Bicycle Mechanics - what derailleur to buy?
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09-26-09, 12:55 AM
I have four bicycles. The one I ride to work is a modified Trek Pure, but I had to modify it considerably as follows:
long handlebar stem (I like to stretch out)
172.5 cranks (had 165)
44 tooth chain ring (had 36 or 39 or something)
9 speed sprocket (had 7)
shift levers (had twist grip)
power grip pedal straps (sometimes use SPD pedals)
Toploader 3 carrier bag
The Pure has a slightly pedal-forward design and much less than a recumbant. For commuting it's excellent because it's easy to put feet down and start off again. The way I have the bike modified, with the slight pedal-forward design I end up being in the same riding posture as my road bike, except my entire body is rotated a few degrees. I use the same muscles and my knees come just about as close to my chest. Because it's a surprisingly light bike, even with fat tires, fenders, carrier, and bag, I can go almost as fast as I can on my road bike. Sometimes I take it on rides with the group and keep up just fine. The problem is, with pedal-forward, my weight isn't directly over the pedals and I don't have as much power, and I have to spin more which is probably a good thing. The flat handlebars and long stem allow me to stand up easily, which was impossible as it was originally, but I don't on this bike.
Anyway, I need to replace the derailleur. It has a cheap Shimano Tourney and the spring isn't very strong. Shifting is also very sloppy. It's the same derailleur I had with 7 speeds. I only have one half turn tolerance on the adjustment knob to have all the gears work, and on some it makes a little noise. If I go over a bump when shifting the chain may jump off the front chain ring, and sometimes it jumps off if I shift too fast under a load. That's pain if I've pulled out in traffic. Because of the pedal-forward design the chain is longer than normal, but if the spring was better there shouldn't be a problem.
My main road bike is a Giant TCR with Ultegra stuff. My other road bike is an old Seaki which I've made current. Both these bikes shift real well with no chain noise. I would like my commuter bike to be the same way.
I looked at several places online and have no idea what derailleur to buy. The Tourney has a long bottom portion with a large red wheel which I don't like much, anyway. Prices at Amazon are really good, but if I bought there the derailleur would come from a participating seller.
Any help would be appreciated. Thanks
09-26-09, 01:17 AM
You will most certainly need a long cage rear derailleur - MTB. Shimano Deore LX/Deore XT are very good for their cost. Light years ahead of the cheapo tourney.
There is a lot of things that can affect shifting. Worn chain. Misaligned derailleur hanger. Old Cable + housing. Then just the standard rear derailleur setup stuff, b-tension etc. Amazon would not be the first place i'd do shopping online. Performance, nashbar, probikekit... probably a bunch more I can't name off the top of my head.
And just as an aside, that ****ty tourney rear derailleur shouldn't shift as badly as you make it sound. Yes it's cheap, but it should work just fine (e.g not the symptoms you describe, if indeed you know what you're describing and it is accurate).
09-26-09, 01:33 AM
The guy at the bike shop does a good job. I do some stuff myself but let them do most of it. I could do anything I wanted, but they do it so much faster. I want to replace the derailleur myself. Two guys there both said I need another derailleur. Why should a MTB derailleur be used, since I ride it on the road?
09-26-09, 02:00 AM
I found an interesting page at http://blogs.phred.org/blogs/alex_wetmore/archive/2005/07/20/67.aspx . By reading I understand some of the issues. If I have just the one chain ring in front since there is no front derailleur, shouldn't I be able to use a short cage length?
09-26-09, 02:02 AM
A long-cage (Mtn bike) RD (rear-derailleur - please learn to use this abbreviation. Our carpal-tunnel syndrome thanks you!) will help you shift a larger range of gears. This allows you to use all your gears with better smooth shifting, rather than having your shifts become spotty and difficult. Stressing your drive-train and causing you problems. The Deore LX/XT mentioned is a good, mid-cost, choice.
The Shimano Tourney is a low-end RD. You can do better - such as the Deore offerings mentioned. You could also buy one that's twice the price for proving to people that you're rich and sexy... count your silverware when she/he leaves.
09-26-09, 02:34 AM
I've been doing some reading. With no FD (front derailleur I assume) I only have to subtract the rear cassette sizes which gives me 20t chain wrap needed, and there's no reason I can see not to use the shortest cage length possible. A short cage length should apply more spring tension to the chain, which I really need because of the longer chain length. Nashbar seems like a good place to buy, too.
09-26-09, 03:03 AM
As Alex Wetmore says on the aforementioned blog, there are two things at play. You have cog capacity and chain wrap. They are related, but different things.
Cog capacity is determined only by the cassette (or freewheel) and is a measure of how large a cog the derailer can handle. This is determined by strange voodoo like parallelogram geometry and black magic. I don't pretend to understand exactly why, but a good rule of thumb, Shimano road derailers, regardless of the cage length can only safely handle a 28 tooth rear cog. Sometimes 30 can be made to work, but that's pushing it.
