Why do pedals have to be tightened so much?

dasho · Jan 11, 2009

I took my bike into the LBS to get the cables changed out and they took it upon themselves to tighten the pedals so tight I will need a breaker bar to get them off.

I can't understand why pedals have to be tightened to such a high torque value. I tighten mine to snug and check them every few rides and in 12 years have never had a problem.

Can someone tell me why it is necessary to tighten them so much and why? I realize they could possibly work themselves loose but isn't snug good enough, especially for a recreational rider?

Also, what is the best (easiest) way to get the suckers off?

Thanks in advance!

BentChainring · Jan 11, 2009

From the park website, they should be putting 300-400 in-lbs on them.

They need to be fairly tight so that your pedaling action does not overcome the preload and separate the joint. Ideally you dont use threaded fasteners in bending like this, but avoiding it would add weight.

tom_h · Jan 11, 2009

dasho said:
[snip] ...Also, what is the best (easiest) way to get the suckers off?

Some pedals have a hex female socket on the end of their axle (part that threads into cranks), I've always found that the easiest to remove or install ... I have hex bits for my 3/8 and 1/2 drive ratchet wrenches.
Pedals that lack a hex socket, require a thin , long-handled , open end wrench. Park (and others) make "pedal wrenches" that will provide the necessary leverage.

Appling grease or preferably anti-seize compound to the pedal threads, makes it easier to remove pedals in the future.

tom_h · Jan 11, 2009

dasho said:
.... I can't understand why pedals have to be tightened to such a high torque value. I tighten mine to snug and check them every few rides and in 12 years have never had a problem.

Can someone tell me why it is necessary to tighten them so much and why? ...

http://www.sheldonbrown.com/gloss_p.html

The right pedal has a normal thread, but the left pedal has a left (reverse) thread.

The reason for this is not obvious: The force from bearing friction would, in fact, tend to unscrew pedals threaded in this manner. The fact is, however, that it is not the bearing friction that makes pedals unscrew themselves, but a phenomenon called "precession".
You can demonstrate this to yourself by performing a simple experiment. Hold a pencil loosely in one fist, and move the end of it in a circle. You will see that the pencil, as it rubs against the inside of your fist, rotates in the opposite direction.
Ignorant people outside the bike industry sometimes make the astonishing discovery that the way it has been done for 100 years is "wrong." "Look at these fools, they go to the trouble of using a left thread on one pedal, then the bozos go and put the left thread on the wrong side! Shows that bicycle designers have no idea what they are doing..."
...
The left threaded left pedal was not the result of armchair theorizing, it was a solution to a real problem: people's left pedals kept unscrewing! I have read that this was invented by the Wright brothers, but I am not sure of this. Note! The precession effect doesn't substitute for screwing your pedals in good and tight. It is very important to do so. The threads (like virtually all threads on a bicycle) should be lubricated with grease, or at least with oil.

velotel · Jan 11, 2009

People who crank down hard on tightening the pedals drive me nuts when the pedals are my own. (Which is one reason I never let anyone mess with my bike.) Or on someone's bike who has asked me to do something for them that requires removing the pedals. There is absolutely no reason to ever tighten the pedals more than firm. As in amazingly light pressure. In more years than I can remember any more of tightening pedals on cranks I have never exerted enough pressure to even come close to doing more than making sure it's threaded up tight to the end of the threads and I have never, ever had a pedal come loose. The pedals naturally tendency when riding the bike is to become tighter with every revolution. Thus there is no reason whatsoever to do more than firm up the pedal to the crank. Et voila with that there is never a problem removing the pedal. Which is one reason why I prefer tightening the pedals with an allen wrench; they offer way less leverage. And I repeat that never have I had a pedal loosen in use. They are in fact always tighter when I want to remove them than was the case when I installed them. Always amazes me when discover the results of someone who felt compelled to put the muscle to the wrench. I mean what in the heck were they thinking!

tarwheel2 · Jan 12, 2009

I had the same problem with a mechanic over-tightening a pedal. I had to take my bike into the LBS just to remove it, and they had trouble as well. Since then, I tighten my pedals until snug and no more. I have never had a pedal come loose, and I've been doing it this way for at least 5 years and probably 35,000 miles of cycling.

danl1 · Jan 12, 2009

That precession that Sheldon speaks of is the very reason they need to be tight first.

Doesn't make sense, does it? That's because the reason is as subtle as the reverse-threading, only one pedalstroke of logic on down the road.

When components are threaded appropriately tight, they are effectively a single unit. If they are too loose, they'll interact in ways you'd rather the didn't - bending of the spindle, galling, and a couple of other fun possibilities depending on the particular metals. It also facilitates intrusion of moisture to the threaded interface.

Riding them too loose can create situations that guarantee you'll never be able to get them disconnected, Funny how that works sometimes.

tom_h · Jan 12, 2009

danl1 said:
... .
When components are threaded appropriately tight, they are effectively a single unit. If they are too loose, they'll interact in ways you'd rather the didn't - bending of the spindle, galling, and a couple of other fun possibilities depending on the particular metals....

