Gates Carbon Drive: Setting Belt Tension

In my quest to learn more about the Gates belt drives I’ve consumed a lot of information from various sources on synchronous drive belts.  One of the things I started to notice was the somewhat ‘generic’ belt pre-load tension measurements used on single bike drive belts, tandem sync belts and (wait for it) Harley Davidson secondary drives.  Yup, ~10 pounds of force applied mid-span to the non-tooth side of the belt using one finger with ~.5″ of deflection is about right for all three of these very different synchronous drive belts.

Gates Carbon Drive Tension Tester

The recommended method for checking pre-load tension is using the Gates (Dayco) Krikit (pronounced Crickett) Tension Tester.  Gates has detailed instructions on how to use the Krikit that anyone can download from their website and that you can find HERE. I’m somewhat amused that the Carbon Drive Krikit appears to be a Gates Krikit I with some stickers that cover the calibrated scale on the Krikit I.  Those stickers seem to add about $20 to the MSRP of a Krikit.

Update:  In the comments you will find that a reader was kind enough to check with Gates on the differences between the Dayco Krikit sold for automotive V-belts and those sold for bicycles. According to Gates, ” …the bike version with the stickers over the engravings uses the same aluminum casting as the auto version, but with a different spring–so the scale and spring tension are different between the two devices. And that the bike version is more expensive because of the lower volume, and that the bike spring is installed by hand (given the low unit volume).”  If I had enough interest and owned a Gates Carbon Drive belt system designed for bikes, I’d almost be tempted to buy one of each so I could compare the difference.

Regardless, the Krikit made for Gates bike belts is probably a good tool to have on hand for anyone who owns a belt and who doesn’t have a good way of judging what 10 pounds of downward pressure feels like.  The following video from Dayco shows how the Krikit should be used (in this case, the larger Krikit II)…  remembering that the Carbon Drive model adds the “red zone / green zone” sticker instead of specifying the tension level hidden under the sticker.

As I mentioned, Harley Davidson motorcycles also use a synchronous drive belt that uses a similar 10 pound force to measure deflection using a slightly different tool (below) that you can see someone using in this video.

Harley Davidson Belt Tension Tester

When I thought about the different length Gates Carbon Drive belts offered for use as a drive belt for bicycles and the much longer sync belt, I began to wonder why both belts had the same pre-load tension: coincidence or is it just a relative amount of tension?  More specifically, the following is what I asked:

TG: I’m curious as to why the tandem sync drives developed with Co-Motion seem to have the same tension pre-load specification as bicycle primary drives?

Is the pre-load simply relative, i.e., 5-10lbs of downward force / .5″ deflection on a bicycle’s drive belt or a tandem’s sync belt is “about right” without regard for the length of the belt, size of the sprockets, or span between the sprockets?  Or, does it just work out that way by coincidence?

Case in point, I’m doing some testing with a tandem sync drive using a Gates 8MGT-1792-12 GT belt & 33t sprockets sitting on a pair of axles that are ~30″ apart.  The tensioning specification is 17-19lbs of downward force / .47″ of deflection which, given the smaller sprockets, seems to make sense.  While I suspect the higher pre-load may reduce bearing life on the bottom brackets, that’s obviously part of what we’re  investigating with the small sprockets.

Just trying to understand more about the belts and related maintenance, care and feeding.

I was pleasantly surprised to get a fairly prompt response from Gates, and even more surprised at how simple their feedback was:

Gates: It has been our experience that the smaller sprockets require a higher tension to function properly.  As for bearing life, it has depended a lot on the bearing quality.  If the bearings have a high tolerance then there seemed to be no reduction in life span.  The bearing with looser tolerances and more play definitely wear out faster.

Pretty straight forward.  In essence, the sync drive belt needs to have enough tension to keep it from ratcheting (aka, slipping) under load.  If the belt ratchets, it’s not tight enough.  If you make it too tight, then you are putting unneeded loads on the belt, sprockets, and bottom brackets.  If you have good bearings with tight tolerances in your bottom brackets, they’ll do just fine. If you bottom brackets or cranks aren’t up to snuff in the first place, you’ll have the same problems you have with chains in terms of wear and tear. BTW, from all accounts thus far, the belts do not ever ‘break-in’ and stretch one iota.

