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Mtn bike crankset on Trek 520

Old 07-13-18, 01:12 PM
  #1  
crandolph
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Mtn bike crankset on Trek 520

I know that this has been done a hundred times but I need some help before proceeding. I have a 2005 trek 520 and want to go with "hill friendly" gearing. The bike currently has 52/42/30 chainrings on a Shimanp Ultegra crankset (175mm) My plan is to go with 44/32/22. I have been looking at Shimano mountain bike cranksets but I really don't know what I need so I'm looking for recommendations. Can I use the current bottom bracket that is on my bike? If not, which one do I need? (BB shell is 68mm wide if that matters). What about any difference in the chainline? I have a clamp-on front derailleur so I'm hoping that I can just move it down a bit to accommodate the smaller chainrings.

Thanks in advance for any guidance. BTW - just doubled my post count. Been a member since 2006 and this is my 2nd post.
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Old 07-13-18, 01:21 PM
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keep the left bar end shifter friction and your path to that goal is simplified.

square taper cranks OK with you?
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Old 07-13-18, 01:54 PM
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Originally Posted by crandolph View Post
I have a 2005 trek 520 and want to go with "hill friendly" gearing. The bike currently has 52/42/30 chainrings on a Shimanp Ultegra crankset (175mm) My plan is to go with 44/32/22. I have been looking at Shimano mountain bike cranksets but I really don't know what I need so I'm looking for recommendations. Can I use the current bottom bracket that is on my bike? If not, which one do I need?
It's not likely that you'd be able to use the same bottom bracket. When talking about three-piece cranksets like your 520 would've originally been equipped with, the required spindle length will depend on the specific crankset make & model you choose. You could even stay with a 'road' crankset whose specs are all the same, but if it's a different brand/model, it could call for a different length spindle. And many recent cranksets are two-piece designs where the "spindle" is integral to the drive-side crank arm. Those use a completely different bottom bracket design altogether.

The good news is that your frame has an English-threaded bottom bracket shell. That was the de facto standard for decades and is still quite common, so you'll have all sorts of options. Whatever crankset you choose, there'll likely be a bottom bracket that lets you fit it to your frame. ...so long as you avoid BB30/PF30 cranksets. And bottom brackets are generally cheap.

Originally Posted by crandolph View Post
What about any difference in the chainline? I have a clamp-on front derailleur so I'm hoping that I can just move it down a bit to accommodate the smaller chainrings.
Chainline could prove to be a little bit of a hassle. Shimano spec for road bike triple cranksets is 45 mm, measured from the seat tube centerline to the middle chainring. For mountain bikes, it's 47.5 to 50 mm. Your road derailleur may not be able to swing out wide enough. If you're using a 3-piece crankset, you could potentially use a shorter spindle to dial in your chainline. Another possible solution would be to use a SRAM Wide Spacing Adapter and a braze-on derailleur to mount your derailleur a few millimeters further outboard.

Alternatively, so long as you're using a friction shifter to control your front derailleur, you could use a mountain bike front derailleur to get enough outboard swing to reach the big ring on an MTB crankset. Mountain bike and road bike front derailleurs have historically used different cable pull ratios, so a road bike indexed shifter may not mate well with a mountain bike front derailleur.

One final concern is that the curvature of a derailleur cage made for a 50+ tooth big ring might not play well with a 44/32/22 crankset. You may find you have better shifting performance with a MTB derailleur whose cage has a tighter curve to match your new, smaller chainrings. Could be another reason to swap the front derailleur to a mountain bike model.
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Old 07-13-18, 07:24 PM
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Yes, you can use a MTB cranskset, either older or modern. Several things to be aware of. Your current road FD is "optimized" for a 52T large ring, so the cage shape wont match the smaller rings well. The FD will still shift fine with a friction shifter but may require more trimming as the back of the cage will be further away from the rings. Chainline shouldn't be an issue. The 520 uses a 135mm rear spacing (versus road standard 130mm), The old Ultegra triple was designed for 47.5mm front chainline if I remember correctly; most MTB is 50mm. Hard to believe the FD wont reach the extra 2.5mm, but if it doesn't you can buy an older Shimano MTB FD on E-bay for next to nothing. The Ultegra 9 speed triple also used Shimano's Octalink bottom bracket standard. So changing the crankset will require changing the bottom bracket. Newer cranksets also generally are for 10 or 11 "speeds". One marketed as for "10 speeds" should work just fine without needing to change chain, cassette, bike, yada, yada, yada.

