Jump to content

Speedo reading fast


scottiedoug

Recommended Posts

scottiedoug

I fitted a Garmen Zumo to the NC750X-DCT and found that the speedometer is reading 70 miles per hour when the satnav is reading 61 miles per hour. To confirm that the bike speedo is reading a higher speed than what the actual speed is  I checked it against the friendly speed check units when you come into towns and at 40mph on the speedo it is actually 33 mph on the speed check unit. Can the speedo be really that far out and can it be tuned closer to the actual speed??

Link to post

I think that changing the gearing - number of teeth on sprockets - can affect the speedo reading on some bikes. I dare say someone will know if this is the case on the NC.

  • Like 1
Link to post

On my Integra compared to GPS, 33 on speedo was 30, 44 was 40, 55 was 50, 66 was 60, 77 was 70  so the speedo was exponentially increasing as speed rises.

The VS sensor reads off the output shaft, behind the engine sprocket so assumes the gearing to the rear wheel is standard. As Integras seem to be less accurate than other models, and the sprockets are different, It would be reasonable to assume they never bothered to do any re-calibrating as the error is on the safe side.

Possibly as yours is wildly out, you have the wrong sprockets fitted, easily done as determining which you should have is not easy there is so much conflicting info published on parts suppliers websites.

  • Like 1
Link to post

That's funny, I just replied to another post about the same thing. Yep, mine is a bad as that. Apparently the law allows your speedo to be 10% out in that direction, but no tolerance the other way. It is a bit disappointing but explains why there are some brilliant mpg figures being claimed. Hey ho, I can live with it but it isn't very good for a brand new bike with all this clever electronic stuff fitted, is it? Maybe someone knows how to recalibrate the speedo?

Link to post
12 minutes ago, Herr Flick said:

That's funny, I just replied to another post about the same thing. Yep, mine is a bad as that. Apparently the law allows your speedo to be 10% out in that direction, but no tolerance the other way. It is a bit disappointing but explains why there are some brilliant mpg figures being claimed. Hey ho, I can live with it but it isn't very good for a brand new bike with all this clever electronic stuff fitted, is it? Maybe someone knows how to recalibrate the speedo?

Just out of curiosity, why would it impact MPG? 

Link to post
Rocker66
Just now, Woody 99 said:

Just out of curiosity, why would it impact MPG? 

Simply because if you calculate your MPG by comparing the distance travelled shown on the speedo with the fuel used the resulting figure will be greater if the speedo reading shows more miles than those actually travelled. Obviously this only affects the MPG calculated and doesn’t affect the actual MPG.

  • Like 1
Link to post

My NC is almost spot on but my AT is 10% off across the range. The error can be corrected by using a speedhealer, and had considered getting one for the AT, before deciding I woudl just live with it and do mental maths, ;-)

  • Like 1
Link to post
37 minutes ago, Woody 99 said:

Just out of curiosity, why would it impact MPG? 

 

It's only my assumption that the odometer will be similarly inaccurate as the speedo. As Rocker says, it would most probably be recording more miles travelled than is true.

I hadn't heard of Speedohealer before either, so thanks for that rjp, it does look interesting. I may just end up living with it but I am in a spending mood at the moment...and a new helmet may be a better idea!

Link to post
56 minutes ago, rjp996 said:

My NC is almost spot on but my AT is 10% off across the range. The error can be corrected by using a speedhealer, and had considered getting one for the AT, before deciding I woudl just live with it and do mental maths, ;-)

 

Yes my AT is at least that out, I would go so far as to say that it's so far out that, at higher speeds you can almost tell without checking against a sat nav, etc, it just no ways feels as fastas the speedo is showing. I may consider a speed healer (whatever that is) as I find myself pushing some speed limits knowing the speedo is so innacurate and I'll get caught out one day

Link to post

The speedo sensor delivers a pulse per revolution of the shaft, the number of pulses per second determines the speed displayed and the total number will display the odo mileage based on the circumference of the tyre per revolution. They are linked.

An overly high reading will show more miles than actually covered and give the impression of a better calculated MPG than is true.

New helmet is definitely a better spend than bothering about the accuracy of the speedo especially at the price of one of those healers.

Link to post

Well mine is giving a near accurate at 30 but at 70 on the  zumo it over reads , but what’s funny is it seems every vehicle I’m following is doing the Same because they are holding a 64/5 mph and I don’t think they are all holding back to be under the limit . 

The movement of the traffic is pretty constant. Unless there is a Honda at the head of the que :0) .

basically if you hold a constant 70 on the gps , see how you catch the vehicle in front. 

