twocicle

Surviving the fork tests. Another success.

Two nights ago we went out to do some serious fork testing, unbeknownst to my stoker

Unfortunately on the first long climb we flatted the rear due to glass shards picked up a few miles back while riding on a littered highway shoulder. Still running on our first set of 25mm Schwalbe Ultremo ZX tires... seem to be getting a tad thin in the back.

Then the real fun began... descent time.

Greensferry Rd is quite steep and twisty, with a max grade in the 14% range. I call out sharp corners to my stoker... left-right-left-right... but these were coming so fast she had a hard time keeping up with the weight shifts. The tandem handled very nicely and recorded max speeds rivaling my single. Honestly, as much as I usually like dive bombing descents, I've never been comfortable on this one because the corners are so close together. Plus, I was leery of the new rear tube we had just installed (and likely under inflated) and so kept the speed down a bit, but we still hit speeds of 36-45mph on this technical descent (and have Garmin file to back this up). Yikes. Later on in the ride there was another good winding descent where we let it go unheeded on the wider road. Surprisingly this descent recorded a lower max speed than we had on the more difficult Greensferry pitch.

The major handling points I can think of are 1) front end feels lighter, and 2) no "understeer" while cornering. Since one of Calfee's default forks is the non-tapered 45mm rake ENVE 2.0, our current 46mm rake 3T Rigida tapered is closer to that setup (or slightly on the quicker handling side) than the optional 43mm ENVE tapered I've just replaced which made the steering a bit too heavy. The Bicycle Trail Calculator has been a good help in reviewing the differences, though it lacks the ability to adjust for different crown heights (you therefore need to assume an adjusted head angle value). Since the 367mm Rigida is 3mm shorter than the ENVE it replaced, I'm guessing there is a head angle difference in the order of .5 of a degree. Difficult to figure out what our current HT angle is, since it could be that the 370mm ENVE (length I measured) was making the head angle shallower than Calfee's 73 degree spec (they also say 367mm is what the tandem design is based on). Regardless, I think the Rigida has moved the geometry in the proper direction.

One thing we decided for sure, bullhorn stoker bars suck when doing very aggressive quick cornering like this. So says my stoker. Drop bars suit aggressive riding much better. We'll use the bullhorns for touring/convenience, but otherwise remounting the dropbars for performance gain.

alexaschwanden

I am wondering how much did the bike cost?

twocicle

A one-time build would amount to less than 1 year depreciation on most new SUVs

I built this up myself (3 times over at this point) and kept costs down (relatively speaking) via internet shopping. However, as we did the Di2 frame modification a year afterward, that added quite a bit to the final total in our case. I thought we would never go Di2, but when the e-tube + Ultegra became available and component prices plummeted and then 11spd came out, I couldn't resist. The Di2 shifting is superb and I'd never want to go back to mech shifting on the tandem

I won't post a cost for ours, but you can start with Calfee pricing: https://calfeedesign.com/product/tandem-frames-pricing/, then add up components. It's possible to get some great deals shopping online. Since we live remotely in N. Idaho and no tandem dealers here, I worked directly with Calfee for my order and follow-up frame modification work.

Bad1

Know what I have into my custom built Macchaito with all Dura Ace, DI2, Lightning cranks, Enve wheelset, and all the other goodies, I figure with all your renditions your well north of 20K.

twocicle

Not nearly that much, even if you tallied everything at full MSRP. It's not like we are running with ubber expensive components as you are. For example, our FSA standard road cranks (not tandem specific) cost a total of $550 combined, and the wheels $900. Also snagged the 3T Zefiro LTD bars for only $450 and very low pricing on the UDi2 components, etc, etc.

Although I still have lots of extra parts left over from the earlier builds, I did sell off some major things like the Spinergy wheels, Ultegra tandem crankset, 10spd Ultegra shifters and the WI MI6 145mm hub. The 10spd UDi2 is destined for my stoker's single that is desperately in need of a component upgrade, so not counting that toward the tandem rebuild costs. Ok, we still have 2 forks, but who's counting? Besides, the ENVE will do fine for tours needing fatter/taller tires

Bad1

Seems like the nicer the tandem you always want to get a little bit more performance out of it which leads to "Folie à deux ". A madness shared by two!

twocicle

Performance is one factor. Last winter I caught the bug to set about rebuilding the tandem with a little experimental approach... ie: single bike cranks (narrow Q) with the Di2 with a same-side-drive Centertrack belt, and so on. A huge Di2 carrot was the availability of 10spd derailleurs for under $200 and recently the 11spd with more default capacity for the same price.

