The Magic of Good Geometry

The Magic of Good Geometry

I hear from riders all the time that they can’t tell the difference between the differing geometries of different bikes. My response is always to give them more credit than they are willing to accept. The body can often discern differences that the brain is unable to articulate. Just because you can’t describe something doesn’t mean you didn’t experience it.

Some years back a buddy told me he was a bad descender. I told him it wasn’t him but the bike he was on; a combination of lousy fit and overly aggressive geometry meant the bike was sketchier than a back alley loan shark. Because were of very similar dimensions, I was able to send him down the famed Palos Verdes switchbacks on one of my bikes.

He got to the bottom exhilarated.

Now transport this issue to the province of children who can’t even pretend to know how a bicycle functions. They have zero ability to tell you what works or doesn’t. They also can’t muddle the issue by being certain that a bike handles poorly because it has a zero setback seatpost or a shallow drop bar. A kid gets on a bike and either their body figures out what’s going on and off they go to indulge their fun center or the device doesn’t made sense and they get off. The Deuce, when frustrated by anything incomprehensible (bedtime is a good example), will pronounce it, “No! Stupid!”


Recently, I picked up an Islabikes Beinn 20-inch, small. This is a review of a different sort as I’m not the person riding the bike, though this isn’t the first time I’ve interviewed another rider about their experience and then written a review based on my notes. With Mini-Shred, making each of the jumps in wheel size has been a trial. I’ll cover that in some depth in another piece I’m working on currently. For now, I’m just going to focus on the jump from 16-inch wheels to 20-inch wheels.

That four-inch jump is enormous. Think about it; in mountain biking we only moved from 26-inch to 29-inch wheels—a measly three inches, slightly more than a 10 percent gain in size, whereas jumping from 16-inch wheels to 20-inch wheels is a 25 percent increase in wheel size. It’s an astounding jump to a tiny person.


The first two bikes we tried were rangy, like putting me on a bike with a 63cm top tube. He fell a bunch, even after I tried swapping out the flat bar for something more back-swept. The 20-inch Islabikes Beinn comes in two sizes, a small and a large. They recommend the small for kids five years old and under and the large for kids six years and up. Because Mini-Shred is in the 35th percentile size-wise for six year olds, he’s small enough to need the smaller bike.

Basic stats for serious bike types: the Beinn features an aluminum frame and chromoly fork, quick release wheels front and rear (handy for car trunk transport), a SRAM drivetrain, linear-pull brakes, a kickstand, bell and tiny person-appropriate saddle, plus Kenda tires that perform both on and off-road.


Islabikes even goes to the trouble to talk about sizing in objective terms, suggesting that a child needs a minimum inseam length of 18.5 inches and a minimum height of 44 inches. Why don’t all the manufacturers do this? Mini-Shred is 45.5 inches tall, just tall enough.

That it was red was cool in his book. He loves red. That it had seven speeds and not six (or one) was even cooler. That the brakes were easy to reach and operate was also to his liking. Liking the bike even before he got on it was a good thing.


All of that is gravy though. I’ve seen him ride a bike and if it didn’t handle well, and by that I mean it was easy to climb on, start and maneuver at slow speeds, he would simply hop back off after a minute or two and want to do something else.

With the Beinn, Mini-Shred hopped on, took off and immediately started carving elegant serpentines. The smile told me all I needed to know. The bike moves in a way that’s natural for him and its maneuverable enough that when he turns from driveway to sidewalk, he can hit that turn without needing to brake.


I could raise the saddle a bit for fuller leg extension, but one thing I’ve noticed with kids this age is that many get nervous if they can’t touch tiptoe to the ground while in the saddle. So I leave the saddle just a touch low.

After our first few rides we headed over to Howarth Park where during the summer Bike Monkey runs a Wednesday night race series. The Dirt Crits are terrific fun. There’s a short fire road climb, a brief flat and then a descent that starts wide and rocky and gradually narrows following a couple of turns. Last summer, on his single speed, coaster brake 16-inch bike, the course was crazy difficult; he had to run the hills. On our recent ride, he did two laps with a couple of dabs and one dismount due to a poorly timed shift. His confidence on trails went way up.