FWIW, I did an informal poll of a few Gates sync belt users a short while back at BikeForums.org and, to a person, all of them used the old calibrated thumb / finger method to check the pre-load tension.  Another person who has installed several belts noted they were using an Ultimate Digital Scale, another belt user relied on belt pitch by plucking the belt, and a few others in the original poll who used finger pressure were considering the use of a more accurate method of measurement in the future.  Other than a couple reports of needing to fine tune the belt pre-load tension to eliminate some perceived drag, no real issues were reported and most are genuinely happy with their belts.  So, similar to torque wrenches, while there are precision tools available to help set the pre-load tension on belt drives, it remains to be seen just how sensitive belts are to ‘approximate’ tension over the long haul.  However, it’s also pretty clear that it doesn’t take a lot of brute force to apply the necessary pre-load to the belt: pin spanners and the like are more than adequate.

Finally, anyone who owns a belt-equipped bike or who is considering one should note that, while Gates’ Carbon Drive belts sometimes touted as being maintenance free, the tandem belts and sprockets do seem to want for some cleaning every once in a while, i.e., soap and water to remove road grime. Additionally, some folks have also reported a little belt squeaking: to resolve they revisited their sprocket alignment to address the noise while others have simply applied a little silicone spray or in one case run a bar of soap along the sides of the belt every now and again to eliminate the noise.

Advertisements

About TG

I've been around a bit and done a few things, have a couple kids and a few grandkids. I tend to be curmudgeonly, matter-of-fact and not predisposed to self-serving chit-chat. Thankfully, my wife's as nice as can be otherwise we'd have no friends. My interests are somewhat eclectic, but whose aren't?
This entry was posted in Technology & Equip.. Bookmark the permalink.

22 Responses to Gates Carbon Drive: Setting Belt Tension

  1. Kelly Milligan says:

    My method…I take a 10 lb. dumbell and rest it mid span on the belt. A before and after measurement tells me my belt deflection. Works perfectly, and I’ve had no issues with our belt at all.

  2. Al Parker says:

    We needed some new tandem excitement, so I installed a Gates carbon belt last weekend on our 2005 CoMotion CoPilot Speedster. It would have required some spacers on the cranks between the chainrings and the crank if I had not already installed 123 mm bottom brackets vs. the 118 mm that came on the tandem. The only other issue was the chainring bolts. I had to use some fixed gear bolts because the Gates chainrings are much thinner than the original FSA chainrings.

    Tensioning the belt has been a slight challenge. I elected to use the Gates Krikit gauge since I am sort of anal and like to see numbers. Even though the chainrings appear to be perfectly true when rotated, there is some significant variation in the tension as the belt is rotated. I suspect it is related to the belt itself. For now, I settled on 45 lbs at the max, and 30 lbs at the min (I peeled off one of the stickers to see the original markings on the Krikit). Gates said 50 – 60 lbs works best for tandems, and Webcyclery (where I bought the belt system) said 30 – 70 lbs is their range. Anything over 45 lbs at the max seemed pretty tight to me.

    My beloved stoker hated the white lettering on the belt, but fortunately it scraped off with my fingernail. She also does not like the blue interior of the belt, but she seems to be tolerating it now. She suspects there is more drag with the belt, but I doubt it. After 40 years of marriage, it’s still nice to have things to argue about. I like the belt because it is much cleaner and does not get chain lube all over everything it touches, including the frame when I am trying to clean it. Plus I won’t have to clean and lube that long chain anymore. Weight reduction is not a factor for me, I could go on a diet and lose far more than the weight saved with the carbon belt.

    • TG says:

      Hey Al:

      That’s funny… Debbie also hated looking at the white lettering and blue flocking on the toothed side of the belt. As the belt gets used the blue flocking — which serves no purpose in use, only during manufacture — becomes less brilliant and I’m told it will eventually wear off. I offered to dye it black once I understood what it was and what it wasn’t, but Debbie said she’d learn to live with it.

      All that said, it is interesting to see that there is absolutely no clear consensus on belt tension.

