JimPap

Actually two questions.

Do 17" tires ride softer than 18"ers.....in general. I know this will vary depending on which tire you put on them, but if you were to use the same model tire, is there a difference in ride?

Also, with either the 17" or 18", is the outside diameter of the tire about the same? Is it only the inside rim diameter that varies?

I'm asking this because I'm getting close to wearing out my original tires and am considering going to an 18" wheel. I like the AMG 18" but don't want to sacrifice ride.

acr2001

The outside diameter must always remain the same when increasing the size of your wheels. This is absolutely necessary or your speedometer would be off, among other problems.

This, obviously, means that the side walls of the tires must become thinner as the wheel becomes larger.

This will effect the ride by making it harder no matter what tires you buy. The difference is certainly noticeable even from a 1" increase in wheel size. On the other hand, it will improve cornering just a bit. Unless you live in a city where the roads are smooth as glass, you should not be riding on wheels larger than 18" on a W204. Those with 20" wheels and super thin side walls are either crazy (very easy to damage your rims with such thin tires) or live where the roads are very well taken care of.

JimPap

Thanks for responding acr2001.

I have an early production 2008 C300 sport in which the ride is already firmer than I want and it has the 17" rims. This was corrected on later model C300s. I was entertaining the idea of going with 18"s just to open up some of the more interesting rims. I a fool for style, but can't make the ride rougher than it already is.

Wargen

One inch makes a pretty significant difference and i would say that the performance gain with 18" is none. 17" is the perfect combination of performance and comfort even if i could see myself rollin on 18" wheels but only for the looks.

AMGTTV8

stop being a ***** and get some 18" rims....

Sportstick

Not sure what those **** mean, but if you want heavier wheels, higher impact harshness (worse ride), and minor but directional losses in acceleration, braking distance, and fuel economy, all due to higher rotating mass, than by all means get 18" wheels....some kid will think you look more cool.


P.S. Based on your comments, you should consider Michelin Primacy MXV4 (check tirerack.com tire survey results for Grand Touring All Season)

rodrigoc350

i'd like to say that i used to have the 17" amg and i just switched for the 18" amg with different tires the 17" had the pirelli pzero rosso which is a hard tire and i fit my 18" with the michelin ps2 which i used to ride on my bmw's and is a low tread tire but it is softer than the pirelli and i don't notice a hardness ride it's also a little bit quiet and also has more grip i really love that tire and i have to say that here in Mexico the roads are awful so if you change it depends of course in the tire you select but for me there was no difference
hope this help

wadgras44

in dirty jersey . . .

going from 17" - 18" (with 40 / 35 front / rear sidewall profile), not much degradation in ride quality

going from 18" - 19" (with 35 / 30 front / rear sidewall profile), it can really hurt the tush on bad roads (and similarly make you mental trying to figure out if that ever-so-slight vibration in the steering wheel is due to a bent rim). In addition, you can easily damage 19" rims doing something as simple as turning into a parking lot with a slightly raised curb. But boy do they look sweet!

kevink2

+1. Wife just got a pinch flat on oem 17" after hitting something on the road, no wheel damage. If we had 18", rim damage would be much more likely.

Sportstick, the higher rotating mass, going from 17's to 18's, will be very little. If scale weight is a 10 lb increase for wheel, rotating weight will be just 5 lbs more, for 15 lbs total per corner.

Rodrigo, your better ride with 18" vs 17" would be the exception to the rule.

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The WRC Rally race cars ( 300 hp 300 ft-lbs ) are a good way to judge best tire choice for diff road conditions. Looks like 60-70 series here on mixed gravel roads:



On smooth tarmac, they run 18" or 19" to get the biggest brakes possible.

.

acr2001

Good posts. Also you can't forget that as you decrease the sidewall thickness you are putting further strain on your suspension.

The SA at my dealer says that he gets tons and tons of vehicles with suspension issues that have upgraded to nice 19" (w203) or 20" (w204) ricer wheels. I find this pretty believable considering that the dealership is located in Brooklyn and we have extremely poor roads in the NYC area.

Having said that, I don't think going up 1" from the stock size is going to be too bad. I did that on my car which has the lux suspension - took a lot of the 'bounce' out of the ride and to me it feels like it's now in between the lux and sport suspension - which is good because the roads here are terrible. If I lived where the roads were in better shape, I would certainly prefer the sport suspension.