antijam
Senior Member
- Joined
- Jul 20, 2008
- Messages
- 1,628
- Reaction score
- 94
- Location
- Gloucestershire
- Your Mercedes
- 2003 SLK320
I’ve whinged-on on this forum before about the evil tramlining from the 18” wheels on my SLK (R170). I bought the car with the wheels fitted so I’ve never been entirely sure how the standard set-up should drive.
Finally got so fed up I bought a set of second-hand original fitment16”s, shod them with Conti’s and swapped them over.
What a transformation – different car! No tramlining at all, a ride that doesn’t dread the smallest pothole any more, and if I kerb when parking (which old fogies tend to do :Oops: ) it’s the tyre that takes the scuff – not the rim.
Comparing the old setup with the new revealed a couple of interesting points.
Old – Front Pirelli P Zero Rosso 225/40 – 18ZR on 8J rims. ET30
Rear Pirelli P Zero Rosso 245/40 - 18ZR on 9J rims. ET35
New – Front. Continental Premium Contact 2 205/55-16WR MO on 7J rims. ET37
Rear. Continental Premium Contact 2 225/50-16WR MO on 8J rims. ET30
The big shock is the difference in offset, particularly on the front. With the wider 18’s fitted the, the contact patch was not just larger but the front track was 14mm wider than standard. I suspect body and suspension clearances prohibit the fitting of an 8” rim while maintaining a 37mm offset, but the increase in track from standard was obviously the root cause of the tramlining.
I’d be very interested to know if anyone else has fitted 18’s to an SLK and if so whether it was possible at an ET of 37 on the front?
The other significant point was that to maintain near correct rolling radius the 18” rears should have been 245/35 not 245/40. This oversize gave a rolling radius increase of about 7mm meaning that my speedo should have read 3.5% pessimistic. I’d calibrated the speedo against my SatNav (which should be more accurate) and found it to be almost exactly correct.
What the oversize was doing was actually correcting for the optimism that all manufacturers build into their speedometers. (Legally they are allowed a tolerance of 0 to +10% - human nature says they are going to try to make their cars look as fast as possible, so almost all production speedos read a few percent optimistic). So now I’m back to an optimistic speedo – as original!
Couple of other downsides. The handling at speed and the sharpness of turn-in are just noticeably less precise, but under normal driving the difference is negligible.
The big downside of course is that my ‘bling’ factor is seriously reduced!! :wink:
(See before and after). If my street cred diminishes too drastically I may be tempted to refit the 18’s. If not, after a minor refurb they may be for sale – watch this space!
Before
...and after
If anyone recognises the 18’s I’d love to know the manufacturer. The only ident markings they carry are the JWL (Japan Light Alloy Wheel) and the VIA (Vehicle Inspection Association) logos. (Incidentally, they may look like split rims, but they are actually one-piece with a lot of non-functional allen bolts!)
Finally got so fed up I bought a set of second-hand original fitment16”s, shod them with Conti’s and swapped them over.
What a transformation – different car! No tramlining at all, a ride that doesn’t dread the smallest pothole any more, and if I kerb when parking (which old fogies tend to do :Oops: ) it’s the tyre that takes the scuff – not the rim.
Comparing the old setup with the new revealed a couple of interesting points.
Old – Front Pirelli P Zero Rosso 225/40 – 18ZR on 8J rims. ET30
Rear Pirelli P Zero Rosso 245/40 - 18ZR on 9J rims. ET35
New – Front. Continental Premium Contact 2 205/55-16WR MO on 7J rims. ET37
Rear. Continental Premium Contact 2 225/50-16WR MO on 8J rims. ET30
The big shock is the difference in offset, particularly on the front. With the wider 18’s fitted the, the contact patch was not just larger but the front track was 14mm wider than standard. I suspect body and suspension clearances prohibit the fitting of an 8” rim while maintaining a 37mm offset, but the increase in track from standard was obviously the root cause of the tramlining.
I’d be very interested to know if anyone else has fitted 18’s to an SLK and if so whether it was possible at an ET of 37 on the front?
The other significant point was that to maintain near correct rolling radius the 18” rears should have been 245/35 not 245/40. This oversize gave a rolling radius increase of about 7mm meaning that my speedo should have read 3.5% pessimistic. I’d calibrated the speedo against my SatNav (which should be more accurate) and found it to be almost exactly correct.
What the oversize was doing was actually correcting for the optimism that all manufacturers build into their speedometers. (Legally they are allowed a tolerance of 0 to +10% - human nature says they are going to try to make their cars look as fast as possible, so almost all production speedos read a few percent optimistic). So now I’m back to an optimistic speedo – as original!
Couple of other downsides. The handling at speed and the sharpness of turn-in are just noticeably less precise, but under normal driving the difference is negligible.
The big downside of course is that my ‘bling’ factor is seriously reduced!! :wink:
(See before and after). If my street cred diminishes too drastically I may be tempted to refit the 18’s. If not, after a minor refurb they may be for sale – watch this space!
If anyone recognises the 18’s I’d love to know the manufacturer. The only ident markings they carry are the JWL (Japan Light Alloy Wheel) and the VIA (Vehicle Inspection Association) logos. (Incidentally, they may look like split rims, but they are actually one-piece with a lot of non-functional allen bolts!)
