Speedo Accuracy

[Phoenixcat]

The speedo in my car is very inaccurate. An indicated 70mph is actually 57mph.

Is this normal and is there any way to correct it?

[roseytvr]

There is a speed sensor on top of the rear of thr prop where it bolts on to the diff that needs to be very close to the sensor wheel but even then you probably need the speedo calibrating= unnecessary expense. Just use a gps and work out your true speed to readings for your key speeds and live with it.

[wuckfitracing]

Yep mine reads about the same. Use a sat nav for better accuracy and set a warning when your about to be banned.

[scruggs]

Mine doesn't work at all below 20 mph! Then suddenly comes alive. Normal?

[haircutmike]

Mine over reads 10% at speed.

[Bassfiend]

haircutmike said:

Mine over reads 10% at speed.

Mine reminds me of being a very young child...

...when I was a little kid my grandad had a barometer on the wall that he used to walk up to and tap on the glass a couple of times to see which way the weather was going to go.

I have to do the same to get my speedo to work.

Phil

[Dr Mike Oxgreen]

scruggs said:

Mine doesn't work at all below 20 mph! Then suddenly comes alive. Normal?

It's certainly normal for mine too.

My speedo is reasonably accurate - an indicated 80 is a GPS 76. I never drive faster than that though. Oh no. Never.

57 at 70 seems an excessive over-read. Do you have standard wheel sizes? Mind you, you'd have to put smaller wheels on to make it over-read; either that or have you (or the last owner) gone back to standard wheels after a previous owner had recalibrated for larger ones?

Edited by Dr Mike Oxgreen on Tuesday 17th July 06:29

[900T-R]

...or put 225/50/16 on an early car that originally came with 225/55/16s (and 205/60/15 at the front)... makes for about 3% differencen on its own, but put that together with the 'natural' overreading...

[TVRmuppet]

Mine was out a lot. So bent the fingers back on the prop one at a time and checked with the sat nav. When happy cut them off with an angry grinder. Diametriacally opposite of course so no problem with dynamic balancing. Now reads pretty well spot on.
Less pulses per revolution reduces the speedo reading. I removed two by the way. Cost £0

[haircutmike]

TVRmuppet said:

Mine was out a lot. So bent the fingers back on the prop one at a time and checked with the sat nav. When happy cut them off with an angry grinder. Diametriacally opposite of course so no problem with dynamic balancing. Now reads pretty well spot on.
Less pulses per revolution reduces the speedo reading. I removed two by the way. Cost £0

Interesting.

[finestjammy]

Yep, mine over reads by approx 10mph over at anything above an actual 30mph. Non standard tyre size wont help my case.

[Phoenixcat]

The wheels are standard I believe. So this means that the 60k on my clock is probably nearer 52-53k.

[Trevor450]

You need to check it with a GPS. Mine is about 10% out but gets more accurate at speed!

[Quietlybonkers]

Mine says zero until I get close to 20 too. Otherwise I think it is fairly accurate. Will calibrate with Thomas Thomas

[OleVix]

Mine showed 70 mph and the gps said 69-70 mph ...

[Phoenixcat]

I checked my odometer against a journey tracked via gps and it is accurate to within 0.1 mile over 80 miles. So how come the odometer is accurate, but the speedo is not?