Bicycle Gear Ratio Measurements
Bike Gearing
Gear Charts for my Bike Fleet
By Steve Robson
The following is a gear chart for the bikes I own. These will help out determine speeds for the bikes. It also show relative gear ratio/ gear inches as it relates to the different tire sizes. Hopefully this will take out the mystery of gearing on a bicycle.
The gear ratios are determined by dividing front gear size by the rear gear size. Here is an example being taken from the mountain bike. Take the large drive gear (48 teeth) and take the mid range rear gear (21 tooth gear) and divide this by two, you get 2.29. This is the amount that the rear wheel turns for every crank turn. The next step is to multiply this number the tire size used on the bike. In the case of mountain bike, the tire measures only 25 inches in diameter. It is not the indicated 26 inches shown on the side of the tire; you get the number 57.14 inches. This is gear inch number that is used to help determine the speed of the bike.
To determine the speed of a bike, take the gear inch and multiply it by 3.14. This gives you the total distance traveled in on complete rotation of the pedals. Divide is by 12 to get the measurement into feet. Then multiply this by the RPM a rider can produce in one minute (eg. 75 RPM). Then multiply this by 60. This represents hour. You get the total distance covered in that time. The measurement will be in feet. Divide this by 5280. That how many feet are in a mile. You now have determined the average speed for that distance. To convert this into metric, multiply the final number by 1.625. This information about the bike gearing will help determine the best combinations to be used for a ride.
As you can see, on some bikes, there are a large number gearing overlaps. More speeds on a bike do not mean more gears. The 14 speed road bike I own has the most overlaps of all the bikes. There are only 4 true separated gear ratios in the drive train. On the mountain bike, there are only 9 independent gear ratios out of 21 speeds. Although the 12 speed road bike has the lowest number of total gears, it also has the most gears that work independent of each other. It has 6 speeds that do not overlap.
There are charts on the net relating to this subject. One of the items I have noted it that the tire size noted does not match the real measurement on real bikes. This affects the gear inch numbers seen in final computed numbers. The numbers shown here is a result using my numbers taken off my bikes. They have been carefully worked out.
Last year I wrote an article on my cycling over the course that year showing the results of different bikes. The results shown here back up some of my findings I did in an older article. A diagram I had drawn goes along this article shows how this looks. It shows the relative moment of different tire sizes with different gear ratios attached to them. As the tire size increases the need for lower gear ratios to get high gears ratios goes down.
Bike designs like the micro bike A-bicycle will always be far behind the levels the larger bikes in terms of gearing. Tires in the 16 and 20 inch sizes have various options to bump up the gearing range into the larger sized tires gear ratios. The use of combined internal (geared hubs) and external gearing allow the design of folding bikes and other special needs bikes to get the same overall gearing of an adult bike if the need is called for.
The drawings show a number of different settings. When two different bike designs are used side by side, there are a great deal changes. I have drawn a diagram showing a 26" wheel with a 3 to 1 gear ratio. There is a matching drawing 25" wheel sharing the same 3 to 1 gear ratio. The overall travelling distance on the road bike is 244.92" (20.41'). The effective gearing used is 42/ 14. On the mountain bike, to get the same gear ratio, a gear combination of 48/ 17, the travel distance is 235.5" (19.625'). In the drawing, there is a difference of only 9.42" in the travelling distance.
These are the gears I use for real bikes I ride. By using the math shown above, you can see just how big a change over an hour ride can make if matching riders where to travel the same distance using the same riding style. Using a 60 RPM as a base for the one minute reading, you get the difference in distance for the one hour make. There is a speed of 13.38 mph (21.74 kph) for the mountain bike. The road bike gets a speed of 13.92 mph (22.92 kph). There is a difference of .54 mile in distance at the end of the ride.
There are a large number of factors that go into determining the quality of a ride besides the gear ratios. The frame design will determine a lot on how much energy is put out for the rider. A full suspension bike will take a lot of power out of the rider while the rider of a normal road bike can get a lot more power to the road. The set-up of the bike will also have large bearing how well the rider can pedal the bike. The weight of the tires can be very important. The smaller lighter road bike tire/ rim combination allow less energy to be used when compared to the heavier mountain bike tire/ rim design. Out of all the weight reduction that one done on a bike, this one really makes a big difference on the road. It allows the most effective use the bikes gearing.
I have found myself getting to use gear ratios that match up when using the road and mountain bike. On the road bike, a gear combination I like using is the 42/ 17. This works out to a gear inch range of 64.24". The gear ratio is 2.47. Using one gear higher gets you into 78 gear inches. On the mountain bike, I like to use the gear combination of 48/ 19. The gear ratio is 2.53. This works out to a gear inch range of 63.16". One gear higher gets you 70.5.
