Speedometer Calibration

[GoldSyncro]

Can someone tell me the best/easiest way to calibrate my speedo? Running larger tyres means my speedo is out by +10kmph.

Thanks

[Aidan]

to change the speedo reading you need to change the speedo drive in the front diff, only a few are still available so depending on which of the three worm gears you have in your front diff there may not be anything you can do, but they aren't accurate anyway originally they overread by 10% speed but the odometer is bang on~ish, which one is fitted depends on which final drive and which tyre size the vehicle left the factory with unless it's been swapped, changing tyre size generally bigger tyres than original fitment speed becomes more accurate but odo underreads
best to just recalibrate your head against gps speed and indicated speed and odo, with electronic pick up speed signal /dash set up you can do more and adjust readouts some of the TDi boys have that sort of stuff

[Simon Baxter]

If its out for the same amount thought out the range then just take to needle off and move it around.

[GoldSyncro]

IS IT REALLY THAT SIMPLE. NOW WHY DIDN'T I THINK OF THAT!!!

[garyd]

yes, you can do that Rob - I have anyway.

Hadn't thought about the odo under-reading though. That would make the fuel consumption better than I thought, wouldn't it?

So what is the percentage difference in circumference between 185x14s and 205/75x15s?

Garyd

[HarryMann]

I don't think it is though, they're usually out by a % age, not alwasy though.

So 10% is 33 at 30 and 77 at 70, so that won't work, though you can compromise and re-set it as Simon says. Say 3 mph or 5 kph slower, but then be careful with your speed cameras down there.

To calibrate your odometer, the best way is using the kilobaords on motorways and a passenger snap reading the odo at 10km, 20 km etc intervals

[axeman]

yes, you can do that Rob - I have anyway.



So what is the percentage difference in circumference between 185x14s and 205/75x15s?

Garyd

my doka speedo reads bang on with 215/75/15 comparing with the sat nav, and sallys van with the 185/14's read about 7% under.

neil

[HarryMann]

It's TRC, equivalent Tyre Rolling Circumference that matters

There are some charts on the syncro website that may help you to estimate that, or some calculators on the web, though the only really correct figures are quoted by their manufacturers for 'as new' state

My Doka (5.43) was bang on with the 15" 205 Machos and still very slightly over-reads speeds with the 15" 195 Marshall/Kumhos

[HarryMann]

That would make the fuel consumption better than I thought, wouldn't it?

That would make the fuel consumption appear worse than it actually is

is perhaps a better way of putting it?

[ELVIS]

Speedy cables in ambercrave used to do it. They did have a good website telling you how they recalibrate it, cost etc. wasn't stupid money either.

[syncropaddy]

Most T3 parts suppliers - Buschmiede, Syncro Services et al - supply a compensating device as they must have something like that for their TUV. Check out their websites.

[HarryMann]

Presumably. moving the speedo needle assy away from the spinning magdisk would compensate (slow response), is that possible?