[Tom Tallon]

So here's my question for you experts.

Two new cars both claimed to have 302 bhp, both claim 0-62 in about 4.9 secs.
However the X2 has 450 nm and the A35 has 400 nm.

Does this matter a damn - is the BMW better in some way - how does the extra 12.5% extra in nm manifest itself?

Grateful for a little education if its not too much trouble.

[CraigUK]

Lots of different factors to take into account that the raw figures just don't show.

1. Traction, 2wd, 4wd etc,
2. Weight
3. Gearing
4. Torque spread rather than just maximum torque figures

And loads more

[Tom Tallon]

Originally Posted by CraigUK

Lots of different factors to take into account that the raw figures just don't show.

1. Traction, 2wd, 4wd etc,
2. Weight
3. Gearing
4. Torque spread rather than just maximum torque figures

And loads more

Hells teeth I knew it wouldn't be simple. One fact - both are 4 wheel drive.

[Techno 9000]

It depends on more factors (including and not necessarily in the most important order):
Weights
Gear ratio
How broad the rev band is for the quoted torque


All things being equal the extra 12.5% torque will lead to slightly greater acceleration in each gear.

Edit: Tooo slow on the keyboard! but at least we agree.

[Sasquartch]

Power and torque are probably the least understood parameters

Power and torque are directly related by engine speed

The specified torque is that produced at a particular engine speed, as is power

The engine speed that maximum power is produced is usually much higher than maximum torque

The torque at the wheels is directly influenced by gearing as well as transmission losses

All the figures give you is an indication of an engine's characteristics.

Looking at the torque / power curves is much more meaningful. If you look at the torque for the 328i the torque curve is almost completely flat however that's the ECU programmed that way

[creepy coupe]

Forget 0-60. It's 30 - 50 or 50-80 mph that matters.

[Wills2]

Another often overlooked but most important factor, is where the torque is made and for how long does the torque last, often described as the area under the curve on a dyno plot.

As an example an M3 makes 550nm a 335d 600nm but the M3 makes that peak figure for 3650rpm the 335d for only 1000rpm hence the M3 is the more powerful faster car despite producing less peak torque.

Bare torque figures give you very little info.

[Tom Tallon]

I think I'm getting it! so I need to wait until the full engine spec is published on both to make a comparison eg when max torque kicks in and how long it lasts etc.

You'll realise that this is not totally theoretical because I'm looking at either of these as next car. One thing I do understand is that Mercedes might shave in at under £40,000 fully equiped whereas the BMW will I guess will be at least £43,000 to my specification!

[dizzy619]

Your butt dyno will tell you more when you test drive them..

[Tengocity]

What you ideally want is both to have a full autocar roadtest where you can see the in gear times for all the 20mph acceleration increments, as well as the 30-70 through the gears time.

[Moleeuk]

BHP sells engines. Torque wins races....

[dopper99]

What you need is lots of both.

[Wills2]

Originally Posted by Moleeuk

BHP sells engines. Torque x revs/5252 = power wins races....

EFA.

And the ability to it lay down on the road helps too....

[Tom Tallon]

Originally Posted by Tengocity

What you ideally want is both to have a full autocar roadtest where you can see the in gear times for all the 20mph acceleration increments, as well as the 30-70 through the gears time.

Thanks T. good idea - I'll start saving up now and look out for periodical when available.

[creepy coupe]

i tell customers Torque gets you there. BHP keeps you there.

[Hooded]

Originally Posted by creepy coupe

Forget 0-60. It's 30 - 50 or 50-80 mph that matters.

Agree, .. it's much more relevant for real world use.

Touching on the torque, .. peak torque that drops off a cliff quickly is not so important, it's better to have a flatter torque curve that doesn't drop off too quickly as the revs climb.

2 identical cars with different ecu tuning...

Car A - 320bhp 660nm torque
Car B - 305bhp 690nm torque

Car B has a big torque peak of 690nm low down but it drops off quickly higher up the rev range hence it makes a maximum of 305bhp

Car A doesn't produce as much torque low down but has a flatter curve and holds onto the torque better higher up the rev range, hence it makes a higher maximum bhp than Car B does.

I wager that Car A is quicker if your in the right gear at the right time!

[creepy coupe]

Originally Posted by Hooded

Agree, .. it's much more relevant for real world use.

Touching on the torque, .. peak torque that drops off a cliff quickly is not so important, it's better to have a flatter torque curve that doesn't drop off too quickly as the revs climb.

2 identical cars with different ecu tuning...

Car A - 320bhp 660nm torque
Car B - 305bhp 690nm torque

Car B has a big torque peak of 690nm low down but it drops off quickly higher up the rev range hence it makes a maximum of 305bhp

Car A doesn't produce as much torque low down but has a flatter curve and holds onto the torque better higher up the rev range, hence it makes a higher maximum bhp than Car B does.

I wager that Car A is quicker if your in the right gear at the right time!

Good analogy. Flat torque curves are key