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Discussion Starter #1
Hi, hope somebody in the known can give me some confirmation. I chatted with Tirerack tech agents, and they were so clueless.... Im a little surprised!!
I have a new sets of tires/rims (OEM) 245/40/17(for the rear), the rims size is 17 x 8.5in (OEM). I wanted to install the SMALLER tires size 225/45/17. Will these smaller tires fit the OEM rims? Will I run into any problem regarding fitment, functional and longevity?? According to TireRack website’s information, most of these tires (225/45/17) indicated the “rims range” from 6.5 – 8.5in, but the “rim width” is 7.5in (some are up to 8in). Since my rims’ width is 8.5in, will these tires fit RIGHT?? Will I have any problem in the long run? Affecting longevity of the tires?? Riding quality?? In addition, will they fit squarely, or being overstretched?? I wanted the car to look “normal”, not funky “overstretch” look. Im going for skinnier tires for fuel economy reason.
 

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your vehicle was setup to run OEM. Usually you can upsize one size, will little issues, so if you down size it might be the same. I don't think you going to see any mileage gain. List you rim size on Tire Rack and usually it shows what tire you can put on it. I have a MotorHome and upgrade to one size larger. I had to correct for the speedo and there was a difference on the transmission when it change gears. Mileage did not change but ride did for the better. I know it did not help. My Slk we are very happy with the way it handles on the OEM and not sure I would play with it much. I sure there are many on here that can help you with better info.
 

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Discussion Starter #4
your vehicle was setup to run OEM. Usually you can upsize one size, will little issues, so if you down size it might be the same. I don't think you going to see any mileage gain. List you rim size on Tire Rack and usually it shows what tire you can put on it. I have a MotorHome and upgrade to one size larger. I had to correct for the speedo and there was a difference on the transmission when it change gears. Mileage did not change but ride did for the better. I know it did not help. My Slk we are very happy with the way it handles on the OEM and not sure I would play with it much. I sure there are many on here that can help you with better info.
The car originally came with 16in (OEM) rims and 205/225 front/rear tires. The ride comfort was wayyyy better, and the mileage was actually 4-5 miles/galon more than the 17in!! But I loved the look of the 17in AMG (OEM) rims with 225/245 front/rear. Im accepting the rougher ride (due to lower profile tires), but hoping by going down to 225, will regain the mileage. I checked out Tirerack, and the issue was most of the 225 tires indicated the "rim range"(I assumed the rim sizes that the tire can fit on) was from 6.5-8.8. But the "rim width"(I assumed the perfect/ideal size) was 7.5in. Since the AMG rims width was 8.5in.... Im sure the tires will fit, but dont know whether it will function right, whether it will look right (dont want the "overstretch" funky look), and whether the longevity will be affected?! I called the Tirerack's people, and they were clueless!!! they just repeated exactly what I stated here without knowing anything more than I was!!
 

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It will have a slight stretch to it, but nothing crazy like you see the stanced cars having. Mileage change will be negligible. What size of tires were you running and what do you have now
(including profile)?
 

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Discussion Starter #6
It will have a slight stretch to it, but nothing crazy like you see the stanced cars having. Mileage change will be negligible. What size of tires were you running and what do you have now
(including profile)?
My car originally came with 205/50/16 (OEM) all around (should be 225 at the back, the last owner made mistake). I consistantly got 23-24/30 on city/highway. Right now Im running 225/45/17 and 245/40/17 (OEM rims). I could not get over 20 for city and around 25,26 at most, for highway!!!. Im thinking of going 205/50/17 front and 225/45/17 rear. Things is the rims are 8.5in width, not sure the tire will fit. My driving including cruising mostly, never involved in any hard core driving.... so I think skinnier tires will be ok?!
 

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My car originally came with 205/50/16 (OEM) all around (should be 225 at the back, the last owner made mistake). I consistantly got 23-24/30 on city/highway. Right now Im running 225/45/17 and 245/40/17 (OEM rims). I could not get over 20 for city and around 25,26 at most, for highway!!!. Im thinking of going 205/50/17 front and 225/45/17 rear. Things is the rims are 8.5in width, not sure the tire will fit. My driving including cruising mostly, never involved in any hard core driving.... so I think skinnier tires will be ok?!
That is what I was thinking, you front tires are 4% larger than the ones you had before, this is throwing your mileage off 4% and also your MPG. So that is about 1 MPG of your difference is just a reading error. The larger tires also have more centrifugal force and are harder to turn, so they take more power. I would suggest 205/45/17 or 225/40/17 for the front and 225/40/17 for the rear. That will get you back down to a 24.1" diameter, you are at 25" now like the AMG's.

Scratch that, you actually had 205/55/16 on the front stock and 225/50/16 rear unless someone had put the wrong size on at some point. The tires you have now are the correct size for the sport version of your car. These are all 25" tires.
 

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Discussion Starter #8
That is what I was thinking, you front tires are 4% larger than the ones you had before, this is throwing your mileage off 4% and also your MPG. So that is about 1 MPG of your difference is just a reading error. The larger tires also have more centrifugal force and are harder to turn, so they take more power. I would suggest 205/45/17 or 225/40/17 for the front and 225/40/17 for the rear. That will get you back down to a 24.1" diameter, you are at 25" now like the AMG's.

Scratch that, you actually had 205/55/16 on the front stock and 225/50/16 rear unless someone had put the wrong size on at some point. The tires you have now are the correct size for the sport version of your car. These are all 25" tires.
Thanks Jet.... I was thinking of 205/50/17 front and 225/45/17 skinnier tires for better fuel economy yet maintain the overall diameter (25" and 25.1"). The issue here is both of these tires are designed for 1" narrower rims!! and Im afraid the tires will be over stretched, look weird and affect functionality and longevity!??
 
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