Hi, just went to a local garage to have my wheels rotated on my 2014 GLK250. Took quite some time and they explained that someone apparently used a standard lug wrench and distorted the "flower" pattern on lugs. It's a CPO with 35k on it so I don't know the history. I looked at the lugs and while there are scuff signs, nothing looked damaged. I also looked at the lug wrench provided by Mecedes in my trunk area and it doesn't haven kind of accommodation for this "flower" pattern. They guys there said that if I get a flat and call roadside services, a lot of those guys don't have the right tool to remove my tire. Seems moot as I have run flats and no spare to change out. Is there any truth to any part of what I was told? They've got me thinking I should buy a set of replacement lug bolts with normal heads to avoid future trouble. Not too concerned about wheel locks or theft. While I believe in having Mercedes handle most of my maintenance, I'm finding it hard to believe that non Mercedes shops can't handle this without a special adapter especially since my supplied lug wrench looks average to me. Thanks for any insight anyone may have. Any links or sources for reasonably priced aftermarket would be appreciated. I did some searching there and it's not super clear what will fit. I did do some searching on the forum and haven't found any answers.

 

 

These below bolts do take a special socket. However some shops don't have the right socket and ram on a 17mm socket which can damage the head. Just because the car is CPO does not mean that some third party shop has not been working on it. CPO is just a sales gimmick to make you think the car you are buying is special,

 

So. the wrench that comes with the car is a 6 point hex, no adapter. Johnnu says that's fine on the bolts pictured by formerjeep guy. But Former jeep guy, are you saying that I'm missing an adapter for my mercedes lug wrench because it's on ly a 6 point? I'm not a tool guy but I googled side by side photos of a 6 point and a 12 point and can see the 6 point can handle high torque and air guns with no slippage. Hard to imagine a garage with 3 lifts and 6 bays wouldn't have a at least one set of 6 point impact sockets and have their staff trained to only use those?? But all I care about is moving forward and if I need to buy and keep an adapter with my lug wrench for future?

 

My glk350 did not come with the right wrench either and I bought it new. Some folks like JohhnyC think its fine to jam a 17mm socket on there but I prefer to use the correct tool for the job so I got one of these:
It is not an adapter, it is a socket.

It is not at all unusual for a shop that does not regularly deal with new german cars to not have the correct tool.

 

 

I own a bunch of obscure Mercedes-Benz tools, and you know which one I don't have because even the manufacturer doesn't have it in their catalog? That would be this special socket. I had these capped lug bolts when i first got my car, went to the dealership asking for the socket they use, they said 17mm. I ended up just buying regular grey hex lug bolts, then eventually going to titanium or black oxide hex bolts.

It is still just a slight variation of a 17mm Hex, clearly the engineer designed it to be removed with a regular hex or that special socket. Capped lug nuts or lug bolts are not durable enough to be hit with an impact gun.

I still retain the belief that there are numerous tools that can interchange just fine; such as 8mm and 5/16 or twelve-point on hex.

 

I see a number of old posts pertaining to star and flower heads on lug bolts as opposed to typical hex head. My question to the group is a bit different. I own a 2011 GLK 350 2WD. Recently powder coated the wheels and now looking to exchange original lug bolts to new. Question....why are these lug bolts threaded on only 20mm of a 45mm shank leaving 25 mm unthreaded? My old lug bolts show wear/use of only 10mm of the 20mm of the threaded shank. The remaining 10mm shows no wear/use. I've located aftermarket lug bolts from a reliable supplier that describes their lug bolts for MB GLK SUV but the shank of 45mm is entirely threaded. I'm of the belief that only the threaded portion, roughly 10mm, and the seat itself against the wheel is what holds the wheel in place. In other words, the threaded and unused portion of the shank serves little purpose in the wheel's function once properly torqued just like the 10mm of the 20mm threaded shank that shows no wear. Please let me know your thoughts on this. Thanks to all who comment. Much appreciated.

 

Selection of wheel bolts by the manufacturer is probably as much convenience, experience, and serviceability as direct design. Note that Mercedes uses essentially the same design on vehicles of varying size and weight.

Shoulder bolts, which are bolts that have a portion of the shank unthreaded, stretch and twist less than fully threaded bolts in high torque/tension applications. Head bolts are a prime example. Head bolts are almost never fully threaded because the tightening force must be fully transmitted to the threaded portion to assure the correct tension is achieved to seal the head against the gasket and engine block. The safety factor on head bolts is usually rather small compared to other applications.

Other applications of shoulder bolts are where shear force will be applied to the bolt shank, the shank will pass through and contact the other component and threads would cause damage, or the shank acts as an axle or pivot point.

I think wheel bolts fall into the head bolt category. The point of shear stress concentration on a wheel bolt would be where the last thread meets the hub, not along the shank. But a wheel bolt should never see shear because the tightening force of the multiple bolts should be sufficient that friction between the wheel mounting face and the hub can withstand the acceleration and braking forces applied to the wheel without slipping. I would also expect the safety factor on wheel bolts to be quite large.

You are probably okay if you’re sure that the bolt manufacturer is reliable (I found some inexpensive bolts to replace the damaged capped ones on my GLK failed on first use). Another thing to note is whether or not the bolts actually have a 1-2 thread shoulder below the head. Many bolts that don’t have to be flush against the device have that small shank because the most likely point of failure when tightening is where the thread meets the bolt head.

 

Sorry for late reply....was out-of-town for several days. Your explanation is well noted and thoroughly understood. I appreciate the time to pass along your comments. The bolts that I'd purchased were advertised "for MB GL GLK SUV's". Of course, that doesn't guarantee that they will NOT fail. But it did provide some level of comfort knowing that that while aftermarket, they are designed for my vehicle. I intend to try them, torque to recommend ft/lbs, and after 1,000 miles, check and torque again if needed. Again, thank you for your response.

 

I think the 1000 mile check is recommended for all aluminum wheels.

I tighten in 4 steps when installing a wheel. For all bolts at each step: snug up, ⅓ of recommended torque, recommended torque in one movement without stopping, recheck at recommended torque.

You will know right away if they’re going to fail. When approaching the recommended torque, it will feel like the wrench needs to be ratcheted to finish tightening because the bolt is stretching. Continuing to tighten will cause it to break.

 

Thank you for your additional comments. Will follow your advice and will advise if anything goes sideways. Thanks again.