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Thread: Upgrade?

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    Upgrade?

    My bike has a 52-42-30 triple crankset in front, 170mm arms. The cassette is 9 speed, and thus for the purposes of this question, non-negotiable (due to expense of swapping out my entire drive train).
    Apparently the 52-42-30 is an extinct beast, which is annoying enough because any replacement rings do not work nearly as well as the original did in terms of smooth shifting and propensity to drop chains or get chainsuck.

    However, I am struggling with chondromalacia and since raising the seat only made the back of the knee sore, I cannot use that to reduce compression of the knee joint. So, I am looking at getting a triple with 165mm cranks. It looks like 50-39-30 is the new standard for triples (I use triples because I need the increased q-factor). This would likely necessitate a new front derailleur, but I am not sure.

    What would be a cost effective solution to getting shorter crankarms and still have a triple? Links, specific suggestions, etc will be greatly appreciated.

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    Bastiges...165mm is out of stock!

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    just pokin' along desertdork's Avatar
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    http://www.universalcycles.com/shopp...s.php?id=14536

    If your current FD worked with 52/42/30 chainrings, I don't see how the same FD would be incompatible with 50/39/30 rings. The difference between the large and middle rings increases by only one tooth with the latter, and the profile of the FD cage should be just fine.

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    I think that the previous poster is right that there is no need to replace the derailleur. You could ask around at bike stores and try to find a used triple, although 165 will be harder to come by.

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    Desertdork-
    That is what is looking like the best option for me to take that isn't stupidly expensive. I called around a few shops just to ask about he chainring differential causing problems with shifting, and they all said a new fd would be required due to trimming issues.

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    just pokin' along desertdork's Avatar
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    Can you tell us what is the make/model of your crankset (e.g., Shimano Sora FC-3403, Truvativ Touro, etc) and your FD (e.g., Shimano Sora FD-3403)?

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    Exact specs are non-existent. This is a 2005 Trek Pilot 2.1. The front derailleur is 105, model number FD-5504. The crank is a doozy. Branded Bontrager, but manufactured by Truvativ. There is nothing on any part of the crankset that tells me anything more specific. Given what I found on the intertubes, Truvativ Touro may very well be what it is. Even Trek doesn't know exactly what it is.

    Last year I had to replace the middle ring as it had been bent somehow and was starting to skip under load, which is quite annoying (as well as hazardous to my crotch). The replacement Shimano ring has never been the same. The original chainring never caused a dropped chain, or any fun chainsuck. The replacement has done both, to the point where I've had to put on a chaincatcher. I still get occasional chainsuck, and when I do, its bloody epic (last time it was so bad it took two guys to wrench the chain out of where it was bound up, and it happened at the top of the hill going from granny to middle with no pressure and very little in the way of grade to even slow the bike down).
    It's bad enough that the combo is extinct, but worse is that 42t rings will not function as well as the original.
    Last edited by deep_sky; 10-01-10 at 08:15 PM.

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    I believe your FD-5504 is quite compatible with the Tiagra crankset I linked in an earlier post. The 50/39/30 rings provide the necessary 10t minimum difference between outer and middle rings, the shape of the FD's cage will still be very close to the shape of the rings on the Tiagra crankset, and both components are engineered for "modern" indexed shifting with Shimano 9-sp road drivetrains.

    As for your issue with your current chainrings, it's possible that the replacement ring was just the wrong match. I don't know enough about the various chainrings available, but I understand that Shimano rings are designed to work as a system. You'll see some Shimano rings sold as "A" type while others are "B" type; each should be matched to its proper mate, so there may have been some compatibility issue there. Also, I believe the teeth on certain Shimano rings (perhaps just the middle or inner rings) have a certain amount of offset (toward inboard); if the spider and/or inner ring on your Bontrager crank wasn't designed for this offset of the middle ring's teeth, then perhaps that could have been the reason for dropping the chain. Whatever the cause, I'm sure you're ready to be rid of it.

    Since it sounds like you're trying to keep the overall cost reasonable, I'd recommend trying your current FD with the 50/39/30 crankset (if you go that route) before worrying about buying a new FD.

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    I'm going to ask that they try the new crankset with my old FD first, before using the FD they have in stock for me. If it works, then all I have to pay for is the crankset and bb.

    The replacement ring has 52-42-B stamped on it. The tooth count is right, but I have no idea if the alpha suffix is correct since there is not a single marking on the 52t ring to indicate either way. Yes I am quite ready to be rid of it. I can protect against a chain drop with a chaincatcher, but there isn't a gizmo to prevent chainsuck. I was lucky I had some of my clubmates with me, or I would have had to call for pickup and a trip to the LBS, the chain was stuck in there that good. As soon as I felt the chain ceasing to go forward I stopped as soon as I could cause I knew what happened. Still jammed up considerable. My clubmates were impressed. However, I wasn't.

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    Frist fo all the front derailleur will work. They are all pretty much the same. Secondly, the most cost effective solution would be to get the new crank set. This will be a good investment. The seat is another thing. the position of the saddle back and fourth is also important. SImply raising the saddle does not fix the problem. You must also take into account the seat angle and the seat position back and fourth.

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    Quote Originally Posted by deep_sky View Post
    I am struggling with chondromalacia.
    I've had that problem with my knees most of my life, at my age the docs call it arthritis.
    I think the smaller chainrings will be good to help you spin the cranks at a higher cadence. A high cadence will let you travel at a higher speed while reducing compression on your joints. I know I feel better after a ride if I keep my cadence above 90, mostly 95 to 105.
    I think the 50-39-30 crankset will be a good idea.
    In my case a narrower Q factor is better, I ride a double with short pedal spindles. But everybody's knee problem is different.

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    Higher cadence and therefore less pressure on the knee is the key, but that can be done independent of crank arm length. If you want 165's there is no problem with that but before you make any change you need to check fore-aft position of your saddle if you have not already done so. I have seen the wrong position (too far forward) cause problems. Be aware that you will be moving your foot back in respect to your knees with the shorter crank arms as well.

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    I've done the work with angle and fore/aft position (allowing for necessary corrections for raising and lowering the seatpost); those are good. The length of my femurs causes a more extreme angle with my knee, similar to what would be the case if the saddle was too low. Since my overall inseam has no more height left to give, I have to reduce the compression another way. Since I am female, the q-factor doesn't force my knees inwards as much, although of course not all women need that accommodation.

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    Senior Member Doug64's Avatar
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    Desertdork is correct-- Your FD should work fine. I run Tiagra 4503 9spd, triple derailleurs on a 52/42/30, 48/36/26 and a 44/32/22 using Tiagra STI shifiers. It works well on all of them.

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