Speedometer calibration
Discussion
Hi,
I'm having problems with speedometer calibration. The car is fitted with the Ultima white dials (VDO instruments). I have repeatedly calculated and compensated and calibrated measured miles (using a GPS). The pulses per mile that I calculate comes out at about 4800. The problem is that with this number plugged in the speedometer reads really really crazy values like 110 mph when doing an actual 70 mph (both via GPS and the surrounding traffic)
. (It certainly felt like 110 mph but that's another story...)
When I stop to use the speedometer's ADJUST function to tweek the indicated speed this allows me to get a very accurate or a slight overread as desired value. When I then check the odometer it is now grossly underreading: indicating about 0.7 miles for every 1 mile travelled. WTF! Going into the manual pulse adjustment the value is now reading 6240 or thereabouts. grrrr.
According to the words I read on this VDO resellers website (www.springfieldstreetrods.com/Install-InstructionsSpeedo.htm). The adjust function can be used to vary the analog pointer without affecting the pulses per mile. The implication being that you can modify a factor on the actual speed (to read higher for example or to trim for parallax or whatever). This doesn't seem to be the case
I had the same issues for SVA but in a last ditch attempt to fix things I re-entered the factory/manual supplied number which gave me a very accurate speedo (but wonky odometer). Of course the SVA is only interested in speed reading not odometer so having got it right enroute to the test centre I left well alone...till today.
As far as I can figure. It's as if the speedo electronics are expecting a different dial to be in place that goes up to say 140 mph and hasn't been told that the Ultima branded dial goes to 200 mph.
Has anyone else seen this? Am I just being hamfisted in adjusting the values and it is possible to adjust the speed independently of the odometer? I guess I can live with a misreading odometer...just have to remember to divide by 0.7-0.8 when calculating mpg or scheduling oil changes. Kinda makes the limited mileage insurance look funny...
I'm having problems with speedometer calibration. The car is fitted with the Ultima white dials (VDO instruments). I have repeatedly calculated and compensated and calibrated measured miles (using a GPS). The pulses per mile that I calculate comes out at about 4800. The problem is that with this number plugged in the speedometer reads really really crazy values like 110 mph when doing an actual 70 mph (both via GPS and the surrounding traffic)
. (It certainly felt like 110 mph but that's another story...) When I stop to use the speedometer's ADJUST function to tweek the indicated speed this allows me to get a very accurate or a slight overread as desired value. When I then check the odometer it is now grossly underreading: indicating about 0.7 miles for every 1 mile travelled. WTF! Going into the manual pulse adjustment the value is now reading 6240 or thereabouts. grrrr.
According to the words I read on this VDO resellers website (www.springfieldstreetrods.com/Install-InstructionsSpeedo.htm). The adjust function can be used to vary the analog pointer without affecting the pulses per mile. The implication being that you can modify a factor on the actual speed (to read higher for example or to trim for parallax or whatever). This doesn't seem to be the case
I had the same issues for SVA but in a last ditch attempt to fix things I re-entered the factory/manual supplied number which gave me a very accurate speedo (but wonky odometer). Of course the SVA is only interested in speed reading not odometer so having got it right enroute to the test centre I left well alone...till today.
As far as I can figure. It's as if the speedo electronics are expecting a different dial to be in place that goes up to say 140 mph and hasn't been told that the Ultima branded dial goes to 200 mph.
Has anyone else seen this? Am I just being hamfisted in adjusting the values and it is possible to adjust the speed independently of the odometer? I guess I can live with a misreading odometer...just have to remember to divide by 0.7-0.8 when calculating mpg or scheduling oil changes. Kinda makes the limited mileage insurance look funny...
I have a standard issue 140 mph VDO item that appears to work OK with calculated pulses, although I have not checked odometer accuracy. Not sure what will happen if I put it off the scale - can't imagine it would break it. SVA did not pick me up on max speedo reading which technically they could have (ie less than car capable of).
Dave,
What was your factory supplied number for setting up your speedo? The number they gave me, 4788, resulted in an over-reading speedo, ie doing 50mph at an indicated 70. After playing with the settings I too achieved an accurate speed reading but a way out odometer ( the factory was suddenly 50miles nearer to home) I too can't understand how the two figures are not linked, ie if one is correct then surely the other must be unless for some reason they have independent processors (unlikely). I like your idea of the wrong face on the speedo - that would explain a lot and if it were the case, surely Ultima owe us an exchange speedo. Still, I've put up with it for 4 years now, and as Nick says, a low reading odometer can have some advantages!