  3. Ron says:

    A bit off subject, but where can you find the best deal on a conversion kit if you have the old chain on your tandem now.
    I have to admit it does look kool… not considering the $$$.
    We would also enjoy the low maintenance I assume.
    Thanks R

    • TG says:

      The original, Gates Carbon Drive tandem sync drive kit is only available for tandems that have a 28.5″ boom tube, measured center-to-center (CTC) between the axles. In fact, it was designed for Co-Motion tandems built in the last 10 years or so which has the 28.5″ spec. So, that’s the first challenge. There are also some bottom bracket & crank compatibility requirements. So, if you have a somewhat ‘current’ Co-Motion, the best deals can typically be found at Webcyclery. Any other authorized Co-Motion dealer as well as Co-Motion has them too. If you have a tandem that doesn’t have the pre-requisite 28.5″ boom tube, you’d need to contact your builder to see if they’ve come up with a solution or our friend Bob if you want to give a custom system a go. He has put together kits for variety of different tandems. Send me an Email if you want to reach Bob.

  4. Al Parker says:

    Actually, Crank2 Performance Tandems has the conversion kit for a little less than Webcyclery. Website: http://www.crank-2.com/store/ Shipping by UPS ground is only $4.95. However, if you want it faster, Webcyclery has better expedited shipping rates and I believe you will save more with them overall.

  5. Ron says:

    Thanks Guys, I do have a 2004 Robusta that we love. This one has been to USA Cycling Nationals 2 times.
    We were trying to decide weather or not the carbon timing belt would make a noticeable difference for us.
    All good info, Thanks, R

  6. Mark says:

    Hi Mark,

    Nice review of the Krikit. I also wondered why this item sells for $44, when the auto version–seemingly the same–can be had for $12. Gates says that the bike version with the stickers over the engravings uses the same aluminum casting as the auto version, but with a different spring–so the scale and spring tension are different between the two devices. And that the bike version is more expensive because of the lower volume, and that the bike spring is installed by hand (given the low unit volume).

    • TG says:

      Appreciate the info. Of course, now I’m dying to know just how much difference there might be in the amount of tension the bike version of the Krikit would yield in the “green zone” vs. the automotive V-belt model. What makes this all that much more interesting is the feedback I continue to receive from folks who are using the belts regarding belt tension, as it would appear that belt tension “in the field” is all over the place.

      As an example, another BF brother with a belt-equipped Calfee posted up a report after recently returned from Santana’s Barcelona to Lisbon tour. In it he noted the following:

      It is only the third time I have put the belt on after traveling and as others as stated when tight to specs its seems to have a lot of friction so I left it a little looser and sometime on the second day it skipped a tooth that neither of us noticed when it happened and in fact probably rode the next day with it out of phase. We think we know when it happened as we came around a blind corner and had a very steep on ramp and didn’t have time to shift and just both stood up and made the hill but in a very high gear. We have no issues with it walking on the sprockets but have had the eccentric move if not tight enough. We love the clean no chain ring tattoo effect of the belt. The other tandems on the trip with belts had tensions all over the place and no one seemed to have any problems with them. There was no consensus among the teams as to what they should be and in fact most didn’t even know gates had recommended tensions.

      As to how different tension settings may affect the life of the belts and/or other sync drive components is anybody’s guess at this early juncture, as I’m not sure if anyone has set a benchmark for just how many miles a belt or bottom brackets of a given type will last. Regardless, I will incorporate the insights you provided from Gates in my entry for posterity. Thanks so much for checking and and passing along the additional info.

  7. Mark says:

    Mark, I have more than a passing interest in this topic, since I have two bikes with Rohloff’s and Gates belts. I sort of agree with you that switching over to a belt for the timing chain on our tandem wouldn’t really add much mojo.

    Someone you may want to connect with at Gates in Colorado is Steve Pardo. I have yet to pose a question to him for which he hasn’t answered with exceptional knowledge and experience.

    By the way, re the Q factor and the sense of greater resistance with belts vrs chains, Gates is coming out with a new belt design that runs the flange down the middle of the belt (rather than on the side), and has in the neighborhood of 10-12 mm less offset to the inside. So the new design can drop 10-12 mm off the width of the crank, AND Gates thinks that the new design will reduce resistance when peddling backwards. For whatever reason, the current design does apparently have measureable resistance above a chain when pedaling backwards, but Gates claims not when pedaling forward. Not sure why that might be, but that’s what Gates says.

    Current Gates thinking on belt tension is that the upper range of tension on the Krikit is better. So cyclists should aim for 3-4 mm of deflection when using the Gates tension gauge–meaning that the leading edge of the marker should be at the extreme left of the green zone, or just outside of the green zone.

