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  1. #1
    Senior Member tergal's Avatar
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    what to look for in a crankset

    Hi so just a quick question ,

    So my trek (4300 mtb) has a Shimano Acera M391, 44/32/22 for the front crank set, and while it is working fine and i have no issue with the range . I wanted to ask what do people look for when looking to replace/upgrade this part .

    I looked at some of the ones in the local stores and it all starts to go way over my head very fast, and online my one cost like 60 dollars and they just seem to go up from there with out providing much more details as to why you are paying 200 more for it.

    so what should i be looking at in regards to

    -- compatibility?

    -- weight ?

    --sizing/range ? ( happy with the current , or am i just ignorant ? )

    -- quality ?

    Thanks for any information posted oh and i did Google this and all i found was places selling and flame wars between riders who weigh less than a packet of crisp.

    o/
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    What are your reasons for upgrading? If its working, I would keep it until it needs replacing. There are likely other parts to upgrade before crankset (derailleurs, shifters, brakes/pads, etc). Unless your abusing it or pushing it to its limits, I would keep the crank.
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    SuperGimp TrojanHorse's Avatar
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    3 critical things to consider:

    Bottom bracket compatibility (e.g. English threaded, Italian threaded, BB30 etc)
    Crank length (170mm to 175mm are common)
    Double or triple
    Bonus - chain compatibility. Most are either Shimano compatible or Campy but you don't want to mix them.

    Upgrading cranks is usually a matter of increasing stiffness or decreasing weight and both are expensive to do.

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    Senior Member Bill Kapaun's Avatar
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    I'm a bit different, but because of my bad knee, I look for a crank with short arms (165MM).

    Your crank has replaceable rings, so if you wear one out, you can simply replace a ring and save some money.
    That's what i would do if I had no complaints with the current crank.

  5. #5
    Senior Member tergal's Avatar
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    Quote Originally Posted by nymtber View Post
    What are your reasons for upgrading? If its working, I would keep it until it needs replacing. There are likely other parts to upgrade before crankset (derailleurs, shifters, brakes/pads, etc). Unless your abusing it or pushing it to its limits, I would keep the crank.
    hi mate,
    primary reason is i like to know what to look for when i look at things
    secondary is i know with my weight and the entry level parts on my bike will be taking a thrashing
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    Senior Member tergal's Avatar
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    Quote Originally Posted by TrojanHorse View Post
    3 critical things to consider:

    Bottom bracket compatibility (e.g. English threaded, Italian threaded, BB30 etc)
    Crank length (170mm to 175mm are common)
    Double or triple
    Bonus - chain compatibility. Most are either Shimano compatible or Campy but you don't want to mix them.

    Upgrading cranks is usually a matter of increasing stiffness or decreasing weight and both are expensive to do.
    Thanks mate, with my serious lack of knowledge I might buy a cheap one or a second hand bike and pull one apart to look at it =) that is how I learn the fastest
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  7. #7
    Senior Member tergal's Avatar
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    Quote Originally Posted by Bill Kapaun View Post
    I'm a bit different, but because of my bad knee, I look for a crank with short arms (165MM).

    Your crank has replaceable rings, so if you wear one out, you can simply replace a ring and save some money.
    That's what i would do if I had no complaints with the current crank.


    good to know , i think mine has a 175 on there
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    2 Fat 2 Furious contango's Avatar
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    Tergal, from what I gather (with limited knowledge of this subject) is that as you get into the most expensive components you start to pay for the extreme lightness, among other things. Which is great, unless you're a heavy rider in which case you're perhaps more likely to wear and break stuff. And from the fact you're posting in the Clydes area and referring to your weight is potentially going to be an issue.

    In many ways think of it as the difference between a Ferrari and a Ford. You can buy your Ford for a fraction of the price, and the Ferrari is hugely quicker. But I don't know that I'd want to run a Ferrari for a couple of years without an oil change or use retreaded tyres on it, or any of the cost-cutting measures you might take if you drive a Ford. If you buy a Ferrari you've got the initial investment in it and then you need to keep on top of it to make sure it stays tuned up.

