Drivetrain concerns

Pedaltothemental
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Drivetrain concerns

Postby Pedaltothemental » Fri Jun 09, 2017 7:55 pm

Hi all, this is my first post on the forum. I'm starting off on the sport of mountain bikes and just bought a 2nd hand 2008 giant trance x1.

The bike has been well ridden by the previous owner and its obvious that the sprokets are in need of replacing. A couple are worn down quite badly.

My question is when replacing the sprokets does the cassette and chain also need doing at the same time?

Are there any suggestions on what brands to look for or avoid? How about a single sproket conversion?

Any advice would be appreciated. Thanks in advance, Jack

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Duck!
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Re: Drivetrain concerns

Postby Duck! » Fri Jun 09, 2017 10:32 pm

if the chainrings are worn, then it's certain the chain and cassette are also worn. However, looks can be deceiving; the chainring teeth do have quite complex shaping and deliberately uneven profiling to aid shifting, and these can appear worn to the untrained eye.

You should be able to get replacement chainrings; if not exactly the right ones, there will be something simlar available; if my memory is correct that should be running Shimano M770 XT 9-sp. Shimano and SRAM chains & cassettes are interchangeable, but I find Shimano chains tend to be better wearing, which will improve the life of the other bits too.

To be honest, I'd stick with the 3x that's on it; you get a better mid-range spread of gears and also the extended range afforded by both the small and big rings. 1x will either give you a good mid-range (tight cassette) with shortcomings at either end, or you can recover some low range with a wide-range cassette, but you blow holes in the mid-range and lose the top end completely.
I had a thought, but it got run over as it crossed my mind.

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bychosis
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Re: Drivetrain concerns

Postby bychosis » Sat Jun 10, 2017 9:08 am

Worn chainrings are usually identified by shark fin profile. If they are mostly symmetrical it may not be too worn.

I ran a single ring front on 9 speed for a while and found the range (using a 32 tooth front on a 26" bike) suitable for all but the very steepest sections, typically I could ride most sections on my local trails with an 11-28 cassette and once I went to 11-34 only ran out of gears in a marathon event where walking was a quick as pedalling but gave my legs a rest. I've since switched to a 36 tooth front and 11-42 11 speed rear mostly to get more top end speed, although it has also given me another power gear.

Note: 'sprockets' usually refers to the rear gear (individual or as part of a cassette) while chainring is the front.
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trailgumby
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Re: Drivetrain concerns

Postby trailgumby » Sat Jun 10, 2017 11:11 am

I'd replace middle chainring, cassette and chain. Big and small chainring are less likely to have been worn as the middle ring is the one that cops the most work on a 3x system.

Regarding drive train life I have gotten into the habit of running 3 XTR chains per bike. When one gets contaminated, the next one goes on while I clean the first. Chains are cheap, cassettes and chainrings are not, and how well the chains wear drives the wear in the rest of the drivetrain. By doing this I triple the life of my drivetrain and as Duck! has said, Shimano lasts longer than SRAM, which is made from cheese.

I'm not sure if XTR/Dura Ace 9-speed chains are still available. You can't get 10-speed any more so I've been using KMC X10SL on my 2x10 Scalpel and my roadie, and they've been quite OK. I'm not sure of the KMC 9-speed chains - my only experience of them was on a bike for my son, and it broke but I am not sure how much work it had done. A fair bit, I suspect.

I have a stockpile of XTR/Dura Ace 9-speed chains and if you are interested I could sell you some. I also have some other 9-speed parts but haven't decided what I'm doing with the bike yet so will hang onto those for the time being.

Pedaltothemental
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Re: Drivetrain concerns

Postby Pedaltothemental » Sat Jun 10, 2017 11:58 am

Thanks alot for the replies.

Having a close look at the chain rings the large and middle chain rings both have a couple of teeth that appear to have chipped off to about half the size of the others.. with this in mind I assume I should probably replace all 3.

Thanks for the offer for the chains trailgumby, I would definitely be interested in getting 1 or 2 off you and it sounds like your method of running a couple is a good idea. After searching prices for chain rings and cassete I certainly don't want to be replacing them too often!

Cheers

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bychosis
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Re: Drivetrain concerns

Postby bychosis » Sat Jun 10, 2017 1:39 pm

Pedaltothemental wrote:Thanks alot for the replies.

Having a close look at the chain rings the large and middle chain rings both have a couple of teeth that appear to have chipped off to about half the size of the others.. with this in mind I assume I should probably replace all 3.


The 'chipped' teeth could well be the shifting teeth. There are a few teeth of a different shape grouped around the ring so that the chain can easily ride up over them or drop off when shifting. You will find the correspond to the pedal stroke being at top bottom and are probably near a pin in the back of the ring designed to help pick up the chain for an up shift.
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RonK
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Re: Drivetrain concerns

Postby RonK » Sat Jun 10, 2017 1:55 pm

It's hard to convince people that modern chainrings do not have a full set of perfectly formed teeth.

It's your money but before you rush to replace them it would be sensible to make they are actual worn.

Try comparing them to other bikes or new chainrings.

If the driveline is not slipping or unduly noisy it probably needs no more than a good clean/lube/adjust.
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Pedaltothemental
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Re: Drivetrain concerns

Postby Pedaltothemental » Sat Jun 10, 2017 4:58 pm

After reading these posts again I had a look at my friends giant talon and it had no teeth missing on the chain rings. However, after looking up 'middleburner' chain rings on google this is how they are meant to be - so thanks to you all. :D

Cheers

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Duck!
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Re: Drivetrain concerns

Postby Duck! » Sat Jun 10, 2017 7:16 pm

Shifting teeth will occur in groups of between three and six teeth, in a pattern that is repeated two or three times around the chainrings. Each cluster of shifting teeth will have one or two very short teeth, a couple of medium-height ones, often with a taller one in between that matches the height of the "normal" teeth between the shifting gates.
I had a thought, but it got run over as it crossed my mind.

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