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  1. #1
    '01 GT ZR 5.0
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    Minimum FD tooth differential

    Hello from a newbie (after years off a bicycle). I've recently obtained a GT ZR 5.0 with Ultegra 6600 derailleurs (I can see the name on the rear, but not specifically on the front one, but I'll assume they came as a pair - bad assumption?). I'm looking to use the bike on some longer fund-raising rides in the range of 50 to 100 miles, but have found the current setup to be less than optimal for me since I'm not strong enough to really use the last two or three high gears. I did a 42 miler a couple of weeks ago on a heavier bike and took 3 1/2 hours with a friend, but I had lots of energy left at the end of the ride. Thus, I believe I can handle 15 mph for at least 4 hours on the ZR.

    Here's my questions:

    I'm looking at changing the chainring from 34T/50T to 34T/40T, to obtain a more usable range (it was originally set up by a very competitive tri-athlete) for the relative flats (minor hills) and some half-step gearing, but I have concerns that the FD can't handle that small a variance. Will the Ultegra 6600 FD still work? Are there any other concerns I need to be aware of before buying the 40T?

    Cameron

  2. #2
    slow as I ever was Ex Pres's Avatar
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    Can you move the FD down far enough to the 1-2mm recommended spacing above the large ring?

    The curvature won't be right, either, so it won't shift quite as well.

  3. #3
    Senior Member mzeffex's Avatar
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    Not sure, but no they are not necessarily a set. Often the rear derailleur is better than the rest of the gruppo.
    Quote Originally Posted by rjones28 View Post
    Are they talking about spectators feeding the cyclists? You know, like don't feed the bears?

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    Senior Member Retro Grouch's Avatar
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    Quote Originally Posted by CameronSmi View Post
    I'm looking at changing the chainring from 34T/50T to 34T/40T, to obtain a more usable range (it was originally set up by a very competitive tri-athlete) for the relative flats (minor hills) and some half-step gearing, but I have concerns that the FD can't handle that small a variance. Will the Ultegra 6600 FD still work? Are there any other concerns I need to be aware of before buying the 40T?
    Before doing anything I'd recommend taking the time to calculate every single gear ratio in gear inches for both chainring sets. Then, after compareing them, ask yourself what you are gaining.

    I'm pretty sure you will be able to make the Ultegra front derailleur work, but the shifting performance is going to be degraded because the derailleur will have to be set too high on the seatpost. Speaking of which, clamp-on or braze-on? If it's braze-on, forget the whole thing because it's not going to work.

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    Bad idea. If your terrain is that flat, change the cassette to a junior gearing model that starts with a 14T.

    With time, your strength will improve and you should find those larger gears useable. All you need is a tail wind or a little down hill slope.

  6. #6
    '01 GT ZR 5.0
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    At a 105 rpm cadence, I figure I won't be pushing more than about 90 gear inches (at 28 mph) since at that speed, I'll be traveling downhill and will be resting. I've calculated the gear inch ratios with 34T/40T, using a 9-speed rear (12T to 27T) and the half-step gears are basically right where I want them, with the 40T - 12T combination topping out at 90 gear inches.

    The front derailleur is attached by a Shimano SM-AD11 band-type clamp, so it should be moveable. On the comment regarding front shift degradation, I'd be sad if I lost the almost silent riding/shifting I'm currently enjoying. How difficult is it to change out the larger ring? Should I be able to do it without removing the crank?

    As far as the terrain, while the majority is flat, I'm at the bottom two gears on some of the steeper ones around home and I feel pretty good that as I get stronger, the steeper hills will get easier.

    Thanks for all your viewpoints. It really helps me to know if I'm on the right track. Knowledge is power and I'm trying to build my understanding as well as my leg strength.

