so whos speedo is correct???
Discussion
Coming back from wales yesterday, a Citroen C4 slowly went past me and I happened to see his speedo (one of those big centre of the dashboard lcd thingys) and it was a good 5-10 mph diferent to mine. So I thought I'd check it again to make sure, so I passed him. Again 5-10 mph difference. This happened several times and each time My speedo was 5-10 mph slower than his.
Anyone else had this?
Looks like I will have to get a Sat nav to find out exactly what I am doing. At least that is what I'll tell the wife. I've been waiting for a good excuse to get one.
Also Which Sat nav to go for, Proper biker one (expensive or) good car one with waterproof bag?
Kwacker
The answer to that will be no ones...and sat navs whilst being a lot more accurate than your stock speedo are not 100% accurate.
Why dont you take yourself along to a straightliners day and see what your bike can really do thru a proper timing trap...but be prepared to be disappointed!
Why dont you take yourself along to a straightliners day and see what your bike can really do thru a proper timing trap...but be prepared to be disappointed!
Because I changed the gearing on mine I fitted a Sigma bicycle speedo to mine and I have a GPS. The GPS and the Sigma speedo are never more than 1mph different from each other so I assume are pretty accurate as they use totally different methods for speed calculation.
My bike speedo used to be about 7% to 8% optimistic but I then changed the gearing by putting a 1 tooth larger sprocket on the front which was about a 6% increase in gearing. This has made the speedo a lot more accurate with 70 on the speedo showing 68/69 on the Sigma and the GPS. Likewise, 100 on the bike speedo shows 97/98 on the Sigma and the GPS.
My bike speedo used to be about 7% to 8% optimistic but I then changed the gearing by putting a 1 tooth larger sprocket on the front which was about a 6% increase in gearing. This has made the speedo a lot more accurate with 70 on the speedo showing 68/69 on the Sigma and the GPS. Likewise, 100 on the bike speedo shows 97/98 on the Sigma and the GPS.
podman said:
The answer to that will be no ones...and sat navs whilst being a lot more accurate than your stock speedo are not 100% accurate.
Why dont you take yourself along to a straightliners day and see what your bike can really do thru a proper timing trap...but be prepared to be disappointed!
A timing trap wouldn't be any more acurate than GPS though - it only gives an average speed for the whole of the measured distance.Why dont you take yourself along to a straightliners day and see what your bike can really do thru a proper timing trap...but be prepared to be disappointed!
Frik said:
A timing trap wouldn't be any more acurate than GPS though - it only gives an average speed for the whole of the measured distance.
I think the distance measurement through a timing trap would be extremely accurate compared to that of a GPS system. (GPS after all only accurate to a few feet.) With timing of the trap being measured to at least 100ths of a second, then the distance/time (speed) calculation will be very accurate.Conian said:
Which should i trust? Hmmmm let me think
French engineering.... or japanese engineering?
Go and slap yourself for even asking!
Although I've tested a few vehicles against a Garmin and at 100mph, actual speeds were;French engineering.... or japanese engineering?
Go and slap yourself for even asking!
Renault Clio 99mph - pretty much spot on
Aprilia 99mph (with smaller front sprocket) They are pretty spot on up to 167mph
R1 95mph
Evo 95mph
ZX6R 91/92mph
All on the autobahn, needless to say.
rsv gone! said:
Conian said:
Which should i trust? Hmmmm let me think
French engineering.... or japanese engineering?
Go and slap yourself for even asking!
Although I've tested a few vehicles against a Garmin and at 100mph, actual speeds were;French engineering.... or japanese engineering?
Go and slap yourself for even asking!
Renault Clio 99mph - pretty much spot on
Aprilia 99mph (with smaller front sprocket) They are pretty spot on up to 167mph
R1 95mph
Evo 95mph
ZX6R 91/92mph
All on the autobahn, needless to say.
Kwacker said:
Coming back from wales yesterday, a Citroen C4 slowly went past me and I happened to see his speedo (one of those big centre of the dashboard lcd thingys) and it was a good 5-10 mph diferent to mine. So I thought I'd check it again to make sure, so I passed him. Again 5-10 mph difference. This happened several times and each time My speedo was 5-10 mph slower than his.
Anyone else had this?
Looks like I will have to get a Sat nav to find out exactly what I am doing. At least that is what I'll tell the wife. I've been waiting for a good excuse to get one.
Also Which Sat nav to go for, Proper biker one (expensive or) good car one with waterproof bag?
Kwacker
I had a C4 Picasso on hire for a bit, and the speedo was about 10% higher than GPS at all speeds.Anyone else had this?
Looks like I will have to get a Sat nav to find out exactly what I am doing. At least that is what I'll tell the wife. I've been waiting for a good excuse to get one.
Also Which Sat nav to go for, Proper biker one (expensive or) good car one with waterproof bag?
Kwacker
Frik said:
podman said:
The answer to that will be no ones...and sat navs whilst being a lot more accurate than your stock speedo are not 100% accurate.
Why dont you take yourself along to a straightliners day and see what your bike can really do thru a proper timing trap...but be prepared to be disappointed!
A timing trap wouldn't be any more acurate than GPS though - it only gives an average speed for the whole of the measured distance.Why dont you take yourself along to a straightliners day and see what your bike can really do thru a proper timing trap...but be prepared to be disappointed!
GPS works by measuring the difference in position from satellite signals and time delays the signal back to the unit which then computes the speed.
Timing traps are mere inches apart in the setting up and give an electronic signal back to the computer which measures the time between signals to compute the speed.
In short a properly calibrated timing trap is a direct scalar measurement as opposed to a calculated vector.
Up to around 100 both id say both reasonably accurate but start putting some big numbers into things and there’s only one set of figures that are really credible.
Just for interest 190MPH on my speedo was a rather disappointing true 176MPH...a chap whazzed his car thru and an indicated 150MPH was a true 137MPH
Mad Dave said:
Also bear in mind the angle you'd be viewing the car's speedo through the window - the view of my car's speedo from the passenger seat is a good 5mph different to the reading from the driver's seat.
Parallax error - not if it's a digi lcd thingy in the car.You could get a feel for your speedo accuracy by riding through one of those nagging speed traps, where they flash your speed at you to shame you into slowing down. I've found they tend to agree with the GPS in the car. You'd need to do several passes at different speeds to be sure.
My ZX-6R is overoptimistic on the speedo as it goes, but I'm not sure how much by.
To accurately guage how close your speedo is... take the following steps...
1) Drive your car with the speedo at precisely 100mph
2) Drive said car at said speed around the M25, covering as many SPECS as possible.
3) Wait for the postman
4) Take an note of all the speeds that you have been summoned for, the more speed traps the better as it will average out innacuracies from the various machines.
5) While in jail, add up the speeds from each of the speeding tickets, and divide by the number of tickets.
6) As you were doing an indicated 100mph, it will be simple maths to work out the percentage that your speedo is out.
1) Drive your car with the speedo at precisely 100mph
2) Drive said car at said speed around the M25, covering as many SPECS as possible.
3) Wait for the postman
4) Take an note of all the speeds that you have been summoned for, the more speed traps the better as it will average out innacuracies from the various machines.
5) While in jail, add up the speeds from each of the speeding tickets, and divide by the number of tickets.
6) As you were doing an indicated 100mph, it will be simple maths to work out the percentage that your speedo is out.
Gassing Station | Biker Banter | Top of Page | What's New | My Stuff