johnboy999 Posted September 10, 2016 Report Share Posted September 10, 2016 (edited) Hi all , this is my other TY 175 which I want to put on road its mot tax insured but find I am unable to keep up with other traffic on A roads 60 mph so I put a 15 teeth sprocket on front this made a different but not enough , I am not a Speed merchant but don't want to be a hazard to other users so I put a 42 tooth on back and seemed brill but it won't pull in 6 gearbo should I put the original sprocket back on front , has anyone had experience with this that can help me please, also do the carbureter need any adjustment after changing sprockets Thankyou. Edited September 10, 2016 by johnboy999 Quote Link to comment Share on other sites More sharing options...
johnboy999 Posted September 10, 2016 Author Report Share Posted September 10, 2016 Ps it's a 1978 been in uk since new. Quote Link to comment Share on other sites More sharing options...
feetupfun Posted September 10, 2016 Report Share Posted September 10, 2016 They are only 12 HP when the motor is in perfect nick so to achieve 60 MPH you have to get the gearing so that you are a bit below the RPM that gives peak HP at 60 MPH. You made a huge change to the gearing going to 42 rear if you had a 49 previously. Front sprockets are much cheaper than rears so I suggest you get a smaller front. If you had a 49 rear 15 front, you had a ratio of 3.267. When you went to 42 rear the ratio went to 2.8. If you fit a 14 T front and stay with the 42 rear you will have gearing about halfway between 49/15 and 42/15, which will be closer to what you want As far as the carby goes, if you are going to ride at sustained full throttle or near full throttle and high RPM along a road, you had better be sure the jetting on the main jet is right or the motor might seize. You need to say what jetting you have in the carby to get feedback on if it is suitable. The carby settings have nothing to do with the gearing. It is the way the bike is used that can make the jetting critical 1 Quote Link to comment Share on other sites More sharing options...
dpyam Posted September 10, 2016 Report Share Posted September 10, 2016 At 60mph you'll be running the engine at pretty much full power regardless of revs, and no engine is going to last long used in that way. I would recommend a different tool for the job - a 360? I've always fancied a DT400 myself. 1 Quote Link to comment Share on other sites More sharing options...
basil Posted September 10, 2016 Report Share Posted September 10, 2016 left the rear sprocket as standard on mine and put a 16 up front for my local commute to work ive still got the 16 in the garage some where I will put it in the van and iff I see you at E/Shilton its yours FOC Quote Link to comment Share on other sites More sharing options...
johnboy999 Posted September 10, 2016 Author Report Share Posted September 10, 2016 Thanks guys for your Imput ,don't get me wrong most of the time it will be just running locally on a Sunday ride out and not very often , I am not going on motorways but occasionally on A roads, I have no intention of thrashing my bike , just wanted the best info on sprocket size so I am not over revving it. Cheers Quote Link to comment Share on other sites More sharing options...
johnboy999 Posted September 10, 2016 Author Report Share Posted September 10, 2016 left the rear sprocket as standard on mine and put a 16 up front for my local commute to work ive still got the 16 in the garage some where I will put it in the van and iff I see you at E/Shilton its yours FOC Basil cheers mate . Quote Link to comment Share on other sites More sharing options...
motovita Posted September 12, 2016 Report Share Posted September 12, 2016 image.jpeg Hi all , this is my other TY 175 which I want to put on road its mot tax insured but find I am unable to keep up with other traffic on A roads 60 mph so I put a 15 teeth sprocket on front this made a different but not enough , I am not a Speed merchant but don't want to be a hazard to other users so I put a 42 tooth on back and seemed brill but it won't pull in 6 gearbo should I put the original sprocket back on front , has anyone had experience with this that can help me please, also do the carbureter need any adjustment after changing sprockets Thankyou. I just want to know what tires those are, they appear to have fantastic grip. 2 Quote Link to comment Share on other sites More sharing options...
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