    Cameron

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    slow as I ever was Ex Pres's Avatar
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    You can usually change out the rings without removing the crankset.
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    I'm surprised that no one has mentioned the difficulty in finding a ramped and pinned 40 tooth outer chainring for a 110mm spider (or any spider for that matter). Unless you go custom or possibly TA rings, the smallest you'll find is a 46.

  9. #9
    slow as I ever was Ex Pres's Avatar
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    Would middle ring work/shift OK? It won't have the chain-drop pin.
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  10. #10
    Senior Member Retro Grouch's Avatar
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    Quote Originally Posted by CameronSmi View Post
    At a 105 rpm cadence, I figure I won't be pushing more than about 90 gear inches (at 28 mph) since at that speed, I'll be traveling downhill and will be resting. I've calculated the gear inch ratios with 34T/40T, using a 9-speed rear (12T to 27T) and the half-step gears are basically right where I want them, with the 40T - 12T combination topping out at 90 gear inches.

    The front derailleur is attached by a Shimano SM-AD11 band-type clamp, so it should be moveable. On the comment regarding front shift degradation, I'd be sad if I lost the almost silent riding/shifting I'm currently enjoying. How difficult is it to change out the larger ring? Should I be able to do it without removing the crank?
    Back in the days of 5-speed freewheels, half step gearing made sense. With 9 cogs on the back, it's usually much easier to find a cassette that has the close spacing that you want and only use the front to give you normal and hill climb ranges of gears.

    I haven't tried it so I can't say for sure but I'm thinking that the issue you are likely to encounter is, with the derailleur at the optimum height, the inside of the derailleur cage is going to contact the 34 tooth chainring. I suspect that you'll be able to make it work, but it's going to look goofy and you'll be only be using the back portion of the derailleur cage. I'm thinking that's going to result in slower and nosier shifts but, like I say, I've never tried it so I can't say for sure. That's the downside.

    What's the upside? Your low gear is going to stay the same so there's no gain there. You will be eliminating some high gears that you never use but that's a modest benefit at best. You may gain some more slosely spaced ratios provided you actually do shift it like a half step but, honestly, that's too much trouble for me even with a perfectly shifting front derailleur. I question if there is an upside.

    On the other hand, plain flat chainrings don't cost very much. Replacing the outer chainring on a compact double can be easily done without removing the crank. If you keep your old chainring you can always change it back if you decide that you don't like it. The effort and money that you spent won't have been wasted because you will have learned something through the process.

    Bottom line, I wouldn't do it but I think that you should try it.

    Be sure to let us know how it goes. I, for one, am genuinely interested.

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    Quote Originally Posted by Bob Barker View Post
    Would middle ring work/shift OK? It won't have the chain-drop pin.
    I'm sure you could get any chainring to work and shift reasonably well but when the OP says something like this...

    Quote Originally Posted by CameronSmi
    On the comment regarding front shift degradation, I'd be sad if I lost the almost silent riding/shifting I'm currently enjoying.
    ...a flat chainring is going to be a big disappointment. He can get a ramped and pinned 42 or 39 tooth chainring if he was willing to compromise a bit. They won't have chain-drop pin as you noted and they'll certainly look goofy as an outer chainring.

    [pause for internet browsing]

    Actually, I'm sitting here trying to find ramped and pinned 39 and 42 tooth chainrings in 110 BCD and not finding anything. A few flat 40 tooth rings in 110 BCD out there though.

  12. #12
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    Quote Originally Posted by CameronSmi View Post
    Hello from a newbie (after years off a bicycle). I've recently obtained a GT ZR 5.0 with Ultegra 6600 derailleurs (I can see the name on the rear, but not specifically on the front one, but I'll assume they came as a pair - bad assumption?). I'm looking to use the bike on some longer fund-raising rides in the range of 50 to 100 miles, but have found the current setup to be less than optimal for me since I'm not strong enough to really use the last two or three high gears. I did a 42 miler a couple of weeks ago on a heavier bike and took 3 1/2 hours with a friend, but I had lots of energy left at the end of the ride. Thus, I believe I can handle 15 mph for at least 4 hours on the ZR.

