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Cranks

Old 03-02-21, 05:57 PM
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Freeheeler1690
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Cranks

My son is approaching 8yrs of age. I recently picked up a specialized allez junior for him. Apparently they have stopped making them and they are very hard to find and stores won't ship them to California

Anyway, he can ride it but it is slightly big for him. He currently rides a frog 67 racing bike and he's comfortable with that. One of the differences is that the cranks on the Frog are 130mm and on the Specialized are 150 so his legs are at full stretch on the Allez. The Frog does weigh a lot more. He is entering the junior national championships this year in Ohio so I'm preparing him for the race (if it goes ahead

I'm not technically minded and I was wondering if I purchased a pair of 130mm cranks could I put them on the allez bike? The cranks are hard to find here in the USA but they are available in the UK but they seem to be a different fitting. Can anyone tell me if these would fit the Specialized bike? The BCD is different

Specialized

FRONT DERAILLEUR Shimano Claris, clamp-on
REAR DERAILLEUR Shimano Claris, 8-speed
11-32t CHAIN KMC X8 w/ Missing Link™, 8-speed
CRANKSET Forged alloy, square taper, 110 BCD
BOTTOM BRACKET BSA, square-taper, 68mm
CHAINRINGS.

From kids racing in the UK.

I cannot post the website, but it's on kids racing co uk and under cranks. if you search it online

130mm: riders approx 120cm to 135cm tall
135mm: riders approx 125cm to 140cm tall
140mm: riders approx 130cm to 145cm tall
145mm: riders approx 135cm to 150cm tall
150mm: riders approx 140cm to 155cm tall
155mm: riders approx 145cm to 160cm tall
  • HUP Kids Cranks
  • Chainring BCD: 104mm, 4-bolt
  • Installation: Single Chainring
  • Aluminum 6061-T6
  • Bottom Bracket: JIS square-taper
  • Arm Lengths: 130mm, 135mm, 140mm, 145mm, 150mm & 155mm
  • Chainline: 45.3
  • Q-Factor (with 107 BB): 145mm
  • Weight: 440g
  • Colour: Black
  • Does not include crank arm bolts, available separately
Top Tip: as with all our kids cranks, we always add helicopter tape to the face of the crank arms to protect from kids feet rubbing (especially without cleats) when the cleat position sets the shoes very close to the cranks.
If using HUP cranks on a non-HUP frame, use the dimensions below to check for fit on your frames chainstays...

103mm BB = approx 115mm inside crank arms
107.5mm BB = approx 121mm inside crank arms
108mm BB = approx 122mm inside crank arms
113mm BB = approx 127mm inside crank arms
115mm BB = approx 129mm inside crank arms
118mm BB = approx 132mm inside crank arms 36/22T

36/22T
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Old 03-02-21, 07:13 PM
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Old 03-02-21, 07:49 PM
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icemilkcoffee 
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Originally Posted by Freeheeler1690
From kids racing in the UK.

I cannot post the website, but it's on kids racing co uk and under cranks. if you search it online

130mm: riders approx 120cm to 135cm tall
135mm: riders approx 125cm to 140cm tall
140mm: riders approx 130cm to 145cm tall
145mm: riders approx 135cm to 150cm tall
150mm: riders approx 140cm to 155cm tall
155mm: riders approx 145cm to 160cm tall
  • HUP Kids Cranks
  • Chainring BCD: 104mm, 4-bolt
  • Installation: Single ChainringT
This crank is meant for a single chain ring though. Which is fine is you want to convert the bike to single chain ring (does the 8yo kid know how to change gears?), but not good if you want to retain the double chain rings in front.
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Old 03-02-21, 08:12 PM
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Originally Posted by icemilkcoffee
This crank is meant for a single chain ring though. Which is fine is you want to convert the bike to single chain ring (does the 8yo kid know how to change gears?), but not good if you want to retain the double chain rings in front.
He can change gears. Good to know. Allez is double ring. Thanks for that
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Old 03-02-21, 08:17 PM
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The biggest 'compatibility' problem I looked for was crank interface, but both of these are using JIS square taper. After that it's chainline, or where the chainring is positioned relative to the frame's vertical center. Some manufacturers will tell you what this is so you can have the appropriate BB spindle length to put the chainrings in the sweet spot to avoid extreme chain angles. Shimano will tell you this (I think) in their technical documents repository.

It was pointed out that the cranks are intended for single chainring installation. I looked at an example on Amazon that looked like it had outer and inner shoulders, so I'd suspect, with appropriate chainring bolt spacers, you could run a double.

This doesn't look like a cheap option, though.
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Old 03-02-21, 10:31 PM
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From my experience dealing with my kids, yours will vary, single rings are perfectly fine with extra gears. I much prefer my kids to ride 1x with 10 or 11 gears though I'm trying to push my soon to be 11yo to ride with a double, success is limited. There are, as a result a number of very nice, light options with a little bit of looking on BMX websites though cost can be a little high. I've got one road bike set up with Crupi Rythm 2 piece cranks, and a track bike with Redline Mini 2 piece cranks. Pick a good chainring and they'll be one of the lightest things out there. Just keep an eye on the 100lb weight limit that mini cranks often have, they are meant for kids who can make some spectacular jumps so they are still durable. Origin8 makes a basic square taper crank arm that will take double chainrings, it will be every bit as good as that UK crank. 2piece bmx cranks will run you 100-170, I've been lucky enough to get them on sale for 80-100 but they're nice. Picking chainrings is important, I mentioned I like 1x10, that cause a 11x34 with the right chainring will let the kid ride a lot of courses but remember you are size limited, they'll roll out your bike at the race and if the chainring is too big your kid is disqualified, surprisingly it doesn't take much of a chainring to get them there.
You also don't mention shifters. I would strongly encourage you to take the kid out and watch them shift, my 8yo is of the taller side for his age and couldn't easily, borderline safely, shift the claris shifters on his Diamondback. The shifting was too stiff and the throw too long, he had to put his whole hand on the shift lever and push it over riding one handed. Short reach microshift are the best way to go, if you can't get a short reach specific then you can buy a faceplate that does the job for a few bucks more. I've found some of the best pricing at 365cycles in PA. All my kids bikes have been converted to these shifters, for the last swap, although it was extra I just bought the rear der, to match and went 10sp. Good luck, its fun to watch them, and maybe I'll see you there.
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