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Best/most cost effective way to lighten a kids bike

Sandwich

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May 23, 2002
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I just scored a kids 20" spec hotrock. I've cleaned it, changed grips, and ditched the kickstand. It still seems heavier than it should be, so I'm trying to figure out where I can safely drop some weight with low cost. Right now the biggest suspcts are the square taper BB and the rear hub. Everything else is aluminum or pretty minimal. Rear hub is a generic freewheel deal and the BB is square taper.

Or should I just forget about weight savings? I feel like a pound on a kids bike is a huge difference....
 

Toshi

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Oct 23, 2001
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Angle grinder cures all. They probably don't need a top tube, right? No hucking the gnar.
 

jonKranked

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also, the problem with changing from a square taper BB to a different interface on a bike that size is that good luck finding anything lighter in an appropriate crank arm length.
 

jonKranked

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well, you could get profile mini magnutanium cranks, which are available down to 145mm, but those are gonna cost more than the entire bike did at retail.
 

slimshady

¡Mira, una ardilla!
Dec 20, 2007
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tubeless?
I went tubeless for my kid's 20-inch bike. I happen to be in possession of a shit ton of Kapton tape and sealant, so I guessed it'd be worth a shot.

On the OP's subject, the main culprit for the heavy bike is surely the frame. While bike brands are starting to figure out kids bikes' geometry, they are still using grown up's tube sets, or even worse, helluva thick straight wall tubes.
 
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jonKranked

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On the OP's subject, the main culprit for the heavy bike is surely the frame. While bike brands are starting to figure out kids bikes' geometry, they are still using grown up's tube sets, or even worse, helluva thick straight wall tubes
They do that because it's cheaper than using lighter higher end tubing. Also the second a kids frame breaks they get sued to high hell.
 

slimshady

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They do that because it's cheaper than using lighter higher end tubing. Also the second a kids frame breaks they get sued to high hell.
Yup, figured that was the case. After weighting my son's Hotrock 12 frame by itself I wondered if it'd be lighter and safer for Specialized to just build a chromoly frame and call it off.
 

Sandwich

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Yeah so thanks for not really any of the help.

The bike is a 2003 Spec Hotrock. I thought it was an aluminum frame, but it's actually chromo. The fat main tubes may increase weight, but I have tremendous doubts that switching to an aluminum frame is going to save more than a pound overall. I was thinking more along the lines of a cheapie titanium ebay BB, or dropping the chain guard, or switching to a freehub from a freewheel, or trying to find light tires (as others have said), or even dropping the gears entirely. If I had known it was a steel frame, I'd probably have looked elsewhere, but I didn't realize that until after I had bought it. Her 14" bike is quite a bit lighter but it's a single speed aluminum frame.

Here's how it started:


Here's where we are now:


I will install the grips properly once I know what length to cut them to. Debating dropping the derailleur guard and lower chainguide as I don't expect her to be hucking much gnar. Reflectors are non-negotiable as I need to safety as much as is possible.
 

Sandwich

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My concern with tubeless is the practicality of having to pump them up regularly like all my other tubeless wheels....

ditching the chainguide may not be a bad idea....especially if I swap out the BB.

Can't really swap cranks due to length, I suppose I could do bars and stem, but I don't have a readily available replacement...
 

jonKranked

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I think 127mm

not a terrible price
 

Sandwich

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I mean, I already have forged aluminum cranks on the bike. I'm trying to ditch the heavy steel components where most logical.
 

Sandwich

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shitposting isn't really helping dude. I'm just trying to see if there's anything I overlooked or haven't considered to make the bike as easy to ride as possible. It certainly doesn't matter as she gets bigger and better, but right now she's kind of at the bottom of the curve for a bike this big. The stampede really was phenomenal in this aspect and in getting her to ride a bike sooner than any of her friends....but another $400 purchase just isnt in the cards.
 

jonKranked

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how is that shitposting? im pointing out the options available to you. aside from the things you've already covered, you're not gonna save any significant weight without spending money, to the point you may be better off buying the fancy kids bike in the first place.

that being said, for the bars and stem - are those steel? i have some older alloy stuff that's in good shape if you're interested. handlebars definitely, stem.... i'd have to check.

seatpost would probably be another thing to consider.
 

jstuhlman

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Dec 3, 2009
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can you ditch the whole chainguide and just run something like a oneup top guide? or even one of those tube-like guides that attaches to the bottom of the chainstay?

and yeah, ditch the rear derailleur guard and maybe compare weights of the bars/stem (maybe seatpost) to some other options.

we have a place here called the recyclery that has tons of loose used parts - somewhere like that if there's one near you might be a good place to dig around. i used it a bit when i was doing this to our kids' 24" bike.
 