Chain wrap is a measure of how much slack the derailer can take up in the chain. It's determined, as you seem to know, by the difference in chainrings, and the difference in the cassette.
With a 1X9, you can easy run a short cage derailer, but if the cassette has a large cog larger than 28, you will need a mountain derailer. They come in short cage (or at least medium cage) if you look hard enough.
Deore level componenets work great, cost almost nothing and are incredibly durable. LX and XT are good if you like a bit of bling (I've been lusting after a shadow derailer myself, I tore up an old Huret Duo-par in some shrubbery).
Is everything clear?
09-26-09, 03:45 AM
I have found, through experimentation and brave applications, that the 27T Shimano rhetoric is usually BS. A medium-cage RD is what was, until recently, called a long-cage. Then as Mountain-Bikes started to come out with GInourmous gearing for climbing El Capitan (or Mt. Everest) - the new LONG-cage derailleurs hit the marketplace. Without knowing what you are running, aside from a 44T chainring, no one can determine if you truly need a long-cage RD. The long-cage of a few years ago is called a medium-cage today. I am guessing that a medium-cage will do fine unless your running a 32 or 34T cog on your cassette in back.
Please tell us what you have back there before you buy a HUGE RD. And the T-count on your chainrings.
09-26-09, 07:22 AM
Unless you have cable adjusters on your downtube or at the shift levers, do not buy a Deore XT rear derailleur. Shimano has eliminated the barrel adjuster from these as they assume the adjuster will be at the shifter.
If your largest cog is 30t or smaller, you could use any Shimano road rear derailleur too. Tiagra and 105 are very reasonably priced and work very well.
As noted, be sure your cables and housing are clean and not frayed as these will have a big effect on shifting too.
09-26-09, 12:26 PM
Thanks for all the help! The cassette is 11-32 and since there's only one ring on the front that comes out to 21t. The only issue is the size of the big cog which is 32, which is a problem for the parallelogram and not the cage length. My road bike has an Ultegra RD. The cog is not nearly as large as 32, but when I observe the motion of it, it would easily facilitate a 32 cog. If I get a Shimano 105, I may have to adjust it so the upper pulley will fit over the 32 cog, and as a result there may be more of a gap between the pully and the 11 cog, but the chain tension will be great. I'm also not concerned with perfection in the highest gears since I rarely get up that far. I think a Shimano 105 SS will work fine, so I'm going to buy one. If it doesn't I'll just have to buy something else. Now to choose where to buy!
My road bike has an Ultegra RD. The cog is not nearly as large as 32, but when I observe the motion of it, it would easily facilitate a 32 cog.
Don't make that assumption. There are several facets to the geometry making it difficult to visualize. You can generally stretch a road RD to 29 or even 30T, but 32T is really pushing it.
09-26-09, 07:23 PM
How about an Ultegra 6500 GS for $40.00?
09-26-09, 09:38 PM
$40 is a good deal! I was comparing the Ultegra 6500 SS and the 105 5600 SS. The current Ultegra is redesigned it says to take up more chain slack allowing people to do more with an SS, though you mentioned GS. Having only one chain ring, I don't need that improvement. The largest cog is still said to be 27, so that hasn't changed. Since the cog limit of both the 6500 and 5600 is 27, and there's no difference in that regard, I want to go with which has the shortest cage length. I'm willing to take the risk that I can get the 5600 to work on a 32 cog and enjoy tighter chain tension. Having no ring change in front simplifies the dynamic somewhat. If I have to I'll modify it, and if I screw it up I'll throw it away.
I might also change the cassette to a 30, then put a 42 on the front instead of a 44. I don't use the last gear which is 11, so having a smaller front ring might make that available. Riding in the city I really like the quick start I get in traffic with the ratios I have, and I can shift and accelerate pretty good from there.
When I get it I'll see what I have to do to make things work. Changing the ring and cassette makes a lot of sense because of one gear I never use and one I only use once in awhile.
09-26-09, 09:51 PM
I have 3 of these 6500's - one on my vintage PUCH racer and another on my hybrid. The 3rd I'm keeping in stock as a backup. They shift flawlessly on the friction-shifters on the PUCH, as well as the 9-spd. index-shifters on the hybrid. I don't give a flip about Shimano's latest models. These things are great! I don't know how Cambria is able to sell them at that price, but that sale has been going on for over a year now.
Maybe they robbed a warehouse. :D
09-27-09, 06:57 AM
How about an Ultegra 6500 GS for $40.00?
Thanks for the lead. I just ordered one as a potential replacement for the 105 GS (5500-series) with over 25,000 miles now on one of my bikes. At that price, i couldn't pass it up.
I assume Cambria bought out either Shimano's or one of the big bike manufacturer's (Trek?) ovestock when the newer 6600 came out.
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