There are lots of options. I like older Shimano MTB 5 arm and 110/74 BCD cranksets because of the huge selection of rings (you can select the ones you want, not the one or 2 combinations manufacturers make for their newer options). They use square taper bottom bracket, which work just fine, are inexpensive, readily available, and you can adjust the chainline. Some model #s are FC-M730 (XT 7 speed) and FC-M60 (Deore 7 speed). Yes, 7 speed but buy new "9 speed" rings with pins and ramps or just use the 7 speed rings, eiither works. You might be able to locate a LBS that understands touring cyclists and can get you the gearing you want but most LBS aren't much help if you don't fit in the box the manufacturers are current;y pushing (road or MTB). Another option is to contact Rivendell Bicycles - they can definitely get you something with the gearing you want.

Good luck.
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Old 07-13-18, 09:50 PM
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Is the Crankset you are looking at hollow tech, the drive side crank and spindle are one piece. If so and your old one is a tapered spindle you will need a new bottom bracket ($20) As your BB is 68mm wide you will need a couple of 2.5mm spacers to make up for the MTB spacing at 73mm.
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Old 07-14-18, 12:01 AM
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https://www.rivbike.com/collections/...riple-46x36x24
Put a 12-32 on the back and you will have very low gearing.
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Old 07-14-18, 05:37 PM
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Originally Posted by wsteve464 View Post
Is the Crankset you are looking at hollow tech, the drive side crank and spindle are one piece.
Just a little clarification: Shimano Hollowtech II cranks are two-piece cranks. The original Shimano Hollowtech cranks were three-piece, with Octalink bottom brackets if I remember correctly.
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Old 07-15-18, 06:03 PM
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Thanks for all of the responses. I have been learning a lot about chainrings and cranksets in the last few days (thanks and RIP Sheldon Brown). Currently leaning towards the older Shimano cranks with square taper. Also decided that it makes sense to swap in a mtn bike FD instead of using the current setup. More questions: Chainring materials - is aluminum OK? For all 3 rings? What's up with ramping & pins? Necessary? On which ring(s)?
Thanks again for your help!
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Old 07-16-18, 08:29 AM
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Originally Posted by crandolph View Post
Thanks for all of the responses. I have been learning a lot about chainrings and cranksets in the last few days (thanks and RIP Sheldon Brown). Currently leaning towards the older Shimano cranks with square taper. Also decided that it makes sense to swap in a mtn bike FD instead of using the current setup. More questions: Chainring materials - is aluminum OK? For all 3 rings? What's up with ramping & pins? Necessary? On which ring(s)?
Thanks again for your help!
I would suggest you lean a different direction. Mountain bike square taper cranks will require a different bottom bracket from your current one. The width is tricky to judge and can require obtaining more than one bottom bracket to get the correct crank position for the derailer to work properly.

Instead, I would suggest a external bearing crank like this one. It's competitively priced with the Sugino crank above. The chainline is more easily adjusted by moving spacers around from side to side. The crank is also much easier to remove and install than a square taper. You have to tighten a couple of pinch bolts instead of loosening crank arm bolts and extracting each crank arm. This bike has them install


2015-01-11 12.20.06 by Stuart Black, on Flickr

Shifting hasn't been an issue even with STI indexed front shifters.

