njgilligan

Firstly, I pay attention to details, sometimes more than is necessary; that may well be the case here.

I've noticed some cars with a staggered setup use tires that have an overall difference in diameter. For example, my W208 CLK came with 225/45/17 in front and 245/40/17 in the rear. The fronts are ~1/4" larger in diameter than the rears. If the factory spec were 255/40/17 in the rear the difference would be less than 1/10". Maybe Mercedes went with this setup because 245s are more readily available than 255s?

The question comes in when upsizing. I see many people keeping this diameter differential when buying new tires. I just bought some new wheels (19x8.5F and 19x10R); is there a reason I should keep the 1/4" diameter difference, or would it be okay to use 225/35/19F and 265/30/19R? If so why does 235/35/19 seem to be more common?

Obviously not a hugely important issue, just something that's been puzzling me a bit.

Kreuzfeuer

For speedometer/odometer calibration reasons, I would try to stay as close as possible to the OEM overall-diameter.

Another thing to consider is the load ratings of the tires... If your car came with an XL load rating factory, dropping to an SL load rating could cause problems.

Finally, if you can fit the 235/35/19, go for that as the 225/35 will make the tire appear stretched (unless that is the look you're going for).

Aside from ride comfort, the slightly taller tire in the rear also gives the car a slight rake... making the fronts disproportionately taller could minimally affect the at-speed mileage and handling.

Hope this helps,

njgilligan

Kreuzfeuer, thanks for the response. Definitely some good points there. I don't intend to stray too far from factory spec, so I think I'll be okay as far as odo/speedo readings (and cruise control I hope). As far as the stretched look, I don't mind it, I just want it to look the same. I think 265 on a 10" rim will look more similar to 225 on a 8.5" rim than would 235.

The part that interests me the most is the potential effect on mileage and handling you mentioned. From the factory, I take it my car has a negative rake angle (bigger tires up front). If I'm not mistaken, this would tend to create lift, and potentially improve fuel economy at the expense of downforce/handling ability. But why would AMG want to do that?

Kreuzfeuer

I misread that earlier, my fault. On my car, the front wheels were significantly shorter OD than the rears... but, we also have a 18/19 stagger from the factory.

I ran a calculator on the OD of your factory front and rear, and it's pretty doggone close. Not sure why they made the fronts incrementally taller, but they did.

Regarding the aftermarket sizing, after looking at the factory OD, the tire you want is DEFINITELY the 225/35/19... the 235/35 would be significantly taller than the OEM front, and throw the balance off even more.

Note on the photos attached, the backspacing can be ignored, I just threw a value in there as a placeholder. One photo shows the difference between front and rear (OEM bias) and the next photo shows the differences between the OEM front and the aftermarket 19" front...

njgilligan

Cool, that's what I thought. The reason I was questioning my initial judgement is that most people seem to be running 235/35/19 front and 265/30/19 rear on their CLKs with 19" wheels. I'm glad to see someone else agrees with my line of reasoning.

Kreuzfeuer

You will just have to watch the curbs

I ran a 225 on a 8.5" wheel for the better part of a year, even tracked the car with no issues. Bridge joints didn't feel too good, though

njgilligan

Yea, on 19s with 30/35 profile tires, I'm not expecting a lot as far as ride quality. As for looks...

Spaded311

very clean