Timing chain rings

[Lonnie Seachris]

Has anyone out there expermented with different tooth count rings on the timing chain?
If so what effect does it have .
Was riding last night and this came to mind.
Would smaller rings give you a lower ratio or larger rings a higher ?

[joeprim]

timing chain? As in in a car to drive the camshaft?

Joe

[JimGullen]

Good morning!

Do you mean different tooth counts from stock, but still the same count for both captain and stoker?

If that's what you mean, yes, you would get lower effective gear ratios with smaller chain rings and higer effective gear ratios with larger chain rings.

If you mean different tooth counts between the captain and stoker (this is your intended question, I think)The effective gear ratios would be somewhere between what you have if you calculated the gear ratio for each ring.

The bigger issue, for me, would be that the phase of your pedals would be constantly changing. I'm not sure that this would be a good thing. Your crank might spin 35 times for the same time that your stoker's turned 40....see what I mean?

On the other hand, My stoker is a masher and I'm a spinner, reading your question got me thinking that maybe a smaller chainring for me would allow me to spin, while my stoker mashed....hmmmm.

I'm not an engineer, but I stayed at Holiday Inn last night...so take everything I type with a grain of salt! :D

Best regards!
Jim

[Murrays]

Good morning!

Do you mean different tooth counts from stock, but still the same count for both captain and stoker?

If that's what you mean, yes, you would get lower effective gear ratios with smaller chain rings and higer effective gear ratios with larger chain rings.

Actually, so long as the captain & stoker chainrings are the same size, there would be no difference in gear ratio. A gear ratio change would come from changes on the drive chain sprockets or differences between the two timing chainrings.

Going with smaller timing chainrings would increase stress on the timing chain. I can’t think of any disadvantages of a larger chainring other than weight.

-murray (I am an engineer, but doesn’t make me any smarter than Jim :))

[JimGullen]

[QUOTE=Murrays]A gear ratio change would come from changes on the drive chain sprockets or differences between the two timing chainrings.

[QUOTE]

Of course this is correct and I'm mistaken in my first post...thanks for setting me straight!

No more Holiday Inn...Super8 all the way! :D

Best regards!
Jim

[TandemGeek]

Would smaller rings give you a lower ratio or larger rings a higher ?

No. 24/24 = 1:1, 32/32 = 1:1, 42/42 = 1:1

You could spend a few beers discussing weight savings, the change in velocity of the chain, potential increases or decreases in chain drag due to more/less chain contact with the chain rings at less/higher loading, and then there are the changes in chain and chain ring life span. However, at the end of the day, unless you're riding off-road and looking for ground clearance timing rings, changing the size of your timing rings will have a neglible change in the average team's performance.

[cornucopia72]

Wait... Jim was on to something in the second part of his posting. If the stocker likes to spin more than the capitan, wouldn't a larger chain ring in the front help accomplish that?

[stapfam]

Wait... Jim was on to something in the second part of his posting. If the stocker likes to spin more than the capitan, wouldn't a larger chain ring in the front help accomplish that?

Think of out of phase cranks

[TandemGeek]

Wait... Jim was on to something in the second part of his posting. If the stocker likes to spin more than the capitan, wouldn't a larger chain ring in the front help accomplish that?

Yes, it would, and it would also create a rolling roulette wheel game where the captain would have to hope that both his his stoker's cranks happened to be up at the same time when cornering since the phasing would be constantly variable.

The easiest way to deal with preferences for cadence or pedal stroke characteristics is to change crank arm length, e.g., if one of the riders on a tandem runs 175mm crank arms and the the other runs 165mm, the shorter crank's pedals will rotate in a smaller arc and at a lower velocity. Taken to its logical conclusion, you'll see why kiddie cranks / crank shorteners are essential for children who ride tandems with adults.

[zonatandem]

As long as pilot/stoker cross-over chainrings are the same tooth count, it will not affect spin/mash rate; all cross-over chainrings do is transfer captain's power to the rear through the stoker bottom bracket and drivechain.
Size of crossover chainrings will minimally affect weight: the smaller the chainrings and the shorter the chain, the less in weight.
However, smaller chainrings will wear out a faster rate.
Have used crossover chainrings (TA) as small as 28T in the distant past.
Have even mixed shape of chainrings: eliptical (by Bullseye/ Durham) for pilot and round for stoker . . . both same amount of teeth . . . works fine.

[ricardo kuhn]

In the trails smaller Chainrings are a big plus since they improve the clearance with rocks and branches, but they do wear faster.

long time ago i did a experiment running TWO brand new sets of chains and rings( 4 chainrings & 2 chains) for a really long and difficult trip, i was just looking for a redundancy backup,,well the experiment work wonderfully and i keep it that way for a long time, as long as the parts wears evenlly is not going to be dissimilar tensions, for this the chain and rings need to be made of exactlly the same material so they don't wear at diferent rates

now for the diferent size TIMING rings,,,I find it kind of silly since the cranks will be off face at diferent proportions at ever stroke,, I guess some of them will be positive but many of the strokes will go to waste,,,on the other hand if you were to run this set up on a bike that feature the "Davinci" independent pedalling sistem makes it into a very interesting concept since the rate of cadance will be kind of irrelevant do to the avility of the freewheels to transmit the power at any given RPM of the cranks independent of the partners speed and pretty much in the same way a "half" bike works, exept for the fact of the pedals coming in contact with the ground sound like a great idea and this is going to happend anyway since each person can pedal at any given rate they preffer, want or are capable off.

is incredible how a silly question like this can become such a interesting topic

[cornucopia72]

Yes, it would, and it would also create a rolling roulette wheel game where the captain would have to hope that both his his stoker's cranks happened to be up at the same time when cornering since the phasing would be constantly variable.

Please excuse my ignorance, but how is that different from the Davinci transmition? As far as cornering, after reading Zonatandem's posts we came out with the understanding that even 90o OOP cranks was not an issue while cornering (except for agressive cornering). I am sure I am missing something...

[TandemGeek]

Please excuse my ignorance, but how is that different from the Davinci transmition? As far as cornering, after reading Zonatandem's posts we came out with the understanding that even 90o OOP cranks was not an issue while cornering (except for agressive cornering). I am sure I am missing something...

With the daVinci system, the stoker can stop pedalling independent of the captain (hence the name of the system, i.e., Independent Coasting System or ICS) which allows the stoker to keep their inside pedal in the up position when cornering -- regardless of what the captain is doing -- thereby avoiding contact with the ground.

With fixed out-of-phase, the captain is responsible for knowing the orientation of the stoker's pedals when cornering thus, if the stoker's cranks are trailing as much as 90 degrees out of phase the captain could be sure that if his inside pedal was forward and leveled his stoker's pedal would be in an up position.

[zonatandem]

As Mark indicated, with the daVinci ICS system, captain will not know in what postition the stoker's cranks are.
With our 90 degree OOP, Rudy knows in what postition Kay's feet are: if his feet are 'up and down' her feet will be paralel, etc.
With daVinci ICS system it is the stoker's responsibility to have her feet in the correct positioning for aggressive cornering/speedbumps.
Pedl on TWOgether!
Rudy and Kay/zonatandem