    • TG says:

      Hey Mark:

      Yes, I’m familiar with Steve at Gates; thanks for that though. As for the new Gates “CenterTrack” system I stumbled across and did an entry on that back in September. I guess the question that I was left with was, what are the odds that they’ll market it for use as a tandem sync drive? If so, will it replace the 1st generation belts? Seems like an expensive proposition for the relatively small tandem market.

  8. Mark says:

    Couple of additional observations re your friend with the Calfee in Spain…

    My experience has been that the belt needs a few miles to wear in, (or whatever one would call it since the belt doesn’t stretch), and that resistance drops once it has been on the bike for a bit. However, it’s easy to get the belt tighter than 3-4 mm of deflection under ten lbs. of load. I’m wondering if some tandemists are routinely over tightening the belt, given that not everyone seems to be measuring the tension, and there are still learning curve issues with Gates belts even in bike shops.

    Rohloff requires a snubber wheel to be installed about 1.5mm behind the rear sprocket to prevent the belt skipping, whereas in using the Gates belt as a timing chain that option doesn’t exist. All in all, I would think that it DOES matter that the belt be within a fairly narrow range of tension, and that many of us would benefit by purchasing some means of checking tension.

    For anyone who thinks that the (seemingly overpriced) $40 Krikit isn’t expensive enough, the Germans have developed a combined alignment/tension gauge which sells for around 160 Euros. I think it’s only available in Germany.

    Also, your stoker will be pleased to know that that blue mold release compound on the belt has apparently recently been changed to black

    • TG says:

      Well, as I said, we enjoyed testing the belt but will likely pass on becoming belt adopters… at least on our existing tandems. If we did a lot of riding in adverse weather, the belt would be a bit more attractive as I think it’s all-weather performance / low maintenance is the belt’s strongest suite, especially for folks who use bicycles as a primary or frequent form of transportation.

      It will be interesting to sit back and watch to see how deeply the belts permeate the new tandem market. As we’ve already seen with Paketa, they’ve now designed a frame around the sync belt to get the most out of what a belt has to offer… others will certainly follow-suit if demand remains strong and early adopters continue to lavish praise on the belt’s performance.

  9. Fred says:

    Just a guess here, but I think Gates probably changed the spring tension so that the red/green decal is centered for the proper belt tension. If you use the automotive version with a range of 30-160 lbs, the recommended tension for bicycles will fall towards the low end of the scale.

    • TG says:

      De-rated, so to speak… Makes sense.

      But, that also suggests the standard KriKit could be used if the recommended tension falls within the tester’s range.

  10. Fred says:

    I agree. In fact, I have a KriKit on order now.

    One word of caution to those who buy the “Gates Carbon Drive Tension Tester” and remove the decal. Since the spring has been changed, the graduations will not reflect the correct tension.

  11. Al Parker says:

    There are two decals. If you remove one, you can see the numeric scale and the color scale at the same time. Then you have a number for comparison when you make changes to the tension or replace the belt. It’s easier for me to remember (or write down) a number than where the reading was on a color scale. Does not matter whether it is right or wrong in this case.

    BTW, here’s where I found the KriKit for about $33 (compared to $44+ elsewhere). Shipping was $9, it arrived in two days: http://www.yourprosolutions.com/

  12. Fred says:

    I ordered the automotive version.

    GATES Part # 91107 Krikit V-Belt Tension Gauge; 30-160 lbs

    I found it at http://www.rockauto.com for $10.41 and $2.31 shipping. Should be here this week.

  13. Fred says:

    I received the KriKit Tension Gauge (#91107) yesterday in the mail. Previously I had been tensioning my belt using the 10 lb no more the 1/2″ method. Using the gauge, the belt tension is right at 60 lbs. Reading previous postings this appears to be right in the range recommended by Gates. The automotive version of the tool appears to work fine.

    On a side note, we have been having a lot of squeaking from the belt on recent rides. I have adjusted pulley alignment, belt tension, cleaned the belt and pulleys without any success. I finally went over every inch of the drive system and found that one of the pulley bolts was slightly loose. It took no more than a quarter turn to tighten it, but no more squeak. Finally we are back to quiet bliss!!

  14. Choco says:

    Hi all, when using the KriKit Tension Gauge (#91107) , what is the correct tension range compared to the gates re branded version? Are the the labels/measurements identical on both?

  15. kevin casey says:

    “There’s an app for that”- there is now an iphone app to listen for the correct tension tone of a gates belt.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s