Understanding gear calculations

Discussion in 'General Cycling Discussions' started by 2wd, 11 Jul 2012.

  1. 2wd

    2wd Canyon Aeroad CF 7.0 Di2

    Location:
    SSG Oldham Cycling
    Ok,I am of reasonable intelligence and during a boring day off (suppose to be painting 30 fence panels but its too windy!) decided I need to understand gear changes,when,why,best for a hill and started google searching for answers

    My bikes a 2011 Specialized Tricross Sport and has a 30-39-50 front and a Shimano 9 speed rear cassette, 11-32

    The results that came back are here and mean nothing to me :sad:

    Ratio (inches)

    73 67 57 50 44 38 33 28 25
    95 87 75 65 58 50 43 37 32
    122 112 96 84 74 64 56 48 42

    Basically I'm trying to determine the best gearing for going up hills (I live in a hilly area and hate the damn things) without either spinning to fast or burning my leg muscles out by grinding in the wrong gear

    I very rarely drop into the granny ring and only venture into the big ring down hills/long flats

    So what are these results telling me......

    Please and thank you :blush:
     
  2. Andy_R

    Andy_R Hard of hearing..I said Herd of Herring..oh FFS..

    Location:
    County Durham
    They're telling you that for every revolution of your pedals your bike will move forward a set number of inches depending on your chainring/cassette settings eg: 50 up front, 11 at the back will move you forward 122 inches for one revolution of the pedals. However, I'd just go with how your legs feel. The best gear for going up hill is the one you're most comfortable using.
     
    2wd likes this.
  3. OP
    OP
    2wd

    2wd Canyon Aeroad CF 7.0 Di2

    Location:
    SSG Oldham Cycling
    Cheers for that Andy

    I was sort of guessing along those lines but needed the good people off CC to confirm

    I'm trying to make best use of the gears and your right on the hills answer, but I was trying to determine if using various combinations of the big ring was in effect the same as dropping into the granny ring as in bold below,or am I way off the mark?

    73 67 57 50 44 38 33 28 25
    95 87 75 65 58 50 43 37 32
    122 112 96 84 74 64 56 48 42
     
  4. Andy_R

    Andy_R Hard of hearing..I said Herd of Herring..oh FFS..

    Location:
    County Durham
    I would never use the highlighted gear combo's as you'll get an horrendous chain line! So drop onto the granny ring to get the 50 or stay on the middle as you've got a 50 there, but you're pretty much on the mark. You may have 27 possible gear combinations, but many of them produce duplicate results (or as near as dammit), and many of them are not suitable
     
  5. MacB

    MacB Lover of things that come in 3's

    Smaller the inch number the easier it is to pedal and vice versa. For a triple I like to think of the middle ring as general riding gears, the big ring as an overdrive and the small ring for when it gets really steep or I get really tired.

    Most riding will be covered in the range 40-100 gear inches and a lot of that in 50-85
     
  6. Stonepark

    Stonepark Senior Member

    Location:
    Airth
    http://www.whycycle.co.uk/gear_calculator/index.php is a good place to start as it gives answers in metric and imperial as well as ratio's​
    SELECT; Wheel Diameter​
    Smallest Sprocket <- - - -> Largest Sprocket
    Chainrings
    30 small
    Gear MM Gear Ratio Progression Metres
    1909.1mm (2.73:1) (PM:6.00m)
    1750.0mm (2.50:1) (PM:5.50m)
    1500.0mm (2.14:1) (PM:4.71m)
    1312.5mm (1.88:1) (PM:4.12m)
    1166.7mm (1.67:1) (PM:3.67m)
    1000.0mm (1.43:1) (PM:3.14m)
    875.0mm (1.25:1) (PM:2.75m)
    750.0mm (1.07:1) (PM:2.36m)
    656.3mm (0.94:1) (PM:2.06m)

