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Dumb Newbie Qs on Gears and Speed
Ok, so the first one is really dumb: does the gear setting affect how
fast you go when you are coasting? My instinct tells me no, since coasting involves not using the pedals, and I presume the only thing affecting speed as you coast down a hill is the gravitational accelleration that Galileo proved. But perhaps the chain setting can affect how fast the wheels are allowed to turn? Second one: can a bike with 30 gears actually go faster in top gear than a bike with only 5 gears? Or is it just a mattter of the 5 speed having less nuance between slowest and fastest speed? If faster, is it proportional Third one: is the coasting speed of a bike without use of brakes its maximum speed? Say I coast freely down a hill and the online counter shows me at 29 kmph. That is faster than I can pedal in my highest, fifth gear (or would want to). But if I were a speed freak on a different bike, could I "refill" the pedalling by upping the gear to thirtieth and outrun gravity by pedalling at my normal rpm? Fourth: I know I'm not allowed to change gear when the bike is not moving. But can I change gear during a coast, or does it have to be when I am actually pedalling? Not long ago I tried changing gear while coasting and there was a problem, the gear did not change well. Since then I have not tried it again, but I don't know whether I did something wrong or it was just a common and garden gear malfunction, due to poor indexing or insufficient greasing. Thanks for your patience. I only coasted for the first time about 3 weeks ago. Elisa Roselli Ile de France |
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Dumb Newbie Qs on Gears and Speed
Elisa Francesca Roselli wrote: Ok, so the first one is really dumb: does the gear setting affect how fast you go when you are coasting? My instinct tells me no, since coasting involves not using the pedals, and I presume the only thing affecting speed as you coast down a hill is the gravitational accelleration that Galileo proved. But perhaps the chain setting can affect how fast the wheels are allowed to turn? No Second one: can a bike with 30 gears actually go faster in top gear than a bike with only 5 gears? Or is it just a mattter of the 5 speed having less nuance between slowest and fastest speed? If faster, is it proportional To speak of the number of "speeds" for a bicycle is an error. The more correct term would be gear "ratios" -- the relation between the pedalling cadence (RPM) and the rear wheel revolutions per minute. A ratio of 1:1 would mean that one revolution of the pedals would produce one revolution of the rear wheel. That would be a "high" gear used for going fast on level or downhill roads. A ratio of 3 or 4 pedal revolutions to produce one wheel revolution would be a "low" gear suitable for uphill travel. Speed depends on gear ratio and pedalling speed (RPM), not the number of ratios available. The "5-speed" usually has greater gaps between its 5 gear ratios than one with more ratios but not always. It depends on the manufacturer and the purpose, not the number. Third one: is the coasting speed of a bike without use of brakes its maximum speed? Say I coast freely down a hill and the online counter shows me at 29 kmph. That is faster than I can pedal in my highest, fifth gear (or would want to). But if I were a speed freak on a different bike, could I "refill" the pedalling by upping the gear to thirtieth and outrun gravity by pedalling at my normal rpm? You can always make the bike go faster by pedalling faster (if you are able). Fourth: I know I'm not allowed to change gear when the bike is not moving. But can I change gear during a coast, or does it have to be when I am actually pedalling? Not long ago I tried changing gear while coasting and there was a problem, the gear did not change well. Since then I have not tried it again, but I don't know whether I did something wrong or it was just a common and garden gear malfunction, due to poor indexing or insufficient greasing. Changing gears is accomplished by "derailing" the chain from one ring to another, hence the name of the mechanism "deraileur". Just as a train could not be derailed when standing still, the chain cannot be derailed unless it is moving (you are pedalling). It is often possible to make a single change in the setting when not pedalling which will not actually happen (cause the derailment) until you begin pedalling again. Thanks for your patience. I only coasted for the first time about 3 weeks ago. Elisa Roselli Ile de France |
