Would you buy a speedometer "corrector"?

[pig]

I had the same problem with my truck when I switched to larger tires. I installed one of these to fix the problem and it works great: http://www.rockymountainsusp.com/TrueSpeed.htm

I don't see why it would not work on the elise. It was very to install.

[hpman]

Tested mine...reads 4 mph high at 90 mph gps. No need to correct this.

[Tyger]

Mine does not seem to have an 8% error.
If there is a "constant" error, the easiest solution would be a new dial, seems to me.

[TimMullen]

Originally Posted by pig

I don't see why it would not work on the Elise. It was very to install.

It won't work on the Elise.

Most vehicles now days use a speed sensor that is essentially a pulse generator (or a voltage generator) and the speedometer counts the pulses (or measures the voltage).

On the Elise, the speed signal is passed to the ECU which accurately determines the speed. The ECU then generates a digital signal that encodes the speed to display on the speedometer - the digital value is transferred via the CANbus.

In simple terms, most cars use an analog speed sensor / speedometer. The Elise is digital...

[reganfin]

I just got a portable gps unit and have an interesting finding.

My speedometer has a FIXED 5 mph error.

Speedometer__________GPS
30____________________25
50____________________45
75____________________70
100___________________95

I know that this is different from others. I haven't tried anything above 100 yet.

It makes the correction pretty easy. No need for any fancy electronics.

[PsychoRallye]

Originally Posted by Ground Loop

Our system is unusual indeed.. here's the system as far as I can tell so far..

First, there are wheel rotation sensors on all four wheels, of course. These are shielded wires that run to the ABS controller.

The ABS controller converts these to a stronger signal and sends them, via four discrete wires, to the ECU in back.

So, the ECU knows all four wheels speeds, and not the tranny speed.

From these (and maybe others?) it derives the speed of the car and sends that to the gauge pod via CANBus, along with some of the other dash readouts.

The dash pod is the guilty party. You could say that either the servo-needle controller is fudging, or even that the silkscreen on the dials is inaccurate, but the effect is the same -- needle reads high.

However, the odometer is dead accurate, as far as I can tell. I've measured long drives against the GPS, and while the speedometer reads ~8% high, the odometer is very close to true.

But here's the kicker.. dorking the speedometer via CANBus DOES NOT seem to impact the rate at which the odometer is racking up miles. Rob12349734 confirmed this some time ago when he had his very cool 160mph stationary experience while accumulating no miles.

So, if it all holds true, then it should be possible to 'adjust' the speed from the ECU to the dash to read 8% lower, get an accurate needle on the speedometer, and still have correct odometer operation. Of course, I'm not comfortable with all that until I know how the odometer is getting its mileage. Nobody wants to have to check the "odometer tells lies" checkbox on the pink slip, right?

A speed-pulse output from the same circuit would be doable.

I think that we're all over-analyzing this entire situation. If you really want the speedo changed, have a new speedo readout sticker/vinyl made with the increments retarded by 8%, don't start thinking about reprogramming dash electronics. Your problem can be fixed by a good silk-screener!

[tvacc]

I have mounted a magnet on the rear wheel which sends a signal to the Panoram Bike Speedo on my dash. good up to 115mph and dead accurate.

Works great for me. I installed the week after I got the car...March 2005.

I just could not put up with an indicated 80 and only doing 73-74 Mine is better at low speeds...only about 2 mph off and increases as you go higher..

Tony V
www.lotusowners.com

[ct_mazi]

Originally Posted by tvacc

I have mounted a magnet on the rear wheel which sends a signal to the Panoram Bike Speedo on my dash. good up to 115mph and dead accurate.

That's a very good idea. I will do the same.

[tvacc]

I have pictures of the install on my SEven...at

www.lotusowners.com

Go to the repairs/upgrades link...


Tony

[Joecooool]

Anyone figure out a fix for this yet?

[turbo2nr]

Originally Posted by Keeper

From what I understand, BMW speedos tend to be off (higher) by a greater amount than most manufacturers.

Yup, it was printed in Car and Driver. My old 540 was the worst. BMW was at the top of the BS list.

[turbo2nr]

Originally Posted by TimMullen

It won't work on the Elise.

Most vehicles now days use a speed sensor that is essentially a pulse generator (or a voltage generator) and the speedometer counts the pulses (or measures the voltage).

On the Elise, the speed signal is passed to the ECU which accurately determines the speed. The ECU then generates a digital signal that encodes the speed to display on the speedometer - the digital value is transferred via the CANbus.

In simple terms, most cars use an analog speed sensor / speedometer. The Elise is digital...

I think that device will work. If you see, it only works on cars with ABS.
Most cars now have digital speedos. My old 1987 Buick has a real cable, but with ABS, there is already a speed sensing device at every wheel, why would a car maker add a fifth one to the tranny? OK, there are a few exceptions, like when an older tranny is used in a modern car,but you understand. GM cars, ford, bmw, mercedes, japanese cars, etc etc all use this style of speed sensing. Now, a Subaru does use the old school tranny reference. I guess because the car was made to spin wheels in bad conditions. Can't use the digital if all four wheels are spinning a wide range of RPMs, can't have traction control either. FUN car! Every car with traction control has to use this method of speed sensing, so the Lotus is not that unique here.

[reganfin]

I used my GPS to check the speedometer on each of my cars. Guess what?

They all read high (SAAB, Ford, Land Rover and a late model SAAB).

I really don't see that there is a problem. I rarely watch the speedometer and prefer to check the tach. I mostly watch the road.

My advice is to put some contact paper over the speedometer and enjoy the ride.

[darkSol]

I'm totally up for a solution to this... either:

a) Fully digital via CANBUS packet modification / replacement. I like the plug/unplug thing. Parts would be about $35 for this.

b) Analog via adjusting ABS wheel sensor frequency. Caveat is that is would affect the odometer. Configurable frequency I/O = about $20 in parts.

c) Gauge face replacement (along with configurable backlighting). I actually like this one the best since the only thing involved would be changing the mph marking scale. The speedo would only go to 150mph instead of 160mph but who cares! A creative artist could actually add a proper 8500rpm redline as well.

d) A hybrid of (a) and (c) above... Transform the CANBUS speedo mph to scale 0-200mph and scale the gauge face to display 0-200mph as well. Have a couple different redline scales available (8500/9000/9500/none) and a couple different electroluminescent backlights available... This option would allow the folks who (eventually) alter their ECU redline / final drive to reach 170mph+ and 9000rpm+...

It grates on my psyche when the speedo reaches 100mph I'm thinking "hang on we're only going 93mph.". It's impressive giving test drives to unsuspecting passengers (the appearance of 7% more acceleration) - but that's not enough for me to live with this. 2% I could live with... not 7%+...

Anyway, enough of this ranting - anyone have a nice hi-res 300dpi/600dpi scan of the stock guage face? I'd like to try some things...

[TimMullen]

Originally Posted by turbo2nr

I think that device will work. If you see, it only works on cars with ABS.
Most cars now have digital speedos.

On most cars... The device appears to receive the pulse from the wheel sensor and send out a modified (corrected) pulse to the speedometer.

The Elise doesn't work that way. The wheel sensor sends the pulse to the ECU. The ECU determines the speed, and sends some formatted information (data bits) to the speedometer that tells the "computer" in the speedometer what to display. The Elise's speedometer does not accept pulses...

You could trick the ECU into thinking it had a different speed, but that wouldn't be a good thing - it actually knows the correct speed. It is just programmed to tell the speedometer that the speed is higher than what it really is...