Speedo Accuracy!!?
Discussion
Went to Le Mans last weekend, one word - Awesome!!
Anyway, we drove down from Calais along side a mate in a BMW 316i (03). During one fairly long fast blat, I was wondering why the hell we weren't pulling away faster so I slowed down and asked (shouted through an open window) what his speedo read...to cut a long story short see below:
BMW 90mph
LIZ 95mph
BMW 100mph
LIZ 108mph
BMW 129mph
LIZ 140mph
Anyone know whether this is an inaccuracy across the board or whether my speedo is RUBBISH!! Of course I am assuming hear that the BMW Speedo is more correct than mine, which may not be the case!! That said - there is no way a fully loaded (or driver only for that matter) 316i saloon will do 140mph!!
What ya think??
T
Anyway, we drove down from Calais along side a mate in a BMW 316i (03). During one fairly long fast blat, I was wondering why the hell we weren't pulling away faster so I slowed down and asked (shouted through an open window) what his speedo read...to cut a long story short see below:
BMW 90mph
LIZ 95mph
BMW 100mph
LIZ 108mph
BMW 129mph
LIZ 140mph
Anyone know whether this is an inaccuracy across the board or whether my speedo is RUBBISH!! Of course I am assuming hear that the BMW Speedo is more correct than mine, which may not be the case!! That said - there is no way a fully loaded (or driver only for that matter) 316i saloon will do 140mph!!
What ya think??
T
Mines about 10mph out from zero up to about 70 ish where the descrepancy becomes less.
Unfortunately mine underreads though. Plenty of old posts about speedo problems and misreads so i think it is just one of those things. You can reset by using following method, but I've not heard of a case where this has resolved it yet:
Drivers door open...press and hold the mileage reset button....switch ignition on (don't start).
The needles wibble around a bit (technical term!) then settle.
Unfortunately mine underreads though. Plenty of old posts about speedo problems and misreads so i think it is just one of those things. You can reset by using following method, but I've not heard of a case where this has resolved it yet:
Drivers door open...press and hold the mileage reset button....switch ignition on (don't start).
The needles wibble around a bit (technical term!) then settle.
Up to 70mph mine (S1 111S) reads to within 1mph of GPS speed.
It's normal for most cars to over-report speed. It's leagal for a speedo to over-read by 5% and under-read by 1%, so most cars over-read by 3-4%. I was told a story that audi carefully set their speedos at 5% over-read so that the services came up 5% sooner. Sounds a bit paranoid to me.
It's normal for most cars to over-report speed. It's leagal for a speedo to over-read by 5% and under-read by 1%, so most cars over-read by 3-4%. I was told a story that audi carefully set their speedos at 5% over-read so that the services came up 5% sooner. Sounds a bit paranoid to me.
eviloverlord said:
It's normal for most cars to over-report speed. It's leagal for a speedo to over-read by 5% and under-read by 1%, so most cars over-read by 3-4%. I was told a story that audi carefully set their speedos at 5% over-read so that the services came up 5% sooner. Sounds a bit paranoid to me.
Interesting point that i wondered about...I checked the MOT requirements out the other day to see what the margins for speedo error might be....no mention of speedo accuracy at all, in fact no mention of the speedo at all. Presumabley this means that the speedo is not required by law (but speeding is illegal so you need some way of knowing what speed you are doing). This has further implications as to the requirements for an odometer and it's readings.
On a similar issue, it's interesting that GPS readings are taken by most as being very accurate. I bet if you read the documentation, it will state at least a 5% margin error in the indicated speed. Not having GPS, I can't comment!
Just a ramble really !
sp60 said:
eviloverlord said:
It's normal for most cars to over-report speed. It's leagal for a speedo to over-read by 5% and under-read by 1%, so most cars over-read by 3-4%. I was told a story that audi carefully set their speedos at 5% over-read so that the services came up 5% sooner. Sounds a bit paranoid to me.
Interesting point that i wondered about...I checked the MOT requirements out the other day to see what the margins for speedo error might be....no mention of speedo accuracy at all, in fact no mention of the speedo at all. Presumabley this means that the speedo is not required by law (but speeding is illegal so you need some way of knowing what speed you are doing). This has further implications as to the requirements for an odometer and it's readings.
On a similar issue, it's interesting that GPS readings are taken by most as being very accurate. I bet if you read the documentation, it will state at least a 5% margin error in the indicated speed. Not having GPS, I can't comment!
Just a ramble really !
From recollection I believe it is a requirement to have a speedometer that works, i.e., moves or reads in a linear fashion, but that it doesn't have to be accurate, silly I know but then there are alot of laws like that.
Edited by Sublime on Monday 26th June 10:05
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