Bolts not screws!

True but not exactly the reason. Torques are specified for bolts because they are the part of the fastening system that actually does the work.

Bolts that are too loose are not pre-loaded and will loosen with vibrations*. (You can add thread locker on under torqued screws to help with this, but the are not carrying the load correctly.)

A properly torqued bolt will slightly stretch. This causes it to be tight enough that it won't back out under normal load and vibration. The load is carried equally against all the threads that contact the nut or other threaded part.

An over tightened bolt will deform or strip and now has to be replaced.

But... the bolt manufacturer specifies the torque based on the fact that it will be used with a similar strength steel nut. This is not the case when you have steel bolts going into aluminum fasteners and parts. So you have to compensate by less torque and more threads touching.



*I just had to repair the part that hold my car's rear view mirror because of this. Two steel bolts went into a shallow pot metal part. Since they weren't tight enough, they vibrated loose, then destroyed the threads of the part. I tapped the part to the next larger size, now I have more thread surface area to carry the same load, and put it back together with thread locker so it won't vibrate out. So far it's holding up pretty well.

I need a torque wrench that dials up to 400 watts, for my crankrings & peddles.

One trick I use when clamping carbon parts is to hold the allen key only two inches from the bolt axis to avoid overtightening accidently. Incrementally tighten all the bolts in sequence until they are all equally tight.

I don't use torque wrenches on a bike for two reasons. First, the published max torque specs are to avoid stripping threads. It has nothing to do with damaging the clamped parts. Second, with the exception of the old tapered bottom bracket bolt standard, every bolt on a bike is too small for a torque spec to correlate well with bolt tension.

On a bike, my general rule is if the bolt and thread is steel, and the clamped part is (relatively thick) metal, I tighten the bolt heavy. If the thread or bolt is not steel, or the part being clamped is not metal, I clamp only tight enough for the part to do its job, holding the allen key close to the bolt so as to keep the torque down.

Also, many times when things like carbon seatposts slip or creak; people tend to respond to this by trying to tighten the clamping bolt tighter. Just reefing on the clamp will probably result in a broken seatpost. 99% of the time, the seatposts slip or creak because the seatpost is undersized. Sometimes carbon paste can be used to fill the gap, but most of the time a shim should be used. Aluminum cans make excellent shims.

i use them. I'm a refrigeration mechanic by trade and my hands are pretty well calibrated. because i typically install my bolts wet, i torque 25% less than the max spec.

OP, a lot of people will tell you that you don't need torque wrenches. I have ruined a couple of seat post clamps on carbon bicycles trying to torque by feel. Thank god, the design results in the seat post clamps cracking before ruining my expensive carbon frames. I have also stripped cleat threads on two or so shoes. I'll be the first to admit that I am a bit of an amateur mechanic gorilla who is kinda heavy-handed tightening nuts and bolts. I do all work on my bikes, and a few years ago invested in some cheap harborfreight torque wrenches and a Ritchey Torque Key. Now, all is swell.

My advice? Unless you are a pro, get the torque wrench. Better safe, right? than sorry!

Well, a torque wrench costs bugger all and if used properly will ensure that you do not over-torque and damage components.

I have one and say they're worth the investment.

cheers

Yes.

Funny, I pulled the trigger last night on a wee one for bikes:
http://ecx.images-amazon.com/images/...8L._SX466_.jpg
I already have larger ones for other wrenching. Mostly, I don't use them unless except on parts where I think it's important to get it right.

You're more likely to gouge the hub shell. Having the cogs tightly clamped together results in them pressing as a unit against the hub splines, distributing the force better. With a loose lock ring each cog essentially acts independently. If you're a rider who's prone to mashing in the middle of the cassette proper torque is essential.

Would you fly on a plane that was maintained by mechanics who didn't use torque wrenches?

Joe

Would you irrelevant question an irrelevant question?

Thread[/close]

The difference is there are torque specs in many applications where you need to hit a tight spec.


They're are few or any in a Bike. Most, like stems are do not exceed.

A few are at least thiis much ( lock rings).

So tighten the do not exceed ones just enough hold. And crank down the ones that are minimums.

Anecdotally, only time I've broken a bolt on bike is thigh turning past snug to hit a torque spec.

I've learned to embrace the word snug as opposed to tighten, and still every now and then I'll snap something, not perfect but I'm beating the odds

Yes, specs and torque wrenches are not a replacement for fundamental skills. A few years back, when I was in daily contact with dealers and their mechanics, I'd hear two common complaints.

1- the bolt broke or stripped before coming to torque spec.
2- the bar (or other part) is tightened to spec and yet slips, what do I do now?

The answer to both was and still is, you use your judgment and skill based on experience.

To those who want to emulate aircraft mechanics ---bicycles are not airplanes, and not built to the same working tolerances. They neither need, nor respond as well to rigid adherence to published specs.

Albatross

Guacamole steam engine.

Did they have torque wrenches when steam engines were invented ?

Could you ride a bike at 550 mph 38000 ft over the ocean?

This.

I tinker on more than just bikes and it seems like most of my problems come less from torque values and more from the quality of the materials. Bolts and the like on bikes are cheap enough (we not talking grade 8 hardware here) that if one is rusty or has imperfections in the thread you should just replace it.

That being said, torque wrenches have come down in price and there really is no excuse not to own one or more. The full price for one from harbor freight is 21.99. Those things are almost always on sale too.

The Ritchey Torque key is another cheap option.

Even if not torqued to the manufactures value using those tools ensures that you have balance on your parts. Having all of your chainring bolts torqued to the same value ensures that there is no wobbling, creaking, or play in your chainrings. Same for stem bolts, pedals, etc...

If torque wrenches are so necessary to work on a bicycle, why don't professional mechanics use them? I've spent a fair amount of time hanging around bike shops, and do not ever recall seeing a mechanic use a torque wrench in a shop.

Also, I've had the benefit of being supported by mechanics with Pro tour level experience. Never saw them use a torque wrench either.

I wouldn't touch a Harbor Freight torque wrench. A badly calibrated torque wrench is far more dangerous than not having one at all, and Harbor Freight is not known for their quality tools.

For my carbon parts I tighten until I hear a crack then back it off a quarter turn.

The only torque wrench I use is a Craftsman Model 1019 Laboratory Edition Signature Series (the kind used by Cal Tech high energy physicists and NASA engineers), that has been calibrated by top members of the state and federal departments of weights and measures to be dead on balls accurate (it's an industry term).

while I agree with you that most of Harbor Freight's tool offerings are kinda hit or miss, their torque wrenches are reliable. Some technician who work extensively with torque wrenches (I think this was on the mechanic's forum) did a lab test of the reliability of those HF click-type torque wrenches, and he was very surprised at their accuracy, as compared to torque wrenches from very famous and up-market brands. Too lazy to search now, but trust me, it is on there somewhere.