chain and spockets for mtx125

[frazer1981]

Hi,

I am looking at replaceing my chain and spockets for my 92 honda mtx125. I am currently running a 15 front spocket and a 53 rear. The bike is paritally derestricted and with the current set up tops out at around 55-60 mph, but get's there pretty quick. The only problem is that there is no choice when it comes to different size spockets only either a 16 or 15 front and a 53 rear. I was wanting to lower the size of the rear for a bit more top end speed and was thinking as there is no choice in size then could i increase the front size and use a 92 cr125 front spocket? Could i do this?? the only problem i can think of is getting the right size of chain? Have any of the other members with mtx's had the same problem's?? Many thanks inadvance for any suggestions anybody leaves.

[Kickstart]

Hi

Quick look on the JT sprockets web site and they list 2 rear sprocket sizes and 6 front sprocket sizes:-

https://www.jtsprockets.com/52.0.html?&L=0&sel_uid=143&p=

edit - Think Sickpup on here or B&C Express, if not your local dealer, will be able to get JT Sprockets for you.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[frazer1981]

Wow that is a great help, as this has been a problem i never thought i'd get sorted... Thanks for the link bud

What would be the best set up for manily road use?(if the bike tops out @ 55-60 mph with a 15 front and 53 rear) I am looking for a gearing that would give me some more top end speed so i could ride @ 55- 60 with out thrashing the bike? was thinking smaller on the rear and maybe a few teeth bigger on the front ??? Any ideas?

[Kickstart]

Hi

Well if it does 60 on the current gearing and would still pull the same revs then switching to a 45 tooth rear sprocket would make it do 70. That would be the same gearing ratio as the Honda MBX125 road bike.

Not sure there is the space to fit a much larger front sprocket (ie, almost certain you could fit a 16 tooth but a 17 tooth one I am less certsin about).

An possible alternative (found with a LOT of luck) would be to use the front sprocket from an MBX125 (JTF329, available in 12, 13, 14 & 16 tooth sizes) along with a JTR 243 rear (no idea what it is for, but 42 teeth and appears to have the same relevant mounting holes). Using 14:42 gearing with these would be the same ratio at 15:45 but would mean using a stronger 520 chain. Might be a clearance issue (but would doubt it) and the other issue is a small change in chain alignment (the 520 is about 1.5mm narrower and with the way Honda front sprockets mount it would offset the front sprocket slightly).

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[stevo as b4]

I would say it needs lower overall gearing than the MBX125, as it's taller and less aerodynamic. The MTX125's redline is 9000rpm, which is lower than the MBX. I would say to gear it for about 75-80mph at the redline, so that 60mph is around 7500rpm. That would probably be about right for a std full power bike, to get decent acceleration. You don't want to cruise a 125 trail bike much over 65-70mph, as it's not very comfortable sat up in the breeze.

A bit of experimentation might be needed to find the gearing compromise that suits you, the bike, and it's intended use the best. All i know is that on the KMX125 for example, going up 1tooth on the gearbox sprocket gives about 5-6mph more at the redline, so you won't want more than +2t on your front sprocket IMO, or alternatively, if you can get a 3-4tooth smaller rear sprocket for the same result.

[Kickstart]

[frazer1981]

Thanks for all the advice i am going to get myself a few different size spockets for the front from JT and see how things feel, will let you guys know how i get on anyway, thanks.