kwekey

Hi, I need some advise.

My current tandem bike setup as follows:

Timing Chainring = 36T
8-speed rear sprocket = 11 ~ 32T
Rear chain stay = 15.5 inch
Distance between the 2 timing chainring = 24.5 in
Front chain length = 134 links
Rear chain length = 98 links

I would like to change the timing chainring to either 42T or 44T.
Can advise my how many links should I add to front and rear chain?

Andrew R Stewart 

The rear/drive chain won't change in length when the other rings and chain are changed. Only if the cog set or drive tings on the crankset were to change would that drive chain also need addressing.

I believe about 3" more chain will be needed on the timing chain if you were to go from the 36T to the 42T timing rings. But, as always, the proof is in the trying and not some interweb answer.

I do agree with increasing the timing ring sizes. Andy

kwekey

Actually, my is a tandem bike where there are 2 timing chainring. I want to change these two chainring from 36T to 42T
By doing so, I believe the length of both the front chain and rear chain need to be extended.

You advise to add 3" more. This is for front chain or rear chain?

Sorry, I am unable to post a photo of my bike

cxwrench

Your tandem has a timing chain and a drive chain, right? As Andy clearly stated you'll only need to increase the length of the timing chain. Why on earth would you need to lengthen the drive chain? It's not even on the same side of the bike. It's completely separate from the timing chain and you're not changing anything related to it. Sounds like you should have an experienced mechanic take care of this for you.

kwekey

Hi Cxwrench,

Thanks for your advice.
To be exact, I intend to change both the timing chainring and the drive chainring.
My tandem bike is Ecosmo 20" where both the timing chain and drive chain are on the same side.

So, I believe besides the timing chain, drive chain will also need to be increased.

I hope my understanding of this basic knowledge is correct.

Alvin

HillRider

You are going to have to change both timing chainrings as they have to remain the same size. As noted they are both on the same side of the tandem and have nothing to do with the drive side chain.

kwekey

Hi HillRider,

I understand that both timing chainrings have to change. I also understand the timing chain will also need to be extended.

So, my next question is if I change the timing chainring size, do I also need to change the drive chainring to the same size as the timing chainring?

HillRider

No, the driveside chainrings are completely independent of the timing chainrings and changing the timing chainings will have no effect on the driveside chainrings or chain. You can change it (or them assuming it's a double or triple crank) if you want to modify the overall gearing but that's a completely different project.

cxwrench

You're not paying attention to our posts.

Bill Kapaun

The timing rings must match for the captain & stoker to remain synchronized.
How big/small doesn't matter, as long as they match. (and fit)

You are talking about rings that are 6T or 3" larger circumference.
since approx 1/2 of the ring is only involved in chain engagement, you'll need a "nominal" 1-1/2" PER RING or 3" total as Andy mentioned.
Exact chain length "might" be a link set different, depending where your adjustment is now.

joeruge

There are a number of different chain and sprocket arrangements for tandems. Most tandems you see around have timing chain on the left side and driving chain on the right. Some, particularly less expensive tandems, used single side drive. (Interestingly, more expensive tandems are using single side drive now that wide range cassettes and rear derailleurs designed for handling that wide range are available)

If a newbie is confronted by an arrangement like this, it may not be immediately apparent to them that you can change the 'timing chain' chain rings without changing the 'driving chain' chain ring. Of course, if the bike is a 'cruiser' type tandem the chain rings may be riveted to the crank (as in an Ashtabula crank) and it could be difficult (impossible?) to change chain rings at all. I wondering if this is the cause for some of the confusion between the OP and those of us trying to help - or maybe I'm the only one confused?

CliffordK

Perhaps we should clarify the goals here.

You have 2 timing chain rings, front and rear. They are generally the same size so the Captain and Stoker pedal at the same rate.
Increasing the ring size for both will not change the force with pedaling. It will simply reduce stress and wear on the bike's components.

You could use different rings for the Captain and Stoker, but that likely will make the tandem seem a bit uncomfortable. Some people also choose different crank lengths, with longer cranks for those who want "faster", and shorter cranks for those who want "slower".

On the rear you will have a drive chainring. If you want to change the pedaling force experienced by both riders, then you can change that drive chainring (while leaving the timing rings alone).

Andrew R Stewart 

I made the same assumption that the OP's tandem had the timing rings and chain on the other side of the bike from the drive side. But it now seems that the bike is more like many track tandems (or tandems of old) where all the rings and chains are on the drive side. But there's one more possibility That's having timing rings feed into the same shaft, this shaft travels through the frame and on it has the drive rings. Like this- da Vinci Designs Tandems | Performance Handbuilt Tandem Bicycles | Independent Coasting Drivetrain (davincitandems.com)

So I would like to know what type of system the OP has. Andy

squirtdad

This is a folding bike it seems? won't increasing the size make folding more difficult? What is the expected benefit?

CliffordK

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kwekey

First and foremost, thank you for all the seniors here for giving me such a good advices. Although I have other folding bikes, folding tandem bike is new to me and I have been riding it for just over 200km.So, I was a little confused with all the name of components on a tandem bike.

I summarize again on my bike setup:
Wheel size : 20”
Timing Chainring setup : 36T/36T
8-speed Driving Chainring setup : 36T/11~32T

Purpose of wanting to increase the chainring size:
Over the first 200km ride, we found that we are riding on the highest gear (ie smallest rear sprocket) most of the time and there is limit to speed that we can go even at a higher cadence.
So, I was thinking to upsize the chainrings from 36T to 42T so that we can have better gear ratio. This is what I learnt from a normal folding bike.

My question based on the purpose state above:
1. I would like to know if I should change the timing chainring (both captain and stoker) or drive chainring? or both? << I think Clifford has answered this question, but I would like to know if I should change both the timing chainring and drive chainring to achieve my goal?

2. If I were to change any of this chainring, how many links should I to the chain?
For timing chain, Andy and Bill has answered my question. Thanks you..
For driving chain, I think I have to increase about 1.5 to 2 inch. Is this correct?

jccaclimber

There will be no change to your riding speed at a given cadence by changing your timing rings.

A larger drive sprocket will help, and your rear chain will probably need to get longer accordingly. This will of course reduce your low gear for climbing hills as it looks to be a 1x drivetrain. There will be a practical limit on this given the small wheel size.
When installing new chains I like to fit them to the bike rather than measure them to the old chain. This is because the old chain may be stretched, an incorrect length, etc.

kwekey

Thanks Climber,

You have cleared my doubts.
As the chain is still quite new only have riden for just over 200km. I will consider to add links to get the required length..

A thousand appreciation..

Alvin

jccaclimber

Adding links works, but you should still go through the (simple and fast) method of checking chain length when you do so.

Different chains have different methods of safely putting in links, you may need a second quick link to do that properly depending on the chain type and brand.

Because you will only need a few links you can save the leftover for the next time you need a new chain.