Tandem Cycling - belt drive timing chain

i'm here at interbike at the demo days, co-motion has a new belt drive to replace the timing chain. the belt drive system is exclusive to co-mo at this time. for you weight weenies they claim it to be 10 ounces ligther than the traditional chain setup. they expect it to be a high performance system as they have it as an upgrade on their top three tandem models. i forget the difference in price, i think it's an extra $300 dollars. sorry no pics.

before you get your hopes too high, as i was demo'ing a mountain bike riding up the road to the trail a riding came coasting down the trail on a belt drive mountain bike yelling "hail to the chain, long live the chain, belt drive sucks!" as he raised his arm aloft carrying the belt

i'm

You're...????


...at Interbike and you've seen something new and exciting???

Yes, I know; pretty cool, eh?

doesn't actually happen very often... maybe i'm just that jaded...

Belts + Off-Road have some real issues, particularly when rocks and what not get sucked into the belt and pulley... which is why you won't find them on anything but motorcycles that stick to asphalt.

However, for the road-going machines my only benchmark is a friend from Florida who has been using his own belt-drive system on his Seven Axiom 007 for several years now without any issues.... to include using the same Gates kevlar reinforced belt that I believe Co-Motion is using.

It will be interesting to see how well it does both from a performance and consumer acceptance standpoint.

Belt drives are nothing new . . .
Photo of a belt drive on a prototype 'unnamed tandem' that I rest rode 2 years ago.
Production tandems with belt drive are something new.

I've often thought that a belt drive system would work well with an internally geared hub. No lube, no maintenance. I'm not sure why they wouldn't work in an off road application.

I design machines that use timing belt drives. The applications are pretty clean but the belt drives themselves are virtually maintenance free.

Now, if somone can just figure out how to make a derailer for belts. The other issue is that for a given amount of tension, a chain will likely be narrower than a belt.

Other than weight savings I do not understand the benefits of a belt drive, seems to me that it would require more energy to "bend" a belt than a chain?

They are supposed to be about as efficient as a chain.

Benefits that I see: less maintenence, cleaner, quieter.

Other than weight savings I do not understand the benefits of a belt drive...

You don't have to oil them and they don't stretch.

I'm not sure why they wouldn't work in an off road application.

Rocks, sticks, mud and other debris are more readily trapped between the belt and the ramps of the splined drive gears which can cause belts to bind, break, or derail.

Some of the gear-drive makers have developed splined drives with open voids between the ramps to help with shedding mud and smaller rocks; however, it doesn't completely solve the problem.

Chain and sprokets don't have this problem with rocks or mud and, while chain drives will occassionally get bound-up by a stick that can't be chewed-up and spit out by the cutting action of the chain and narrow sprocket interface, that's the exception and not the rule.

The benefits to roadies have already been mentioned:

- Low maintenance
- Longer service life
- No lubrication / fairly clean
- Belts are lighter than chains

I'm not sure about the reduced noise in that, belts don't eliminate noise... they just change the pitch as they have their own unique noises.

Belts also seem to lock tandem builders into a fixed stoker compartment length, that is unless there will be a range of belt lengths and/or different size splined gears to allow for shorter or longer boom tubes.

Again, the pros and cons have apparently been weighed by Co-Motion and debates based on theory and hearsay will hopefully give way to first hand impressions as the first gear-drive Robustas, Machiattos, and Supremos make their way into true consumers hands.

Belts also seem to lock tandem builders into a fixed stoker compartment length, that is unless there will be a range of belt lengths and/or different size splined gears to allow for shorter or longer boom tubes.

That's interesting; something I hadn't thought of.

That's interesting; something I hadn't thought of.

If you're Co-Motion and use the same 28.5" long stoker compartment on all of your stock size tandems -- regardless of frame size -- this isn't an issue, as 'one size fits all'.

However, if a client wants a custom-sized tandem with an extra 1" or 1.5" in the stoker compartment I'm guessing the belt wouldn't be an option.

Belts also seem to lock tandem builders into a fixed stoker compartment length, that is unless there will be a range of belt lengths and/or different size splined gears to allow for shorter or longer boom tubes.



Belt molds are available in a limited number of teeth. As the belts get longer, the jumps in length get bigger. A belt mold can be custom made to any integer number of teeth but the larger the mold, the higher the cost. So, it would be cheaper if tandem makers could agree on a limited number of lengths to amortize the cost of the mold.