The Beinn small is $439 in red, and $469 in pink or green. That’s multiplicatives more expensive than a Huffy, but this bike will survive both Mini-Shred and The Deuce, and I’ll be able to sell it to another family for continued use. Simply put, it’s rare I don’t come down on the side of quality.

The reason to look at Islabikes isn’t just the construction or handling of the bike. It’s the whole of the buying experience. You can call them for advice. You buy direct from them and it’s shipped to you, and they have a 90-day return policy. The Beinn was the most throughly assembled bike I’ve encountered. Someone with zero bike knowledge could turn the bar and add the pedals; it’s that simple.

Final thought: You don’t need to understand bike geometry to know good handling.

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  1. harris

    Great, and thanks. I had recently arrived at Islabikes independently and was hopeful. You gave a nod to it in your review, but do you think their sizing guidance is sufficient? I have boys 14 months apart and will be buying two bikes of this or similar ilk very soon; more importantly, I can’t wait to see the jump from their BMXers to a real ‘grown up’ bike, as they call them.

    1. Author

      The challenge is that no one that I’ve seen has created a more sophisticated sizing system for little people. And then there’s the fact that it’s hard to account for all the discrepancies between the dimensions of kids. No one is producing a variety of bars and stems for kids, so right now, guidance on height is about all we have, and honestly that’s good enough. Kids aren’t going to ride these bikes nonstop for two hours while producing 100 watts. In short, what they are doing is good enough.

  2. John

    My soon-to-be 9 year old has a comparable Specialized Hotrock, with the Shimano version of GripShift (Revo-Shift). He’s tall for his age, but those grip shifters have been nothing but problem for his right hand.

    Because of the bulky shift mechanism, it puts the hand farther to the right than it would be on the other side, so reaching for that brake lever is really challenging. The lever is adjustable, but even with it as close as I can reasonably get it, he finds grabbing that lever to be very hard. His hands are just not big enough to grab it while they are around the thick section that houses the shift mechanism, and he can’t reach it when his hands are resting on the thin, non -shifting part (like he can with his left hand). Because of that he tends to want to grab the front brake, which is obviously an issue.

    The Revo-Shift seems thicker than the picture you have of the SRAM mechanism there. Also, the brake lever / shift body interaction is also really lousy with our system because the shift body is not entirely flat, and has a little area which bows out slightly. The brake lever body does not fit entirely flush against it, which pushes the brake lever even more away from where it needs to be.

    I’ve looked at many levers online and even bought one which I thought had a longer lever, but in reality it did not address the problem. From what you’ve posted, the SRAM shifter/brake seems like a better thought-out solution than the Shimano one.

    1. Arthur

      Grabbing the front brake isn’t really an issue on the Cnoc 14 and the Beinn 20 that we own. The geometry of the Islabikes is such that the kids are pretty far back and there is very little chance of going over the bars on even the steepest city streets.

      One thing to keep in mind with the SRAM mechanism is that it is harder for smaller hands to twist. The smaller diameter means less leverage and I’ve found that it takes my 5 year old more than a normal effort to twist the shifter. Also, keep in mind that the Beinn 20s in the picture uses special kid friendly levers that are closer to the bar for small hands. That may affect how they sit with the twist shifter.

      I’ll second Padraig’s comment in saying that these bikes got our kids to really enjoy biking. They were really well assembled prior to shipping, and the customer service was fantastic. Yes, they are pricey, but to see the joy in their smiles when biking around on adventures with me is pretty amazing too.

    2. Author

      In Mini-Shred’s experience with the Specialized Hotrock (which we will get to at a later date), he was able to keep his right hand in a position that allowed him a good grip while also staying close to the brake lever. It’s true that the Revo shifter has a larger diameter than the SRAM X4, but it hasn’t posed a problem for him. I have noticed that when he isn’t braking or shifting he slides his hand out a bit to the thinner portion of the grip. I’m sorry to hear it’s been a problem for your son. Little details like this can really sour a kid on a bike, and that’s just tragic.

