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460332
Date registered: Apr 2006
Location: Europe
Vehicle(s):
| RE: big wheels--odometer off. how much?
nugat - 6/26/2007 1:40 PM
let's make sure we are using the same definitions:
odometer-measures distance
tachometer-measures engine revolutions
speedometer-measures vehicle's speed
aaah, now it all comes to me too,  -you meant the trip-meter!
It's counts are mechanically locked up to the wire's revolutions,
the tachometer get signals from crankshaft...... 
Edited by 460332 6/26/2007 4:21 PM
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nugat
Elite Veteran
Date registered: Jan 2007
Location: Warsaw, Poland
Vehicle(s): 280GE, 290GD, c303
Posts: 876
| RE: big wheels--odometer off. how much?
and how does the speedometer work (gets signal from...)? |
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460332
Date registered: Apr 2006
Location: Europe
Vehicle(s):
| Re: big wheels--odometer off. how much?
Thats the angular gear: TC - angular gear - speedo wire - speedometer!
Trip meter is mechanically locked, speedometer is magnetic "drag".
Tach is magnetic puls - receiver/transmitter - switch box - signal to instrument. |
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4x4abc
Date registered: Apr 2006
Location: La Paz, Baja California, Mexico
Vehicle(s): 02 G500
| RE: big wheels--odometer off. how much?
speedometer = engine rpm
tachometer = vehicle speed
odometer = total miles driven |
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Jonathan Joseph
Expert
Date registered: Oct 2006
Location: Charleston, South Carolina
Vehicle(s): 2004 G55
Posts: 1538
| RE: big wheels--odometer off. how much?
Harald are you trying to make this more difficult than it already is??
Jonathan |
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VonEpp
W124 Host
Date registered: Sep 2006
Location: Australia
Vehicle(s): w114, w124 & w460
Posts: 357
| Re: big wheels--odometer off. how much?
This is really not complicated!!
Percentage increase in tire circumference = Percentage that your odometer will be out.
If junior high mathematics is too much for you, use a GPS.
Adding 3.5% per inch tire increase will not work either as the circumference to diameter ratio is not linear. |
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VonEpp
W124 Host
Date registered: Sep 2006
Location: Australia
Vehicle(s): w114, w124 & w460
Posts: 357
| RE: big wheels--odometer off. how much?
4x4abc - 6/27/2007 9:21 AM
speedometer = engine rpm
tachometer = vehicle speed
odometer = total miles driven
Did you mean speedometer = vehicle speed, tachometer = engine speed?
Edited by VonEpp 6/27/2007 5:40 AM
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Bill K
Date registered: Dec 1899
Location:
Vehicle(s):
| RE: big wheels--odometer off. how much?
Here is a site that will clear ( I hope most peoples definition's ).
Also helps in other areas.
http://www.pelicanparts.com/techarticles/Mult_gauge_repair/mult_gau...
Good luck
P.S who's on second  |
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4x4abc
Date registered: Apr 2006
Location: La Paz, Baja California, Mexico
Vehicle(s): 02 G500
| correction - sorry
sorry for my goof
speedometer = speed of car
odometer = miles driven
tachometer = speed of engine - rpm
Nathan,
you are right, 3.5% is not correct - but its an easy rule of thumb number to get a fast result without using a computer or calculator (given that you can do easy math in your head) |
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KERR
Date registered: Dec 1899
Location:
Vehicle(s):
| Re: big wheels--odometer off. how much?
i went from stock tires to the 33.4's and then had the computer restet to closest tire size. Then i used the link to the miati boards as posted above. Now at 60 mph im really going 65 mph.
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nugat
Elite Veteran
Date registered: Jan 2007
Location: Warsaw, Poland
Vehicle(s): 280GE, 290GD, c303
Posts: 876
| Re: big wheels--odometer off. how much?
I checked my speedometer and odometer values with GPS.
With 33 inch wheels the they are both off by 10%. i.e. Speedo showing 100km/h GPS 110km/h.
Strangely at lower speeds the deviation seems to be smaller, something like 7-8%, but maybe thats accuracy of the equipment.