How about belt drive for both sides with an internally geared hub? A couple we met were touring with internal hub transmissions. He said that high gear was about 10:1. I think these are 5 or 8 speed hubs. If these hubs could take tandem loads, this could make for a pretty low maintenance drivetrain.

Rohloff does a 14 speed internal hub, which could be adapted for belt drive. However, Rohloff's a bit hefty, both in weight and price. Hear they may also be working on a higher count internal hub.
A whole new market could open up for this type chainless system.

If timing belt folks don't standardize lengths, then a rather good sized investment in proprietary belts in custom length/tooth profiles and pulleys would be required for the specific losads needed on a tandem.
Co-Mo sells far more ready-made models than customs.
No doubt they've done their market research before taking the leap from chain to belt drive.

I'm assuming that the belt must be less stiff than a chain, so I wonder if you can feel any difference as a captain.

Webcyclery has them on their website as a retro kit for $525. If you are a weight weenie, that's a pretty good $/gram payback.

Does anyone have hard numbers on efficiency difference between the belt and the chain?

It does look a bit odd, but I expect you'd get used to it pretty quickly. If it really lasts 10 times as long as a chain then that would mean for all practical purposes you would never have to do anything with it, as I only replace my timing chain every 3 or 4 years.

Plus the captain would NEVER have a chainring tattoo:)

From a different tandem discussion forum where the Gates Carbon Drive belts are being discussed came this report from a friend and the former Editor/Publisher of Tandem & Family Cycling Magazine who was one of the Beta testers...



My son and I rode a CoMotion with the belt this summer and in several races:

http://app.obra.org/results/2008/Criterium/13287#race_125239
http://app.obra.org/results/event/13187
http://app.obra.org/results/event/13187#race_128797
http://app.obra.org/results/event/13188

We fell in love with the setup from the first ride. The first things
we noticed is that it is very quiet with a noticeably smoother
pedaling feel. We were unaware of how much cog vibration was coming
from our timing chain until it was gone, replaced with a belt.

We both felt a more "direct" connection with the rear wheel - that is,
maximum attack efforts, both on climbs and sprints, translated
directly to forward motion of the team. Traditionally, a tandem can
often feel like you're winding up a "elastic" connection to the drive
wheel. But with the belt we felt the team could respond nearly as
quickly as a single bike.

In our first crit, we could attack at will and drop the field - though
they would catch-up over time as there were MUCH better TT teams in
the bunch. But we used this explosive acceleration to win both the
Prim and the overall victory. A great quote from that race was from
the Mick Walsh, captain of the second place team. "I've never seen a
tandem accelerate like that."

At the CoMotion classic you can see were we sat after the TT - some
very strong teams in the field. At the crit we were bested by the
Canadian National Paralympic team, but were able to get away from them
and the reset of the field on the last climb of the road race.

We sadly gave the belt-drive back to CoMotion and went back to our
timing-chain for the Oregon State Crit Championships:

http://app.obra.org/results/2008/Criterium/13297

.where we finished 5th over all. We were both shocked at how sluggish
the tandem felt! On the drive home we were both laughing a bit about
how we had been convinced before that our previous performance was due
to us as athletes, but now realize it may have been more belt than
men. ;-)

YMMV,
Greg

I'm wondering if belt driven bikes are going to be the new fad. Here's an article on Trek's prototype cross bike. http://www.cyclingnews.com/tech.php?id=/tech/2008/news/10-03

Trek also has a belt driven commuter bike on their website.
http://www.trekbikes.com/us/en/bikes/urban/district/district

If you're Co-Motion and use the same 28.5" long stoker compartment on all of your stock size tandems -- regardless of frame size -- this isn't an issue, as 'one size fits all'.

However, if a client wants a custom-sized tandem with an extra 1" or 1.5" in the stoker compartment I'm guessing the belt wouldn't be an option.or maybe different size chainrings could make up the difference in pretty small amounts since the teeth are much more tightly spaced than a chain. obviously you couldn't go too far with it but would allow less belt sizes to handle a range of lengths. the next question would be what's easier/cheaper to make? chainrings or belts?

or maybe different size chainrings could make up the difference in pretty small amounts since the teeth are much more tightly spaced than a chain. obviously you couldn't go too far with it but would allow less belt sizes to handle a range of lengths. the next question would be what's easier/cheaper to make? chainrings or belts?

