bobthib

Tapping in to the cosmic intelligence captured in the BF, what is the pros and cons of lg vs sm timing chaing rings? I read some where that 60T (I think) was a a good size. If so, why? What's the - of a smaller size?

Thanks in advance.

andr0id

39 or 42 are pretty common... 60?? Never seen anything so big.

bobthib

Come to think of it, it was 48 not 60. 60 was a drive chain big ring. Sorry. None the less, the ? stands.
What's the difference in performance?

conspiratemus

Smaller rings weigh less and require shorter (therefore lighter) total run of chain.
Larger rings wear more slowly and are slightly more efficient because the chain links don't have to bend as fast or as far as they come on and off the rings. (This was actually tested in a lab and reported somewhere on Bikeforums.)

Difference is probably academic, since it is possible that you will not be able to tension the chain with the available "throw" in the eccentric if you use rings of different size from what the builder provided as part of his design.

Chris_W

Mountain bike tandems often use smaller timing rings so that they have more clearance for trail obstacles. I saw one last weekend that must have had timing rings that were no larger than 32 teeth each, maybe smaller, it certainly looked a bit weird. It also had the 14-speed Rohloff hub gear, so only had one smallish-sized chainring on the drive side.

On the road, as has been stated before, larger rings are more efficient but also weigh more. 42-tooth rings seem to be a good compromise between efficiency and weight, but maybe a time-trial tandem could justify using larger ones.

Phantoj

Big rings would have less chain tension - less bending of the frame under pedaling forces, less chance of derailing the timing chain.

bobthib

Is this proof of your contention? These timing rings look a bit small.

uspspro

I actually tightened it a little bit, I guess I need to press a bit harder when doing the deflection test.

FWIW, the timing rings are 34t.

I don't think the frame flexes enough to cause that much slack. I think the 27+ % grade and 300lb of riders moving up a hill maximized the amount of slack in the chain much more that you get by pressing on it with your finger, unless you press hard.

Check out the garmin plot for that hill:

bobthib

Yup, that's a hill! Don't got nuttin like dat here in So. Fla, cept maybe an overpass. Naw, day ain't dat steep.

Read somewhere that OOP will reduce chain strain, but I see you guys are "up and at 'em." That's a bit of a ballet with POOP (Pedals OOP)

zonatandem

Currently running 38T on our Zona; but have run as small as 28T (TA) back in the '70s on our Assenmacher.
Smaller rings/shorter chain = lighter.
Bigger rings last longer than smaller.
Your choiice!

jnbrown

How did the Calfee handle that steep grade? Better than your previous frame?
That's pretty impressive, I have ridden up similar hills on my single but would or could not on a tandem.

uspspro

The Calfee felt better, and it feels even better every time we ride it (probably got used to the feel, and am more in-tune with the machine).

This is one that we did last weekend... not psycho steep like Marin St., but much longer and unrelenting.



The Calfee just seemed to climb much more effortlessly on Quimby, which is one of the benchmark hard climbs around here.

It was part of this lovely ride (not our data.. our friend's)
https://connect.garmin.com/activity/12666851

jnbrown

Thanks for the feedback. I have all but decided to order a Calfee, just have to convince myself to spend the money.

TandemGeek

As our good friend Rudy / zonatandem might offer....

We've put 50k miles on 34t timing rings on five different tandems over the past decade two-gether to no ill effect, on road and off-road and I'll be darned if there's any detectable loss of efficiency vs. the 42t ones that came on our '95/'96 Santana Arriva.

Why 34t? Because that's the way daVinci sells 'em. Actually, the only real decision we have to make when it comes to buying timing rings is, "what color would you like: ti grey or black anodized?

Bottom Line: So long as both timing rings have the same tooth count, timing ring size is only an issue if you have a chain stay clearance issue or play around off-road on technical single track where tall timing rings are apt to lead to more broken sync chains than shorter rings...

dvs cycles

I've been told by some of my fellow Santana owning friends that they have to be even number tooth rings suchas 38. 40, 42 etc......
Is this truth or fiction?

