Speedo issues - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

Venator · 02-12-2014, 10:17 PM

So I was looking at some 18 x 8.5 wheels and found that it puts the speedo all out of whack:

Is there a way to compensate for this?

Burrcold · 02-12-2014, 10:24 PM

Don't look at your speedo?

jvincent · 02-12-2014, 10:30 PM

Quote:

Originally Posted by Venator

Is there a way to compensate for this?

No. Geometry is geometry.

If you car about a better match for the speedometer, go with 245/35. If you really want 255, subtract 1 when you look at your speedometer.

Of course you are assuming that the speedometer was actually 100% accurate with the stock tires.

Venator · 02-12-2014, 10:31 PM

Quote:

Originally Posted by Burrcold

Don't look at your speedo?

Venator · 02-12-2014, 10:32 PM

Quote:

Originally Posted by jvincent

No. Geometry is geometry.

If you car about a better match for the speedometer, go with 245/35. If you really want 255, subtract 1 when you look at your speedometer.

Of course you are assuming that the speedometer was actually 100% accurate with the stock tires.

Agreed, I was just curious if this was something that a tune could "sort out"

kidgogeta · 02-12-2014, 10:50 PM

Quote:

Originally Posted by Venator

Agreed, I was just curious if this was something that a tune could "sort out"

the tune for my dodge ram takes into account tire and wheel size and adjusts the speedometer accordingly, not sure if there is anything out for the twins

Imrac · 02-12-2014, 11:15 PM

While driving subtract one when going more than 30MPH (assuming it rounds)?

KONVERTER · 02-12-2014, 11:42 PM

get a tire size with the exact same diameter as the stock tires... But make sure they never ever ever wear, because the slightest amount of tire wear even on the stock tires is going to change the speedo readout... air pressure too for that matter... get Nitrogen quick so air pressure is constant.

h4nh · 02-13-2014, 12:17 AM

1 mile per hour off.. seriously?

mwjcyber · 02-13-2014, 12:55 AM

Quote:

Originally Posted by h4nh

1 mile per hour off.. seriously?

This^

Venator · 02-13-2014, 01:59 AM

Quote:

Originally Posted by KONVERTER

get a tire size with the exact same diameter as the stock tires... But make sure they never ever ever wear, because the slightest amount of tire wear even on the stock tires is going to change the speedo readout... air pressure too for that matter... get Nitrogen quick so air pressure is constant.

No need to be sarcastic, it was an honest question... Obviously tires wear and that alters the accuracy but I was curious if there was a way to minimize the margin of error.

KONVERTER · 02-13-2014, 03:07 AM

It is already very minsized. Plus you are putting less miles on your car, better for you when it comes to warranty.

Never heard of a dealer saying they aren't going to warrant something because mileage isn't Accurate due to tire size putting o n false mileage.

JP · 02-13-2014, 04:23 AM

have you checked the accuracy of your speedo on stock tyres? Mine reads high by 5% on the stock setup

JS86JS · 02-14-2014, 01:25 AM

Use a navagation system.
Not the cars one obviously, but one you stick to your windscreen. Or download the 'Tom Tom' app from App Store to test.
2 different brand of navs at 100km/h (cruise control on car) read 95-97 on the navs.
So I can only assume the stock car odometer is 4-5% slower than what it says for speeding issues etc.
it's reported that on average all car speedos are anywhere between 2-10% out of actual speedo readings to save you if you accidentally go 65 through a camera it's actually 60 or so (according to wheels magazine)

Or get an incredibly thin tire, same diameter as stock or become comfortable with going "60" but actually doing 61!!

The choice is yours :p

Injen Catback, Injen CAI, Borla UEL headers, ecutek tune w/ racerom, alloy pulley kit, Yokohama Neova AD08; 189hp at the wheels best dyno

02-12-2014, 10:17 PM	#1
Venator Senior Member Join Date: Feb 2014 Drives: Asphalt FR-S Location: Central PA Posts: 315 Thanks: 159 Thanked 59 Times in 43 Posts Mentioned: 1 Post(s) Tagged: 0 Thread(s)	Speedo issues So I was looking at some 18 x 8.5 wheels and found that it puts the speedo all out of whack: Is there a way to compensate for this? __________________ And Jezza spake unto them and proclaimed that he who shall be last, shall be sideways and smiling.

02-12-2014, 10:24 PM	#2
Burrcold Senior Member Join Date: Jul 2010 Drives: Subaru BRZ Limited Location: Toronto, Canada Posts: 2,624 Thanks: 763 Thanked 1,586 Times in 776 Posts Mentioned: 10 Post(s) Tagged: 0 Thread(s)	Don't look at your speedo? __________________

02-13-2014, 12:17 AM	#9
h4nh Senior Member Join Date: Oct 2013 Drives: Turbo BRZ & Supercharged E90 M3 Location: Dallas, TX Posts: 559 Thanks: 4 Thanked 452 Times in 225 Posts Mentioned: 24 Post(s) Tagged: 0 Thread(s)	1 mile per hour off.. seriously? __________________ my build thread instagram.com/mod_circle

02-14-2014, 01:25 AM	#14
JS86JS Member Join Date: Mar 2013 Drives: 2013 Toyota 86 GTS, Marine Blue Location: Sydney, Australia Posts: 52 Thanks: 20 Thanked 5 Times in 4 Posts Mentioned: 0 Post(s) Tagged: 0 Thread(s)	Use a navagation system. Not the cars one obviously, but one you stick to your windscreen. Or download the 'Tom Tom' app from App Store to test. 2 different brand of navs at 100km/h (cruise control on car) read 95-97 on the navs. So I can only assume the stock car odometer is 4-5% slower than what it says for speeding issues etc. it's reported that on average all car speedos are anywhere between 2-10% out of actual speedo readings to save you if you accidentally go 65 through a camera it's actually 60 or so (according to wheels magazine) Or get an incredibly thin tire, same diameter as stock or become comfortable with going "60" but actually doing 61!! The choice is yours :p Injen Catback, Injen CAI, Borla UEL headers, ecutek tune w/ racerom, alloy pulley kit, Yokohama Neova AD08; 189hp at the wheels best dyno __________________ check out my on-going build here: My blue 86

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02-12-2014, 11:42 PM	#8
KONVERTER Senior Member Join Date: Jul 2013 Drives: BRZ Location: LA Posts: 225 Thanks: 1 Thanked 69 Times in 44 Posts Mentioned: 4 Post(s) Tagged: 0 Thread(s)	get a tire size with the exact same diameter as the stock tires... But make sure they never ever ever wear, because the slightest amount of tire wear even on the stock tires is going to change the speedo readout... air pressure too for that matter... get Nitrogen quick so air pressure is constant.

02-13-2014, 03:07 AM	#12
KONVERTER Senior Member Join Date: Jul 2013 Drives: BRZ Location: LA Posts: 225 Thanks: 1 Thanked 69 Times in 44 Posts Mentioned: 4 Post(s) Tagged: 0 Thread(s)	It is already very minsized. Plus you are putting less miles on your car, better for you when it comes to warranty. Never heard of a dealer saying they aren't going to warrant something because mileage isn't Accurate due to tire size putting o n false mileage.

02-13-2014, 04:23 AM	#13
JP Backyard Fabricator Join Date: May 2012 Drives: JZX83, SF5 GT, ZZE82 turbo Location: Australia Posts: 303 Thanks: 47 Thanked 166 Times in 83 Posts Mentioned: 40 Post(s) Tagged: 0 Thread(s)	have you checked the accuracy of your speedo on stock tyres? Mine reads high by 5% on the stock setup

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