Specialized Hotrock A1 24" Build

[Wveddy]

I think I encountered the same issues most of you will when you start the "build a better 24" bike" thought process. I found several posts in this forum on builds similar to this one. I do have to say it is a complete pain in the butt.
I had two goals: build a bike that rides better and shed as much weight as possible.

I started with a Craigslist find on a 2005 A1 FS. Good deal and just needed some TLC.


I rebuilt the Capa Fork and was surprised how heavy and useless it was. It weighed in at a heavy 1950 grams. The worse part was it did not really work. My daughter is not heavy enough to compress it at all.

Luckily I have a friend who is a vintage bike collector and he hooked me up with a 2000 Sid SL dual air that was set at 63mm. The hope is the air fork can run the pressure low enough that it can be tuned for her weight. It was even the right color.



I will say if you cannot rebuild a fork yourself, this part can be expensive. Old used forks have hard to find parts and your local shops may or may not be able to get parts. Luckily the SID still has rebuild kits available.
The SID weighed in at a scant 1275 grams. That is pretty damn light.

Now the fun part about running a 26" fork on a 24" wheel. It means making a v-brake adapter or going disc. Going Disc basically means new wheels for all intensive purposes. You could just do the front if you wanted.
I went the disc route, since dropping weight on the wheels was part of the plan. The v-brake route would have been way cheaper in hindsight. Plus discs add weight to the bike. The single front disc added 135grams over the v-brake set up. But the brake post adapter could easily weight that much.

I went light on the hubs. 415 gram Novatec 711/712 hubs. this is about the cheapest lightest hub set you can buy on ebay. and they are pretty nice. Do the express shipping, it is worth it. I will weight the old hubs when I get the wheels back.


The worst part on this whole thing is the wheels. Rims for 24" bikes are stupid heavy. I really don't know why. Alex Ace20 is one of the lighter rims at 390-400 grams, but they don't make them anymore. Velocity Aeroheat is the only other light rim available. Luckily her bike already had Alex Ace20 rims, so I choose to reuse them to save a few $$.
2 weeks later, the wheels are still being built. Apparently the large flange hubs and small rims equals a spoke length shorter than any dt comp spoke is available in. Yippie. The shop is cutting and threading some spokes to make it work.

So here she sits, a sweet Hotrock A1 with a Sid and no wheels.

[Wveddy]

As a side note, the A2C only went up about 30-35mm. So the impact to the geometry should be minimal. That is also a good reason to find a 63mm fork.

[joe_bloe]

That looks great. I went through similar issues and decisions for my son's 24" build. I went with the Sun CR-18 rim on a generic disc hub - certainly not as light as the Novatec / Ace20 combination, but the price was right. I had to get custom spokes cut, too. Cambria did them for me, cheap. Other cheap ways I saved weight on his bike:

Drilled out the steel 3rd ring on the super-heavy riveted crankset; 2x7 works fine for the kind of riding we do
Kenda Small Block 8 tires with lightweight BMX tubes (this saved two pounds)
cheap, light alloy seatpost, handlebar & stem - it's amazing how heavy these things are on kids' bikes

[Wveddy]

Thanks for the tips. I have the Kenda Small Block 8s ready to go. Would like to do ghetto tubeless, but not right now. I replaced the seat post and stem too. Thinking of cutting the seat post since she is not using even close to all 400mm. I think i already did the bars, but you are right that the stock components are heavy. I did find a Sinz light BB. that is on the way and shaves about 120 grams. Building a light 24" is way harder than a 26" or 29" bike. kids get the shaft. they are less likely to break light stuff and can benefit the most from the weight lost. just crazy.

[joe_bloe]

Yeah, the Sinz Expert BB is on my list of possible Phase II upgrades. I thought about tubeless, but I had a few reservations: 1) Kendas are known to act funny with sealant in them, and 2) I'd hate to make recovering from a flat more difficult for him. I decided it was best to keep it simple for now.

As for cutting the seatpost, you certainly could do that. It all depends on whether you think it'll transfer to her next bike. For my son's bike, I'm thinking a large number of the parts (bars, stem, seatpost & saddle, rear derailleur, possibly fork) may move to an XS 26er for his next bike. So, I'm trying to keep things like steer tube and seatpost long, so they'll fit other frames.

[Wveddy]

I will double check the BB weight of old vs new and let you know. but for $35, that is one of the cheapest ways to drop over 100 grams. This bike is getting passed down to the little sister when she outgrows it, so nothing is moving. the XS 26 build is for another day. love to find a fat chance yo betty, but those are pretty rare and not cheap.

[Vxc961]

Nice! I'm a year or so away from a 24" build, so I love seeing ideas that don't break the bank!

[Wveddy]

finally got the wheels done. they look awesome and feel light.

The old wheels were not super heavy, so not much on savings here. The Cassette is a lot lighter than the freewheel though.
All in all, it turned out pretty good.



Still have to switch the bottom bracket and maybe go tubeless. Now it is time to ride.

[jh_on_the_cape]

How is this working out?

