Turbotandem

I'm completing a tandem project that seems worth sharing the spec and results. I'd enjoy addressing questions about the thought process, spec, and how it functions.

6 months in the planning between myself, some time with Calfee but ultimately Paketa offered to develop a new geometry 29-er gravel bike for us to use on ultra-distance back country gravel road racing. We wanted a bottom bracket clearance only just a fraction higher than a road bike, but not too high a center of gravity like a mountain bike would have. We matched our current MT300 cdale clearance on the pedals that we've seldom smacked on the roughest stuff we get stuck riding when seeking better gravel. The lower center of gravity helps performance on long windy courses. Double curved chain stays and single curved seat stays allow a 2.2" tire, while at the same time clear the tight q-factor Lightning road cranks and the stays need to clear the teeth of the chain ring on a a triple 22-34-44 we'd spec'd. The tight q-factor road cranks are important for both mine and my wife’s knees. The frame geometry accommodates a 397mm axle-to-crown cross fork, I did not want a bent top tube mtn bike style 470mm fork. Fork is Whiskey Cross No 7 which lists "no weight limit" and is far more robust than enve, trp and others I studied. Oddly, the no 7 Cross has more tire clearance than the no 9 Cross. While they were at it, Paketa re-engineer the frame making the down tube the same 60mm diameter tube as the bottom tube, added rear triangle gussets on both side (and clears the chain in the small cog), and uses a straight 44mm head tube. I’ve also worked with a local frame bag make to coordinate additional bolt mount points for back country frame bags rather than having the usual Velcro straps all around the frame tubes. Internal wired. Frame is 5.75# unpainted, 6.25# painted. Spectrum Powder Works came up with a special powder coat base with liquid paint top coats for pearl finish but mostly developed for better all weather performance than powder alone. Notice the wicked "reveal" logos in the over-painted black bottom tube and chain stays with the base metallic brown showing thru.

XTR Di2 RD on 10x42 11 spd SRAM cassette. Yes, the 10x44 high gear works well for us, and the intended ultra-distance bike packing, back country races will take advantage of the low 22x42. Crazy. XTR Di2 FD on 22, 34, 44 chain rings, shifts fine but oh so close to not working. I think the the FD is intended for a mountain style 74mm bottom bracket. On a road bike bottom bracket 68mm wide the FD is set at its very inner most limit both with mechanical and programmed limits. Also only just clears the inside face of the tight Lightning crank Q factor without striking the FD cage. The wide range of rings serves our need, and one might agree with santana recent testing that my 22 tooth range in the chain rings could be duplicated in a 30-52 tooth rings. I can't confirm that. The chain wrap far exceed the rear derailleur spec'd capacity, but with the sychro-shifting and a bit of adjusting the program to shift out of the large ring early, you are prevented from severe cross chaining. Road bike shift brake levers are now out of production limited availability, Ultegra 6770 coupled with a the XTR display. Back-up would have been sprint shifters. Display is really nice.

TRP Hy/Rd brakes on 203mm rotors front and back. The Whiskey fork spec is for 185mm max rotor. But both the no7 Cross and no9 cross clear a 203mm rotor (I had both in hand and mocked up). I found the mounting of the caliper for 203mm was more stable with an adaptor than the 185mm. I have pics of that comparison if someone wants to see them. One could argue the stress on the fork would be higher on 203mm, but on gravel I am assuming the tire brakes loose from the surface of the road before reaching a higher stress. And you could also consider the hits of the fork over rocky terrain would be higher than the brake force. Rear brake is using a Power Cords cable.

Wheels are Nox Composite A36D with 28 aero spokes. Nox can do the A36D with 32h, but not until their next run who knows when. My wheel builder did some math on Nox’s offset spoke hole pattern and felt comfortable that 28 spokes would work for us, but if 32h was available I'd have done it. The Farlow and other rims work with fewer tires due to those rims' lip-less design. Built on American Classic 135mm and 100mm hubs with 10mm and 9mm “thru QR” axles. Custom laced to tandem tension. Nice true rim to start with.