    Here's my questions:

    I'm looking at changing the chainring from 34T/50T to 34T/40T, to obtain a more usable range (it was originally set up by a very competitive tri-athlete) for the relative flats (minor hills) and some half-step gearing, but I have concerns that the FD can't handle that small a variance. Will the Ultegra 6600 FD still work? Are there any other concerns I need to be aware of before buying the 40T?

    Cameron
    For a double half-step, yes the 6600 will work. For a triple, it would not, as the 10 speed stuff no longer has the travel the previous version had.

    What you're choosing is not half-step gearing though. I looked at the gear chart of a 34/40 12-27 9sp. Now, I'm a bit of a gear freak myself, and I do use half-step gearing.. .. . . but this combo has me scratching my head. The gears are still crossed over. An even semi- half step cannot be had with that cassette, as the cogs are spaced closely already. It's not needed.

    The only 40t rings you can get are Sugino "regular" ones. They can be used inner or outer. No shift ramps or anything like that. I have no idea about indexed front shifting. http://www.lickbike.com/productpage.aspx?PART_NUM_SUB='0096-34'

    A more functional half-step would be say a 39/42 with a 11-12-14-16-18-21-24-28-32 . That's not what you're thinking , but it's an example of half-steps in the mega cluster era. Good luck !

  13. #13
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    Quote Originally Posted by Garthr View Post
    The only 40t rings you can get are Sugino "regular" ones. They can be used inner or outer. No shift ramps or anything like that. I have no idea about indexed front shifting. http://www.lickbike.com/productpage.aspx?PART_NUM_SUB='0096-34'
    Vuleta makes a 40T flat chainring too (in black):

    http://www.universalcycles.com/shopp...9&category=674

    I've used the Sugino standard rings with Shimano Sora brifters. Indexed shifting will work with flat chainrings but upshifts are a bit slower and require you to hold the shifter in the shifted position while the shift completes.

  14. #14
    cycles per second Gonzo Bob's Avatar
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    Quote Originally Posted by Retro Grouch View Post
    I haven't tried it so I can't say for sure but I'm thinking that the issue you are likely to encounter is, with the derailleur at the optimum height, the inside of the derailleur cage is going to contact the 34 tooth chainring. I suspect that you'll be able to make it work, but it's going to look goofy and you'll be only be using the back portion of the derailleur cage. I'm thinking that's going to result in slower and nosier shifts but, like I say, I've never tried it so I can't say for sure. That's the downside..
    Actually, the large min tooth difference specs are for some triple FDs. A road double FD should be able to handle a tooth difference as low as 4. And it will be the front of the cage that shifts the chain. I know this because I set up one of my bikes with 29x44 and use a normal road double FD to shift it. It works fine but it is also not indexed shifting. And yes, shifting will be slower (esp going back up to the "big" ring).

    Quote Originally Posted by Retro Grouch View Post
    Bottom line, I wouldn't do it but I think that you should try it.
    +1

  15. #15
    '01 GT ZR 5.0
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    Wow, that's a whole lot of information. Much of it is over my head at the moment as I don't understand indexed shifting, flat chainrings, chain drop pins and BCD. But I hope that will come with time.

    As a newbie, I started my education by trying to understand gearing and the purpose of having what appears to be redundancy in my current gear ratios. That's when I came upon this website - http://www.geocities.com/SiliconVall...ars/Gears.html Using the charts, I put in the lines on the second chart at 34 and 50, as well as the diagonals for 12, 13, 14, 15, 17, 19, 21, 24 and 27. Gear inches on the 34/13 is basically identical to the 50/17 and 34/14 = 50/19. By dropping to a 40, that places more half-steps between the midrange of the 34, while also reducing the number of shifts necessary to obtain the half-step from 4 or 5 (ie going from 50/24 to 34/14) down to a more manageable 2 or 3. Sorry for my ignorance. Again, I'm new at this and learning as I go.

