Torque in the real world

[scatteredsun]

Had a question about torque.

I've run various numbers through kart calc and I know my 420cc, 18" tires, 6:1 gearing, 40 series TC, on 600lbs of cart and people will give me max torque of 374ish nm. My question is, what the **** does that mean?

If I drop everything to a 212cc and a 30 series with the same above stats, I get 297 nm. 80ish nm more doesn't seem like a whole lot for A LOT more $$$.

Anyone have real world examples of how much torque can move what? I'm especially interested in how much torque can tow how much weight.

 

[anickode]

Torque converters make the equation tricky because they don't have one set gear ratio at any particular rpm. It depends on many factors.


Since the 212 and 420 both deliver peak torque at 2500 rpm, you cannot assume a drive ratio for the torque converter. It will be somewhere between engagement and Max ratio.

The 212 delivers 8.1 ft/lb at 2500 rpm

The 420 delivers 18.6 ft/lb at 2500 rpm

Torque converter ratio at 2500 rpm =????

Sprocket ratio of 6:1

Tire size doesn't change torque delivered to the axle, just force delivered to the ground, assuming zero wheel spin.

You just can't say that one setup will pull x amount of weight vs another setup pulling Y amount. There are too many other factors at play.

 

[scatteredsun]

Ok, I knew it wouldn't be an easy 1:1 comparison and there are a lot of factors that would change things.

I guess I'm missing something in my head about the whole thing. Some dots aren't connecting.

 

[anickode]

Since the only constant that can be relied on with a torque converter is the max ratio, assume 1:1 for a 40 series and 1:0.9 for a 30 series. Granted, the engine's peak torque is not delivered at the same RPM the torque converter maxes out at, but again it's the best we have to work with.

That would yield 113 ft/lb at the axle for the 420 with a 6:1 ratio and 43 ft/lb at the axle for the 212.

On 18" tires (9" radius), that's 150# of forward thrust from the 420 and 57# of forward thrust from the 212.

 

[itsid]

Had a question about torque.

I've run various numbers through kart calc and I know my 420cc, 18" tires, 6:1 gearing, 40 series TC, on 600lbs of cart and people will give me max torque of 374ish nm. My question is, what the **** does that mean?

If I drop everything to a 212cc and a 30 series with the same above stats, I get 297 nm. 80ish nm more doesn't seem like a whole lot for A LOT more $$$.

Anyone have real world examples of how much torque can move what? I'm especially interested in how much torque can tow how much weight.

the series 30 has a better reduction than the series 40
(2.7:1 vs 2.4:1 or thereabouts )
that's why the difference is rather small despite the engines are indeed quite different in oomph

And what can be done with torque..
torque is THE ONLY thing you want to be honest..
it's THE goto value... most plausibly explained by going through the SI

1NM of torque is 1 kg*m²/s²
(huh? come again?)
hold one end of a 1m pole (weightless ideally... ~3ft that is)
have that? good.. have a buddy attach a 1kg weight to the far end (~2lbs)

you now have to hold the pole horizontally palm up for bonus points (a bit itchy, not?)
what you have there is ~10Nm of torque trying to twist the pole out of your hand.

1kg *1m * gravitational constant (1kg *1m * 9.81m/s²) = 9.81kg m²/s²... 9.81Nm

m/s² is acceleration btw...
You can translate that equation to lateral movement as well..

say you want 3m/s² of acceleration and you work with 360NM of torque (for the sake of easy math )
just divide and you get
120 kg*m (intermediate number to keep in mind.)

You say you have 18" wheels... that's 9" radius (22.8 or so...closer to 20cm radius since tyres collapse under load and we like simple math])

120kg*m /0.2m = 600kg!

So there you have it.. if all you would want is to accelerate with 3m/s² and you have 360Nm of torque at your disposal...
then your kart could be as heavy as 600kg (that's ~1323 lbs!!)

And yes, real world values are much worse due to frictional losses, imperfections all over the place and whatnot.
But still, it's a good direction to point your mind into when you think about such things as torque

Or you can try to hit 1G of acceleration (say 10m/s²) in which case your intermediate number would be 36kg*m
and your kart could weigh (36/0.2) 180kg with you in it!
(~397lbs)
theoretically ...

that's a nice thing, isn't it?

