Darth Lefty's kids' 20" Hotrock
 

Well, after posting a thread last month about kid bikes, here we went and bought a used one. This is a Specialized Hotrock. I guess you'd say "late model" since it's maybe a year or two before the Riprock came out. It was solid, but filthy. I've started cleaning and lubing it. I so far have taken the following notes. This was partly done with voice dictation so there may be some amusing typos I've missed.Hotrock notes

Weights

4.36 pounds suspension fork with crown race and brake posts, it has coil spring, steel stanchions and steerer

3.68 pounds frame with headset and derailleur hanger and rack bolt.

1.34 pounds steel handlebar

3.15 pounds front wheel assembly with tire (tire is 1.2 lb worn out Specialized Roller, tube 0.28 lb)

4.38 pounds rear wheel assembly with tire & free wheel

1.93 pounds alloy cranks and plastic pedals. 36t steel ring swaged onto drive side crank, plastic bash guard

0.82 pounds bottom bracket and bolts. The bottom bracket is a weird half and half thing, the fixed cup is a cartridge and the other side adjusts like old times

0.50 pounds tensioner/guide - just remove. Note this means the included BB is for 73 not 68

1.32 pounds derailleur and chain

1.50 pounds seat, post, and collar. Post is aluminum single bolt - not steel and topper as feared

2.67 pounds control levers and brake arms and cables, stem spacers and cap. The top of the race is a big steel thing weighing a few ounces and I don't know why.

Sum 25.65 lb

Spacing is 135. Head tube 1-1/8. Seat post is 27.2 mm diameter. BB shell 68mm. Kickstand plate included. Frame and fork both have provisions for both disk and V brakes, V included.

Cranks are 127 mm long. Bottom bracket is 118 square taper. Hubs have aluminum shells and nutted solid axles, crusty. Prior owner replaced drivetrain w Altus RD, 7 speed FW, trigger shifter, bypassing the chain guide. Rear brake replaced with a Tektro lever & arms. Lock on grips.

I planned to paint it and told kiddo to pick colors. He at first told me that he wanted it to be black on one side and green on the other side with pink in the back. I had a pretty cool plan for this in mind using spray.bike paint cans, but now he tells me he was just kidding. Ha, Ha, Ha. I think he’s pleased with how it looks now that I cleaned up the frame. I know I am. But I was really looking forward to trying the paint job.

The only immediate project is cleaning it up and making it run smoothly, new tires, new BB (Ali Express Ti), replacing the handlebar (Amazon carbon). I'm not sure what to do about the suspension fork, it is a typical cheap Suntour unit. Heavy AF and no damping but not likely to break down, way better than a Walmart bike. I'll probably just leave it unless one of the kids begins to exhibit shredding talent before they all three outgrow it. I hope the hubs are ok. Can the axles be replaced with hollow ones, if I buy a complete axle assembly? If so that's cheap and I can get Ti skewers, if not I have a nice 135 x 32h disc hub from the Box'O'Crap V6 that I could build a wheel on.

https://cimg8.ibsrv.net/gimg/bikefor...972a54481.jpeg

Nice....my 9 year old has that bike got it last year. Loves it!!

It is possible to convert solid axle to quick release (hollow) axles. RJ on youtube has all sorts of helpful videos, search hub axle conversion solid to quick release, you'll find the one he made specifically for this.

I rebuilt the hubs, or tried. At least I did the front one. The rear axle is bent, as is traditional. I didn't do a very good job cleaning up the drive side because I don't have a remover that fits the Sunrace freewheel, and something in there is rubbing. I'm going to build in that other hub I mentioned. This will also give the option of disk brake and 8+speeds.

Kiddo still hasn't really decided about the color. We were at the bike shop and we saw a few and he got a case of the well-actually.

All three kiddos went to the city bike park for the first time yesterday. Oldest was a little slow but could pedal on the pump track. Balance biker girl twin is scary fast and fearless, balance biker boy twin just isn't getting it yet but loves to have his bike.

Just ordered two 40-packs of 192mm DB spokes from CRC. Would not have bought DB because it's just a kid bike but these were crazy cheap (40/$13).

Sad state of affairs

Kiddo still can’t pick a color. Today it was green.


https://cimg9.ibsrv.net/gimg/bikefor...81ce77fff.jpeg

What is crc? I'd like to rebuild a couple kids wheels.
its a good looking bike as is. I just ordered some schwalbe rocket Ron from bike24, their flat rate 20
Euro shipping is rough but I needed 4 of those and 2+shipping is less than the cost of one here in the states made 4 real cheap. They also have 20 and 24" air shocks around the 100.00 price range, haven't found the same shock for less than 180 from US sellers. The kids air shocks are lighter. About an 80g savings over stock, but the stock 24" I'm replacing is lighter than you 20" so you'd do better still.
The rocket Ron is one of the lightest kid's tire as well, the small block 8 they're replacing is close though and available at decent prices. Just the RR performs better and my kids are trying to ride harder. Either tire will shave some weight and get them moving off-road.

Glad to have you along!

CRC = Chain Reaction

I'm going for durable and cost effective not ultralight. If I can save some gauche amount of weight that’s great but it’s got to survive three kids in sequence and it’s already used. I’m probably getting some of those classic BMX tires

My 7yo is within an inch of the 9yo so the youngest gets double the hand down bikes. So mine only have to survive 2 kids. I made the mistake of buying used trek 220 which are hopelessly heavy but at 2 for 50.00 it's not a big deal. Just meant new bikes from Santa since both took to the trails and pump track. Just means the treks make good ride to school bikes since those get kicked around at the racks by everyone and the nice bikes only get scratched and dinged by the rocks. Having kids who love bikes is a joy to keep up with though.

