View Full Version : average foot pounds of torque for a 3/8's ratchet?

07-22-2010, 08:43 PM
im buying a bunch of air tools, and i want to know the average ft/lbs of torque that a person puts on a 3/8's ratchet or a 1/2 ratchet, and with like a 2 foot breaker bar or something like that.

cause im looking at air ratchets, and i see them range from 45ft/lbs to 100ft/lbs and i dont know if thats alot..

ive already bought a 625ft/lbs impact wrench for my stupid axle bolt. but i was thinking a regular 3/8 air ratchet with 50ft/lbs would be a decent amount?? i dont know

someone help me get into perspective

02 5SPD
07-22-2010, 09:10 PM
If you have a 24" breaker bar, and you put 50 lbs of force on the end of it that's 100 ft/lbs (or is it lb/ft?). If your ratchet is 8" long, that would be 150lbs of force on it. Does that help you any?

07-22-2010, 09:15 PM
that would make sense, but what does the average person exert?

wait.. if you put 50lbs of force on the end of an 8" ratchet, wouldnt that mean its like 80ft/lbs of force?

02 5SPD
07-22-2010, 09:51 PM
Depends on the person...how strong are you?

The equation is the length of your lever arm multiplied by the force exerted (Lbs is a force, metric equivalent is Newtons, Kg is a mass- it isn't proper to use Kg in this equation, the mass should be applied by the gravitational constant to make it a force. This is also asuming the force is at the end of the lever. Otherwise you use the distance to where the force is being applied)

Force * distance from point of rotation = torque applied
50lbs * 2ft = 100 lbs/ft
150lbs * (2/3)ft = 100lbs/ft [8in = 2/3 of a foot]
2lbs * 50ft = 100lbs/ft
2/3lbs * 150ft = 100lbs/ft

See how they all net the same torque on the nut?

50lbs * (2/3)ft = 33.333lbs/ft

You could use a torque wrench to test how much force you exert. To make it simple you can grip it 1ft out, so the maximum torque rating you can achieve would be the same as the force you're exerting.

Let's say the air ratchet is 1ft long. If it exerts 100lb/ft, and you're not capable of matching the force the ratchet will rip out of your hand (assuming the nut doesn't loosen first). I've seen adjustable ones, so you could get a really strong one, and turn it down to where you can handle it.

07-22-2010, 10:13 PM
hmm that makes sense, so i guess ill buy just a 50lb/ft rachet then, sense its like 17 bucks at harbor freight.. and i figure if i need more that 50lb/ft, i can but the ratchet in the other direction that its turning at the same time?? or will that brake it? lol. also, why doesnt an impact wrench shoot out of your hands then? i have a 625lb/ft impact wrench..

02 5SPD
07-22-2010, 10:31 PM
i can but the ratchet in the other direction that its turning at the same time??
Can you clarify this?

Impact guns are designed differently than air ratchets.. I haven't seen the internals of either, so I can't tell you much more than that. I've only used an air ratchet a couple times and I hated it. Busted a few knuckles open.

I'm headed to bed, but I can tell you more in the morning. My mind will also be clearer, haha.

07-22-2010, 10:46 PM
Get the highest one you can afford or you'll hate yourself.

Lug nuts only take 87 ft/lbs and with a torque wrench it doesnt take much pressure since they're like 2' long (43.5 lbs exerted which isnt anything). Usually my impact on click 1 forward gets it to about 75-80 ft lbs then I finish woth a torque wrench.

07-23-2010, 06:05 AM
For me, an air ratchet is really only useful if you have a lot of long, fine-thread bolts that aren't torqued down hard. Good for valve covers.

I've never relied on them to actually break anything loose because I can always put more force on it with my hands than an air ratchet can do. Well, the ones I've owned, anyway.

I don't know how an air ratchet works exactly, but my inkling is that you trying to turn it won't actually put any extra torque on the bolt.

02 5SPD
07-23-2010, 06:47 AM
I've only used air ratchet when I need a ton of extension, and I can tell I'm going to slip off with a regular ratchet. The air ratchet I could focus more on holding it steady, as a regular ratchet introduced a weird torque with a lot of extensions. I used it as a last-ditch effort type of thing. If he ratchet is exerting it's maximum force while you turn it the other way it would increase the overall torque, however, you might risk breaking the ratchet, as you would be overloading it.

07-23-2010, 07:46 AM
Any air tool depends on the air supply to it. PSI, volume, size of the hose etc.
Any impact wrench is a rotary hammer where the air ratchet is an air motor.
A 1ft breaker bar with 100lbs force will have a lot different torque than if it has 200lbs of force at the end.
So it depends on the force going in.

07-23-2010, 12:22 PM
I would look at air tools other than at Harbor Freight too. They are not always the cheapest. Sometimes you can get a Cambell Hausfiled at like Tractor Supply for less. You might still want to get the CH is a few bucks more as it would be slightly better too. The CH is still made in China, but with a little better quality control. I don't use an air ratchet to break things loose. At least I don't use the air. I break it loose with my hand then use the air to spin it out. I have broken a Harbor Freight air ratchet in half breaking bolts loose with it. I have probably exerted at least the same force on a CH one. When I broke the one in half, it had a vane motor in it and I think a planetary gear reduction. That output of that goes to an offset arm which moves the ratchet mechanism back and forth as it spins.

02 5SPD
07-23-2010, 12:43 PM
I've heard harbor freight i crap; you basically plan on one use out their stuff, then plan on replacing it because it's on borrowed time. I think the only time I've actually successfully used an air ratchet was replacing the starter on a Saturn. I was able to bract it against something and let the tool do the work. I hadn't been able to use a regular ratchet because of the mile of extension I had. Other times I ended up using something else, or going about my work in a different way. As I said above, I generally don't like them.

07-23-2010, 03:26 PM
CH 3/8 air ratchet. 50 lbs/ft. at 4.8 CFM and 90 psi. with 1/4" line.
I have a 3/8 battery impact,14.4 V. which I find handier than the ratchet.

07-23-2010, 04:26 PM
I use my air ratchet pretty much daily. I have a snap on far7200 that has 70 ft/lbs. of torque and it does a very good job. my snap on dealer told my today that the going rate for one is $399. good thing i got mine in school for half.

07-23-2010, 08:47 PM
haha i love snap on. i wish i could afford their tools.. lol

02 5SPD
07-23-2010, 08:53 PM
Snap-On is good stuff. The best.

07-23-2010, 10:52 PM
With a 3/8 air ratchet, you generally break it free by hand [with the lever pulled] , and then the air tool spins it off faster and easier.
Keep it oiled internally, as any air tool should be.
A 100 lb 3/8 ratchet can hurt your hand as it snaps on. There is a power knob to attenuate this.

07-24-2010, 10:55 AM
yea, i got the 50 lb 3/8n ratchet, and it's alright i guess.. i love my impact wrench more

07-24-2010, 07:29 PM
I should of brought my 3/8 snap-on gun. You would of jizz all over your self

07-24-2010, 07:35 PM
You shouldve!

02 5SPD
07-24-2010, 08:31 PM
The self-jizzing would have been epic!