Raleigh RX24 - 24" Kids Road/CX Bike Project

Constraints breed creativity.  Or so they say.  Well, my bike storage is quite constrained.  And there are these growing kids with bigger and bigger bikes -- and expectations that they get to share that limited space.  So, while being constrained to 3 bikes sounds an extravagance of 2 (or 3) bikes to most of the world, it has made me hone those choices to maximize the range of cycling activities I'm equipped to enjoy.  I still change things around every now and then, but I've pretty much figured out (and designed) exactly what I want.  And so, if changing my own bikes doesn't sound at all appealing, how do I find outlet for my desire to fritter away time and money researching and sourcing bike components for exciting and different bike builds?  The kids' bikes, of course!

My older son has been saying (or said at least once, which was all it really took to seed the plan) that he wanted a road bike.  And he's agreed to give the juniors cyclocross team a try when that becomes an option next year (we suggested that he needs to pick something one sport-like thing to do for extra-curriculars next year, and this was the least offensive to him).   We might be a year and a size of clothes away, but it's obviously time to start on that road/cx bike project!

The Field

There are a few road bikes for kids.  Specialized Allex, Felt F25, Scott Speedster 24.  But if this really is to do dual duty, it needs to be a CX bike (have clearance for 'cross tires).  And, so this rules out the road bikes.

In the world of 24" kids 'cross bikes, there are also a few options.  Most have rim-brakes, but there are a few disc-brake options.  (Disc brakes are pretty much a hard requirement for me on this bike, for reasons that will become clear.)  But standing out head-and-shoulders above the other options, value-wise, is the Raleigh RX24.  So - spoiler alert - that is what I bought.

(Here's a good survey of kids CX bike options: https://rascalrides.com/the-best-kids-cyclocross-bikes/)

Project Overview

So for most people -- smarter, less frivolous people -- adding the $340 RX24 to cart and having it arrive 2 days later (Amazon Prime), would be the end of the story.  The bike, after all, has a solid set of components spec'd; it doesn't really need to be changed at all.

That's boring.

Surely we can find something that "needs" changing.

The highlights of what I set out to change / improve:

1. The wheels -- and the wheel size.  Not only build something that will be better and lighter, but rethink the wheel dimensions to work better for a road-bike setup.
2. The brakes.  The stock brakes would probably be fine, but for smaller/weaker hands, I'd like to improve the braking performance.  Especially if thinking about road speeds.
3. The drivetrain.  Switch to a drop-free 1x setup.  Expand the gear range and top-end speed.

And a sidecar goal to these overhaul changes was also a desire to reduce weight.  At claimed 21lbs (actual 22lbs, w/o pedals) this bike isn't excessively heavy, but I think is a few lbs heavier than it should be.  And when that's 1/3 of your body weight, saving some weight makes a noticeable difference.

And of course to do this all as economically as possible.  It's coming out of my fun-money account, which means these things have to compete with other bike-related purchases.  Informally my goal is to get this to something that is comparable (in terms of features, maybe weight) with the Isla Luath 24 Pro Series, but costing significantly less.

The Wheels

A tangent on wheel size

So, there are actually two different, incompatible wheel sizes being used to refer to "24-inch" bicycles.   The definitive online reference on this is Sheldon Brown's page, but the short-version is that we have bikes like the Isla Luath 24 that are using the kids mountain-bike 507 ETRTO size and bikes like the Raleigh RX24 that are using the British youth 540 ETRTO size. ... Also shared by wheelchairs.

That 540 size is pretty tricky if you actually want to find tires.  Well, other than wheelchair tires.  And this difficulty provided inspiration for one of the key goals of this bike project.

Can we change the wheel size?

Since this is a disc-brake bike, there's nothing stopping you from running a smaller wheel (well, almost -- see below).   The ETRTO number refers to the diameter between the bead shelves on the rim.  A 540 (mm) ETRTO is obviously quite a bit larger than a 507mm ETRTO that is the more common size, so putting smaller wheels in this frame is certainly an option.   But frames are designed with bottom bracket drops/heights for a specific size wheel, so while it may work fine in theory, in practice it might increase the risk of pedal strike (pedal hitting the ground when turning) if you drop the bike by 16mm ((540-507)/2).

