Is there a way to code speedometer correction?? - BMW 3-Series (E90 E92) Forum

PyroZona · 05-07-2012, 11:11 PM

Hi all,

Ok, I know about the coding to deactivate the 5-10 mph over actual reading on the speedometer, what I'm asking about is the possibility of a way to compensate for changing the sidewall height of the tires. I have the stock sizes on my '08 E60 M5 now (285/35-19), but will be changing to 305/30-19s on the rear and 275/35-19s on the front. I know this will cause the speedometer to read low, but not sure exactly how low. I'm hoping that perhaps just re-enabling the BC_DIGITAL_V_KORRECTUR would match the error in the reading, but won't be holding my breath. So if there's a way to code in an exact correction for the speedo, I'd love to know how to do it.

Anyone?

Thanks,

Peter

Bendercle · 05-08-2012, 10:24 AM

Nettodat coding maybe... I know DVD in motion was solved this way and that also referred to specific speed. I'm too busy right now but someone could try looking at what bits the Korrectur line changes and see if it refers to an actual speed.

GenePoole · 05-08-2012, 01:00 PM

BC_V_KORRECTOR only has two values: aktiv and nicht_activ with a binary mask so nothing to be gained there. I've played around with K_ZAHL_TACHO and K_ZAHL_TACHO_KOMPL with the normal values (wert_0x, etc) but there may be some room to play with these using NETTODAT coding. They both have WORD values (2 bytes) with FF mask so there's a lot of possibility there (0 to 65535 or -32768 to 32767 if it's considered a signed WORD). K_ZAHL_TACHO* values are supposedly for calibrating the speedometer for different tire sizes.

If I get a chance tonight, I'll play around and see what happens.

GenePoole · 05-08-2012, 10:16 PM

It does work. I've got some calculating to do, but I changed it by a huge amount just to test and I was showing 52 mph on my GPS and 84 on the speedometer.

K_ZAHL_TACHO_KOMPL seems to be the 1's compliment of the K_ZAHL_TACHO value. I'm not sure what the relationship is of the two, but I deliberately made the K_ZAHL_TACHO_KOMPL a 1's compliment of my modified K_ZAHL_TACHO value before flashing it to the KOMBI.

The original value at address 00300201 was B2, 5E, 4D, A1. Converted to little endian, it gives 5EB2 (24242) and A14D (-24243). I changed them to 4E20 (20000) and B1DF (-20001) or in the NETTODAT.TRC file, 20, 4E, DF, B1. It looks like I need to use a higher value for a lower speedometer reading. I'll try this again with like 26000/-26001 and see what it gives. From these, I should be able to calculate a proper ratio and a correction.

everlast · 05-08-2012, 11:14 PM

A - fucking - mazing.

I'll bite: does it affect the odometer? If so, we've just found one new way to be leery of a low mileage car.

GenePoole · 05-10-2012, 07:34 AM

Quote:

Originally Posted by everlast

A - fucking - mazing.

I'll bite: does it affect the odometer? If so, we've just found one new way to be leery of a low mileage car.

From what I've read, the odometer is affected by the K_ZAHL_WEG, and K_ZAHL_WEG_KOMPL values. I haven't touched them.

GenePoole · 05-10-2012, 07:39 AM

My first attempt at a solution. My speedo reads about 63 mph when my gps says 60 mph. I changed the K_ZAHL_TACHO word (from default of 24232) to 24800 (0x60E0 -- and the KOMPL to -24801/0x9F1F ) then drove to work this morning with my Android GPS in the dock. It made about a 1 mph difference at 60 mph (still 2 mph high) so I'll need to bump that a little higher. I'll try 26000 when I get a chance and see where that puts me.

Motastic · 05-10-2012, 10:18 AM

if this gets done, would love to fix it on my damm car, i hate seeing incorrect speed

GenePoole · 05-11-2012, 07:31 AM

I noticed an unwanted side effect: the digital speed display always reads zero. I'm going to give up on this approach. Although it seems to work in that it definitely changes the way the speedometer registers actual speed, I still think there must be a simple toggle that accomplishes the same thing. The digital speed reading is always spot on (when BC_DIGITAL_V_KORRECTUR is set to nicht_aktiv) so there must be some simple way of getting this information. I'd rather have a good bc_digital speed and the speedo off than the other way around. The digital readout is always where my eyes go when I see a speed trap anyway.