Lot’s of other fun spec things. Self made sew on leather bars (front not done yet). Custom alu/carbon 195mm 30 degree 170g stoker stem. Ti bolts throughout build. Speedplay Syzr pedals for good power transfer. KMC DLC black chains (11 rear, 10 timing even though frame is belt length I find the sprockets wear out quickly in the dust)

PS there will be studio pictures shortly.

colotandem

That is an awesome looking machine!

Remind me why you did not want to use full hydraulic brakes?

Is 44t the max chainring that Shimano claims for that front deraileur? The triple looks really appealing. If there were just a slightly bigger gear, I'd contemplate this kind of set up and ditch the road tandem (just have a skinny tire set up to swap out). But when it comes down to it, we have different bikes for different purposes. Having a "do all" bike can work, but will not be optimal in all conditions (I think I've had a similar discussion on the mtb tandem forum).

Regardless, this bike is sweet! I can't wait to see it and chase you guys around in the dirt!

merlinextraligh

Very cool. Are you going to do Dirty Kanza?

Turbotandem

Full hydraulic was another $600 and did not seem a big advantage over cable actuated hydraulic. The Hy/Rd gets the self adjusting aspect of hydraulic ,and just a little flex in the cable. I used all compression less housing. I was also not 100% certain the hydraulic version of the brake shift levers were compatible. I think they might be. FYI, I got my 6770 brifters for $59 for the pair a few months ago. Now the remaining stock has gone up dramatically.

Max spec for the XTR FD is 40t. My 44t works fine. What santana is apparently testing is the same 22t range, but from 30 to 52. That would be a build as you suggest. Our 44 large on 10t small cranks us up to 38mph at a cadence of 100rpm, (40mph at a cadence of 106 doable for us). Either is plenty for gravel surfaces.

Turbotandem

we hope to get in to DK200 rush registration. If so, it would be a good training ride. It would also be good to validate our DK200 time from 2014 to assure ourselves our performance that year was not just a fluke!

waynesulak

Great looking bike. The Wiskey forks are so large that they seem oversized on a single to me but it blends in perfectly on your tandem. large tires fit in as well. A very balanced looking bike.

It is easy to see the large amount of thought you put into this project. Did you look at a ceramic coating the frame?

Nice to have you back posting on the Forum.

twocicle

Cool.

I would like to hear more about your Lightning crank spec/setup as you mentioned narrow Q a few times plus triple rings.

For Linda, we need a rear crank no wider than 157mm. Lightning said they would mfr anything we want, but going that narrow would only allow a double ring - at least for their normal chainline spec. We are running an effective 135mm rear spacing (12x142 thru axle), so not overly wide. I was hoping for some chainring mount wiggle room (ie: perhaps moving the spider) but from your feedback it sounds like the FD/crankarm clearance is pretty much at the minimum on your setup so no further space to move the spider outboard.

I've heard the XTR Di2 RD is designed only for the 11-40 cassette slant and unlike previous clutched Shimano RDs does not allow adjustment for other cassettes (ie: 11-28 or 11-32 are more in our usual range in a double chainring setup). Have you tested the XTR RD with more typical road range cassettes?

jnbrown

I am also interested in this, what is the Q factor on the lightning triple cranks?
Is your rear hub 145mm and how does the chain line work?
We have a FSA Gossamer crankset on the rear and it has a very wide Q factor which isn't best for wife being 5'2".
I am in process of changing her bars from 42cm to 38cm and there isn't going to be much clearance between her knees and elbows when she is in the drops since her feet are so wide apart.

I just noticed you are using a 135mm rear hub so that explains how the chain line works.

Also I see you have an SQlab saddle on the back, are you using one on the front also, how do you like them?

waynesulak

What diameter are your seat tubes? It is possible a smaller diameter seat tube might buy a few mm of inward adjustment of the FD.

