mr_ankylosaur

Hi all

I'm looking to buy my son a new bike for his 3rd birthday in Nov but don't know enough to choose between two different models.

He's 94cm and 14kg, riding without training wheels, and is pretty good at pedalling but still needs help up even minor hills.

The two bikes I'm picking between have different chain wheel/cog sizes and I'm not sure which would be best.

Commencal Ramones 14 (2020): 28T x 18T
Spawn Yoji 14: 22T x 12T

I get that the ratio is important, but not sure about the sizes - are these two combos very different in how easy they'll feel to pedal?
Which would you recommend?
I'd be so grateful for a noob-level explanation or recommendation on which to pick.

Thanks!

dabac

28/18= 1.6
Meaning the rear wheel will turn 1.6 times for each turn of the pedals.
22/12= 1.8
Meaning the rear wheel will turn 1.8 times for each turn of the pedals.
About a 12% difference between the two.
Compared to regular road bike, this is a bit more than you generally shoot for as one gear’s difference.
Assuming same crank length and wheel size, the 28/18 is the lower gear and the one that climbs easier.

You might want to look at what sprocket styles they have. The 18T sounds like it might be a freewheel, the 12T maybe a bmx style cassette hub.
Might be easier/cheaper to change the gearing on the 22/12 than the 28/18 If you should need it.
If you change the 22/12 to a 22/14, it’ll pretty much be the same as the 28/18. If parts exist to let you get to 22/16, you’ll have a lower gear still to go to.

pickettt

Your kid won't care, nor know any better. At this point, just keep him pedaling.

VegasTriker

If there is much of a difference, choose the lighter bike. It's just as important as the gearing especially when the child is small. Few parents think of this when they buy a bike and sometimes saddle the child with a bike that is not much fun to ride because it weighs too much for their size.

mr_ankylosaur

Thanks so much, that's really helpful. You're right, the 12T is a cassette hub, and I'll def look into getting a 14T if I end up getting the Spawn (which I probably will since it's lighter and easier to change the gearing on)

One thing though - I'm still not clear what the effect of the actual chain ring/sprocket size is.
i.e. why would you choose 28/18 vs 22/14, what's the actual difference given the ratio is the same?

Thanks a million

mr_ankylosaur

Thanks for that, it's a good point. Neither are as light as I wanted, the Spawn is about 6.3kg and the Commencal is 7.something. Unfortunately it costs like a million dollars to ship a Woom/Islabike/Prevelo/most other bikes to NZ, so choice is limited.

His current PJ Masks steel Kmart bike is 7kg so I guess they're not going to be much worse at least

mr_ankylosaur

I really hope that's the case! If he hates his new bike and insists on riding his old $75 12" steel PJ Masks bike, I'm gonna cry.

dabac

Also an important factor. It's a common complaint among bicycling parents that their kids' bikes are heavier than their bikes, despite being so much smaller and intended for much lighter riders.

W/o looking up the spec of the bike, I assume the 28/18 is a freewheel - as opposed to a (BMX) cassette hub.
With a f/w, the sprocket makes up the outer face of the assembly that holds the clutch mechanism (the thing that lets you coast). This means there's a limit to how few teeth you can have, usually 16.
So to get a certain ratio, if you can't go low ath the rear, you have to go big at the front.
I'd also assume that f/w hubs are cheaper than casssette hubs.

If you're looking to put together a high-mileage, high-load bike, there's a (small) advantage in going big. Big chainrings and sprockets means more teeth engaging the chain, which reduces wear. There's also a tiny gain in efficiency from looping the chain round a bigger radius.

OTOH, smaller rings and sprockets saves you some weight and increases your ground clearance a bit.

mr_ankylosaur

Ah! Finally makes sense! Thanks so much

pickettt

Can I ask what your kid's (or your) aspirations are for his bike riding?

Viich

The spawn is a great bike. I do bmx racing with my kids, they're of similar quality to some nice race bikes, and I told someone at the track their son would be fine on that bike ( that they already have) to race. Don't overthink the ratio or tooth count yet.