OEM Alloy Wheels & knocking sound

[Mark with the SLK]

Hi

I'm new to the forum and will be grateful for any help. I fitted a set of OEM alloys (with tyres) to my 2001 SLK 230K, they are all sized 205/45/17 ET35. My original MB alloys are sized 225/50/16 ET37 on the rear and 205/45/16 ET30 on the front.

I've now got a light tap..tap..tapping sound at the back mid section of the car, sounds like a cable is being scuffed or flicked, no heavy or drastic banging sound, just the light tapping. I used the shorter bolts that came with the new wheels.

I realise that we are talking just millimetres here, is everything really that critical?

I looked over, under, everyhwere on the car but can't find where the tapping is coming from. I put back the originals and everything's fine now, sept I don't have the great look of my new alloys.

If you can shed some light I will be very grateful.

Regards

Mark

 

[Tony]

You don't say how wide the wheels are - I'd guess they're 7 or 7.5J from the tyres. Have a look at:

http://www.chris-longhurst.com/carbibles/

Go to the wheel and tyres section - it tells you everything you'll ever need to know. The problem must be that the wheel and tyre combination are bigger than the original or offset wrongly. The standard SLK rear wheel is 8J ET30, so if you had 8J ET35, your wheels are going to be set outwards by 2mm (wider track) - so they might touch the bodywork. But if they're 7.5J ET35, they're going to be inset by 4mm (1/2 inch / 2 - 2mm). Et cetera. Also check the rolling radius on the calculator. If this is too big there will be problems. If your rolling radius is more than 3% out various stuff doesn't work - like the cruise control and ABS. It should be kept within 1% ideally.

 

[Mark with the SLK]

Tony

Thanks for the advice and link, you're a star, I appreciate you taking the time to write a response. I'm trying to understand a lot more about the dynamics of wheel engineering, although it?s not perfectly clear to me yet.

I can't believe that 2 or 3mm can make that much difference under the wheel arch. What if I was to ride over a bump or something, my existing wheels can't surely be riding 2mm from the bodywork or shocks?

My existing MB rear alloys are stamped ET37 and the front are ET30. These wheels were delivered on the car when I bought it new on 26th March 2001.

so....

existing front ... 205/55/16 8J ET30
existing rear ... 225/50/16 8J ET37

new (all round) ... 215/45/17 7.5J ET35

Rolling radius calculator shows a variance of less than 1%.

I've checked the bodywork and new tyres for scuffing marks, but I've found nothing.

The noise is like the glue of a new-tyre sticker is sticking to the tarmac on every revolution. It's like a "sticky-tapping" sound (I realise that?s a crap description).

All and any advice welcome. Thanks again Tony

Regards

Mark

 

[Tony]

Those wheels should fit. (I think you'll find the standard SLK front wheels are 7J not 8J). All SLKs can be fitted with optional wheels:

Front: 17X7.5J ET37 (Although ET35 is also OK)
Rear: 17X8.5J ET30

So your front wheels are to spec and your rear wheels will have more clearance than the above both between the bodywork and the suspension mounts. Also if you look at the SLK board of the American site benzworld.org you'll see that some people put some pretty wild wheels on without any ill effects (except on their spine).

I hate to suggest a visit to the dealer, but I can't think of any alternative. I'd be interested to know what the problem is. I've bought some new alloys for my SLK - I got some CLK alloys which are 17X7.5J ET36 and 17X8.5J ET30 (in the pattern of the SLK320 standard 5 spokes but a bit bigger). I was surprised that the set of 4 cost £500 from the dealer. I haven't fitted them yet.

 

[Mark with the SLK]

Problem solved!

Tony

Sorted! I took the car to City Tyres this morning (a recommendation from Peter at the local MB stealer). Those guys were great at fault finding. They eliminated everything in a logical fashion and found... wait for it... the (new shorter) bolts that came with the new alloys were irregular in length. Some of the bolts were up to 3mm longer. Hence, the longer (irregular) bolts were (just about) scraping the inside of the hub mechanism.

All of the bolts were then cut down to a standard length and guess what...no noise anymore. The wheels look fantastic, take a look below.

Thank you for your help, it is very much appreciated to know that I was not alone in my time of need. I hope I can be of assistance to someone on here one day.

Regards

Mark

 

[Tony]

Glad it's sorted Mark. BTW, I can't see the picture - it's just a red cross, maybe my browser is duff.