changing sprockets? using 6th gear?

stirlinggaz · World Chat Champion Joined: 22 Jul 2007 Karma :

hi all,
im currently using the little mtx for commuting the 30mile round trip to work. (& loving every minutee of it)
its got the 125 engine in it. (so no atac Crying or Very sad

)
the sprockets at present are 16/53.
i think its meant to have 15/53 or 15/55.
it runs fine but doesnt have much power low down, (like most small 2 strokes) but im finding 6th gear useless.
if i dont completely redline it in 5th, when i change to 6th, the revs will drop to 6000rpm & the speed will drop a bit & will take forever to get over 50mph.
whereas if i completely redline it, off the clocks,, then change into 6th, it will happlily go up to 70mph, no problem. (will likely do a bit more)
indicated speeds mind.
just wondering, would messing with the sprockets give me a useable 6th gear?
as it cant be good for the top end, revving the tits off it like that.
cheers,
GAZ

The Artist · Super Spammer Joined: 06 Jan 2008 Karma :

yes, lowering the number of teeth on the front sprocket will increase acceleration.

binge · Emo Kiddy Joined: 03 Jul 2004 Karma :

I had this exact problem with my TZR powered Pit bike.

By changing the sprocket ratio, It doesnt mean your gear changes will keep it in the "powerband". It will still drop the same amount of RPM between gear changes, But you will have more torque to get it back into the power easier with shorter final drive gearing.

Dropping the front to a 15t will probably solve your problem. If you go the whole hog and fit 15/55 (standard fitment?) then your current top speed in 5th will now be your current top speed in 6th (Or there abouts).

Ben

stirlinggaz · World Chat Champion Joined: 22 Jul 2007 Karma :

hi,
oem sprockets are 15/53 or 15/55 depending on whether you beleive the jt sprockets website,honda or haynes, lol
think its more likely to be 15/53.
so i have stuck a 15 tooth front on, & will see how that goes.
thing is, i was quite happy with the acceleration, up to 50mph.
i just had to rev it up to 9000rpm to make changing to 6th worthwhile.
another strange thing, took a 15 tooth 428 sprocket off ma wee gamma & it wouldnt fit on the mtx????
looked almost identical but the hole wasnt quite big enough to go on the shaft.
thing is the jt sprockets site say the same sprocket should fit either.
the code stamped on the gamma sprocket wasnt recognised on the jt site (15E425)
oh well........
cheers,
GAZ

binge · Emo Kiddy Joined: 03 Jul 2004 Karma :

May be that its just a really tight fit. I bought replacement sprockets for my CBR400 last year and I was adamant the front sprocket was wrong.

My mate had a go and got it on first time. It just had to be lined up smack bang in line.

Ben

stirlinggaz · World Chat Champion Joined: 22 Jul 2007 Karma :

hi,
nope the sprocket off the gamma wont fit, minute differences in the ridge shaped bits.
never mind, found another 15t sprocket in the shed.
bit disapointed tbh, pulls away great but lost a bit of top speed.
gets to max revs/speed fairly quickly, oh well guess you cant have everything, lol
but tbh, think i preferred the higher top speed i had with the 16t, just didnt like revving it up so high in 5th to get the benefit from it, lol
i was always a bit wary that it would go bang!!!!
(the rev conter only goes to about 9500/10000 rpm & redline starts at 9000rpm & have to get it to pretty much on the 9k before changing into 6th, to get to 70mph +, which is handy for overtaking.
cheers,
GAZ