'sid

ps slightly more complicated examples:
https://www.engineersedge.com/calcu...ing-up-slope/vehicle-driving-slope-forces.htm
Oh 1000mm = 1m etc.., so the 370Nm are 370000Nmm and (0.2m) 20cm are 200mm
etc.

 

[65ShelbyClone]

I'm especially interested in how much torque can tow how much weight.

Any non-zero torque can adequately move any amount of weight when time and distance are omitted. We don't have enough information to answer the question.

 

[bob58o]

Torque is in Lb-Ft.
Tire diameter is in feet.
Gear Ratio is a multiplier.

If you have 10 Lb-Ft of Torque...
And if you have a 6 :1 Gear ratio...
You have 60 Lb-Ft or Torque at the axle.

If you have 12" Tires, then the radius is 0.5 Ft.

Divide Torque at the axle (in Lb-Ft) by the radius of the tire (in ft) to get a linear force.

60 Lb-Ft / 0.5 Ft =

120 lbs of linear force.

Torque spins stuff. Linear force pushes things forward.
If you haven't heard me say this before...

F=ma
(good for at least 1pt partial credit on every Physics homework, quiz or test on the planet)
Linear Force = mass x acceleration

If you want to increase acceleration, you have to decrease mass or increase the force.
To increase the force you need more torque, a shorter gear ratio (bigger number), or smaller tires.

10 Lb-Ft at the crankshaft, 6:1 Gear Ratio, 12" Tires... Equals 120 lbs of force pushing the vehicle forward. Smaller Tires means the same torque yields more linear force. Bigger Tires with the same torque will yield less linear force.

As RPMs increase, tq will generally fall off. So when an engine gives max TQ specs, it will usually be at like 2500 RPM. Highly modified engines might make peak torque at a higher RPM like 4000 RPM.

---------- Post added at 12:58 AM ---------- Previous post was at 12:44 AM ----------

PS in 'Merica we don't use newton meters. I'm not on a diet. Ain't nobody counting my cookies. LOL

---------- Post added at 01:16 AM ---------- Previous post was at 12:58 AM ----------

Any non-zero torque can adequately move any amount of weight when time and distance are omitted. We don't have enough information to answer the question.

I agree if you say time, distance and FRICTION are omitted.
Since you did say move, we can assume distance is greater than zero.
But, the force has to be enough to overcome Static Friction to begin moving and the force has to be equal to the kinetic friction to keep it moving at a constant speed. Force has to be greater than the kinetic friction to accelerate the mass.

So if you consider friction, I have to disagree about "any non-zero torque can adequately move any amount of weight".

Unless, of course, you mean any amount of TQ output, before the gearing reduction. You can always use gearing to increase force.

 

[anickode]

Yep... A single ant on a hamster wheel could winch an aircraft carrier up out of the sea with a big enough gear ratio and NO FRICTION!

 

[KartFab]

so real world,
1) a small light two seat go kart should be geared for 28 mph @3600 rpm with a 30 series torque converter
2) any large/heavy kart should have an 11-18 hp engine and geared for 40 mph @3600 rpm with a 40 series torque converter
3) a small single seat go kart can be geared for 35 mph @3600 rpm with a 30 series torque converter


Sounds like you have a big go kart, or will have two adults in it, so what you have planned with 420 predator and the 40 series is what you want

 

[65ShelbyClone]

I agree if you say time, distance and FRICTION are omitted.
Since you did say move, we can assume distance is greater than zero.
But, the force has to be enough to overcome Static Friction to begin moving and the force has to be equal to the kinetic friction to keep it moving at a constant speed. Force has to be greater than the kinetic friction to accelerate the mass.

So if you consider friction, I have to disagree about "any non-zero torque can adequately move any amount of weight".

Yeah, I glossed it over as a consequence of trying to keep my answer as vague as the original question.

Unless, of course, you mean any amount of TQ output, before the gearing reduction. You can always use gearing to increase force.

That is more of what I meant. A 79cc Predator could conceivably move an 80,000lb semi truck up the Grapvine grade with enough torque multiplication. It may not do it in the engine's serviceable lifetime though.