    3. John

      Just to respond Padraig – there’s nothing tragic! My son like riding, was very very early to get off training wheels, and at the age of 5 could do a near trackstand on the bike. The only worry is from his father, who is convinced in a panic situation he’ll grab all front and endo. It hasn’t held him back, just made things a little more challenging.

      Interesting point on the shifting – it’s true that he has had no issues from day one selecting gears. Maybe that’s the trade-off.

  3. luke

    While Isla bikes sure are nice, Frog-bikes are smashing it right now with light weight, well designed kids bikes with sizing based on rider in-seam and currently a lot cheaper than Isla to boot!

  4. Fausto

    The importance of a great LBS that has years of kids bike experience. It is more complicated in so many ways versus the average adult bike. Safety and user friendliness at another level. Can you imagine if your only choice is Target or Wal Mart? Support the good LBS!

  5. Kimball

    About 10 years ago I looked into buying an Islabike for my then 5 year old daughter, but they were not officially importing to the US so shipping cost as much as the bike. Glad to see they have entered the US market.

  6. Tom in Albany

    Padraig, I n reading the letters, I’m seeing you’ve got Mini-shred the Hotrock AND the Beinn? Why two, if you don’t mind my asking?

    FWIW, my son LOVES his Hotrock. Hasn’t had an issue with the brake lever. He’s 10 and probably going to be nearly 6′ when he’s fully grown so, he’s big enough. The bike is green. He knew it was his the moment he laid eyes on it. He had to have it. The shop guy was OK about fitting my son to the bike. Like you, I lowered the seat a touch when we got home so he could get both toes on the ground. He’s not racing so, who cares?

    Great article. thanks!

    1. Author

      There are a couple of reasons for the two bikes. The first, most honest, reason is that the Hotrock is on the big side for him. It’s just not the right bike for him at this size. The second is that no one reviews kids bikes and I very much want RKP to be a resource on that. The Islabikes Beinn is a great response to both of those needs/goals. I plan to keep my eyes peeled for other bikes for kids. Hoping to cover Cleary soon.

  7. Jared

    Mini-Shred was ripping this bike last night. Great to see him out there mixing it up, an inspiration to me to get the kids out on the dirt young. I will have to look into this bike for my monsters.

    1. Author

      Good to meet you and thanks for the kind words. He was pretty stoked on the race when we got home. Too bad next week is a bye.

  8. peter

    Do you really think that a quick release front and rear is really a great idea on a kid’s bike. It sounds like a lawyers dream to me

    1. Author

      With some parents, maybe not. In my household, where I’m the only person both strong enough and knowledgeable enough to open those quick releases, it’s perfectly fine. I suspect that most of the people who would consider buying this bike to be knowledgeable enough to properly open and close a quick release.

      History has proven me frequently wrong, though. That said, I really do object to the idea of enlisting lawyers because someone got hurt due to an improperly adjusted quick release. That’s user error, not a defective device, and we really shouldn’t be able to sue someone due to our own ignorance.

  9. Jarvis

    Great review Padraig, been a few years since I commented here, but we’re just starting into the second year of the Beinn 20 for our twins and their third Islabikes, they make such good bikes. As for the QR concern that’s just paranoid talk, our two have never even tried to open the QR’s and they will try most things, they are 5 after all. We’ve also swapped the grip shift for SRAM trigger shifters as even with new cables and outer they weren’t able to shift into the lowest gears or out of the highest. Thy took to trigger shifting really easily and we aren’t the only ones to have done this. I don’t understand why Islabikes continue with grip shift otherwise they are brilliant bikes though and I agree with most of their philosophies, I’ve got no interest in their carbon rabbit hole though

  10. JaC

    While this thread is quite old, in the meantime Islabikes closed its US representative office but another company WOOM (from Austria) started its North America operations. The WOOM bike are even lighter then Isla’s while having more conservative geometry worth trying. Similarly to Islabikes in UK, in Europe secondhand WOOM bikes have very good resale value.

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