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  1. #1
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    Islabike Beinn 20" mods: Converting to 2x7 drivetrain

    Hi All,
    I've been doing some mods to my 9 year old daughter's Islabike Beinn 20" Large, and thought I'd post the status here (both what has worked and what has not worked thus far).

    The geometry of the Islabike Beinn is outstanding, but my tiny 9 year old (49" tall, 45 lbs.) is ready for more hill climbing capability than the stock 32/32 low gear allows. She loves challenging herself on climbs, and is often limited by the trails she can ride due to lack of a granny gear. I'd hoped she was going to be big enough this season for a 24" bike and therefore a 2x10 drivetrain, but she's still too small. The Beinn 20" large fits her perfectly---so time for a custom build.

    Changes:
    - Quick release seat collar that kid can self-operate.
    Salsa Fliplock 28.6mm is perfect. It's not the cheapest quick release, but the long lever means she raises and lowers the seat herself for uphill, downhill, and pump track modes.

    - Rear trigger shifter.
    After a couple of years with grip shifters on her Beinn 20" small, she found a number of times where she was not able to shift when she wanted on the trails (and would end up with blisters from the grip shift bump on the bars, even through her gloves). Conversion to SRAM X-3 trigger shifter was straight-forward, and she's shifting much more often now (had to buy the replacement full-length grip from Islabike). Not sure if this is universal for all kids, but the trigger shifter is far easier for her to shift than the grip shift.

    - Tires.
    Convert to Schwalbe Blackjack 1.9. This definitely added some weight to the bike compared to the stock Kenda tires, but it's been worthwhile for trail riding (though I will say I was surprised how well the lightweight stock Kenda's worked for trail riding, despite their anemic tread).

    - 2x7 drivetrain.
    This has been a journey. The stock gearing is 32T chainring with a 32T low on the 7-speed cassette.

    In my quest for lower gears, I considered converting the back to a 1x10 setup with a 42T conversion, but the price and complexity of the change scared me. I was also worried the out-stretched derailleur would come too close to the ground on the 20" wheel. And so I set out to add a 22T granny gear to the front.

    Ginger at Trailcraft Cycles suggested I take a look at a custom cut SRAM S600 (2x chainrings with the 3rd slot used for a pant/bash guard) from Mark at Bike Smith Design. Mark sells you-pick-the-length SRAM S600s for this purpose (the Beinn 20 large comes with 127mm cranks). See Short Bicycle Cranks. However, I was worried about the wider q-factor and heavier weight compared to the stock Islabike/Lasco cranks. Mark's prices are great for the service he provides, but I was hesitant to spend almost $200 for custom cranks on an otherwise $400 bike.

    Instead, I decided to drill a 64 BCD bolt pattern in the existing all-in-one Lasco chainring/spider. A machinist friend (who builds custom bike frames on the side) carefully drilled the bolt holes (see pictures). I make no claims about the resulting structural integrity of the chainring, but so far so good (the kid is only 45 lbs after-all). From here, it was easy to bolt on an old Shimano XT 22T chainring. I am currently using 5mm spacers between the chainrings, but these are too thick (I'll post an update when I figure out the ideal spacer size).

    Chain line.
    I removed two links from the chain to make the higher rear gears accessible with the 22T ring. It seems to run fine in any of the gears, though the usual cross-chain gears are questionable.

    The chain line seems fine with the 22T ring except for the highest 2-3 rear gears. These gears are usable/rideable, but with some clicking due to the chainring teeth catching the inside face of the chain links. I'm fairly certain all 7 gears will work cleanly with the 22T ring when I find the right chainring bolt spacer size (guessing 3mm or 4mm). The 5mm spacers push the 22T chainring too far inward.

    Front derailleur.
    I've tried a few different SRAM and Shimano mountain bike front derailleurs, and so far, none of them work. The challenges are finding a derailleur with a cage that doesn't hit the chainstay when on the 22T ring and doesn't hit the crank arm when on the 32T larger ring. The clearance between the 32T chainring and crank arm is very tight (thanks to Islabike's well-intentioned/appreciated push for low q-factor cranks).

    Any ideas which front derailleur might work? Maybe a road bike derailleur?

    At this point, I'm tempted to give up on the front derailleur. She's going to ride this as a 22T 1x7 on almost all mountain bike trails, and I'll manually shift it to the 32T for pavement rides. Leaving off the front derailleur and shifter also avoids adding close to 1 lb. to the bike.

    Overall, the mods seem to be working well, and she's having a blast learning to climb steeper and steeper hills with the lower gears.

    Islabike Beinn 20" mods: Converting to 2x7 drivetrain-img_5019.jpgIslabike Beinn 20" mods: Converting to 2x7 drivetrain-img_5020.jpgIslabike Beinn 20" mods: Converting to 2x7 drivetrain-img_5022.jpgIslabike Beinn 20" mods: Converting to 2x7 drivetrain-img_5025.jpgIslabike Beinn 20" mods: Converting to 2x7 drivetrain-img_5027.jpgIslabike Beinn 20" mods: Converting to 2x7 drivetrain-img_5023.jpg

  2. #2
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    i was just at sea otter and found this company. i met isla and she is so passionate about kids bikes. she showed me how the bars are smaller for their hands, the grips are large at end so the bars wont cut thru them and impale the child on a crash, her own cranks and brake levers, super light wheels, all designed smaller for kids.

    but what sold me was the weight and price. my son's 12" wheeled with a coaster brake specialized hot rock is 16.5 lbs and isla bikes beinn 20" wheeled geared bike with 2 hand brakes is 17.5 lbs. only 1 lbs more for way way more bike. thats really cool to see.

    my wife is only 4'11" and may order isla's road/cx bike.