I suspect the marketing success or failure of the basic system on Co-Motion's tandems will be the the gauge by which Gates decides just how many different size pulleys (new word for the tandem bike lexicon here) and/or belts to offer. Moreover, I suspect by limiting the introduction as a Co-Motion exclusive and making the retrofit cost somewhat high ($525) Gates and Co-Motion are trying to put a throttle on demand until they get a feel for how these things will hold up in the hands of consumers who use them and the home mechanics and bike shops that work on them. Remember, the problem with making things fool-proof is that fools can be pretty resourceful when it comes to screwing things up and faulting a design vs. their own shortcomings.

Anyway, as far as compatibility, it's also worth noting Calfee's standard size stoker compartments are pretty darn close (28.35") to the Co-Motion spec. of 28.5" so it will be interesting to see if the Gates belts are a bolt-up option for Calfee owners as well.

A Santana-compatible set of slightly larger pulleys or slightly shorter belt would seem to be the next logical offering given just how much of the market is comprised of Santana-branded tandems.

For folks like us who have unusually long stoker compartments -- 30" on the Calfee and 31" on the Erickson -- unless we back into an existing pulley size spec'd for single bike cranks, a belt drive may just never be an option.

As one final note, I've been corresponding with yet another friend -- one who works at Webcyclery -- who tells me the Gates belt & pulleys actually have a much lighter weight than the one, 295 grams vs. the 363 grams referenced on Co-Motion's Blog entry. Webcyclery.com has now updated their website with this "as weighed" data and I've asked for the individual component weights for the belt and pulleys.

Trek actually has two belt-drive commuter bikes in the works. The second, with an 8-speed Nexus hub, is here: http://www.trekbikes.com/us/en/bikes/urban/soho/soho/

I have ridden a prototype of the above bike and was impressed. Belt drive will be more than a fad if it works as well every day on the road as in theory and in the test lab. With Trek jumping in, there will be much more empirical data before too long.

TG, how much movement does the front eccentric provide? Could it take up enough slack to go from Calfee's 28.35 to 28.5? It is only 1/6". Or do you know if the 28.5 is the minimum, does it matter?

According to Gates they make 4 different sized belts (113, 118, 122,125T), unless the tandem belt is very specific to Co-Motion.

I'm guessing that the "exclusive" part of the deal with Comotion is that the longer belt for a tandem (which would be on the order of 180 teeth - 1.5 times the length of a half bike belt) is only available through Comotion or their dealers). Maybe Comotion paid for part of the mold cost? Just idle speculation on my part - not trying to start any rumours here.

An eccentric easily takes up one full chain link, which is 1" total or 1/2" of eccentric movement so it would seem that if you are within a 1/4" or so of the Comotion spacing you could be ok.

It's early, but it looks like more than a fad to me. There appear to be some solid technical reasons for adopting this technology. Given some time I'm sure prices will drop dramatically too, Gates isn't the only high tech belt company out there (Brecoflex, are you listening?). I just hope they can agree on a standard pitch and tooth profile.

TG, how much movement does the front eccentric provide? Could it take up enough slack to go from Calfee's 28.35 to 28.5?

It varies based on the different eccentric designs, but crank axle fore/aft adjustment seems to fall into the 3/8" to 1/2" range... so double that relative to how much play there is in chain / belt length.

Based on the photos of the Periscope with the belt drive (http://i157.photobucket.com/albums/t75/pedalforce/DSCF2820.jpg), it would appear that the eccentric is rotated to the rear-most position, maybe a tick of the clock forward for fine-tuning of the tension. That being the case, someone would have to try and install it on a Calfee just to see if it would fit without binding and they'd need to check it on both a pre-March '08 and a post-March '08 Calfee with stock-sized stoker compartments given the change in eccentric size that was implemented in March.

As for belt lengths and pulley sizes, I'd guess what Co-Motion has is what Gates has produced in line with the rationale expressed in my earlier comments.

So who's going to be the first kid on the block?

I have to say the anecdotal report of improved acceleration, and the weight savings are both seductive.

I've got a couple of hesitations though: 1) I'd like to see actual efficiency data,

2) the price penalty for early adopters, and

3) aesthetically, I'm thinking it may look kinda cheap (in spite of the fact that it's expensive.)

Another thought,

We need ASU_GT to test this out on his power meter rigged research tandem.

I called CoMotion asking about availability for a bike I am having built, they said they were not selling a kit and that it was only available as a factory installed upgrade. They were surprised to here that web cyclery was offering it on their web site. I will have the new bike built to accommodate the belt drive should it prove to be more than just a fad.

They were surprised to here that web cyclery was offering it on their web site.

