Amoeba

Why is it that 18s on the cl will improve handling compared to stock wheels

2slow4u

Never Heard that. I always was told that a 17" was a good size but

drewJ32A2

wider rims improve handling because the tires are wider which means there is more grip taller wheels do not improve handling

Amoeba

So 17 inch rims wider than stock would be ideal for handling?

Rod

I think it also has to do with sidewall height, with lower profile tires allowing for less flexing of the sidewall. So it's not that bigger diameter rims are better, but that the lower profile tire required for the larger rims are better. But maybe someone else can elaborate on this.

lemansteve

Yes, tire sidewall size does influence handling, as well as steering responsiveness. With relatively large tire sidewalls, there is more rubber to absorb bumps, potholes, etc. It also means the rubber will deform more under a given lateral load, such as the force induced by going round a bend. Other factors, namely bushing material, damping rates, spring stiffness, vehicle weight, center of gravity and chassis stiffness, will also affect handling. This is why a Ford Expedition will never win a handling competition against, say, an M3. The Expedition has larger tire sidewalls, softer suspension, a higher center of gravity, and weighs about 1000 pounds more (thats a guess). Not to mention it is fitted with dull touring tires, or even light off-road tires.

So to answer your question about the 18s improving handling, as long as i havent bored you to death already, they will most directly improve steering responsiveness and improve general handling. But be careful: if your new wheel/tire combo weighs significantly more than stock, your shocks will wear out quickly, due to the increase in mass it has to handle. You will also be a little slower off the line. Hope this helps...

azian21485

18's don't necesarily bring better handling..the diameter of the rim doesn't matter...what counts with handling concerning the rim and tire is the weight of the rim and dimensions of the tire...and overal diameter of rim AND tire

weight of rim: pretty simple..lighter rim is less rotational mass which allows your engine to start turning the rim and stopping the rim faster...results? quicker acceleration and stopping

tire dimensions: what you want to run are low profile tires (which stated earlier above me) offers less flexing which allows better control and feel. You'll notice you'll be able to "read" your tires limitations and they break their grip and such

next, you want to run the widest possible tires...wider tires equals more contact equals more grip

rim and tire diameter: what you want to do is run an overal combination that is as close to stock as possible..going bigger or smaller will throw your speedometer off...so if you have a 215/45/17 tire for example, to keep the same diameter when running eighteens you'll need a 215/40/18 tire <---this is the reason people say 18's offer better handling..you are able to run a lower profile tire which improves response

HOWEVER! you must take into consideration that 18's usually weigh more, puts more weight to the outside of your wheel&tire combination (so even if they weight the same as 17's, they'll still make your car slower due to polar momentum)....running a 215/40/17 tire will be more ideal than running a 215/40/18 tire because of this...so it's up to you what size rims you want...sorry for the long post it's late and i'm bored and new here =)

cliff notes to answer: no not necessarily..read above for reasons

EricL

The widest tire is not always the best tire. If you are in the wet, you reduce contact loading and the tire can hydroplane easier. The CLS can only accept a 235/45-17 or 245/40-17 with stock springs, and gets to be a tight fit depending on tire brand (they are not all the same).

The car has problems with 235/45-17 combined with wider wheels (17x8") and lowering.

There are rub issues to consider. One of the members went with 19” lightweight forged wheels with 235/35-19 Nittos on them, and had zero rub problems with a +51 offset and 2" of lowering. Also, depending on tire, compound, and other issues, you can actually find a tire that is so wide – for a given application – that you can actually reduce traction. Unfortunately, tire friction coefficients are not always linear with increased loading. So, unless you have a very large wing or underbody design (etc) to provide downforce, you can actually reduce traction by going with a too-wide tire. (I doubt it would be an issue on this car up to any size that would fit without sheetmetal mods.)

It's not the polar moment, but rather the rotational inertia that is of concern when changing tire and wheels sizes. If you find a light enough 18", that has its mass concentrated at the inside, you could very well end up with lower rotational inertia in an 18" wheel that weight the same as a 17" wheel. It's not the norm, but it is something that should be considered. (I noticed you mentioned rotational inertia first, and the impact of weight change has considerable impact on acceleration when the mass is increased on the outside of the tire/wheel combo. OTOH, the polar moment of a car is of very little concern when you're talking about 1-2 lbs per corner.)


Also, the makes of tires are different. It is possible to find someone with some really heavy belts at the outside of the tire with floppy sidewalls (the stock MXM4s come to mind with their weight of appox. 26 lbs.) The Toyo T1S, with their weight of 23.8 lbs have a very, very robust casing and thick sidewall, and can't be compared by weight alone.

So, what you’re saying is basically correct, but, people need to be "careful" about weight (actually mass) when comparing tires and wheels. If the brand and make are IDENTICAL, the 18" tire will generally weight more than a 17" tire of the same construction. And, if you see a rim with a very, very thin rim/flange (e.g. forged) vs. one of similar weight with a thick rim (e.g. cast), the weight CAN be rather misleading.

azian21485

cool..thanks for clearifying and correcting my points...the reason i don't know about rubbing issues or traction issues is because i never had to deal with going over a width of 225 nor an 18 inch rim =)

pimpscls

most simple explanation less rubber= better handling period unless the rims weigh to much

azian21485

too simple...too thin would dramatically affect handling as well...no/weak sidewall = bad