Help ! Dont want a uni-cycle
 

Want to add a little bit more poke into mine and been looking at 47 tooth rental rear sprocket but don't want a wheelie machine! Just want a bit better go when bike is in second and wants to go into first when going round the bouts and pulling out of corners e.t.c. who's done this mod and is it better or should I go 46 tooth rental rear from motorcycle race parts UK HELP don't want a UNI-CYCLE :blob10:
(Bike is stock)

Check this out.

I hear what you say and I'd recommend 46T

https://www.xt660.com/showthread.php?t=27426

Does altering the rear sprocket affect the speedo by much?

Short answer is yes but will vary to the ratio you choose.... My ratio of 15 / 46 (lowered gearing) makes the speedo over-read the speed, and I'm guessing it would actually make the odometer click over the miles in a shorter distance, but that's a guess as I haven't bothered to check that.

When my GPS is on the bike the difference between a satellite indicated 60 mph and the speedo is 6 mph (speedo showing 54). The faster I go the the bigger the difference between actual speed (GPS) and indicated (speedo) . This is assuming a GPS is NASA standard accurate as well. The original ratio 15 / 45 will still be over reading, set by factory standards, but not as much I suppose as part of 'Type Approval' safety margins. From memory the maximum allowed margin is 10%. With my ratio I am at 10-11%

Changing up the gearing, making it higher (say going to a 44 T rear from a 45 T rear would make the speedo under-read, and guessing again would actually bring the factory margin of difference, (between actual and speedo reading) more in line with actual speed so what your speedo shows will be closer to reality.

It's a personal thing but I wouldn't understand why someone would want to up-gear the 660 because it would be less manageable in slow maneuvers requiring the use of 1st instead of 2nd more often and would make the bike jerky in response to minor throttle grip adjustments whilst in 1st. The only advantage for this, I guess, would be if someone does a lot of constant high speed road commuting to bring the revs down (arguably improve MPG) but then they're probably on the wrong type of bike. Like I say it's personal and some may find this OK and report accordingly.

Having said that the Aprilia Pegaso Factory 660 uses the exact same engine with the exact same internal gearbox ratios but Aprilia put a 15 on the front and a 44 on the rear, so it must work for some.

Okay! I thought if that the scenario
If doing 30 mph on 15/46 ratio I thought it would be doing 24 mph (no speeding ticket)
if doing 30 mph on 15/44 ratio I would be doing 36 mph ( nee nor nee nor:ban-em[1]:)
Wheel turns faster bigger rear sprocket but won't go as fast
Smaller sprocket less acceleration more speed
Front sprocket bigger =speed
Smaller =acceleration
Chalk two you said if your doing 60 mph on satellite the speedo reads 54 mph
Just want to get this right before buying nice new 46 tooth sprocket that I won't get a extra new 3 points to go with that sprocket! As if I was doing 30 mph on speedo with 46er I would be doing 36 mph I would go :tongue6: or have I just confused myself as I am writing this his opinion sound right ahh! let's hear anyone else opinion
May just get speedo reset if I do this mod!

Sorry buddy. It sounded correct in my head. If you buy 15 46 your actual speed will always be less than your speedo reading. You will always be on the safe side of the law if you refer to your speedo.

You'll enjoy the 46T rear

i also think about going 1 tooth up rear, so 15/46. engine is not so smooth at about 90-95km/h in 5th gear.
i want to be able to cruise at that speed in top gear.
15/45 gives about 3500 rm at that speed.
will 1 tooth rear give me what i need?

apparently i got 15/46 gearing already.
installed a 14t front sprocket and found it spot on, as it should come from factory i.m.o.
but since the 14t might be a little too close the the swingarm i'm thinking to change total gearing from 14/46 (3.28) to 15/49 (3.26)
this seems very short geared though, but in reality it feels very usable.
as reference, engine makes 4500rpm at 120km/h (speedo) wich makes the engine run nice and smooth.
anyone else using a 'short gearing' as what i suggest?

It might help, but at 3500 rpm you may well be in the area where the fuelling is switching from 'closed loop' to 'open loop'

If you ask Kev in the 'ask Kev' section he will be able to explain what's happening here, especially if you're experiencing 'lurching' or 'surging' at, or near, that range. Changing gearing will just move that surging to a different point in the rev range. I would definitely recommend the O2 mod if this is the case.

i don't know if my 2009 xtz has an O2. as i read here, not all 660 engines have an O2 sensor...
i did do a sort of kev mod :-p and decat today.

check your exhaust pipes..if you have an o2 sensor you will see it on a pipe with the wires coming from it..