Should I upsize my tires or stay stock? 18x8" style 397s

thatgarrett · 12-12-2023, 09:24 AM

Car: 2012 335i, RWD w/ Sport Suspension
Rims: OEM 18x8 Style 397s (square)
Use: Daily Driver, ~26k a year, mix of 200 mile interstate commute, 30 mile country back roads, VA (so not much snow), no track, just spirited driving
Tires: Looking at performance all seasons, non-RFT (top two are Conti DWS06+ or Michelin A/S 4+) but open to other options

The dilemma: Tire size

I've read dozens of threads here and on other forums for other BMW's and am torn on what size tire to go for based on my usage. I have on the stock(?) Pirelli C7 in 225/45 R18, and while I like the firmness, sometimes it feels a little harsh over expansion joints, potholes, rough roads etc. I don't want to compromise on the handling and feel, but since I drive so much I think the non-RFT would be a nice upgrade in terms of noise and comfort.

Now, on to my question- I have read a lot of people go for 245/40 sized on the 18x8, which is undersized by 0.26 inches in diameter, and also a lot go for 235/45 as well, which are oversized by 0.35 inches in diameter. I also know the stock staggered fit, 255/40 are essentially the same diameter (0.06 inches taller in diameter), but are typically fit on 18x8.5 wheels, even if the conti website claims an 8 inch wheel can accommodate it.

All that to say- am I overthinking this? I like the wider look, and a bit more rim protection, but I don't want to throw off the speedometer and odometer (even if it is not by much at all) since I put so many miles on it. I know there is a bit of a price difference between tire sizes but that is not as big of a factor for me in deciding which to go for. What size would you all recommend?

Ennoch · 12-14-2023, 08:06 AM

FWIW I've got 245/45/18 winters on and the speedo still slightly over-reads, so 70mph on the speedo is about 69.5mph on the GPS. You won't need to worry about it under-reading but the downside is there's less mental leeway between reality and the speed gun getting you. Some pictures on my thread here.

RobotDoctor · 12-14-2023, 01:04 PM

I have the same wheels on my F36 with 225/45/18 Pirelli Cinturato P7 run flats. I am planning on going to 245/40/18 Continental ExtremeContact DWS06+ for my next set.

tturedraider · 12-16-2023, 11:02 AM

235 or 245, whichever you like best. Either one will be just fine. Personally, I wouldn’t do 255.

gaijin · 12-17-2023, 10:20 AM

I very recently upgraded from factory 17's to aftermarket 18's at 8.5 widths. Went with the newest Bridgestone A/S at 245/40R18. I noted a 3 mph difference between the car and my iPhone's digital speedometer.

Additional point. I upgraded from OE 225/50R17 Conti Run-Flats. The non-R/F rides are much nicer and quieter too.

tturedraider · 12-17-2023, 03:38 PM

Quote:

Originally Posted by gaijin

I very recently upgraded from factory 17's to aftermarket 18's at 8.5 widths. Went with the newest Bridgestone A/S at 245/40R18. I noted a 3 mph difference between the car and my iPhone's digital speedometer.

Additional point. I upgraded from OE 225/50R17 Conti Run-Flats. The non-R/F rides are much nicer and quieter too.

fyi - the speed difference is mostly the way the speedometer is set from the factory. A 3 mph difference is pretty standard on all BMWs (and most German cars).

gaijin · 12-17-2023, 06:00 PM

Quote:

Originally Posted by tturedraider

fyi - the speed difference is mostly the way the speedometer is set from the factory. A 3 mph difference is pretty standard on all BMWs (and most German cars).

Wow! I didn't know that. Similar but wider disparity with Harley-Davidson motorcycles.

thatgarrett · 04-18-2024, 07:06 PM

Well it’s finally time for some new tires! Costco has a sale on Michelin’s right now, and I checked with the tire shop and they’re fine installing non-run flats that are a slightly different size from the OEM ones, so I’m ordering some Michelin Pilot Sport AS4’s in 245/40R18, should be fitted the first week or two of May. Came in at right under $950 out the door too, so pretty decent price. Excited to feel the difference and see the wider look, and have a bit extra protection from curbs!

I got around 55k from the Pirelli Cinturato C6 and the tires are just above 2mm in the center and 3mm on the outside edge, rotated pretty religiously

keithyo88 · 04-18-2024, 09:48 PM

[thatgarrett] hey, thanks a lot for the costco info.

danb1979 · 04-19-2024, 09:47 AM

FWIW I run 18x8 405Ms and 18x8 397s on my F31 (405Ms = summer / 397s = winters)

They run 235/45/18 tyres all round and they've been spot on; not stretched like 225/45's and with a straighter sidewall/better rim protection too

397s:

405Ms:

View Poll Results: Which size tires?
(Stock) 225/45	2	18.18%
235/45	5	45.45%
245/40	4	36.36%
255/40	0	0%
Voters: 11. You may not vote on this poll