TandemGeek

Fiction...

Rather than me blathering, here's a link to what Sheldon wrote on the subject:
https://sheldonbrown.com/synchain.html#chainring

Note that most folks who have even numbered timing rings DON'T mark their sync chains and chainrings so that they put the chains back on after removing them (for various reasons) in the same orientation that yields the possible longer life mentioned in Sheldon's article. About the only thing someone will notice if they do this after there has been significant wear on the sync chain and timing rings will be a subtle grinding sound from the slightly mismatched pitch of the chain links and timing ring that will go away after a short time as the parts re-seat.

Homeyba

You only live once! Pull the trigger, you won't regret it!

dvs cycles

This is more the issue my friends have mentioned:
"Since the eccentric has only a limited range of adjustability, in some cases, it may not be possible to use even-size synch chains: if you replace a pair of 39 tooth rings with a pair of 40s, you need to adjust the eccentric 1/4" closer to the fixed bottom bracket, or you can add a link to the synch chain and move the eccentric 3/4" farther. Some eccentrics may not permit this amount of adjustment."
And I don't think you BLATHER.
You know more on the subject of Tandems than I ever want to and I appreciate your sharing with us.

TandemGeek

I believe most tandem eccentrics will 'cover the spread'. In a worst case scenario, you could find that as offered by your friends that your bottom bracket may end up being rotated well forward or well back in the eccentric shell. It's actually the length of the boom tube that really determines how it will all play out.

However, if you found yourself with the bottom bracket axle sitting too far forward or backward to be practical you can install a 1/2 link in the sync chain that will move the bottom bracket axle into a more central position where you'll then need to decide if you want it sitting high or low.

The point is, there are always lots of alternatives and options.

FWIW, our Calfee would probably be better-off with a set of odd-numbered timing rings because I spec'd the boom tube at 30" on the dot without running the numbers. Therefore, running even numbered timing rings causes my bottom bracket axle to end up biased well forward or well backward... a less than ideal situation for me that I addressed with a a 1/2 link.

dvs cycles

Mine is in a low centered position with 40t rings so I'm guessing a 39 would not be desireable but a 38 would be a better choice if I want to go smaller.

lhbernhardt

Apart from the obvious physical characteristics of larger vs smaller timing rings, there is also the less obvious:

In track racing, there's the supposed old wives' tale that sprinters should use a small chainring with small cog and pursuiters should use a large ring with large cog. If you think about it, this is because for a given pedal rpm, you don't need to accelerate the chain as fast if you use a smaller chainring.

Example: If you spin a 48-tooth ring at 120 rpms (2 revolutions per second), you are moving 96 links of chain (48x2) each second. To spin the same gear at the same crank rpm with a larger 52-tooth ring, the chain must move at 104 links per second. This is a 6% difference in chain speed, and the chain does have some weight. Thus, it should be a little easier to accelerate a bike with smaller chainrings.

Transfer this to the timing rings on the tandem, and you can see that 34-tooth rings should let you accelerate a tiny bit more easily than 42-tooth rings because the chain only needs to move about 80% as fast. However, once you get a tandem up to speed with larger timing rings, you should get a bit more inertia from a faster-moving chain to keep the bike rolling.

My tandem uses 34-tooth timing rings. PS: You might even consider using a 1/8" track chain as a timing chain. You can run a track chain a bit looser (less possible damage to bearings at "tight spots" and looser chains just run more easily) because track chains are not designed for easy sideways deflection, as are 3/32 road chains which must be able to deflect easily in order to make for easier shifts.

Luis

jnbrown

Ordered it today, delivery in December.
Now I have go parts shopping.

Homeyba

Well, it's about time! It's an awesome bike, you're going to love it!

jnbrown

Yeah, I've been debating it for so long and waiting until we had enough money.
Now another 2 or 3 months until we can actually feel how good it is.
Another motivator was Calfee raised their prices but gave me the old price.
I was also wanting to get a Time single bike but that will have to wait now.