Which fasteners need the most torque? Will just one torque wrench with a wide torque range be enough?

Question

To service my car I'm in the market for a torque wrench. I've found an electronic torque wrench with a wide torque range from 10 – 135 Nm / 7.4 - 99.57 lb ft. This is high enough for the wheel nuts and low enough for many, but not all, of the other fasteners.

I'd like to know whether I'm likely to come across fasteners that need more torque than the wheel nuts. If so, I may have to buy two more torque wrenches - one for higher torque and one for lower.

A secondary, but related question - do I really need a torque wrench below 10Nm? Here are some examples of low torque fasteners - specified to two significant figures!

The torque wrench: https://www.machinemart.co.uk/p/clarke-pro236-38-drive-digital-electronic-to/

Answer 1

TBH with you, unless I'm doing some serious wrenching, about the only thing I use a torque wrench on is the wheel lugs. Beyond that, it's all done by feel. Obviously I'll use one for things like engine work, where tightening things equally is of the utmost importance. The small fasteners underneath and throughout the car, just tighten them down snug. If you tighten them too much, they'll break in a heartbeat. You just have to be careful. In most cases, tighten it until you feel it get snug, then tighten it just a little bit more ... "little" meaning 5-10° more. Some things, like spark plugs, require a little bit more, but are usually done by a 1/4 turn after it goes snug.

As far as the torque wrench itself goes, ensure you've got plenty of range past where you want to go to. For instance, wheels are torqued ~80 lb-ft for steel wheels and ~100 lb-ft for aluminum (that's a ballpark ... pay attention to what the manufacturer states). If your torque wrench only goes to 100 lb-ft, it won't be overly accurate. It's fairly easy to find a torque wrench which goes up to about 150 lb-ft for a reasonable price. It is by far to have far more range than you'll ever need, rather than it to only go up to the top end. On a side note ... if you get a click type torque wrench with the twisty grip to adjust, run it back to the bottom of the scale after every use.

Answer 2

Another application that is common for torque wrenching is axle nut installation. If you anticipate doing suspension work of any kind, you will need a torque wrench that exceeds 150 ft lbs. I have a torque wrench with a range of 25 ft lbs to 225 ft lbs. I also have a torque wrench that measures in inch pounds. I've never had the need for more,but both are very useful.

Answer 3

I'd like to know whether I'm likely to come across fasteners that need more torque than the wheel nuts. If so, I may have to buy two more torque wrenches - one for higher torque and one for lower.

Yes, there are fasteners on many cars that have a higher torque specification than the lug nuts. For example I have a car that calls for 88 ft-lbs. on the lug nuts but the crankshaft pulley bolt is 120 ft-lbs. PLUS another 180 degrees. Some suspension parts call for torque in the 100+ ft-lbs. range.

Having worked on cars and motorcycles for a long time I have found that I need at least 3 torque wrenches. A 1/2" drive one, a 3/8" one, and a 1/4" one. Between these 3 nearly the entire range of likely fasteners is covered. One rule about torque wrenches is that you should avoid using them at the limits of their range if possible. That's because the accuracy of the torque tends to be off near the limits. This is especially true at the bottom end of the range.

A secondary, but related question - do I really need a torque wrench below 10Nm? Here are some examples of low torque fasteners - specified to two significant figures!

I also have a "precision" torque wrench that I use on my bicycle where you have very tight tolerances for torque like 2 Nm, 3 Nm, etc. My standard 1/4" torque wrench is not able to be accurately set for 2 Nm. My point is that sometimes I encounter automotive fasteners that are in this range and I've also used my bike torque wrench on those. For example valve cover fasteners for an aluminum engine. As I recall I recently needed to torque some of those at 4 Nm.

The best approach, in my mind at least, is to buy what you need when you need it. That way, over time you build up a nice collection of tools. Unless you're a professional mechanic, you probably won't want to just buy everything you can think of up front.