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Discussion Starter · #1 ·
a few weeks back one of the ladies asked for a simple explanation. Here it is courtesy of Aaron Wilson, owner of Naillin Racing in Colorado:

>I would take 100 horsepower/70 lbsft TQ over 100 lbsft TQ/70 horsepower any day as the former will wax the latter from a dead stop, a roll, where ever
> as it is making better use of it's available TQ (assuming all other things
> being equal).

Let's just say, for argument's sake, that these two bikes are going down
the road side by side, same speed, and that speed amounts to 500 rear
wheel rpm, whatever speed that works out to.

The first bike has 100 horsepower, right? Well, 100 horsepower at 500
rear wheel rpm is 1050.4 ft-lbs of torque at the wheel.

The second bike has 70 horsepower. 70 horsepower at 500 rear wheel rpm
is 735.3 ft-lbs of torque at the wheel.

If the bikes are the same weight, the 100 horsepower bike is going to
walk away from the 70 horsepower bike, because even though it has less
torque at the crank, it has more at the rear wheel, and torque at the
rear wheel is what accelerates the bike.

The bike making the most horsepower puts the most torque to the rear
wheel at any given speed, it's a mathematical fact. That's why we talk
in terms of horsepower when talking of performance.
 

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exactly. The key is to look at the entire powertrain (output at the wheel) rather than just output at the crank. If the motor cant spin up, then youll need to upshift sooner, reducing the torque at the wheel. Thus, even if an engine with peak torque that is higher than another engine than has more ability to rev and thus produce more HP, it will lose out because it will have to be upshifted sooner.
 

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I feel that the "truth" about hp vs torque is beginning to spread on the internet. There are still many confused people, but I definately think that there are more people who now this stuff now than it was just a couple of years ago. I don't know, Maybe it just feels that way.

Edit: Btw, was it Shelby that stated "Horsepower sell cars, torque win races"? You often hear that quote in horsepower vs torque discussions and it's just BS. You'd think Shelby would've known better...
 

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Torque is what gets the mass rolling, massive torque = good launch. Ponies are where the peak power is located, sometimes near peak torque, often not. HP offers the ability after launch to continue acceleration on the high end of the RPM range.

A good example is my Dodge Ram 2500 P/U, it weighs in at 7200 lbs. The 5.9 diesel Hp output is 245 and the TQ is near 450, with that torque I can accelerate equal to some and better than many V8 cars. A slightly modified Cummins Diesel in a friends truck puts out approximately 450 HP and a WHOPPING 1000 ft lbs TQ, this is a "dually" truck weighing in above 8000 lbs, he clocked a 1/4 mile pass last year at MIR of 13.8 @ 101 mph. Pretty respectable for a low HP to weight ratio...but look at the torque! Now to keep things in perspective if you consider a race like the Daytona 500 where RPM's remain above 8500 most of the time torque has little value...so how often do we motor around at redline???
 

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swmnkdinthervr said:
Torque is what gets the mass rolling, massive torque = good launch. Ponies are where the peak power is located, sometimes near peak torque, often not. HP offers the ability after launch to continue acceleration on the high end of the RPM range.
Actually that's not true. You could have an engine with 50lb/ft of torque and 1000hp at a zillion rpms. You would still launch faster than a the Dodge Ram with 245hp and 450lb/ft in your example below. The key here is rear wheel torque and torque multiplication in the gearbox. A car could have 1000lb/ft but if it doesn't make good power it would still barely be moving. The peak torque number tells you nothing about a cars/bike performance.

swmnkdinthervr said:
A slightly modified Cummins Diesel in a friends truck puts out approximately 450 HP and a WHOPPING 1000 ft lbs TQ, this is a "dually" truck weighing in above 8000 lbs, he clocked a 1/4 mile pass last year at MIR of 13.8 @ 101 mph.
A Formula 1 V10 makes approximately 950hp and a poor 260lb/ft of torque. Still, put that engine in a similar truck and the Cummins truck would get wasted, despite the massive 1000lb/ft of torque.

Here are some good read. Among other things they explain why a ZX1100 is faster than a modified Harley despite the fact that the Harley even makes a little more torque:

http://motorcycleinfo.calsci.com/Horsepower.html
 

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You miss the point...torque has it's purpose..to provide impetus for moving mass...the more mass the more torque required, you couldn't even budge my truck with 1000 HP and only 100 ft lbs torque...the same is true for a Harley as it has greater mass than most "racing" bikes though we're only talking at low RPM...BTW, most diesels have a relatively low redline yet are more efficient at making both HP & TQ than a gas engine with lower fuel consumption. Audi Diesels powered cars just took 1st and 2nd in a Lemans style race...torque off the corners was considered amazing!!! (they evidenced a 2-1 torque over hoesepower ratio)

A Formula 1 V10 makes approximately 950hp and a poor 260lb/ft of torque. Still, put that engine in a similar truck and the Cummins truck would get wasted, despite the massive 1000lb/ft of torque.


