225/45/18 to 255/35/18 ... 3.78% difference

XKxRome0ox · 03-21-2017, 11:57 AM

using an online tire calculator, it shows that going from 225/45/18 to 255/35/18
will make -3.64% in diameter difference ...
and that speedometer will read 3.78% too fast.

and the rear 255/40/18 to 255/35/18 will make -3.86% in diameter difference...
and that speedometer will read 4.01% too fast.

is this within acceptable range? am i taking a risk? risk of what?
i'm ready for any and all feedback

goj · 03-21-2017, 01:31 PM

This is not something that anyone would advise you to do. You would want to maintain 255/40 R18

XKxRome0ox · 03-21-2017, 01:56 PM

Quote:

Originally Posted by goj

This is not something that anyone would advise you to do. You would want to maintain 255/40 R18

yes
but what am i facing by doing this?

the online tire calculator mentions that there could be brake failure if the tire diameter is off by more than 3%......
trying to understand how

goj · 03-21-2017, 02:32 PM

Quote:

Originally Posted by XKxRome0ox

Quote:

Originally Posted by goj

This is not something that anyone would advise you to do. You would want to maintain 255/40 R18

yes
but what am i facing by doing this?

the online tire calculator mentions that there could be brake failure if the tire diameter is off by more than 3%......
trying to understand how

Your speedometer is set from the factory to state a bit faster than actual speed. By reducing the overall radius your speedometer will then read even faster. It will also make the wheel look too small for the wheel well

wdeerfield · 03-21-2017, 02:34 PM

why would you want to go with that short of a sidewall?

Feddersen · 03-21-2017, 02:47 PM

You will not encounter any issues if you also go down to a similar size in the front (225/40-18). The tires will look a bit small, the car will be lowered a tiny bit and thats about all. I have this setup for my track tires and know another guy who did the same.

XKxRome0ox · 03-21-2017, 02:48 PM

Quote:

Originally Posted by wdeerfield

why would you want to go with that short of a sidewall?

i don't
but the wheels i'm buying have those tires on them right now
255/35r18 Bridgestone RE-71R

worst case scenario, i have to sell the used tires and get another set to use with the wheels

XKxRome0ox · 03-21-2017, 02:50 PM

Quote:

Originally Posted by Feddersen

You will not encounter any issues if you also go down to a similar size in the front (225/40-18). The tires will look a bit small, the car will be lowered a tiny bit and thats about all. I have this setup for my track tires and know another guy who did the same.

it's 18x8.5 et45 with 255/35/18
SQUARE setup

Feddersen · 03-21-2017, 02:54 PM

Then there is not problem at all. They will just look small and lower the car a bit. I use 225/40 + 255/35 for the track.

Yes, the speedo will show your speed as beeing a bit faster as you're actually going but that is no problem. The car will work as intended and expected.

Heel328 · 03-21-2017, 03:04 PM

255/35 18 is an E90 tire size, which is a bit smaller than F30.

XKxRome0ox · 03-21-2017, 03:13 PM

Quote:

Originally Posted by Heel328

255/35 18 is an E90 tire size, which is a bit smaller than F30.

i had an e46 with 225/40/18 and 255/35/18 which was the factory sizing for the ZHP wheels and tires
and then later had e90/92 wheels with same size wheels and tires on the e46

Quote:

Originally Posted by Feddersen

Then there is not problem at all. They will just look small and lower the car a bit. I use 225/40 + 255/35 for the track.

Yes, the speedo will show your speed as beeing a bit faster as you're actually going but that is no problem. The car will work as intended and expected.

cool
so it will keep me from speeding as much

anyway
i'll give the 255/35/18 a try
hopefully my wheels will not fall off and the car won't blow up

and when time comes for replacement tires, i'll get 255/40/18 or maybe go with 245 all around

wdeerfield · 03-21-2017, 08:20 PM

18x8.5 et45 will require spacers up front to clear the brake caliper and the strut. im running 18x8.5 et40 and have about 3mm of clearance with 235/45/18s

XKxRome0ox · 03-21-2017, 08:30 PM

Quote:

Originally Posted by wdeerfield

18x8.5 et45 will require spacers up front to clear the brake caliper and the strut. im running 18x8.5 et40 and have about 3mm of clearance with 235/45/18s

that was a concern
i was planning on using 5mm spacers ......... and i guess that'd put me at where you are with the et40 wheels?

iki4life · 03-21-2017, 09:25 PM

Im running 245/40/18 squared. I think its a 1% difference, and the tire looks nice and fat/wide when looking from the back.
If you plan on running a squared setup, then 245/40/18 is the way to go....a select few also consider 245/45/18.

