Johnny Appleseed Posted November 3, 2011 Share Posted November 3, 2011 On the Newbies' forum, I have been told that if I increase the size of the front sprocket on a 125i YBR it is unlikely to have any effect as the bike probably won't reach a high enough rpm - many thanks for that information. Currently, the bike reaches about 8000rpm, which (according to "Gearing Commander") means a top speed of about 60mph. In reality although I have made it to the mid to high sixties (GPS), in general the bike runs at about 55 to 60mph. My problem is that at those speeds you become prey for vans or small lorries. I find that on dual carriageways, I find myself catching up with them, but as I attempt to overtake I am struggling to do so. I know there will be some back draft cause by them, but I am positive there are also some idiots who speed up on purpose. So my question: If I drop the front cog (and it may be significant that the only two sprockets available are a 14 and 13 teeth) to a 13T, could the bike reach a higher rpm, and thus a higher top speed even taking into account a change of the gear ratio? many thanks Johnny Link to comment Share on other sites More sharing options...
neversaydie Posted November 3, 2011 Share Posted November 3, 2011 Although I dont doubt others will disagree, my experience on the Dragstar 125 did prove just that, went down a tooth on the front and just reached 75mph flat out. Standard sprocket (which I think is 15) 65 to 70, one tooth up no more than 65mph. Engine revs at those speeds will increase But its not about flat out speed, going down a tooth will also make acceleration a little more lively. As I'm sure Taskmaster will say, planning/anticipation/decision making on smaller capacity bikes is an essential part of safe riding Link to comment Share on other sites More sharing options...
Johnny Appleseed Posted November 4, 2011 Author Share Posted November 4, 2011 Thanks for the reply - I did think there was a reason why I could find smaller front sprockets, but not larger ones. There certainly looked room to increase sprocket size. Johnny Link to comment Share on other sites More sharing options...
Georgiev Posted November 7, 2011 Share Posted November 7, 2011 Hi, I changed the front sprocket on my YBR125 to 13 T last year. The positive effect was significant increase in the torque in 5-th gear - in my case (88 kg body mass, my self only ) this means successful slow acceleration even when the road goes a bit up hill. Negative effect - no more than 65 mph before reaching the red zone. It is still not safe to overtake vehicles running with more than 45-50 mph. Just not quick enough acceleration to feel safe. Georgi Link to comment Share on other sites More sharing options...
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