Torque Wrenches - Questions for a Mechanic

[TexTexTex]

I'm looking for a mechanic who knows their way around tools.

So I'm finding myself in need of a torque wrench for multiple uses lately and I currently have a set of 3/8" drive impact sockets and impact wrench. Most of my uses for a torque wrench are going to be for fasteners that need 100 ft/lbs or less, however my truck (2022 Ram 1500) requires a 130 ft/lbs of torque to secure the lug nuts. My thought was to purchase a 3/8" drive torque wrench so it was easily be compatible with my existing sockets, BUT i'm finding that it's extremely difficult to find a 3/8" torque wrench that can handle torque specs above 100 ft/lbs. It seems most of them are 1/2" drive when venturing above the 100ft/lbs mark. Is there reason for this?

I can't seem to find a clear answer in my search through forums. Anybody have a recommendation for what I should do? It seems silly to buy a 1/2" torque wrench simply for lug nuts on my truck, but maybe there will be other uses for it later? I can't think of any at the moment. My preference is to "buy once, cry once" so if there's a quality tool that is worth the splurge, I'd be interested.

Any insight is greatly appreciated.
Thanks

[FINate]

I prefer two torque wrenches, one smaller 3/8-in drive for lower torques, and a 1/2-in drive for higher torques.

Or you can buy 1/2-in drive torque wrench that goes up to 130 ft-lbs and get 1/2-in drive female to 3/8-in drive male adapter to use your existing sockets.

Either way, I would get a 1/2-in drive torque wrench and socket for your Ram.

[GilesMM]

I got a torque wrench just for the lug nuts on the car.  They need to be tightened to the correct spec. I think I used Harbor Freight.  I use it a couple times per year but have found occasional other uses.  The extra leverage is handy.

[lthenderson]

Is there reason for this?

Yes, physics is the reason. To get 130 ft-lbs of torque on a 3/8 torque wrench with around a 10 inch lever arm on it you would have to apply 156 pounds of force to the handle. A 1/2 torque wrench will have a lever arm around the 15 inch range meaning you only have to apply 104 lbs of force to the handle to get 130 ft-lbs of torque on the business end. I'm just guessing on handle lengths based off past experience but the longer the handle length, the less force you have to apply to get the desired torque.

[Boll weevil]

Is there reason for this?

Yes, physics is the reason. To get 130 ft-lbs of torque on a 3/8 torque wrench with around a 10 inch lever arm on it you would have to apply 156 pounds of force to the handle. A 1/2 torque wrench will have a lever arm around the 15 inch range meaning you only have to apply 104 lbs of force to the handle to get 130 ft-lbs of torque on the business end. I'm just guessing on handle lengths based off past experience but the longer the handle length, the less force you have to apply to get the desired torque.

And the problem is even worse on the driver end… a 1/2 inch drive provides >30% more bearing area between the driver and the socket and >75% more area within the driver to react the internal shear stresses in the driver.

[HPstache]

I also agree that a 1/2" and 3/8" torque wrench are great to have in a tool box.  A 3/8" torque wrench feels like the "wrong" tool for tightening lug nuts to me, even if the torque you are shooting for falls within the far range of it.  That's just me though, there's no technical reason you couldn't... but if you can't find one with that high of a range, then it's time to add a 1/2" torque wrench to your tool box.  That or just torque it 'til your elbow clicks ;).

[uniwelder]

If you wanted a torque wrench, I'd just get a 1/2" drive and then use a 1/2 to 3/8 reducer to adapt to your existing sockets.  If you wanted better accuracy, then perhaps a 3/8" torque wrench which can be more finely tuned, but might not be necessary for what you're doing. 

Beam style torque wrenches never lose their accuracy and are much more durable than click-it ratcheting styles, but the graduations aren't as fine and you'll need to see the dial as you're using it.  Just an FYI, as you look around for what to buy.  I'd purchase a beam style second hand, but not a ratcheting one.  If you get a ratcheting one (new), make sure to dial it back to its lowest setting before storing it away.

If it's just the lug nuts driving this decision, I wouldn't bother at all.  Did vehicles recently become more fragile?  I've never heard of people using a torque wrench to tighten lug nuts until this thread, with the exception of torque limiting extensions for impact wrenches.  Just tighten as much as you can by hand with the lug nut wrench.  If you're on the road and have to change the tire, you'll need to get it off by hand, so you don't want it tighter than you're physically capable of.  Mechanic shops are notorious for over torquing, so I don't think you have to worry about going too hard by hand.

Is there reason for this?

Yes, physics is the reason...

And the problem is even worse on the driver end… a 1/2 inch drive provides >30% more bearing area between the driver and the socket and >75% more area within the driver to react the internal shear stresses in the driver.

Yes.  You risk breaking your wrench trying to put that much torque on a little nub of metal.

[Posthumane]

I only have a 1/2" drive torque wrench, and it's really been all I've needed for 90% of the jobs that actually require a torque wrench. The 10% of jobs that required a torque wrench below a spec where my 1/2" drive was accurate was on things like engine rebuilds or small, fiddly motorcycle parts.

I'm with uniwelder in that I generally don't bother with a torque wrench on things like lugnuts. They are not that sensitive to the actual torque value as long as you don't significantly under-torque them. Just use a longish ratchet or lug wrench and put most of your weight into it. You'd be hard pressed to over-torque lugnuts on a truck.

[JAYSLOL]

I have a 1/2” for everything in ft/lbs, and a 3/8” for everything in inch/lbs. the 1/2” should work with a 1/2-3/8” adapter for your sockets, though I recommend you picking up the 1/2” set of sockets or at least the one size you will use to torque the truck lug nuts since that adapter might not handle 130ftlbs