DubT

Here are the notes that I made about the CDX belt drive on our Calfee: Oct 5, 2012. The new Gates Center track belt drive came today. It took less than an hour to install it and tension the belt using the iPhone app.

The Wipperman 8 speed chain weighed 426 grams and the Shimano chainrings each weighed 43 grams for a total of 512 grams. The new belt weighs 108 grams and the new chainrings each weigh 86 grams for a total of 280 grams.
The total weight reduction is 232 grams / .51 pounds / 8.16 ounces. The new belt is 1/2 inch wide.

Your results might vary, I was using a fairly heavy sync chain.

Wayne

TandemGeek

FWIW, 77" KMC 9SL Sync Chain @ 352 grams.

Pic

Just ordered my CDX today. I will find out which chain I have and weigh it also.

TandemGeek

I didn't include the timing rings since we have daVinci cranks with the one-piece, spiderless rings.

Therefore, you have to compare the weights of the entire cross-over crankset & sync chain to get an apples to apples comparison between MegaExo type cranksets and the daVinci cranks + traditional ST bottom brackets.

My guess is, the total weight difference ends up being somewhere around 100 grams (equivalent of 3.5 oz of water).

jnbrown

KMC 10-SL 302g

twocicle

Good point Mark. We switched from larger & heavier Polar 26oz capacity bottle to the mid-size 22oz Camelback (verfied by measuring cup test). Yes we lose 4oz fluid per bottle, but the bottle itself weighs quite a bit less too.

The Polars were much taller and a constant source of dripping water and sport drink on the frame. The more compact Camelback bottles have a top that locks & a squirt mechanism takes a bit to get used to while riding, but otherwise seems superior. The smaller bottle size solved access issues for the stoker that she had on both the tandem and her compact single. see: https://www.bikeforums.net/showthread...1#post14467249

Overall, for the 4 bottles we switched out, that saved equal "empty" weight to the entire CDX setup, and quite a bit more when factoring in the water load.

Polar:
26oz capacity
146gm empty
total full weight each: 852gm
4x 852gm = 3408gm (3.4kg!) = 7.51lbs for full Polar bottles. Yikes!!

Camelback:
22oz capacity
100gm empty
total full weight each: 722gm
4x 722gm = 2888gm (2.9kg) = 6.37lbs <<< still, that weight is near equal to the 2007 Calfee frame!

Camelback weight savings (4 bottles):
empty: 184gm (.4lbs)
full: 520gm (1.15lbs)


Fun factoids:
The 4oz less per bottle in the Camelbacks has not been noticable to us from a hydration point. My take on it: the time it takes my stoker to use up 2 full 22oz bottles is about the max time she can handle between potty breaks

As always, the biggest weight diff is usually body composition. Reviewing photos in the link above will reveal a lot more than 1lb savings in the 2nd photo taken some 3 months later.

DubT

Please forgive my ignorance, but I have no idea how this comment addresses the weights that I recorded. Did I miss a post or something?

budhaslug

I think what TandemGeek was getting at is a particular feature of the daVinci cranks: the most popular option for timing rings are one piece spiderless 34t rings that attach directly to the spider attachment point on the cranks. These weigh about 20g more than a spider alone, but come in significantly less than a spider+34t ring+chainring bolts. The issue is that when you go to the Gates system, you have to put on a spider to attach the gates rings to (unless daVinci decided at some point with Gates to develop a spiderless belt drive ring). So you are not just replacing a 34t timing ring with a gates 86g ring, but replacing a 34t spiderless ring with an 86g ring + daVinci spider + chainring bolts.

In other words, with a daVinci, the weight savings are far less because attaching the gates to the cranks weighs a good bit more which counts against the savings from belt vs. chain.

TandemGeek

OK. I'll run the numbers....

I believe the Ultegra tandem cross-over cranksets weigh about 1,890 grams (arms, BBs, rings, bolts), so add 426 grams for your chain and your original cross-over crank system weighed about 2,316 grams. You dropped 232 grams with your CDX drive so your cross-over crankset's total system weight is now something like 2,084 grams.

The starting point for a daVinci crossover crankset with lightweight BBs is 1,637 grams (cranks, Ti BB's w/alloy cups, rings, bolts), so when you add-in the weight of a KMC 9SL chain at 352 grams the total system weight is around 1,989 grams, or about 95 grams less than the Ultegra CDX drive on your Calfee.

Again, as budhaslug surmised from my comments, there may not be a whole lot of weight savings to be found by going to a CDS or CDX drive if someone is running a daVinci cross-over crank system. This is because perhaps 1/2 to 3/4 of the potential net gram reduction in chain to belt weight would likely be consumed by switching-out the pair of 75 gram, one-piece, spiderless 34t timing rings for the 69t (86 gram) CDX sprockets + the added weight of two crank arm spiders.