My stoker asked me last night "are you finished yet?". Pretty much YES is my reply. Other than..., LOL

Bad1

To funny! I hear that quite frequently myself!

twocicle

More 3T Rigida feedback: Tire Clearance

I got around to installing a couple other tire choices and taking a look at the fork crown clearance on the 367mm Rigida.

We have been running Schwalbe Ultremo ZX 25mm on the 23mm wide rims (BHS C472w / Kinlin XC279). This setup has IMO the bare minimum clearance... just a couple millimeters. Mounting Continental 4-Season 25mm tires seems to be the same clearance, though I had expected more since these tires measure wider then the Ultremo ZX. So, on par with either 25mm tire... adequate.

Next, mounted a Continental 4-Season 28mm tire. Clearance might be .5mm. Enough to clear the crown, but not practical to ride as even the smallest amount of grit stuck to the tire hits the carbon crown.

Since the Rigida is purported to support using 28mm tires, I had expected more clearance, especially given that we have 23mm rims and assumed this width would pull-down the tire height a little more than something like a 19mm rim.

As we typically run 25mm tires the Rigida will do fine. However it is not adequate for running 28mm tires (I'd reinstall the 370mm ENVE for that size).

Turbotandem

Super interesting.

I call this configuration an "outboard right side drive" to distinguish it from "inboard right side drive". The outboard configuration produces a greater bending forces in the frame bottom tube (and crank spindles) since the captain's pedal force is loaded thru the belt further off the frame center. The force induced in the bottom tube increases at a square to the distance of the belt from frame center, times two to account for the lever length at both the captain and stoker. Some of the flex you may perceive as if from the chain ring spacers may be the frame. I've not done testing to see if the loss in bottom tube flex is less than keeping a left side drive closer to the frame center but accepting all the drive train flexing of a left side timing configuration. I've heard riders with outboard right side timing say this configuration is better than left, plus you get to use standard cranks vs left side drive.

Left side timing is about 50mm from belt to frame center, outboard right side is something like 60mm?? So right side outboard induces 1.5 times more bending in the bottom tube at the captain, and another 1.5 times the force at the stoker (whether the stoker is pedaling or not...), so 3 times the bending force compared to left side. I don't know how to calc flex in the left side drive train (spindle twist, spider, etc). If the bottom tube and its connections to the BB's are radically stiff, the loss may be negligible. FYI, right side inboard configuration has 40mm belt line so induces less than 25% the bending force of the outboard configuration.

Sorry, back on topic of the spacer idea:
With the CDX belt (and even CDC belts) it is not critical that the belt line be truly straight. There is no mechanical loss, at the power levels a human can induce, with the belt angled a fraction of a degree. Doing so would at least allow the belt line at the captain's position to be closer to the frame center and partially reduce bending forces in the frame. The flex in crank spindles, frame, spider, and sprockets produce more "angle" to the belt as it crosses the sprocket; than the 0.25 degree angle you get from 3mm over 725mm frame length. And that 3mm just at the captain's BB equates to 11% less bending force in the bottom tube (assuming 57mm belt line vs 60mm belt line to frame center, while the stoker remains at 60mm)

I like the chain ring as spacer idea. This happens on both inboard and outboard right side drives. On the inboard the belt sprocket it actually has spacers to bring it nearer the frame. (with some shinanigans to allow the sprocket to be placed without hitting chain stays and bottom tube.)

I have also seen left side belts spaced inward, so long as they clear the chain stay. On a left side timing, at the least always place the sprockets on the inside of the captains spider, and the stoker's spider if the chain stays allow it, just to get the belt closer to frame center and reduce the bending of the bottom tube.

oldacura

So, if right side synch chain (belt) increases frame bending, what are the advantages over left side?

twocicle

As Andy noted the timing location offsets and potential torque inducements, he is also correct that those figures do not take into account the immense torque/twist/and perhaps energy loss through the rear BB/axle.

The "outboard" right-side drive we had used with the FSA single cranks always felt very solid. I never noticed a micron of frame flex. My captain power always seemed to be a direct link to the rear cogs with no apparent sponginess. We are now back on a tandem crossover setup with the Lightning triple rings, BB, etc, and to be honest I am not noticing any onset of twist or sponginess in this configuration either. I think that credit is due to 1) a stiff Calfee frame and 2) the beefy Lightning 30mm axles with outboard bearings. We do not seem to get much in the way of chainring deflection no matter how hard we have pushed it.