  3. #3
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    Thanks for posting.
    I have decided to get an Islabikes after looking at a number of slightly less expensive and several much more expensive options. In the end, for the $100 more that you pay for an Islabike over HotRock or Cannondale, you get a ton of weight savings and some nice kid-centric design. I finally did the calculations and I can't get a $350 bike down to this weight with an additional $100 investment. So I am going Islabikes from the start. I'll do the trigger shifter and better seat QR too as you did, with some stuff I have in the parts bin.
    Rather than try to do 2x, I think eventually I will move to 1x9 or 1x10 to increase range that way, but I think we'll be fine with the stock gearing for now.

  4. #4
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    Quote Originally Posted by backinmysaddle View Post
    Thanks for posting.
    I have decided to get an Islabikes after looking at a number of slightly less expensive and several much more expensive options. In the end, for the $100 more that you pay for an Islabike over HotRock or Cannondale, you get a ton of weight savings and some nice kid-centric design. I finally did the calculations and I can't get a $350 bike down to this weight with an additional $100 investment. So I am going Islabikes from the start. I'll do the trigger shifter and better seat QR too as you did, with some stuff I have in the parts bin.Rather than try to do 2x, I think eventually I will move to 1x9 or 1x10 to increase range that way, but I think we'll be fine with the stock gearing for now.
    I'm admittedly among the converted, but you're making the right choice. Even if you could get the weight to match, you'll miss out on the Islabike geometry, which is a key part of their special sauce.

    Over our 3 kids, we've tried a Strider, 12" hot rock, 16" hot rock, 16" Spawn Banshee, and now have replaced them all with Islabikes. In addition to the light weight, correctly-sized cranks, kid-size bars, and brake levers, what sold us on the Islabikes is the geometry. Our kids simply progress faster, ride better, are more stable, and have more fun on the Islabikes because the geometry is dialed.

    Our most recent case study was watching our 6.5 year old son transition from a (customized 3-speed) Spawn Banshee to the Islabike Beinn 20" small. In the 3-4 weeks he's been on the Beinn, his skill level, trail speed, and confidence have skyrocketed. Yes, he's on bigger wheels with more gears, but I don't think those add up to the changes we've seen in his riding. I credit the Islabike geometry with the bulk of the change (admittedly we'd need to see him on the same size Spawn and Islabike to do a fair comparison).

    One detail I'll note about the trigger shifter conversion. The one downside it has is that tiny hands do have to move inward on the grip to reach the shift triggers, then move back out to reach the brakes. I tried switching the position of the shifters and brakes on the handlebars, but it doesn't work (they are designed for the shifters to be mounted inside of the brake lever mounts). This may be why manufacturers put grip shifters on kids bikes. However, the trigger shifters seems to be the lesser of the two evils, with both my 6 and 9 year olds shifting more often and more easily with the triggers, even though the setup is not perfect.

  5. #5
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    BTW, I just weighed the modified 2x7 Beinn 20" large shown in the pictures above on the bathroom scale, and it comes in somewhere between 17.5 - 18.0 lbs. (can't get an exact reading with my scale). I'm pretty happy having a 2x7 with a 22T/32T low gear on a sub-18 lb. bike.

    I'm not going to bother trying to add a front derailleur unless my daughter starts maxing out the 22T/12T high gear on trail rides.

  6. #6
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    I went 1x10 on my daughter's 24" Beinn, to get a lower gearing.

    I agree that a 42t rear cog, or even a 36t brings that rear derailleur awful close to the ground on a 20" wheel.

    One more vote for the Salsa Fliplock seatpost quick release. The long, comfy lever really helps to make it usable for kids on their own.

    Before I went 10 speed I let my then 6 year old try both trigger and twist 10 speed shifters on adult bikes and she liked the gripshift better. Who knows how she would do if she were actually riding the triggers, but she seems to do fine with the gripshift.
    I have to say though, this is the X0 shifter, so it is likely a lot smoother and grippier than the cheaper old versions for 9 speed and less.
    DI2 would be perfect for kids ;-)

  7. #7
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    Good to hear about a 10sp Beinn conversion.

    Does anyone know if a 10sp or 11sp SRAM casssette will fit on to the 7-sp hub on the 20" Beinns, or will that conversion require a new hub?

  8. #8
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    the 7 speed cassette probably has a spacer, so it should work. 8,9 and 10 speed use same hub.
    SRAM 11 speed requires a special hub to fit the 10 tooth cog. Shimano makes 11 speed 11-42 casettes though, and there are complete 11-42 or add-on 42t coggs for 10 speed.

    Note that my 10 speed conversion is on a Bein 24", which came with an 8 speed cassette.

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