There's another option, which would be fitting larger wheels in the frame.  As it turns out, the very common 26" MTB wheel size is not that much larger -- its ETRTO is 559mm.  So 9.5mm increase in radius.  But for a road tire, that might actually work out perfectly.

The nominal size of the stock tires is 37-540  (37mm tires), which theoretically indicates an overall diameter of:

37 * 2 + 540 = 614

If I were to fit a set of 28mm road tires on 559 rims, the theoretical diameter would be:

28 * 2 + 559 = 615

That's pretty close.

In practice, though, nominal tire sizes and measured tire sizes are only loosely related, so this isn't quite as cut and dry as it looked on paper.  (Spoiler alert) In practice everything measured smaller than claimed, so the new wheels are maybe a few mm bigger -- but it all works out just fine.

The Wheel Build

I'm always looking for an excuse to build wheels, so this is certainly a fun part.  Sourcing parts for a 26" road wheel (esp. w/ quick-release dropouts) is actually really easy.  For one thing evolution of trends plays into this nicely: older MTB rims were quite narrow by modern (MTB) standards -- and looked much more like what are now being sold as road-width rims.  And the using QR for disc-brake wheels is definitely a thing of the past, so it's quite easy to find hubs on clearance, etc.

Most 26" (MTB) rims, though, do tend to be drilled for 32 spokes.  I really wanted a 24-spoke wheel.  This is a road bike, after all.    Luckily there were some lightweight rims drilled 24h and 28h for XC racing.  I picked up a set of 24-hole Sun UFO rims for $50 shipped; these are eyeleted rims which weigh around 370g each.  For hubs, I turned to BDOP cycling clearance bin and picked up a Novatec D612SB and D711SB hub for around $70 total.  I laced these up with Sapim Laser spokes.  At 1377g, they are certainly some of the lightest "normal-sized" wheels I have built.

So, that wheel build was very economical [by wheel-build standards, anyway!], I ended up going completely off the deep end when it came to tire choices.  To be fair, the options for road tires in this size are fairly limited (though vast in comparison to the stock wheel 540 size).  After looking at ~$50 prices for a Schwalbe Pro or Conti Grand Prix tire, I ended up buying $78 Compass Elk Pass tires, which are absolutely the nicest tires any 26" road wheel could have.   And completely excessive.  But I kinda love my Compass tires and I'm happy to support this smaller outfit.

On these rims, which measure 17mm internally, the 32-559 Elk Pass tires measure around 27-28mm high.

I also picked up a set of the Isla Greim 26 tires for when this swaps to 'cross season.  On these rims these 31-559 tires measured ~30mm wide and~29mm high.

Tire Clearance

As hinted at earlier, the nominal size of the stock tires (37-540) was larger than they measured (closer to 32mm), but in the end even the Isla CX tires fit fine  Here are a few clearance photos with the Compass tires:

10mm of side clearance in chainstays.

I used some 10mm-thick rubber tracks to provide a visual on clearance.

Demonstrating that ~10mm of extra clearance exist at seatstay.

Plenty of room in fork.

Demonstrating clearance at chainstays (bike is upside down).

And here are a few with the Isla/Greim tire:

~8mm of clearance to the seat tube.

~8mm clearance from chain stays.

Photo of chainstay clearance.

So, these both fit quite comfortably, which is great since they should address the complete set of purposes for this bike.

The Brakes

If money were no object, I would have replaced the SRAM brake/shifter levers with a full-hydraulic 1x setup.  But that would be a $400+ investment, and that seemed a bit much even for me.  Plus, even though they offer reach-adjust, the SRAM road hydraulic brake hoods are really big for someone with such small hands.

At first I considered TRP Spyre calipers, but in the end decided that these probably weren't going to offer much of an improvement in braking over the stock Promax 300R calipers. 

I then turned my attention the cable-actuated hydraulic calipers.  These should provide better bite than stock calipers but would work with the existing SRAM S500/Apex lever set.  The TRP Hy/Rd was an obvious choice, but upon further research discovered the Juin Tech R1, which was not only cheaper but also was quite a bit lighter (as light as TRP Spyres).

