Decathalon Triban 520 Gears

majster

Hi there

Just got my son a Triban 520. It’s a lovely bike with Sora shifters, derailleur and a SunRace 12-25 rear cassette

It’s quite hilly where we live and he’s new to cycling so want to get the gearing lower for him, ideally with some that goes down to 32 or 34 T on the back

What do I need to achieve this

Any cassette recommendations please? Will the rear mech need to be changed also?

Thanks

Matthewfalle

You’ll need a new cassette, new chain as it will need to be longer and, dependant on what mech you have on there, maybe a new mech.

Can you find out if you long, medium or short cage- offhand some shortcages will allow up to 30 teeth, otherwise pop a medium cage on there and all should be good.

Merlin have a Shimano sale on at the mo if it helps.

Just go Sora cassette and a KMC chain and it’ll work lovely.

N0bodyOfTheGoat

http://sheldonbrown.com/gear-calc.html

Swapping the cassette to an 11-28 will give that triple chainring 30/39/50T Triban (28.3-119.9) a very similar gear inches range to my Cube (28.0-119.9), which has 34/50T chainrings and 11-32T cassette, with a 25mm rear tyre.

Sticking with a 28T largest sprocket also means there are very good odds of the existing rear derailleur working.

If the chain length was set to snugly work with the existing gear setup, it will need extending (2 full links?), to prevent catastrophic damage should 50/28 ever be accidentally selected.

arlowood

You can source a Shimano HG50 11-30 9 speed cassette from SJS Cycles

https://www.sjscycles.co.uk/cassettes/1 ... -cassette/

That should give him plenty low enough gearing with the triple chainset. Also the fact that it is a triple suggests that the rear mech will probably be a medium or long cage so it should cope with the 30 tooth largest sprocket. Give Decathlon a call if you are unsure which rear mech model has been fitted.

As suggested above you will most likely need to fit a longer chain. If so you can use the following to calculate the optimum length

http://www.lightreel.com/chain-gear-calculator.html

dj58

Shimano specs. suggest it to be a RD-R3000-GS for a triple set up. Max low sprocket is 34T, Min low sprocket 28T.
http://productinfo.shimano.com/#/lc/2.4/sora/3x9

majster

So would an 11-34 cassette such as the one below fit, do you think? Prefer to go for 34 if possible to make it as easy as possible for him

Thanks

https://www.sjscycles.co.uk/cassettes/1 ... -cassette/

dj58

Yes, if you look at the cassettes available in that line up chart you have the choice of 11-28, 11-32 and 11-34T for the CS-HG400-9 cassette. As mentioned above you will need a longer chain. You will need to adjust the B-Tension screw on the RD for the upper guide pulley wheel to clear the 34T sprocket when in the 30T - 34T combination.

majster

Thank you. I am going to purchase the 11-34 cassette. Thank you for the Merlin suggestion. Quite a good sale on at the moment

I have selected this chain - https://www.merlincycles.com/shimano-hg ... 44671.html

Is this the right one? Can you recommend a closing link for this? Would any one work or do I need a specific type?

Sorry for all the questions - really appreciate the help

arlowood

Majster wrote:

Thank you. I am going to purchase the 11-34 cassette. Thank you for the Merlin suggestion. Quite a good sale on at the moment

I have selected this chain - https://www.merlincycles.com/shimano-hg ... 44671.html

Is this the right one? Can you recommend a closing link for this? Would any one work or do I need a specific type?

Sorry for all the questions - really appreciate the help

The one you link to would be fine but if it were me I would be looking to buy a KMC 9-speed chain

http://www.wiggle.co.uk/kmc-x9-93-9-spe ... 1252028062

Comes with a "missing" link that makes fitting and splitting the chain much easier IMHO than the Shimano version. KMC chain is also a bit cheaper

dj58

I agree with arlowood above, buy a 9 speed KMC chain as it comes supplied with quick link.

majster

All ordered including KMC chain. Thank you for all you help and guidance, otherwise would have struggled!

majster

Ok so here’s the update, fitted the 11-34 cassette with the chain and works well, however, we are planning a long tour ver the Summer with fairly hilly terrain and also luggage to be carried

Hence want to drop the gearing further

I’d rather he not struggle and be out of cycling

He has has triple crank at the front

Any suggestions how I can change the current smallest 30T chainring to say a 26? What would fit the existing crank system on the Triban?

chippyk

Our son has Sora on his Giant, I think the inner ring is 74mm BCD, make sure you get the right 4 arm or 5 arm one. You could be able to go as low as a 24, which with a 34 on the back is a very low gear. You may need to check the mech can handle that small a chain rings

arlowood

Yup - 24, 26 and 28 tooth rings available with 74mm BCD and 5 arm design to fit your Sora triple chainset.

https://www.sjscycles.co.uk/chainrings/ ... ng-silver/

However I share Chippyk's concerns about whether the rear mech will cope with the potential 24/34 combination

I have seen instances where people have opted to switch to a MTB rear mech which will be fine for a 9-speed set up and will definitely cope with the spread of gears. However some of the suitable mechs do not come with a barrel adjuster like on your road mech and you would need to consider an in-line adjuster to allow you to set up the indexing.

majster

Is there any way I can check what is the lowest chainring the sora rear mech can handle (it’s the long cage rear mech that I have)

I’d be happy to for the 26T chaingring ie. aiming for 26/34 combination. Is this possible with rear mech?

arlowood

Majster wrote:

Is there any way I can check what is the lowest chainring the sora rear mech can handle (it’s the long cage rear mech that I have)

I’d be happy to for the 26T chaingring ie. aiming for 26/34 combination. Is this possible with rear mech?