Now, there are other good reasons that teams might want to adopt the belt drive. However, I just don't think there's a lot of grams to be shaved if someone is running daVinci's already very lightweight cross-over cranksets. About the only lighter options would be some of the very light carbon cross-over cranksets or moving to a right-side drive.

DubT

Thanks for the clarification, being unfamiliar with the Davinci cranks I was totally in the dark as to what you were saying.

twocicle

I chose the Ultegra 67(nn) series tandem cranks (comes with regular Ultegra BBs) for it's stiffness and better durability over carbon cranks, and definitely not the weight, which is pretty much middle of the road. The only other cranks I loosely considered was the SLK-Light, but they run at over $1000 for the set. Basically, only looked at the MegaExo/HollowTechII configuration (outboard BB, etc) and no others.

How do the DaVinci cranks stack up as far as stiffness of the cranks and titanium square tapered axle with internal BB/bearings? Is there any real test data for these specific cranks and Ti BB ?

colotandem

I don't know of any "real test data" regarding DaVinci cranks. I can say that we have thousands of miles on Davinci Cranks. First set was on a DaVinci road bike, very happy with these cranks. We spec'd them on our Ventana mtb tandem (not with TI BB). Then on our 29er full suspension tandem, we put DaVinci cranks with Phil Wood Ti BBs. Zero issues with the cranks or BBs. I am not sure how to compare them to Ultegra or Carbon cranks though.

One other thing that I'll add is that we had our most recent set of DaVinci cranks annodized black and they look pretty sharp! I only mention this b/c some like a dark look as opposed to the polished aluminum that is standard. The other thing that is a selling point with DaVinci cranks is that you can mix and match just about any crank length, whereas most tandem cranks are limited to 175, 172.5 and 170.

waynesulak

I have used Phil steel BBs but have a couple questions about the Ti BBs:

Do you use Ti or Mag Ti version?
BB widths used for captain and stoker?
Do you use Aluminum cups or Magnesium?
Do you use on stoker BB as well?
Mileage before replacing, and do you ride in the wet very often?
Do you use BB covers (they add a few grams)?
When replacing do you buy new BB or replace bearings?
Ti is the about the same stiffness per weight as steel, 60% as heavy is 60% as stiff. Do you feel any flex?
Steel crank bolt used?


Thanks, Wayne

colotandem

See repsonses above in red

TandemGeek

Do you use Ti or Mag Ti version? MagTi, Titanim axle w/magnesium shell
BB widths used for captain and stoker? 108mm Captain & 111mm Stoker w/145mm rear spacing
Do you use Aluminum cups or Magnesium? Options are Stainless Steel or Alloy: we use alloy
Do you use on stoker BB as well? Yes, see above: 111mm MagTi w/alloy cups for stoker
Mileage before replacing, and do you ride in the wet very often? 15k & still going. Grease still looks good. Very little wet weather riding. PW BB's are not reknown for sealing out water & need more service if used for all-weather / wet riding. Adding a weep hole to the shell & aligning it to drain might not be a bad idea for those who do a lot of wet riding w/PW square taper BBs.
Do you use BB covers (they add a few grams)? We're talking Square Taper, not outboard BBs so N/A
When replacing do you buy new BB or replace bearings? PW's bearings are replaceable.
Ti is the about the same stiffness per weight as steel, 60% as heavy is 60% as stiff. Do you feel any flex? Short of instrumenting the BB axle, BB shell & frame in a fixture I'm not sure how anyone would be able to isolate BB axle deflection from normal front BB shell frame deflection on even the most laterally rigid tandem they could find. As for the stoker position, I can tell you that our Erickson Ti BB axles had sufficient deflection under load to cause end cap & cup damage. I have seen nothing that would indicate that the MagTi stoker's BB is being subjected to excessive torsional deflection from the opposing sync & drive side loads. Then again, we're only a 280lb team and neigher of us are elite level cyclists putting out mega-watts.
Steel crank bolt used? Middelbrurn self-extracting stainless steel bolts with aluminum theaded retaining cap.

waynesulak

Thanks for the answers. These are the mud caps I was referring to which are for square taper BBs:


BB Cup Mud Guards

Our mud guards are designed to help protect your Phil Wood bottom bracket cups from getting dust, dirt and mud that can accumulate in and around the bottom bracket cup splines. They are designed with a drain opening to allow any moisture between the bearings and mudguard to vent out. They are designed to install onto any Phil Wood square taper bottom bracket cup sets. Each set of mud guards comes with 4 rubber o-rings, (preinstalled and two replacement).



https://www.philwood.com/products/bbp...dcupguards.php

Comments from anyone else that wants to address Phil Wood steel or Ti BB durability are welcome.

TandemGeek

That's a new one on me. Never heard of nor seen those before. Thanks for the enlightenment.