help with cranks

Kev,

for a Square Drive Bottom Bracket (UN26, etc), contact Greenspeed in Vic, they have "TA" Crank Arms and Chainrings in all the sizes you want. 😉 http://www.greenspeed.com.au/

bigkev said:

i have a bb-un54 bottom bracket on a mtd bike with i ride about 250km per week i need a new set of cranks i would like to beable to change the chain rings i would like 175 mm cranks with 32/48/52 teeth any one knows what would be the best type of crankes that would fit on this bike i would like ones a bit stronger than i had my ones have worn after only 3500km on a 2005 giant boulder and i weigh about 120kg the rear gear is 11t-38t i am a hard rider any help thank you all.

You can fit a "standard" ROAD crank on the existing BB spindle and achieve chainring clearance for the stays ... OR, if you were to update to an ISIS-or-Octalink BB, you would spec the 118mm spindle length. A square taper ROAD crankset would ALSO probably require a BB with a ~118mm spindle.

The standard ROAD triples generally have a 42t-or-39t middle ring. The 32t granny is most often found on tandems, so the triple you get off-the-shelf will probably have a 30t.

I think that I am the only person who seeks out steel inner chainrings ... steel chainrings are common on the less expensive cranksets (e.g., Sora?) which still usually use square taper BB spindles OR available off of eBay-and-the-like. Something to think about. I may have the only Dura Ace 7700 crankset on which you'll find a steel 39t chainring!

Also, something to think about is to superficially "clean" your chain on a weekly basis ... brush any road-crud off with an old toothbrush ... that will extend the life span of your chainrings & cogs.

what is wrong is the square in the arm has rounded and snaaped the top off two teeth on the chain ring not much good now.

alfeng said:

You can fit a "standard" ROAD crank on the existing BB spindle and achieve chainring clearance for the stays ... OR, if you were to update to an ISIS-or-Octalink BB, you would spec the 118mm spindle length. A square taper ROAD crankset would ALSO probably require a BB with a ~118mm spindle.

The standard ROAD triples generally have a 42t-or-39t middle ring. The 32t granny is most often found on tandems, so the triple you get off-the-shelf will probably have a 30t.

I think that I am the only person who seeks out steel inner chainrings ... steel chainrings are common on the less expensive cranksets (e.g., Sora?) which still usually use square taper BB spindles OR available off of eBay-and-the-like. Something to think about. I may have the only Dura Ace 7700 crankset on which you'll find a steel 39t chainring!

Also, something to think about is to superficially "clean" your chain on a weekly basis ... brush any road-crud off with an old toothbrush ... that will extend the life span of your chainrings & cogs.

bigkev said:

i have a bb-un54 bottom bracket on a mtd bike with i ride about 250km per week i need a new set of cranks i would like to beable to change the chain rings i would like 175 mm cranks with 32/48/52 teeth any one knows what would be the best type of crankes that would fit on this bike i would like ones a bit stronger than i had my ones have worn after only 3500km on a 2005 giant boulder and i weigh about 120kg the rear gear is 11t-38t i am a hard rider any help thank you all.

1. I'd rethink the 32/48/52 idea. That's a half step crankset. They made sense when rear freewheels only had 5 cogs but I don't see any value at all when paired with an 8 or 9 speed cassette.

2. Rounding the square hole in your crank arm is a common problem that is easily solved by properly torqueing the crankarm during the initial installation. Unfortunately, once the hole has been hosed, the crankarm is junk.

3. The "snapped" teeth in your chainring are almost surely designed-in shifting aids. Check your chainring exactly opposite the misshapen teeth and see if you find another pair that looks exactly like them.

4. What chainring sizes does your bike have now? If you have a 46 tooth big ring now you might find you have clearance issues and front derailleur problems if you try to install a crank with a 52 tooth big ring.