    If you're replacing something because it's broken or worn out look at what you had in the first place in terms of crank length, chainring tooth counts and bottom bracket size. If you've worn out a single chainring some groups will let you replace just one chainring. If you've worn out the bottom bracket you can replace just that part (I wore out my MTB bottom bracket after about 8 months and 800 miles and had it replaced under warranty)

    If you're wanting to upgrade to something better the obvious question is what you mean by "better". As a Clyde myself I'm not interested in paying lots of money to save a few ounces on my bike when I've got more than a few surplus pounds still sitting around my middle. If I want to save 100g I could either spend a fortune upgrading this part or that part, or just eat a smaller piece of pie for lunch.

    If you're wanting to change from a double to a triple (or vice versa) you'll have some work to do to also change your shifters. If you want to change your gearing (I looked at putting slightly larger chainrings on my MTB some months back) you'll need to consider whether your front derailleur can work with whatever you're wanting to put on.

    If you're wanting to mix-and-match components check things like the bolt spacing on the chainrings, the bottom bracket dimensions, chainring toothcounts (your FD will have a maximum difference between largest and smallest chainring) etc.
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    Senior Member tergal's Avatar
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    [QUOTE= If I want to save 100g I could either spend a fortune upgrading this part or that part, or just eat a smaller piece of pie for lunch..[/QUOTE]


    hah i was saying that to a friend today , durability is my primary concern, if i want speed and weight it can come from me first then the bike
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    Captain Big Ring tractorlegs's Avatar
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    If it's working fine, I'm thinking the only thing your would want to replace is the chainrings which would be easy. And you would only need to do that to accommodate personal taste by giving yourself a different gear range. Your crank is going to last a loooong time if it's like mine (I ride a 2005 model 4300 I call The Rig so replacement probably won't be necessary for a while. The chainrings are generic 4-bolters that you can pick up anywhere and can be swapped out in just a few minutes (unless you're changing the granny)
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    Senior Member Rona's Avatar
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    in my opinion (so take this with a grain of salt) ... cranks are cranks mostly. As long as you don't get bottom end, press punched cheap metal ones, you're good. Higher end Shimano, Campy, SRAM, Suntour, Stronglight are all good. They aren't a complex part and tend to last a long time. I care more about the moving parts falling apart like derailleurs and bottom bracket before I worry about cranks.

    I will admit though I am a bit picky about how crank sets look. I like the look of Campy and Rene Herse, Stronglight and high end Suntour. Shimano looks horrible to me, even though I have a Shimano biopace triple on my touring bike. I'm also a vintage nut...So YMMV.
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  12. #12
    SuperGimp TrojanHorse's Avatar
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    I'm not sure why 165 mm cranks would be better if you have bad knees - you're putting more pressure on your knee for an equivalent pedal stroke with shorter cranks. I have no cartilage left in my right knee to speak of and I prefer longer cranks, so YMMV.

    As for buying them to take one apart - no point. There's very little going on there. I have no clue how old my cranks are but I'm guessing wicked old - the bike is a vintage 1988 Ti frame with some bizarre small BB size, so the square taper cranks I have in there now are going to be with me till I get rid of the bike. No modern parts will fit, and I periodically have the bearings in the BB rebuilt.

    As for chain rings - if you wear them out they're easily swapped but they are not all compatible! Compact doubles have a different bolt diameter so don't be thinking you can stick a 34 tooth chain-ring on your standard crank, or vice versa.

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    Senior Member Seattle Forrest's Avatar
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    Quote Originally Posted by nymtber View Post
    What are your reasons for upgrading? If its working, I would keep it until it needs replacing. There are likely other parts to upgrade before crankset (derailleurs, shifters, brakes/pads, etc). Unless your abusing it or pushing it to its limits, I would keep the crank.
    I found this hard to believe when I first heard it, but a change to your crankset (or just the chain rings) is likely to have more effect on your front shifting, than a change to your derailleur. The FD basically just pushes the chain around, but the teeth in the chain ring are what's in contact with the chain as it shifts. Their exact shape can either trip the chain up, or make it a smooth transition.
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    Senior Member Seattle Forrest's Avatar
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    Quote Originally Posted by contango View Post
    If I want to save 100g I could either spend a fortune upgrading this part or that part, or just eat a smaller piece of pie for lunch.
    I guess that's fine for a ride around the block, but nutrition is an important part of cycling, and skimping on meals really isn't a good idea. As you start to push yourself and go on longer rides, you'll have to abandon this line of thinking.
    Don't believe everything you think.

