I was thinking of lowering my gearing on my J2 but don’t want to make my speedo read wrong for speed cameras etc. Some people have said it doesn’t make a difference and others say it does? Any ideas if it does or doesnt?
If you drop one tooth down on your front sprocket it will make your speedo overread by 7%
Did it on my J1 and A1 and wasn’t an issue, coz if anything it makes you actually ride slower for speed camera’s/police/small dogs etc.
Thats not bad at all cause I go through speed cameras at least a good 5mph slower than the limit anyway.
Does one tooth make a noticable difference?
Yep, it does, it’s equivalent to going up 2-3 teeth at the back, so you’ll lose a fraction of top speed (not important in this day an age) but gain low down acceleration (extremeley important!!), it revs slightly higher in each gear so petrol consumption is up a bit but not noticeable (unless your name is Eugene and you like doing Excel spreadsheets!) anywaythat aint important, you have a performance boost for about £10 
Two words for you Terry…Wheelie School.
Do it, it’s the best and cheapest modification you can do, you get instant ‘power’ upgrade and no ill side-effects. On all the bikes I’ve done it to, the speedo hasn’t really changed hardly anything, and I’ve never been flashed by a camera.
Wheelies mmmm there coming as you saw yesterday in first the front starts to lift then it’s a no go lowered gearing will help!
I’m going one down on the front on my R1. As stated previously in the thread it will actually make you’re speedo over-read. Seeing as speedos can over-read up to 10% anyway I’ll be investing in a ‘Yellow Box’, which is a little electronic box which intercepts and corrects the signals coming from the speed sensor and recalibrates them. Once installed, I’ll calibrate the speedo using my GPS for a perfect reading!
A yellow box isnt necessary as the clocks are not digital. David I’ve got one going cheap if you want it.
Ah, I thought the J2 models were digital. I’m doing the upgrades little by little - got all the parts but I want to see the effect they have - so it may be a little while before I need the yellow box.
In the pipeline for the R1 are:
Goodridge braided hoses front & back
Free-er flowing air filter
Power Commander
15T front sprocket
Digi gear indicator
Should be having fun tinkering in the next month!
I went one down front two up back and love it… might actually do the rear again… 
Whats the difference between changing the front over the rear cog, or isn’t there any difference apart from the smaller front cog costing less?
It comes down to this, though each point is pretty small in comparison to the contary, it’s down to personal preference most of the time:
Pros of front:
- Easer to change
- No longer chain needed (as more extreme changes can be made with minimal chain length difference)
- Lighter sprocket than rear
Pros of rear:
- Compliments front sprocket changes
- Can look more visually appealing
Most people change the front first, then change the rear as well if they have to, to get a certain gearing solution.