i was just wondering, as i looked on the mercedes boards, an slk owner was asking others what they thought about 19's and 20's. and a lot said:

A) the ride would be like crap.
B) the car would be slower due to the extra mass of the tires.

so i think about it and i remember that the srt-4 actually downsized the stock tires for a lil extra acceleration. so would the crossfire be faster with say 17's and 18's? I was just wondering as i'm not real familiar with the specific topic of tires.

 

Not much, not really worth doing it at all. Better off throwing a bottle on the car.

 

The SRT-4 your referring to with the "downsized" tires is the ACR, a limited production version. The rest of them have 17's still. BTW, those "downsized" rims are 16's and are made by BBS, nice rims!

 

I've always been of the school of thought that changing wheel/tire size without changing other suspension components is done just for cosmetics. People who engineer cars for major manufacturers consider each element of a car for best ALL-AROUND performance, safety and handling on public roads. There's a very good reason engineers are well paid professionals. Haphazardly adding an aftermarket part without considering cause and effect of other associated components can seriously sacrifice structural integrity. For example, I have a friend who had an amateur put a lift kit on her Dodge truck. It had the desired "look" she wanted but then one day she ran over a curb and quickly tipped the truck on its side.
The Crossfire was not designed for drag racing or terrific 0-60 ETs. The car is mostly about handling and stylish good looks.

 

drag racing and terrific 0-60's = srt, but i thought with such little aftermarket performance every little bit could help. i guess it was "cheap/alternative" idea to drop a few tenths.

 

smaller rims and tires will make your crossfire slightly quicker. usually lighter weight and less mass to rotate will equate to an improvement.

old post...

https://www.crossfireforum.org/forum...4&page=1&pp=10

 

Actually, this has been done for a long time. You can gain acceleration by effectively lowering you rear gear ratio (a tire/wheel combo that is less diameter than stock) from the stock ratio (3.27 I think, to something lower 3.45 whatever). I think because of our wheel tire combo 19/245 series it might be difficult to fit a smaller wheel and therefore a smaller tire. Good thought cheap performance.

 

Go to the drags, make your best run, swap your front tires with your rear tires and see if there's any difference. Only problem is when you put your rear tires on the front, they may rub your fender.

 

i mentioned this about a year ago and all the usual haters came out. only thing that bothers me about it is the fact that i wouldn't want a much skinnier tire than what we have and an 18 that wide would be expensive. and to whoever said that the smaller wheel would throw off the suspension geometry, don't forget we are driving slk's and they come with 16's and 17's. our 19's are purely cosmetic.

 

Well I hate for my first post here to be on such a controversial topic. I have noticed a couple of threads on here about tire size during my lurking and hope to clear things up a bit or muddy the water depending on you view. Their are two separate issues here regarding tires. One, is changing the rim size, the other is changing overall diameter. To the extend that a new rim does not hit the brake caliper, there would be no adverse effect to changing a rim size if overall tire diameter remains the same. The result of which could mean losing some unsprung weight, losing unsprung weight could improve 0-60, however it should be noted the same effect could be had going with a lighter stock size rim.

 

Do all of these posts assume that Chrysler didn't change the final drive ratio in the transmission to account for the increased tire diameter on the Crossfire versus the SLK?

 

Does the slk have a different diameter tire or just a smaller rim? Keep in mind one can up or down a rim size, but still keep the same overall diameter, just the tire will have different side wall heights. I forget the formula but I remember that hearing that losing a pound in unsprungs weight was like losing several pounds in the car. I thought it was like 1 to 5. Maybe some one could confirm that ratio. I would like to keep stock sizes rims, while going with a lighter rim but I have not found a rim that would make a difference.

 

i guess someone will have to find the final drive ratio for the two cars, also tire and rim sizes (stock) and then just compare the cars. If you keep the same rim size, just getting a thinner tire helps? such as low profile, which the crossfire pretty much has already? i'm not real familiar with the tire and rim aspect of cars as far as the technical and performance aspect goes, that's kind of why i posted it, just trying to learn new things thanks to all that have replied.

 

According to what I've read so far,everything in the XF's drive train is supposed to be the same as the SLK's, ratios and all. I'm not sure, but I'm guessing that the diameter of the XF's 255/35-19 is the same, or close to the SLK's 225/50-16s. After all you only need 1.5 inches of side wall to make up the difference in wheel size, and we're talking 50 series vs 35 series.
Motor Trend magazine's Dec. 03 issue had a comparison test of the SLK vs the XF, both were automatics. Even though the SLK weighed 70 lbs. more, it still beat the XF in the 1/4 mile by .24 sec., on tires "skinnier" than what the XF uses on the front. This is the reason I suggested using the front tires on the rear to lower your 1/4 mile times. I think it would perform more like you were running 3.50 gears instead of 3.27s. The best times I've read on the non-supercharged stick shift XF is 14.7. It wouldn't surprise me if it knocked 2 or 3 tenths off that. (Assuming you get a good launch without to much wheel spin). Just practice.
I have to commend you for looking for inexpensive ways to improve your cars performance without throwing tons of cash at it, and keeping it mostly stock. There's nothing like spanking some "Tuner Boy" (at your local drag strip) who just spent his whole paycheck on a new "Wright Brothers" wing and a "fart" can muffler only to have him ask, "what did you do to your car?"
And you can reply,"nothing, it's stock".

 

+fireamx, you make some good points.

Crossfirekid setting up the car the way you like, depends on many factors, particularly how you intend on using your speed. If you looking for top end speed than wide tires will be an asset. If you want to jump the line than thinner tires to keep down rotational mass would be best. Note the differences between a drag race care and a formula 1, different agenda's different tires.

 

cross00m, I agree with your thinking, don't think the comparison drag to F1 works though. F1 tires are wide to put power down, stability etc, heat gain and wear being the biggest issue over time.

Drag tires are also wide, don't know why they look like they do but love to see the way the side wall twists up on the centre and then once the wheel spins the outer diameter 'grows'.

Overbearing factor in 0-60 will always be overall gearing and tire sizes have a effect on that.