Timeline for How do on-road mountain bike speeds translate to road bike speeds?
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21 events
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| Nov 3 at 21:28 | comment | added | LeopardShark | Accelerating is part of the reason bikes have lower gears, but far from the main one. Specifically: bikes have lower gears to let you pedal efficiency at low speeds and accelerating from zero is one of the reasons one might want to cycle slowly (other examples being hills, and wanting not to put as much effort in). However, the most obvious counter-example to your theory is track bikes: they go faster than road bikes, with a single gear. This is typically near, but not quite at, the top of the road bike range. | |
| Nov 2 at 3:08 | comment | added | zenbike | You're ignoring the benefit of momentum. Getting to a position to push that gear at that cadence isn't somethiing you can do with pure power. If it was, gears would be unecessary. You need to start in a gear you have the power to push, and slowly build throught the gears to take advantage of momentum and mechanical advantage to maintain a cadence you coiuld never push if you started in your top gear. You are arguing my point, and calling it backawards. | |
| Oct 31 at 19:28 | comment | added | LeopardShark | The point of gears is that human legs are only efficient at a narrow band of cadences. Changing gear allows you to trade off torque and cadence to keep the latter in this region when the speed of the bike changes. So if you're spinning at 150 rpm, then shifting up will let you go faster for the same apparent effort (though the power your legs will be putting out will actually be higher). If your cadence isn't too high, then there's no benefit to a higher gear. You don't have to worry about this problem at all until you're in your top gear, since you can just change up to drop your cadence. | |
| Oct 31 at 19:18 | comment | added | LeopardShark | Gears do give you mechanical advantage, but mechanical advantage does not let you go faster or slower for the same input power at the cranks. All it does is, for a constant speed, change whether that power comes from a low force on the pedals at a high cadence or a high force on the pedals at a low cadence. Your example is instructive: if you maintain the same cadence in a 44/12 as a 53/11, then indeed the 53/11 will go faster. But doing this requires much more force on the pedals, so the power you are required to put out is significantly higher. | |
| Oct 28 at 0:01 | comment | added | zenbike | @LeopardShark Really? What is the point of gears, then, if they give you no mechanical advantage to produce speed more efficiently? "Drivetrain efficiency" is what exactly? Because in my book, "drivetrain efficiency" is anothe term for "how much mechanical advantage can my gears give me". Yes, the amount of effort you put in to the crank is important, and more effort will produce more speed. But if you put the same effort into a 44/12 gear combination, it does not produce the same speed as matching that effort on a 53/11 combination. This is not hard to understand. | |
| Oct 26 at 19:41 | comment | added | LeopardShark | In your example the cadences are equal and the road speeds are higher, but that's because the road bike takes more torque to turn at that speed (or, it would, given the same rolling resistance, drag, weight, etc.). Power = torque × cadence. | |
| Oct 26 at 19:28 | comment | added | LeopardShark | Gearing does not let you achieve a greater speed for the same power in this way. Bike speed = power output at wheel ∕ resistive force (which depends on speed). Power output at wheel = power input at cranks × drivetrain efficiency. The latter is near-enough constant (about 95 %), so bike speed depends only on the power put in at the cranks. (A road bike drivetrain will tend to be more efficient than an MTB one, but it's marginal. The difference is dwarfed by the things mentioned in other answers.) | |
| S Dec 22, 2021 at 11:26 | history | suggested | CommunityBot | CC BY-SA 4.0 |
fixed a typo
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| Dec 22, 2021 at 5:43 | review | Suggested edits | |||
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| Dec 22, 2020 at 13:58 | comment | added | zenbike | Ross, the question wasn't "can I go as slow on my road bike as you do on a MTB". It was what mechanical difference is there between usi g a road bike and a MTB. You can obviously go slower on a road bike than it's maximum capability. For that matter not all road bikes have the same maximum capability. But the maximum speed on a road bike is higher than the maximum speed on a mountain bike. And gearing is a significant reason why. There are other reasons, most of which can be minimized. But the average speed of most road bike riders has little to do with this question. | |