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Dumb Newbie Qs on Gears and Speed
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Dumb Newbie Qs on Gears and Speed
On Fri, 18 Jul 2003 14:14:32 +0200, Elisa Francesca Roselli
wrote: snip Fourth: I know I'm not allowed to change gear when the bike is not moving. This is true only for external gearing. Internally geared hubs (the Classic Sturmley-Archer, SRAM, et al.) require shifting while _not_ pedalling. If you can't see gears, then you shift while not pedalling; if you can see gears, you shift while pedalling. snip -- Nobody but a fool goes into a federal counterrorism operation without duct tape - Richard Preston, THE COBRA EVENT. |
#5
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Dumb Newbie Qs on Gears and Speed
Elisa Francesca Roselli wrote:
Ok, so the first one is really dumb: does the gear setting affect how fast you go when you are coasting? No. A coaster gear/freewheel is not like an automotive transmission and so it won't slow you on a downhill (at least not enough that you'll notice). My instinct tells me no, since coasting involves not using the pedals, and I presume the only thing affecting speed as you coast down a hill is the gravitational accelleration that Galileo proved. Essentially correct. Your speed is also affected by your initial velocity when you begin coasting and, of course, wind direction and velocity. But perhaps the chain setting can affect how fast the wheels are allowed to turn? No. Second one: can a bike with 30 gears actually go faster in top gear than a bike with only 5 gears? Or is it just a mattter of the 5 speed having less nuance between slowest and fastest speed? If faster, is it proportional Not exactly. The number of gears here is less important than the gear ratios of the two bikes. You could have a single gear bike that has a higher gear than a 30 gear bike's highest gear. In fact, when one has many gears, the gears will be a lot closer together than on a 5 speed bike. The highest gear will probably be higher but not by a huge amount. The lowest gear will also probably (but not neccessarily) be lower. It all depends upon how the people who put the bikes together set up the gears. Third one: is the coasting speed of a bike without use of brakes its maximum speed? It depends upon the gearing and how fast you can pedal. Say I coast freely down a hill and the online counter shows me at 29 kmph. That is faster than I can pedal in my highest, fifth gear (or would want to). But if I were a speed freak on a different bike, could I "refill" the pedalling by upping the gear to thirtieth and outrun gravity by pedalling at my normal rpm? Yes. If you have a high enough gear you can go faster down almost any hill by pedaling though somewhere around 75kph it starts to get a little on the crazy side. A gear big enough to pedal at that speed is almost useless anywhere but on a long steep downhill. Fourth: I know I'm not allowed to change gear when the bike is not moving. But can I change gear during a coast, or does it have to be when I am actually pedalling? Not long ago I tried changing gear while coasting and there was a problem, the gear did not change well. Since then I have not tried it again, but I don't know whether I did something wrong or it was just a common and garden gear malfunction, due to poor indexing or insufficient greasing. You can move the lever but the gear won't usually change until you pedal. You can pedal to change gears even when you're going too fast to pedal to make the bike go faster. I do this every time I ride. Typically, when I'm approaching a red light, I will coast and shift to a lower gear, pedaling only enough to change the gear but not enough to make the bike go faster or even maintain speed. That way, I can start from the green light in a lower gear; which tends to be easier and get me back up to speed faster. Thanks for your patience. I only coasted for the first time about 3 weeks ago. Keep at it! --Bill Davidson -- Please remove ".nospam" from my address for email replies. I'm a 17 year veteran of usenet -- you'd think I'd be over it by now |
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Dumb Newbie Qs on Gears and Speed
Elisa Francesca Roselli wrote in message ...
