Thread: speedo out by 8-10km/h

Ringwood Speedo 98742260 have been around FOREVER...and they know what they're doing.
Cheers, Pickles.

Originally Posted by bacicat

The 101 reads well below the actual speed due to the tyre size.

Mine is the opposite - reads about 10% fast - when changing tyres I decided to get a decent tyre and got BFG MT KM2s - these are slightly smaller in diameter than the 9.00x16s but so much a better tyre. In making this decision I accepted slightly less ground clearance which is not an issue on a 101 but the vehicle runs so much sweeter because of the slightly smaller diameter of the tyres - fuel consumption is unchanged as the engine sits in its torque range a bit better.

Garry

In a mechanical speedo (i.e. 101) there are two devices that drive off the speedo cable.
The speedometer and the odometer.
If you want both to be accurate, you adjust the input revolutions by mechanical means such as a ratio box or different outputs on the gearbox.
If you want just the speedometer to be accurate, a good instrument mechanic can do this by adjusting the spring.
The fellow that built my ratio box was in Mt Alexander Road. This was back in the mid eighties. I must go for a spin down there. See if he's still around.

Originally Posted by garrycol

Mine is the opposite - reads about 10% fast - when changing tyres I decided to get a decent tyre and got BFG MT KM2s - these are slightly smaller in diameter than the 9.00x16s but so much a better tyre. In making this decision I accepted slightly less ground clearance which is not an issue on a 101 but the vehicle runs so much sweeter because of the slightly smaller diameter of the tyres - fuel consumption is unchanged as the engine sits in its torque range a bit better.

Garry

What ratio diff do you have in yours Garry?
We suspect mine has the standard GS ratio and Gav's has the higher ambulance ratio.

Originally Posted by Mick_Marsh

What ratio diff do you have in yours Garry?
We suspect mine has the standard GS ratio and Gav's has the higher ambulance ratio.

The standard 101 diff ratio is 5.57:1 and I was not aware that any other ratios were fitted as standard to any model of 101 including the ambulance.
4.7:1 ratios can be fitted and certainly assist with onroad driving but it does make 1st high and bit high for any steep work.

Garry

My speedo is out by miles on standard rubber. Looked in to changeing the drive gear. But my odo is spot on so I decided to just leave it alown and drive at 110 in 100k zones. Fixed

Originally Posted by Tombie

I love the comments up higher...

"My speedo is out by 10%... At 100km/h I'm actually doing 90...."

Umm.....

Sorry Tombie, I was still half asleep and isn't that close enough to 10%... or are you having a go at my grammar. you know what I meant anyway. :P

Originally Posted by debruiser

Sorry Tombie, I was still half asleep and isn't that close enough to 10%... or are you having a go at my grammar. you know what I meant anyway. :P

Not at all.

One could argue 100 is close enough to 110, but a lot of cops don't agree

It's relevant because a 10% error at 100 is 10km/h
At 60 it's 66
At 80 it's 88

But at 8% and at the speeds most vehicles spend the majority of time at.

At these speeds and given most motorists propensity to creep the needle marginally past the indicated posted speed tends to run them at almost the exact posted legal limit.