03-21-2017, 11:57 AM	#1
XKxRome0ox e90noob 1588 Rep 1,862 Posts Drives: '08 E90 M3 Join Date: Mar 2012 Location: Los Angeles, CA iTrader: (4)	225/45/18 to 255/35/18 ... 3.78% difference using an online tire calculator, it shows that going from 225/45/18 to 255/35/18 will make -3.64% in diameter difference ... and that speedometer will read 3.78% too fast. and the rear 255/40/18 to 255/35/18 will make -3.86% in diameter difference... and that speedometer will read 4.01% too fast. is this within acceptable range? am i taking a risk? risk of what? i'm ready for any and all feedback __________________ 2008 E90 M3 / LCI trunk + euro tail swap Production date - 2008-04-22
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03-21-2017, 01:31 PM	#2
goj Brigadier General 2253 Rep 3,622 Posts Drives: 2016 EBII 340i 6-MT Join Date: Aug 2015 Location: Bay Area, CA iTrader: (0)	This is not something that anyone would advise you to do. You would want to maintain 255/40 R18 __________________ BMW CCA Member #516012 2016 340i, Estoril Blue, Manual Transmission, MPE, MPBBK, HRE FF04 Instagram: @brandons340i
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03-21-2017, 02:34 PM	#5
wdeerfield A family of bimmers 2747 Rep 7,742 Posts Drives: '18 G01 X3M40i Join Date: Jan 2012 Location: Clifton Park, NY iTrader: (0)	why would you want to go with that short of a sidewall? __________________ 2018 PB/Black G01 X3M40i \| 699M \| ZDA \| ZPP \| ZPX \| Maxton front lip \| X3M vents \| 15mm Spacers \| Diamond G20 style grills
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03-21-2017, 02:47 PM	#6
Feddersen Lieutenant 451 Rep 469 Posts Drives: X1 xDrive25i Join Date: Jan 2015 Location: Denmark iTrader: (0)	You will not encounter any issues if you also go down to a similar size in the front (225/40-18). The tires will look a bit small, the car will be lowered a tiny bit and thats about all. I have this setup for my track tires and know another guy who did the same. __________________ DD: F48 X1 xDrive25i '20 - https://f48.bimmerpost.com/forums/sh....php?t=1703083 For fun: F22 M240i '19 - https://www.2addicts.com/forums/show....php?t=1644646 Previous BMW: Fully loaded F30, 335i https://f30.bimmerpost.com/forums/sh....php?t=1681247
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03-21-2017, 02:54 PM	#9
Feddersen Lieutenant 451 Rep 469 Posts Drives: X1 xDrive25i Join Date: Jan 2015 Location: Denmark iTrader: (0)	Then there is not problem at all. They will just look small and lower the car a bit. I use 225/40 + 255/35 for the track. Yes, the speedo will show your speed as beeing a bit faster as you're actually going but that is no problem. The car will work as intended and expected. __________________ DD: F48 X1 xDrive25i '20 - https://f48.bimmerpost.com/forums/sh....php?t=1703083 For fun: F22 M240i '19 - https://www.2addicts.com/forums/show....php?t=1644646 Previous BMW: Fully loaded F30, 335i https://f30.bimmerpost.com/forums/sh....php?t=1681247
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03-21-2017, 03:04 PM	#10
Heel328 First Lieutenant 79 Rep 369 Posts Drives: 2013 328i 6MT Join Date: Mar 2015 Location: Carolina iTrader: (0)	255/35 18 is an E90 tire size, which is a bit smaller than F30.
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03-21-2017, 08:20 PM	#12
wdeerfield A family of bimmers 2747 Rep 7,742 Posts Drives: '18 G01 X3M40i Join Date: Jan 2012 Location: Clifton Park, NY iTrader: (0)	18x8.5 et45 will require spacers up front to clear the brake caliper and the strut. im running 18x8.5 et40 and have about 3mm of clearance with 235/45/18s __________________ 2018 PB/Black G01 X3M40i \| 699M \| ZDA \| ZPP \| ZPX \| Maxton front lip \| X3M vents \| 15mm Spacers \| Diamond G20 style grills
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03-21-2017, 09:25 PM	#14
iki4life Second Lieutenant 49 Rep 273 Posts Drives: 2013 BMW 328i SportLine Join Date: Aug 2015 Location: Harrisburg, PA iTrader: (0)	Im running 245/40/18 squared. I think its a 1% difference, and the tire looks nice and fat/wide when looking from the back. If you plan on running a squared setup, then 245/40/18 is the way to go....a select few also consider 245/45/18.
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