woodrow5

So the XTR M972 SGS is 9spd rear derailleur right?

I'm having a difficult time when using the BIG Chainring and shift to a biggest cog. I'm thinking to change a smaller size cassette or adding more links to the chain.
I'm currently using M771 or 772 RD with 112Link 10spd chain.

twocicle

Correct, the XTR M972 is the same spec as the XT M772... both are classified as 9spd derailleurs. However, the throw ratio is perfectly fine for these to work with 10spd cassettes too. You did not mention if you have the GS or SGS M7nn series. If you also have a 34 cog on the back, then you need the SGS (super long cage).

Otherwise, your problem could be a number of things including chain length, jockey wheel distance, alignment, preload tension.

woodrow5

Thank you so much for answering!!


As shown on the picture. Current the chain is on middle chainring and biggest 32t cog.
I just checked back the purchase history, it's "SRAM PG 1070 Cassette 11/32t". If I shifted to biggest ring, it will stretch to the red line position. For most of the time it just struck and could shift.

Should it be the chain problem? I'm using KMC 114L 10spd chain + 10spd shifters.

Thanks )!

twocicle

Yes, chain is too short to allow for big-to-big.

One of the more consistent methods to determine the correct length is to run the chain from big cog-to-big chainring without running the chain through the derailleur, get the chain tight and align to the next whole link configuration, then add 2 links (needed for jockey wheel routing). Then go install the chain through the derailleur for normal use.

Adjust the derailleur tension screw just to the point where the chain is not slapping the chainstay when running in the small-small sprockets. Increasing the derailleur's pull to the rear will increase the tension on the chain, but don't go too far as this descreases the amount of chain wrap around the rear sprockets. Depending on the status of your derailleur springs, you may not be able to develop enough derailleur tension to keep from chain slap in the small-small. but then you shouldn't be riding in that combination anyway.

twocicle

I took a first solo spin this afternoon around the block a couple times for a quick checkout ride. Handles very nice, light feel, quick and nimble steering. All the shifting and braking worked great, so those components are all good. Sweet!

I may consider installing cable liner along the top tubes as the rear brake wire run sticks out more to the side than under, and it may prove bothersome having the bare wire there rubbing legs, tights, etc.

Other todo: replace the 130mm captain stem with a 120mm (in transit). The eccentric orientation with a tight timing chain is now in the 7 o'clock position which is somewhat further back than I anticipated. Adding 2 links is not possible as the eccentric does not have enough uptake to tighten the chain. This setup will now require moving my capt saddle back approx 1 cm and hence the shorter stem.

TandemGeek

I've successfully used 3/32" half-links on our tandem's sync chains to solve similar set-back issues. It's not a perfect match to 9-speed chains, but since the sync chain is a direct drive it doesn't really matter.

twocicle

Super! Thanks for the tip, I never thought of that. Duh.

Using a couple of these links seems a much better option than an entire (and very heavy) half-link chain. These just might work to keep the chain short enough to let the eccentric work in the forward, 4-5 o'clock position: https://harriscyclery.net/itemdetails.cfm?ID=1274

Now, for the timing chain I am using a Sram PC 1051 P-Lock 10-Speed chain. In the past I found that using non-straight links (ie: not BMX style) seemed to track a lot better, so I currently use the same Sram PC1051 on drive a timing. Do these 3/32" 1/2 links work alright with this type of chain (10spd) or do I need a 9spd chain, and is there a better choice of chain for the timing side that is not really heavy?

TandemGeek

Any lightweight 8 or 9 speed chain would be a better choice vs. 10 speed, if only for the longer service life of the somewhat larger roller/pin contact faces. I;ve been using the 116 link KMC X9 SL chains in recent years (I stock up when they go on sale); these are pretty darn light at 257g. The 106 link SRAM PC991 hollow-pin and Shimano CN-7701's are also pretty light at 278g - 280g (you have to factor up the weight for the link count to get apples to apples with the KMC) but also fairly durable.

Again, the difference between a light and not as light is usually around 30-40 grams and about $20.

twocicle

Ok, I'll stick with the Sram chain theme and use the 9spd PC-991 for timing, then keep the 10spd PC-1051 chains for the drive side. I had some Dura Ace CN-7701 chains stocked for our singles, but I wanted to make use of the Power Links with the Sram chains on the tandem. The Sram 991 can be had for a few dollars cheaper too. I wasn't concerned about a few 10s of grams, just didn't want it to venture into the 100s as it would have with a full half-link chain.

I remember when our Santana had first come with a straight link, KMC BMX type chain for the timing side. It was always catching on the sprocket teeth like it wanted to jump off, even when tensioned tighter than normal. It was noisy and clunky looking too. Once we changed to shippable drive type chains with the rounded sides, no more problems and very smooth tracking.

twocicle

Photos & album updated in the first post

DubT

Looks Great! So have you and your stoker had it out for it's maiden voyage. What is the current weight without the gates belt?

Wayne

twocicle

As currently shown, it's 29.5lbs, but some addnl component weight reduction will be implemented. Could lose 1/2lb using the rear rim brake instead of the disc and Ultegra cassette instead of the big XT.

Amazing how it goes from a 7lb frame to something over 29lbs even with lightweight wheels at 1650gms, etc. The stems, seatposts, handlebars all weigh in at the magic number of around 150gm each; saddles at 260 & 270gms; crankset a not so light but stiff 1880gms(?); and so on.

Strategic space left open for GPS, Computer (Polar), etc.