Interesting that whomever you spoke with was surprised since I first learned of the Webcyclery info from Co-Motion's own Blog entry made this past Monday: http://co-motion.com/blog/?p=26

In fact, I had wondered if Co-Motion was trying to divert Co-Motion owners who are now interested in the Gates Carbon Drive system away from themselves (an OEM production house, not really a parts retailer) and towards Webcyclery.com who seems to actually have the item in their inventory all ready.

Toothed belts come in a wide variety of tooth profiles, pitches and cord construction. Some are optimized for accurate positioning and others (like this application) are for power transmission. The cord construction can be fiberglass, poylester, steel or Kevlar.

The cost of pulleys depends on how they were designed and how many are sold. Low production pulleys are typically machined out of aluminum and are fairly expensive per pulley. High production pulleys can be injection molded plastic with glass fibers molded in. The pulleys are relatively inexpensive but the tooling could be quite high. The other factor is how the belt is held to track on the pulleys. Some use flanges on both sides. Even with molded pulleys, at least one of the flanges has to be attached after molding. In some cases, the pulleys can be made with a ridge down the center corresponding to a groove down the center of the belt that holds the belt to track on center. Most of this stuff is highly production volume dependent. Since the only bicycle application at this point appears to be as a synch belt on a tandem, I doubt that the volume will ever be high enough to get the cost down.

As far as efficiency goes, my guess is that the difference from a chain would be very small. A belt will have a very slight non-elastic stretch (a damping factor) each time tension is applied that will not get returned to the stoker's crank.

I'm guessing the main attraction is light weight and low maintenance.

As far as efficiency goes, my guess is that the difference from a chain would be very small. A belt will have a very slight non-elastic stretch (a damping factor) each time tension is applied that will not get returned to the stoker's crank.

I'm guessing the main attraction is light weight and low maintenance.


However, even a very small efficiency disadvantage would trump any weight advantage pretty quickly.

The speed increase from saving 10 ounces on flat ground would not be measurable Even on a very hilly course 10 ounces would make very little difference.

Conversely, a drop in the efficiency of power transfer from the captain from say 93% (the numbers I've seen for a conventional tandem, to say 92.5% would make a measurable loss of speed on the flats and climbing.

This is only going to sell on racing tandems if it's as efficient or more efficient than a timing chain. The anecdotal reports from CCTR give hope that it could be more efficient.

Efficiency in this case would be power lost to friction. The only place I could think where a chain would have more loss than a belt might be in the chain joint motion (just a guess on my part).

We could do that...they can send it off and we will try it out.

J


Another thought,

We need ASU_GT to test this out on his power meter rigged research tandem.

MTBR review has some detailed information including a copy of a study conducted by a company hired by Spot bikes (who are producing single speed belt drive bikes). According to this there is no significant difference (in fact they found slightly higher efficiency from the belt drive). It ends with the promise of a more detailed study looking at worn/dirty belts and chains rather than brand new stuff.

http://reviews.mtbr.com/interbike/spot-bikes-belt-drive-carbon-drive-system-bikes/

Webcyclery has added some additional information regarding the Gates Carbon Drive system to its web page (http://www.webcyclery.com/product.php?productid=18445&cat=469&page=3):


Lighter, cleaner, quieter, longer lasting, smoother, more responsive... New for 2009, this belt and timing ring set shaves more tandem weight than a carbon fork upgrade.

Already gaining popularity in the single speed world, this Gates belt drive system is the perfect drivetrain upgrade for tandems!

Here's a quote from Greg Shepherd who raced the Co-Motion Tandem Stage Race using the Carbon Drive timing belt...

"We fell in love with the setup from the first ride. The first things we noticed is that it is very quiet with a noticeably smoother pedaling feel. We were unaware of how much cog vibration was coming from our timing chain until it was gone, replaced with a belt. We both felt a more "direct" connection with the rear wheel - that is, maximum attack efforts, both on climbs and sprints, translated directly to forward motion of the team. Traditionally, a tandem can often feel like you're winding up a "elastic" connection to the drive wheel. But with the belt we felt the team could respond nearly as quickly as a single bike." And we'll point out that Greg and his son, Davis, won the road race. It's gotta be the belt drive. :)

We can tell you that the Carbon Drive lasts ten times longer than a traditional chain and chainrings and never needs lube, so it's cleaner. Your stoker will never have a grease chain tattoo on their left calf again! Sorry, we can't help you with the right leg just yet.

Our belt and ring system weighs in at 295 grams on our scale. This setup saves about 225-280 grams (8-10 ounces!) compared to a traditional timing chain and chainrings.