Kiwintas

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Oct 22, 2018
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can you ditch the whole chainguide and just run something like a oneup top guide? or even one of those tube-like guides that attaches to the bottom of the chainstay?

and yeah, ditch the rear derailleur guard and maybe compare weights of the bars/stem (maybe seatpost) to some other options.

we have a place here called the recyclery that has tons of loose used parts - somewhere like that if there's one near you might be a good place to dig around. i used it a bit when i was doing this to our kids' 24" bike.
I replaced the stem, handle bars and seat post on the boys bikes. The stock ones were so heavy and finding cheap second replacements was easy as what you are after is not the latest or greatest. Old school 680 bars are about as wide as you are ever going to go on a kids bike. Most people have replaced there light seat posts with droppers etc.
I do recommend throwing some new brake cables and outers at the bike as small hands and v brakes need all the help
They can get.
 

Sandwich

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can you ditch the whole chainguide and just run something like a oneup top guide? or even one of those tube-like guides that attaches to the bottom of the chainstay?

and yeah, ditch the rear derailleur guard and maybe compare weights of the bars/stem (maybe seatpost) to some other options.

we have a place here called the recyclery that has tons of loose used parts - somewhere like that if there's one near you might be a good place to dig around. i used it a bit when i was doing this to our kids' 24" bike.
I think we can get rid of the chainguide entirely, and probably the guard (even though that's probably not heavy). I have a set of narrow carbon bars, but they are 31.8. These bars are alloy,I think and the stem is 25.4.

I replaced the stem, handle bars and seat post on the boys bikes. The stock ones were so heavy and finding cheap second replacements was easy as what you are after is not the latest or greatest. Old school 680 bars are about as wide as you are ever going to go on a kids bike. Most people have replaced there light seat posts with droppers etc.
I do recommend throwing some new brake cables and outers at the bike as small hands and v brakes need all the help
They can get.
Thanks for the tips. Hadn't thought about replacing cables but that's an easy and cheap upgrade in performance.

Also, keep in mind I spent 40 on the bike and 20 on the grips and saddle. Spending 50 on an eBay ti bb still keeps me far under the investment into a "high end" kids bike.
 

Nick

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Sep 21, 2001
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behind you, don't wait up.
My concern with tubeless is the practicality of having to pump them up regularly like all my other tubeless wheels....
That sounds like you need to up your toobless game. Id try more sealant and double check your tape job.

I think my 1st bike as a kid weighed more than I did, and it never kept me from having more fun than anyone on the planet. Maybe just let her ride it? Take off all the extraordinary BS like chain guides ect.
 

Katz

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Jun 8, 2012
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...I have a set of narrow carbon bars, but they are 31.8. These bars are alloy,I think and the stem is 25.4....
Your spare carbon bar + ebay 31.8 x 40mm stem (the stock one looks like 80~90-ish) = profit ?

Kenda SB8 Pro is available in 20" sizes and folding bead, according to Kenda website. Probably fair bit lighter than those questionable tires with Special-ed hot patches on.

https://bicycle.kendatire.com/en-us/find-a-tire/bicycle/bmx-race/small-block-8-pro/

I saw some online BMX retailers carrying 20" Tubolito tubes.

I don't think your little girl needs 32 spokes, especially up front. Maybe take one spoke out of every four.
 

Sandwich

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okay, mea culpa, you were right, I was wrong.

I "curb alert"ed (trash picked) a 2007 Hotrock, which is virtually identical in specification, but it has a suspension fork and aluminum frame. The hubs are alloy instead of steel, and otherwise the spec is virtually identical. The whole setup is 3-5lb lighter than the pink hotrock, based on my tightly calibrated arm scale. I'll probably swap out the bars and stem (that's like a $10 upgrade) and bottom bracket (the spacing is fucky) but otherwise I don't need to drop weight on this.
 

Sandwich

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Now grab the rigid fork from the 2003, put it instead of that boat anchor, drink beer, profit!

I'm a bit apprehensive to do that as the fork works surprisingly well for what it is (coil and elastomer, I think) and also the old fork is apparently hi-ten (not chromo) and probably weighs a fuck ton as well. I'd rather have some level of suspension than none at all...but I'll take them both out for a weight test at some point this evening.