This particular vehicle weighs about 1200 lbs...in the real world a V10 Ford P/U (at about 5000 lbs)against any diesel with similar ponies and the 2-1 torque difference is no match...
 

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No, it's a widely spread misconception that you need lots of torque to move a heavy vehicle.

As I said it's all about rear wheel torque and not engine torque. Take your friends 8000 lbs truck as an example. With 1000hp and 100lb/ft of torque he could put much more torque to the wheel in each gear, and still be as fast in each gear, as if he was using the Cummins diesel. Rear wheel torque equals acceleration btw.

The Cummins diesel is more suited for that type of vehicle, and of course it's alot easier to drive, but as far as performance goes it wouldn't stand a chance against a 1000hp and 100ft/lb engine.

The concept of torque multiplication and rear wheel torque is explained in the link I provided.
 

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Discussion Starter · #8 ·
for purposes of a recreational motorcycle forum it is better to talk about how it feels than physics. My highly modified Sportster 1200 of the past could suck your doors off when I passed you and God knows what the top speed was as I never came close to it. However, my modified Superglide Sport 1600 "feels" a bunch stronger and the G-forces offer a very big grin factor.
The top speed is way lower than the Sportster's. I kinda prefer the feeling of power over breathtaking acceleration.
Fred
 

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Here's one for you swmnkdinthervr:

2004 BMW 730iA:
PS - UMin 231 PS - 5900/Min
Nm - UMin 300 Nm - 3500/Min

Test in ams 02/2004
Gewicht 1933 kg
0 - 80 km/h 5,8 s
0 - 100 km/h 8,4 s
0 - 120 km/h 11,7 s
0 - 130 km/h 13,4 s
0 - 140 km/h 15,5 s
0 - 160 km/h 20,9 s

---------------------------------

2005 BMW 730dA:
PS - UMin 231 PS (170 kW) - 4000/Min
Nm - UMin 520 Nm - 2000/Min

Test in Auto Zeitung 08/2005
Gewicht 2000 kg
0 - 80 km/h 5,7 s
0 - 100 km/h 8,5 s
0 - 120 km/h 11,5 s
0 - 130 km/h - s
0 - 140 km/h 15,8 s
0 - 160 km/h 20,6 s

Source: www.einszweidrei.de


The cars have the same body, weigh almost the same, have the same power. The only difference is that one have 73% more torque than the other. Did it help? No it didn't. That's not a light car, still 300nm have no problem running with 520nm.
 

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Fredda said:
Here are some good read. Among other things they explain why a ZX1100 is faster than a modified Harley despite the fact that the Harley even makes a little more torque:

http://motorcycleinfo.calsci.com/Horsepower.html
This link has a lot of good info but the following statement (from the article) is what i keyed in on the most: "So, those riders who claim to prefer torque over horsepower really mean they prefer engines with power at low rpm." Peak power at low to med rpm is what most Harley riders prefer.
 

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Fred1369 said:
I kinda prefer the feeling of power over breathtaking acceleration.Fred
You kinda lost me there. Breathtaking acceleration is the feel of power.

Edit: Actually you can't feel power at all since it is just a mathematical figure.
 

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Breathtaking acceleration is the feel of power, yes, Fredda. However, and respectfully, hp = torque x RPM / 5252.

Physics can get you where you want to go, with the feel you want, but nobody's found a way to break the laws of physics - yet.

If my math is right and if a 100 ft/lb torque engine is developing 1,000 hp, something's turning 52,520 RPM. That's some impressive gearing.
 

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thedog said:
Breathtaking acceleration is the feel of power, yes, Fredda. However, and respectfully, hp = torque x RPM / 5252.

Physics can get you where you want to go, with the feel you want, but nobody's found a way to break the laws of physics - yet.

If my math is right and if a 100 ft/lb torque engine is developing 1,000 hp, something's turning 52,520 RPM. That's some impressive gearing.
I overexaggerated to get my point through. If I didn't know the relation between hp and torque I wouldn't even consider participating in this discussion.
 

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Torque is an element of making HP, as well as crankshaft revolutions per MINUTE(TIME), so folks........... you need BOTH. Everybody seems to forget about TIME. You have to observe the RATE at which the power is made to get WORK and by the way, horsepower is WORK. The higher the RATE, the more HP is made.

The Dynojet dyno is an inertia type dyno that measures the acceleration RATE of spinning the drum up. The DJ measures HP directly and then back calculates TQ.

