM.
Reason: More information
post a pic.
Are you using the correct bolts for the wheels? Conical or spherical contact?
I have been on mercedes forums for 13 years and never heard of this problem.
Have you contacted Forgerstar?
1991 964 Turbo, 2002 Black E55, 2002 Black E55 " The Beast"- 2014 E63s
I agree , you need to know what type of bolts the original wheels take and what kind the forgester takes? I am sure Mercedes uses Ball seat kind and the aftermarket uses conical type. Hoe that helps
I agree , you need to know what type of bolts the original wheels take and what kind the forgester takes? I am sure Mercedes uses Ball seat kind and the aftermarket uses conical type. Hoe that helps
took a quick look at the forgestar site and not easy to find the bolt type on the spec sheets... These aftermarket companies are so vague. puzzling.
Hello,
I emailed Forgestar and got the following reply:
"All Forgestar Wheels are made for a 60 degree conical lug nut!"
This makes sense to me as that is the type of lug bolt that was provided with the wheels by the distributor I bought from, SonicTuning.
When I feel the lug seat, it has a sloped (cone) shape to it. So I think I have the correct lug nuts.
They are 12x1.5 conical seat with a 17mm hex head and a 28mm shank length.
what do you mean by cracks in the threads? where are the cracks? in the thread that is in the hub or out of the hub?
Are you sure the 80ftlbs torque is correct? Seems a bit low. Should be in the tire change/spare section of your owners manual. I have seen 130nm/95ft-lbs. Are there signs of wear on the rim?
what do you mean by cracks in the threads? where are the cracks? in the thread that is in the hub or out of the hub?
Are you sure the 80ftlbs torque is correct? Seems a bit low. Should be in the tire change/spare section of your owners manual. I have seen 130nm/95ft-lbs. Are there signs of wear on the rim?
I pulled all 5 lugs and 3 of the lugs have cracks between the 8th and 9th thread from the tip. This is right about where the wheel surface meets the hub flange surface, so just out of the hub. (See pictures.)
I checked my manual and it says 80 ft lbs is the correct wheel lug bolt torque specification. (See picture.)
I inspected the wheel lug seats and they actually seem worn, but I cant tell if its abnormal. The conical lug bolts still seem to fit into the hole ok, the Forgestar F14s are definitely to be installed with conical seat lugs. However, I noticed that each of the lug bolts has a band worn in it at the top 1/3 of the cone of the lug bolt, I would think it should be more spread over the entire surface.
The Forgestar F14s are made hub centric with a centering ring. I checked to see if the ring on the wheel hub was deformed or rusted away, but it seems fine. When I fit the wheel onto the hub, it appears to be supported by the hub and is not sliding around on the hub. All I can do is spin the wheel on the hub to line up the lug holes so I can installed the lug bolts.
wow a mystery. and you are sure the hub adaptors seat well on the hub? They seem embedded into the wheel
Something is moving to stress the bolts. Very odd. btw you dont use a bit of oil or grease on the bolts?
The hub rings are nice and snug in the bore of the wheel. They take the stock Forgestar hub size of 72.6mm down to the Mercedes size of 66.6mm. They fit into the bore of the Forgestar F14 wheel and are just inside the hub surface of the wheel. They are not so deep in the bore that the ring would not make contact with the wheel flange on the Mercedes. When I hold the wheel onto the wheel flange it seems the hub ring installed in the Forgestar wheel is slipping onto the formed ring on the wheel flange so that the stress of the wheel is on the hub itself and is not resting on the 5 lug bolts.
The purpose of the lug bolts is to clamp the wheel to the wheel flange of the car, but over time, as a drive, the lug bolts are forming cracks in the threaded section of the lug bolt.
My next move is to simply get rid of the Forgestar wheels, I have no idea what is causing this to happen at this point.
I sourced a new set of Mercedes wheels to replace the Forgestar wheels with and wanted to verify if I have an issue with how much thread is going into the hub.
Getting about 20mm of thread with the Forgestar setup versus 17mm of thread with the OE setup. So that can't be the issue.
01-01-2023, 05:34 AM