The Chain Reaction spoke order never left the warehouse so ordered another batch of straight gauge ones from Jenson

Shoot - I would have recommended J&R bicycle (BMX supply) as a good source for double butted.

https://cimg5.ibsrv.net/gimg/bikefor...e659f159dc.jpg
Hubs, nipples and DB spokes for a BMX race wheel build for my oldest's next bike

I finished truing up the wheel. The DS spokes are a skosh too long thanks to the deeper dish of the free hub and larger flange on the drive side. The rim is deep single wall style, I guess I can use some folded over tape.

And what the heck is up with this spacing? (Edit: I left out the derailleur hanger, that's what's up)

https://cimg3.ibsrv.net/gimg/bikefor...d7dcffbb6.jpeg
https://cimg4.ibsrv.net/gimg/bikefor...feb2c1f26.jpeg

I think I found the same when I converted my son's 24" hotrock street to a hollow axle to use on my Wahoo Kickr Snap - it pulled in with the skewer no problem as I remember.

Nope, I did a stupid. That's with the derailleur hanger out. :o

Oops. To be fair, your picture showed that clearly and I didn't pick up on it either.

Looks like a great build.

I missed kiddo's birthday by a week, but it's coming together. I need a skewer for the rear wheel and tape for the rear rim, and then a tuneup, and then he's off. The cassette and hub are 8s while the shifter is 7s so I'm going to lock out top gear with the limiter, which seems like a better option of the two possible. I found a front hub that came from the previous round of the BOC so I can do the front qr too someday if I want.

It's a serious looking little bike in solid color with the big carbon handlebar. The handlebar is about 2" wider than the original but the grips are the extra wide ones too so the controls are about the same location as before.

Some things I maybe ought to do and will evaluate later... I need to stuff some more bearings into the headset (don't ask). Bigger tires (these are listed 2.125 but measure <2, but they are not worn out yet), rigid or "real" fork. The idler has been deleted so need to watch out for chain drops. If that turns out to be a problem we might go Zee which would be cooler or we might put the idler back on which would definitely be cheaper.

I can't wait to see him ride it fast but I know he's going to resist at first for lack of coaster brake.

Looks sharp, for tires I like to check out bike24.com and pick up schwalbe, put 4 brand new rocket rons on the kids bikes for 5.00 more then the LBS wanted for one tire. Shipping is a little steep at 20.00 but I bought some tubes for 2.50 each and a couple of tires for me to cancel out shipping. The rons shaved 10g off the bike vs a folding bead kenda small block 8 that was narrower which speaks to how light they are. I had other bikes that could use the 8s and wanted to kids to have wider and more aggressive for off-road which was my justification on spending the money. Vs a cheaper tire schwalbe makes some really light, weight saving kid's tires.

The last part arrived today and I finished the bike. I rode around myself for a few hundred feet adjusting the shifter, and then we were ready to go for a bike ride. He’s definitely pretty stretched out. I should try him on a shorter stem. He successfully downshifted going up a hill, but has not yet upshifted the other way. He did a sweet seven foot skid learning the back brake

https://cimg8.ibsrv.net/gimg/bikefor...b3cd513db.jpeg

Looks great!

Off we go. Note pink Spawn at left, that’ll be the 3yo girl’s when she can reach the ground.


https://cimg2.ibsrv.net/gimg/bikefor...4670cb35a.jpeg

Kiddo made a 0mph capsize and managed to find the top of a low post with his two front teeth. He’s a year or two early to lose those, but it’s not definite that he’s keeping his first set yet. I always think my wife is going to give me a really bad time about the kids having bike accidents because she had one that has given her lifelong complications, but she never does, she just shrugs it off and gets to work fixing the kid. Relevant to the bike, I lowered his seat back down as far as it would go, and ordered a very short stem to go with the wide bars. I also found a crack in the cage of the original pedals, so I need to swap those out with some other ones I have.

This frame looks like it would accept BMX racing tires on 451 rims. I think if I were going to do that, essentially making a hybrid, I would try to find a rigid fork. The fork would be about the same length as a 24 inch bike rigid fork. It would also need the disc brakes because the V brakes would be in the wrong place. Heck, if you cut out the bridges you could make it a 24” road bike.

I'd not recommend the 451 switch - not a lot of benefit to it. There are BMX racing tires in 20×1.5 now, not much heavier than the narrowest 451 tires, and you're likely to have to custom build the wheel again, as BMX rear spacing is 110mm. Powerblock tires are a pretty good value - I haven't run them on the road long term, but other than rear wheel skids, kids don't wear out tires much. They last pretty well in race use, even take my son to the (concrete) skate park with his race bike sometimes.

For future projects, cruiser wheels are the best source for 520 BSD rims - I am getting a set just to use the front rim on my older boy's Peugeot junior road bike, while I build a rear from a FH-1055 hub and Aryra rim I got my hands on. One of the boys might want to try racing cruiser in the future, and I can always sell the rear later if not.

My 10 yo daughter has this bike and loves it. She is just on the border between the 20" and the 24", so we opted for the 20".


The only issue is that we ride as a family and she has trouble making it up hills that my wife and I can handle on our hybrids. So I'm interested in lightening the bike. I'm not sure if we can do it meaningfully enough to make a big difference. From the dates of your last post your son has probably ridden it some. Can you share your thoughts re: what has worked well?