Pedal installation torque

[Samuel D]

Shimano says to torque pedals to 35–55 Nm after greasing the threads. I don’t have a torque wrench that goes that high, but my best estimate is that the upper end of that is pretty darned tight; probably far tighter than many pedals are fitted.

Shimano also says that a 6 mm Allen key cannot generate the needed torque, so a pedal spanner must be used on the 15 mm flats. Well then why does the same Shimano make most of its pedals with a 6 mm Allen key fitting? Some pedals (including some Shimano ones, e.g. Dura-Ace) have 8 mm fittings instead. That seems more sensible.

I’ve changed the pedals on my bicycle a few times recently and noticed the following:

• despite having installed pedals on new FC-5600 cranks with subjectively a lot of torque, when I removed the pedals the cranks were marred from pedal movement
• this marring of the crank face is apparent on practically all used cranks on eBay, etc. Some are terribly eroded
• many people (e.g. the power-meter reviewer ‘DC Rainmaker’) claim they don’t tighten their pedals more than ‘snug’ or similar, the better to remove them later. This presumably allows even more movement and crank damage.

I conclude that pedals should be tight. But this led me to wreck a Park Tool PW-5 pedal spanner when it slipped on errant grease on the slightly undersized flats of cheap Look pedals. I haven’t stripped crank threads yet but I wonder how much safety margin I have there.

How tight do you go, what sort of spanner or key do you use, and do you use a torque wrench?

[mjr]

Snug, a jobsworth spanner and I've got a big beam torque wrench that goes high enough but no way to attach it to pedal flats.

[pwa]

Some high end pedals have no flats for spanners and can only be tightened by allen key, so that tells you how little torque is needed. If using a spanner I get it so that the last bit of tightening is done with the crank (pedal arm) and the spanner acting like the two arms of scissors, so I can get my hand around both and draw them together. I do it until a bit of a squeeze has been applied, but not full on max tightening. I've had trouble getting overtightened pedals off in the past.

[Paulatic]

I’ve never read Shimano instructions or anyone else’s either.
I use an Allen key and just nip it up and no more. Never had one come loose and they’re always tight enough when you remove them.

[roubaixtuesday]

Surely it's pretty irrelevant as they self-tighten due to the RH and LH threads so won't come undone whatever the original torque?

The only pedal I've ever had come loose was on a set of kiddycranks where both pedals had RH threads, where I then realised a screw was provided to lock the pedal in place.

Or have I totally misunderstood something?

[mjr]

Surely it's pretty irrelevant as they self-tighten due to the RH and LH threads so won't come undone whatever the original torque?

That's the theory, but I have had pedals loosen enough to rock back and forth along the thread with a disconcerting clunk until they were removed, threads and crank face cleaned and greased and retightened. I suspect the rotational force can sometimes be overcome by the wiggling of being pushed down upon in some circumstances, especially if a unshouldered steel pedal axle gouges an aluminium crank unevenly... which is part of why "pedal washers" exist, isn't it?

[Brucey]

no torque wrench, I avoid pedals with allen key fittings only, and try to use pedal washer on ones without a full shoulder. ~30ftlbs is usually enough if the pedals have a full shoulder.

You know if your pedals have precessed (and therefore might do again in the future), because they will be tighter than you installed them after a few weeks of use.

FWIW the pedal shoulder always scuffs the crank as the pedal is installed. If there is not grease or waxoyl or something at/near the interface, then corrosion near where the two metals touch one another will also mar the cranks.

cheers

[Mr Evil]

You get fretting between the pedal and crank even if you do them up really tight, because the forces involved are very large. Jobst Brandt suggested a chamfered interface as a solution, but sadly it never caught on. Personally I use washers and don't do the pedals up very tight.

[Cyril Haearn]

no torque wrench, I avoid pedals with allen key fittings only, and try to use pedal washer on ones without a full shoulder. ~30ftlbs is usually enough if the pedals have a full shoulder.

