What length derailleur?

[Watchman]

Hi all,

I'm building a bike for my son based on a Planet X London Road frame/forks and I'm stuck trying to understand whether to use a short or medium cage.. It will be a 1x9 with a 32T chainring and an 11-32 cassette. For aesthetic reasons, I would prefer smaller but will obviously go with the advice of this forum.

Thanks.

[Watchman]

My wife's bike has the exact same gearing but appears to use a long cage. I could copy this without thinking but I can't really see the justification for the long cage.




And Planet X has a Shim 105 short for £20.

http://www.planetx.co.uk/i/q/RMSHOEM1055701/shiman...

[P-Jay]

Watchman said:

Hi all,

I'm building a bike for my son based on a Planet X London Road frame/forks and I'm stuck trying to understand whether to use a short or medium cage.. It will be a 1x9 with a 32T chainring and an 11-32 cassette. For aesthetic reasons, I would prefer smaller but will obviously go with the advice of this forum.

Thanks.

What derailleur are you thinking?

If it was an MTB it would be short cage territory easy.

[SoliD]

Just replaced my bike with a 105 5800 medium cage for a 50/34 - 11-32 cassette.

[Watchman]

P-Jay said:

What derailleur are you thinking?

If it was an MTB it would be short cage territory easy.

I don't think I understand the difference between a roadie and MTB type... unless it's to do with the shift lever, in which case the bike will have flat bars and an MTB shifter.

[rhinochopig]

Watchman said:

Hi all,

I'm building a bike for my son based on a Planet X London Road frame/forks and I'm stuck trying to understand whether to use a short or medium cage.. It will be a 1x9 with a 32T chainring and an 11-32 cassette. For aesthetic reasons, I would prefer smaller but will obviously go with the advice of this forum.

Thanks.

I would consider 36 cassette if a) your son will be riding lumpy terrain and or b) he's young or not a strong rider.

[Watchman]

Yes, that's good advice thanks, however I may actually leave the cassette as is and see if I can get a smaller chainring. I prefer smaller sprockets really - many benefits including shorter chain and better ground clearance (although I don't think that will be a problem).

That also should mean I can use a shorter cage I guess.

[BadgerBenji]

The length of cage is decided by the difference in Terry on the cassette plus the difference in teeth on the front chainrings, some also have a maximum size rear sprocket.

So in your case you have a difference of 21 teeth, you will be fine with a short cage rear mech. I'm running a short cage mech on my 1x10 setup which has a 11-36 cassette and a 32 tooth oval ring no issues. I always prefer the shortest rear mech I can use as chain tension is better.

[gazza285]

My 1x9 cyclocross bike has an 11/32 cassette, I'm using a 105 short cage derailleur, trouble free so far...

[Watchman]

Fabulous news gents. Many thanks for that.

I think I've landed on a 30T chainring (been experimenting with some of the bikes in my garage - plenty to choose from) so this will make it even easier for my son to pedal and makes the case for a short cage even stronger.

[rhinochopig]

Watchman said:

Fabulous news gents. Many thanks for that.

I think I've landed on a 30T chainring (been experimenting with some of the bikes in my garage - plenty to choose from) so this will make it even easier for my son to pedal and makes the case for a short cage even stronger.

Got a link to the 30t 9 speed. I was looking a while back for the 24" wheel full suspension bike I built for my 7 year old and could only find 10sp narrow wide ones. No 9sp versons

Eta ignore me, found some.

Edited by rhinochopig on Tuesday 19th April 20:59

[Watchman]

Truth is, I am not sure whether what I've ordered is right. It doesn't specify in the auction to be fair.

See if I made mistake. Ebay 172070744785

[Herman Toothrot]

Single chain ring a short cage like a Zee would work fine.

[Watchman]

Thanks - there's some differing opinions on using the Zee in a 9-speed config. I may buy one for my own 10-speed MTB but I don't think there's enough of a need for a clutch mech over 9-speed shifting on my son's bike.

[rhinochopig]

It seems most are 9, 10, and 11 speed compatible so you should be fine. I ordered a 30T superstars one for £25.99.

[With these feet]

On both my bikes Ive found with my XT the clutch mech makes the shifting stiffer and less reliable - more susceptible to missing changes especially down. 1x10 on both, 30 - 11/42 & 34 - 11/36 setup with medium cages.

[Watchman]

Thanks for all the suggestions.

A bit of context - I am trying to build a quality bike for my lad (who is currently 11yo) "economically", and I may not give him the completed bike until his birthday at Christmas or possibly even next year. His current bike has "growth" remaining and the one I'm building will be a bit big right now.

By buying parts much earlier than needed allows me to take advantage of offers. His use is very much tramping around with friends, and weekend family rides with the rest of us. The bike will be a "dirt" bike but not for MTB use. We tend to ride in places like the family trail in the Forest of Dean, and other converted railways. Occasionally cycle paths but we're on the dirt often enough to warrant some CX tyres.

A clutch mech isn't necessary in this context but I like the idea of them in principle so I will see if one comes up at a good price.

So far I have wheels, tyres, tubes, hydraulic disc brakes (complete with a choice of two sizes of rotors), crank, BB, chainring (on order), seat, handlebars, stem, grips.

I'm waiting for Planet X to offer the "Zesty Lime" London Road frame at a better price (the blue one is half the price of the lime one but my son loves bright green), and I'm yet to decide which derailleur (hence this Q) and lever but apart from that, it's shaping up.

Thanks again, everyone.