Bicycle Mechanics - Torker Graduate Gear Ratio
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09-13-10, 08:21 PM
I've recently purchased a 2010 Torker Graduate, which is a mighty fine commuter, I think. But the gear ratio is a bit steep. It has a 42t chainring and an 18t rear cog. Replacing the cog, I've read starts to involve changing a good amount of this and that, that just doesn't sound like a good amount of fun. Plus, the Graduate has a SA 5-speed internal, and cogs are not much fun to find, I guess.
I've also read elsewhere that if you change the chainring from its 42t to a 39t, the gearing is far more hill friendly, as it were.
Assuming everything I've said so far is correct - I'm a noob and at this point only parroting what I've read - I'd like to know exactly what kind of chainring I'd need to purchase to install.
Any and all help appreciated.
Thanks in advance,
09-13-10, 10:58 PM
Not fun to find ?, they are about the most common cog made !
3 spline cogs are common to all 3 speeds
(and S/A hubs go back a century ),
every one adopted Sturmeys standard even Shimano.. & Sachs
5 speed use the same cog, it's really 2 ~3 speeds in there 2 planetary gears a narrow and a wide , sharing the same direct gear in the middle..
and only their Sturmey 8 speed uses a different cog, [its got bigger hole in the middle] so 25 is the common size on those ..
13 to 22 tooth in 1/8" thickness , on AW3 Brompton I can get 13,14, 15t in 3/32 thick cogs .
Heres Math to play around with ... http://sheldonbrown.com/gears/internal.html
If you're comfortable removing the rear wheel(as for fixing a flat) replacing the rear sprocket isn't much of an issue. It's held in place by a lockring, which can be pried out with a pair of fairly thin screwdrivers.
You can get up to a 22T from here:http://sheldonbrown.com/harris/sturmey-archer-parts.html.
Depending on how your bike i set up right now, you might need a new(longer) chain to go with that. So, budget for a chain breaker tool as well.
Or you can go with a smaller chainring, as you've found out already. You'll have to figure out your BCD(bolt circle diameter) before getting a replacement.
I believe you should be able to replace that one w/o pulling the crank off, but I'm not entirely certain.
Depending on how your bike is set up right now, you might need to shorten the chain to go with that.
But Torker really should have better ad men: "You read that right – all-weather, low-maintenance DRUM brakes; just like on your automobile."
I know that the US is rarely considered to be the forefront of car development - but drums on cars? Still today?
(OK, so maybe at the rear)
Then they top it off with "The Gradute is a lifestyle bike".
I don't know which is worst, the typo on something that highly exposed, or the concept of a "lifestyle bike". A "ridestyle bike" I'd buy straight off, but this is just plain silly.
And those fork legs looks rather slender to be used with a hub brake wheel. There'll be a bending moment developed where the reaction arm attaches. For disc brakes, it's entirely possible to bend a fork leg right above the caliper mount if the fork isn't strong enough.
The reaction arm attaches higher up though, and drums (as a rule) aren't as powerful as discs, so maybe it's OK.
Or maybe hard braking isn't considered part of the "lifestyle" this bike is designed for....
09-14-10, 06:42 PM
I'd go with a 21 tooth cog, 22 might void the warranty. If you not comfortable doing it yourself, take it back to the shop you bought it from and have them do it, ask to watch so you'll know how to get the wheel off and on when you get a flat. Tim
09-15-10, 01:29 PM
Thanks, mister. That's sound advice. But why would the 22 void the warranty when a 21 would not?
09-15-10, 01:59 PM
May have a no lower than 2:1 ratio specification .. 42:21 = 2:1..
09-15-10, 03:59 PM
aha. thanks. What do you think about swapping the chainring? I think even I could do that myself. I'm not so sure about the rear cog.
09-15-10, 04:07 PM
No clue as to what parts the product manager specifies to be on that bike.
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