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I have a recumbent trike with 26 gears. While normally I would shift to a low gear when going up a hill, I found that I can go up hills in the highest gear, the configuration that gives me the fastest speed on a flat. This may be because the bike relies on pressure between the seat and pedals instead of pressure from gravity, so I can put more force into the pedals.

Does riding a bike in high gear up a hill put unusual stress on the parts? It does not have high-end parts. E.g. the front and back derailleurs cost $75 together and many of the other parts can be found at Walmart. Does riding up a hill in high gear put too much pressure on a bike that the bike's parts are not designed to handle?

  • I think the chain is under more tension – paparazzo Jul 25 '17 at 13:56
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    The front derailleur is under no load at all, same with the RD that merely guides the chain returning to the front chain wheels. Chainwheel, bottom bracket and cranks, cassette, rear axle, cassette carrier and freewheeling system and the chain will be under load. Most of the load will probably by taken by the chain and the chainwheel assembly. – Carel Jul 25 '17 at 16:18
  • Added the recumbent tag. – RoboKaren Jul 25 '17 at 18:02
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    3x8 is common for 24 in total. 8 speed systems are tried and tested - good and strong in principle, though of course you can get flimsy parts – Chris H Jul 25 '17 at 19:14
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    Just for a laugh I once challenged some mates to a "ride up this hill in top" competition. At a speed of almost walking pace, with a cadence somewhere South of 1rpm, I snapped the chain. So, yes, there is a point where you'll break something! – Grimm The Opiner Jul 26 '17 at 15:24
36

The bike will be fine -- the riding conditions are within the specifications of the bike components.

The bigger issue is you -- you don't want to end up damaging joints and what not by overexerting yourself.

  • The bike won't be fine, you're putting heavier stress on the parts. – Pieter B Jul 26 '17 at 9:06
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    Depends on the parts. Some parts (like the cranks) get heavier stress when you pedal in a high gear, some parts (like the drive train) get heavier stress when you pedal in a low gear. – R. Chung Jul 26 '17 at 11:09
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    @PieterB: heavier stress doesn't matter if its well within the design specs of the parts, which it will be. – whatsisname Jul 26 '17 at 18:14
  • @whatsisname, it would be more accurate to say that the stress should be within the design specs of the parts. However, that depends on the design. It should be noted that in a recumbent bike, the stress on the seat, cranks, chain, frame, etc. is significantly higher than on a standard model bike (usually, well more than double), which may be an issue for some parts. In a standard bike, the stress placed on these parts is limited to your arm strength (not commonly used, but possible) + your weight. In a recumbent, the limit is your full leg strength, which is usually much higher. – Makyen Jul 27 '17 at 18:41
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A very strong rider will put a lot of strain on the bike doing that. Wear on the sprockets will be slightly increased by grinding a small sprocket, but that's not a big deal. What's more significant is that if a part is going to fail (or a worn part is going to skip), it will fail when under high load. A friend of mine has snapped several chains on the same hill and now walks it, because he's very strong and fairly heavy and doesn't have the low gears to spin up 20% (I've been known to ride up it at his walking pace, in a very low gear). If something fails when you're working so hard, you're likely to hit the road -- not too badly at such slow speeds, but still to be avoided especially in traffic.

Your knees are likely to wear a lot faster than spinning a lighter gear though.

  • Is your friend closing chains using a quick link or special rivet? – Batman Jul 25 '17 at 15:11
  • @Batman I don't know. I haven't seen him in a while as I now work in another city, so we no longer coincide on our commute (we only saw each other a few times a year apart from that). – Chris H Jul 25 '17 at 15:14
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    @Batman defects, wear, damage, bad installation, etc. I agree. But all those happen. And a damaged part is most likely to fail under unusually high forces. While the wheel is applying the same force to the ground at the same speed, achieving that at lower cadence requires higher torque on the cranks and higher tension on the chain than normal riding. – Chris H Jul 26 '17 at 5:53
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    Other times I've seen chains break have been hard starts, again suggesting that they're going to fail under high load situations – Chris H Jul 26 '17 at 12:26
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    Elaborating on @R.Chung: The tensile force on the chain when going uphill at constant speed depends solely on the size of the back sprocket (and the wheel size, of course). Notably, changing into a smaller front chain ring eases the load on the rider's knees and the cranks, but not on the chain or back sprocket. For the chain it is good to use large sprockets. (Not to encourage diagonal shifting but installing appropriate sprockets.) Large sprockets also reduce friction (see e.g. bikeradar.com/us/road/gear/article/…). – Peter - Reinstate Monica Jul 27 '17 at 12:14
11

A friend of mine broke a crank (the "arm" of the pedal) in the Alps, so yes, parts can fail under load. It's not always the case that cheap parts fail earlier; sometimes they are actually sturdier: she would likely not have broken a cheap steel crank. Besides, I wouldn't be very concerned about my cheap parts to begin with. (I would be concerned about my Campagnolo needle bearings, perhaps, because I plan to eat next month.)

That said, I would be concerned about my safety. Pedal cranks, chains, axles etc. breaking in the middle of a full-force stride1 can throw you off course and onto the road, or down a cliff. Make sure you are on a wide bike path far away from the next truck. If veering could be fatal adjust your style so that you can control contingencies.