5. Not that it matters, but I'll bet that your rear cassette is either an 11/32 or 11/34.

hi most of the teeth are rounded with two broken there is a few shorter teeth on each ring but not the two i am talking about i have 48/38/28 now on this arm i would like 30 -32 a little higher and i find i ride a lot on flat road in top gear and would like to go a litle faster but i think it is a bit of my problem to as i am hard on the arms as i start off in a high gear to as i have a habbit off standing on the pedals thanks i would like a shamanio cranks but dont know what model to go with even a 36-53 teeth wi would not mind to try trying to find better gear but i dont want to change my bottom bracket as it is only 4 weeks old now thank you

Retro Grouch said:

1. I'd rethink the 32/48/52 idea. That's a half step crankset. They made sense when rear freewheels only had 5 cogs but I don't see any value at all when paired with an 8 or 9 speed cassette.

2. Rounding the square hole in your crank arm is a common problem that is easily solved by properly torqueing the crankarm during the initial installation. Unfortunately, once the hole has been hosed, the crankarm is junk.

3. The "snapped" teeth in your chainring are almost surely designed-in shifting aids. Check your chainring exactly opposite the misshapen teeth and see if you find another pair that looks exactly like them.

4. What chainring sizes does your bike have now? If you have a 46 tooth big ring now you might find you have clearance issues and front derailleur problems if you try to install a crank with a 52 tooth big ring.

5. Not that it matters, but I'll bet that your rear cassette is either an 11/32 or 11/34.

Retro Grouch said:

5. Not that it matters, but I'll bet that your rear cassette is either an 11/32 or 11/34.

Shimano 8 sped 'huge gear' cassettes probably came on Giant boulders. They included 7 closely spaced cogs and an absolutely huge one. 38t does sound a bit big though.

the rear cluster is 11-34 on the rear

bobbyOCR said:

Shimano 8 sped 'huge gear' cassettes probably came on Giant boulders. They included 7 closely spaced cogs and an absolutely huge one. 38t does sound a bit big though.

bigkev said:

hi most of the teeth are rounded with two broken there is a few shorter teeth on each ring but not the two i am talking about i have 48/38/28 now on this arm i would like 30 -32 a little higher and i find i ride a lot on flat road in top gear and would like to go a litle faster but i think it is a bit of my problem to as i am hard on the arms as i start off in a high gear to as i have a habbit off standing on the pedals thanks i would like a shamanio cranks but dont know what model to go with even a 36-53 teeth wi would not mind to try trying to find better gear but i dont want to change my bottom bracket as it is only 4 weeks old now thank you

Standing on the cranks shouldn't be a problem ... however, as noted, maintenance issues can have an effect on premature wear.

You should let your budget be your guide ... try to stick with Shimano ONLY BECAUSE some of the non-Shimano cranks still have square tapers which are Campagnolo/Sugino compatible (a slightly different "size"😉.

You can certainly get USED "road" cranks with square tapers on eBay for under $30US ...

You can often get a USED Ultegra triple in the $50US range ... but, you would need an Octalink BB (118mm spindle), too.

You can spend hundreds if you want to buy a new crankset, particularly if you get it at your local bike shop!

bigkev said:

hi most of the teeth are rounded with two broken there is a few shorter teeth on each ring but not the two i am talking about i have 48/38/28 now on this arm i would like 30 -32 a little higher and i find i ride a lot on flat road in top gear and would like to go a litle faster but i think it is a bit of my problem to as i am hard on the arms as i start off in a high gear to as i have a habbit off standing on the pedals thanks i would like a shamanio cranks but dont know what model to go with even a 36-53 teeth wi would not mind to try trying to find better gear but i dont want to change my bottom bracket as it is only 4 weeks old now thank you

OK, how about this:

Your 48 tooth big ring is the puzzlement. That's right at the "cusp" for road vs. mountain bike front derailleurs. I suspect that you have a mountain bike front derailleur that won't handle a very much larger chainring. How does the arc of your derailleur cage look vs. your 48 tooth chainring? If they match pretty close, you might be able to cheat up to a 50 tooth ring. If the back of the cage is noticeably closer to the chainring than the front, I'd suggest forgetting the whole thing.

If the above test is OK, I'm going to suggest trying a 50/34 compact double crankset. You'll have to get a new bottom bracket to go with it. That'll give you the faster high gear that you're looking for at the expense of your easiest hill climb gears that you say you don't need. Your front derailleur should be able to handle the 16 tooth difference even if you have to raise it up a bit to make the heel of the cage clear.