    I guess what I'm trying to get at is if half-step gearing isn't necessary with 9 in the rear, why do they have overlap between the gears at all. Make the variance between the front rings bigger to the point where there's no redundant gear ratios. Yes, that'll make transition from low to high (or vice versa) difficult, but once you get there, the steps could be smaller. What am I missing?

    Thanks again.

  16. #16
    Senior Member CACycling's Avatar
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    Quote Originally Posted by CameronSmi View Post
    ...why do they have overlap between the gears at all. Make the variance between the front rings bigger to the point where there's no redundant gear ratios. Yes, that'll make transition from low to high (or vice versa) difficult, but once you get there, the steps could be smaller. What am I missing?
    You are missing 2 things. The first is cross-chaining. You typically don't want to use your smallest cog or 2 with your small chainring or you largest cog or 2 with your big ring because of the angle it places the chain. Second is that, when you find yourself in a situation where you are shifting up or down one gear over and over (because of wind conditions, road condition, rolling hills, etc.), you don't want to have to make a ton of shifts every time. It is more efficient to be able to stay on one chainring and shift the rear up and down as needed in those situations.

  17. #17
    cycles per second Gonzo Bob's Avatar
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    What you're missing is that with 9-speed, single cog gear changes are usually small enough that there's no need to double shift to get a suitable "close-by" gear.

    I have two road bikes with very similar gear ranges - a 6-speed with 53x42 and 13-26 and a 9-speed with 53x42 and 12-27. The issue with the 6-speed is that the cog jumps are big (13,14,16,19,22,26) and I often find myself double shifting when I need a gear that is roughly 10% smaller or larger. With the 9-speed, I just shift one cog in the back to get a gear roughtly 10% smaller or larger and usually double shift only when encountering a terrain change. The irony is that the 9-speed bike is actually easier to double shift (the 6-speeder has down-tube shifters while the 9-speed has bar-ends).

    As far as why they don't make bikes with "no" gear overlap between rings? Even with the tightest 9-speed cassette of 12-21, you'd need the large chain ring to be about 55% larger than the small chain ring to have no overlap. So if you run a large ring of 53, your small ring would need to be 34. That's way outside the spec of what current front derailers will handle well (although it could probably be made to work). And if you ran a wider range casette to get lower gears, you'd need an ever larger difference between rings.

  18. #18
    Senior Member Retro Grouch's Avatar
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    Quote Originally Posted by CameronSmi View Post
    I guess what I'm trying to get at is if half-step gearing isn't necessary with 9 in the rear, why do they have overlap between the gears at all. Make the variance between the front rings bigger to the point where there's no redundant gear ratios. Yes, that'll make transition from low to high (or vice versa) difficult, but once you get there, the steps could be smaller. What am I missing?
    A certain amount of overlap is good.

    I once built a bike with a 28/38/48 crankset and a 14/18 5-speed freewheel. NO overlap at all.

    It was a PITA to ride. Everything was fine as long as I could stay on one chainring. The steps between gears were close and shifts, with only a 1 tooth difference, were both fast and crisp. When I ran out of gears, however, that ment I had not only had to make a front shift but I also had to shift all the way across the block on the back. That was neither fast nor crisp.

    Worse, I didn't have much choice when to make the front shift. Going up a hill for example, if I could get to the top in the middle ring, fine. If I couldn't quite make it, however, you can imagine what happened. I lost every bit of momentum while making the complex double shift and had to resort to my lowest gear. PITA!

    My conclusion is that a certain amount of overlap is good. Half step gearing systems, that require constant double shifts, not-so-good.

  19. #19
    '01 GT ZR 5.0
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    And here I was as a newbie trying to outthink the engineers who came up with what is probably the best combination to begin with. Perhaps I'll just add a motor and then it won't be so tiring to move these two wheels. :^) Guess I'll keep working with what I have and see if I can strengthen my legs enough to grow into this bike.

