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Anyone have good info on determining chain length on a MTB?

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Anyone have good info on determining chain length on a MTB?

19 Sep 2015 22:03

I'm moving from 32 to 28 teeth on my front chainring and want to see if I need to remove links. Rear suspension appears to be making it a bit more complicated than on a road bike due to the variable geometry. Anyone have good tips or a good article on this? I've found some stuff but it's as clear as mud to me.

Thanks!
User avatar red_flanders
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19 Sep 2015 22:37

What's your rear derailleur look like? Long cage, short cage, somewhere in-between?
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19 Sep 2015 23:12

if shimano......good start will be here

http://si.shimano.com/#categories/17

will write more later....just out the door to go see the new Everest Movie
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20 Sep 2015 04:25

Thanks both of you. It's SRAM X01, 1x11. Looks like short cage to me. I put in the new chainring. Took it down to Performance Bike (closest to me with a shop) and they were super cool, as these guys generally are. Asked them to have a look at my install and they ended up tightening up the crank after I re-installed it. I didn't know what torque setting to put on it. I did 30 and they recommended 40. Other than that, all good. Didn't need to take out any links.

They were free enough to do it right then and no charge. Nice.

Heading out to Marin (Olema) tomorrow morning, and looking forward to the extra low gears.
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20 Sep 2015 16:39

Awesome!

Have a good ride, RF! :cool:
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20 Sep 2015 19:04

great movie - i highly recommend it

ok
replacing the chain on a full sus mtb......
if you have the old chain you can just size off that one and cut to the same length

if not, or you have made some changes to the drive train in terms of chain rings, cassettes or rear mech you need to take into consideration the maximum travel of the rear suspension with respect to chain length.....ie you need to ensure your chain has enough length to work with the respective suspension of your bike

there are some frame suspension designs (single pivots especially) that when they reach full compression result in some chain growth (increased distance between the cassette and chainring)

we thread the chain through the large chain ring up from and largest sprocket in the rear (not through the rear mech) and add 2 links to size the chain

for a full sus bike you need to allow for ALL the travel in the rear shock
you can either completely deflate the shock and bottom out the suspension - a velcro strap or toe clip strap comes in handy here and then size the chain with this consideration
or
remove the lower attachment bolt of the shock, lift it out of the way, move the bikes frame to the maximum allowable movement and then size the chain allowing for that degree of movement

you should be able to cycle the suspension through all its travel without the chain becoming too tight If the chain becomes rigid before the suspension reaches the extreme of its travel you will have to add some links

just as an added note - there is more than one way to skin a cat.....

another popular chain sizing technique is
small up front, small in the back, threaded through the rear mech and then taking the size length to ensure the chain is not touching the pulley body on the rear mech

here is a nice video demonstrating that method
http://www.artscyclery.com/learningcenter/installshimanoroadchain.html
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21 Sep 2015 12:46

Thanks! Very good explanation.
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21 Sep 2015 18:27

Good call on the suspension stuff, JRS. (I don't own a suspension mtb., but the way it's being explained makes sense to me.)

Here's another video - I personally get a kick out of what jargon the pros use, how wordy they get, the way they look, and how they go about things. (Jargon alone can vary so much that you feel like you need to learn a whole new language each time you watch a new video.)

https://www.youtube.com/watch?v=OQ33HOy6thE
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Re:

26 Sep 2015 03:24

JackRabbitSlims wrote:...just out the door to go see the new Everest Movie
Not sure anybody ventures into this dark, greasy, and sometimes totally mentally exhausting place anyway, so we may be able to steer off course -

How did you like the movie? Was there anything about Everest you hadn't seen or read before?
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Re: Re:

26 Sep 2015 04:12

Tricycle Rider wrote:
JackRabbitSlims wrote:...just out the door to go see the new Everest Movie
Not sure anybody ventures into this dark, greasy, and sometimes totally mentally exhausting place anyway, so we may be able to steer off course -

How did you like the movie? Was there anything about Everest you hadn't seen or read before?


the movie was great thanks!

having read the book (into thin air) a few times, being a NZer & having been to everest base camp twice in the past 3 years - the movie pulled all that i already knew into a nice little, very exciting but sad, cinematic experience

if you get the chance, i highly recommend going to see it
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Re: Re:

27 Sep 2015 03:01

JackRabbitSlims wrote:the movie was great thanks!

having read the book (into thin air) a few times, being a NZer & having been to everest base camp twice in the past 3 years - the movie pulled all that i already knew into a nice little, very exciting but sad, cinematic experience

if you get the chance, i highly recommend going to see it


I've seen many documentaries (and read stuff) about Everest, being it seems to be more of a tourist attraction for the rich rather than an athletic endeavor these days Everest doesn't really appeal to me at all. But if the movie comes out on Netflix streaming (I won't have to pay extra since I already have it), I might see it.

Why do you keep on trying for Everest, or, do you? (If you want a challenge as a true climber I suppose you'd go for K2?)

My favorite climbing movie is Touching the Void, btw. (Would also prefer to admit that I am not a climber. :o )
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27 Sep 2015 04:00

i am not a climber - i just like trekking / hiking in the big mountains

i am not trying to go for everest and never will

the trekking in Nepal is world class and i love the experience of carrying all my stuff and spending a couple months in the himalayas trekking from village to village
the trek up to base camp is spectacular, especially up the gokyo valley and then over into the khumbu.....even better if you have time and trek all the way in from jiri rather than fly to lukla.
if you go in the off season (last time i went in the middle of winter) there are no tourists....

the actual everest base camp is not much at all....just a bunch of tents and whole bunch of tweaked out looking climbers - but, if you trek all the way to Gorak Shep (the last huts before base camp) you might as well go all the way to base camp for a look and a chat.

thats what i do :)

K2.....ahhhhh, no way
although i am looking at the trek into K2 base camp one day in the future when the political situation in pakistan chills out a bit, if ever

suppose to be one of the most incredible treks on our planet

touching the void is a great movie.
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30 Sep 2015 18:44

I ended up taking it the LBS and they didn't think I needed to remove anything. I still don't feel as though I have a great grasp on this.
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Re:

04 Oct 2015 17:50

red_flanders wrote:I ended up taking it the LBS and they didn't think I needed to remove anything. I still don't feel as though I have a great grasp on this.
Anyone with a full suspension bike here want to help RD out? (I don't own one, but I think I get the basic concept of it.)

If you post some pictures of your bike, and your understanding of how it's supposed to function, RD, we might be able to be confused together. Or, we might be able to figure things out on our own... you and I, mean. :)

Also - in order to lure some mtb bike repair people in here we'll probably/might need some 4:20, which I'm perfectly okay with their usage of. (Just cannot partake in with my current job seeing as we get tested.)
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