I beleive the 10% is less than expected from the change from standard to 33 inch wheels. |
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Joe Dirt
Member
Date registered: Jun 2006
Location: Yorba Linda, CA
Vehicle(s): 2007 G500, 2008 GL 550, 2007 ML500
Posts: 23
| Re: big wheels--odometer off. how much?
Is there a simple fix ( like maybe a new gear size ) to recalibrate the speedometer for larger tires? I am running 275-70-18 on my 2007 G500. I am off about 7%. If it is not a gear does anyone know if it is electric and can be updated? Thanks
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Loki Laufeyjarson
Date registered: Apr 2006
Location: 66°N, 19°W
Vehicle(s):
| Re: big wheels--odometer off. how much?
Joe Dirt - 7/11/2007 5:02 PM
Is there a simple fix ( like maybe a new gear size ) to recalibrate the speedometer for larger tires? I am running 275-70-18 on my 2007 G500. I am off about 7%. If it is not a gear does anyone know if it is electric and can be updated? Thanks
This http://www.speedcalibrator.com/ has been used a lot in 4x4 with elecrtic speedometers. I dont know, if or how, this effects esp...
Loki
Edited by Loki Laufeyjarson 7/11/2007 1:34 PM
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W5YK
Extreme Veteran
Date registered: May 2006
Location: San Diego
Vehicle(s): 2002 G500, Unimog U2450,
Posts: 543
| Re: big wheels--odometer off. how much?
The best you can do is to get the dealer to set your computer for the largest tire size that Merc has pre-programmed in the system, which is 235/85 R16. You will still be off by 3.5% or so, but it's better than being off by 7%. Unfortunately there is no mechanical part that you can adjust, like a gear, or an angle, it's all computerised. You can also set the tire size in the Nav system, but that is only used within the Nav, not by the odometer, speedometer, ESP, ABS etc.
Your only option for getting it absolutely correct is to use an electrical pulse converter like the one linked to in another post. I don't know of anyone having done that on a G500 - I suspect it is difficult to access the point in the circuit where those pulses are, it's probably on a bus. You'd have to be brave to do that, plus you'd have warranty issues.
Incidentally, do you have any rubbing with those tires? I'm going to replace my 265/75R16 tires soon, and I'm thinking of going up a size.
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Joe Dirt
Member
Date registered: Jun 2006
Location: Yorba Linda, CA
Vehicle(s): 2007 G500, 2008 GL 550, 2007 ML500
Posts: 23
| Re: big wheels--odometer off. how much?
I am going to try the MB dealer and see if they will set the computer up. Thanks
Incidentally, do you have any rubbing with those tires? I'm going to replace my 265/75R16 tires soon, and I'm thinking of going up a size.
No they did not run any where. They do take up a little bit more in the wheel well, but it did not run a full articulation. The tires raise up the truck about 2 ". |
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nugat
Elite Veteran
Date registered: Jan 2007
Location: Warsaw, Poland
Vehicle(s): 280GE, 290GD, c303
Posts: 876
| Re: big wheels--odometer off. how much?
nugat - 7/10/2007 2:24 PM
I checked my speedometer and odometer values with GPS.
With 33 inch wheels the they are both off by 10%. i.e. Speedo showing 100km/h GPS 110km/h.
Strangely at lower speeds the deviation seems to be smaller, something like 7-8%, but maybe thats accuracy of the equipment.
I beleive the 10% is less than expected from the change from standard to 33 inch wheels.
Now really strange one. In the afternoon I checked the values again and they are off by 5%. The only change that happened during the day was sucking out 1 liter of excess ATF. Could it influence the read out somehow?
Or is the speedo off by different percentage once in a while? |
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caar
Veteran
Date registered: Jul 2007
Location: Calgary, Alberta, Canada
Vehicle(s): 85 230GE, 86VW MK1
Posts: 110
| Re: big wheels--odometer off. how much?
the easiest solution is to use a GPS to tell you the speed and compare it with the speedo |
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Joe Dirt
Member
Date registered: Jun 2006
Location: Yorba Linda, CA
Vehicle(s): 2007 G500, 2008 GL 550, 2007 ML500
Posts: 23
| Re: big wheels--odometer off. how much?
I went to the dealer and they said that the computer could not be changed because of the esp going of the wheel size. If they changed the code you would get a fault in the sensors. |
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