Question about change of gearing

[nuke]

Hey folks.

A bit different question on gearing, as a lot of threads are speaking about more highway speed, but I’m on the opposite side.
I’m searching a bit more torque from my ‘81 XS400SE - 95% city driving.
Not a lot of kilometers on the bike early - around 2000km.

I’m thinking about 16/38-39 or 17/41-43. The price of the set is almost the same.
I saw a lot of posts stating that 17 on front saves the chain, but is it meaningful for 2k km per year?
Is anyone driving with such a setup? How many segments is the chain or how it must be changed? Any ideas how to calculate it?
What would you recommend? Why?

As always any feedback will be highly appreciated!

 

[MrStubb]

If you go down on the front sprocket & up on the rear you'll loose top end but gain in torque. The issue I see is first gear will be nearly useless unless you're pulling stumps trailers or a side car.

 

[NewHavenMike]

I have the factory setup on my 360. 17/40. I still have a new setup for a 16/38 but I haven't gotten around to installing it. I need taller gears for highway runs but am unsure about it cruising around. The 360/400 have the same internal gearing so at 65mph(104kph) you should be revving around 6200rpm with the 17/40 set up. I used a 101 link chain also.

I had always heard about when you are using chain drives, even in bicycles... That you should always use an odd/even setup. Never use something like a 16/40. It has something to do with one tooth getting more wear than the others instead of a constant overlap you get with an odd/even setup.. I don't not remember all the science behind it, or if its even relevant in chain drives anymore??

This is one reason why I might see if I can find a 16/39 setup, as I also feel that the gearing is slightly too high for normal cruising.

 

[xschris]

Stock gearing for an 81with a stock 120/90-16 rear tire is 16-37. So if you went to a 39 rear sprocket it would rise your rpm's by around 250. I run 17-37 with my 81 so it drops the rpm's by 250. I ride in city and highway without issues.

 

[nuke]

According to Haynes the stock gearing of XS400SE (4G5) is 16/36 (I bought it like this) with rear tyre 120/90 R16 (I bought it with 130/90).
I'll use 130/90 R16 (need the same diameter in front and rear) and after a bit of calculations with https://www.gearingcommander.com/ I'm thinking about 16/38 gearing. It's a great site, by the way.
According to it on 120km/h on 6th gear, stock gearing with stock tyre the RPMs are 6482
- with 130 rear tyre and 16/36 the RPMs will be 6300 - change of -182 RPMs
- with 130 rear tyre and 16/38 the RPMs will be 6650 - change of +168 RPMs, i.e. it's compensating the bigger tyre.
- with 130 rear tyre and 16/39 the RPMs will be 6825 - change of +343 RPMs

 

[nuke]

@NewHavenMike, I've not heard about such requirement for odd/even gears. Any references?
@xschris, I'm 100kg and I need a lot of torque to start moving Are you using standard chain or any kind of O,Z,X, etc. rings? I'm thinking to take the DID 50 530 chain - https://yambits.co.uk/xs400se-did-530-102-link-chain-p-73433.html
Not sure if the amount of links will be enough and I don't know how to calculate it.

 

[NewHavenMike]

I read it a long time back on a cycling website, I tried to find the article on that site but couldnt. I did some more research and I guess the odd/even ratio is something called "hunting tooth ratio". It does in fact apply to motorcycles and normal gear drives. I guess its not so much about the odd/even thing, but more about ratio numbers being not divisible into each other? I honestly dont have the energy to read it in depth right now, just got home from work...

 

[xschris]

I run a standard chain that is nickel plated. I would buy a longer than needed chain (120) link and cut it to fit what ever you come up with. With a 17-37 sprocket and 120/90-16 tire my bikes run around 4800-5k at 60mph. They pull plenty hard with that setup. But I weigh around 175 lbs and maybe closer to 200 with all my gear/clothes.

 

[nuke]

@NewHavenMike, thanks for the info. I did a bit of reading, still not an expert on the subject, but it appears that this is more relevant when speaking for directly working gears. In the case of a chain it's not such an issue. What I've been able to find for chains is that the chain must not be divided by any of the gears with integer result, though I've not read it in any scientific document.

I've been playing with gearingcommander and after all that reading I've found that there is a table at the bottom which is exactly for the same tooth - same link frequency. Apparently if I have 16/38 with 105 links on the chain, the setup will be great. I'll continue reading on the topic when I've the time to see why in most of the cases the chains are with even links.
Nevertheless, anything the same or better than the factory settings is good for me!

@xschris I've found 114 links chain, which I'll buy and on 16/38 setup it should be sufficient, I believe. Why do you find the "correct" length? Just position the rear tyre closest possible to the front and then decide how many links, including the free play of the chain?

 

[nuke]

And to be in help of others that are interested in the topic, here are few links that I've found useful:
- http://www.gearingcommander.com/ - quite useful for calculating different front/rear sprockets and chain length - RPM change, speed change, same tooth - same link calculator (at the bottom). The most useful resource IMHO when speaking about gearing and chains.
- http://www.mobiusinstitute.com/site...aft frequencies and gearmesh frequencies.</p> - gearbox calculator - gearmesh frequencies; Gear Assembly Phase Frequencies; Hunting Tooth Frequency
- http://www.vibrationschool.com/mans/SpecInter/SpecInter50.htm - explanation of the hunting tooth frequency

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