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    Quote Originally Posted by Seattle Forrest View Post
    I guess that's fine for a ride around the block, but nutrition is an important part of cycling, and skimping on meals really isn't a good idea. As you start to push yourself and go on longer rides, you'll have to abandon this line of thinking.

    I'm guessing that comment was mostly tongue-in-cheek. I'm sure he's not advocating anorexia.

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    Quote Originally Posted by tergal View Post
    Hi so just a quick question ,

    So my trek (4300 mtb) has a Shimano Acera M391, 44/32/22 for the front crank set, and while it is working fine and i have no issue with the range . I wanted to ask what do people look for when looking to replace/upgrade this part .
    Ring tooth counts which match your power/weight/climb length and grade/pedaling style and limit shifting are a good idea. Machined rings look nicer than stamped but I couldn't say whether the ramps on otherwise identical (same brand) rings work better.

    Pinned and ramped chain rings made by Shimano and Campagnolo tend to shift better than those made by by other companies.

    The small bearings used in ISIS (and Octalink) bottom brackets don't last too long.

    Otherwise it's cosmetic.

    Since society frowns on men wearing jewelry and accessorizing their daily wear like women lots of guys get into it when engaged in sport, accenting stylish bicycle frames with pretty bits of carbon or silver alloy for the more traditional crowd (nothing is more classy than Campagnolo parts from around the end of the C-Record era and dawn of Ergo).

    -- compatibility?
    Identical bottom bracket dimensions (ex English 68mm on most road bikes), same speed count (you can have chain rub on the big ring when you pair a wider chain with the narrower chain ring setup like a 9 speed chain with 10 speed rings), chain line, and bottom bracket type (ex square taper) + spindle length if you're not swapping it too (I wore out my big ring and bottom bracket about the same time).

    -- weight ?
    Speed gains up-hill are proportional to the total weight reduction. A barely Clyde on a moderate weight road bike totaling 220 pounds or 100kg will be 0.1% faster (saving 3.6 seconds an hour) up the steepest grades for each 100g he saves.

    In practical terms it doesn't matter unless you're an otherwise competitive racer, have the body morphology conducive to climbing (about 2 pounds per inch or 140 pounds for a 5'10" rider), and are racing in the mountains off the front to an up-hill finish where 4 seconds might keep the peleton from eating you.

    --sizing/range ? ( happy with the current , or am i just ignorant ? )
    It's too personal and dependent on the cogs you're running to make a call.

    -- quality ?
    Shimano (although an FSA carbon crank shifts well enough if you want to compromise to get more contemporary looks) unless you want to spend a lot (Stronglight has some nice looking cranks in the $300-$500 range which I'd hope to have better shaped rings than FSA)
    Last edited by Drew Eckhardt; 02-13-12 at 12:00 PM.

  17. #17
    Senior Member Seattle Forrest's Avatar
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    Quote Originally Posted by Wolfwerx View Post
    I'm guessing that comment was mostly tongue-in-cheek. I'm sure he's not advocating anorexia.
    Oh, he's not actually suggesting anorexia, and my reply was mostly tongue in cheek, too.

    I think "I don't care about 100 grams - that isn't even 1/4 pound" makes sense, but "I'll eat less or go without water to make up for 100 grams" is silly.
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  18. #18
    Senior Member nkfrench's Avatar
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    Quote Originally Posted by Bill Kapaun View Post
    I'm a bit different, but because of my bad knee, I look for a crank with short arms (165MM).
    Me too. I ride with 170mm cranks due to my bad knee. 175 or even 172.5 cranks would be an issue and those are what I'm finding on new bikes my size.
    Some days it takes a while to loosen up where I can bend the knee enough to get over the top of the pedal stroke. A few rides I never got loosened up and had to quit, usually when a weather front was coming in/barometric pressure changes.
    Even loosened up, standing on the pedals the 170mm seems too tall. I blow up very quickly climbing out of the saddle.
    The knee is actually better range of motion than it used to be. A few slips/falls injuries broke some of the scar tissue/adhesions/whatever leftover from a injury/surgery 20 years ago.

    Back to cranksets and such - I believe that the high-end gearing should be quite sturdy as well as being light. Pros can generate a lot of watts and put a lot of torque on the drivetrain.
    I do think that they routinely replace some of the components (cranks) before cracks develop, did I read around 7,000 miles?

