Nearly all speedometers read about 5 to 8% higher than the actual speed, probably this is done both to avoid any suit to the manufacturer in case of a fine, and to give a higer speed feeling. back in the 90s the alfa romeos speedos were about 25%!!!!! higher.

However nearly all odometers are accurate, if you install a speedo healer then the odometers becomes inaccurate, I do prefer to install a cheapo Sigma bicycle speedo on the front wheel, if will be accurate even if you change sprockets.

have fun,

j.�

I agree with the reasoning for the speedos being "optimistic" - if you fit taller gearing or larger profile tyres then you would be going faster than indicated if the speedo was spot on. (although altering the gearing wouldn't effect front wheel driven speedos - assuming your front wheel is still on the ground! )

Yep - whilst the speed can be as much as 10% out when compared to a GPS (Zumo), I've found that the odometer is only 1-2% out. Which is what got me thinking.....if the speedo is measuring distance accurately enough the indicated speed can only be out because the speedo is not counting time correctly ie too slowly(making the speedo's brain think that the bike has covered a certain distance in a shorter time ie faster!)

I suppose it is wishful thinking that the fix would be as simple as a tweek on a variable potentiometer??? Any electronics whizzos out there?

BTW, I was close to buying an Acewell speedo for my DR800 months ago prior to buying the Tenere. They look well neat with loads of useful functions and can be callibrated just like a bicycle speedo.

I'm an electronic eng. and most modern speedo are 100% digital, there are no analog parts, no potentiometer to adjust :(, in fact the optimistic reading is done inside the software of the speedo, without reprogramming it it is not possible to have both the odo and the speedo accurate, and it is almost impossible to reprogram it.

As you say, Acewell and trailtech Vapor are good alternatives, not as cheap as the bicycle ones, but they have more functions, and you can see them in the dark too.
have fun,

j.

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OK - I've tried to follow this thread - when my head recovers I'm sure I will adopt my original plan and fit an 18 inch rear wheel now that Jmo has shown the way forward. This should look better than the original - work better than the original and give a reasonably accurate speedo reading.

Will be looking for a little more power at sumtime in the future anyway (when funds allow) so that should take care of the over-gearing brought about by the greater rolling radius the 18 incher brings.

givit

Hi Givit - while it's true running standard gearing with an 18 inch rear wheel makes the speedo pretty accurate, you'll find that the gearing itself is now way too high (by the corresponding 10% or so)... it's fine for general road-riding, and gives a lovely relaxed top gear, but it is akin to having a six speed gearbox with no first gear!

I have had to fit 14/48 to get it back to near what it felt like with standard gearing on the 17 inch rear wheel (with the corresponding speedo error - around 10mph at 70mph) and am now running 14/50 which is really peppy, but obviously puts the speed out even further...

I think the only way to sort the speedo is with a healer unit, and then run whatever gearing you like with the wheel size you choose?

xxx

I have just fitted a 14 front and my speedo is 15% out
reads................. true speed mph
..34=...................... 30
...80=..................... 70
103= ..................... 90

Here you go, a few tools to see what happens when you change your gear ratio. Enter your sprocket ratio's.

http://ranni.altervista.org/xtx/

http://www.xt660.com/attachment.php?...5&d=1170400565

http://www.xs4all.nl/~ator0437/gc/

http://www.wotid.com/tls/files/gearing_v12.xls

http://www.4strokes.com/tech/gearing_calc.xls

http://www.gearingcommander.com/

http://www.mr2ownersclub.com/converter.htm

Jen,
The easiest thing you could do is take your bike for a ride at say 60mph on the speedo and just see what your sat nav tells you what speed you are actually going at. If you set the averaging feature to medium (I cannot remember what is called on your Garmin) it should give you a reasonable average.

Once you get the figure, the sums are fairly easy and examples are on the SpeedoHealer site. If you get stuck, just post the figures and we can sort it. The only other consideration is as to wether you want the speedo accurate or the ODO ! You cannot have both.

I say this as the only other alternative, due to the fact that you have an 18" wheel, is to do some complicated sums involving measuring the "rolling" circumference of your rear wheel when loaded and then compare that to another Tenere with a standard wheel on. Due to the tyre size being different, not just the rim size, the sums would get complicated.
Ray

Hi Ray - I'd forgotten all about this thread! I know exactly what your saying, and when the bike comes back (it's on a boat at the moment, hopefully not in the hands of pirates!) I'll have a look as you say...

I've seen a speedo healer device on Ebay for around �55 so that is probably what I'll get, although to be honest with the IMO fitted now I have a very accurate speedo/odo anyway of course...

As I recall, at a true (GPS) 60mph the bike is now reading 72-73mph... make of that what you will...

J xx

Hi Ray.

If your speedo was reading 77MPH and in fact you where traveling at 70MPH how will the addition of this gizmo make the situation better for your travel in camera mad London? I would have thought it beneficial to have an 'optomistic' speedo rathr than a 'pessimisitic', sort of a safety margin, no?

I presume when you got in trouble for speeding rather than your speedo reading 30MPH in a built up area it would have read 25MPH and that is a good safety margin for error? See my point. Now if the speedo was the other way IE reading 70MPH but actual speed was 77MPH then THAT would need addressing.

Just a thought?

I hope you have safe travel for the future.

Best wishes,

Ryland