I wish I owned a power meter for my bikes these days (long gone is my old Polar power meter). Returning from Tucson and now buried in snow, my riding is relegated to the Tacx trainers. Those power readings are supposed to be somewhat accurate to a degree, and my current wattages are 500-600 watts for my out of saddle "climbing" efforts of 1-2 minutes and 450 watts for longer climbs. When I do this IRL on the tandem, Linda has given me enough feedback for me to smooth my effort enough for it not to bother her while she remains seated (she can stand and peddle but the injury from 2015 is still bothering her so she limits standing now). For IRL terrain comparison (Andy) think of the Tucson Mtn ride clockwise with those rolling climbs and going to max effort standing.

To be completely honest, if I am not careful with my upper/lower torquing, our Whisky disc fork w/thru axle and WI Centerlock hub seems to flex more than I like. Referring to the disc rotor rubbing the pads if I get messy with my standing pedal action and arms pulling.

Bottom line, my guess is that the 2013 and 2015 Calfee frames we have ridden with the belt drive, are both very stiff in the drive torsion aspects, from captain's effort to stoker's effort. I am keeping my eyes on the lookout for new ENVE forks to become available at the spec we need. It was the stiffest fork we ever had and I would like to get back on one if they ever product a tapered 1.5" disc version with an offset > 43mm.

I think the ultimate timing torque test may need to be performed on a much less rigid frame to notice any real differences.

Turbotandem

Whether inboard or outboard, the drive force is still more direct than a left side.

The left side forces from the captain need to transit the rear sprocket, thru the chain ring bolts, down thru the stokers left spider, thru the crank spindle torsional-ly, also inducing bending in the spindle, thru the connection of the spindle to each spider (or thru a mid-crank-axle connection), back up thru the right side stoker spider, thru chain ring bolts, into the drive chainring where it pulls the chain. There is a lot of loss and flex in that path.

In comparison Right side inboard or outboard need only go from the right rear sprocket thru the chain ring bolts to drive the chain ring. Both left and right rear spiders and the crank spindle torsional force are effectively out of the equation. In right side outboard configuration the spindle does experience bending.

The unknown is whether all those gains of a right side outboard timing are undone by the somewhat more bending force in the bottom tube due to the wide belt centerline to frame center. Again, in a radically stiff frame, as Calfee's are reported, that bending loss may be negligible. I don't know how to measure those, but riders who have been on the same calfee that converted to right outboard from left timing configurations, say the right outboard is more stiff.

Right side ~inboard~ belt configuration (think Paketa V2r) has the additional advantage in stiffness because the belt is nearer the frame center than either left or right outboard configurations. Frame bending force is 35% that of a left side timing, and 25% of that of a right outboard timing . Further, the inboard right side configuration applies the captain's belt force ~between~ the frame BB and the drive chain. Therefore the crank spindle does not undergo either torsional OR bending forces.

Right side get to use any single bike cranks, so some teams opt for super stiff high end cranks that are not available in tandem specific parts, so they get a bit more advantage for super strong riders.

That said, right side belts can be persnickety beasts.

Turbotandem

In our recent gravel tandem build we had the down tube matched in diameter to the bottom tube. Knowing the bulk of a tandems stiffness climbing and standing comes from those two tubes. Both are 60mm dia. with the intention of heavy loads and off-pavement abuse. The connection of the down tube to the head tube is ovalized and something to behold. What I notice is that single change from our other 60mm bottom tube, 50mm down tube tandem with an Enve 1.5 tapered fork; noticeably increased the apparent fork stiffness to the 60mm/60mm whisky no9 tandem. Altering the fork alone does make notable changes in stiffness between some of our other tandems, but the down tube is part of the equation.
PS: don't let the pictures confuse you, after initial trials, we changed to a custom ti 1.5 tapered fork from Blacksheep with 70mm offset; but it's the same tandem!

twocicle

I wouldn't think the downtube should effect the wheel deflection within the fork, which I can both see and hear. Whisky claims the No. 9 thru axle road disc fork (367mm) which we have was made very stiff, a bit too stiff in their minds according to a product support guy I spoke with. However with only a medium out of saddle effort and some side-side torque the front 180mm disc rotor will rub quite loudly. To be fair, I have no experience with any other road disc forks... yet. Whisky does not have any new road forks posted, and we are hitting March! Whisky's cross forks should be stiffer yet, even with the longer 397mm axle to crown length.

ENVE finally has their new road fork posted, with 43 and 50mm rakes available, slightly longer at 370mm and a 32mm tire max spec. On the downside, max 160mm rotor, flat mount disc, 12mm thru axle instead of 15mm, and only a 1 1/4" tapered steerer. https://enve.com/products/road-disc-fork/