  19. #19
    Senior Member tergal's Avatar
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    Quote Originally Posted by Seattle Forrest View Post
    Oh, he's not actually suggesting anorexia, and my reply was mostly tongue in cheek, too.

    I think "I don't care about 100 grams - that isn't even 1/4 pound" makes sense, but "I'll eat less or go without water to make up for 100 grams" is silly.
    Ha i was more talking about how i could just lose the 100grams, instead of paying a silly price to save 100grams on part note so much skipping food as in the long run that won't help. (saying this while eating a nice bowl of hot porridge and apple bits)
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    Senior Member tergal's Avatar
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    Thanks Drew Eckhardt , now need to take all this in to account when reading and looking

    wonder how much trouble i would get in for pulling my partners bike apart to understand how it works more
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  21. #21
    Senior Member Ken_onabike's Avatar
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    tergal, I'm guessing that chain rings etc for cranks like yours and the even lower spec one one in my FX7.1 are stamped out by the millions rather than being light weight precision machined engineering masterpieces. Even so, I don't think the crank is likely to break in a hurry, and on the off chance that it did the $60 price tag would make it a cheap repair. My only concern with mine is that I think I'd like something like your 22 tooth small ring rather than the 28 tooth that I've got now, but that's only because I'd like to drag a loaded trailer behind it for short weekend trips at some stage.

  22. #22
    2 Fat 2 Furious contango's Avatar
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    Quote Originally Posted by Seattle Forrest View Post
    I guess that's fine for a ride around the block, but nutrition is an important part of cycling, and skimping on meals really isn't a good idea. As you start to push yourself and go on longer rides, you'll have to abandon this line of thinking.
    Not at all... my point was that for as long as I've got a good 40lb of surplus weight on my body it's pointless spending a fortune to shave a few ounces off my bike.

    When I'm on a long ride I carry food and water, which also weighs much more than the few ounces here and there a lot of lightweight components might save.
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  23. #23
    2 Fat 2 Furious contango's Avatar
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    Quote Originally Posted by Seattle Forrest View Post
    Oh, he's not actually suggesting anorexia, and my reply was mostly tongue in cheek, too.

    I think "I don't care about 100 grams - that isn't even 1/4 pound" makes sense, but "I'll eat less or go without water to make up for 100 grams" is silly.
    My point was just that most of us in here are in here for a reason, and I suspect most of us could afford to eat 100g less at lunchtime and it not make a big difference to anything. I know I could still lose 4oz from a good number of my meals and not feel deprived as a result.
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  24. #24
    I am the Snail~! Peter_C's Avatar
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    Quote Originally Posted by TrojanHorse View Post
    I'm not sure why 165 mm cranks would be better if you have bad knees - you're putting more pressure on your knee for an equivalent pedal stroke with shorter cranks. I have no cartilage left in my right knee to speak of and I prefer longer cranks, so YMMV.
    There are many reasons for going to shorter cranks, two of them being 5'2" or shorter, and having knee and/or hip issues. If you have a bike already, there is really only two ways left to change maximum angles, one is seat position, and the other is changing the crank length. The basic idea is with shorter cranks you pedal is smaller circles, therefore your knees (and hips) do not close to as great of an angle.

    This is very noticeable in recumbents, but also applies to DF bikes as well. Here are a few links to check out if you wish to learn more:

    http://bikesmithdesign.com/Short_Cra...anks_faqs.html

    http://www.myra-simon.com/bike/cranks.html

    Of course, the downside to shorter cranks is a loss of torque. But if a person can ride longer, and more comfortably, then it may be a good change.
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  25. #25
    Senior Member tergal's Avatar
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    Quote Originally Posted by Ken_onabike View Post
    tergal, I'm guessing that chain rings etc for cranks like yours and the even lower spec one one in my FX7.1 are stamped out by the millions rather than being light weight precision machined engineering masterpieces. Even so, I don't think the crank is likely to break in a hurry, and on the off chance that it did the $60 price tag would make it a cheap repair. My only concern with mine is that I think I'd like something like your 22 tooth small ring rather than the 28 tooth that I've got now, but that's only because I'd like to drag a loaded trailer behind it for short weekend trips at some stage.
    trade you my 22 for your mud guards after this mornings ride to work
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