Serenity5

I am putting together a multi seater for long distance(cross country) family adventure. I am like the low maintenance of the Gates belt as we will be riding everyday and having a LOT of chain management is not my idea of fun. I want to keep it on the right side so I can get specific crank are sizes for the kids 140,150,160. Current offering for left drive is normally 170or 165 and then use shortener's ( I don't like them) I think i can make it happen but will have to use different length BB spindles, I am going with square taper so getting different lengths is not a problem. I just have never seen it done before. I also have not seen folks run 1x12 any thoughts on using it for a multi seater? we are a lighter team 2 smaller adults and kids 12,10,8 so we are not going to develop huge force but it will be more than a 2 person team. Love to hear thoughts and ideas

Darth Lefty 

I know that earlier this year I saw a multiple hole crank set for tandem rear that was in several popular kid lengths. I will have to see if I can dig it up again.
Edit: Thorn, from SJS in England, 115/140 length, 104x4 bcd, square taper, black https://www.sjscycles.co.uk/cranks/t...0464-plus-104/
I must be mis-remembering, I thought there was a longer version. 115/140 is kind of odd too, would expect more like metric equivalents of 4, 5, 6 in

da Vinci also makes one. It was way more expensive, though.
https://www.davincitandems.com/components/

You can also get the drill and tap, use them on a sufficiently beefy aluminum crank. That also kind of solves the 2-sided problem, you can use a right side crank on the left side and put new left side holes in it

OneIsAllYouNeed

I personally like a wider and closer set of gears than you can in a 1x12. There are a handful of 2x11 drivetrains that can achieve about 650% overall gear range and reasonable jumps between gears. With 2x11, you could use Shimano or Sram, flat bar or drop bar, mechanical or electronic shifting. The 12-speed options aren’t quite as versatile. On the other hand, another forum member has been using 1x12 on their bikepacking tandem for a few years:
https://www.bikeforums.net/tandem-cy...m-project.html
The bike in that post now has Campy 12-speed shifters, Shimano hydraulic brake calipers, and Sram 12-speed derailleur and cassette — the challenge of wanting a 1x12 dropbar MTB groupset before one was ever released.

If you don’t have your frame yet, the chainstays could be setup to allow double chainring, and a right side timing belt or timing ring, and relatively low Q-factor for your rear admiral.

For left-side-timing kid stoker cranks, it’s perfectly reasonable to helicoil cranks with the correct handed threads. Drilling and tapping longer crankarms is fine, too. My tandem has 175mm Sram S350 crankarms drilled at 100, 125, and 150mm for my growing stoker.

Serenity5

i have though about drilling out the crank arms. like most things when its only one its not a big deal but i would have to buy tandem specifc cranks for every position and then turn around and modify them anyway. we have used the kid stoker rig (130mm length) on one of our tandems which has worked but we are not going to be using a kid stoker assembly for this new rig. I am also not averse to 2x11 but the shimano line now has closer gearing steps for their 12 stack and more reasonably priced than sram. I have also toyed with Pinon or rollof but i think we would make too much torque, Pinion limits at 250KN and 100KN for the speed hub. I dont know if anyone has tried it with a multi seater or ran a power meter on one. I would be curious to know. thanks

OneIsAllYouNeed

To be fair, I’d opt for using unmodified BMX cranks for all the middle stokers, too. Keeping all the chains/belts on the right side is best for overall efficiency, reducing bottom bracket wear, and theoretically lowest upfront cost.
Pinions have a 250Nm input torque limit. That’s measured at the final crankarm — a 1:1 gear ratio with all the cranks. Sum the product of all your weights and crankarm lengths. Is that number over 250Nm? If it is, you’d risk damaging the gearbox if you all pedal out of the saddle.
Rohloff’s 130Nm limit is AFTER the gear ratio change from the last chainring and cog. They recommend a lowest gear ratio of 2.5:1. Effectively, this means the last crankarm torque (the calculation from above) can be 325Nm.

Serenity5

" Sum the product of all your weights and crankarm lengths. Is that number over 250Nm?"