12-12-2023, 09:24 AM	#1
thatgarrett Second Lieutenant 788 Rep 207 Posts Drives: 2012 335i Sport Join Date: Dec 2022 Location: USA iTrader: (2) Garage List 2012 BMW 335i [8.60]	Should I upsize my tires or stay stock? 18x8" style 397s Car: 2012 335i, RWD w/ Sport Suspension Rims: OEM 18x8 Style 397s (square) Use: Daily Driver, ~26k a year, mix of 200 mile interstate commute, 30 mile country back roads, VA (so not much snow), no track, just spirited driving Tires: Looking at performance all seasons, non-RFT (top two are Conti DWS06+ or Michelin A/S 4+) but open to other options The dilemma: Tire size I've read dozens of threads here and on other forums for other BMW's and am torn on what size tire to go for based on my usage. I have on the stock(?) Pirelli C7 in 225/45 R18, and while I like the firmness, sometimes it feels a little harsh over expansion joints, potholes, rough roads etc. I don't want to compromise on the handling and feel, but since I drive so much I think the non-RFT would be a nice upgrade in terms of noise and comfort. Now, on to my question- I have read a lot of people go for 245/40 sized on the 18x8, which is undersized by 0.26 inches in diameter, and also a lot go for 235/45 as well, which are oversized by 0.35 inches in diameter. I also know the stock staggered fit, 255/40 are essentially the same diameter (0.06 inches taller in diameter), but are typically fit on 18x8.5 wheels, even if the conti website claims an 8 inch wheel can accommodate it. All that to say- am I overthinking this? I like the wider look, and a bit more rim protection, but I don't want to throw off the speedometer and odometer (even if it is not by much at all) since I put so many miles on it. I know there is a bit of a price difference between tire sizes but that is not as big of a factor for me in deciding which to go for. What size would you all recommend?
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12-14-2023, 08:06 AM	#2
Ennoch Colonel 2257 Rep 2,048 Posts Drives: F31 335D XDrive Join Date: Sep 2020 Location: Scotland iTrader: (0)	FWIW I've got 245/45/18 winters on and the speedo still slightly over-reads, so 70mph on the speedo is about 69.5mph on the GPS. You won't need to worry about it under-reading but the downside is there's less mental leeway between reality and the speed gun getting you. Some pictures on my thread here.
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12-14-2023, 01:04 PM	#3
RobotDoctor Professional Nomad 679 Rep 128 Posts Drives: 2019 440i F36 Sportline Join Date: Mar 2023 Location: Florida's first coast iTrader: (0)	I have the same wheels on my F36 with 225/45/18 Pirelli Cinturato P7 run flats. I am planning on going to 245/40/18 Continental ExtremeContact DWS06+ for my next set.
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12-16-2023, 11:02 AM	#4
tturedraider Major General 4975 Rep 6,241 Posts Drives: 2018 340i M Sport Join Date: Apr 2006 Location: Chicago, Edgewater (via Texas & Tennessee) iTrader: (0) Garage List 2018 BMW 340i M Sport [9.38] 2020 BMW M340i xDrive [10.00] 2018 BMW 340i M Sport [8.00] 2006 BMW 330i Sport [4.50] 2004 BMW 330i ZHP [7.25] 2000 BMW 328i [6.00]	235 or 245, whichever you like best. Either one will be just fine. Personally, I wouldn’t do 255. __________________ www.bmwcca.org member #388003 - Use me as a referral & you could win a one day ///M Driving School!! ___________________________________________
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12-17-2023, 10:20 AM	#5
gaijin Mess Deck Commando 244 Rep 807 Posts Drives: F30 Join Date: Feb 2013 Location: Florida iTrader: (4)	I very recently upgraded from factory 17's to aftermarket 18's at 8.5 widths. Went with the newest Bridgestone A/S at 245/40R18. I noted a 3 mph difference between the car and my iPhone's digital speedometer. Additional point. I upgraded from OE 225/50R17 Conti Run-Flats. The non-R/F rides are much nicer and quieter too. __________________ ///Sursum Ab Ordine
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04-18-2024, 07:06 PM	#8
thatgarrett Second Lieutenant 788 Rep 207 Posts Drives: 2012 335i Sport Join Date: Dec 2022 Location: USA iTrader: (2) Garage List 2012 BMW 335i [8.60]	Well it’s finally time for some new tires! Costco has a sale on Michelin’s right now, and I checked with the tire shop and they’re fine installing non-run flats that are a slightly different size from the OEM ones, so I’m ordering some Michelin Pilot Sport AS4’s in 245/40R18, should be fitted the first week or two of May. Came in at right under $950 out the door too, so pretty decent price. Excited to feel the difference and see the wider look, and have a bit extra protection from curbs! I got around 55k from the Pirelli Cinturato C6 and the tires are just above 2mm in the center and 3mm on the outside edge, rotated pretty religiously
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04-18-2024, 09:48 PM	#9
keithyo88 Second Lieutenant 116 Rep 211 Posts Drives: 340i msport rwd Join Date: Oct 2022 Location: san jose, ca iTrader: (0)	[thatgarrett] hey, thanks a lot for the costco info.
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04-19-2024, 09:47 AM	#10
danb1979 Idiotic lifter of heavy stones... 1897 Rep 2,090 Posts Drives: 2015 F31 325D M Sport touring Join Date: Feb 2022 Location: Preston, Lancashire - UK iTrader: (0)	FWIW I run 18x8 405Ms and 18x8 397s on my F31 (405Ms = summer / 397s = winters) They run 235/45/18 tyres all round and they've been spot on; not stretched like 225/45's and with a straighter sidewall/better rim protection too 397s: 405Ms: __________________ My car: 2015 F31 325D M Sport Touring in Glacier Metallic Silver - Keeping it OEM 'Plus' Project: https://f30.bimmerpost.com/forums/sh....php?t=1982298 Last edited by danb1979; 04-19-2024 at 10:43 AM..
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