My 6y/o daughter has a Carrera Luna 20″ and she’s loving riding it.
Slight issue we’re having at the moment is hills – she wants to do longer rides but after a while is struggling on the hills due to the slightly rubbish gearing on the bike.

Current gearing is 36t front and 7spd 13-28t on the back.

This set up give the following gear ratios:
High – 1:2.8
Low – 1:1.29

So on low when on hills she’s still having to work quote hard.

Now my initial thinking is to just get a wider range rear freewheel – these are available in either 12-32t, 14-34t and 11-34t.
This should help on the climbs as it brings thing closer to 1:1 at the low end (1:1.12 for 32t and 1:1.05 for 34t).

But I then got to thinking that I could improve things further by swapping the front ring. This would mean changing the crank – but I can get a 152mm Suntour with bolt on rings for £24 – and sticking a 32t single ring up front.

This would improve the climbing a bit more and would give a 1:0.9 ratio for a 34t freewheel.

Question is, is it worth changing the front or should I just swap the freewheel and see how she gets on?

The ‘bike-tart’ in me is thinking change the front a stick a purple chainring on for extra coolness and ‘Dad points’.

So do I spend £12 on a freewheel only or another £30 on new crank & ring?

Am I missing anything?

My lad recently got a Whyte T403 which comes with a 32 instead of the 36 he had on his CUBE, the difference is quite dramatic.

I’d swap the cranks myself, £30 ain’t a lot in the grand scheme of things.

Am I missing anything?

Either she is way too big for the Luna or 152mm cranks are way way too long.. I’m betting the latter. 8)

My lad is a bit over 130cm and has fairly long legs and he isn’t even close to being able to ride trails with 152’s….

He can ride DH/bike parks…on 152’s as he doesn’t need to pedal much and he’s out of the saddle 100% anyway… but just like he can ride my adult 27.5’s round a car park.

If she’s not really tall she’ll end up having to put the saddle down to pedal on the flat and stood on every climb and knackered pretty quickly

Where abouts are you…. I could lend you a set of 152’s to try with a 30T or 32T if you are close to Swinley…this weekend???

At the same time I could lend you a 20″ wheel with a wide ratio 7 sp freewheel…

Hi Steve thanks for the offer but I’m in Cannock.

Don’t follow what you’re saying about crank length – cranks are 152 currently and will swap to same length suntour ones.

150mm ish cranks are what you would expect on an xs 26er, so seems a bit long on a 20er.

OK I get what you mean now.

What about these

https://www.evanscycles.com/pinnacle-hoy-bonaly-20-chainset-EV252534?esvt=55132-GOUKE2420002&esvq=&esvadt=999999-0-1224550-1&esvcrea=189745839481&esvplace=&esvd=m&esvtg=pla-299431958386&esvo=EV252534-32-BLK&esvaid=50080&gclid=CKKl__CL0dQCFUO-7QodwMMOzg

Looks about the right length.
Yes, that’s the same length as a 20″ islabike crank, so 114 is going to be right.

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OOPS ^

We had a Pinnacle Ash 20er… (indeed still do)…
Cranks are very short (122 from memory)
The Evans listing doesn’t seem to really say much about length or BCD…

We used those for his 9 month on a 20er and then transferred them to his 24 for a short time (as he could’t pedal it as it came with 152mm)

They worked pretty well with the mega-range on the 20 er….

I’d check the Highpath chart…. see what size she should be on… (this is IMHO the best chart – but there is no right answer.. but I’d say 152 is definitely wrong for any kids 20er)

Crank Length Calculation

The problem with the 20er is the limited use you may get. My kid was only just too small for his 20er day 1…. but 9mo later was only just too small for a 24… from my experience of him and his classmates this just seems one of those fits and starts growing spells …. he’s had his 24er a year (almost) and he’s already pushing the cutdown seatpost that was slammed a year ago…. (in terms of insertion)

He still had plenty of growth left in the 20 ….but it was a matter of spending money on what would never really be great (cassette hubs and no disc mounts – no suspension) so he moved onto the 24er as soon as practical…

I totally get wanting to upgrade… but I’d say you’re better sticking to the limits of the Luna … or you potentially would change wheels for a cassette hub etc. add ineffective heavy forks… etc. etc.

By the time you are looking at a 24er you have more options… and in our experience know if its worth spending or not and what they like riding…

If you’re unlucky like me then she’ll be an all rounder … and you end up buying 2 bikes!

I’d go 11-34 with a 32t up front, nice wide range then.

I just quickly measured the pinnacle one .. don’t have time to count teeth… but its about 115mm bolt centre to pedal centre

I can’t tell if its the same one as your link to Evans but if you collect in store you can always check…

That worked really quite well with the megarange…. at least over the 9 months he went from a bit of pushing or “Dad Assist” to no pushing or “Dad Assist” at Swinley …

Cheers Steve – Evans cranks are 115 apparently.

Will check the High path chart and see what length is recommended.