An online acquaintance tipped me off that the sprocket from a Suzuki GS300L will bolt up to my GS450T rear wheel, which originally took a 530 chain, but match the 520 chain size of my Bultaco front sprocket. I just ordered a 37-tooth GS300L rear sprocket, and I already have a 12T Bultaco front sprocket. Now that I have my rear tire installed, I was able to determine my gearing:
The 37 tooth rear is the smallest available, and even with that the bike will probably a little short-geared. Even though the redline for street Buls was traditionally 7500 RPM, and Pursangs routinely rev’d to 8 grand and beyond, I’d like to build a pipe heavy on mid-range and keep the crank speed of my (admittedly amateur-built) motor below 6,000–6,500. The old Mercurio 175 and Metralla 200 street bikes could easily pull past 80 MPH, so I am confident that I’d still be able to take it to my self-imposed redline with the taller gearing.
I could go up slightly on the front sprocket, but the largest countershaft sprocket for Bultacos for 520 chain is 13T, one tooth larger than what I currently have. That’s an 8.33% difference, which would only drop the revs @ 60–70 MPH by around 500 RPM. That may be worth it, or it might not.
If I am able to get near 70 MPH on this thing, I’ll be tickled. And probably petrified. That’s certainly as fast as I ever wish to go on this. After all, I know what sort of doofus built the thing.