| Dec 21, 2020 at 3:17 | comment | added | Ross Millikan | This is nonsense. Most people on road bikes spend little time above 26 mph. The impact of that time on an average speed is small. Most time is spent riding well within the range of the mountain bike gearing you quote. | |
| Oct 16, 2020 at 21:21 | comment | added | Brian Fernandes | If we assume everything else is the same except for the gears, you would need a lot more effort to do 90 RPM at 50x11 (4.5:1) than 90 RPM at 44x12 (3.6:1). One pedal stroke in the former turns the wheel 4.5 times, in the latter, it's 3.6 times, requiring drastically different amounts of effort! You don't even need to bring an MTB into the equation. If you were on the 14t cog at the back of your roadie (not 11t), the ratio would be (3.5:1), similar to 44x12 (3.6:1).You're effectively saying that pedaling 50x11 & 50x14, at the same cadence, on your roadie,would require the same amount of effort! | |
| Jul 16, 2019 at 18:21 | comment | added | zenbike | Also, to say that gearing does not reduce the required effort for a given speed, but “allow you to put in even more effort” is an oxymoron. If I agreed with you that gearing up allows for more effort (I don’t), then by definition, gearing down would reduce the effort required. | |
| Jul 16, 2019 at 18:17 | comment | added | zenbike | Nobody said the same speed. I said the same level of effort (power/wattage/work/whatever you want to call it, with different gearing, produces a different speed result. I’m not really sure why that seems to be controversial. Isn’t that the point of putting gears on a bike? Gears do not, by the way, allow you to “put in even more effort”. Effort (defined as the amount of energy you are producing with your legs) is controlled only and completely by the rider’s strength and endurance. Gears allow you to use that effort more efficiently to produce more speed from the same wattage, as I said. | |
| Jul 15, 2019 at 17:35 | comment | added | relatively_random | Resurrecting an old question and not really a bike pro, but my engineering guts say your "same level of effort" argument makes no sense. If you're riding the same bike at the same constant speed, your power output is the same no matter which gear ratio you use (equal to the sum of drag and other inefficiencies plus the climb). So aren't they only useful if you are already fit enough to max out the MTB? The gears just allow you to put in even more effort and they don't reduce the required amount of effort, unlike tires, riding position and stiff frame. | |
| Dec 20, 2014 at 8:49 | comment | added | zenbike | Yes. Wattage = Power = Work = Effort. | |
| Nov 24, 2014 at 8:02 | comment | added | Vorac | You keep saying "the same level of effort". I don't think I understand your definition of "effort". The same cadence at different gearing is maintained by different pedalling wattages. | |
| Jul 29, 2014 at 22:32 | comment | added | Ross Millikan | If he is running 10-12 mph, he is probably in the middle of the gear range. Yes, the gear limited top speed will be lower due to lower gearing, but he has the gears he needs for his cruising speed. | |
| Sep 4, 2013 at 18:29 | comment | added | zenbike | @Kevin, yeah, I use it a lot. I kind of disagree that gearing is not a limiting factor, though. Even if you are not in your top gear all the time, the gearing is radically different throughout the range. I am including wheel size and tire dimension in the drivetrain and gearing. Obviously, fitness and rolling resistance, and bike weight and many other things play a part, but gearing is the largest mechanical differential between mountain and road bikes. | |
| Sep 3, 2013 at 20:51 | comment | added | user8019 | Zenbike, cool app. At first I was thinking you were off with those numbers, and then it occured to me you were talking in miles and I'm used to kms:) One thing you've remember though is that the gearing isn't the limiting factor most of the time. I mean, who spends 80% of their time at 90rpm in top gear? I even rode with my roadbike (an old one that weighs exactly the same as my hardtail MTB) gears locked at 53,18 and I was still noticeably faster than on my MTB (a decent entry-level) and that's even counting bumpy dirt roads and gravel. Stated simply, you can't gear your way to speed. | |
| Apr 30, 2012 at 4:09 | history | answered | zenbike | CC BY-SA 3.0 |