    39 Middle

    2481.8mm (3.55:1) (PM:7.80m)
    2275.0mm (3.25:1) (PM:7.15m)
    1950.0mm (2.79:1) (PM:6.13m)
    1706.3mm (2.44:1) (PM:5.36m)
    1516.7mm (2.17:1) (PM:4.76m)
    1300.0mm (1.86:1) (PM:4.08m)
    1137.5mm (1.63:1) (PM:3.57m)
    975.0mm (1.39:1) (PM:3.06m)
    853.1mm (1.22:1) (PM:2.68m)

    50 Large

    3181.8mm (4.55:1) (PM:10.00m)
    2916.7mm (4.17:1) (PM:9.16m)
    2500.0mm (3.57:1) (PM:7.85m)
    2187.5mm (3.13:1) (PM:6.87m)
    1944.4mm (2.78:1) (PM:6.11m)
    1666.7mm (2.38:1) (PM:5.24m)
    1458.3mm (2.08:1) (PM:4.58m)
    1250.0mm (1.79:1) (PM:3.93m)
    1093.8mm (1.56:1) (PM:3.44m)
     
  7. betty swollocks

    betty swollocks large member

    A 122 gear inch ratio is the equivalent to a directly driven wheel of 122 inch diameter going round. Therefore if you want to calculate amount of forwards movement per pedal revolution in a 122 inch gear, you need to calculate pi x 122.
    The lower the gear ie the fewer gear inches, the easier it will be for you to pedal.
     
  8. betty swollocks

    betty swollocks large member

  9. OP
    OP
    2wd

    2wd Canyon Aeroad CF 7.0 Di2

    Location:
    SSG Oldham Cycling
    Thanks everyone

    Much appreciated :thumbsup:

    Now lets see if it helps to drag nearly 13 stone more efficiently up these hills ^_^
     
  10. MacB

    MacB Lover of things that come in 3's

    much as grinding a big gear(higher gear inches) feels powerful it can be a lot more efficient to spin your way up and just spin an easier gear faster in general. You could buy a cadence thingy and all that but it's fairly easy to work out if you know your gear inches and have a computer telling you your speed.

    For example you'll probably spend a fair bit of time in your 65 and 75 inch gears which are 39x14 and 39x16 roughly. So if you're tooling along in one of those then:-

    65 inches gives you about 11.5mph at 60rpm up to 23.5mph at 120rpm with every 5rpm being worth another 1mph

    75 inches gives you about 13.4mph at 60rpm up to 26.8mph at 120rpm with every 5rpm being worth another 1.1mph

    From a training perspective it's good to mix it up and a lot of folks would favour using the smaller gear. Say you wanted to tool along at 17.5mph you can do that via the smaller gear at 90rpm or the bigger gear at about 78rpm
     
    2wd likes this.
  11. OP
    OP
    2wd

    2wd Canyon Aeroad CF 7.0 Di2

    Location:
    SSG Oldham Cycling
    Seems like a lot of science goes into gearing

    I do have a cadence/speed computer which I bought a few weeks ago purely with the aim of
    making sure I was changing gear whilst keeping the same err ...well yes cadence!

    I tend to try and hover around the 90/95 mark and occasionally wander into 100 plus
     
    Boris Bajic likes this.
  12. Pennine-Paul

    Pennine-Paul Goth on a bike............

    I've hit 180 coming down Grains road :eek:
    Considerably slower going up tho:laugh:
     
    2wd likes this.
  13. OP
    OP
    2wd

    2wd Canyon Aeroad CF 7.0 Di2

    Location:
    SSG Oldham Cycling
    I've never come down there as i cant get to the top ^_^
     
  14. Pennine-Paul

    Pennine-Paul Goth on a bike............

    I can get up on 72" just, lots of weaving going on mind
    Usually come down when returning from a ride over in Saddleworth
    Last 2 miles all downhill weeeeeee..........................:bicycle:
     
  15. gaz

    gaz Cycle Camera TV

    Location:
    South Croydon
    Btw that is incorrect. A link has been provided in post number 8 that explains gear inches.
     
    tyred likes this.
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