Made by Gates exclusively for Co-Motion Cycles tandems. This is the same system that is now standard equipment on the 2009 Co-Motion Supremo, Robusta, and Macchiato race tandems.

One length only - which means that this system will work on all stock sized (28.5 inches or 712-724mm from BB to BB, center to center) Co-Motion tandems. Custom Co-Motion tandems with lengthened (or shortened) stock compartment may not work.

Includes the amazingly light Co-Motion Gates Carbon Drive timing belt and a set of the Gates Carbon Drive 130 BCD timing rings.

NOTE: These are only recommended for use with the new FSA adjustable chain-line cranks. If you're running the new FSA tandem cranks these will bolt right on in place of your current timing rings. Ask us if you have questions regarding compatibility.

Set up takes a bit more time as chainline is now extra important, but once aligned and tensioned you'll seldom need to touch it again.

Weight: Rings 95 grams each, Belt 105 grams
Belt Length: 2000mm
Ring Size: 71T (equals 42T)
Pitch: 8mm (Width is specific to tandem timing belts. MTB and commuter SS belt drive is 11mm)

I'm still trying to ascertain if they actually have these in stock or if they have a pre-production model and are simply taking pre-sale orders.

One gentleman with whom I've corresponded who is not associated with any of these businesses indicated he's spoken with the folks at Gates and they have not as of yet made the first production run of belts or pulleys. Moreover, it was purported that Gates will also sell direct to consumers and the pricing has not yet been finalized. However, it was inferred the pricing at Webcyclery appeared to be high... like way high.

Back to the specs, I did some back of the envelope rough estimates and it would appear the Gates system installed on a set of FSA SL-K cranks is about 77 grams lighter than our daVinci crankset using Phil Wood Ti BB's and DuraAce chains. This assumes the weight for the FSA cranks on Webcyclery's web site is accurate. MSRP costs -- again, based on what Webcyclery has published -- for both configurations would appear to be about the same or perhaps even less for the FSA/Gates system given the cost of the Phil Wood BB's, alloy cups, and lightweight self-extractors.

Again, at this point I'd have to say this is all interesting information and A LOT OF HEARSAY. It will become more interesting once product makes its way to consumers who will have the final say.

I'm still trying to ascertain if they actually have these in stock or if they have a pre-production model and are simply taking pre-sale orders.

One gentleman with whom I've corresponded who is not associated with any of these businesses indicated he's spoken with the folks at Gates and they have not as of yet made the first production run of belts or pulleys. Moreover, it was purported that Gates will also sell direct to consumers and the pricing has not yet been finalized. However, it was inferred the pricing at Webcyclery appeared to be high... like way high.

Are you indicating Gates will be manufacturing both the belt and the pulleys? If so, who did the engineering? I dropped the Webcyclery page off at R+E when I was by there yesterday and Scott was surprised that someone else was advertising a belt-drive system for sale. From our conversation it seems that Dan has been trying to come up with his own belt timing system but was having problems getting the belt (Scott mentioned Gates in particular). Are you implying that the price will drop on this system once it's in production?

Also: Isn't "belt drive timing chain" an oxymoron?

Are you indicating Gates will be manufacturing both the belt and the pulleys?

No, I'm merely passing along information someone shared with me, i.e., this is hearsay and is labeled as such for that very reason.

We could do that...they can send it off and we will try it out.

J

I would ask them for one in exchange for testing it. It would be interesting to see if they took you up on it.

I'm betting there aren't many other people with the setup and scientific testing knowledge that could do an accurate test.

Follow-Up:

There was purportedly a relatively small, initial run of the belts and pulleys produced for Co-Motion. Co-Motion released a very small quanity of those kits to Webcyclery who, as you might expect, sold them rather quickly. They received another small allocation of the kits (2) from Co-Motion today.

I haven't wanted to bother anyone at Co-Motion given it's now crunch time as they work to gear up for '09 production, finalize pre-orders, nag suppliers for the parts needed to build their tandems, etc... so I'll leave it at this for now: it would appear Co-Motion has a large stake in this product and will be the primary distributor. Pricing is what it is until Co-Motion updates their catalogs and web site.

Gates' other belt and pulley products are sold directly to retailers but, at least at this point, it appears as though the tandem kits must be acquired through Co-Motion or one of their authorized dealers.