Turbotandem

Lightning stated Q-factor is 150mm, I get 156mm, must be a special way of measuring it... They make both a standard triple 5-bolt spider and a 54/104 triple spider that is reversible to adjust the chain line a few mm. I am using the 65/104 4-bolt, and I did need that 2-3mm adjustment to get this set up to work. I have the 5-bolt triple by lightning for another of our road tandems with lightning crank (also with 135mm rear hub) and have not had issues.

I am on either a 611 or 612 SQ Labs seat depending on the bike. My stoker just discovered the 610 which is light but more compliant than 611 or 612. I did Dirty Kanza 200, Hoodoo 500 and RAAM (2015 4-tandem team set a new course record!) on the SQ Labs and love them. The 610 is new to my stoker. She had to change saddles on hoodooo to remove the 611 for the later half, she is very sensitive to seats. I hope the 610 is a winner.

Turbotandem

Crank just answered in post above. I based the spec for the SRAM 10-42 cassette and XTR longest derailleur on blogs about that topic. The experience is good. Plenty of room in the b-tension adjustment. But you're right that the chain tension is not clutched or sprung in any way. It appears to be actuated somehow. That is, once it is in a gear the derailleur cage is un-movable, locked in some way. There is actually a release lever in gold at the top of the cage one needs to flip in order to release the cage and remove the wheel. But it does work with the foreign SRAM cassette, so there must be some smartness to the actuator to place it in gear and then lock up the cage so you get no chain slap.

Turbotandem

Seat tube is 35mm. The XTR FD mounts are made in 2 clamp variety and 2 braze-on variety. I have the SM-FD 905H high mount which is only available in 34.9mm, with shims down to 31.8 and 28.6. So no, smaller seat tubes won't hold the FD closer to the frame centerline. Good thought though. It may be the low mount version or one of the braze-on mounted attachments may be more slim, but from the pictures online none appear slimmer.

Turbotandem

OMG, you should see the Whiskey Mountain No 9! I saw one in person and the legs are as big as baseball bats. FYI, the Cross No9 is wider, but oddly has a flat spot across the top of the fork under the crown that limits tire size more than the traditional shape of the no 7 Cross. I had to trade the no 9 cross after waiting 3 months for it to be back in production, and then had to trade it with a friend to get the no 7.

The project was 6 months in the works, much of it crafting the geometry and figuring out what could be fabricated, and working on the spec. Even so, the spec changed every time I placed and order, and the thing nearly didn't work in the final assembly. Zero to 0.5mm tolerance I guess means it works as planned! It was during my experience working on the spec reading blogs and technical data every evening for months (and talking to experts when the info online was not definitive) that suggested I ought to share what I learned on the project on this forum.

Next step I have to work out the programming of the shifting to refine it where I want it.

twocicle

Sounds like a product opportunity here... some people may want a "cammed shim" to adjust FD in/out position more than the limit screws allow. I'm not aware of any cammed shims in production.

Just FYW, Calfee's seattube spec is 34.9mm with either a removable shim or a fixed carbon wrap sleeve. Our Dragon build came with the fixed carbon (Di2 reinforcement) in the FD mount area, so no way to use an aftermarket shim.

twocicle

So at 150mm Q factor (you measured 156mm) this means you are using the standard road spacing (double chainring = 43.5mm chainline). Interesting and glad to hear it works for your Paketas with triple rings. How much granny/chainstay clearance do you have on your road tandem (non-Vr version without the rightside drive special yoke) and with what size ring?

Also, do the mtn and road triple spiders have the same offset (chainline the same, but with different BCDs)? Both reversible?

jnbrown

Thanks for the saddle info, I am going to try a Selle SMP Drakon, if that doesn't workout I might try the SQlab 611.