Not ridden with my stoker yet as it's still in the build stage. The slight lack of attention to the crank phasing will be addressed once the Half Links arrive to sort out the timing chain length & eccentric rotation position.

TandemGeek

It is indeed.

The journey to a svelte tandem on a fresh build where you tally all of the grams as they make their way on (and off) of the frame is always an education unto itself in terms of what you discover about the various weight contributions of different components, many of which are sometimes taken for granted. I suspect a fair number of folks who have acquired high-end, lightweight tandems have all taken this journey.

What's more interesting is to look at four different weights as you do a build like this:
- Frame Only
- "Comparison Weight" which is the built-up tandem without pedals, waterbottle cages since this is typically how manufacturers list the weights of their tandems
- Final build weight, which is what most of us probably thing of, where we've now put those pedals and waterbottle cages on.
- As-ridden weight, which is what it actually weights when we hit the road for a ride with pumps, computers, mud-guards, bicycle bells, rear racks, trunk packs with parts or other "stuff", those evil and very heavy filled water bottles, lights and seatpacks* for weigh-in.
*Note: For the folks who eschew seat packs as a cycling fashion faux pas, all the junk they carry in jersey pockets vs. a seat pack needs to be put in a baggie and taped to the frame for a true apples to apples comparison of static bike weight.

Guess which weight is the one that really matters? Yup, it's that last one that represents the total bike mass that you're hauling up those hills or launching in a sprint for the county line sign. I've set up my scales at tandem rallies on Saturday mornings before the ride and offer folks a chance to see just how much their tandems weight as ridden: it's eye-opening to say the least. 33lb tandems can quickly become 46lb - 50lb tandems.

waynesulak

You make a very good point but I would add the weight with the team including personal gear is what is really hauled up the hills. Guess you might need a special scale for that.

DubT

This is very true however, the difference between a 40 pound tandem and a 27 pound tandem is still 13 pounds even when you add all of the aforementioned items, it is still 13 pounds less weight to haul up those hills. There is absolutely no way that I would want to go back to our old 40 pound bike.

It will be interesting how much actual weight the belt drive will save over the chain, Ritterview put together a spread sheet and his calculations indicated about 3 ounces, however he was using a very light timing chain in his calculations. When the Gates CDX system is available this winter our Calfee will get upgraded. Primarily to get rid of the dirty chain.

Wayne

twocicle

It doesn't take a spreadsheet or calculus or physics to determine the weight savings of belt over chain. Drop the two sets of components on a scale and there you go. , basic math. The diff was over a 1/2lb.

Now, I have begun implementing a plan to chop off another 15-20lbs. Meaning, this tandem will be lighter than my wife's single once I'm finished. Component reduction includes: no beer, no salsa & chips, etc. and it has begun to take effect in spite of the sucky weather up here - it's mid April and we're lucky if the temp reaches the high 50s, like last night after work a whopping 57F and trying to rain again. Yikes.

Target weight... -33lbs, 3 decades ago?

wheelspeed

Congrats! It looks gorgeous. I think under 30 lbs is amazing for a "real-world" tandem bike that has a rear disc, broad gear range, and comfy stoker hoods.

twocicle

Thanks. About those stoker hoods (Cane Creek), they are surprisingly heavy +300gms, and after "finger" tightening the clamps the plastic base already started to crack. I wouldn't mind finding some lighter weight, comfy and durable replacements. Wish Calfee made some carbon hoods

wheelspeed

Yes, I have the Dia Compe ones, and they're heavy also. I'm working with Bob Davis on getting some info on lengths available for CF pegs that are a lot lighter. I've seen the typical short ones in various photos of peoples' bikes, but apparently he might offer a longer version if desired.

I wonder what size is preferable.

rhino919

I would like some that are about 30 to 40 mm long. How do I contact Bob Davis?

Thanks, Ryan

wheelspeed

PM sent to you. Thanks to Rudy for pointing me in the right direction.

twocicle

Wish list:
- lightweight short or standard reach stoker pegs - small hands.
- carbon stoker stem w/31.8 bar end clamp. ideal seatpost clamp is 27.2, but can shim to any size.

twocicle

Equipment feedback:

I am liking this new (2012) Avid BB7 version better than the original one we had back in 2003. The new BB7 added the outboard pad adjustment, actuator arm spring adjustment, and better/higher default tension so the arm return has a nicer pull on the brake lever up front.

This new BB7 has a very firm, natural (ie: single bike rim brake) feel, not the soft and mushy slop of the previous version. Although we had good quality brake cable on the previous tandem, I think the Jagwire Super Slick Stainless wire used on this new build is really good no-stretch stuff. I get immediate and solid clamp down on the rear brake (Avid) with zero sponginess.

waynesulak

Is Bob Davis some sort of stealth businessman? He makes and i understand sells tandems, does he not want his contact info posted?

I have looked at his web site. Tandems look cool but didn't see contact info.

twocicle

Here is a pic of what you suggested... PC991 (9spd chain) + 3/32" half-link. While the half-link is the same length (1/2") and roller width (3/32") they appear to have no desire to match the height of regular chains. Also, while KMC does have a missing-link parts page for each model, they do not provide size or any other specification info. It isn't a perfect link size match but seems to work on the timing side and did let me lengthen the chain by +1 to allow moving the eccentric position to a 5 o'clock orientation.

For my initial install I've used a Sram Powerlink (provided with the Sram chains) to join the half-link to the standard inner PC991 link. The Powerlink is a little on the tight side, so I'll monitor it to see if it works its way in or needs a standard pin/outer link.