The differences in the bike designs really come out. I have tried to match the two bikes for fit but the small detail make for different personalities. Getting a match on the gearing range used is important to me as well. Please note that the mountain bike has to get into high gear range to get the same gearing found on the road bike. By looking at the other bikes I have liked to use, the gearing is in the same range. The single speed CCM bike has 68.99 gear inches. The folding bike 3 speed bike has 67.39 gear inches in its high setting.
Looking at this part of cycling is important. By seeing what gearing combinations being used on a bike can help you out get the most out of your ride. Having more speeds on a bike does not mean more gear ratios. Gear overlaps will mean duplicate gear ratios. The wider rear gear cluster range allows more overlapping gears. The person with the old dated 10 speed bike could have the best range of gearing on it while a person buying new 24 speed bike will not have this. The real advantage the 7 and 8 speed gear clusters are the smoother transitions between gear shifts when using whatever front chain ring is being used.
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CCM Roadster single speed bike
- Tire size- 28 by 1 3/8th (27" real)*
- Front Gear- 46
- Rear Gear- 18
Gear inch of the bike- 68.99
Eaton’s Folding Road Bike- 3 Speed model **
- Tire size- 20 " by 1.75 (19" real)
- Front Gear- 48
- Rear Gear- 18
Gear inches of the bike
- 1st gear- 37.99 (.75 of 100% gearing), 2nd gear- 50.66 (neutral position), 3rd gear- 67.39 (1.33 of 100%)
The Schwinn Folding Bike- 6 speed model
- Tire size- 20 " by 1.75 (19" real)
- Front Gear/ 38 teeth
- Rear Gear Cluster-28, 25, 21, 19, 17, 14
Gear inch chart for bike
- 1st gear- 25.79, 2nd gear- 28.88, 3rd gear- 34.38, 4th gear- 38, 5th gear- 42.47, 6th gear- 51.57
Super cycle Mountain Bike- 21 speed model
- Tire Size- 26" by 1.95 (25" real)
- Front Gears- 48, 38, 28
- Rear Gear Cluster- 28, 25, 23, 21, 19, 17, 15
Gear inch chart for the bike
- 1st gear- 25, 2nd gear- 28, 3rd gear- 30.43, 4th gear- 33.33, 5th gear- 36.84, 6th gear- 41.18, 7th gear- 46.66
- 8th gear- 33.92, 9th gear- 38, 10th gear- 41.3, 11th gear- 45.24, 12th gear- 50, 13th gear- 55.88, 14th gear- 63.33
- 15th gear- 42.86, 16th gear- 48, 17th gear- 52.17, 18th gear- 57.14, 19th gear- 63.16, 20th gear- 70.5, 21st gear- 80
Gear overlaps- 4 and 8/ 5, and 9/ 6, 10 and15/ 7, 11 and 16/ 12 and17/ 4 and 19/ total over laps- 12/ 66.6% overlap
Kurahara Road Bike- 12 speed model
- Tire Size- 700 by 25c (26" real)
- Front Gears- 52, 42
- Rear gears- 25, 23, 21, 19, 17, 15
Gear inch chart of the bike
- 1st gear- 43.68, 2nd gear- 47.47, 3rd gear- 52, 4th gear- 57.47, 5th gear- 64.24, 6th gear- 72.8
- 7th gear- 54.08, 8th gear- 58.78, 9th gear- 64.38, 10th gear- 71.16, 11th gear- 79.53, 12th gear- 90.13
Gear overlaps- 4 and 8/ 5 and 9/ 6 and 10/ total overlaps- 6/ 50% overlap
Vision Orion Road Bike- 14 speed model
- Tire Size- 700 by 25c (26" real)
- Front Gears- 52, 42
- Rear Gears- 28, 25, 23, 21, 19, 17, 14
Gear inch chart of bike
- 1st gear- 39, 2nd gear- 43.68, 3rd gear- 47.47, 4th gear- 52, 5th gear- 57.47, 6th gear- 64.24, 7th gear- 78
- 8th gear- 48.29 , 9th gear- 54.08, 10th gear- 58.78, 11th gear- 64.38, 12th gear- 71.16, 13th gear- 79.53, 14th gear- 96.57
Gear overlaps- 3 and 8, 4 and 9/ 5 and10/ 6 and 11/ 7 and 13/ total overlaps- 10/ 71% overlap
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*- The bikes rear drive wheel size. The front is a smaller 26 by 1 3/8th tire.
**- The bike uses an internal 3 speed geared hub
