Smaller single 152 chainset help please.

oxoman

My youngest has done a couple of harder trails recently and is struggling with his 32 single front to 36 rear. Currently running 10 speed Deore on 24" so can't really fit a bigger rear cassette ? I'm assuming. So looking at fitting smaller front if possible, I know there's a few people on here who modify smaller bikes heavily so advice please gents. Looking at cheaper options as I suspect by next Xmas he will be on a 26" full sus if I can find one at the right price.

Steve-XcT

Either a smaller front chain-ring or bigger rear big cog .... or both ?

We used an intermediate setup this weekend.... The 32T from his 20" er and 14-28 on his new cannondale 24
That definitely required some pushing up hills or Dad assist when on firetrails where I can ride alongside.

Next week he'll have a 1x10 on the front (I shortened some SRAM 600's) and a 11-36 on the back and hopefully if someone manages a 40T expander on the back.

Technically (I think) the easiest is with a XT 11-36 cassette for the expander as you simply take off the 12T and add an expander ring and bigger lockring. From what I understand some others can involve drilling out the cassette pins and or adding a ring in the middle..

oxoman

Hi Steve the bike already has a 36 on the rear so wouldn't be any good as the same, the problem I have is that whilst I can go for a smaller chain set up front I would have to get the cranks shortened unless somebody knows of something better. I'm taking him to Llandegla on Wednesday so will see how he copes, suspect I may be assisting occasionally.

Steve-XcT

oxoman wrote:

Hi Steve the bike already has a 36 on the rear so wouldn't be any good as the same, the problem I have is that whilst I can go for a smaller chain set up front I would have to get the cranks shortened unless somebody knows of something better. I'm taking him to Llandegla on Wednesday so will see how he copes, suspect I may be assisting occasionally.

I shortened some SRAM's, I'm still waiting for the taps to be delivered to put in the thread but... here they are with a 30T


I left the 68BSD mounts on the back (hardly worth grinding/filing for 5g) so you could put on a real granny ring like a 22T....

Anyway, they aren't perfect, the holes are not 100% centred but they are straight, I just used a battery powered drill (though a pretty meaty one) and 5,9 and 13mm bits. I made a jig to hold them from some 18mm plywood - I'd probably do better a second time.. but they are perfectly serviceable.

All in all a lot easier than I thought... after all your just drilling 2 holes!

You're up against time for this weekend though... unless you have a tap wrench... (or damn the cost)

By my calcs: Your current 1st is 0.8888 with 32/36(compared to 0.75 you'd get on 30/40)

That's a reasonably significant difference. By comparison a 24/28 (as fitted to my sons as the easiest gear when it arrived) would be 0.857.
Just going from a 32 to a 30 up front would be 0.888 - 0.833
Just going to the 40 on the back 0.888 to 0.8

oxoman

Shortening the cranks was not really an option I wanted to do if I can help it, although I could do it at work using the miller or radial drill easily enough. Putting a 40 on the back makes the rear mech lower down and more susceptible to catching stuff as he rides along given only 24" wheels. I'm currently looking at possible individual sprockets with either correct centres or enough meat on them to redrill to correct centres, either way it won't get done for tomorrow,s trip to Llandegla.

Steve-XcT

oxoman wrote:

Shortening the cranks was not really an option I wanted to do if I can help it, although I could do it at work using the miller or radial drill easily enough. Putting a 40 on the back makes the rear mech lower down and more susceptible to catching stuff as he rides along given only 24" wheels. I'm currently looking at possible individual sprockets with either correct centres or enough meat on them to redrill to correct centres, either way it won't get done for tomorrow,s trip to Llandegla.

What cranks are you running?
Mine have the granny 68 BSD on them even though its not used ..
If yours are similar why not just put a 22T on instead of the current 30 ?