Link to post

When I am in 30, 40, 50 zones I use the speedo on the bike, that way I know I will not be speeding. The GPS gives a true reading though so I know how far I can push it and still be safe. I set the cruise control at 32mph on the speedo and that will be a real 29 - 30 mph.

Link to post

My speedo is out compared with my tom tom but I have changed the gearing  will shortly be putting new chain and standard  spkts on my old girl  so will see if speedo reading alters 

  • Like 1
Link to post
8 minutes ago, Tonyj said:

Well mine is giving a near accurate at 30 but at 70 on the  zumo it over reads , but what’s funny is it seems every vehicle I’m following is doing the Same because they are holding a 64/5 mph and I don’t think they are all holding back to be under the limit . 

The movement of the traffic is pretty constant. Unless there is a Honda at the head of the que :0) .

basically if you hold a constant 70 on the gps , see how you catch the vehicle in front. 

 

If that's correct, then the odometer isn't directly linked to the speedometer and our mpg figures are probably accurate. I'd assumed distance was accurate and many speedometers were deliberately set to around 10% below true throughout the range. Hence 75mph indicated is probably 68 true and speeding enforcement wouldn't be too concerned anyway.

 

About time I went out early Sunday morning and timed a standard distance at various speeds!

  • Like 1
Link to post

Check the sprocket sizes fitted to your bike. Manual sprockets 17/43 fitted to a DCT 17/39 will give over readings of around 10%. If this was the case on your bike, an indicated 70mph would then be more like a true (satnav) 67mph (i.e. 61+10%)

My 700 Integra is remarkably accurate, over-reading speed by only a few mph (maybe +3mph at 70).

There's no reason why the accuracy of the speedo (regulations require no under-reading) and the odometer (not regulated as such) should be linked, they are the results of calculations, which can have different fiddle factors applied even though they use the same sensor signal.

  • Like 2
Link to post

All my Hondas have had accurate mileage recordings but as already stated they all showed 32mph for a true 30mph, and 64mph for a true 60mph. If there is a 10% error on mileage I agree it is most probably a gearing change.

  • Like 1
Link to post
Spindizzy

My car at 70 is a real world 67. volvo..

 

My scooter at 60 (70 yeah right) is actually 54.5

 

NC not sure but at 75 indicated I seem to be matching the cars with cruise control on. 

 

Top two checked against tomtom and iphone.

Link to post

Using Garmin satnav to confirm (which I've been assured is pretty accurate) my AT at 85 displayed is 76, that's way too far out IMO. No gearing change alhtough not on stock tyres they are the same dimensions, allowing for wear of course.

Link to post
Scootabout

AFAIK the law allows speedos to over-read by 10% plus 2.5 mph (but not under-read). 

Hence why, I've always assumed, ACPO guidelines for speed enforcement allow a similar amount (actually 10% + 2 mph), presumably so no-one can reasonably claim they had assumed their speedo over-read to the max even though it was spot on, IYSWIM. 

 

FWIW my NC seems to over-read by about 5%.  I wouldn't worry what the actual amount is, provided you know it and can adjust accordingly.

Link to post

My AT was about 10% over on the speed, but accurate on the mpg, I haven't measured the NC but it certainly feels about the same.

 

I remember reading a long thread on another forum and the unanimous conclusion  was that the speed inaccuracy does not effect the mpg at all.

Link to post
scottiedoug

I think I have found the problem to the speedo reading very fast. I just checked the sprockets on my 750x-dct and the front sprocket is 17t but the rear sprocket is 43t. As embee says the rear sprocket should be 39t so at some point the rear sprocket has been changed. 

  • Like 1
  • Thanks 2
Link to post

I suspect my Integra was the same as it might also go some way to explaining the funny gear selection it chose to use at times when in D. The dealer fitted new ones and a chain before I got it but if it was wrong they now have it back again as I just traded it back to them so it's their problem now :)

Link to post

All satnavs get their readings via GPS so are accurate,  although theoretically going up or down hill, and riding on twisty roads can give false mph readings, the errors are very small, certainly not anything like 10%!

Link to post
Guest machinman
2 hours ago, scottiedoug said:

I think I have found the problem to the speedo reading very fast. I just checked the sprockets on my 750x-dct and the front sprocket is 17t but the rear sprocket is 43t. As embee says the rear sprocket should be 39t so at some point the rear sprocket has been changed. 

Is your DCT working correctly? The reason i ask is a member had problems and was unsure if a sprocket change was the culprit.

Link to post
Graham NZ

Even with new tyres it's normal for speedos to read higher than true speed.  About 6% it seems.  In NZ the law allows for a 9 km/h tolerance, so up to an indicated 115 km/h  should see you ticket free on the open road with a 100 km/h limit.

Link to post

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...