Giraffe chain question (tight spot in chain)

General
1

On a giraffe last night, we noticed the the chain was very loose.

we tightened it, so it was fairly snug. Now when we rolled the giraffe along the floor, there would be a tightspot in the chain, like it was pausing momentarily.

I noticed the the top cog isn’t directly above the bottom cog. should it be?

If we loosened the chain, it ‘solved’ the problem, but the chain fell off. :angry:

I think we found a happy medium.

So my question is, if the chain is too tight, should it pause like it did? What’s a good rule of thumb on chain tension?

Has anyone bought a 3 wheeler, just to alleviate all this crap with the chain? Does a 3 wheeler ride just like a giraffe?

2

Giraffe chain question (tight spot in chain)

Look closely at the “tight spot” in the chain… is it always pausing/hanging-up at the same spot? Rotate the chain so that tight spot is out in the open, away from the cogs. Try flexing the chain at that point. Sounds like one of the pins is too tight, maybe where you put the chain back together after breaking it to shorten it. If so, you can loosen it up with you chain-breaker tool.

3

If by “cog” you mean “tooth” then the top cog on the chainring in question will only be above the bottom cog if there are an even number of cogs on the chainring.

Giraffe chainrings are not the most precicely cut or welded components around. They exhibit some eccentricity and, as such, the chain will alternately go through a tight limit and a loose limit for each rotation of either the pedals, the wheel, or for both. I say for both because the eccentricities are not necessarily synchronous since it is not a requirement that the pedal chainring and wheel sprocket have the same number of teeth.

I spoke with Sem Abrahams about this problem. It is pretty much apparent in all giraffes to some extent. He graciously sent me a new crank axle set to try on mine (that was the one that was clearly eccentric) and the new one behaved almost identically. Search the fora using the keyword “eccentric” and you will probably find a couple of threads devoted to the topic.

To determine if one of the chainrings is eccentric, mark both of them, turn the pedals and observe the points at which the chain goes tight. It will be clear if it is for each pedal rotation or wheel rotation. If they have the same number of teeth, some optimization can be made of the rotation of one ring with respect to the other to cancel the effect. I found that repositioning the cranks by 90 degrees minimized the perceived effect because it happened in a different part of the pedal rotation cycle. In any case, set the chain tension at its tightest point in the cycle.

Giraffes are fun, eh?

4

Check for rust in the chain and a bent sprocket, either of which could cause this problem, and both of which are easy to fix. You might be able to fix this problem by filing between the teeth, [judiciously] . Is your giraffe a name brand one or a cheap import? carjug

5

i’m not sure about eccentric, but by ‘on top’ i meant that if you are on the seat, looking down, the bottom cog is about an inch further out than the top goc…making for an angled chainline. should they be directly above each other?

it wasn’t my giraffe, he said it waqs about 10-15 years old

6

The centers of the two chainrings should be in a straight line that projects parallel to the seatpost when the giraffe is lying on the floor. I think it would be difficult to accurately determine the colinearity of the two cogs and the frame looking at them while seated on the camelopard. If these items are not all in line, the frame or seatpost could be bent.

Your freemount on the video looked great. Very smooth. Are you hitting close to 100%?

7

thanks, i’d say i’m getting it about 75% (there weren’t to many more tries after I got it…short attention span, don’t ya know)

Now that I remember, his seat post was slightly bent…perhaps therein lies the trouble

It has a 24" wheel, the other one i tried had a 20"

So, loose chain…if it is tight enough not too fall off, (but it sways) is that fine?

8

By making parallels with my bicycling and motorcycling experience, but never having owned a giraffe:

A tight spot could be a stiff point in the chain. Check, lubricate, and loosen any stiff pins using a chain tool. Cheap and easy.

Cogs (chainrings, sprockets, call 'em what you will) which are not perfectly circular. All you can is adjust as well as possible, or replace the components.

Axles/spindles which are slightly bent. If the top spindle is bent then as it rotates, the top chain ring will move slightly up and down.

Chain rings out of alignment. Especially if the wheel isn’t in straight. Check with a straight edge. Always tighten the two tensioners by the same number of turns.

Chain rings not on the same plane - i.e. parallel but not in line. Could presumably be addressed with spacers.

9

I tighten mine so that at the tightest point of the travel it still doesn’t bind. It can be pretty tight at that point and if it’s too tight you can tell because it suddenly becomes difficult to hand crank through that point. My chain is loose enough at the loosest point that it almost sways. It is nowhere near loose enough at that point to fall off.

10

Re: Giraffe chain question (tight spot in chain)

It should be, but a bend ‘in the seat post’ as you said shouldn’t change this. Your frame would have to be bent in the area between the wheel and bottom bracket (crank barrel). I think some giraffes are built with a little bit of offset in the chain. This is probably okay to a certain point. Deraileur bikes run on offset cogs.

In any case, the loose-tight problem isn’t because your chain is out of line, because that should be constant. As Harper and Sem said, in unicycle parts, there is usually some degree of off-centeredness of the center hole in either the top or bottom cog (or both). It only takes a tiny deviation for this to be noticeable with the tightness of chain we use on giraffes. On a bike you don’t need so much tension, and giraffe unicycles are usually made from cheap bike parts, not the fancy stuff.

If your loose-tight cycle is consistent with rotations of either cog, that’s your problem. It could also be a combination of both cogs being at a certain orientation, if your ratio is not 1:1 and both cogs are off-center.

If your chain is old or has tight links, it might be a good time to replace it. Nobody wants their giraffe chain to break. You can land really badly in a giraffe dismount when there’s no warning.

That’s what you have to do. It’s okay if the chain is a little loose, but it should never come off. You need enough tension that it will stay on even under high torque, such as catching your balance or hard idling. Too tight, though it causes wear & tear, is better than too loose. My Schwinn Giraffe chain also cycles loose to tight, but within acceptable limits.

Oddly some early multi-wheelers had chain drives. The Bill Jenack collection included a three-wheeler that Steve McPeak used to use in shows. There was a chain hidden inside the two-tube frame. This gave him a safer ride, so he didn’t have to worry about tire pressure vs. friction every time he rode it.

3 wheelers do not ride like giraffes of equivalent height. They are much heavier, which makes them more sluggish. They fall a lot harder, which makes them more likely to bend cranks or otherwise get damaged after a while. And you have to constantly monitor tire pressure to assure enough traction. A “safe” amount of traction on a 3 wheeler makes for a drivetrain with a fair amount of friction in it.

But at least you can walk the wheel up there…:smiley: