innaccurate speedo - tyre circumference required please

[holla]

Hi all, I was told when i bought the bike that the speedo wasnt very accurate, it doesnt seem that bad at low speeds, Its sort of 2 mph high for every 10mph so 20 reads 25 and 30 reads 36ish but when you get it up to 80 then its close to 100.

This woulnt usually bother me but i was given a brand new speedo with the bike so i was wondering if any of your 907's were the same ??

I didnt want to split the dash board if there was going to be no difference.

Another possibility could be this, The bike has new tyres fitted but they look lower profile than probably would have been fitted originally. If any of you have pretty much standard front tyres could you please measure the circumference. A piece of string or wire would probably be easiest then measure the length.

My lower profile tyre wold show a smaller measurment that a higher profile one so my tyre will be going round faster than a tyre with a higher sidewall and larger measurment. I would just like to know what the difference in measurment was.

Thanks

[persempre907]

The stock front tire is a 120/70-17.
I don't think is a problem of tire.
All the 907's gauges aren't so accurate, but I think the worst is the gasoline gauge.
I wouldn't worry .
Ciao

[holla]

The stock front tire is a 120/70-17.
I don't think is a problem of tire.

just had a look at mine its a 120/60/17.

The circumference must be smaller than a 70,

Did you say that your speedo isnt accurate either or have you never checked it ?

I know what you mean about the fuel gauge, i came to a sudden stop and according to the gauge it was between 1/4 and full

Thanks

[Laddie907]

My 907 runs a Pirelli Diablo (sounds positively evil, huh?) 120/70 17
the speedo is about 10% optimistic; it shows 100kms/hr (high) at 90kms - which has given me a few nervous moments when I see a police radar...

My 900SS has a Michelin 120/70 17 [the speedo on this is accurate...]

The 907 tyre is on it's last gasp for tread but measures almost the same OD as the near new Michelin on the SS at 23" (57cms).

the "70" [or in your case "60"] is a relationship of the tyre profile height / divided by the width...so the 70 will give a better result than a 60 in the case of speedo accuracy in this case.

probably the best fix is the speedo drive at the wheel hub...
in the case of cars it used to be easy to buy different speedo pinion gears (fitted to the gearbox) to suit the diff ratio; similar to re-ratioing a rear or front sprocket...
it will be something like add a tooth to the nylon pinion (to slow the cable revolutions)...just finding the right auto model to match.

no doubt Ducati would want about $US250 for this item...

[gail]

Speedo on mine is optimistic also by 10%. Its good to have this built in, especially when the long arm of the law is about. Always better to be reading higher than lower in my book . In some states over Oz you can lose your licence for going 30 kmh over any posted limit. So its satisfying to know that you will only get a huge speeding fine rather than loss of licence. Its a hard way to get one up on the wallopers but at least you can finish off your ride, minus the cash content of you wallet. ......Such is Life!.........Marty

[jetboy]

if it really bothers you - you can get an aftermarket inline adjuster - they are about 60 bucks. my speedo is terrible - it says im doing 80 when im doing about 65.

its nearly not worth having. if i find a cheap adjuster im gonna get it.

[Rogero]

It's much better to have an optimistic speedo, my ST3 ( recently purchased ) has a digital readout and I now know how slow I've aqctually been riding on the 907 !!


But it always seemed fast to me!!!!

[higgy]

There are shops around that can calibrate any speedo. The vast majority of speedo's are optimistic

[franksnively]

I had always figured that the Ducati is no different from many other bikes, they deliberately set it so the speedo reads high. And the odometer reads further than I have really gone also. There are several advantages to doing it this way.

First, we don't get as many traffic citations; that's a good thing in my case!

Second we can brag about how fast the bike is.

Third, Ducati saves a little on warranty claims. Fortunately, mine ran fine around the REAL mileage which would go over the distance, so I never had to contest with the dealer or Ducati USA.

My part of Colorado has open roads except during tourist season, and with an electronic stopwatch (cheap at Radio Shack) it is easy to calibrate up to 90 mph (the Ducati speedometer says 102 indicated). That's fast enough for this oldster.

I have not found that tire wear makes all that much difference: I can't use the speedometer as a substitute for actually looking at the tread.