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Old 2nd April 2010, 16:06   #1
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Default What is the most important factor affecting speed? Power, Torque, or Gearbox?

Sample this.

Skoda Superb = 160 Bhp. 1800 cc.
Honda Accord = 180 Bhp. 2400 cc.

The Skoda Superb weighs more than the Honda Accord.

Yes, the Skoda Superb has more torque (250 Nm vs 222 Nm)

Yet, the Superb is faster to 60, 100, and 150 than the Accord. (for AT)
Part of this could be due to the 7 speed DSG with its 40 ms shifts.
But how is the manual superb so much faster than the manual accord?
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Old 2nd April 2010, 16:35   #2
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What are the 0-60, 0-100 and 0-150 times for both cars?

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Old 2nd April 2010, 16:49   #3
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Superb (DSG)

0-60 4.52 s
0-100 9.10

Accord (MT)

0-60 4.30 s
0-100 9.19 s

Source: Autocar India
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Old 2nd April 2010, 17:16   #4
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Superb is slightly fastr than the Accord from 0 - 100. This has to do with Superbs Torque and it's power delivery. The superb probably has a better torque curve than the Accord. The Accord is faster from 0 - 60 as per the timings mentioned by you but not by much.

Also for top speed the weight, BHP and the CD of a car is more important, if only how fast a car can go and not how much time it takes to get there is what you are looking at. If the timing is also important than the Driver, speed of the upshifts also count.

For 0-100 times the torque,cubic capacity, weight and driver skills come into the picture.

This is what I can say with my knowledge.

Last edited by Yusha : 2nd April 2010 at 17:22.
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Old 2nd April 2010, 17:32   #5
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The Skoda's TSi engine is technologically light years ahead.It combines turbochargers with high pressure direct injection.It produces more torque(250 Nm From 1500 rpm) at lower engine speeds right from 1500 rpm as compared to Accords 222Nm coming in at higher engine speed(4000 rpm+).

This means the superb and the laura are at their maximum torque at lower engine speed meaning they can be in higher gear at lower speeds and have much better driveability.The laura is about 5-6 seconds faster than civic and corolla from 40-100 in 4th gear.

The gearbox and the gearing are the controlling factors.Taller gear ratios have slower acceleration but higher top speed and vice versa for the shorter gear ratios.
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Old 2nd April 2010, 17:35   #6
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holysmoke, you are correct! DSG does save a huge amount of time with its super quick shifts - should be around a second less for the 100 kph dash.

Also, Honda usually selects the transmission ratios more suited for better fuel economy. I am not sure about Accord, but Civic has lower reductions all across the range as compared to Altis. Same is the case with City.
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Old 2nd April 2010, 18:08   #7
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Quote:
Superb (DSG)

0-60 4.52 s
0-100 9.10

Accord (MT)

0-60 4.30 s
0-100 9.19 s

Source: Autocar India
In this case its the transmission that plays a big role in performance. Having 7 gears lets you have ratios that are shorter and closer with the DSG system allowing the car to switch from one gear to another without any drop in acceleration.

Watch this video from the 11min mark.



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Old 2nd April 2010, 20:47   #8
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Quote:
Originally Posted by holysmoke View Post
Sample this.

Skoda Superb = 160 Bhp. 1800 cc.
Honda Accord = 180 Bhp. 2400 cc.

The Skoda Superb weighs more than the Honda Accord.

Yes, the Skoda Superb has more torque (250 Nm vs 222 Nm)

Yet, the Superb is faster to 60, 100, and 150 than the Accord. (for AT)
Part of this could be due to the 7 speed DSG with its 40 ms shifts.
But how is the manual superb so much faster than the manual accord?
To answer your question, I'd think the most important factor affecting acceleration is peak power to weight ratio.

Low-end torque is not used much anyway during flat out acceleration, except in first gear. And greater torque in the higher rev ranges means greater peak power.

If two cars are close enough in the power to weight stakes, factors such as area under the power curve, traction off the line, gear ratios and Dual Clutch transmission might tilt the balance in favor of the car with the slightly lower power to weight.

I don't subscribe to any Indian car magazines. Can you tell us the times for all the cars (Superb DSG, Manual; Accord Manual, AT) ?

1. DSG vs Manual: DSG can shift in 0.04 sec as you say. The fastest humans can probably shift in 0.15 at best. If the magazine testers are not competent enough, they can easily give up a quarter second or more to the DSG every gear shift.

2. Were the tests performed on the same day and by the same driver? I doubt the magazines in question correct times for altitude, temperature and humidity. The turbocharged Superb won't lose as much power as the Accord in higher altitudes (thinner air = lower power). Was the Superb tested in colder temperatures? Were the tests performed in both directions to correct for wind speed and inclination?

3. Superb = 160 hp, Accord = 177.5 hp. Though I am not a great believer in factory freaks, what if the Superb was a particularly strong example and/or the Accord was a weak one? Or what if the factory power ratings itself are off?

