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Discussion Starter #1
I've browsed through tons of posts on this board and others trying to find the widest possible wheels and tires we can fit on our SLK. I autocross regularly and compete very well with others on street tires. I want to make the move to slicks to see what I can make the SLK do compared to the usual suspects at autocrosses.

I want wider wheels that are relatively strong and light, but don't need to withstand potholes (race only.) Wide tires without rubbing with a lowered SLK55.

I've come across these posts from member PropDr as he also was trying to find the widest wheels and tires for his SLK.

In this post: http://www.slkworld.com/125682-post14.html
According to conditions as found on my car 245/35/18 tires can be fitted to the font on 8.5” wheels with an offset of 30 to 35mm (best would be about 32-33)
The rear can take up to 285/30/18 on 9.5” wheels and 295/30/18 on 10”wheels. For the 9.5”wheels you need an offset around 40mm and on the 10” wheel about 44mm.
All this is just me theorizing without any guarantee.
In this thread, he describes the troubles he had with a wide Hankook 285/30/18 in the rear with a 42.5mm offset
http://www.slkworld.com/tires-wheels-brakes-suspension/22052-285-18s-lowered-171-a.html

This is my plan
Front: TSW Interlagos - 18x8.5 ET32, Hoosier A6 245/35/18
PropDr says our stock rear wheels and tires (18x8.5 ET30, 245/35/18) fit perfectly in the front, and explains that a 32-33 offset would be even better. TSW just so happens to make that exact size.

Rear: TSW Interlagos - 18x9.5 ET40, Hoosier A6 275/35/18
Again, right on PropDr's recommended offset. His 285/30/18 rubs a bit on the inside, but his offset of 42.5 puts his wheel 2.5mm closer inside than the TSWs with ET40. Also, the extra tire width of a 285 will cause issues. I believe he previously had a 275/35/18 that fit fine on the inside.
EDIT: 255/35/18 Hoosier A6 has equal width without changing diameter too much. See specs below.


According to TireRack Comparing tire size specs.
Numbers below are: Section Width | Tread Width | Overall Diameter​
Front:
OEM (F) Pirelli P-Zero Rosso 225/40/18: 8.9" | 8.1" | 25.1"
OEM (R) Pirelli P-Zero Rosso 245/35/18: 9.6" | NA | 24.5"
Hoosier A6 245/35/18: 9.8" | 9.1" | 24.7"
  • Hoosier will be 0.4" shorter, but a full inch wider than OEM stock front
  • Results in 0.2" taller ride height
  • Extra 2mm offset of TSW wheels should compensate for slight increase in size compared to rear stock wheel in front
Numbers below are: Section Width | Tread Width | Overall Diameter​
Rear:
OEM (R) Pirelli P-Zero Rosso 245/35/18: 9.6" | NA | 24.5"
Hankook RS-3 285/35/18: 11.4" | 10.1" | 25.9" (PropDr's thread link above)
Nitto NT-05 275/35/18: NA | NA | 25.63" (PropDr's setup before above)
Hoosier A6 275/35/18: 10.7" | 10.3" | 25.5"
Hoosier A6 285/30/18: 11.5" | 10.9" | 24.9"
EDIT: Checked the 255/35/18 Hoosier specs and was surprised!
Hoosier A6 255/35/18: 10.8" | 10.3" | 24.8"

  • Hoosier 275/35 will be 1 full inch taller than stock rear
  • Results in .5" ride height increase
  • #1 Rear spring pad will reduce rear ride height by 8mm
  • Hoosier 275 is 0.7" less wide than PropDr's Hankook 285 that rubs
  • 285 is significantly wider than 275, too much tire to fit
  • Hoosier 255 is actually 0.1" wider than Hoosier 275
  • Hoosier 255 has the same tread width as Hoosier 275
  • Hoosier 255 is only 0.3" taller than rear stock, no rake issue
Overall I think the setup will be ok. I would gain just a little bit more rake, but that should allow for rotation (cornering.) If anything, I believe lowering springs lower the rear slightly more than the front, so the Eibach springs I have coming from Germany should help with reducing additional rake.

I guess I'll use the Hoosier 255 instead. Equal width without the height increase. Let this be a lesson: pay close attention to ALL specs. In the end, I would be gaining an inch of tread from each corner without altering tire diameters much.

Very excited for this setup. I'll keep you guys posted as it comes together. First autocross of the season is in July.

TSW Interlagos Wheels here: http://www.tsw.com/alloy_wheels_interlagos.php
Price is around $1100 for the set.

Hoosier A6s at around $1400 for the set.
 

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Sounds interesting, good luck getting it all fitted correctly..

Do you have a race over the same course, that you can compare times to say last year, with the old setup, so you can actually see the new investment as having paid off.?
 

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Discussion Starter #3
Unfortunately no, the course changes every event. The change in rubber alone will make a huge difference though, going wider will be the bonus. The only way I'll be able to compare is to see how well I do against the competition in relation to last year.

However, the first event in July is a "Test & Tune" event so I will be able to run the same course before and after switching to the race tires. I'll be driving to the event in last years setup (Dunlop Direzza Z2 tires) and my girlfriend will be driving my daily driver ('99 C280 Sport) with the set of race rubber in the back. I'll make a few runs with the street tires first, then swap to see the difference.

Since deciding on 255s rather than the taller, but not wider 275s, I won't need the high +40 offset of the TSWs. Instead, I'm going to use Bremmer Kraft BR08 wheels from Tirerack.com. The Bremmer Krafts are only $680 compared to the TSW $1100.