05-07-2012, 11:11 PM	#1
PyroZona Registered Drives: '08 e60 M5 - Indianapolis Red Join Date: May 2012 Location: Phoenix, AZ Posts: 1 iTrader: (0)	Is there a way to code speedometer correction?? Hi all, Ok, I know about the coding to deactivate the 5-10 mph over actual reading on the speedometer, what I'm asking about is the possibility of a way to compensate for changing the sidewall height of the tires. I have the stock sizes on my '08 E60 M5 now (285/35-19), but will be changing to 305/30-19s on the rear and 275/35-19s on the front. I know this will cause the speedometer to read low, but not sure exactly how low. I'm hoping that perhaps just re-enabling the BC_DIGITAL_V_KORRECTUR would match the error in the reading, but won't be holding my breath. So if there's a way to code in an exact correction for the speedo, I'd love to know how to do it. Anyone? Thanks, Peter __________________ __________________________________________ Unfortunately, common sense isn't really that common after all!!
	Tweet

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

05-08-2012, 10:24 AM	#2
Bendercle Banned Drives: 2007 335xi 6MT Join Date: Jan 2012 Location: North Shore MA Posts: 264 iTrader: (3)	Nettodat coding maybe... I know DVD in motion was solved this way and that also referred to specific speed. I'm too busy right now but someone could try looking at what bits the Korrectur line changes and see if it refers to an actual speed.

05-08-2012, 01:00 PM	#3
GenePoole Lieutenant Drives: '06 E90 330i Join Date: Apr 2010 Location: Brighton, IL Posts: 521 iTrader: (0)	BC_V_KORRECTOR only has two values: aktiv and nicht_activ with a binary mask so nothing to be gained there. I've played around with K_ZAHL_TACHO and K_ZAHL_TACHO_KOMPL with the normal values (wert_0x, etc) but there may be some room to play with these using NETTODAT coding. They both have WORD values (2 bytes) with FF mask so there's a lot of possibility there (0 to 65535 or -32768 to 32767 if it's considered a signed WORD). K_ZAHL_TACHO* values are supposedly for calibrating the speedometer for different tire sizes. If I get a chance tonight, I'll play around and see what happens.

05-08-2012, 10:16 PM	#4
GenePoole Lieutenant Drives: '06 E90 330i Join Date: Apr 2010 Location: Brighton, IL Posts: 521 iTrader: (0)	It does work. I've got some calculating to do, but I changed it by a huge amount just to test and I was showing 52 mph on my GPS and 84 on the speedometer. K_ZAHL_TACHO_KOMPL seems to be the 1's compliment of the K_ZAHL_TACHO value. I'm not sure what the relationship is of the two, but I deliberately made the K_ZAHL_TACHO_KOMPL a 1's compliment of my modified K_ZAHL_TACHO value before flashing it to the KOMBI. The original value at address 00300201 was B2, 5E, 4D, A1. Converted to little endian, it gives 5EB2 (24242) and A14D (-24243). I changed them to 4E20 (20000) and B1DF (-20001) or in the NETTODAT.TRC file, 20, 4E, DF, B1. It looks like I need to use a higher value for a lower speedometer reading. I'll try this again with like 26000/-26001 and see what it gives. From these, I should be able to calculate a proper ratio and a correction.

05-08-2012, 11:14 PM	#5
everlast Malt'm'n'Salt'm Drives: 2008 328xiT Join Date: Jul 2008 Location: Ottawa, ON Posts: 197 iTrader: (0)	A - fucking - mazing. I'll bite: does it affect the odometer? If so, we've just found one new way to be leery of a low mileage car.

05-10-2012, 07:39 AM	#7
GenePoole Lieutenant Drives: '06 E90 330i Join Date: Apr 2010 Location: Brighton, IL Posts: 521 iTrader: (0)	My first attempt at a solution. My speedo reads about 63 mph when my gps says 60 mph. I changed the K_ZAHL_TACHO word (from default of 24232) to 24800 (0x60E0 -- and the KOMPL to -24801/0x9F1F ) then drove to work this morning with my Android GPS in the dock. It made about a 1 mph difference at 60 mph (still 2 mph high) so I'll need to bump that a little higher. I'll try 26000 when I get a chance and see where that puts me.

05-10-2012, 10:18 AM	#8
Motastic Major Drives: E92 335! Join Date: Apr 2011 Location: Arlington, TX Posts: 1,359 iTrader: (4)	if this gets done, would love to fix it on my damm car, i hate seeing incorrect speed

05-11-2012, 07:31 AM	#9
GenePoole Lieutenant Drives: '06 E90 330i Join Date: Apr 2010 Location: Brighton, IL Posts: 521 iTrader: (0)	I noticed an unwanted side effect: the digital speed display always reads zero. I'm going to give up on this approach. Although it seems to work in that it definitely changes the way the speedometer registers actual speed, I still think there must be a simple toggle that accomplishes the same thing. The digital speed reading is always spot on (when BC_DIGITAL_V_KORRECTUR is set to nicht_aktiv) so there must be some simple way of getting this information. I'd rather have a good bc_digital speed and the speedo off than the other way around. The digital readout is always where my eyes go when I see a speed trap anyway.