Speedo 10mph out

[Tony9r]

My wife's 1999 IS200 speedometer is reading nearly 10mph slower than actual road speed which is a pain at speed cameras etc!

Been like this since we bought it. Wheels and tyres are all standard size.

Is there a fix... I've reset ecu but no different?

TYIA.

[NemesisUK]

Not only a pain but also illegal...

What are you comparing it with?

[ColinBarber]

What are the size of the tyres?

[Tony9r]

2 minutes ago, NemesisUK said:

Not only a pain but also illegal...

What are you comparing it with?

Driving alongside in other cars, also those radar speed sensor displays at the side of the road.

[Tony9r]

Just now, ColinBarber said:

What are the size of the tyres?

215/45 17

[ColinBarber]

Is this a UK vehicle or import? Auto or manual?

Can't rule out a sticking needle but could also be because the wrong diff has been fitted.

[Tony9r]

10 minutes ago, ColinBarber said:

Is this a UK vehicle or import? Auto or manual?

Can't rule out a sticking needle but could also be because the wrong diff has been fitted.

It's a UK auto Colin. How would I know if diff has been changed?

[ColinBarber]

I don't think there are any obvious markings so you can really only tell by actually testing the ratio. jack up a wheel, put it in neutral, then turn the wheel one revolution whilst at the same time counting the revolutions of the prop shaft. There isn't much in it, just under four revs for a manual diff, and just over 4 for the auto.

IS200 manual 43:11 (3.900)

IS200 auto 41:10 (4.100)

[Tony9r]

17 minutes ago, ColinBarber said:

I don't think there are any obvious markings so you can really only tell by actually testing the ratio. Jack up a wheel, put it in neutral, then turn the wheel one revolution whilst at the same time counting the revolutions of the prop shaft. There isn't much in it, just under four revs for a manual diff, and just over 4 for the auto.

IS200 manual 43:11 (3.900)

IS200 auto 41:10 (4.100)

Thanks, will take a look next time I'm under the car.

[gdh300]

Is that 10mph consistent across all speeds? That's quite odd, suggests the speedo may be sticking as anything tyre or differential related you'd imagine would a percentage out, not a fixed amount. My IS under-reads by about 10% compared to road side displays and satnav.

[Tony9r]

16 minutes ago, gdh300 said:

Is that 10mph consistent across all speeds? That's quite odd, suggests the speedo may be sticking as anything tyre or differential related you'd imagine would a percentage out, not a fixed amount. My IS under-reads by about 10% compared to road side displays and satnav.

Yes it's consistent. When pulling off, the Speedo only starts to move after around 8mph...