Speedo Calibration...

[rosella]

I run 245/45/18 and my error is approx 3% against GPS, which I'm quite happy with. Where in the mountains are you Rosella? I'm at Faulconbridge, I'll have to keep my eyes peeled.

I noticed on google maps the distance is 114km down but 115 up and whereis is 115.7 down and 117.1 up. Maybe need a GPS to work out an accurate reading. Where did you buy your tyres, BTW? I've got Pirelli Nero Zeros or is it Zero Neros. They came on the car with the rims (Advan T7s). I'm located in Blackheath and work in Nth Ryde near Macquarie Uni. I come down the mountain on Mondays and Wednesdays only. Maybe we should catch up at some point?

[Daleo]

Rosella, the tyres are just Khumo KU31's, just bought from JAX in Penrith, a pretty budget tyre ($260 each), 245/45/18 size is common to VE Commo 18's, so should get cheaper as time goes by, but I have used the Khumo's before & was quite happy. Not quite up to Pirellis tho'!

You basically drive straight past my place (near Ugg Boot Man) on your commute! Would be good to catch up, not many M35's up our way! I'll PM my email this week if you like. Cheers, Dale

Apologies for thread hijack.

[bentwagon]

Has anyone tried this?

http://autospeed.co.nz/cms/title_Speedo-Corrector/A_108415/article.html

[scotty nm35]

It would work on your C34, unfortunately our speed data is sent down the CAN communication line. There is an accurate signal coming out of my OBD2 port and the Greddy Informeter Touch displays it perfectly.

[andy65b]

It would work on your C34, unfortunately our speed data is sent down the CAN communication line. There is an accurate signal coming out of my OBD2 port and the Greddy Informeter Touch displays it perfectly.

+1

[KiwiRS4T]

Has anyone tried this?

http://autospeed.co....15/article.html

I have one of these to correct my speedo for the 300km/hr dial faces I have had printed. Car is about a month from being on the road so will report when it is running.

[bentwagon]

Can you shed some light on where to wire it up? I think the hardest part of this job is knowing which wire is the sigal wire.

[Commsman]

It would work on your C34, unfortunately our speed data is sent down the CAN communication line. There is an accurate signal coming out of my OBD2 port and the Greddy Informeter Touch displays it perfectly.

Are you saying the Informeter has a different reading to that on your speedo? How does it know if you've changed tyre size for instance?

I haven't compared my informeter speed reading with my GPS yet as I only recently got the CAN port to output the speed (long story ), but my speedo is still wrong nonetheless & I would like to make it more accurate. I would almost wager that behind the dash itself would be a wire that feeds a signal to the speedo to display the speed. And mine is out by about 7km/h at 100.

You are correct Aaron, the hardest part is finding the right wire. I have one of these kits built but haven't had the time to pull the dash apart to see if i can get it working on my car. You wil have a much higher chance of success on your Stagea tho.

[scotty nm35]

Yes the informeter has a different speed output. I think the CAN line goes straight into the dash so you may need to attack the pcb. Perhaps the needle can be moved a bit?

[Commsman]

Yes the informeter has a different speed output. I think the CAN line goes straight into the dash so you may need to attack the pcb. Perhaps the needle can be moved a bit?

I don't want it that bad lol. This mod is a long way down my priority list and slipping even further down if it ends up being that hard. But I must check the Informeter speed wrt GPS to see how close they are.

[bigkevracer]

Has anyone done any more on this?

Might be easier now that we know where the speed sensor wires are from Leon's work on the cruise control?

The tyres I'm looking at don't come in 245/45R18, closest I can get is 245/40. I can get something similar in a 245/45, but it's an extra ~$100/corner, and not quite as good.

[bentwagon]

I have the jcar kit made but not fitted yet

[KiwiRS4T]

This is where it is on a C34:

[bigkevracer]

Thanks guys. I get the impression that the M35 is slightly different, working through the CAN bus?

Has anyone managed to get their speedo calibrated in their M35?

[Commsman]

I've given it a bit of thought - even built the Jaycar calibration kit - and here's what I've come up with:

I believe it is possible but you will need to break into the VSS wire at the TCM (same yellow/black wire on pin 27 that you connected the cruise control). This means you can modify the signal before it gets inserted into the CAN & hence control the speedo. BTW, it shouldn't matter which side of the Jaycar box you extract the CC signal, ie before or after it has been modified.

Now the kit modifies the signal frequency in a linear way, but I think our computers don't display speed in the same way. I could be wrong, but I don't think our speedo's are out by the same amount across the usual driving range. In my brief experience (comparing various speeds with the GPS), the speed seems pretty accurate up to ~80km/hr. Above that it gets progressively less accurate till it's out by ~7km/h at 100km/h - depending on tyre/wheel sizes.

It's been widely reported (ask Scotty) that the Informeter displays speed accurately. This leads me to believe that the computer knows exactly what speed you are doing, but chooses to be 'socially responsible' & display a higher speed to slow you down / keep you from getting booked etc.

Having said all that, if someone wants to adjust for wheel size that is noticeably different from standard, or correct for highway speeds, I think the speedo correction kit will work on the M35 (but with some linearity flaws).

Cheers, Leon.

[bigkevracer]

Thanks Leon. I guess I'll wait and see how far out it is, before I work out if I want to do that.

You're right about being linear. I'd say its a fixed percentage. I know mine at present is out by a couple of k's at 60 (maybe 5%?).

I'll have a look around for a progressive one too. But if the issue is the computer, that complicate things a bit. I should permanently mount the informeter anyway, I'll use that for speed.

[Commsman]

So are you saying you think that the speedo is out by a fixed percentage? If that is the case, then the Jaycar calibration kit should work perfectly.

BTW, that isn't what I've experienced (but I could be wrong). I thought the speed was accurate up to a point, and then became progressively less accurate.

In any case, I'm pretty sure you could find some happy medium with the calibration. If you got it bang on at 100, it won't be out too far at lower speeds.

[bigkevracer]

Nope, I thought it was out by a fixed percentage but the more you make me think about it the more I think it's variable. I was thinking it was a fixed 5-10%. I'll measure again when I get the new wheels and tyres on and see how I go.

[Commsman]

I can't help myself. Had to go downtown so did a speedo v's GPS check on the way. I had to hold each speed for maybe 5 seconds for the GPS to stabilise.

Results show it's more linear than I expected, and anything under 50km/h is pretty well on the money. Also I didn't want to be irresponsible & check the next 10km/h increment, but it would be interesting to see if the speedo error remained at 6km/h.

Of course these results are for my car with my tyres - 245/45/18 - so the error could be more or less for another car. However, the slope of the graph would be similar for everyone & so the ability to calibrate it if desired.

Edited June 6, 2012 by Commsman

[PN-Mad]

Leon, does the ECU read speed the same as the speedo or GPS?

Ie, get the laptop out, cipher cable on, and monitor the speed that the ECU reads.

I only ask because when tuning, we noticed a difference in the tach- the ECU would read considerably lower revs that the tacho needle.