1 And that is when they break.

4

Parts can and do fail. For example of broken bike parts, you don't have to Google much to find this: http://pardo.net/bike/pic/fail-001/000.html

There are broken chains, chainrings, sprockets, cranks, handlebars and stems. All of these are highly loaded if using a high gear to go up a hill.

However, that said, I don't believe you can cause too much force in your recumbent. There's a reason why recumbents aren't used often, and that's because going up very steep hills you cannot exert a lot of force by putting your entire weight over the pedal.

Cyclists often accelerate uphill by standing on the front pedal, pulling up from the handlebars to get more leverage and also by pulling up with the cycling shoe attached to the back pedal. Just calculate the force of a heavyweight rider and you'll understand the amount of force. So, for example 0.17 m crank having 100 kg of body weight, 2*25 kg of pulling up with the shoe attached to the back pedal (2 times that because both back and front pedal are exerting torque) and 30 kg of pulling up from the handlebar is 180 kg * 0.17 m * 9.81 m/s^2 = 300 Nm. That's more torque than in my car engine!

So, as summary, if you're using a racing bike with a handlebar from which you can reasonably pull up and shoes that attach to the pedals, and your weight is high (100 kg or more), I would be concerned about parts failing due to high stress. But in your recumbent? No way, parts are tested with so high loads that they aren't going to fail in the relatively low loads of a recumbent. You can use whatever gear you like in your recumbent.

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    I don't ride recumbents but most I've seen have at least something to support your back. The most force I can physically exert is leg pressing with my back against something solid. So don't dismiss the recumbent so lightly. – Chris H Jul 25 '17 at 17:44
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    As a cyclist, I can leg press a huge amount of weight compared to my bench press weight. – Criggie Jul 26 '17 at 4:26
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    @Criggie yes (about 3:1 for me based on PBs in both cases). With respect to recumbents I reckon I can leg press more than I can squat with the weights held in front (taking into account body weight) but haven't tried the latter in anything like a handlebar position – Chris H Jul 26 '17 at 12:24
  • @juhist Fascinating link - thank you. I've been working my way through it looking at all the carnage. – Criggie Jul 26 '17 at 20:16
2

No

For a given pedal force the chain is under less tension when using the biggest chainring (think of a lever from the pedal spindle to where the chain runs). This also means less force on the sprockets and if using a small sprocket it also means less force/torque on the back wheel.

Edit: As Peter Cordes in the comments added: For a given sprocket and speed (i.e. power output) the chain tension will be the same, independent of the chainring. With a small chainring you’ll pedal fast and lightly while with a big chainring you’ll pedal slow and powerfully but the chain will move at the same speed and will be under the same tension. Pedaling slow but powerfully will of course put more load on the pedals, crank arms and bottom bracket.

The highest load possible is probably when you accelerate with all your power from a standstill using the smallest chainring and largest sprocket.

You can try to minimize wear by using a relatively large chainring + relatively large sprockets. The larger the chainring/sprocket the slower it will wear, since there is more material (assuming they are all made out of aluminium, sometimes the smaller ones are made out of steel for this reason).

I dimly recall a test in a bicycle magazine where the larger chainrings allowed for more efficient power transfer, which is interesting because the rear derailleur’s spring will put the chain under slightly more tension which should actually increase friction and make it less efficient. They theorized that this increased tension resulted in reduced vibrations, which in turn increased the efficiency.

All that being said: Use a gear where you feel comfortable and can pedal at a fast enough speed, otherwise your knees and other joints will suffer and you’ll tire faster. Generally >70 crank rotations per minute are advised, with ~90rpm often considered the optimum. Bicycle parts are easier to replace than joints.

  • Yes, "For a given pedal force", but that's not what's being held constant here. The OP is holding power output constant but reducing cadence by not downshifting. That requires more force on the pedals. – Peter Cordes Jul 27 '17 at 0:06
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    The right point to make is that for the same rear sprocket at the same speed&power, the chain tension should be the same whether you're pushing hard on a big chainring or pushing fast on a small chainring. (same speed & same power are equivalent when you're not accelerating; just doing work against drag and gravity.) So: using a bigger chainring is fine, but using a smaller sprocket will put more load on the chain and the gear teeth. – Peter Cordes Jul 27 '17 at 0:09
  • That assumes that the peaks are the same for fast/slow pedalling. If the peaks are higher and the valleys lower for a lower cadence, it will put more strain on the gears. – Peter Cordes Jul 27 '17 at 0:11
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It may damage your bike parts if they are really cheap, but there is no such thing as "too much pressure" on a good bicycles, so if you suddenly get any part of your bike broken because of your high efforts riding, you should pay your attention to choose an upgrade for you bicycle or even buy a new one.

Let's consider is it useful for you to overwork on uphill. Even thou you can win about 5km/h on a few minutes of hill riding, u lose many energy and your total average speed is tend to decrease.

Another question is does it really makes sense on riding the biggest speeds uphill. It hurts your knees a lot on a short-term and long term periods, so you may get a problem with your health.

I would generally recommend to increase your cadence rather than your power if you want to make a short speed up. For a long speed up i'd recommend keep your cadence and switch to a higher cog.

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