I have a six foot Semcycle giraffe that I bought from Jeff Lutkus. He was so cheap he took the air out of the tire before he shipped it to me. It also seems that he removed two of the teeth from the hub sprocket, perhaps to replace those he has knocked out doing various extreme performances.
The tire wore down to the carcass today so I figured that when I replaced it I would adjust the hub bearings and the chain tension. After doing so, I noticed that the chain became slack at one crank position and tight 180 degrees (pi radians, 1/2 revolution) from that. I decided to mark the crank and hub sprockets, remove the chain, and reinstall it after moving the wheel 1/2 revolution so that the eccentricities of the two sprockets would cancel. While marking the sprockets, I noticed that they did not realign after one revolution. I counted sprocket teeth. The crank sprocket has 32 and the hub sprocket has 30. Those are the two teeth Jeff made off with. No wonder I go so fast on it, it’s geared up 16/15.
Unfortunately, with a nonunity gear ratio, there is no way to line up the eccentricities in a way that would minimize the variation in chain tension through each crank revolution. Is this problem of sprocket eccentricity common to Semcycle giraffes? Is it common to all giraffes? Is the sprocket tooth difference in which there is a gear ratio other than 1:1 a common setup? Have I spelled all of my words correctly and formed valid sentences free of grammatical errors that express my thoughts in a coherent manner as if I were somewhat lucid?
Superb job on grammar, punctuation, and wording (as far as I as a non-native speaker can tell). Your last question leaves me puzzled, though: Were you trying to say you only pretended to be lucid? You had me fooled there…
Sorry, I do not know anything about normal (or abnormal, for that matter) gear ratios on those long-necked beasts.
This doesn’t really solve your problem, but I think 2 tooth differentials are a common way to achieve even tire wear. My own giraffe has a 12T differential, though admittedly this is more for speed than tire wear.
I don’t have a Sem giraffe to look at, but I would guess you could get a replacement sprocket (of better quality?) at your local bike shop to fix your eccentricity. Well, it’d fix the giraffe’s eccentricity anyway.
I, too, have a 6 foot savage. I am not yet deft enough to feel some of the problems. It feels like either the crank isn’t perfectly straight, or the tapped hole for the pedal isn’t straight because I feel the pedal camber change as I pedal. As for the chain, I think my sprockets must be pretty close at least for now. They are 28/28 so it looks like I can look foward to a tire with a bald spot if I am lazy.
Also I don’t keep my chain REALLY tight, which may help. Should I Keep it tight, or does it just cause everything to be overstressed. I like the idea of making the bottom sprocket 2 teeth smaller. Do you all remember when the bike industry tried those biopace rings that were elliptical? That is kind of funny in retrospect.
Of course Harper’s evil spam twin might have sabotaged his ride
I have had no issues with the sprockets. I usually notice those things. Maybe your thingies are bent a bit. Sometimes when they get old andd abused, they begin to warp. try looking at is sideways, and see if you can make sense of it. your best bet is to just get a couple new sprokets.
Following David’s suggestion I examined the whole drive train more carefully. Rotating the cranks I discovered that the slackness in the chain always occurs at the same pedal position so the eccentricity is almost entirely in the crank system. The crank sprocket seems perpindicular to the crank bearing housing (is it also called a bottom bracket on a giraffe?) to within about half a millimeter. However, the crank bolt on the sprocket side is not centered in the hole bored in the crank itself. In fact it is off center by as much as a millimeter. The sprocket is welded to this crank. Someday I’ll pull off the crank and see if the axle is bent or if the square taper in the crank is off center. For now, I’m having too much fun riding it.
> If I am not mistaken, I believe that Dave Stone’s old Schwinn
> had a 1:1 ratio.
The Schwinns came with a 1:1 ratio (though I forget the number of teeth; 26?
27?). But toward the end I believe they were moving toward a smaller
sprocket on the bottom, so you would have something like 27:26 gearing. I
don’t know if the smaller sprockets ever went on the production unicycles,
but I got mine from Tom Miller many years ago. My tires have always worn
smoothly since then, though I’m running out of my aging Schwinn “unicycle”
>Scott Kurland wrote:
>> *Spelled sprocket wrong too. Spellchecker would’ve caught it. *
>But I spelled it right all of the other times.
Ha! In that post was only one occurrence of sproket/sprocket. So “all
of the other times” is zero times. But about 5.5 hours later you made
the same spelling mistake in another post. I’m normally not so
nitpicky about spelling but couldn’t stop myself this time.
“To trigger/fool/saturate/overload Echelon, the following has been picked automagically from a database:”
“Refah, Hillal, Halibut”
>The Schwinns came with a 1:1 ratio (though I forget the number of teeth; 26?
26 teeth is the correct number.
>But toward the end I believe they were moving toward a smaller
>sprocket on the bottom, so you would have something like 27:26 gearing. I
>don’t know if the smaller sprockets ever went on the production unicycles,
>but I got mine from Tom Miller many years ago. My tires have always worn
>smoothly since then, though I’m running out of my aging Schwinn “unicycle”
Schwinn had a 25 tooth sprocket as a part you could buy and replace the
lower 26 tooth sprocket with. I don’t think this 25 tooth sprocket was
ever put on a Schwinn giraffe at the assembly plant. A few bike shops
may have replaced the 26 tooth sprocket by the 25 tooth sprocket prior
to the initial sale.
I have removed the crank sprocket which, on the Semcycle at least, has the crank welded to it. I adjusted the bottom bracket (if it is called that on a giraffe) which was too loose and needed attention. I saw nothing out of whack with a visual inspection but I was at home and, without the correct tools, it is difficult to indicate the assembly. Even calipers don’t help because the reference surfaces are square, tapered, and in the center of an otherwise circular geometry.
The bearing sets are now correctly adjusted and that makes for a somewhat smoother ride but I am still plagued with the sprocket eccentricity. One of the guys in the Arizuni club in Phoenix had a 20 year old giraffe which exhibited the same problem in both sprockets. Kaplan says his Savage does not have this problem. Mine does not appear to be worn out. Has anyone else observed this kind of behavior? I wrote to Semcycle to ask about spare parts (the welded crank/sprocket assembly clearly does not have a replaceable sprocket) but have not yet heard back.