JSimonds

Howdy everyone. We are longtime tandem riders/racers about to order a new tandem. We could use some expert help with specs.
Mrs J.S. uses 175 cranks. This bike will have boost spacing (steel bike) presume a 53.3/54 chainline. I would like to set this up as a double with 110 drive / 130 timing. The distance between BBs will most likely exceed specs. I've come to understand are acceptable for Gates so that's out this bike will have a chain for timing. I've used DaVinci in the past with success however am not certain about BB spec. and performance.
What tandem cranksets will meet these needs?
TIA, J.S.

Leisesturm

I'm sorry but you are both supplying information and not supplying information such that makes suggestions difficult. The BCD of the cranks is not needed. The spindle length(s) of the planned cranks IS needed. The distance between BB's is also irrelevant and not important since you are using a chain timing. Why not supply the planned make/model of bike and what component groups you like? An IPS (DaVinci) drivetrain is not usually a performance choice. Boost spacing is mainly a new option for steel All Road or MTB half-bikes. I could be very wrong but I think tandem cranksets with 53mm chainlines will not be commonplace. Still, if you are willing to buy a 3rd party BB spindle of a suitable length (and there is plenty of wiggle in the chainline spec) you can get whatever you want within reason. This doesn't have to be a difficult proposition.

JSimonds

Thanks for the help. I'm going to use conventional cranks on a steel all road tandem using Boost hubs. This chainset has the right specs.: ( FSA SL-K BB392 Tandem Crankset ) however it appears that the stoker position is only made in 170, we need 175. Thus, I'm looking at DaVinci cranks made by White Industries (not their independent drive) as an option.

The sticking point is getting a 175 stoker crank and a good chainline.

Leisesturm

Looks like you can get a 53mm chainline on the drive side and 53.3 on the non-drive side with the stock BB spindle options. That is as good as it gets and more than good enough IMO.
Edit: Never mind. This crankset is 170mm only. If the DaVinci cranks are JIS (square taper) there are a bazillion 3rd party spindles in 2mm length increments so it is just a matter of finding the length that gives the desired chainline. Usually the chainline for a 'standard' length of spindle (~120mm) will be given and you can size up or down from there for your unique application.

Krenovian

Welcome to the forum!

I like the DaVinci cranksets and their modular spiders. I've had success with the Omni Racer square taper BBs. I think this may be the brand DaVinci sells, though I buy direct from Omni Racer.

If you contact DaVinci they may be able to tell you what length spindle you'll need to achieve the appropriate chainline for boost spacing using their crankset. I use the trial and error method myself as I have a collection of square taper BBs with different length spindles to choose from.

With respect to the Gates belt, I recently was looking at the Precision Tandem website and came away with the impression that there are three different lengths of belts available. https://www.precisiontandems.com/cat...belt_drive.htm. Maybe one of those lengths would work for you. There were instructions on the site as to how to measure your frame to determine the appropriate size belt. Someone with more knowledge may be along to confirm or debunk this.

rocknrollin

Welcome!
The crankset you are looking at has 30mm spindles. Are bottom brackets compatible with that? Did you plan to use BSA30, or does your frame have pressfit?

If you go for 30 mm spindles, you could also have a look at cannondale hollowgram crankarms & spindles. The 125 mm spindle should give a chainline of 51.5 mm. You can buy all parts separate and choose between different cranklengths.
To run the belt, there have been several pictures in this forum from people running the gates beltring on the outer position of the drive-side next to the double chainring (you can buy double or triple spiders for cannondale cranks)
Please check the dimensions yourself, as i have no experience with it myself yet - i have been looking into it for our next build.

Joint Venture

With the da Vinci cranks you can choose from a number of different chainring BCD options when ordering due to the replaceable spiders. So you’ll have flexible gearing options, as well as being able to choose crank lengths and, of course, bottom bracket spindle length to get whatever chainline you like!

OneIsAllYouNeed

You have a handful of options for 175mm stoker cranks with boost chainline and those bolt circles. My Chinook has Sram Rival BB30 cranks; the rear left is a helicoiled right crank. I can use 110bcd or 130bcd spiders, or direct mount chainrings on both sides. Most of the newer Chinook tandems have Sram Force cranks in a similar configuration. Lightning tandem cranks are available in any length and spider size. They’re lighter and pricier than a Sram Force setup. All of the above options use 30mm bottom bracket spindles.
Davinci cranks are also available in nearly any length and spider. You’d have to verify what square taper spindle length would be appropriate for the boost chainline. Note that it’s only 2mm narrower than the common 145mm tandem quick release standard, so the usual spindle length is probably fine.
What length captain cranks do you need?

JSimonds

GREAT replies. I may never leave this place.
Just got off the horn with DaVinci and confirmed that either a 107 or 110 BB will give me 53/54 chainline respectively so in short fat city.
I'll buy the DaVinci Cranks. I've used these with great success for my singles.
Changing the topic a tad...DaVinci makes a really slick 34 tooth one piece timing ring that is perfectly round which is a nice thing for tandems. I've always setup our tandems with 40 tooth timing rings. Unless there is a compelling reason not to use 34 for this rig I'll go with it.
-J

jim_pridx

We just switched to a Gates belt system for our timing setup on our Bob Brown bike, but prior to that we used the da Vinci 34t rings with no problems at all. I have heard that a smaller ring will tend to wear out a little quicker over a larger one, but ours are still in great condition after 10 years of regular usage. Even though I prefer the belt over a chain, I would never have any qualms about using the 34t rings again.

JSimonds

This is good intel. I'm waiting for a drawing so I can get a spec. on the distance between BBs. Gates option does look compelling.

jim_pridx

As it turned out, the distance for our Gates system was spot on, so I ran with it! We ended up using the da Vinci spiders with it as well.

EDIT: In the even you're interested, here's a photo of the Gates system that I took just after I installed it last summer:

Joint Venture

We’ve put a lot of miles on two different sets of the “one-piece” 34t da Vinci spider/rings on two different tandems and can recommend them without reservation.

JSimonds

Jim, nice job on the Gates drive.

My choice for cranks boiled down to DaVinci or Lightning . DaVinci I know would be fantastic because I've run their single bike cranks for years. Ultimately I had to have 180 captain cranks and I'm keen to stick with direct mount BB bearings for alot of reasons. There is only one maker currently in business who fits that ticket and that is Lightning. Once I have the cranks installed and have a few rides on them I'll report back. Confidence is high.

Meanwhile, the new tandem design is final and has been put into the production schedule.

Looking forward to a BIG box of parts and all the time in the world to build it right.

WheelsNT

A possible thing to worry about with 34T timing rings is excessive frame flex in the boom tube. Usually this is only a concern for multi-seat tandems (3, 4, 5 seats) but since you and the stoker are running long cranks, maybe you are a super powerful team. The guts of it is that larger timing rings pull more chain, faster, with less tension, per revolution, while smaller rings pull less chain, slower, with more tension, per revolution. So smaller rings flex the boom tube sideways more than larger rings. On a multi-seat tandem with a powerful team, this can lead to significant slack in the lower runs of timing chains while the top runs are taut. At that point derailing the chain when hitting a bump becomes a possibility and a concern. As i mentioned, probably not a concern for you, but mentioned for completeness.

JSimonds

Appreciate this Wheels. In fact, I went with 40 tooth timing rings as that worked flawlessly in the past. Peter White has my CC on file Those TA Zephyr rings are the jam.