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I want to switch to compact crank

Old 04-06-19, 04:02 PM
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trek330
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I want to switch to compact crank

I have a 1993 Specialized Allez Comp with a 52/39 front gearing.I want to switch it to compact 50/34.How do I know what size crank I have and what tool do i need to remove it?Thanks!
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Old 04-06-19, 04:41 PM
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No idea about what crank the factory bought , back then.. do tell..
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Old 04-06-19, 07:12 PM
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Most crank arms have their length indicated, often on the back side. Next up is the BB/axle compatibility. Most likely the crank and BB have a tapered square interface and the BB cups are internal (traditionally threaded into the shell). Expect to need a different BB axle length to have the new rings sit at the best chain line. If you change the interface design then a new BB will be a must. The ft der will want to be lowered on the seat tube to maintain the large ring/cage gap (about 3mm typically). Andy
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Old 04-06-19, 07:42 PM
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Originally Posted by Andrew R Stewart View Post
Most crank arms have their length indicated, often on the back side. Next up is the BB/axle compatibility. Most likely the crank and BB have a tapered square interface and the BB cups are internal (traditionally threaded into the shell). Expect to need a different BB axle length to have the new rings sit at the best chain line. If you change the interface design then a new BB will be a must. The ft der will want to be lowered on the seat tube to maintain the large ring/cage gap (about 3mm typically). Andy
Wow,It's alot more complicated than I would hope.Also more costly if it involves a new BB.The old crank BTW is Shimano 105.
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Old 04-06-19, 08:15 PM
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Shimano 105 cranks have a few different model depending on year. The exact model # should be stamped on the back next to the pedal attachment hole. Looks something like "FC-1056" (if 1992 original crank). Let us know the model # and someone will probably know the bottom bracket length & spindle interface. Most 105 doubles use a 130 BCD and takes a 39t small ring (38t on some generics) minimum since the chainring bolts would not allow any smaller.
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Old 04-07-19, 08:08 AM
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OK.I'll check KCT1986!
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Old 04-09-19, 04:54 PM
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Need to think about a few more things.....not to say it won't work but there are fiddly considerations to making sure it works and works well

How many speeds? what is the rear derailler? will it handle the increased range ?
will the front derailler handle the new range? Will it need to be adjusted in height?
need to be sure chain length is ok
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Old 04-09-19, 05:58 PM
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What is wrong with your old crankset? Chainrings worn out? Busted up in a crash?

Being the mind reader we've been expected to be in this thread, I'll assume you want lower gearing for climbing hills. Going from a 39 to 34 little ring will get you 13% lower gearing.

Now assuming you have a 26 tooth biggest cassette cog, going to a 30 will provide lower gearing than the crankset swap.

I just did this on a road bike I recently picked up at my local bike Co-op for $150. The 42/52 chainrings and the 12-26 cassette cogs were a bit challenging on the hills.

So I pulled the cassette apart, and swapped out the 2 largest cogs to give me a 30 toother in the back. Didn't even have to lengthen the chain. Cost me $2 for the cogs.

I assume the compact was recommended by a bike shop, who naturally gravitate towards the very most expensive solutions to problems. I assume they also tacked on the recommendation that you have to upgrade your entire drivetrain to the latest 12-speed gear, because they cannot source ancient 10-speed gear any more.
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Old 04-09-19, 06:43 PM
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If you're thinking of switching for lower gears, consider a "sub-compact" crankset like a 46/30. This doesn't make it any easier for you to replace stuff, but I'm a strong believer in subcompact double cranks for most people who aren't just doing fast group rides.
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Old 04-09-19, 07:01 PM
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Is this what your bike looks like? This is 14spd (7x2) Shimano 105 with gear and brake lever combined. Some Allez's appear to have gear shifters on the frame.
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Old 04-28-19, 06:53 AM
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Yeah,that's my bike Bluehills 3149, which was originally gears on the tubes and converted to brifters thank God!It's an 8 speed now but I assume it was originally 7.
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Old 04-28-19, 06:55 AM
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Originally Posted by KCT1986 View Post
Shimano 105 cranks have a few different model depending on year. The exact model # should be stamped on the back next to the pedal attachment hole. Looks something like "FC-1056" (if 1992 original crank). Let us know the model # and someone will probably know the bottom bracket length & spindle interface. Most 105 doubles use a 130 BCD and takes a 39t small ring (38t on some generics) minimum since the chainring bolts would not allow any smaller.
It does indeed say "FC-1056"!What would be the BB size and type?
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Old 04-28-19, 06:57 AM
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Originally Posted by Dave Mayer View Post
What is wrong with your old crankset? Chainrings worn out? Busted up in a crash?

