Rear end ratio and ECU changes? - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

mid_life_crisis · 01-19-2015, 02:20 PM

Poking around in the tables and came across this. If this is what it says it is, shouldn't these be changed if the rear end ratio is changed?

I can't get the image to display properly, but it's a table from
Miscellaneous - Thresholds

Gear Determination Thresholds

Gear thresholds Vs Rev/Mile

Toyota John · 01-19-2015, 03:16 PM

I think this is true and maybe someone else can back this up. I believe that the speed is taken from the ABS sensors in the wheels so rear gearing changes shouldn't have any effect. How ever tire diameter will.

Kodename47 · 01-19-2015, 04:16 PM

Quote:

Originally Posted by Toyota John

I think this is true and maybe someone else can back this up. I believe that the speed is taken from the ABS sensors in the wheels so rear gearing changes shouldn't have any effect. How ever tire diameter will.

Correct mate

mid_life_crisis · 01-19-2015, 06:14 PM

That is true, but I don't think the table is about the speedometer. It has multiple values that pretty clearly tell which gear the transmission should be in depending on the rotational speed of the tires. 65 mph with 4.10 gears could call for a different minimum gear selection than with 4.88, for example. That's why I wonder exactly what the table does and if it should be edited.

Toyota John · 01-19-2015, 11:23 PM

I think that is related to Auto Trans?

steve99 · 01-20-2015, 04:52 AM

Quote:

Originally Posted by mid_life_crisis

That is true, but I don't think the table is about the speedometer. It has multiple values that pretty clearly tell which gear the transmission should be in depending on the rotational speed of the tires. 65 mph with 4.10 gears could call for a different minimum gear selection than with 4.88, for example. That's why I wonder exactly what the table does and if it should be edited.

I believe that table is to calculate what gear number to display in the dash

if you need to adjust speedo error i believe that can be done with techstream software its got a limited range for speedo correction. you can get the software for free but you will need an J2534 adapter to talk to obd port, unless you have a tactrix cable or ecutek cable .

you can get the elcheapo j2534 adapters for techstream software on ebay, just search for techstream.

dont buy the imitation clone tactrix adapters from china, they are rubbish and likely to brick your ecu buy the real one from e tactrix site www.tactrix.com if you want a tactrix adapter.

makinen · 01-20-2015, 08:31 AM

Hi,

Gear Determination Thresholds is basically related to the gear indicator in your cluster.
With modified final gear ratio, you'll see unmatched gear number in your cluster. To say, 1-2-3-3-4-5 rather than 1-2-3-4-5-6.

wootwoot · 01-20-2015, 10:41 AM

I would LOVE it if we could find a solution for this..... As would everyone with an upgraded final drive.

Toyota John · 01-20-2015, 04:03 PM

Quote:

Originally Posted by wootwoot

I would LOVE it if we could find a solution for this..... As would everyone with an upgraded final drive.

Which problem are your talking about? The auto trans showing the wrong gear with a different final drive?

PantsDants · 01-20-2015, 04:44 PM

Quote:

Originally Posted by mid_life_crisis

Poking around in the tables and came across this. If this is what it says it is, shouldn't these be changed if the rear end ratio is changed?

I can't get the image to display properly, but it's a table from
Miscellaneous - Thresholds

Gear Determination Thresholds

Gear thresholds Vs Rev/Mile

The only thing this table controls is the gear display on the dash for manual cars. It doesn't have any impact on gear readout on automatic cars.

You can adjust the table by multiplying all of its cells by the percent change you induced by changing your final drive. Ex: If you went to 4.88 from stock 4.1, you increased the ratio by 19%. Another way of saying that is you're at 119% of stock. So take that percentage (1.19) and multiply it against the table. Your gears should read correctly now.

mid_life_crisis · 01-21-2015, 07:15 AM

It doesn't make sense to me for that table to be for gear display. At pretty much any speed (leaving out extreme high or low) there are multiple gears you could be in for that speed. This table can't account for that by itself.

shif7i7down · 01-21-2015, 10:32 AM

@makinen is correct, with the mfactory 4.67 final drive I get 1,2,3,3,4,5 on the display

PantsDants · 01-21-2015, 02:14 PM

Quote:

Originally Posted by mid_life_crisis

It doesn't make sense to me for that table to be for gear display. At pretty much any speed (leaving out extreme high or low) there are multiple gears you could be in for that speed. This table can't account for that by itself.

The ECU also knows what your current RPM and speed are. It uses that table as part of the calculation to determine the current gear, not just by itself.

01-19-2015, 02:20 PM	#1
mid_life_crisis Senior Member Join Date: May 2013 Drives: FR-S 10 #103 AT Location: NC Posts: 1,519 Thanks: 101 Thanked 599 Times in 347 Posts Mentioned: 5 Post(s) Tagged: 0 Thread(s)	Rear end ratio and ECU changes? Poking around in the tables and came across this. If this is what it says it is, shouldn't these be changed if the rear end ratio is changed? I can't get the image to display properly, but it's a table from Miscellaneous - Thresholds Gear Determination Thresholds Gear thresholds Vs Rev/Mile __________________ Necessity may be the mother of Invention but Desperation is quite often the father. “Sex is like Bridge. If you don't have a good partner, you'd better have a good hand.” - Mae West Papa said, "son there's a lot of evil temptations out there. Best to try 'em all so you know which ones to avoid." Last edited by mid_life_crisis; 01-19-2015 at 02:39 PM.