What was your factory supplied number for setting up your speedo? The number they gave me, 4788, resulted in an over-reading speedo, ie doing 50mph at an indicated 70. After playing with the settings I too achieved an accurate speed reading but a way out odometer ( the factory was suddenly 50miles nearer to home) I too can't understand how the two figures are not linked, ie if one is correct then surely the other must be unless for some reason they have independent processors (unlikely). I like your idea of the wrong face on the speedo - that would explain a lot and if it were the case, surely Ultima owe us an exchange speedo. Still, I've put up with it for 4 years now, and as Nick says, a low reading odometer can have some advantages!
This is sort of interesting. Unfortunately, I don't have the VDO gauges (I have the Stack Dash), but having spent a good deal of time calibrating my system I can sympathize. I've got two observations. First, it sounds like the speed and odometer are linked together by some other variable besides pulses/mile. Could the problem be that the 140mph face was taken off and replaced with a 200mph face and this is making it impossible to match up the speed and odometer? What it sounds like is that the number you are inserting calibrates the speed, but the odometer is being calculated from the indicated speed not the pulses. Have you guys tried to contact VDO?
Also, one other point, is that all of these different gearbox models will have different # of pulses per mile. This variable needs to be considered. For me, the easiest way to calibrate my stack, was to make a gear chart with RPM, Speed, and selected gear and tape it to my steering wheel. Then I could see at 3500 rpm in 3rd gear I should be going "X" speed.
Just a little food for thought.
Cheers!
-Mack
Also, one other point, is that all of these different gearbox models will have different # of pulses per mile. This variable needs to be considered. For me, the easiest way to calibrate my stack, was to make a gear chart with RPM, Speed, and selected gear and tape it to my steering wheel. Then I could see at 3500 rpm in 3rd gear I should be going "X" speed.
Just a little food for thought.
Cheers!
-Mack
bigmack said:
......For me, the easiest way to calibrate my stack, was to make a gear chart with RPM, Speed, and selected gear and tape it to my steering wheel. Then I could see at 3500 rpm in 3rd gear I should be going "X" speed.....-Mack
This is the one thing I forgot to do. When the box was on the bench I should have found out what the actual ratios were. I know the model for my box but I keep finding info giving different ratios for US, UK or european versions.
Steve
Mike, thanks for your comments/article about this issue in Ultimatum a few years ago...it was helpful to know I wasn't alone!
That's what it seems like. The variation is just a nice constant factor throughout the speed range.
The numbers I've used were:
6400 - Ultima manual number (virtually perfect speed)
4730 - My own calculated number based on chalk marks on the ground for one rev of the wheel
4840 - GPS calibrated measured mile
5960 - eyeballing adjustment of the speedo needle to over-read by about 3 mph at 60
6260 - eyeballing adjustment to over-read by about 1mph at 60
They all seem fairly consistent with the method/results.
I'm very confident that the sender is properly installed. Spent ages during the build making sure the actual coil in the sender was lined up exactly on the cutter plate teeth. The gap between sender and cutter plate is less than about 0.5mm with minimal variation during revolution. This is with a standard Ultima 6 tooth wheel and VDO inductive sensor. The speedo reads from 1-2mph upwards and is very stable and maintains the speed calibration from 20mph through to 70.
When I used the calibrated value of 4840 and drove 3-4 miles the trip value was exactly on the money.
Will drop a note to Ultima. It may be that the cost of modifying the speedometer software was too much for the small production numbers they could run to.
bigmack said:
Could the problem be that the 140mph face was taken off and replaced with a 200mph face and this is making it impossible to match up the speed and odometer?
That's what it seems like. The variation is just a nice constant factor throughout the speed range.
The numbers I've used were:
6400 - Ultima manual number (virtually perfect speed)
4730 - My own calculated number based on chalk marks on the ground for one rev of the wheel
4840 - GPS calibrated measured mile
5960 - eyeballing adjustment of the speedo needle to over-read by about 3 mph at 60
6260 - eyeballing adjustment to over-read by about 1mph at 60
They all seem fairly consistent with the method/results.
I'm very confident that the sender is properly installed. Spent ages during the build making sure the actual coil in the sender was lined up exactly on the cutter plate teeth. The gap between sender and cutter plate is less than about 0.5mm with minimal variation during revolution. This is with a standard Ultima 6 tooth wheel and VDO inductive sensor. The speedo reads from 1-2mph upwards and is very stable and maintains the speed calibration from 20mph through to 70.
When I used the calibrated value of 4840 and drove 3-4 miles the trip value was exactly on the money.
Will drop a note to Ultima. It may be that the cost of modifying the speedometer software was too much for the small production numbers they could run to.
steve_D said:
It's a G50/20 six speed.
I believe it came from a 993 in the US.
Steve
I'm not sure about the Euro vs. UK ratios, but these US ratios are probably correct.
www.993faq.com/archives/cat_transmission.html#000146
Cheers!
-Mack
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