Not to discourage you from asking questions here, but there are many other useful resources. I think you'll find a lot of information at the fount of all knowledge, aka http://www.sheldonbrown.com There's a glossary of terms, articles for beginners, as well as articles on repair, links to other bicycle sites, etc. Even if you don't plan to fix your own bike, it's good to know why they're charging you $30 for a new lefthanded framwhizzer bolt. www.chainreactionbicycles.com is another site I've found handy. Probably tons more - I often find what I need with a GOOGLE search of the web, or GOOGLE GROUPS search for old articles posted here. The latter can be confusing, since a lot of mythology and opinion and general pigheadedness is mixed in with useful information. There's a frequently asked questions (link posted here periodically). A GOOGLE search turned up: http://www.faqs.org/faqs/bicycles-faq/part1/ number of speeds and how it affects top speed, there is a gearing calculator at www.sheldonbrown.com which shows speed in a given combination (front chainring and rear cog) at a given crank rpm. Third one: is the coasting speed of a bike without use of brakes its maximum speed? Coasting speed depends on the length and slope of the hill and factors such as wind (tailwind helps, headwind hinders) and rolling resistance (related to tire width, tread, and inflation pressure.) I can coast faster down some hills than I can pedal on a flat road, but I'm a puny weakling. I can usually increase my downhill speed by pedalling. I choose to limit my top speed, so usually coast, and have been known to brake. Oh, the shame :-( Fourth: I know I'm not allowed to change gear when the bike is not I infer that you have a derailleur-equipped bike, rather than an internally geared one. Now to illustrate why you're better off reading sheldon brown's explanations :-) If you're at a bike shop (or at home with a co-operative friend) ask to see how the chain is moved from one rear cog to the next. This means holding the rear wheel off the floor and shifting the dearilleur(s) back and forth while turning the pedals. A shop may put the bike in a work stand. You'll watch the chain run over the rear pulleys which shift it sideways so that it "walks" from one cog to the next. If you move the pulley without rotating the cranks the sideways force just bends the chain, it doesn't "walk" from one cog to the next. If you shift several steps without pedalling, the chain is bent at a sharper angle and will complain loudly when you next try to pedal. "Ho-ow can you treat a poor chai-ain so ...." The front derailleur nudges the chain from one chainring to the next - nowhere near as elegantly IMO as the rear, and if you move the front cage (metal part through which the chain passes) without pedalling, it can just jam against the chain. It's also possible for the chain to drop inside the smallest chainring or outside the largest chainring (misadjusted derailleur and/or faulty technique). I've had the chain drop between the chainrings on my older bike (new chains are narrower than old). And the chain can drop bewteen the largest rear cog and the spokes (ouch) or outside the smallest rear cog (ouch). This is usually due to misadjusted or bent rear derailleur. I consider the embarassment of having a plastic spoke protector (prevents the chain from jamming into the spokes) a small price to pay. I'm sure there are illustrations of front and rear derailleur operation somewhere. Picture is worth 1000 words, etc. hth |
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Dumb Newbie Qs on Gears and Speed
Elisa Francesca Roselli wrote:
: Third one: is the coasting speed of a bike without use of brakes its : maximum speed? The maximum speed is when you drop your bike from an airplane... But really, I think you meant to ask if it's somehow related to gears. Well not really. Bicycles are not automobiles, but when it comes to speed they are quite similar. I see two factors limiting the maximum speed: power and resistance. If your engine is a high-performance one, it can push very hard to overcome resistance and achieve high speed. The other part of the equation is having low resistance on your vehicle. For cars and bicycles this means mainly that they need (for speed) good aerodynamics. Aerodynamics is one reason why racing bikes are faster: you have a lower riding position so your upper body provides less resistance. It is one reason why some recumbents are faster than racing bikes: the riding position is very low, so your body in general provides little air resistance. People obsessed with maximum speed can build a fully closed cover around the recumbent, still dramatically improving aerodynamics. World-class athletes are occasionally able to reach speeds of 120 km/h or so on such bikes, in short sprints on flat ground. There are some