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Discussion Starter #1
want to use these sl500 wheels, bolts for the r170 are 12x1.5x61 are too long for these wheels. the sl's run a 14x1.5. I cut some original r170 bolts to match the length of the factory sl500 bolt but threads on the r170 bolts don go all the way up the shank. i have 12mm spacers for the rear which does not require cutting bolts but that increases offset in the rear to 43 et. Which bolts work? Is cutting the way to go...help! See images.
 

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Registered 2007 SLK350
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562 Posts
Cant help specifically, but the normal specification for bolt length is:




Bolt must screw in for MINIMUM depth equal to the bolt diameter for maximum strength.




So for M12 you need to screw in for a depth of minimum 12mm (or approximatly 10 full turns in this case)



If you can, cut your bolts to achive this. Be careful that the bolts are not running out of thread before tightening against wheel, as shank is probably not fully threaded.



However more concerning is you say that the holes in the SL500 wheels are 14mm, which is too big for the M12 bolts.


I believe it is possible to buy bolts with M12 thread, and 14mm shoulder to allow this.


Spacers will put more load on the bolts, but I do not know how much and if it affects your application.
 

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Premium Member 2001 SLK320/2000 SLK230
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Sorry to say trying to use a 14mm wheel with 12mm bolts is a really bad idea. If I had to (and have done some strange things before) a set of these with 14mm lug nuts might work but do not know how much torque they can take. Caveat y'all.

ps in general a spacer decreases the effective offset. 12mm is nearly 1/2 inch and will require a hub centric spacer and not a flat one. My experience with SLKs is the clearance issue is usually over the front brake caliper and under the rear fender lip.

pps 7-10 turns on both ends would be a minimum. Less can do nasty things.

ppps that picture of the rear wheel is scary, looks like the wheel is an inch past the lip and doubt that you can roll them that far. Lose the spacer. At one point I tried a 19x9 with 22mm offset & 255x35R19s on my 320. The tire just touched the rear fender lip.
 

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Discussion Starter #4
Thanks for the information. Ruled spacers out completely for the rear, protruded out too far as you could see on the image. Yes, ran out of threads before things snugged up with cut bolts, "factory bolts only have threads up to a certain point on the shank" so I have to order new bolts. See image and advise...I won't purchase until Friday this week. The 14 to 12 conversion looks like a good option as well, that would change things from bolts to lug nuts which would work as well. ball seats are required. I have a full set of lug nuts with proper ball seats which would work with the 14 to 12 conversion so I now have that option as well. However as you mentioned, not sure about torque at that point so I think I'll pursue the 28mm set but I really would like to hear your opinion on this! My front factory 16" wheel offset is 37, the SL 18" wheel for the front are 30 but it fit and didn't make any contact with caliper, just ran out of thread with the cut bolts prior to things tightening up! Is that 7 to 10 turns until things become too tight to tighten by hand? Thanks for taking time reference my issue, I'll let you know once I get things sorted out!
 

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Registered 2008 SLK350
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The 14 to 12 conversion looks like a good option as well, that would change things from bolts to lug nuts which would work as well. ball seats are required. I have a full set of lug nuts with proper ball seats which would work with the 14 to 12 conversion so I now have that option as well
Instead of using nuts for the 12 to 14 conversion you might consider these type of M12R14 bolts.
https://www.spurverbreiterung.de/index.php?language=en&currency=EUR&cat=c354_nach-Gewinde.html&gw=2&kf=30&

Also sold on your side of the pond afaik.
 
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