Carbon Drive Calculator iPhone App

Gates iPhone App

Gates recently released their Carbon Drive Calculator (CDC) for the iPhone. The CDC just might be the ultimate app for the combo tech-nerd/bike-geeks in the crowd. Besides calculating center distance, drive speed ratios, and optimum pulley size, the app uses the iPhone microphone to test belt tension. Yup, believe it or not, you pluck the belt like a string and the CDC estimates belt tension by pitch. I haven’t tested it yet (I’m not an iPhone user), but it sounds way cool if it actually works. If there are any iPhone users in the crowd who also run a Gates Carbon Drive, I’d love to hear how it works for you.

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12 Responses to “Carbon Drive Calculator iPhone App”

  • sygyzy says:

    Alan, can you explain how to read the gear ratios for an IGH and a Gates belt? For example, on the Civia webpage for my Kingfield, there’s a gear ratio chart.

    I apparently have a 118T belt and a 24T cog. If I look where that meets up I see a 50 Ring and 2.08 gear ratio. I don’t know what this is trying to tell me. I have 8 gears in my IGH so shouldn’t I have 8 gear ratios?

  • voyage says:

    If there were more, better apps there would be be more, better cycling? What did cyclists do before iphones and apps?

  • Andrew says:


    As with almost all things bicycling related, Sheldon Brown’s site has the answer:

    Just put in 50 for your chainring, 24 for your custom sprocket, and select Shimano 8-speed from the internal hub dropdown, and you can have your gear ratios in whatever format you like.

  • Sam says:

    Very happy to see this app. A few weeks ago I tried to order a tension tester from Gates but they never shipped (or charged) it to me. My new Norco Ceres has been great but I did slip the belt off the pulley once climbing a really steep hill and realized the LBS didn’t tension it enough. I set it myself by feel and so far so good. Very thankful it didn’t ruin the belt, at least I think it is fine.

    Using the app I got about 64 Hz. I measured it 3 times in 4 different locations. Always seemed to be between 60-68 Hz. The app recommends 55 Hz for big riders on internal geared hubs (45 Hz for light bikes with IGH, 65 Hz for light SS, 85 Hz for heavy duty SS use). I think I will leave it since the belt has been tracking so well recently. Overall really cool app to use frequency response to set belt tension.

  • Alan says:

    That’s awesome, Sam. Thanks for the report!


  • Sam says:

    The guilt got to me and I went out and adjusted the belt. The app does seem to be sensitive to even minor changes in belt tension. Just a quarter of a turn of the tension bolts seemed to equal about 3-5 Hz in the area I was adjusting to. Even tightening the lock down bolts (see Alan’s review of Norco Ceres) increased the frequency about 5 Hz and I had to reset it. So now I am sitting between 52-55 Hz with a soar finger from strumming my belt like a guitar.

    Every 10 readings or so it does give a wacky number. Sometimes 20 Hz and sometimes 160 Hz. Not sure if it is just it picking up the frequency of the frame or something else vibrating. I am a bit of a dork about this stuff so playing with this app has been some fun. Pretty ingenious solution by Gates. No surprise though since they have been designing belts for a long time.

  • John Ferguson says:

    I think the most helpful thing for me would be for Gates to try to design at least one more cog for IGH hubs. 24 and 26 tooth options would be nice; as it is we don’t have enough control of final ratios to be able to fully justify a belt drive.

  • Joseph Eisenberg says:

    I love that it calculates gain ratio! For those who don’t know, gain ratio is a unitless way to compare gearing (instead of gear inches or meters development), and it also calculates the effect of crank length. It was invented by Sheldon Brown:

  • Eric says:

    It worked well enough for me. I have the cricket to set my belt tension and the app registered between 72-75Hz. It gave me a few rogue 33Hz measurements, but that was when my finger struck the chain stay or rather belt stay. This will be handy for quick belt checks.

  • Matthew says:

    It’s a free app which is nice. My finger is sore from all the strumming as well, but after some 20 HZ readings, I got a semi-accurate 50 HZ. I’ll stick with the Krikit Gauge to check tension. The gear ratio calcs are a nice feature.
    The technology is sound though. I have the Guitar Machine app. as well, and it is a very accurate tuner and chord measuring device.
    I think I have carbon fibers embedded in my finger. ; )

  • Thor says:

    they forgot 20 inch wheels ……. :-(

  • Doug Robertson says:

    Alan, I don’t have an iPhone, but I downloaded it to my 4th generation iPod Touch. And it works. My Gates Belt Tension gauge showed I was on the very lower end of proper tension and the app gave me a reading of 41 hz….repeatedly. Need to tighten it up a bit. This app is ingenious. Today’s technology blows me away.

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