IMO less important nitty gritty details affecting maximum speed. For example, smooth high pressure tires provide less rolling resistance. There are also some differences in how much power you can put out in a certain riding position and type of bike. The role of gears is simply that turning the cranks at a reasonable rpm must make the wheel turn at the required speed. This is very easy to achieve, so we can assume that gearing is optimal. : Say I coast freely down a hill and the online counter : shows me at 29 kmph. That is faster than I can pedal in my highest, : fifth gear (or would want to). If you could pedal at a higher rpm you would go faster. I used to top at 40 km/h on an old 3-speed upright bike on the flats. : But if I were a speed freak on a : different bike, could I "refill" the pedalling by upping the gear to : thirtieth and outrun gravity by pedalling at my normal rpm? That's actually a good question that I think hasn't been answered. I think theoretically, if you want to go faster you need to provide power through pedals, ie. there needs to be some resistance felt at the pedals. I think this only happens if your rpm * gear is higher than the speed you are doing just by coasting. So you need to pedal fast or use a big gear, maybe both, depending on the hill and the bike. (Dunno if this is comprehensive enough, and I'm not entirely sure of it either...) Practically though, pedalling can increase air resistance so you might not go faster by pedalling than by simply coasting. I read about a guy who did some unscientific tests which yielded very little benefit from pedalling. I guess there is a huge load of anecdotal evidence against this, but still... I know it's complicated but you like intellectual challenges I think :-) -- Risto Varanka | http://www.helsinki.fi/~rvaranka/hpv/hpv.html varis at no spam please iki fi |
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Dumb Newbie Qs on Gears and Speed
On Fri, 18 Jul 2003 14:14:32 +0200, Elisa Francesca Roselli wrote:
Ok, so the first one is really dumb: does the gear setting affect how fast you go when you are coasting? No involves not using the pedals, and I presume the only thing affecting speed as you coast down a hill is the gravitational accelleration that Galileo proved. I think you mean Newton, but that's OK. Second one: can a bike with 30 gears actually go faster in top gear than a bike with only 5 gears? Or is it just a mattter of the 5 speed having less nuance between slowest and fastest speed? Typically, a bike with 5 gears will not have as high a top gear, nor as low a bottom gear, nor as many choices in between, as one with 30. The number of gears has nothing to do with the speed the bike can go, however. The fastest bikes, land speed record machines, tend to have only one gear. It's a matter of rider comfort, and adaptability to all sorts of riding conditions (like big hills), that give the bike with more gears the advantage. Fourth: I know I'm not allowed to change gear when the bike is not moving. But can I change gear during a coast, or does it have to be when I am actually pedalling? Depends on the type of gear. Internally-geared hubs are often changed by a momentary coast, but derailleur-geared bikes need to be pedaled to change gears. -- David L. Johnson __o | Accept risk. Accept responsibility. Put a lawyer out of _`\(,_ | business. (_)/ (_) | |
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Dumb Newbie Qs on Gears and Speed
archer wrote: ... If your gear ratios are high enough, you can can easily pedal yourself to speeds higher than you could achieve just by coasting. You will probably find that as you ride more, you can comfortably pedal faster than you could at first, so you can drive yourself faster down the same hills.... However, pedaling will also increase the overall drag. This can be demonstrated by coasting down a hill, then pedaling backward at a normal cadence. At what point pedaling becomes counter-productive will depend on rider strength and bicycle configuration, but I suspect in most cases it will be at a speed of 70 kph or greater. Tom Sherman - Quad Cities USA (Illinois side) |
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Dumb Newbie Qs on Gears and Speed
"John Bartley K7AAY (ex-KGH2126)" wrote: On Fri, 18 Jul 2003 14:14:32 +0200, Elisa Francesca Roselli wrote: snip Fourth: I know I'm not allowed to change gear when the bike is not moving. This is true only for external gearing. Internally geared hubs (the Classic Sturmley-Archer, SRAM, et al.) require shifting while _not_ pedalling. If you can't see gears, then you shift while not pedalling; if you can see gears, you shift while pedalling. The Rolex, er Rohloff 14-speed internally geared hub will shift under load. Tom Sherman - Quad Cities USA (Illinois side) |
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