Does anyone know if it's possible to have your speedo electronically calibrated to improve its accuracy?

I think mine is about 10% out. I realise 100% accuracy is unrealistic, but I'd like it to be as accurate as possible. Even allowing for different tyres, changing pressures, etc., it must be possible to get considerably closer than this.

Alternatively (and less attractively), can any of these 'speedo shops' re 'paint' the face to provide a closer match to reality?

 

[QUOTE]Originally posted by John Boggiano

I think mine is about 10% out.

-----------------------------------------------------------------

Hmmmmmm. All this speed talk JB. It makes me think you're..........up to something. Is there something we should know about, like maybe an NIP or something like that???

Cheers

PS. NIP = Notice of Impending Prosecution.

 

Dave,
So glad you clarified 'NIP' - I thought it was 'Nude in Public'!

This is just something I've thought about for a good while. It was brought back to the surface by my abortive experiment with the Origin B2, which displays your actual speed via GPS-determination.

 

Yes to both of your questions. Here in the U.S., many speedo
shops can calibrate and alter the face of speedos. I'm sure
that in most countries this can be done as well.

Good Luck
Loren

 

OK, so does anyone know a UK shop? Might try Porsche-apart as they do a repair service.

 

When I had my 911SC speedometer converted from the 85mph face to the 150mph face, they calibrated it, and it was spot on. 30 was really 30 and 70 was really 70. Kind of refreshing not to have to interpret the speedo error. There's got to be some shops in UK that do that sort of work. Worst case, post it to North Hollywood Speedometer in California, which I used and would recommend.

 

John:

Quick answer is I don't know. I do know the speedo is digital, and therefore has no cable driving it. I don't recall where the speed signal comes from, but it is either on the transmission or possibly the ABS sensor on one of the wheels. There is a chip in the speedo that interprets the pulse string that is the speed signal that goes to the spoiler amp, the engine controls, and who knows where else.

If you did not change the tire size, I suspect that you have a component failure in the speedo. The hall effect sensor that sends the speed signal typically cannot go out of calibration, since it is simply sending a pulse each time a magnet on a mechanical component passes it.

I once tried to repair a failed Porsche speedo, but it was the electronic chip, and I could not locate the replacement part.

I think it would be expensive and complicated to repaint the speedo markings, especially if the electronics are failing.

Like I said at the start, I don't know how to fix this, other than to try another speedometer and see if that fixes the problem. 10% is way high for speedo error. 1% is typical.

 

I changed to 17" wheels, but I don't think the error was much different even on the original 16".

In the UK, AFAIK, speedo must not under-read and is allowed an error of up to 10% at 30mph.

Result is that they all over-read by roughly 10%.

 

John, are you sure about this? Sounds like a bit of an urban myth to me. I can't believe that manufacturers would tweak the speedos to read over by that much just for the UK market!

Cheers

 

Pretty sure.

Anyone else got any data about their speedo's accuracy?

 

John,

I thought that speedos had to be accurate at 30mph. The faster you go, the less accurate the speedo becomes. I may be wrong however!

Andy

 

Mine has always been out by at least 15%. When it shows 140 kms/hr, I'm really going about 120. I figure that its cheaper than adding additional hp. It doesn't start to stray from accurate until north of 60 kms/hr. I've grown so used to it, I had forgotten about it until this thread.

Thanks so much, John.

 

When I was learning to drive my instructor always used to say that a speedo was only reckoned to be accurate to +/- 10%. I'm not sure if there is an official position on this though but it would appear to be something widely accepted. Might be worth a try if I get caught doing 55 in a 50.

Jim.

 

I think in the UK, you need to be going more than 10% over the limit before you get a ticket. Seems like they've already taken inaccuracy into account!

 

Andy.

10% over the limit is urban myth, ACPO guidelines suggest 10%+2mph, but it aint no guarantee.
Speedo inaccuracy is allowed I think to be 10%+ but not under, hence you should always be under the speed limit if driving by your speedo. at the speed limit.