Still contemplating options for larger wheels and tires on the family 500E. My current reckoning is that a 17-inch wheel (of appropriate offset) and a 245-40/17 fitment at all four corners is maxing out. Could get wider, but that gets into clearance hassles or staggered setups.

And with that in mind, I'm looking at 17x8, 17x8.5, and 17x9 wheel options, but I'm also thinking about sidewall flex issues. My appreciation for the sheer concentrated mass of the 500E has grown after driving it a lot lately. This car imposes -serious- loads on its tires!

The physics of sidewalls seem pretty clear. A sidewall that is only minimally curved outward from the plane of the rim should flex less. A sidewall that is curved out more considerably from the plane of the rim (as a 245-section tire would be on an 8-inch wheel) would have more flex. More flex certainly means more compliance over bumps, but also probably means more squirm and less control.

What have other owners' experiences been in this regard? I'd very much value some feedback as I hone my thinking and begin to narrow the candidate field for purchasing.

s/b

See my response to "Mercedes Wheels 101" below for another factor to consider.

The appropriate 17" tire is a 245/45-17; 245/40 is too short (but will fit).

I run 8.5" wide AMG 17s on my car-no clearance issues whatsoever. 8.25 or 8.5" wide is that standard upgrade on these carsFWIW I really like Michelin tires, as their stiff characteristics (Pilots anyway) suit the suspension setup

__________________
"If God had meant for us to walk, why did he give us feet that fit car pedals?" Sir Sterling Moss

Michael
2014 E63S Estate
2006 SLK55
1995 E500
1986 Porsche 944 turbo

Fimum, excellent point, thanks.

Michael, you wrote:

>The appropriate 17" tire is a 245/45-17; 245/40 is too short (but will fit).

I'm trying to match the effective diameter of the 16-inch stock wheel, which is fitted with the 225/55-16 tire.

Check my math here:

Original sidewall height: 225*0.55 = 123.75mm

New sidewall height of 245/40-17 tire, excluding wheel: 245*0.4 = 98mm

Effective combined sidewall height of 245/40-17, with one inch of wheel diameter added in,
because of the move from 16-inch to 17-inch wheels: 98mm+25.4mm = 123.4mm

Seems okay, yes?

But if I rerun that second calc for a 245/45-17, I get (245*0.45)+25.4 = 135.65mm

Which is considerably taller than the original effective sidewall height of 123.75mm.

Or am I making an elementary mistake here?

s/b

>Or am I making an elementary mistake here?

D'oh!

Rerunning those calculations some weeks later, this time with some coffee in my system:

I realized/remembered that one has to add in TWICE the sidewall height to the height of the tire to get the overall rolling diameter.

In the calc above, I've only added in sidewall height once.

Michael's correct. In this application, 245/45-17 is what is called for.

s/b

S/B,

Here's a website you can use if you want to compare various tire sizes and wheel sizes.

http://www.miata.net/garage/tirecalc.html

I tried it earlier and it was a bit slow so be patient.

__________________
Afshin

Current:
02 C32 AMG

Previous:
92 500E
84 190E 2.3 5 Spd

Hey, an excellent resource (and no speed issues when I tried it). As expected, it confirms the recalc above.

I'll be keeping that URL close to hand for sanity checks on tire sizing. Thanks, Placo!

s/b