Hee-hee ... as inexperienced car mechanics (or rather, their customers) may have discovered if connecting rod or cylinder head bolts are not torqued to specification .... ka-boom!

paper warrior · Jan 12, 2009

I threaded pedals loosely the result was it reammed out the cranks. So I ordered a crank threader- hope it works.

cxwrench · Jan 13, 2009

wow...some of you guys crack me up. "don't tighten 'em up too much, mine have never come off..." you'd think the ONLY force affecting pedals is the bearings spinning. when people pedal bikes, they actually exert some pretty large forces perpendicular to the axle. if the pedal is 'sorta tight', it can come loose. won't always happen, but it can. and all it takes is once to ruin your day. if you can't get properly tightend pedals loose, have someone show you the right way to do it. you don't need to use a 3' long bar to get 'em tight, but just spinning them in there at 2nm is NOT a good idea.

wim · Jan 13, 2009

The pedals naturally tendency when riding the bike is to become tighter with every revolution.

This has always been one of my favorite pieces of misinformation. If you believe that, why use a wrench at all? From the first pedal stroke on, the pedals will get torqued tighter and tighter and tighter—by, hmm, what? Bearing friction?

russotto · Jan 13, 2009

As danl1 points out, If you don't tighten pedals enough, you'll gall the threads (both on the crank and on the pedal, but of course Murphy says the more expensive one gets damaged worse), because the threads will move against each other, even though they don't unscrew.

If you're having to "snug them" every few rides, they're too loose; you're likely not able to "snug" them because they've unscrewed slightly, but rather because the threads have been damaged.

jmlapoint · Jan 13, 2009

I always install my own pedals. I have a set of pedal taps that I usually spin into the crankarm threads to make sure the threads are clean, and I apply grease to both pedal spindle and crankarm threads before assembly.
I start them by hand until I know the threads are engaging easily and smoothly to avoid cross-threading. Then I use my Campy 15mm Pedal Wrench to complete threading and tighten. I check for tightness after first few rides on newly installed pedals and then leave them alone. I have never stripped a crankarm, nor have I had a set of properly installed pedals loosen. Probably just lucky, but I've been doing it for 40 years.

jmlapoint · Jan 13, 2009

I also wonder if it might have to do with litigation.
If your LBS lets a bike leave their shop and the pedals loosen and you get hurt riding them, maybe they figure we only get 1 shot at preventing this so let's make sure they are really tight before they leave the shop.
Just a thought.:idea:

tom_h · Jan 13, 2009

jmlapoint said:
I also wonder if it might have to do with litigation.
If your LBS lets a bike leave their shop and the pedals loosen and you get hurt riding them, maybe they figure we only get 1 shot at preventing this so let's make sure they are really tight before they leave the shop.
Just a thought.

But you could say the same about nearly every other critical fastener: stem, handlebars, seat post, etc.
"Specified torque" is preferable to "really tight".

roadfix · Jan 13, 2009

I torque mine down just plenty enough so I have no problem removing them when I do using a long handled pedal wrench.

Same thing goes for car lug nuts. I don't have to jump on my tire iron to loosen these nuts. I also torque these just enough to a point where I have no problem removing them.

tom_h · Jan 13, 2009

roadfix said:
...
Same thing goes for car lug nuts. I don't have to jump on my tire iron to loosen these nuts. I also torque these just enough to a point where I have no problem removing them.

Let's hope you don't drive aggresively , or take long trips on rough roads, or mostly drive curvy roads ...

While conical seat nuts are more resistant to precession-induced loosening, critical fasteners that are not pre-loaded with enough torque to actually create specific amounts of bolt-stretching, are at risk of premature failure.

ie, what seems "tight enough" may be too loose for durability and safety, due to the cyclic tension/compression loads a fastener is subjected to -- fastener could fatigue and break.

baker921 · Jan 13, 2009

IME pedals tighten in use, I have broken regular spanners trying to loosen them, ergo they make special spanners to undo pedals and call it a pedal spanner/wrench. Now when you need to refit the pedals you use? - "the pedal spanner" which has that extra long handle so you can really tighten them! Logic's at its finest when its circular.

AlexCad5 · Jan 13, 2009

BentChainring said:
From the park website, they should be putting 300-400 in-lbs on them.

They need to be fairly tight so that your pedaling action does not overcome the preload and separate the joint. Ideally you dont use threaded fasteners in bending like this, but avoiding it would add weight.

What is "pre-load", and what does "seperate the joint" mean?

tom_h · Jan 13, 2009

AlexCad5 said:
What is "pre-load", and what does "seperate the joint" mean?

http://www.arp-bolts.com/Tech/Tech.html

Pre-Load
Finally, although not a design parameter, the subject of bolt installation preload must be addressed. It is a fundamental engineering concept that the force in a bolt in an ideal preloaded joint will remain equal to the preload until the externally applied force exceeds the preload. Then the force in the bolt will be equal to the external force.

This means that fluctuating external forces will not cause fluctuating forces in a preloaded bolt as long as the preload exceeds the external force. The result is that fatigue failure will not occur. ...

.... The objective, then, is to preload a bolt so that it just exceeds the external load, and no higher.
To sum up: both insufficient preloads and excessive preloads can lead to fatigue failures.

Why do pedals have to be tightened so much?

dasho

BentChainring

tom_h

tom_h

velotel

tarwheel2

danl1

tom_h

paper warrior

cxwrench

wim

russotto

jmlapoint

jmlapoint

tom_h

roadfix

tom_h

baker921

AlexCad5

tom_h

Top Contributors this Month

Recommended Communities