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Low gears for Trek 520?

Old 05-06-19, 10:32 AM
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mars2020
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Low gears for Trek 520?

Hi, I'm a newbie but I read as much as I could and I appreciate all inputs.

I have a 2016 Trek 520.

- On Trek's web site archive, it showed the 2016 has Alivio front derailleur and Deore rear derailleur but searching Shimano's site showed several different 'Deore' and 'Alivio' derailleurs. How do I tell what model do I have? Anybody knows the details of my year?

- The 2016 came with 26/36/48 front rings and 9-speed 11-32 cassette. I like to get it as low as possible by replacing the rear cassette. What's the lowest I can go with the existing RD? I saw a 12-36 is available and also 11-40. I don't really care about the high gear, I'm not a racer :-)

- Will they work if I just replace the cassette? Or more exactly, will the existing RD handle the bigger cog?

Thank you so much in advance.
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Old 05-06-19, 10:59 AM
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You should easily be able to drop the 26 to a 24 (did that with my Surly LHT) and maybe even a 22. Cheaper solution than a new cassette and chain. A 22x32 is pretty darn low, especially if you are not doing any loaded touring.
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Old 05-06-19, 12:52 PM
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Thanks for the advice, appreciate it. I think I'll go with 22.
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Old 05-06-19, 03:50 PM
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Originally Posted by mars2020 View Post
Hi, I'm a newbie but I read as much as I could and I appreciate all inputs.

I have a 2016 Trek 520.

- On Trek's web site archive, it showed the 2016 has Alivio front derailleur and Deore rear derailleur but searching Shimano's site showed several different 'Deore' and 'Alivio' derailleurs. How do I tell what model do I have? Anybody knows the details of my year?
You can usually find the model number on the back of the parallelogram on the rear derailer and on the back plate of the front. You can then search for the model number on-line. You likely have a Shimano Deore RD-M591-SGS 9-Speed which is a good solid derailer.

Originally Posted by mars2020 View Post
- The 2016 came with 26/36/48 front rings and 9-speed 11-32 cassette. I like to get it as low as possible by replacing the rear cassette. What's the lowest I can go with the existing RD? I saw a 12-36 is available and also 11-40. I don't really care about the high gear, I'm not a racer :-)
You can use an 11-36 Sunrace 9 speed cassette so that you don't lose the high gear or go to an 11-34. A 36 tooth cog may have issues with the derailer, however, and it would struggle with a 40 tooth. You can use a Wolf Tooth Road Link if the derailer won't work with a 36. The Road Link says for 10 and 11 speed but I've put one on my Cannondale T1 with an older XTR and it works quite well. I would suggest you try your existing derailer unmodified with a 36 to see if it works as yours may have a slightly wider range.

As for the gearing, it is simple and easy to swap to a 22 tooth inner. You shouldn't experience any problems. I have modified a similar crank to yours to take a 20 tooth inner ring.

It was simple and it works well. My touring bike and several of my mountain bikes now have 20 tooth inner chainrings with 36 tooth cogs for a low gear of 15". On the touring bike, I can fly down hills with a 118" gear and crawl up the other side with that 15" gear.

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Old 05-06-19, 05:30 PM
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Thank you so much for your input. I appreciate it.

- didn't know the model # is in the back. Will take a look. Trek did say that the crank is Shimano M590.

- I just checked the M591 RD manual and it said it supports only up to 11-34. In your experience do you think 11-36 will work as manufacturer's spec must leave some margins? It also said the RD supports only up to 22T front chain wheel difference. Then if I put in a front 22 then my front chain ring will be 48-22=26.

I saw plenty of 22T front with 64mm BCD on Amazon.

Thanks again!

PS: by replacing the cassette with a larger low gear, is the B screw the only thing I'll need to readjust? I assume if I only replace the cassette then the chain could stay the same.

Last edited by mars2020; 05-06-19 at 05:36 PM.
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Old 05-06-19, 05:45 PM
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On my 2015 520 I have a 22 tooth chainring but I think 34 tooth cassette was largest could go when I looked up the derailleur. You may have to look up your derailleur to see if different.
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Old 05-06-19, 09:24 PM
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Originally Posted by mars2020 View Post
Thank you so much for your input. I appreciate it.

- didn't know the model # is in the back. Will take a look. Trek did say that the crank is Shimano M590.

- I just checked the M591 RD manual and it said it supports only up to 11-34. In your experience do you think 11-36 will work as manufacturer's spec must leave some margins? It also said the RD supports only up to 22T front chain wheel difference. Then if I put in a front 22 then my front chain ring will be 48-22=26.
I’ve successfully used a 46/34/20 which has the same chain wrap as you have. That’s without the Wolf Tooth modification It’s not been a problem. My current set up is a 48/34/20 that works well with the Wolf Tooth Road Link. The link makes the body of the derailer longer so it can wrap more chain.

I saw plenty of 22T front with 64mm BCD on Amazon.

Thanks again!

PS: by replacing the cassette with a larger low gear, is the B screw the only thing I'll need to readjust? I assume if I only replace the cassette then the chain could stay the same.
The derailer might work with a 36 tooth cassette but it might not. It’s hard to say. There is some wiggle room in the specs so it would be worth experimenting. The B screw is all you should have to adjust on the derailer. You might need a new chain but, again, you might not. Try it and see.
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Old 05-07-19, 09:48 AM
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Originally Posted by hillyman View Post
On my 2015 520 I have a 22 tooth chainring but I think 34 tooth cassette was largest could go when I looked up the derailleur. You may have to look up your derailleur to see if different.
Thanks for sharing your experience. I looked up the 2015 Trek 520 and it has the identical specs as my 2016. The same green color too.

So, you just replaced your 26T front chainring with a 22T and that was it? Anything else you needed to do? Does anything on the front derailleur need to be readjusted?

What are you running on the rear?

I need to get some tools to remove/install the crank and tools to remove the cassette lock ring...

Thanks again.
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Old 05-07-19, 12:35 PM
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I had them put on a set of mountain bike set chain rings when I bought new. I'm sure they had to lower front derailleur a little. To me the 520 comes too high geared for touring. But maybe just me.
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