Gear ratio to top end speed.

Trying to figure the mechanics on this, but for the life of me can't.  L Plate Son has a Hyosung 125RT and whilst its OK tootling around to and from college, he is struggling on top end.  It max's out at about 60 and getting to that speed, especially on an incline can take some time. I'm not overly keen on him going too quick, but would like him to be able to keep with the flow of traffic.  I know changing the gear ratio could help, but don't know which way to do it - larger final and smaller drive. or vice versa,  bigger or smaller both?  Also what would the 'downside' be?  Can anyone advise?

All the current crop of 125's are strangled to death with restrictors, so raising the gearing will make it chew even harder, lowering it will give him more acceleration but his top speed will suffer and it's already low enough.

It's ridiculous really as most 125's nowadays can't even outdo granny mcfanny in her pleb pot Nissan Micra and I think it puts learner riders in a great deal of danger as they can't compete with the flow of traffic.

A few times now I've tucked in behind a learner rider just to protect them from the bad tempered car driving idiot that was mercilessly tailgating them, it's time the learner limit was raised back to 250cc.

As for the gearing if you want to try it:

Larger sprocket on the back lowers the gearing.

Smaller sprocket on the back raises the gearing.

And vice versa for the front sprocket.

Here's a useful link for you http://www.gearingcommander.com/

Unfortunately a little over 60 is the most your going to get John unless your going downhill with a strong wind behind you    , as Mart said they are 'strangled to death', mostly by design.
Back in the day when two strokes were king, you could at least 'tamper' with them to get a bit more oomph,these days you just have to grin and bear it!



"Granny Mcfanny in her pleb pot Nissan Micra"   

The 125s like toms are not restricted, they are built to perform like mini cruisers from the start. Did look into it and even if you could get the replacement parts they would make so little difference as to not be worth the money.
Rule of thumb though, increase the rear sprocket size (like the orange one on the ktm) and you will slightly increase the acceleration BUT slow down top end (2 extra teeth will knock of about 4mph from top end)
Decrease the number of teeth and increase the teeth in the first sprocket will increase top end but slow acceleration which is ok but it shows even MORE on hills, and puts strain on an engine that's built to spec, if it was a Honda, yam etc not really a problem but even the "better" Chinese bikes like Hyosung and kymco are only just built to tolerate the specs there made too.

Like skid said persevere getting him competent and confident then take the next test up and get something bigger 250/300

Thanks for the advice guys - All very sound and sensible.  Rick'll have to grin and bear it for a while, but it will give him an incentice to move to the next grade.  Cheers.

Don't let him test ride anything bigger til he does! trust me I have had too put up with toms constant bellyaching ever since I let him "test" the hd street, my bikes crap, its too slow, I cant find the gears it sounds like a girls bike..........................