My philosophy is its always imperfect because we are forced to use components designed for adult bikes so you just do the best within the constraints ...

oxoman

Took him to Swinley forest in the end due to the dodgy weather in Wales, whilst he loved it he found the short sharp climbs a bit of a struggle. Going down the LBS tomorrow to try and find something compatible, the running gear is deore sadly the front crankset is a bespoke merida,s one.

Steve-XcT

oxoman wrote:

Took him to Swinley forest in the end due to the dodgy weather in Wales, whilst he loved it he found the short sharp climbs a bit of a struggle. Going down the LBS tomorrow to try and find something compatible, the running gear is deore sadly the front crankset is a bespoke merida,s one.

Does it has removable chain-rings ? What pattern/BSD ???

Couple of options ....
a) Just change the crankset
I considered drilling out the riveted chains on the Suntour that came with his Cannondale.... not impossible but I still needed to shorten them as they are 152mm and he needs about 10mm less.

The SRAM S600 is the crankset of choice for shortening as its solid (not hollowcore) and flat and wide at the bottom.
(Even if you aren't drilling the raised bit on say a S650 it still makes holding it in a vice a step harder)

He theoretically should be about 141mm according to a chart bit I drilled at 142.5mm (like buying kids shoes ).
I finally got the tap wrench I was waiting to be delivered and tapped out the pedal screws last night.
I put it all together and it's pretty good.... I'd do it better a second time though.

You can get the SRAM's for £30-£35 with 42-32-22 steel rings (square taper is harder to find than splined BB but ...).

I spent as much on the pedal taps and tap wrench as the cranks but you are welcome to borrow them ... for postage or meet at Swinley one weekend ?

You could run this as 2xX (32-22) on anything between 7-9 speed ... and take a chance with the 10 speed chain (I'm guessing you already are with the Merida chainset) ? Or try just the 22 ...

b) Find a chainring
Of course that depends on the Merida crankarm fittings....
I've got a spare 22T 4hole- 68BSD ... but if you have/had a "standard" type fitting you have a fair choice.

oxoman

The main problem is it's 1 x 10 with 32 up front. The hole centres look around 70mm with measuring accurately, nipping up to the LBS shortly to see what they have. Another thing I have to look at now is his forks, going to either get air version or reduced strength springs.

Steve-XcT

oxoman wrote:

The main problem is it's 1 x 10 with 32 up front. The hole centres look around 70mm with measuring accurately, nipping up to the LBS shortly to see what they have. Another thing I have to look at now is his forks, going to either get air version or reduced strength springs.

If your 70 then good chance its probably 68 if it's four mounts???

If that's the case your welcome to try the 68BSD 22 tooth I have from the SRAM 600.(its easy to post) .. and see how 22T feels for him.
Based on how that feels for him you might look at something between 22 and 32 ....

oxoman

LBS has just told me I'd measured it wrong it's 104 not 74 I had measured it from hole to hole and apparently you measure hole to hole across the centre. Every days a school day. Just been given a 2nd hand 28t chainring to try him on so will see how he goes.

Steve-XcT

oxoman wrote:

LBS has just told me I'd measured it wrong it's 104 not 74 I had measured it from hole to hole and apparently you measure hole to hole across the centre. Every days a school day. Just been given a 2nd hand 28t chainring to try him on so will see how he goes.

Trail and error is probably key.... I know when I am doing "Dad Assist" I'm not actually having to push that hard... he's still doing 90% of the work ... so the small difference may be all he needs.

oxoman

The Dad assist was ok on wider trails but now that he is progressing to harder stuff with a lot of singletrack it becomes hard to help. Plus he hates me pushing anyway, I tend just to remain him to change gear because he's still got 2 left to go, get the same issue going downhill as well. He's ok on his road bike but still struggles a bit get the right gear at the right time, but at least he can actually use them on this bike from day one I had to modify his old 20"giant to triggers as grip shift was useless. Practice makes perfect as they say.

