Speedo way off

[Gert]

I would recommend reading my reply in #7 above again.

Sadly one can't have it both ways when changing from the factory designed sprocket size. You can either correct the speedo and learn to live with the tripmeter reading being wrong (this includes the mpg reading), or you learn to live with the speedo reading being out in order to retain the tripmeter reading (and mpg reading) close to accurate.
Same thing applies when using a speedo healer from Healtech.

In the case of the 1st gen Wee and Vee, there used to be a recalibrated face plate available to correct speedo reading with the stock sprocket setup (http://raceratb.com/austin/car/buyGauges.htm), but when the digital display was introduced, it became a different ball game.

[vstroman]

I'm not too worried about it to be honest as long as this is the reason the bikes showing around 55mpg now with a 16 tooth front rather than around 60mpg before when it was a 15 tooth.
I'll likely go back to standard gearing next time though anyway, in the meantime I'll do a check with a phone app and compare it with the displayed speed.

[nigel s]

Just to complicate matters, it could also be true the taller gearing IS using more fuel.
When actually cruising at say 70mph 16t may well give more mph. But every time you accelerate up to a certain speed takes longer with a 16t compared to a 15/14t.Longer with the throttle open means more fuel used.( watch the live mpg on the dash for how the throttle effects mpg on a long uphill/headwind on the motorway, a 1000/1050 uses less fuel in that situation due to not having to open the throttle so much to maintain speed , probably)
Not tried 16t. But my '22 650 did 275 miles to a tank on 15t and after changing to a 14t still did 275 miles on a tank ( most I ever saw was 310 miles), but was much livelier getting up to speed. Lowering the ratio obviously helps  acceleration because the revs are slightly higher when you start to accelerate (240rpm as I remember ) but because the torque curve is not a flat line it also means the motor gets to the "fun " bit past 4k,ish quicker (  edging up to peak efficiency at peak torque and less time with the throttle open again ) so as long as I keep to the same cruising speeds as before the change to 14t uses the same fuel for more performance.
 I will happily caveat all that by saying I spend as little time on duals/motorways, main roads as I can feasibly get away with so others may find a different outcome

[nigel s]

"when actually cruising at say 70 mph 16t may well give more mph " should read mpg obvs..too late to change ..sorry.

[MilozFolly]

All interesting/good points!  I think I'll replace with standard gearing and cushioned JT stuff!  Save any additional faff 

[vstroman]

Tempted to throw on a 14 tooth now just to try the increased acceleration!
easy and cheap to switch so I may give the 14 a try now as well.

[nigel s]

For what it costs