I don't think i am following this right, how do you incorporate crankarm length to get the total Nm I must be missing something

OneIsAllYouNeed

There's a factor of 1g (9.8m/s^2) missing to translate from mass*millimeters to N*m
Here's are two examples you can paste into the google search bar:
170lbf*175mm+120lbf*165mm+110lbf*150mm+100lbf*140mm+90lbf*130mm to N*m
(70kg*175mm+60kg*165mm+50kg*150mm+40kg*140mm+30kg*130mm)*9.8m/s^2 to N*m

WheelsNT

We have a multi-seat bike with 12, 10, 6, and 4. 12 and 10 are on 170s with no problems. Maybe you don’t have as big a problem as you think? If you only need to address the 8-year-old, that’s only one set of cranks to deal with.

merlinextraligh

I don’t have experience with 1x12 on a tandem (we are running 2x11 which works well for us.)

I do use 1x11 on my mountain bike, and that experience tells me that I don’t believe I’d be happy with a 1x setup on a road tandem.

On my mountain bike, to get a sufficiently low end, and decent spacing, the top end is a bit limited. I could go to bigger chain ring to up the top end, but that would also require a cassette with a bigger big cog and poorer spacing.

It’s not a big deal on the MTB, where top end speeds are typically much lower. However on a road bike, if you want to be capable of pedaling in the mid 20’s at a reasonable cadence, while also having a relatively low climbing gear, even with 1x12, it’s going to be a challenge to do so with reasonable gear jumps.

Of course all this depends, on how fast you want to go on the top end; how low a climbing gear you need, and how big a jumps are acceptable to you.

tandem rider

This is an interesting website for shorter cranks. https://bikesmithdesign.com/

Serenity5

[QUOTE=tandem rider;21761098]This is an interesting website for shorter cranks./QUOTE]
Thanks for the link. Love that cottage industry is still alive and well for some, maybe there is hope for some of my ideas.

on a side note this min of 10 post thing before you can post pictures or URLs is kind of a pain, I even had to edit my"quote" so it would post

Paul J

[QUOTE=Serenity5;21761143]To get your post count up got the the introductions forum and introduce yourself and welcome a few new people any you will have your 10 posts in minutes. :-)

sdodd

We have the DaVinci three hole cranks and they are beautiful! (we also have a davinci tandem making the stoker cranks just a left side chainring) I have really enjoyed the multiple hole cranks as we have been playing with different combinations of crank lengths between captain/stoker to achieve a good RPM for both of us. 20mm difference in the holes is 'a lot' but we have some other fixed length cranks than we swap in that are between the 170/150/130 lengths to supplement.
I too have never liked the bolt-on crank shorteners. the extra width makes me feel like I'm riding a pedal powered horse.

Carbonfiberboy 

A quick feasibility study seems in order.
I would stress Merlin's last point more strongly - it's all about how low a climbing gear you need. Hop over to a bike calculator like:
Bicycle Speed (Velocity) And Power Calculator
Enter your all-up weight including touring gear, your maximum gradient, and the lowest speed you think you could manage on this multi. Then calculate and see the power necessary. Adjust until the power seems possible. You might need to draw the more mountainous parts of your route in RidewithGPS to establish gradients.

How to estimate your stokers' climbing power? Put them on their single bikes and have them climb a long hill of known gradient with you on your single. See how fast they go and get their all-up weight on the bike. Go back to the calculator and find power.

Then go to a speed and cadence calculator like:
Bicycle Bike Gear Ratio Speed and Cadence Calculator
Enter your lowest final drive gears and some possible climbing cadence, like 70. Then look at the required gear-inches. See if you can achieve that with your 1 X 12 and available Gates Belt lengths.

This is how rocket science is done. One really wants to know if it's going to fly before one spends a few billion on the device. IOW, nothing worse than a tandem that's never ridden, especially an unsalable multi-seat.

72andsunny

I’ve got a Rohloff on our quad. I don’t know how much power we put out (my kids are young and have child stoker kits), but with what you’re trying to do, the only reason not to go Rohloff is cost and weight. I’ve got the shifter mounted as a bar end on drop bars. I’m not in love with it; I might eventually upgrade to brifter controls, but I’m living with it for now. If you’re doing flat bars, then not a problem at all.

sch

Since gates belts are available in a limited # of sizes, I assume you are coordinating your build with manufacturer
who can do the slightly dicey math of 4 separate belts and bottom brackets. This brings up the ? do all the BB
in a multiseat bike have eccentrics (except the rear most), seems logical they would, just never thought about
it til now or would alternate BB with eccentrics be enough.