4. The Superb is rated at 160 hp from 4500 - 6200 rpm. The fact that the Superb develops peak power over such a wide range, the range in which the engine spends most of its time in acceleration tests, is one reason why the Superb is an over achiever. That's technology for you.

5. Superb's DSG = 7 speed. Accords MT/AT = 5 speed. This means the the Superb can use closer ratios to keep the engine running in the power band.

6. The Superb DSG = 1567 Kg and Accord MT = 1500 Kg according to their respective web sites. Are both weights under comparable conditions? (Engine fluids, Fuel etc)

Quote:
Originally Posted by avmaxfan View Post
Superb (DSG)

0-60 4.52 s
0-100 9.10

Accord (MT)

0-60 4.30 s
0-100 9.19 s

Source: Autocar India
Thanks for the figures. But we shouldn't take just one test as gospel. It is possible that ACI's figures themselves might vary by half a second to 100 from test to test.

In this particular example, though the Superb reaches 100k an instant before the Accord, the Accord itself was inching away from the Superb at every instant of time before the Superb reached 100 (or somewhere in the 90s). At 100, the Superb has just started catching up and it probably has some way to go before it passes the Accord

Last edited by tacho : 2nd April 2010 at 20:49.
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Old 2nd April 2010, 21:08   #9
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Quote:
To answer your question, I'd think the most important factor affecting acceleration is peak power to weight ratio.
Actually theres no such thing as most important factor. All factors are equally important.

Another thing you're getting wrong is the torque. If you take a 2ltr Na car which does 200bhp/200nm and race it against another 2ltr Turbo car doing 200bhp and 300nm (both rwd, identical chassis, 5 speed M/T and weighing 1000kgs). Technically they have identical power to weight ratios but the Turbo engined car will still be way quicker bcoz torque also plays an equally important role in performance.

Had that Skoda been a NA 1.8 with 160bhp and 175nm, it would not have beaten the Accord to 100kmph (even with the DSG gearbox). But its also true that if the Skoda had the same 250nm engine but without DSG, it would have still been slower. So every factor becoms important, in the end.

Shan2nu

Last edited by Shan2nu : 2nd April 2010 at 21:13.
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Old 2nd April 2010, 21:13   #10
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I think all of them are important in their own way. And there are other factors that affect it to a great extent.
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Old 2nd April 2010, 21:37   #11
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Torque is what gets you moving. Power is the work done and torque is the force that accelerates.

For the best acceleration you need as much torque on the wheels per ton.

Acceleration is affected by the following factors:

By the torque delivery of the engine (throughout the rpm range. Peak figures are rather meaningless). As much as high torque figures are desirable, too much torque can make a car accelerating slower than the right amount of torque, as it ends in wheel spin. This is why launch control is used in racing.

By the weight of the car. If you double the weight of your car, it will take you about double the time to accelerate it to 100 kph.

By the drag. But the drag is not only wind resistance, but affect the car the more at higher speed than at lower speed. Tyre width and compound determine the rolling resistence.

Gear box ratios are important for acceleration because the gear box is the torque multiplicator for the wheel torque.

Weight of rotational mass. The more the wheel weighs, the more effort it is needed to spin it. Same goes for parts of the braking system.

Different sppeds can affect the ability to take air in, which would affect acceleration times at higher speeds in some cases adversly in other cases beneficially.

If you have a given engine power output then the factors to get the most power on the wheels are the following (other than above mentioned ones):

Number of gears. The more gears, the more gear box drag.

The gearbox oil viscosity and the ambient air temperature.

A live axle loses more power than other transmissions.

The rotational mass of all components other than wheels and brakes.

There is quite a few other technical factors, but they are not as critical.

And last but not least is the driver itself, who decides how quickly to change gear and when to change gear.
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Old 2nd April 2010, 21:49   #12
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Quote:
Different sppeds can affect the ability to take air in, which would affect acceleration times at higher speeds in some cases adversly in other cases beneficially.
But will vehicle speed make that much of a diff in the performance of a regular car where the intake is placed inside the engine bay?

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Old 2nd April 2010, 23:38   #13
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Quote:
Actually theres no such thing as most important factor. All factors are equally important.
I disagree. Don't you think it's difficult to say all factors are equally important? A granny in a 200 hp/ton MT car will be faster than Schumacher in a 100hp/ton DSG car. A 200hp/ton, 100 Nm car will be faster than a 100 hp/ton 300 Nm car, no question. It's only when the power to weights are reasonably close that the other factors can become decisive. I already implied that in my previous post and that's probably what you mean anyway.

Quote:
Another thing you're getting wrong is the torque. If you take a 2ltr Na car which does 200bhp/200nm and race it against another 2ltr Turbo car doing 200bhp and 300nm (both rwd, identical chassis, 5 speed M/T and weighing 1000kgs). Technically they have identical power to weight ratios but the Turbo engined car will still be way quicker bcoz torque also plays an equally important role in performance.
I disagree with the bolded part. I think they will be pretty close. But I am no automobile engineer. You have to come with some pretty airtight examples to make me think otherwise.

