245/45r vs 245/40 on a 17x9 - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

Toyobaru808 · 08-01-2013, 01:03 AM

Are there any advantages to running a 245/40 over a 245/45?

Im specifically looking at Continental extreme contact DW

This would be for my DD and occasional spirited drive

cdo221 · 08-01-2013, 01:37 AM

One advantage is that 245/40s are significantly closer to the OEM tire/wheel overall diameter than the 245/45s.

If your speedo says 75 and you're on 245/45/17s, you're going to actually be going 78 mph but with 245/40/17s, you'll actually be going 75 if the speedo says 75.

Toyobaru808 · 08-01-2013, 01:46 AM

Huh, yeah youre right....

I thought that since our stock tire has a sidewall of 45 that getting a 245/45 would the same.. weird. why would increased width affect diameter??

WolfsFang · 08-01-2013, 01:53 AM

245 is the width of the tread in millimeters

45 means the sidewall height is 45% of the tread width.
Stock tire: 215 * 0.45 = 97MM
Tire 1: 245 * 0.45 = 110MM
Tire 2: 245 * 0.40 = 98MM <-- Winner! Winner!

So the 245/40 is closer to the oem sidewall tire.

Toyobaru808 · 08-01-2013, 02:03 AM

^^^^

AHH i see, i always thought the sidewall number was a fixed measurement like mm or something like that.

Thanks for clearing that up

cdo221 · 08-01-2013, 02:29 AM

I was thinking about this in the shower just now too..

Generally speaking, the lower profile the tire (shorter the sidewall), the stiffer it will be. It translates into better handling/acceleration/braking usually - so aside from the speedometer accuracy, the 245/40/17s should have a performance benefit over the 245/45/17s as well. The downside is of course decreased ride-quality going over pot holes/bumps due to the stiffer ride.

Felix · 08-01-2013, 05:49 AM

What are people's thoughts on 17/40/255's?
Compared to 245's?

I'm thinking about going 255's and a little worried about clearance issues... It'll be dropped fairly low on coilovers

ft_sjo · 08-01-2013, 05:51 AM

40's will have less compliance than 45's.
40's (of the same tyre) will have less ride comfort.
40's will have less grip over typical roads.
40's may provide better suspension/arch clearance.

So the bottom line; if the 45 clears the suspension/arches, then it's the better tyre.

djdnz · 08-01-2013, 09:50 AM

Quote:

Originally Posted by Felix

What are people's thoughts on 17/40/255's?
Compared to 245's?

I'm thinking about going 255's and a little worried about clearance issues... It'll be dropped fairly low on coilovers

Wheel specs? 255 on a 9" is not a prob, just offset matters

TrogDor the Burninator · 08-01-2013, 09:57 AM

I'm running 18x9 wheels with 255/35 ZIIs ... no issues with rubbing. I'm running RCE Tarmac 2 coilovers as well with a 1.5" drop ...

I would think a 17x9 +40 would be fine if you dropped an inch ...

bkblitzed · 08-01-2013, 02:28 PM

technically anything lower than a 235 you would want a 45 or more sidewall. Anything more than a 245 tire and you would want a 40 or less sidewall.

Felix · 08-01-2013, 08:10 PM

Quote:

Originally Posted by djdnz

Wheel specs? 255 on a 9" is not a prob, just offset matters

RPF1's 17x9 +35
17/40/255's all round.
Lowered on coilovers so there is no wheel gap (hopefully), maybe a little tuck if possible

08-01-2013, 01:03 AM	#1
Toyobaru808 Senior Member Join Date: Jul 2012 Drives: FR-S Location: Hawaii Posts: 112 Thanks: 22 Thanked 14 Times in 13 Posts Mentioned: 0 Post(s) Tagged: 0 Thread(s)	245/45r vs 245/40 on a 17x9 Are there any advantages to running a 245/40 over a 245/45? Im specifically looking at Continental extreme contact DW This would be for my DD and occasional spirited drive

08-01-2013, 01:53 AM	#4
WolfsFang Scrape Master Join Date: Jun 2012 Drives: Goal: Oldest FRS State Side Location: North NJ Posts: 1,161 Thanks: 238 Thanked 412 Times in 238 Posts Mentioned: 10 Post(s) Tagged: 0 Thread(s)	245 is the width of the tread in millimeters 45 means the sidewall height is 45% of the tread width. Stock tire: 215 * 0.45 = 97MM Tire 1: 245 * 0.45 = 110MM Tire 2: 245 * 0.40 = 98MM <-- Winner! Winner! So the 245/40 is closer to the oem sidewall tire. __________________ You do realize comparing the BRZ to the FR-S is like comparing which hand you love masterbating too right? Last edited by WolfsFang; 08-01-2013 at 02:08 AM.