    Thanks again everyone. The WOTL was very helpful.

  20. #20
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    CameronSmi,

    It comes down to preference. With a double crank you're better of with a 9 or 10 speed cluster. Unless you're running a corn cob or close rings, you'll always get some large jumps and awkward gears. It's fine for racers and mountain bikers, but it's not for everyone.

    With a triple however, you can use 6,7,8 or 9 and get useful gears that isn't painful to shift. Take a 26/44/48 with a 12-32 8sp or 11-32 9sp. You can ride over most terrain in either the 44 or the 48 ring. I've not tried over 8 speeds, but with 8 you can use the entire middle ring. The 44 will more or less get you over any rolling terrain short of severe hills. I switch between the 44 and 48 to fine tune gears, the only pattern I follow is up and down on the cassette, left to right on the big rings to fine tune. The 26 is only used on big hills and when fatigued.

    You can apply this to small rings, say a 34/38 or a 36/40 etc. but the smaller the rings, the less defined the gears become. That's why half-step rings are usually 44/48 and above.

    To contradict myself though, as I said earlier a 39/42 would work well for you with a 11-32 9sp cassette. Do the chart here: http://home.earthlink.net/~mike.sherman/shift.html .

    You can outhink the engineers though, they make what THEY THINK appeals to the masses. There's a lot of people out there on a bike, we all don't ride the same gears. Todays gearing is all copy cat, throw on as many cogs as you can and you're good to go. Me .. . I have two hands. . .I like using them both.

    So, if you want to use chainrings close together, more power to you.

  21. #21
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    A standard front mech at the correct height for a 40t chainring will foul the chainstay.

  22. #22
    headtube. zzyzx_xyzzy's Avatar
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    Quote Originally Posted by joejack951 View Post
    I'm surprised that no one has mentioned the difficulty in finding a ramped and pinned 40 tooth outer chainring for a 110mm spider (or any spider for that matter). Unless you go custom or possibly TA rings, the smallest you'll find is a 46.
    Well, with a 6 tooth difference between chainrings, ramping and pinning doesn't gain you much, and a non-ramped middle will work fine as an outer.

    Half step (or step and a half, as the 34-40 would be) on a 12-27 cassette is total overkill though. You do not need to adjust your gear ratio in 5% jumps. 39-42 or 42-45 with an 11-34 9sp cassette is a more sensible half step arrangement, giving 7% jumps, though that requires using a mountain rear derailleur.

    I have a 11-30 8sp with 24-39-42 chainrings setup on my loaded touring bike and like it a lot -- you don't have "constant double shifts" as someone said, in fact over rollers I usually don't touch the front shifter at all, where the half steps come in handy is over slight changes in a steady climb or shifting winds over level ground. The way half step makes sense is that if you're in a hurry to get to a different gear you probably want more than a 10% change, and half step makes big changes fast using only the rear derailleur; and if you find yourself wanting less than 10% gear change you're probably not in a huge hurry to have it, so you have time to execute a double shift.

    It is possible to set up half step with front indexing too. Use a standard road front derailleur (not a triple or compact), and you will have to make some shims and experiment with shimming the chainring into the right position. Shimming the outer chainring 0.6mm to the right dials it in perfect.

  23. #23
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    Gearing

    I wanted to express my thanks to the list for assisting this newbie on my quest to get the best gearing for my ride. I've been riding more and longer and have been able to get to 78 miles in about 5 hours, so I should be good to go for this weekend's American Cancer Society ride from Philadelphia, into the heart of New Jersey. Now, I just gotta' get my wife to agree to drop me off (at 5:30 a.m.) and pick me back up at the end point.

    I have a new issue relating to my feet falling asleep, but that'll be on a new thread.

    Thanks again.

    Cameron

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