What does your bike have for shifters? If the front shifter is some non-indexed Grip Shift thing, that's good. If it has an indexed front you might need a real careful front derailleur adjustment to make it work.

For another alternative, forget about changing your gearing and work on spinning your feet faster. 48/11 gives you 113 gear inches. That should easily be enough to get you up to 25MPH or so which is pretty fast. I'm still not convinced there is anything wrong with the teeth on your chainring because I've never seen that kind of damage before. On the other hand, lots of people mistake the shaped shifting aid teeth for damage. Worn chainring teeth look pointy but that takes several thousands of miles to do.

Retro,

His Boulder has a Shimano FC-TX71 28/38/48 crankset, all steel and a FD-CO51 Front Derailleur 48 tooth max capacity.

The Cranksets cost about $40, the FD $15, a UN26 BB is about $26.

Shifters are Rapid Fire Shimano, 8 speed MTB.

gclark8 said:

Retro,

His Boulder has a Shimano FC-TX71 28/38/48 crankset, all steel and a FD-CO51 Front Derailleur 48 tooth max capacity.

The Cranksets cost about $40, the FD $15, a UN26 BB is about $26.

Shifters are Rapid Fire Shimano, 8 speed MTB.

Well then, that leaves my plan "B" alternate, learn to spin faster. That's a much better thing to do anyway and it's free.

there is enough room on the derailer and the bottom bracket is a problem because of the frame size its a bb-un54 on now because of the width and dia of it not much will fit its also a 23 in frame oversize thanks

Retro Grouch said:

OK, how about this:

Your 48 tooth big ring is the puzzlement. That's right at the "cusp" for road vs. mountain bike front derailleurs. I suspect that you have a mountain bike front derailleur that won't handle a very much larger chainring. How does the arc of your derailleur cage look vs. your 48 tooth chainring? If they match pretty close, you might be able to cheat up to a 50 tooth ring. If the back of the cage is noticeably closer to the chainring than the front, I'd suggest forgetting the whole thing.

If the above test is OK, I'm going to suggest trying a 50/34 compact double crankset. You'll have to get a new bottom bracket to go with it. That'll give you the faster high gear that you're looking for at the expense of your easiest hill climb gears that you say you don't need. Your front derailleur should be able to handle the 16 tooth difference even if you have to raise it up a bit to make the heel of the cage clear.

What does your bike have for shifters? If the front shifter is some non-indexed Grip Shift thing, that's good. If it has an indexed front you might need a real careful front derailleur adjustment to make it work.

For another alternative, forget about changing your gearing and work on spinning your feet faster. 48/11 gives you 113 gear inches. That should easily be enough to get you up to 25MPH or so which is pretty fast. I'm still not convinced there is anything wrong with the teeth on your chainring because I've never seen that kind of damage before. On the other hand, lots of people mistake the shaped shifting aid teeth for damage. Worn chainring teeth look pointy but that takes several thousands of miles to do.

bigkev said:

there is enough room on the derailer and the bottom bracket is a problem because of the frame size its a bb-un54 on now because of the width and dia of it not much will fit its also a 23 in frame oversize thanks

Okay, one more time ...

I have an ISIS splined, 52/39 ROAD crank mounted on an old "hardtail"/MTB frame (see attachment).

The "normal" BB spindle length is 113mm when used on most road frames ...

The BB is an ISIS with a 118mm which is normally used for MTB & ROAD triples ... the longer spindle allows the 52t ring to clear the chainstays. IF I had an ISIS crank with a granny, it would use the same ISIS bottom bracket with a 118mm.

The front derailleur is an 8-speed XT ... the outer plate is essentially the same as on a road double ... the inner plate IS wider/taller.

I used a 9-speed chain.

Despite the seemingly mismatched chain & front derailleur, the shifting was FINE when mated to a 105 STI 9-speed triple front shifter -- fortunately, a third click was available to nudge the cage far enough to shift smoothly.

The current shifters (pictured) in the early pic (and, now), are Campagnolo ... and, the front shifter is indifferent to the front derailleur used.

As always, your results may vary.