Had a go with the chain length calculator I posted above inputting the two smallest chairing sizes (26 and 30t) into the parameters and keeping everything else the same. Comes out with exactly the same chain length. Not surprising I guess since the main concern would be a potential cross chaining event with the 50t chainring and the 34t rear sprocket.

One other empirical way is to look at the way the rear mech sits when you have the 30t/34t combination selected on your current set up. Is there a decent gap between the top jockey wheel on the rear mech and the 34t sprocket on the cassette. If so you could probably get away with it. The smaller 26t chairing will mean that the rear derailleur will have to pull back a bit more to maintain the tightness on the chain and that will probably push the top jockey wheel closer to the cassette sprocket.

If the jockey wheel is too close you can adjust it away from the rear sprocket by winding in the B-screw. Attached link to adjustment video

https://www.youtube.com/watch?v=QRhKaZd6GWQ

At the end of the day it might just be worth a suck it and see approach. The outlay on the 26t chairing is minimal and if it works you're good to go. If it doesn't then you might have to spend a bit more (new RD??)

dj58

^^ This, is what I would do in your situation, the cost to try it out is negligible, try it with the bike in your work stand and observe what happens in the three largest rear cogs.

majster

Thank you with the detailed response. I will order the 26T ring and see how I get on. Thanks again

majster

Ok, sorry it's taken so long to come back but only just got round to doing the ring swap. So I have changed the inner ring to a 26T which works well. However, when on outer big ring at front and big at back the derailleur is very stretched and I am worried it will snap - I know you would never want to use this combination, however, my young son will be using the bike so want to be prepared in case.

If I lengthen then chain to accommodate big-big then chain too loose on other gears

Is there anyway I can change the outer big front ring to something slightly smaller to make all gears works? What Sora Outer ring would work ?

Many thanks

Mad_Malx

Majster wrote:

Ok, sorry it's taken so long to come back but only just got round to doing the ring swap. So I have changed the inner ring to a 26T which works well. However, when on outer big ring at front and big at back the derailleur is very stretched and I am worried it will snap - I know you would never want to use this combination, however, my young son will be using the bike so want to be prepared in case.

If I lengthen then chain to accommodate big-big then chain too loose on other gears

Is there anyway I can change the outer big front ring to something slightly smaller to make all gears works? What Sora Outer ring would work ?

Many thanks

If he's currently on 30/39/50T then it should be easy to swap the outer 50 for a 48 or 46. Just need to match arms and bolt centre diameter (BCD) for the outer. Since the cassette is now 11-32 the 50 front is too big anyway (many half-decent cyclists are happy using a lower top end than this).

However, there will now only a small change at the front which is making the big ring a lot of faff for only one and a bit more gears.
Might be easier to go double with something like 26-42 up front. The front shiffter should still work if you set the limit screws. A 42-11 is a reasonable high gear for a youngster.

majster

Do you think I could trouble you for a link for a suitable smaller outer ring that would work on the Sora system already. I think for simplicity of installation may stick with a triple.

This would really help me out as there seems to be a myriad of options. The current Sora seems to be R3000 I think

milemuncher1

Majster wrote:

Hi there

Just got my son a Triban 520. It’s a lovely bike with Sora shifters, derailleur and a SunRace 12-25 rear cassette

It’s quite hilly where we live and he’s new to cycling so want to get the gearing lower for him, ideally with some that goes down to 32 or 34 T on the back

What do I need to achieve this

Any cassette recommendations please? Will the rear mech need to be changed also?

Thanks

I’ve changed the rear cassette on my Triban 520 for an 11-30. Not only does that give you a very low ratio on the granny ring and 30 tooth sprocket, but the Shimano 11-30 cassette I use has a nice ratio progression as well. Not many people will need anything bigger with a 30 tooth sprocket and the granny ring, IME.

Mad_Malx

^We've moved on. He's already changed the little ring and cassette and is happy with the low gears. He's now looking at the big ring.

Mad_Malx

Majster wrote:

Do you think I could trouble you for a link for a suitable smaller outer ring that would work on the Sora system already. I think for simplicity of installation may stick with a triple.

This would really help me out as there seems to be a myriad of options. The current Sora seems to be R3000 I think

The Sora 3030 is the triple, and has I believe a 130 mm BCD (but check).
If that's correct then the 46T in this should work

https://www.ebay.co.uk/itm/Bicycle-Stro ... 1499347804?


There are lots of others, and as I said I'm not convinced it's worth the bother.

milemuncher1

Mad_Malx wrote:

The Sora 3030 is the triple, and has I believe a 130 mm BCD (but check).
If that's correct then the 46T in this should work

https://www.ebay.co.uk/itm/Bicycle-Stro ... 1499347804?


There are lots of others, and as I said I'm not convinced it's worth the bother.

I’d agree.