[nino]

hi Guys,
i thought i might get help in here as some of us do have kids and i guess you as a dad also look around for better equippment for your boys/girls.

anyway - my 7 year old son has a nice bike but the cranks are too long. They are 150mm and i would need 140mm. So i'm looking for 140mm cranks for square BB that can take a 28t chainring!!

i already have a FSA 140 crankset but they have 110mm bolt pattern.that's the same pattern BMX bikes have and i can't find any smaller rings than 34t for it. the standard crankset on the bike has now a 28t somehow combined with a bigger ring like 36t , oth out of steel. but we use only the inner ring right now. no front derailleur. i already fitted one of my 9s titanium prototype cassettes instead of the original 6s steel cassette which only went up to 28t...so now with that 32 cog in the rear he can do pretty steep uphills already. so i really need that 28t up front.

any help is apreciated - thanks!

 

[MessagefromTate]

hi Guys,
i thought i might get help in here as some of us do have kids and i guess you as a dad also look around for better equippment for your boys/girls.

anyway - my 7 year old son has a nice bike but the cranks are too long. They are 150mm and i would need 140mm. So i'm looking for 140mm cranks for square BB that can take a 28t chainring!!

i already have a FSA 140 crankset but they have 110mm bolt pattern.that's the same pattern BMX bikes have and i can't find any smaller rings than 34t for it. the standard crankset on the bike has now a 28t somehow combined with a bigger ring like 36t , oth out of steel. but we use only the inner ring right now. no front derailleur. i already fitted one of my 9s titanium prototype cassettes instead of the original 6s steel cassette which only went up to 28t...so now with that 32 cog in the rear he can do pretty steep uphills already. so i really need that 28t up front.

any help is apreciated - thanks!

You can always cut down a 175mm crank and then tap the new hole for the pedals (a machine shop can do this no problem). Unless you have a drill press, then you can.

 

[nino]

cool

You can always cut down a 175mm crank and then tap the new hole for the pedals (a machine shop can do this no problem). Unless you have a drill press, then you can.

that's a great idea. it shouldn't be that hard to do. thanks!!!

 

[f3rg]

This should give you an idea of what size crank to start out with:

http://bikesmithdesign.com/Short_Cranks/shorten.html

 

[slaw]

I had some cranks shortened with 2 sets of holes for the kiddy cranks on one of our tandems. Done by Greenspeed, the trike people, who also brazed up the shell for the bolt-on bottom bracket.

Our other tandem has external crank shorteners bolted on from here. Not a WW solution though.

 

[nino]

thanks guys!!

especially the link from f3rg...that's a great link. i might get in touch with them.

i don't think those shorteners are what i'm looking for.besides the weight penalty i guess those also make for a much wider Q-factor. but also a cool link.might pass that to my friend who has a tandem and a rather small girlfriend.

thanks

 

[CaseyS]

At one time this site had 140mm dotek cranks listed. Looks like 155 is the smallest in the online list. May try giving them a call

http://www.danscomp.com/452006.php?cat=PARTS

Also look at www.fmfbmx.com. They have 140mm cranks in sq taper and isis. Looks like their site is down right now for maintenance so no linky.

Oh yea, also search for bulletproof available in 140mm

http://harriscyclery.net/itemdetails.cfm?ID=1215

What kind of bike is this going on. I'm looking at upgrading my sons diamondback octane20 from a steel OPC crank. Let me know what you find

Edit: missed the 28t requirement. These are all 110 BCD and I think 32t is the smallest you can go. I've got my son setup with a 36 front and a 13-34 7s it the rear. You shouldn't lose much from a 32-34 combo vs 28-32 gearing on the low end. The smaller circle should let him keep cadence up.

Some other info on the doteks
http://bikesmithdesign.com/Short_Cranks/dotek.html

 

[DeeEight]

33T is the absolute smallest you can find for a 110 bcd and that was only from specialty makers like Boone. 34T is as low as any major chainring producers have bothered with.