UKC

My lad has his first full sus MTB in the form of a Giant Trance. It is stock set up with a single chain ring on the front (with a chain director plated off the bottom bracket) and 9 spd cassette. It means it doesn't really have the range for the rises we are starting do together. It means getting off and pushing sometimes (I treat that as a blessing!).  So I see options as converting the front end to a triple or going for the more contemporary mega cassette on the back and keep a single on the front. I've not really any experience of the latter set up and needs. Thoughts on which route  to go down and the relative costs (parts only). Thx.

Look at a 12 speed cassette. You’ll most likely need a new derailleur also to accommodate it, but it should be sufficient for the steepest of hills. No need to go back to a triple. A double if you must, but the frame may not have fittings for a front mech...

Switching to a 1 by was the best change to my biking in recent years, on par with getting my first dropper post. Much simpler, loosing a lever and derailleur, getting rid of all those duplicate or unusable combinations from a 3by7. 
I’d consider a 11 speed cassette, with the right size chain ring there should still be a useable granny gear, and the current 12 speeds are pricy due to their newness.

Definitely don't go triple. 1x9 is a bit odd. what's the range on the cassette? If the big sprocket is a decent size (42+), you could consider changing to a smaller front ring too - what size is it now? 

This is an easy issue to sort, it just depends on how much cash you want to throw at it. You haven't said what range his current cassette is but I'd guess not wide. The cheapest option is to buy an 11-40 cassette for about a tenner from eBay and a cheap narrow wide 28 front ring for about £5. You woul also need a derailleur extender to clear the wider cassette. These are only a couple of quid from eBay. You could improve things a lot for less than £20. Or, do it properly and buy a 10 speed set up, new mech, chain, cassette, shifter, possibly a new front ring (I'm assuming it doesn't have a narrow wide if it has a chain guide as I have never needed one). This set up could be done for about £100-£120. I don't think you can go 11 without a new free hub but might be wrong. Let me know if you want me to send some links. I've done the 9 speed wide range setup to my wife's bike and it works a treat.

a 1x 10 or 11 cassette with a 42-11 and a 34 to 30t narrow wide front ring, depending on strength, wheel size and where you live, as long as it's a clutched mech. 

I switched from 2x10 to 1x11 11-42 by 32 on a 27.5 trail bike and didn't feel I lost much other than spinning out downhill on fireroads. 

Hope all that makes sense

9 speed is junk the chains are notoriously fragile, either go back to an 8 speed with a triple which is indestructible and the indexing easy. Or upgrade to 10 speed with an 11-42 cassette and a 30T front ring or smaller to get up the hills.

Never encountered especially fragile 9 speed chains. Why should they be more so than 8 or 10?

This is likely to end up more expensive than people are suggesting unless your son just has a unusually small range cassette or a large front ring.

Changing to 10+ speed cassettes will likely involve a new rear wheel on top of the new shifter, chain and mech.

You can fit a 10 speed cassette onto a 9 speed free hub. I've done it. However, for cheapness an 11-40 9 speed and 28/30T front narrow wide is a really cheap fix but looses some top end although not too much.

Surely that setup would leave you spinning out massively. I have an old school 3x9 with a 11-34 cassette and a 22-32-42 up front and find myself spinning out down moderate hills and very rarely using the 22 up front. And I'm by no means a strong rider, although I am running smaller 26 inch wheels and the OPs son is likely running 27.5 of 29s and it all seems easy compared to road bike gearing.

This is a full sus we're talking about remember, so it really depends on how much riding the OPs son is doing on trails where they're spinning the highest gear and how much help they need uphill. My wife's full sus has an 11 -40 reR and a 32 up front with 26" wheels and she rarely struggles to climb anything and rarely runs out of gears at the high end. 

Not sure why this would change a great deal, if anything a more gravity orientated setup would show up the short higher range as he's be descending faster. But a full sus could be a

Anyhow, just looking at how cheap narrow wide chainrings are on ebay now, the OP could pick up a few different sizes for very little and give it a go.

If I had a 40 out back and a was determined to go 1X I think I'd look at a 34 and 36 for the front, probably a 34 if on bigger wheels. But IMO, without a massive cassette out back like the 10-50 SRAM Eagle I'd consider a 1X setup a compromise. I'm not fully onboard with 1X in the lower price range as my front mech and shifter etc cause so little trouble and don't really weigh much so I can't see the problem.

So what exactly is the current gearing?

Up front: 28, 30, 32, 34t ?

Out back? what range cassette is it currently?

Does he spin out on the way down?

26 or 27.5 wheels?

And is it Shimano or SRAM system.

In reply to :

In reply to gethin_allen:

blackmountainbiker is right at what he is getting at - depends on what type of riding/trails the OP is doing.  Fulls sus 'usually' need lower gearing to help get the bike winched up the hill.  And the best adopted gearing will depend on how fast they are on the downs.

I ride a 1x10, and my highest gear is 30-11 - which is a smidge too low for sections of the road-commute I do. 

When actually hurtling downhill off-road though, I'm not really pedalling, so don't really miss it - only occasionally on some fast firetrack stuff.

Uphill, I've got 30-40 as my lowest which is plenty low - and useful when towing the kids' trailer.

I'd consider going to a 32/34 up-front, but I don't think my frame could take it (Cannondale BotE) as it's got a wide rear for the 27.5+ tyres.

Once you've worked out what the current system is, use this to work out cuuretn range and the impact of any changes or upgrade options:

http://gears.mtbcrosscountry.com/#26I1I1

(can be a bit fiddly, but persevere)

My 1x set up on full-susser gives ratio range (easiest, low number to hardest, high number)

0.72 to 3.69

on my 1x hardtail it is:

0.79 to 3.32

You got my point exactly. I run a 30 up front and an 11-50 up front on my Trek Remedy full-suss and as I never use it for any substantial road riding I never feel I run out of gears and it is all I need for up hill. I think if you need a bigger gear downhill off road you need to be sponsored!

thanks for all the info ...now need to decipher into a solution. The current set up is 40F and 11-34R so i had already done some maths on what might work...its gonna be more a case of what fits without blowing more than small african nations wealth.

40t on front?

If that is right, then I pity the poor lad on a 1x! No wonder he is finding it tough.

The typical range on MTB 1x front is 28t-34t (some do go as big as 36t) , with 'most' people settling on a 30t or 32t, assuming rear biggest gear is in the range 36- 42t (or bigger)

I'd try him to a 30t or 32t front, without changing the rear at all. 

Nobody needs a 40/11 on a mountain bike being ridden off road. Just get an 11-40 from ebay (£12) a 32t narrow wide ring (£5), some spacers (£4) and a derailleur extension (£2) and he will be fine and all for less than £25 - I have done this on my wife's bike. If he needs it a bit easier on the hills get a 30T front ring.

Jesus! Who created that? Must be set for roads or flatlands. Swap to 30 or 32 on front for starters, and you may get away with what you have for now, but something a bit bigger on the back would be good. 

I know, its a bit bonkers on an MTB like a Trance. The poor lad must have been suffering, lol.