[SVO]

Two options: $1k Isla that has a sweet custom 24" air fork- never seen the like anywhere else. Second: My DIY. Basic Schwinn- kept frame, brakes , bars and stem only. 3x8 drivetrain, 165mm Truvativ cranks, good quality steel fork off Ebay, custom wheels (had to get custom cut spokes- not expensive). I have $450 into it. Great for my son. As he grew went to 80mm Manitou fork for 64er set-up. With a good quality 7000 gusseted frame, and a sub 100 lb rider, no worries about frame stress.

22.5 pounds without pedals.

[Wveddy]

How is this working out?

So this setup has been pretty good. I will say, the difference is the fork and the overall weight reduction. The fork actually works and looks like she gets close to full travel. Getting the air pressure set was not easy. My kids are super light, so changing 2lbs of air pressure makes a big deal. Plus the other thing I found was the older SID 99-00, dampener has such a heavy oil in it that it restricts compression of the fork. Plus the negative spring is problematic. I would recommend a 03 or later SID if possible. Given all this low pressure tuning required to make an air spring work for kids under 70lbs, I cannot image a cheap air fork would even work that well. The 04 SID Race I have is awesome and perfect for my daughter. I would recommend that upgrade to anyone. The wheels are super nice too, a little bling in addition to dropping a few lbs.

[Wveddy]

I liked the first one so much, i built another one.

[xc71]

So this setup has been pretty good. I will say, the difference is the fork and the overall weight reduction. The fork actually works and looks like she gets close to full travel. Getting the air pressure set was not easy. My kids are super light, so changing 2lbs of air pressure makes a big deal. Plus the other thing I found was the older SID 99-00, dampener has such a heavy oil in it that it restricts compression of the fork. Plus the negative spring is problematic. I would recommend a 03 or later SID if possible. Given all this low pressure tuning required to make an air spring work for kids under 70lbs, I cannot image a cheap air fork would even work that well. The 04 SID Race I have is awesome and perfect for my daughter. I would recommend that upgrade to anyone. The wheels are super nice too, a little bling in addition to dropping a few lbs.

One thing you might want to try thats worked very well for me in other applications is change the heavy fork oil out for 2.5 wt. shock oil. Rebound will speed up, but adding more rebound damping via the external adjustment will solve that. Most motorcycle shops would have this. Great looking bikes the girls have.

[Wveddy]

One thing you might want to try thats worked very well for me in other applications is change the heavy fork oil out for 2.5 wt. shock oil. Rebound will speed up, but adding more rebound damping via the external adjustment will solve that. Most motorcycle shops would have this. Great looking bikes the girls have.

So the pure delight dampener is completely sealed with no way to change to internal oil weight. If anyone knows how, please let me know. On the newer fork with the new dampener, I am running 5wt oil and it is fine.

[traffic002]

Great info on the wheel build. My son has a Cannondale 24" and I've been wanting to rebuild the wheel for him but having a hard time tracking down parts. His bike comes with the Alex Ace 20 rims as well. So that with the Novatec hub combo seems like a great fit.

The jury is out whether to switch to disc brakes though... So I might just run the rim brakes for a while longer. But re-using the same rims should provide the most flexibility.

I'll have to verify BB to see if I can pick up a set of Sinz crank arms. The 152mm arms it comes with are too long and he has frequent pedal strikes which un-nerves him.

[traffic002]

BTW, what spoke lengths did you end up using?

[Wveddy]

Spokes were custom cut dt Swiss and then threaded. I could not find a double butted spoke short enough to work with the nova tech hubs. The big flange just makes it tough. I wanted lighter straight gauge spokes, but again the short length is an issue. Luckily my shop has a spoke threader and quickly resolved the issue. You could probably reuse your current spokes and cut them down. Save you a few bucks.

[Wveddy]

I weighed disc vs vbrake. Vbrake is way lighter. Only reason I run a disc on the front is the 26" fork alignment issue. Vbrake on the back is plenty of stopping power for an 80lb kid

[GrayJay]

Spokes were custom cut dt Swiss and then threaded. I could not find a double butted spoke short enough to work with the nova tech hubs. The big flange just makes it tough. I wanted lighter straight gauge spokes, but again the short length is an issue.

Instead of trying to source short butted (or titanium) spokes for weight savings, just lace the wheel with fewer spokes. For a 32 spoke rim/hub, you can either go with 16 spoke (8 per side) or else use all 16 spokes on the flat dished side (drive side on rear or disk side on front) tension balanced by just 8 spokes on the other side (24 total). The 24 spoke pattern also helps to increase spoke tension on the loose side, actually makes it less likely to fatigue and break the spokes compared to conventional pattern with high imbalance in spoke tension from side to side.

[Wveddy]

Kids are still kids, and these bikes get ridden to a friends house and tossed in a yard. 32 spokes gives you better side impact resistance and a truer wheel over the long haul. There are always compromises.

[Wveddy]

This is my 7yr olds 11" frame hotrock


And here is my 10yr olds 13.5 frame