The latter makes a lot of sense, given the long-term success of a product like this will necessitate making sure anyone who buys the kit has a Co-Motion tandem + crankset + chainline that is compatible with the belt system and a qualified advisor to make sure they install everything correctly. It can't be over-emphasized how important pulley alignment (chainline) is for belt-driven systems

I spoke with web cyclery today, they said kits would be arriving tomorrow and would be available if I wanted it. Seems a bit early to pull the trigger on actual purchase. New bike will be speck'd to accommodate the belt drive system unless builder feels there is a compelling reason to spec a boom tube of a different length. New bike is intended as a travel bike and the idea of not having to deal with a big greasy chain has some appeal to me.

So, what is the tolerance on the chainline misalignment? I read the details and they are also recommending the newer FSA cranks which have some kind of chainline adjustment. What does that consist of, actually? As discussed in another thread, there is a lot ability to move the CoMo eccentric laterally (and a lot of ability to mess it up), so is there a procedure and measurement tolerance they are documenting?

We had opportunity to test ride a tandem (not Co-Motion) with a belt drive synch system a couple years ago. Like lots of prototype stuff, the ideas are great, but development and production costs tend to negate the slight weight/performance advantage.
Time will tell whether synch belt drive is just a flash-in-the-pan or a new standard.

So, what is the tolerance on the chainline misalignment? I read the details and they are also recommending the newer FSA cranks which have some kind of chainline adjustment. What does that consist of, actually? As discussed in another thread, there is a lot ability to move the CoMo eccentric laterally (and a lot of ability to mess it up), so is there a procedure and measurement tolerance they are documenting?

Scroll down to the lower part of this web page (http://www.carbondrivesystems.com/installation.php)and you'll find a section with .pdf links entitled "Installation Resources". It's not tandem specific, but it gives you the gist of the process.

The "Belt Alignment & Tensioning (http://www.carbondrivesystems.com/downloads/tech_docs/Belt_Alignment_Tensioning.pdf)" is the one you're looking for. To their credit, Gates has provide pretty straight forward, easy to use instructions that don't require special tools to properly execute. Pretty basic stuff regarding hand pressure checks for tension, lots of warnings and pictures regarding the "don't dos", and a back-pedal technique for verifying alignment. Of course, while it's simple it still demands attention, discipline, and patience.... and that may be its downfall.

I suspect the tandem belt will call for more deflection given the length, but would otherwise seem to be able to follow this level of guidance.

Friend Henry, web guru for Webcyclery has, finally installed the Co-Motion / Gates Carbon Drive tandem timing belt & pulley system on his Macchiato.

You can find his comments and photos of his installation here: http://webcyclery.com/pages.php?pageid=72

So while I was looking into this after reading TG references, I measured our timing chain alignment. I was shocked to find that it is about half an inch out of whack, like 12 mm. This is on a CoMotion Primera, with FSA Gossamer ISIS cranks. The rear is further out than the front. So I am wondering how common this amount of misalignment is. It doesn't look like we could go to a belt drive without completely replacing the cranksets.

It doesn't look like we could go to a belt drive without completely replacing the cranksets.

I would think that since it is an ISIS drive there may be a mis-match in front BB axle length, that is unless the chain rings are on different sides of the timing cranks (sorry, just one of those things that goes on the root cause fish-bone). You'd also want to make sure the front eccentric is flush with the shell and not accidentally off-set a bit.

Anyway, you'd want to check with your Co-Motion dealer or Co-Motion's customer support folks to see what the spec's on the front & rear BB axles was for your year/model Primera and compare that to what you have. I'd be surprised if the crank arms have a different off-set if they're a matched set but, then again, I've been surprised before.

Once you know what you have, then it's just decision time on how to address it. If it just so happens that the rear is using a 118mm spindle and you've got a 108mm on the front, it could as simple as switching the front to the same 118mm bottom bracket used on the rear.

Side Note: Chains are incredibly forgiving and I'm glad you haven't had any derailment issues with your sync chain. Then again, if you have had sync chain derail issues, you may have found the root cause.

Side Note: Chains are incredibly forgiving and I'm glad you haven't had any derailment issues with your sync chain. Then again, if you have had sync chain derail issues, you may have found the root cause.
Well, I am the guy who "unshipped the timing chain at speed" (see other thread), so this certainly has to be a contributing factor. Although I would still say I don't have "issues"; just the one incident. But I have a complete spare set of cranks and BBs, so I think I can mix and match to get things to line up. Then I can think about the belt drive!

Brief review & test ride on the carbon drive is below from webcyclery. . . .

http://www.webcyclery.com/pages.php?pageid=72