TSW Interlagos Front: 18x8.5 ET32
Bremmer Kraft BR08: 18x8 ET35
  • Compared to the TSW, Bremmers = 3mm more clearance inside, 9mm outside
  • The minimum size for 245 tires is an 8" wheel.
TSW Interlagos Rear: 18x9.5 ET40
Bremmer Kraft BR08: 18x9.5 ET35
  • Compared to the TSW, Bremmers = 5mm more clearance inside, 5mm LESS outside
  • We already knew 255s fit just fine, so no need to push the wheels towards the inside with a higher offset. 9.5 ET35 with a 255 is a common fitment for SLKs.
Some pictures of the Bremmer Kraft BR08s on a C55 (same offsets as our SLK55s.)


 

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Discussion Starter #5
I think 285/30/18 would be the widest in the rear as proven by PropDr. I'm going back and forth between 245/255 and 245/285. 275 Hoosier A6s aren't any wider and would only make the rear taller. I would have to find a 10" rear wheel in a low to mid 40s offset to fit a 285/30 tire on it though...
 

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Discussion Starter #6
Also, going too wide in the rear while only having a 245 in front may add some under steer back to the car after correcting it with a wider front. My specific purpose is autocross where front grip matters more.
 

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Discussion Starter #8
New developments!

I placed an order for these. It'll be another 3-4 weeks until they're in stock. 18x8.5 ET35 in front, 18x9.5 ET35 in the rear. I'll use a 5mm spacer in front to keep it the same as fitting the stock rear wheel in front.


I went to the local SCCA region's awards banquet this past Saturday and was lucky enough to win this grand prize drawing:


That'll go towards a set of Hoosier A6 slicks. 245/35/18 in front, 255/35/18 in the rear. More front grip should help the car in the corners.
 

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Wheels that you are looking like buying - based on bolts, are they three piece split rim wheels?
In which case, can you avoid using a spacer by different (inner/outer) rims.

Lots of (turning) weight, can be lost or found on wheels (through using different styles).

Not looking for an answer, just want to make sure you have considered this.

Wheels look good, and wish you luck for the season.
 

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Discussion Starter #11
They are actually just one-piece replicas made by a reputable company that has TUV and JWL certifications for the wheel. I've done my research and found that wheel weight really doesn't make much of a difference in autocross run times. Grassroots Motorsports did an article on this awhile back. Either way, it'll be close to 5lbs lighter per corner than the OEM AMG P30 Package wheels that are close to 30lbs each.
 

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Discussion Starter #12
Update:

The wheels arrived today!.. And I'm currently sitting in a McDonalds across the street from the performance shop that's lowering my car. Sometime in the next week, I'll be getting my car on a lift in my friends garage (yes, he has a lift in his garage, the lucky bastard.) his lift lifts cars from the tires so I plan to see what kind of clearance there is after lowering to see what tires I can fit on the race wheels.

Here's a shot from the box.
 

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No go. These wheels do not fit over the P30 calipers. Posted them for sale on craigslist and already have someone picking them up for what I paid. Now to find something that will clear the brakes.
 

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Those BBSs are beautiful! I'm very unhappy they don't fit, one of my favorite wheels.

Shameless plug but I have a set of Renntech Monolites 18x8.5F and 18x9.5R - I was running Neova AD08's (these run wide) 225F/255R. You can probably go wider in the rear but I was lowered. These are forged and very lightweight wheels if you're interested give me a shout - made for Benz as well so you know they'll fit. Had them on my 06 P030 SLK55. I can get you some pics if you'd like.
 

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Discussion Starter #15
Those BBSs are beautiful! I'm very unhappy they don't fit, one of my favorite wheels.

Shameless plug but I have a set of Renntech Monolites 18x8.5F and 18x9.5R - I was running Neova AD08's (these run wide) 225F/255R. You can probably go wider in the rear but I was lowered. These are forged and very lightweight wheels if you're interested give me a shout - made for Benz as well so you know they'll fit. Had them on my 06 P030 SLK55. I can get you some pics if you'd like.
Saw those wheels, and love them! They're just more than what I was planning to spend on race wheels that I would use only 12 events out of a year. I am thinking I may end up with a custom Forgestar set ($1300) to get the exact offsets I need.
 

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You've stated that the BBS's in the front ran into trouble with the caliper. Is that a typical 55 thing? I have a 350 that comes standard with 17" whilst the 55 is standard equipped with 18", maybe the 55 also has bigger calipers upfront?

Just want to make sure that when my 8.0-18 ET35 on the front show up there is not going to be a fitting around the caliper issue.
 

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Discussion Starter #17
The slk55 brakes are significantly bigger than the 350 brakes. I can't guarantee it but you can try it. The diameter isn't the issue, the issue is the lip of the bbs lm style wheel pushes the face too far inward.
 

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Hi Mark,

did you end up finding a wheel that fits?

I was wondering on a slk55 can you fit a 9.5 wide 18" offset 45mm in the rear? if so what will be the widest tire?

the front is 8.5 wide 18" offset 45mm

will these rims fit?

thank you in advance
 

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Here is what I did.....

Front: 18x8.5 32 offset; Michelin Pilot Super Sport 235/40ZR18XL 95Y
Rear: 18x9.5 53 offset; Michelin Pilot Super Sport 265/35ZR18XL 97Y

No issues in clearing calipers, no rubbing. The rears are REAL close to rubbing on the inside....maybe 1/4 inch clearance.
 

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Here is what I did.....

Front: 18x8.5 32 offset; Michelin Pilot Super Sport 235/40ZR18XL 95Y
Rear: 18x9.5 53 offset; Michelin Pilot Super Sport 265/35ZR18XL 97Y

No issues in clearing calipers, no rubbing. The rears are REAL close to rubbing on the inside....maybe 1/4 inch clearance.
Are you sure on the ET value in the back? I've got almost the same set up but my ET values are 35 both front and rear with the same tires. No lowering BTW.
 
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