Steve-XcT

oxoman wrote:

The Dad assist was ok on wider trails but now that he is progressing to harder stuff with a lot of singletrack it becomes hard to help. Plus he hates me pushing anyway, I tend just to remain him to change gear because he's still got 2 left to go, get the same issue going downhill as well. He's ok on his road bike but still struggles a bit get the right gear at the right time, but at least he can actually use them on this bike from day one I had to modify his old 20"giant to triggers as grip shift was useless. Practice makes perfect as they say.

I didn't mean Dad Assist is a desirable condition What I mean is my experience is you are pushing less than you might think. My experience on even the 1:4 firetrails at Swinley (and I have a specific one in mind) is a lot of the effort is actually keeping your bars straight ... and the amount your hand is pushing is pretty small... just a top up.

Based on that I figure that you might not need a really radical change in gearing...just a small bit of extra?
From your present 32T it might be that 28T is just enough difference rather than jump down to a granny 22T ?

I'd be interested to know how it works out ... we are trying a 30T Front and 36T rear at Swinley today for the first time.
I have some messing about to do on the chainline ... and not certain on how to go about it but I think I need to lose aboout 10mm.... (Shorter BB + mover spacer, add some spacers - and does that then mean finding longer bolts, add a spacer to the inside of the cassette - not really preferred)

In 5th gear....

Steve-XcT

30/36 seems pretty good .... we did some pretty steep hills until remembering I had forgotten to pay for the parking and mad rush back .... We did drop the chain twice though and it wouldn't go back on easily without washing off the mud/sand mix at Swinley...

Maybe it will be less sensitive when it beds in ???

Steve-XcT

Steve-XcT wrote:

30/36 seems pretty good .... we did some pretty steep hills until remembering I had forgotten to pay for the parking and mad rush back .... We did drop the chain twice though and it wouldn't go back on easily without washing off the mud/sand mix at Swinley...

Maybe it will be less sensitive when it beds in ???

How was your testing ???

We had a second day with the 30/36 combo..... only one chain drop (in 10th through mud/sand) ....
We covered 15 miles of which a significant part was single track.... and he climbed almost everything... (and with determination and perhaps more fitness I suspect he could have climbed everything within reason)
(excluding really technical with 1' roots and stuff where he needs to develop skill more than gearing)

Observation wise on his 24" wheels the 30/36 is pretty close to my granny 26/36 on 27.5" .... doing the same speed the cadence is nearly the same.

The flat blue trails he was using 5-6th .... and really motoring (I didn't clock the speed but it was significantly better). We caught quite a few adults on decent bikes and also didn't need to let many people past.

The RST F1rst continues to exceed expectations on the technical red's.... I'm very impressed!

oxoman

Got on fine just need to something to stop the chain coming off as its not a narrow wide, suspect shadow plus rear mech will be ordered plus a couple of better tyres. Took him out today as off school with inset day and did the local trail centre and some cross country / lanes we know and he struggled with the claggy mud in places by spinning out. Current tyres are similar to Kenda small block eights.

Steve-XcT

oxoman wrote:

Got on fine just need to something to stop the chain coming off as its not a narrow wide, suspect shadow plus rear mech will be ordered plus a couple of better tyres. Took him out today as off school with inset day and did the local trail centre and some cross country / lanes we know and he struggled with the claggy mud in places by spinning out. Current tyres are similar to Kenda small block eights.

I'm having a few teething issues with the narrow wide... mainly mud and perhaps bedding in.
However you will probably still need a chain retainer from what I've read without a narrow wide.

I got the used XT Shadow+ for £25 (less than a new tyre) and I paid £15 for the narrow wide (on sale) but you should be able to get a new 28t for £30 and delivery...which might not be much more than a chain retainer ??? and reduces weight not adds ??

POAH dislikes the Rocket Rons (doubtless with good reason)... but I got Ollie some and they performed well.
He recommended hutchinson toro's rear and kenda kenetics on the front.
I didn't because I bought on availability/delivery time since the tyres it came with were useless on anything but a canal towpath.