Being the mind reader we've been expected to be in this thread, I'll assume you want lower gearing for climbing hills. Going from a 39 to 34 little ring will get you 13% lower gearing.

Now assuming you have a 26 tooth biggest cassette cog, going to a 30 will provide lower gearing than the crankset swap.

I just did this on a road bike I recently picked up at my local bike Co-op for $150. The 42/52 chainrings and the 12-26 cassette cogs were a bit challenging on the hills.

So I pulled the cassette apart, and swapped out the 2 largest cogs to give me a 30 toother in the back. Didn't even have to lengthen the chain. Cost me $2 for the cogs.

I assume the compact was recommended by a bike shop, who naturally gravitate towards the very most expensive solutions to problems. I assume they also tacked on the recommendation that you have to upgrade your entire drivetrain to the latest 12-speed gear, because they cannot source ancient 10-speed gear any more.
Excuse my delay in answering everybody but i was out of action for a while between apts!Yes it would be for handling hills.I have an 8 speed cassette with 28 largest cog.I could go up to 32 but that would mean another derraileur wouldn't it?
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Old 04-28-19, 07:05 AM
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I would switch to an external bearing BB while changing crank. Really not that expensive.
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Old 04-28-19, 08:18 AM
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Before you switch the bottom bracket maybe just find a square taper/JIS compact crank and just swap those on the existing BB/spindle. You'll end up a lot closer to what you already have that way and won't have to fiddle with anything else. I looked on ebay and they are available.
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Old 04-28-19, 10:47 AM
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You may not need another rear derailleur. In my past, I've run a Shimano 105 short (yes, short) cage rear derailleur with a 34 tooth cog on a Shimano Megarange cassette. It worked, but chain length was critical. Plus I only had a 10 tooth jump on the chainrings.
Regardless, a new mid or long cage derailleur would put you back like $30 for a functional Shimano Altus-grade unit. Plus $20 for a larger cassette.
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Old 04-28-19, 12:28 PM
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Originally Posted by zacster View Post
Before you switch the bottom bracket maybe just find a square taper/JIS compact crank and just swap those on the existing BB/spindle. You'll end up a lot closer to what you already have that way and won't have to fiddle with anything else. I looked on ebay and they are available.
Unless OP gets the square taper crank for cheap (co-op etc.), he would invest a lot of money in an outdated BB standard. that BB may be on its way out anyway. You can get Deore external BB for $15, a crank is $60 or some other significantly higher price. BB are wear items, the crank may live for nearly forever.

OP: you also should check BCD of your cranks if you can install smaller chainrings. Check local co-ops if they have old stuff for cheap. there should be thousands of old square taper cranks flying around.

Edit: check the gear calculator to see if you need to adjust cassette in addition to chainrings. As many mentioned here, a sub compact crank is more suitable for mere mortals. Not many people are able to spin out a 52:11. Going from 39 to 34 may not be enough. Once you go through the expense of replacing half the drive train, you may as well get 100% of the result you desire.

Last edited by HerrKaLeun; 04-28-19 at 12:32 PM.
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Old 04-28-19, 02:13 PM
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Originally Posted by zacster View Post
Before you switch the bottom bracket maybe just find a square taper/JIS compact crank and just swap those on the existing BB/spindle. You'll end up a lot closer to what you already have that way and won't have to fiddle with anything else. I looked on ebay and they are available.
I see on ebay"Origin8 Race-CT Compact Crankset, 50/34t, 172.5mm" for $52.Is that 8 speed compatible?How is the quality?
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Old 04-28-19, 08:12 PM
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I've got a 1992 Trek 1400 that I want to go compact with as well. I'm not strong enough to push the 53t chainring presently, and I have compact on another bike and really like that. I'm hoping to find at least a 50t chainring for the old 105 1055 crankset. Hoping that will be sufficient.
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Old 04-28-19, 11:10 PM
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Originally Posted by trek330 View Post
I see on ebay"Origin8 Race-CT Compact Crankset, 50/34t, 172.5mm" for $52.Is that 8 speed compatible?How is the quality?
Probably fine. Looks thick, like it might be on the heavy side for durability.

Just because it's square taper, doesn't mean that your old BB will be the right length for it. This link says it needs a 110mm spindle: https://www.ebay.com/itm/Crankset-Or...-/152516868016
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Old 05-04-19, 11:59 PM
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Originally Posted by trek330 View Post
Wow,It's alot more complicated than I would hope.Also more costly if it involves a new BB.The old crank BTW is Shimano 105.
BBs are cheap, less than $30.

Get whatever new crank fits your specifications and budget. Get a new BB to match it, and you're gold. The new BB is not a significant cost consideration or hassle.
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