Sprocket and speedo trouble!

[FuzzyBallz]

The original gearing on my bike is 14/40 but when I bought it the sprockets have been changed to 13/43, which I don't mind because it makes it more punchy, but I'm aware of my speedo being way out!

Is there any website I can put my altered ratio in and it will tell me, when you are going 30mph, your speedo will read "blah blah"

I can then learn the speeds I need to get my speedometer up to to travel at 20,30,40,50,60 and 70, without risk of people being up my hoop because I think I'm going fast enough when I'm not, and so I don't just guess it and get a speeding ticket.

I did go on www.gearingcommander.com but it was all a bit confusing tbh and I am still non the wiser.

Thanks.

[Monkeywrenche...]

I don't know if it's applicable...

https://www.healtech-electronics.com/products/sh/

[barrkel]

Short answer: your speedo reads (14/40) / (13/43) of stock reading. That works out to 1.15769, or almost 16% over.

Multiply your target speed by 1.16, and you'll get the speedo reading. 30mph => 35, 40 => 46, 50 => 58, 60 => 70, 70 => 81.

The stock ratio will have overestimated speed though.
____________________
Bikes: S1000R, SH350; Exes: Vity 125, PS125, YBR125, ER6f, VFR800, Brutale 920, CB600F, SH300x4
Best road ever ridden: www.youtube.com/watch?v=s2MhNxUEYtQ

[Vincent]

Use a sat nav with a speedo
____________________
Space Is Deep

[Casper]

What bike you got? If the speedo is gear driven from the front wheel then changing sprocket size should make no difference. BTW as Vincent says use a sat nav for to test. My bike is only doing 65 when sat nav says 70 mph and my car is about the same. Good thing about that is i do 80 odd mph through the speed cameras on the motorway and feel a rebel where in reality i am only doing 74/5 mph.

[FuzzyBallz]

Wow thanks Barrkel you have just made my life alot easier

I knew 35 on my speedo would be 30ish as my mate followed me in his car and when my speedo said 30 he said I was doing 26, so the rest of the speeds all sound about right! I'll have to revise them

I was looking at the speedo healer but the cheapest I could find it for was £80 on ebay and I don't really want to spend out that much, I'm happy with speedo being out aslong as I know how much faster i should go to do the actual speed limit.

A Satnav is a good idea and I did think about it but I don't have one so that idea went out the window

It's a CRF250L, I'm guessing it reads from the back wheel as when I have the bike on the work stand, if I put it in gear and start twisting the throttle to spin the back wheel (don't ask) the speedo will start going up

[Casper]

[FuzzyBallz]

[Casper]

I would do a couple to compare speeds. This is what i sometimes use. Spend 5 minutes learning how to use it as in landscape you can get big font on its speedo.

https://play.google.com/store/apps/details?id=com.chartcross.gpstest&hl=en_GB