01-19-2015, 06:14 PM	#4
mid_life_crisis Senior Member Join Date: May 2013 Drives: FR-S 10 #103 AT Location: NC Posts: 1,519 Thanks: 101 Thanked 599 Times in 347 Posts Mentioned: 5 Post(s) Tagged: 0 Thread(s)	That is true, but I don't think the table is about the speedometer. It has multiple values that pretty clearly tell which gear the transmission should be in depending on the rotational speed of the tires. 65 mph with 4.10 gears could call for a different minimum gear selection than with 4.88, for example. That's why I wonder exactly what the table does and if it should be edited. __________________ Necessity may be the mother of Invention but Desperation is quite often the father. “Sex is like Bridge. If you don't have a good partner, you'd better have a good hand.” - Mae West Papa said, "son there's a lot of evil temptations out there. Best to try 'em all so you know which ones to avoid."

01-21-2015, 07:15 AM	#11
mid_life_crisis Senior Member Join Date: May 2013 Drives: FR-S 10 #103 AT Location: NC Posts: 1,519 Thanks: 101 Thanked 599 Times in 347 Posts Mentioned: 5 Post(s) Tagged: 0 Thread(s)	It doesn't make sense to me for that table to be for gear display. At pretty much any speed (leaving out extreme high or low) there are multiple gears you could be in for that speed. This table can't account for that by itself. __________________ Necessity may be the mother of Invention but Desperation is quite often the father. “Sex is like Bridge. If you don't have a good partner, you'd better have a good hand.” - Mae West Papa said, "son there's a lot of evil temptations out there. Best to try 'em all so you know which ones to avoid."

01-21-2015, 10:32 AM	#12
shif7i7down Erected Member Join Date: Mar 2014 Drives: frs Location: Wisconsin Posts: 391 Thanks: 69 Thanked 185 Times in 100 Posts Mentioned: 10 Post(s) Tagged: 0 Thread(s)	@makinen is correct, with the mfactory 4.67 final drive I get 1,2,3,3,4,5 on the display __________________ https://www.facebook.com/profile.php?=87912848

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Shorter spring with FRS front rear rate ratio?	Mars2	Suspension \| Chassis \| Brakes -- Sponsored by 949 Racing	1	05-28-2013 08:15 AM
Rear End/Gear/Differential Ratio	fly2low	Engine, Exhaust, Transmission	9	02-09-2013 11:53 AM
Rear End Ratio	White64Goat	Engine, Exhaust, Transmission	6	07-07-2012 11:37 PM
FR-S to BRZ Ratio	MannyO	New England	11	03-08-2012 02:23 AM
86,BRZ MT gear ratio	Yobiwan	Engine, Exhaust, Transmission	1	01-26-2012 02:40 AM

01-19-2015, 03:16 PM	#2
Toyota John Calle Atun Join Date: Sep 2013 Drives: 13 FRS, 93 Mr2, 85 ae86 Location: CT Posts: 158 Thanks: 12 Thanked 11 Times in 10 Posts Mentioned: 1 Post(s) Tagged: 0 Thread(s)	I think this is true and maybe someone else can back this up. I believe that the speed is taken from the ABS sensors in the wheels so rear gearing changes shouldn't have any effect. How ever tire diameter will.

01-19-2015, 11:23 PM	#5
Toyota John Calle Atun Join Date: Sep 2013 Drives: 13 FRS, 93 Mr2, 85 ae86 Location: CT Posts: 158 Thanks: 12 Thanked 11 Times in 10 Posts Mentioned: 1 Post(s) Tagged: 0 Thread(s)	I think that is related to Auto Trans?

01-20-2015, 08:31 AM	#7
makinen Senior Member Join Date: Jan 2013 Drives: Toyota 86 Location: South Korea Posts: 267 Thanks: 127 Thanked 201 Times in 115 Posts Mentioned: 5 Post(s) Tagged: 0 Thread(s)	Hi, Gear Determination Thresholds is basically related to the gear indicator in your cluster. With modified final gear ratio, you'll see unmatched gear number in your cluster. To say, 1-2-3-3-4-5 rather than 1-2-3-4-5-6.

01-20-2015, 10:41 AM	#8
wootwoot Senior Member Join Date: Jul 2012 Drives: FRS Location: Cali Posts: 1,558 Thanks: 188 Thanked 461 Times in 264 Posts Mentioned: 9 Post(s) Tagged: 0 Thread(s)	I would LOVE it if we could find a solution for this..... As would everyone with an upgraded final drive.

User Name		Remember Me?
Password