cdritt

Hi - I'm a newbie to this site. I have a 2005 C230 sport sedan. I just purchased new OEM (take off's) 2005 C55 wheels. I put on Pirelli Pzero Nero M&S tires on. The front are 225/40/18.

I observed that the new wheel/tire set up makes my car's steering feel like driving an old Buick. It's sloppy feeling and not as sharp off of center as it was before. I think you may call it "turn-in" feel? (in this case, poor turn-in).

Shouldn't the new set up feel tighter and stiffer than the old stock 17" wheels with the OEM Michelin Supermacy tires? The tire shop told me that the Pirelli has a much stiffer side wall and also the front 18" has 40 series side wall and not 45 like the 17"s had. Seems to me I should be a getting a more sharp/harsh ride and not more plush like I am experiencing. Worth noting, perhaps, is that the c55 front wheels have a 30mm offset; stock had 34 I believe. Does 4mm of offset make the difference?

Help! I want the sharp steering feel back when moving the steering wheel slightly off of center. Any ideas? Could this be due alignment or bushing problems due to banging the wheels off (they where stuck on pretty good).

Thanks!!

Cintoman

I have a very similar problem with my car, and I've been talking to LUKE in the wheel/tire/suspension forum under this link:

https://mbworld.org/forums/wheels-tires-suspension-brakes-forum/245198-luke-oem-tires-wider-rim-now-bad-turn.html

In my case, I bought new Eurotech replica C55 ///AMG twin-spokes wheels. 17" size, but offsets are different than the stock C230 SS wheels (2005 funnel style). The other difference is that the front wheels are now 8.0" width, versus the OEM's 7.5" widths. Same tires in the front (OEM Michelin Pilot Primacys), but new General Exclaim UHP's in the rears. Rear wheels are the same width as OEM, but again, I believe the offset might be different than OEM.

Since then, my steering has been just like the OP's, very very vague, very floaty, as if I'm running on severely underinflated tires in the front, and very Buick-like. Turn-in is a dangerously more hazardous maneuver, where previously, it was very sharp.

My thoughts are that the wider wheel width in the front makes for a tire that "bulges" out less now than when it was on the OEM narrower wheel. The tire edge is basically on the same vertical plane as the edge of the wheel, whereas before, the tire would bulge out maybe 1/2" inch more. As such, the sidewall might be a bit higher, causing it to be softer and more prone to rolling under during turn-in.

The turn-in feel is TOTALLY more Buick-like. Horrible now. My wife's 98 Subaru Forester now has sharper turn-in.

What I was thinking of doing was replacing my OEM Primacy's stock 225/45R17 size tire with either 235/45R17 or 235/40R17 instead. The reason for my thinking is that going onto tirerack's site, they list the "measured width" for tires and what wheels they can be mounted on. Don't know the exact specifics, but as an example, a 225/45 series tire can be mounted to a rim width size of between 7.0 and 8.0 inches. But the standard measured width for 225/45 would be on a 7.5" rim, which is what the OEM setup is. However, a 235 series tire can be mounted on anything from 7.5 to 8.5 inches, with the measured width being an 8.0", which is the width I have now with the replica setup.

In my original thread link above, I've been talking to Luke, and wondering if I should go with a 235 series tire. Anybody have any advice? The other questions I'd have would be if getting a 235 series tire would in fact help bring the handling back to the way it was with the OEM wheels? And if so, should it be a 235/40 series or a 235/45 series?

I did a comparison below of the sidewall heights (aspect ratio):

OEM 225/45R17 - sidewall height is 101.25mm
235/40R17 - sidewall height is 94.00mm
235/45R17 - sidewall height is 105.75mm

I'm thinking speedometer reading will be affected as the heights are different than OEM

Of course, the other question would be if handling would improve, and if the BAS, ABS, and ESP would get messed up with a 235 series tire.

The final thing I was thinking of doing was actually what the OP did...buy C55 wheels and mount them onto my car. Surely I didn't expect to hear what he posted, as the C55's wheels/have a lower aspect ratio, and the handling should have been MUCH more improved and harsher. I was thinking about buying some C55 ///AMG wheels, but if my handling is going to be as horrible as the OP's, then

Suggestions on what's going on??? cdritt, did you ever get your issue resolved? Could the different offsets be the case? Front/rear tire pressure is 36psi across all 4 tires. Tires are mounted correctly ("outside" is facing outside), and alignment was done right after the wheels/tires were mounted.


Thanks,
Paul
(Cintoman)

tj40

"I'm thinking speedometer reading will be affected as the heights are different than OEM"

In my experience the speedo reads a higher mph than you are actually doing, I've seen errors of up to 10% on stock wheel sizes. Bizzarely I've seen differences of around 5% when switching from summer to winter tires which are nominally exactly the same size.

So I would not worry too much - if you are you can either buy/beg/borrow a decent GPS unit and put it into speedo mode and see how well this corrlelates to your speedo reading. Stick your car in cruise on the highway and let eveything get into a nice steady state and see how far out you are.

Sorry but I can't be much help on the steering but I know a differnet wheel/tire sizing will change the caster on the front wheel which can affect the feeling of the turn in.

Cheers

TJ

e1000

what tire pressures are you guys running. Contrary to what a lot of sources say, low profile tires need a lot more pressure than normal.

Also, 10% error is HUGE. You usually want to stay within 3% from stock overall diameter sizes.

tj40

e1000 - to clarify I was referring to a 10% speedo error - I agree you want to stick to 3% max from a rolling diameter perspective. In my expereince the speedo's are typically optomistic and I have seen the speedo read 10% more than the actual speed measured on the GPS (yes I know you could debate the accuracy of the GPS but knowing and understanding how the GPS chipsets work I believe it more than the speedo).

I've seen this across a number of makes and models. Personally I believe that the manufacturers do it to avoid liability.

So going to a plus size fitment on my C320 Coupe actually improved the accuracy of the speedo.

TO actually correct my previous post, changing the size of the wheel/tire will change trail, not caster. Trail is the distance from the imaginary point where the steering axis hits the ground in front of the wheel to the point directly under the axle. Increase trail and you will increase the self centering on the steering and the effort required to turn the wheels from straight ahead. Not sure of this is the cause of the 'vagueness' described but it's one mechanical effect from increasing the diameter fron stock.

Cintoman

I'm running 36 psi on all 4 tires.

As I mentioned before, the only things I changed were going from 17x7.5" front wheels to 17x8.0" front wheels. Not sure about the offsets, and if they're different from the stock funnel wheels. Same Michelin Pilot Primacy 225/45R17.

Actually...also replaced the rears with new General Exclaim UHP's. Stock size.

Cintoman

kickR

Not saying that it is the tire pressure, but you should stick with the manuf. numbers which are 28 front and 32 rear. If you go low profile tires like 30's and 35's its reommended to add about 10%.

Offset can play a big role too when it comes to how your car handling feels like on the road. Easiest thing would be to find out what the wheels offset is and accordingly maybe buy some spacers which is gonna give your car a wider tire track which usually improves handling.