Tire Recommendations 18" or 17"

[JohnnyJohnny19]

Hey All

Im currently driving an 2013 328i xdrive sportline which has 18" wheels and Pirelli Conturato P7 sized 225/45/R18.

I had to bring my car to the dealer for some repairs and they gave me a loaner with 17" wheels. They ride is COMPLETLY different and how it should be.....given that are roads up here are awful!

Therefore, any recommendations on a set of tires. Should I keep the 18" or change to 17" for a more comfortable ride.

Also.... the loaner car is a 2017 320i x drive and somehow seems to have much more power than my 2013 328i xdrive sportline???? Am I missing something?

Thanks all!!!

[TostitoBandito]

Wheel diameter won't influence the ride much on its own. That's mostly the tires. The tire type, size, and whether or not they are run-flats all matter. I'd recommend leaving the 18's on your car if that's the diameter it came with, and looking at other tire options.

As for power, the 2017 320i has 180hp @ 3450lb while your 328i has 231hp @ 3590lb. Your 328i should be faster, though the character of the engines will be different since your car is naturally aspirated while the 2017 is a turbo.

Also keep in mind that the 2017 loaner is on a completely different chassis/generation than your 3 series, so handling will be different.

[pbonsalb]

17s will have more sidewall, which can absorb bad roads better, but as noted, tires vary. If you have runflats now, for example, they tend to ride worse than non runflats. You could change to a more comfortable 18 inch tire or you could change tires and wheels to 17s. Look at Tire Rack reviews for comfortable tires. I am familiar only with high performance tires and you may have all seasons on your xdrive model.

I thought the 2013 328i was a turbo 4 cylinder? If so, it should be very much like the 320i motor but have more power since the 320i is detuned.

[TostitoBandito]

Well technically the wheel size has nothing to do with the sidewall size or stiffness, that'll be determined by the tire choice and the aspect ratio. You can get 18's that have just as much or more sidewall as the 17's, and vice versa.

In this case with these Pirelli tires, a 225/45-17 will be 25.1 inches tall with 4.05 inches of sidewall, and a 225/45-18 will be 26.1 inches with an identical 4.05 inches of sidewall. The aspect ratio is independent of the tire diameter, and only depends on the width. Now if you were to go out and get a thicker sidewall tire like the 225/50-17 which is exactly the same height as the 225/45-18, then yes that would make a difference. You have more sidewall in that case, so the tire has more room to compress vertically.

I suspect that any difference in ride feel here can be chalked up to differences in the chassis and suspension, and possibly different tires.

[pbonsalb]

I disagree. Lower aspect ratio tires have shorter, stiffer sidewalls and generally ride worse. To maintain the original tire diameter, you go down in aspect ratio when going to larger diameter wheels and up in aspect ratio if changing to smaller diameter wheels, when using the same tire width. Your example of maintaining aspect ratio as is currently on the 18s and dropping down to 17s in the same width would not be advisable because as you note, you would lose 1 inch of tire diameter.

I use 17 inch wheels on my E36M3 even though many run 18s and I use 18 inch wheels on my E90M3 even though many run 19s, because I live in New England where roads are not always good and I want a little more sidewall to cushion the ride.

I don't know the answer on the suspension differences for the 2013 vs 2017. If the OP has P7 runflat all seasons, I suspect that may be the issue. People have been complaining for years about poor riding runflats on 3 series. Many go to non runflat tires and a mobility kit since there is no room for a spare. I have no spare in my E90M3, which came from the factory with regular non-runflat tires, no spare and a mobility kit.

[TostitoBandito]

I disagree. Lower aspect ratio tires have shorter, stiffer sidewalls and generally ride worse. To maintain the original tire diameter, you go down in aspect ratio when going to larger diameter wheels and up in aspect ratio if changing to smaller diameter wheels, when using the same tire width. Your example of maintaining aspect ratio as is currently on the 18s and dropping down to 17s in the same width would not be advisable because as you note, you would lose 1 inch of tire diameter.

Yeah, I understand. The point I was trying to make was just that it's the tires and their aspect ratio and width, not the wheels specifically. I also suspect he may have run flats, and I've heard many complaints about them as well. If he wants to go to a 225/50-17 it would definitely feel slightly different (more compliant) than his current 225/45-18, but I suspect there's more variables at play here than just the rim diameter and aspect ratio.

Downsizing from stock wheels as the OP is suggesting is pretty uncommon. People often upsize to bigger rims for aesthetic reasons, but there's not really any performance benefit except perhaps different tire options. I know in the case of the E36M3 a lot of people, myself included, prefer to stay on 17's for both appearance and cost reasons. If you track the car, 17 inch tires tend to be significantly cheaper than 18's. I also think 18's just look too big on the E36, proportion-wise.

[JohnnyJohnny19]

Hi All

Thanks for all the great answer and comments.

Yes. My tires are run flats and obviously tend to be a little harsher. Would 225/50R18 be adequate?

[TostitoBandito]

Hi All

Thanks for all the great answer and comments.

Yes. My tires are run flats and obviously tend to be a little harsher. Would 225/50R18 be adequate?

That wouldn't be recommended since it's a taller tire than your stock tires. You might have fitment issues, and it will impact your speedometer (will read lower than actual speed).

My suggestion would be to look into a good non-run-flat tire in your stock size. First thing off the top of my head would be a Michelin Pilot Sport AS3+ which is their high performance all season. Should perform at least as well as your Pirellis, and should be more civilized to ride on since it's not a run-flat. There are a number of other comparable tires as well.

I assume you have no spare, so there's somewhat of a tradeoff there. However, even a run-flat is only meant to be driven a short distance, like home or to a nearby shop, when flat. If you pack a tire sealant/plug kit and a portable 12v inflator in your car you can usually address most routine punctures and get at least as much mobility as a run-flat gives you. Emergency roadside service from your insurance can fill the gap in the case of a rare catastrophic blowout or something along those lines. Personally, if I owned a car with run-flats I wouldn't hesitate to switch them out to better performing standard tires. My M3 has a spare, but the two punctures I've acquired in the nine years I've owned the car were both slow enough leaks that I was able to drive home or to a shop without issue. The only time I've actually had to use the spare is when one of those punctures couldn't be repaired, and that was only for a couple days until my new set of tires arrived (they were worn out anyways).

[pbonsalb]

Pilot Sport AS3 gets excellent reviews. Probably the most performance oriented all season tire on the market. And as a non runflat, it will ride better.

You should not change aspect ratio unless you are also making other changes that will maintain the same diameter, such as going down to 17 inch wheels and running a 225/50/17, or going narrower on the 18s -- a 215/50/18 (assuming tires are made in that size) might be about the same diameter. A rough rule of thumb is stay within 3% of your current diameter one way or the other and you will have no issues. You can look this stuff up in Tire Rack specs for each tire series.

[JohnnyJohnny19]

Thank you very much for the information!! Much appreciated