You may also want to downgrade the front derailer. Shimano's more expensive derailers are marvels of engineering but awful derailers. They tend to be too narrow and too "sculpted" to work well with very wide gear ranges. They simply rub too much. Their less expensive offerings...Tiagra and below...aren't nearly as "marvelous" but they work better over a wider range of gears. You can try the 105 you have now but be aware that it can be finicky and difficult to adjust so that you don't rub in many useful gear combinations.
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Old 07-16-18, 10:53 AM
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Originally Posted by cyccommute View Post
Instead, I would suggest a external bearing crank like this one. It's competitively priced with the Sugino crank above. The chainline is more easily adjusted by moving spacers around from side to side. The crank is also much easier to remove and install than a square taper. You have to tighten a couple of pinch bolts instead of loosening crank arm bolts and extracting each crank arm.
Is there a name for this style of crank? What BB is used? I would probably look for something on used ebay but I'm not sure what to search for. Thanks for your help!
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Old 07-16-18, 03:14 PM
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Originally Posted by crandolph View Post
Is there a name for this style of crank? What BB is used? I would probably look for something on used ebay but I'm not sure what to search for. Thanks for your help!
External bearing or Hollowtech II. The "trekking" version comes with a 48/38/26 chainring set. I'd change out the inner ring for a 22. You could use a mountain triple (44/34/22) and just change out the outer ring as well. A 46 tooth outer with an 11tooth cog gives a nice high gear of about 115". A 44 tooth outer is a respectable 110" gear but the derailer might have issues with a ring that small. A 48/11 gives a 120" gear which is pretty tall for just about anything.
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Old 07-22-18, 11:50 PM
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Originally Posted by crandolph View Post
Is there a name for this style of crank? What BB is used? I would probably look for something on used ebay but I'm not sure what to search for. Thanks for your help!
Sorry was out for a few days. Yes the newer Shimano "trekking" cranksets are pretty nice. Reason I did not recommend them earlier is you are pretty much stuck with using Shimano's limited number of chain rings (versus the nearly unlimited options for old 110/74 BCD 5 arm cranksets), but that isn't a show stopper. I actually am using a Shimano MTB crankset on my touring bike and have made do just fine with their chain rings. I looked and did not see any Shimano Trekking Cranksets on e-bay. Plenty of Shimano MTB cranksets though. The difference is generally the number of teeth on the chainrings, the trekking will have more than the MTB.


The other reason I didn't recommend the Shimano trekking cranksets is that its nearly impossible to find in the US (we are all about road, tri, adn MTB and not touring)l but are available from European suppliers. Some to look at are Shimano XT FC-T780 or FC-T781, LX FC-T671, and Deore FC-T611, or even Alivo level FC-T4060 (lower quality than the others but still works). These all use external bottom bracket, which shouldn't cost more than $20 or $30. Have no idea what the cranksets cost, even if you can find them. I'm not having any luck locating any but the last one on the internet. May just need to go with the MTB crankset (if triples are even available anymore). Good luck.
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Old 07-23-18, 12:28 AM
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More questions: Chainring materials - is aluminum OK?
there are cheaper , softer and harder more expensive types of alloys
For all 3 rings?
because force is higher climbing on a smaller chainring , with less teeth,
steel has been offered..

What's up with ramping & pins? Necessary? On which ring(s)?
Indexed shifting depends on shifting aids, friction it's less important,

It's not needed on inner most chainrings,,


​​​​​​​....
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Old 07-23-18, 09:55 AM
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Originally Posted by Eggman84 View Post
Sorry was out for a few days. Yes the newer Shimano "trekking" cranksets are pretty nice. Reason I did not recommend them earlier is you are pretty much stuck with using Shimano's limited number of chain rings (versus the nearly unlimited options for old 110/74 BCD 5 arm cranksets), but that isn't a show stopper. I actually am using a Shimano MTB crankset on my touring bike and have made do just fine with their chain rings. I looked and did not see any Shimano Trekking Cranksets on e-bay. Plenty of Shimano MTB cranksets though. The difference is generally the number of teeth on the chainrings, the trekking will have more than the MTB.
If you are talking about Shimano "brand" chainrings, I would agree. But you won't find many (or any?) chainrings from Shimano in 110mm BCD.

On the other hand, it's relatively easy to find 104mm BCD 4 bolt pinned and ramped chainrings. Vuelta has flat ones...i.e. with out pins...in several different sizes. Black Spire sells pinned and ramped rings from 48 tooth to 32 in 2 tooth increments.

Originally Posted by Eggman84 View Post
The other reason I didn't recommend the Shimano trekking cranksets is that its nearly impossible to find in the US (we are all about road, tri, adn MTB and not touring)l but are available from European suppliers. Some to look at are Shimano XT FC-T780 or FC-T781, LX FC-T671, and Deore FC-T611, or even Alivo level FC-T4060 (lower quality than the others but still works). These all use external bottom bracket, which shouldn't cost more than $20 or $30. Have no idea what the cranksets cost, even if you can find them. I'm not having any luck locating any but the last one on the internet. May just need to go with the MTB crankset (if triples are even available anymore). Good luck.
Yes, they are hard to find in the US but you can find them elsewhere for a reasonable price. Or you can just order new rings.
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