You know if your pedals have precessed (and therefore might do again in the future), because they will be tighter than you installed them after a few weeks of use.

FWIW the pedal shoulder always scuffs the crank as the pedal is installed. If there is not grease or waxoyl or something at/near the interface, then corrosion near where the two metals touch one another will also mar the cranks.

cheers

What is 'precessed' please?

[Mr Evil]

Precession is what causes pedal spindles to try to rotate relative to the crank as you pedal, tightening them. There's an animation in the Wikipedia article that shows how it works, and why the rotation is backwards compared to what you might expect.

[atoz]

Surely it's pretty irrelevant as they self-tighten due to the RH and LH threads so won't come undone whatever the original torque?

The only pedal I've ever had come loose was on a set of kiddycranks where both pedals had RH threads, where I then realised a screw was provided to lock the pedal in place.

Or have I totally misunderstood something?

I have never used anything other than an open ended spanner to take off/put back pedals. I've found Allen keys don't have enough leverage to remove them when they've been on a while. I would be wary of overtightening pedals. Some cranks have tighter threads than others, as do some pedals. The Exustar single sided clipless/flat pedals are a bit loose when first tightening them until you get past the first couple of threads. Shimano ones are precise. I bet Campag are too. Old cranks can be less tight eg old style SR/Silstar cranks, and sometimes the alloy is softer eg Ofmega. In my experience they do self tighten. I've often wondered what can happen if you ride fixed though..

[mercalia]

torque wrench? just tighten it, it aint a engine block

[Samuel D]

I’m surprised how many people are happy to ignore Shimano’s torque specification, given that Shimano isn’t a company to idly make such recommendations. Maybe this is a case of suboptimal practices working okay because damage occurs slowly enough not to be a problem within the typical lifespan of a crank.

Some high end pedals have no flats for spanners and can only be tightened by allen key, so that tells you how little torque is needed.

How little? What if it’s an 8 mm Allen key? These things somewhat depend on the depth of the hexagonal hole, although torsion in the key limits the benefit of increasing depth (much as stretch in the pedal axle limits the number of threads exerting significant axial force). Spanner flats are thin and so are pedal spanners, so they don’t support as much torque as you might assume.

I’d like to find a book that outlines the principles of threaded fastenings, max torque for different bolts, head types, head sizes, materials, etc., in a way that someone who enjoyed high-school physics but has no subsequent experience can understand. Any recommendations?

Never had one come loose and they’re always tight enough when you remove them.

Surely it's pretty irrelevant as they self-tighten due to the RH and LH threads so won't come undone whatever the original torque?

I’m concerned about erosion of the crank face and the threads in the crank over years of use, not the pedals falling off.

Personally I use washers and don't do the pedals up very tight.

I don’t see how washers help unless the pedal doesn’t have a complete shoulder. There will still be radial movement at the threads and movement between washer and crank face in the absence of sufficient fastening tension.

torque wrench? just tighten it, it aint a engine block

But one half is made of soft aluminium and the threads are subject to large radial forces in use. Aren’t you interested in best practices? I am.

[pwa]

The only time I have had a problem in this area was with a pedal that had to be installed and removed by allen key, not a spanner. It had been put on too tight. The hex hole rounded off and I had to wreck the rest of the pedal to create something I could get a spanner on. Even then it took a good bit of grunt to get it off. So I use plenty of copper slip grease when I put a pedal on and use only a moderate squeeze when installing. They don't work loose.

[Samuel D]

They don't work loose.

That’s not my worry.

Have a look at used cranks. Ones that have been used for a few years are often terribly pitted and worn at the crank face. When fixing someone’s old bicycle the other week I noticed that the pedals had a worryingly loose fit in the cranks. One or the other was badly made or else the crank threads were eroded by movement in use. I fitted the pedals as tight as I dared which wasn’t nearly as tight as my own pedals or Shimano’s specification.