For now, this is one from my side.

All figures from Car and Driver

BMW 330i Manual, 255hp, 220 lb-ft, 3450 lbs. Power/Weight: 163 hp/ton
0 - 60: 5.6
0 - 100: 15.3
1/4 mile: 14.3

BMW 335d Automatic, 265 hp, 425 lb-ft, 3800 lbs. Power/Weight: 154 hp/ton
0 - 60: 5.7
0 - 100: 14.2
1/4 mile: 14.2

BMW 335i Automatic, 300 hp, 300 lb-ft, 3584 lbs. Power/Weight: 184 hp/ton
0 - 60: 4.9
0 - 100: 12.1
1/4 mile: 13.4

I couldn't find an automatic 330i Car and Driver road test (335d only comes with the automatic in the US). The 335d has the worst power/weight but is faster than the 330i by a tenth in the quarter mile probably because of it's humongous torque (90% more than the 330i). Even if we disregard the 330i figures for being a manual's, the 335i is easily faster than the 335d despite having way low torque (8 tenths in the quarter mile at those speeds is 40 meters, or the length of 2 cricket pitches)

Quote:
Had that Skoda been a NA 1.8 with 160bhp and 175nm, it would not have beaten the Accord to 100kmph (even with the DSG gearbox). But its also true that if the Skoda had the same 250nm engine but without DSG, it would have still been slower. So every factor becoms important, in the end.

Shan2nu
I agree. But power to weight is the most important IMO
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Old 3rd April 2010, 20:50   #14
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I disagree with the bolded part. I think they will be pretty close. But I am no automobile engineer. You have to come with some pretty airtight examples to make me think otherwise.

I couldn't find an automatic 330i Car and Driver road test (335d only comes with the automatic in the US). The 335d has the worst power/weight but is faster than the 330i by a tenth in the quarter mile probably because of it's humongous torque (90% more than the 330i). Even if we disregard the 330i figures for being a manual's, the 335i is easily faster than the 335d despite having way low torque (8 tenths in the quarter mile at those speeds is 40 meters, or the length of 2 cricket pitches)
Thats bcoz the torque produced by the 335D is not enough to propel its 154bhp/ton body quicker than the 184bhp/ton 335i.

Power to weight is important but it not the most important factor. A car with a higher power to weight ratio can be beaten by making use of the other factors.

An Ariel Atom is 600bhp/ton, Veyron is 520bhp/ton (80bhp/ton less) but the Atom does the 1/4 mile in 10.8 secs where as the Veyron does it in 9.95 secs.

If power to weight was the most important factor, a 520bhp/ton vehicle should be slower than a 600bhp/ton vehicle. Let alone beat it by close to a sec over a 1/4 mile (and going from 10.8 to 9.95 isn't a joke).

Acceleration depends on a combination of power to weight ratio, torque to weight ratio, resistance, traction, gearing, etc.

You cannot rely on the power to weight alone and expect your car to be quick. And this rule applies for every other factor that affects performance.

Shan2nu

Last edited by Shan2nu : 3rd April 2010 at 21:05.
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Old 4th April 2010, 21:48   #15
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Quote:
Originally Posted by Shan2nu View Post

A car with a higher power to weight ratio can be beaten by making use of the other factors.
Never disagreed with that. Heck, my own example (330i vs 335d) shows that it can be done.

Quote:
An Ariel Atom is 600bhp/ton, Veyron is 520bhp/ton (80bhp/ton less) but the Atom does the 1/4 mile in 10.8 secs where as the Veyron does it in 9.95 secs.
Put an 80kg driver in each car and the p/w difference is right down to around 25 hp/ton.

But I agree that 9.95 vs 10.8 is a huge difference. At those power levels, traction is a big issue and the Veyron's AWD helps immensely, and the Atom definitely lost a few tenths of a second on manual gear changes compared to the Veyron's ultrafast DSG (or some variation).

But these are two cars on opposite ends of the spectrum. I was hoping you would come up with some 'normal' cars with similar drivetrains.

Quote:
Acceleration depends on a combination of power to weight ratio, torque to weight ratio, resistance, traction, gearing, etc.

You cannot rely on the power to weight alone and expect your car to be quick. And this rule applies for every other factor that affects performance.

Shan2nu
Sure. When I said power to weight was the most important, what I meant was this: Give me some power to weight figure and I will come up with a ball park figure for the quarter mile, as long as it's not some extreme machine like a 15 hp Bajaj motorcycle or an open wheel racer. The same cannot be said about Torque to weight, gearing, traction etc.

The OP has disappeared. I would be interested in seeing the figures for the Manual Superb vs the Manual Accord especially because the Skoda website doesn't even list the Manual Superb
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