Lsjc1001

Hello everyone,


I'm needing help with a tire selection on my car. I know the rear is calling for 245/40-17 but I am getting a good deal on some Serenity 245/45-17. Will this hurt the car at all to make this minor change? Thank you for your help and time.

Yidney

That will be just about 1/2" bigger in radius, 1" in diameter. Look under there by your shock towers and make sure you have room for 1/2" more.

Lsjc1001

Thank you! I definitely have extra room in there.

bobtuba

It will affect your speedometer readings somewhat – you will be going faster than indicated. At highway speeds, it's about 3mph more.

Lsjc1001

Thanks! I think I can live with the 3mph difference as long as it doesnt affect the car or give it any mechanical issues.

megacrazy

That's quite a hefty difference. Most people would recommend a max of 3% difference from stock. You're talking about a 1 inch diameter difference as stated before. I personally would not run the tires. It may mess with traction control etc etc.

Fatz

There is a reason you lower the profile height of your tires when you upsize your wheels. I am sure you will alter the driving dynamics of the car; whether good, bad, or near neutral is anybody's guess. You generally try to keep the diameter of the wheel/tire combination the same.

I think it would work ok; but it is not something I would do.

DanielFD

Agreed, not recommended. The whole setup of the rear suspension is made for a tire at a specific dimension. By increasing the wheel diameter your stressing parts in the back by moving the pressure points along the rear suspensions parts. Its also going to cause weird things with your ESP and ABS for sure.

Yidney

Although I personally would not put on a different size tire just to save a few bucks, can you explain or verify any of what you said? I think you are just making things up to make our cars sound like more precision instruments than they are. A tire changes diameter at least half that much just by tread wear. And I'm sure all the people who change wheel sizes from 17" to 19" do not always maintain exactly the same diameter. How does that change "pressure" points "along" the parts or stress them?

DanielFD

Id really like it if you didnt make me look like an idiot; telling me im making things up. Second no i cant verify them, im no engineer, but i have a friend that offroads his wrangler a lot. He explained once the amount of stress suspension parts and joints go though. For example a car with 19" rims is more probably to eat up suspension parts more then a car with 17" because of the less amout of soft matter (tire) the wheel can absord before suspension parts are stressed. He also explained the similar effect of bigger tires. And that through his experiences he noticed the bigger his tire the more stressed his parts would get; and he would end up changing suspension parts more. I dont know if this applies to the problem at hand. Would 1 in. make that much of a noticable difference? I dont know, but it does make a difference. Personally, i think the issue is with the center of gravity becoming higher, more wiggling in the back. Again I repeat, i dont know if its that much a difference with 1 in. We're not all engineers from mercedes benz; there is a civilized way to say "please explain to me what you meant by stressing parts"; no need to say im making things up for whatever reason. I don't gain anything if i make our cars look any more precise. We all own the same model here.

megacrazy

Everything in a car is engineered very accurately and thinking that an inch won't make a difference is like saying buying shoes an inch bigger won't affect the way you walk.

Everything in the suspension and ESP/ABS is affected by the wheels. Sure, you might make a case that your modded suspension lasted you X miles but nobody knows how long it would've lasted stock. Probably a lot more than X miles. There are plenty of articles on this you can Google yourself.

Anyway, I think the main issue I would worry about is ESP/ABS. They're tied to tire diameter. What makes you think the software some guy wrote based on some very specific parameters will work if you make the wheels 4% larger? I bet if you did some testing there would be issues.

Anyway, it's not something I would risk on my own car. As a rule of thumb (in addition to the 3% max difference rule), I would not skimp on brakes and tires. That's just asking for trouble.

__pierce

I've been running 245/45 R17 rear tires on my CLK for awhile now. No issues what-so-ever with ESP/BAS, even my cruise control works perfectly.

I bought my car with 16" wheels that were: Rear 225/45/R16 and Front 205/50/R16. My current wheels are wider and larger circumference.

I'm also not an expert.. I asked the knowledgable person I purchased my wheels from if 245/45 would be an issue, due to huge pot holes in the NE and they told me they'd fit and clear the rear suspension easily. I was warned not to go 225/50 in the front though, as it leaves very little room for clearing the struts. So far they are perfect and have driven a few thousand miles with no issues.

DanielFD

I ran 235/45/17 rear tires instead of 225/45/17 on my w203 for a time. My tires wouldn't get the correct traction. I used to use Toyo T1R tires at the time and the car used to literally start jumping in the back if I tried to burnout because of they were so sticky. When I switched to the wider tire that stopped happening, in fact I could actually drift the car when the tires were still new (still Toyo T1R tires). I changed out my rear shocks a year later; but I cant tell you if that's related in anyway. So still not recommended in my book.

Rudeney

My set of Michelin Pilot A/S tires on the rear are nearly bald after 15K miles. Talk about drifting! I've been playing around with ESP off (just the dash button not "dyno mode") and I can leave some really nice "S" shaped marks on the pavement with a full-throttle takeoff. The entrance to my office building is a sharp right-hand curve and it's always wet from a leaky sprinkler head. I have mastered the perfect "drift" running up that turn. I have tried some dyno mode antics and, well, it's pretty scary without a locking diff - no control

DanielFD

HAHA when if first got my CLK it had a really old set of Kumho tires in the back. I intentionally didn't change them out.. Lebanon's country roads with almost slick tires.. a dream come true for people who like to drift . Eventually after about a month I managed to rip the tread clear off the tire I then changed up to Kumho KU39 tires. After a year and 30,000KM they still stick to the asphalt. But still had my fun during the winter with snow and all.