Chain Length Calculators:

http://www.rebelgears.com/chainlengthcalculator.html

https://www.rbracing-rsr.com/chainlength.html

http://carbonfibervalvecovers.com/tools/belt_rpm_calc.html

http://www.botlanta.org/converters/dale-calc/sprocket.html

Just converted to chain.Went really tall. 40/17. I used JT sprockets, RYCA stainless spacer (outboard of countershaft sprocket) original locking washer etc.
Over the last half century I've had seven bikes, 4 chains, 2 shafts, and 1 belt. Mt last chain, a 650cc Yamaha Twin XS-650 was a perfect candidate for gearing up. It turned 4000 rpm @ 60 mph and was truly tiresome trying to cover much ground. In stages (as chain and sprockets wore out) I'd gear up even higher than before, finally ending at 19/30 (after starting at 17/34). This brought my rpm at 60 mph from 4000 to only 2700. @ 60mph I had the same rpm in 3rd gear I use to have in 5th! I had given myself 2 overdrives. It was great for fuel economy and comfort. Once, with a straight face, I told the owner of a 1050cc, 6 cylinder Honda CBX that I did it so I won't hit red line in 5th until I was going 130mph. As his jaw dropped and his eyes widened I said, "JUST KIDDING!" Anyway, it is with this experience as a backdrop, I decided to go really tall at first. I figured that a 530 chain will last just about forever coping with about 31hp and 33 lb/ft of torque, and if I didn't get it right the first time, I might not be able to wear out the set in this lifetime. Secondly, My XS650 was in a much higher state of tune than the S-40, producing 81hp/liter where the S-40 supplies just 48hp/liter. As is the case with low stressed engines, the torque peak occurs at a greatly reduced rpm. In this case 3400rpm. This made the bike ideally suited to such tampering.(I hoped) Well I got lucky, it's a very civilized machine on the open road and my wife even likes it better around town (for some reason). I get 66 mpg @ 55mph and 56mpg  at 65 to 72 mph. At high speeds it's a tolerable tingle instead of a belligerent buzz at the grips. In town I can expect about the same milage as I get at high speeds.
From a standing start, keeping rpm moderate, I ride the clutch to about !0 mph, after that everything's the same. Doing this I don't make an obstacle of myself in traffic or feel that I'm torturing the clutch unmercifully. In a residential neighborhood when school is letting out or there are witnesses about (when you're behaving yourself), the tightest turns or U-turns are best executed in 1st gear least you sound like the little engine that (almost) could.

I do have a few questions for members.
First, I've located a few sources indicating the S-40 turns 3940rpm at 60mph. Here I read 3733rpm. Has the final gearing changed?
Second, has anyone used the Trywin D1 GPS computer on their S-40? I understand it works with PC's and "supports" whatever. All I need is something to clamp on my handlebar and give me my speed and distance. It's simple and cheap. Any data on this or any other low-buck GPS handlebar computer or even a normal speedometer would be greatly appreciated. The speedo is even more useless now than it was before since I wear a full coverage helmet and don't feel safe doing a bobble-head routine in Phoenix traffic.I hope to hear reaction or feedback soon. (if I don't get my as killed 'cause I left my turn signal on)

roadkill

I just realied what ratio you are using. 2.35:1!!!

Most guys have a difficult time with 43/17 (2.53:1). Have you modded the engine to compensate for the extremely high gearing? I assume your clutch will probably wear out a little faster because you are slipping it more than usual.

That's waaay too much work!  

Using my way won't be "dead on" accurate (because of tire mfr's tolerances) but you'll only be off by 2 or 3 RPM. Close enough for me.

I have made the conversion and it only took 2 hours to change the whole thing. The spacer was exact what the chain needed and after cutting the chain I was very happy looking at the old parts laying at the floor. Many thanks for the info about how thin the chain needed to be so I bought a 500 chain and everything could be mounted back as it has been.  

You may find that the 14T CS will make contact with the swingarm under normal riding conditions. I know your swingarm is modified, but my unmodified swingarm and 18/52 sprockets will make chain contact if the shock is extended beyond 13-1/4".

I did the conversion today, sprockets 16-44 and the chain will occasionally hit the swingarm because I have 320mm rear shocks. Glued a plastic slider in there, hope it works.

batman wrote on 04/11/18 at 13:48:36:


So I've heard. Not too much odd sizes available when sprocket size increases, going to replace those 16 and 44 with 18 and 52. Hope the chain will clear the swingarm then.

And for the spacers: Two M24 flat washers is just the right thickness. 1 inch should work, too.