The Juin Tech R1 calipers are also rebranded as the Yokozuna Motoko -- and I found a set of these  domestically for $160, which was quite close enough to the $150 that the Juin Tech R1 cost -- plus they would include the notoriously good Yokozuna Reaction housing (which sells for $75 by itself).

I did order separate Avid HS1 rotors, though.  The Avid rotors offer excellent stopping power and they're inexpensive (I got them lightly used on ebay for $20 for the set, though Amazon also has them new for not much more).

I haven't actually ridden this bike, but from what I can tell these do a great job stopping the bicycle.  I gave my son instructions for bedding in the pads/rotors; I think he followed them.

(I should probably mention that the brakes added a little net weight to the bike.  The stock Promax 300R calipers were around 130g, compared to the 142g for the Motoko calipers.  But the point here wasn't to save weight, but to improve braking.)

The Drivetrain

The goal was to expand the gear range, move to a modern 1x system (drop the bash guards sandwiching the front ring), and reduce system weight.

The stock bike came with a 32t chainring and an 11-32t cassette.  I found a lightly used XG-1080 11-36t cassette on ebay for under $80, which is a lot for a cassette, but they aren't quite wear-and-tear parts on kids bikes.  I paired that with a Deckas 38t, narrow-wide chainring.

And swapped out the Apex WiFli rear derailleur (max 32t cog) for a used SRAM GX short-cage, clutch rear derailleur (max 36t cog).

So we moved from a 291% gear range to a 327% gear range, while lightening up the overall system and quieting it down (from chain slap).

Other Odds and Ends

I found some used Bontrager 38cm carbon XXX bars on ebay for $40, which weighed about half of the stock 36cm bars with compact drop/reach.

The 60mm Uno stem didn't save much weight, but I had it on hand, and I like them.  (I've actually ordered a 40mm Wren stem to pull the bar in a bit, so I'll swap that in when it arrives.)

I kept the stock cranks, but replaced the square-taper bottom bracket with a "Week Eight" titanium + alloy model available on ebay for $39.  Generic square-taper bottom brackets are ridiculously heavy.

For the saddle, I did some research and settled on the WTB SL8 as a good option to anatomically fit young riders (narrow and not too long).  At $90 this was one of the more expensive components, but it seemed like a decent investment.  The stock saddle on the RX24 is probably one of the worst parts of the stock spec.

The seatpost is a Hylix 27.2mm carbon post.  Quite inexpensive on ebay/aliexpress.

The Final Product

I'm really happy with how it turned out.  The wheel size upgrade is a huge win for tire options/versatility -- and the wheels are much lighter.  The brakes are a nice improvement (or so I'll just have to assume based on all reviews) while using the existing levers and the drivetrain is expanded and lightened up.

Ready in all his mountain-biking gear to test out this road bike!

In terms of the weight savings, we got the bike down from 22.0 lbs to 17.3 lbs (both weights w/o pedals).  My son helped me do some part weighing so we could see what were the biggest wins weight-wise.  This is obviously not comprehensive, but there were a few surprising items.  There are certainly many places to save further weight, if someone were so inclined (and less budget constrained) -- e.g. the crank arms.  Unfortunately, there's no option that I'm aware of for a 3rd party carbon fork at this size; that would likely save significant weight.

Part	Stock Part Weight (g)	New Part Weight (g)
Stem	115	91
Saddle	321	189
Seatpost	294	156
Bottom Bracket	305	135
Cassette	329	213
Rear Derailleur	208	266
Handlebars	356	181

This was a fun project.  I don't think there is anything at this point that I would do differently, though certainly if I wasn't trying to stay in any sort of budget, I would have found a way to do full hydraulic brakes.  As it is, my son still isn't comfortable using the brakes from the hoods; it's just not enough leverage to quickly stop the bike from there.  Hydraulics, if he could fit his hands around the larger hoods easily, would not have that problem.  But he is happy to use the drops and I've positioned the bars a bit higher / less-aggressive to make that more comfortable.