Steve-XcT

Insane amount of work yesterday but got a few hours at Swinley today.

The chain behaved perfectly .. didn't drop a beat (and I forgot to put the clutch on, which I didn't notice till we got back)
Must have done 15 miles ... all the way over top Bagshot and lots in-between and

The 30/36 worked (almost) everywhere .... only Dad assisted at a couple points but that was him being tired/lazy (big hill going up the the reservoir and coming back from Baby Maker) .... because he did a lot steeper up single track when Dad can't help....

Giraffoto

This thread includes my experience of building up a child's bike with a 152mm crankset - the one I found (there are links in that thread) has a 104mm BCD and will fit standard chainrings. One of the two that I've now bought has a Superstar narrow/wide chainring, and I know they do those down to 30T.

oxoman

Currently trying superstar 30T up front on original crankset and await delivery of sunrace 11 to 40 cassette following major hissy fit from youngest when he couldn't get up some local trails non stop. Also going to try some better tyres as struggling in the wet and mud at the moment, standard merida block 8 look alikes are ok for the usual tracks and trail centre but struggled at Cannock and Llandegla in the clag off piste. Will sort some pictures out when it's complete. The 28t front ring contraption that I true from LBS was a mackled up affair which wasn't in very good nick, so ended up being binned after first trip out. Will probably end up with replacement clutch mech on the back as well, current deore one is looking battered and slightly bent although functional from recent off. Having to do things a bit at a time as financial controller is starting to question expenditure on bike bits. Contacted fork people and they suggested cutting down the elastomer as he is light weight to make it handle better so will probably try that as well, rather than replace forks when he will probably upgrade to a 26" bike after Christmas depending on growth. The beauty of most of the upgrade stuff is it will slot onto his next bike and I can refit the OEM stuff back onto the Merida be for its flogged on.Giraffoto liked the build but when I tried my youngling on a 26 xs frame he struggled on the reach hence the 24", how's your lad get on with this on his. Nice build by the way, good way of building it as well so hopefully they appreciate it more and also learn the skills required to look after it themselves.

Steve-XcT

oxoman wrote:

Currently trying superstar 30T up front on original crankset and await delivery of sunrace 11 to 40 cassette following major hissy fit from youngest when he couldn't get up some local trails non stop.

I found the 30 front 36 rear is OK.
I'm considering a 40T rear but I think the hissy fits are as much to do with being tired as the gearing.
Last Sunday he climbed some really steep stuff. Indeed stuff the adults on downhill bikes couldn't and we passed quite a few people on climbs....

2 hours later .... he was tired and not climbing anything half as hard .... with accompanying hissy fits...
Much as I think he will get the 40T eventually .... he is still working out HOW to use gears and cadence effectively so in our case I think a few more weeks with the 36T until he demonstrates an ability to picjk the right gear. Part of the reason he's tired (other than being 6) is the choice of gear ...

Also going to try some better tyres as struggling in the wet and mud at the moment, standard merida block 8 look alikes are ok for the usual tracks and trail centre but struggled at Cannock and Llandegla in the clag off piste.

The Rockets are performing well.... no punctures yet...

Will probably end up with replacement clutch mech on the back as well, current deore one is looking battered and slightly bent although functional from recent off. Having to do things a bit at a time as financial controller is starting to question expenditure on bike bits.

The used XT Shadow+ we got was £20 or less (I think) from ebay.... My financial controller is also questioning... :twisted: .... 10 speed stuff is quite cheap if you are in no rush....

Contacted fork people and they suggested cutting down the elastomer as he is light weight to make it handle better so will probably try that as well, rather than replace forks when he will probably upgrade to a 26" bike after Christmas depending on growth.

Sounds like you need to start looking for the frame/wheels??? (Financial controller may need convincing)
My observation is that they are becoming less plenty-full .... as many of those switching to 27.5/29 seem to have already switched... but its' certainly a lot less than 6 months ago.