If you can get your head around this concept, it then allows you to see why F1 motors are the way they are and why Cummins diesels are the way they are.
 

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Fredda, don't let 'em wear you down.
Fellas, you never hear about the 'torque to weight ratio' because it's meaningless. However' HP to weight' will tell you a lot about a vehicles acceleration capability
Torque figures without a time factor tell you nothing. HP is the measure of how much work is being done. You have to factor in the time!!!
 

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I have always understood horsepower to be torque measured over time.

If a force is allowed to act through a distance, it is doing mechanical work. Similarly, if torque is allowed to act through a rotational distance, it is doing work. Power is the work per unit time. However, time and rotational distance are related by the angular speed where each revolution results in the circumference of the circle being travelled by the force that is generating the torque. This means that torque that is causing the angular speed to increase is doing work and the generated power may be calculated as:

Power(horsepower)=torque x angular speed

Mathematically, the equation may be rearranged to compute torque for a given power output. However in practice there is no direct way to measure power whereas torque and angular speed can be measured directly.

Consistent units must be used. For metric SI units power is watts, torque is newton-metres and angular speed is radians per second (not rpm and not even revolutions per second).
 

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swmnkdinthervr said:
Torque is what gets the mass rolling, massive torque = good launch. Ponies are where the peak power is located, sometimes near peak torque, often not. HP offers the ability after launch to continue acceleration on the high end of the RPM range.

A good example is my Dodge Ram 2500 P/U, it weighs in at 7200 lbs. The 5.9 diesel Hp output is 245 and the TQ is near 450, with that torque I can accelerate equal to some and better than many V8 cars. A slightly modified Cummins Diesel in a friends truck puts out approximately 450 HP and a WHOPPING 1000 ft lbs TQ, this is a "dually" truck weighing in above 8000 lbs, he clocked a 1/4 mile pass last year at MIR of 13.8 @ 101 mph. Pretty respectable for a low HP to weight ratio...but look at the torque! Now to keep things in perspective if you consider a race like the Daytona 500 where RPM's remain above 8500 most of the time torque has little value...so how often do we motor around at redline???

I think I agree with you. We have a Nissan Titan for a work truck. It is a 5 speed automatic. I don't know the weight(a lot) or torque and HP numbers but I can say this, it has a lot of torque.
The other day I was hauling a bunch of metal to the recycling plant. I was going up a steep hill at 60 MPH and when I looked at the tack it was at about 1700 RPMs. It never shifted out of 5th. Then when I got into town at 25 MPH the tack was at 7-800 RPMs. It was still in 5th because there is so much power. All this tells me the truck was using TORQUE to push all the weight. I don't think there is enough HP at 800 RPMs to move so much weight. Of course this is just keeping the speed constant. If I tromp on it it downshifts but it is still using torque.

Anyway, I like the feel of the low RPM pull on my bike, that's all that matters to me. In reality, this is equal to a political/religion/oil/best color thread!
 

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hdmarsh77 said:
I think I agree with you. We have a Nissan Titan for a work truck. It is a 5 speed automatic. I don't know the weight(a lot) or torque and HP numbers but I can say this, it has a lot of torque.
The other day I was hauling a bunch of metal to the recycling plant. I was going up a steep hill at 60 MPH and when I looked at the tack it was at about 1700 RPMs. It never shifted out of 5th. Then when I got into town at 25 MPH the tack was at 7-800 RPMs. It was still in 5th because there is so much power. All this tells me the truck was using TORQUE to push all the weight. I don't think there is enough HP at 800 RPMs to move so much weight. Of course this is just keeping the speed constant. If I tromp on it it downshifts but it is still using torque.

Anyway, I like the feel of the low RPM pull on my bike, that's all that matters to me. In reality, this is equal to a political/religion/oil/best color thread!
Mating a motor with certain TQ/HP characteristics to the right GEARING is also an important consideration. So a high torque motor needs fewer gear changes. A high HP, high revving motor needs gear changes to stay in it's powerband.

Love my DD6. ;)
 

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hdmarsh77 said:
All this tells me the truck was using TORQUE to push all the weight. I don't think there is enough HP at 800 RPMs to move so much weight.
Again, hp and torque are related. It's not like you can say "I use torque at low rpms, but at high rpms the hp kick in". Torque is what you feel all over the power band, not just down low. Power is a mathematical figure that state how much work can be done by the engine.

I don't know the horsepower in that truck but the main thing here is that an equally powerful engine but with half the torque would do the same work, the only difference being that you'd have to keep higher revs, and of course use lower gearing. That's not suited for that type of vehicle, but it would still get the work done just as fast.

And once again, it's the torque at the wheels you feel when you accelerate. The bike/car with the most torque in the engine doesn't have to be the one with the most torque to the wheels.
 
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