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I have an old mountain bike and want to change to a Pashley style girlie bike. I use my bike to go to the shops, pop to places and go out and about with my dog running along side. I find the seating position of my old bike very uncomfortable in all areas. My concern is, Pashley style bikes only have a max of 7 gears and I currently have 21 gears, of which I only use maybe 4. My speedo shows that I cruise between 5 - 15 mph on my old bike but I'm concerned how fast I can go on a bike with only 7 gears. Is there any way of roughly working this out as I've not found a shop that will let you ride a bike at full speed before you buy it. Thanks in advance, Sarah

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Top speed has little to do with the number of gears but much more to do with gear ratio ("gear inches") -- the larger the max "gear inches" the faster you can go. Also, the width and pressure of the tires is a significant factor, as is the aerodynamics of the bike. –  Daniel R Hicks Aug 28 '13 at 14:49
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Take it on an airplane; real fast ;-) –  dumbledad Aug 30 '13 at 12:11
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Throw it off a cliff, also fast. –  Nick T Sep 1 '13 at 18:21
    
Many thanks Daniel, that's really helpful. You other two plonks have too much time on your hands! –  user7962 Sep 6 '13 at 16:49
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4 Answers

There are various gearing calculators available on the web. Here is one of them: http://sheldonbrown.com/gears/

The top possible speed will depend on your gearing, wheel size, and max cadence. Of course, your ability to reach that theoretical top speed will be limited by your own strength and fitness.

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+1 for using Sheldon as "one of them." –  Carey Gregory Aug 31 '13 at 4:53
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If you're just riding around the city, stopping frequently, and even expecting your dog to run along side, a Pashley bike will go "fast enough". Step-through bikes are intended expressly for that kind of riding.

The only consideration I would give to gearing is whether or not the gearing is LOW enough for the types of hills that you'll encounter.

If, for example, you live in Philadelphia there are virtually no hills and a single speed bike is perfectly fine. If you live in Pittsburgh, you'll want consider having at least some gears for climbing those hills. Your candidate bike has 7. That will be plenty of choices.

The old Raleigh's traditionally had three speeds and this was/is good enough for all casual urban riding.

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As a simple measurement, look at the size of the chain ring (the big gear that the pedals attach to). If it's bigger than the biggest one on your current bike, you'll probably be able to go faster.

If the chain ring on the new bike is about the same size as the biggest one on your current bike, look at the little gears on the rear wheel. If the smallest one is about the same size as the smallest one on your bike, then then new bike will have about the same top speed.

If the new bike's chain ring is smaller than the one you have now, it will probably be slower, unless it has a much smaller gear on the rear wheel as well.

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But to a significant degree that goes out the window with a "compact" setup. –  Daniel R Hicks Aug 30 '13 at 22:52
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I'm late to the party but, if you only use 4 gears or so, figure out with Sheldon's calculator what gear inches you are using. Chainring teeth x rear sprocket (with wheel size) to figure out what gear inches you are using. Does the Pashly-style 7 speed cover that range? Bueno! Rule of thumb is larger chainring goes faster (pedal speed being equal), but large chainrings, 50, 50+ can be harder on your knees. What is the chainring size that you use now? A midsize ring (in the 40's) can make pedaling easier and easly increase speed by inreasing pedal revolutions. I am running a 46x16 on 27.25 wheels on my single speed, resulting in 77.6 gear inches and 13.9 mph at 60rpm, to 20.8mph should I achieve 90rpm. 77.6 is a large gear where I live with hills, but where I plan on riding, mostly flat, should be Ok. (not my primary ride)

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