Turbotandem

Sounds like I need to do some measurements to provide this info. Here is what I know, the double and triple 5-bolt compact Lightning spiders are the exact same piece. Just add the inner most ring on a spacer, and it is not reversible per say. The only thing asymmetrical about it is the shallow recess for the crank arm escutcheon which could be reversed to move the chain line 1-2mm in or out. The dedicated double spider, the one with the shallow arch to it, only go on one way, but I've busted these from just chain tension as they are very light so I don't use them. The 65/104 4-bolt spider is reversible (image below) to allow moving the chain line about 3mm in or out. I've never put too much stock in chain line specification except on my single speed bikes. What my builder and I did check was using the Park Chin Line Tool, camp it to the center cog of the 11spd on a 135mm frame, and it lines up withing 2mm of the center chainring of the triple. The chainring, if anything, is a little further outboard than would be spec, but we couldn't get the FD to come in any more inboard. On a 74mm bottom bracket, the rings and FD would be further out and probably right on spec for chain line centered on the rear cassette of a 135mm spacing.

FYI, I also procured an out-of-production 65/104 4-bolt sworks spider for the drive to compare to the lightning spider. I liked the Sworks spider which is more robust than the Lightning, but it held the chain line far too close to the frame. S-works spiders are compatible with the lightning crank spline.

For the timing chainrings I am using S-works 130bcd which are more robust than the Lightning. Wish I could have found the carbon version that I have on other of our tandems, or even the 110bcd carbon, but could not longer find them, so went with alum which are only slightly more heavy. My feeling was the carbon would have been more resistant to cracking should we plow the front timing chain ring into a rock. And the 110bcd would have accommodated a smaller timing chain ring should I find the need. Current timing chain rings are 38t which is a good compromise between clearance, and big enough to induce less bending in the bottom tube. It seems counter intuitive, but the smaller the timing chain rings the greater the chain tension from the captain and thus the more bending force on the bottom tube.

PS, I posted pictures of the chain line in high and low chainrings here: https://www.bikeforums.net/tandem-cyc...l#post18326051

Turbotandem

26.75 pounds measured the "usual way" without pedals and bottle cages, but in my case with real saddles and tires not studio versions. My goal was to be under 30 pounds with pedals, cages, aero bars, and tires worthy of Tour Divide rather than the gravel racing tires on it right now: I'll hit that weight with 8 oz to spare.

Turbotandem

FYI, posted a cross-over post about the stem on this bike here:
https://www.bikeforums.net/tandem-cyc...l#post18333953

Turbotandem

Twocycle, more info on the road triple lightning spider just posted here: https://www.bikeforums.net/tandem-cyc...l#post18334233

twocicle

Smaller timing rings (plus chain) instead of Gates belt setup due to clearance preference?

Also, if concerned with abusing the front timing ring, why not put on a bash guard ring too?

Turbotandem

The frame is belt length, but we find on dusty rides that the tight belt induces quick wear on the sprockets. The chain and sprockets seems to do better in a dusty environment. I'd looked at bash guards but did not find anything I like for a 39t ring. THey seem to be made for smaller diameters.Ultimately I decided the odds of hitting it were low for the gravel road we target, and only sometimes getting stuck on bad trails.

twocicle

Is that tight belt and wear feedback for the older CDC model or the newer CDX (Centertrack)? I've never had an issue running our CDX at lower than spec tension. We've ridden in some "submarine
and "cement truck" conditions that would make a chain unridable unless relubed mid-ride, plus dealing with that mess.

Turbotandem

We run both CDC and CDX belts on different tandems at about 65psi, well below the 85psi recommended by Gates. Below that I find the wedge shaped teeth of the belt ride up on the sprocket under captains pedaling load, which in turn frays the belt rather early. We have ridden in plenty of dire weather with the belt and like it for that on the road tandems. But when dusty the belts squeak a lot and seems like we get under 5000 miles on a sprocket, even rotating it once to flip the wear surface. We get a lot more than that on timing chain and chain rings where the wear does not matter like it does on a rear chain. Same chain a chain rings on our old gravel tandem for 5 years and still no need to change. It's a close call, but common on mountain tandems to run chain instead of belt. The chain is about 200g weight penalty.

twocicle

Last year after a few Camelback bottle ejections from our tandem, we removed all the Arundel Sidewinder cages and replaced with death grip Mandibles. A little tougher to extract a bottle, but nice to not worry about losing one or worse (cause a mishap).