Questions of torque
Questions about torque wrenches, torque and threadloc
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By Lennard Zinn
I’d like your recommendation on a reasonable home-shop torque wrench to tighten the exotic materials I and my friends are accumulating on our bikes. I have asked at local bike shops (here in Boulder.) replied with the jaw-dropping answer that they don’t bother. Perhaps a professional wrench trusts his fingertips enough to work on a $300 carbon bar – but I certainly don’t.
Who makes one suitable for a shade-tree mechanic once a month or so?
On a bike, you really need two torque wrenches, a big one and a small one. You need a big, long-handled one that goes to high torque for tightening the big bolts on the bike to avoid creaking and loosening, like crankarms, bottom bracket cups, and pedals. For that, I have a Wrench Force ratcheting socket torque wrench that I really like. Snap-On makes it, and I’ve used it happily for perhaps 10 years, as have the other mechanics assembling our bikes in my shop. The Snap-On brand is the best I’ve tried – very expensive, but lifetime no-questions-asked warranty.
Since you are talking about exotic materials, I am assuming you want to avoid over-torquing small bolts, in which case you need a small wrench. I have a two really nice ratcheting wrenches with small socket drives; one with a 3/8-inch drive from Wrench Force and a Ferrari-spec one with a ¼-inch drive from ITM.
However, the one that I now use the most and find the simplest to use is the Effetto Mariposa Giusaforza. I have a photo posted above, and you can find it here.
The Giustaforza (meaning “Correct Force” in Italian) is an elegant little torque wrench that accepts the same little hex drive bits as a power screwdriver. That make the drive bits far cheaper, easier to replace individually (you’ve seen the grab bins of these things by the checkout counter in hardware stores) and easier to store in your tool box.
It shares features of the other wrenches I mentioned above, namely a rotating adjuster, a graduated torque scale, and the head clicks over when the torque setting has been reached. The scale goes from 2 Newton-meters to 16 N-m (18-142 inch-pounds) in 0.5 N-m increments. It does not have a ratcheting head.
For stem bolts, Ritchey now has a slick little torque wrench with a built-in 4mm Allen wrench on it that we often use as well due to its ease of use. It is torque limited both by the short wings on it so you can’t get much leverage on it and that it “clicks out” at 5Nm of torque. Many mountain bikes have numerous other bolts that should also be tightened to a range around 5Nm but take 5mm hex keys, not 4mm like the Ritchey has installed. A reader alerted me that the hex bit in the Ritchey tool is only lightly glued in and can be removed with little effort and then replaced with a hex bit of another size.
Are the torque values listed on components for dry threads or wet threads? If dry, what should I reduce the torque value if I am using grease versus anti-seize, or something such as Tacx dynamic paste compound.
You hit on an important problem – there is no consistency from manufacturer to manufacturer on this, so you are never comparing apples to apples.
While some manufacturers list maximum torque, some list both minimum and maximum, while others suggest ideal torque. Often you won’t know which it is. You would not have this issue working on the Space Shuttle (or at least I hope not.), but the chances of getting the bike industry to agree on a standard way to determine torque settings would be like herding cats.
Nonetheless, using a torque wrench to a recommended setting from the manufacturer (and in my maintenance books listed below I have an extensive torque table) is going to be way better than freehanding them. I also recommend, regardless of how the torque value was originally determined, greasing or threadlocking (which when wet will also lubricate the threads) all threads before tightening; your torque measurements will be more consistent then.
With bottom bracket cups being one of the highest torque specs on the whole bike I am curious of just how hard it is to install the cups without using a torque wrench. For external bearing bottom bracket cups I use the Park bbt-9, which is not an overly long wrench like torque wrenches are. Shimano cups recommends 35-50 Nm each side. Should it be just about as hard as you can pull up on the wrench without putting your weight on the lever? Would it be possible to strip out a frame’s bottom bracket shell or would the bottom bracket cup threads be damaged?
Yes, with that short-handled wrench, you should pull on it about as hard as you can. Unless the threads are already damaged, you should not be able to strip them doing this.
I have a Bianchi carbon frame, and I have the torque limit for my seat post (Easton EC 90) of 60 inch-pounds. Is there a way to get the torque settings for other bolts on the bike?
Also, for anyone who is interested in getting a torque wrench, I got a really nice dial type one on the Web that is calibrated in inch pounds for about $30. I had to go to a store specializing in metric hex wrenches to get the bit for it though and that cost almost $10. A really worthwhile investment because I am sure I would have over tightened the seat post without it.
Check “Zinn and the Art of Mountain Bike Maintenance” or my road or triathlon-bike maintenance books listed below; they all have a torque table in them. Otherwise, you can try looking up tech manuals on the Web sites of manufacturers of each component on your bike.
VeloNews technical writer Lennard Zinn is a frame builder (www.zinncycles.com), a former U.S. national team rider and author of numerous books on bikes and bike maintenance including the pair of successful maintenance guides “Zinn and the Art of Mountain Bike Maintenance” and “Zinn and the Art of Road Bike Maintenance” as well as “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.”
Zinn’s VeloNews.com column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn ([email protected]) Zinn’s column appears regularly on VeloNews.com.