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08-01-2013, 01:37 AM	#2
cdo221 Senior Member Join Date: Nov 2012 Drives: 2013 Ultramarine FR-S, 2015 RS 1.0 Location: SF Bay Area Posts: 532 Thanks: 285 Thanked 174 Times in 110 Posts Mentioned: 13 Post(s) Tagged: 0 Thread(s)	One advantage is that 245/40s are significantly closer to the OEM tire/wheel overall diameter than the 245/45s. If your speedo says 75 and you're on 245/45/17s, you're going to actually be going 78 mph but with 245/40/17s, you'll actually be going 75 if the speedo says 75.

08-01-2013, 01:46 AM	#3
Toyobaru808 Senior Member Join Date: Jul 2012 Drives: FR-S Location: Hawaii Posts: 112 Thanks: 22 Thanked 14 Times in 13 Posts Mentioned: 0 Post(s) Tagged: 0 Thread(s)	Huh, yeah youre right.... I thought that since our stock tire has a sidewall of 45 that getting a 245/45 would the same.. weird. why would increased width affect diameter??

08-01-2013, 02:03 AM	#5
Toyobaru808 Senior Member Join Date: Jul 2012 Drives: FR-S Location: Hawaii Posts: 112 Thanks: 22 Thanked 14 Times in 13 Posts Mentioned: 0 Post(s) Tagged: 0 Thread(s)	^^^^ AHH i see, i always thought the sidewall number was a fixed measurement like mm or something like that. Thanks for clearing that up

08-01-2013, 02:29 AM	#6
cdo221 Senior Member Join Date: Nov 2012 Drives: 2013 Ultramarine FR-S, 2015 RS 1.0 Location: SF Bay Area Posts: 532 Thanks: 285 Thanked 174 Times in 110 Posts Mentioned: 13 Post(s) Tagged: 0 Thread(s)	I was thinking about this in the shower just now too.. Generally speaking, the lower profile the tire (shorter the sidewall), the stiffer it will be. It translates into better handling/acceleration/braking usually - so aside from the speedometer accuracy, the 245/40/17s should have a performance benefit over the 245/45/17s as well. The downside is of course decreased ride-quality going over pot holes/bumps due to the stiffer ride.

08-01-2013, 05:49 AM	#7
Felix Member Join Date: Jun 2013 Drives: Toyota 86 GTS Location: Australia QLD Posts: 20 Thanks: 0 Thanked 5 Times in 5 Posts Mentioned: 0 Post(s) Tagged: 0 Thread(s)	What are people's thoughts on 17/40/255's? Compared to 245's? I'm thinking about going 255's and a little worried about clearance issues... It'll be dropped fairly low on coilovers

08-01-2013, 05:51 AM	#8
ft_sjo Banned Join Date: Oct 2012 Drives: GT86 Location: The Motherland Posts: 1,398 Thanks: 140 Thanked 473 Times in 271 Posts Mentioned: 22 Post(s) Tagged: 0 Thread(s)	40's will have less compliance than 45's. 40's (of the same tyre) will have less ride comfort. 40's will have less grip over typical roads. 40's may provide better suspension/arch clearance. So the bottom line; if the 45 clears the suspension/arches, then it's the better tyre.

08-01-2013, 02:28 PM	#11
bkblitzed is better than you Join Date: Jun 2013 Drives: 2013 raven FRS Location: Norcal Posts: 1,293 Thanks: 591 Thanked 1,347 Times in 745 Posts Mentioned: 25 Post(s) Tagged: 0 Thread(s)	technically anything lower than a 235 you would want a 45 or more sidewall. Anything more than a 245 tire and you would want a 40 or less sidewall.

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