Why do diesels 'feel' fast compared to faster petrols?
Discussion
I'm sure this has been covered before but just wanted to check my understanding - Is it the big slug of low down torque that makes the diesel feel fast? What causes that perceived sensation of acceleration - I can only assume it's the torque that you feel. The example that I can give is a e90 320d vs an e36 M3. You only have to look at the speedo in the M3 to know that you're accelerating faster by a huge margin but the sensation of acceleration is greater in the 320d - what fools the brain?
832ark said:
I'm sure this has been covered before but just wanted to check my understanding - Is it the big slug of low down torque that makes the diesel feel fast? What causes that perceived sensation of acceleration - I can only assume it's the torque that you feel. The example that I can give is a e90 320d vs an e36 M3. You only have to look at the speedo in the M3 to know that you're accelerating faster by a huge margin but the sensation of acceleration is greater in the 320d - what fools the brain?
Havig driven a new 320d from London to Newcastle, I was pleasantly suprised by how quick it 'felt' pulling away from junctions compared to my 325i. It still sounded awful and had an unpleasant power delivery but lets not turn this into a petrol vs diesel thread 
But I'm not talking about an equivalent NA petrol. I know that diesels can actually be faster at lower RPMs and that people don't use the full rev range. What I'm talking about is the actual feeling - in my example above both cars have their full rev ranges used. Obviously the M3 destroys the 320d but something is fooling the brain.
It's not even the low rev power, quite. I think it's more the rate of change of torque as they come on boost. The human body is very poor at judging constant forces, however it's very good at judging rate of change of force. So the perception of speed comes not from the second derivative of position with respect to time (acceleration) but the third (apparently called jerk).
So diesels feel faster because they have a higher jerk value.
So diesels feel faster because they have a higher jerk value.
kambites said:
It's not even the low rev power, quite. I think it's more the rate of change of torque as they come on boost. The human body is very poor at judging constant forces, however it's very good at judging rate of change of force. So the perception of speed comes not from the second derivative of position with respect to time (acceleration) but the third (apparently called jerk).
So diesels feel faster because they have a higher jerk value.
This, the Evora has two different throttle maps. Try and find an owner that doesn't think the car has significantly more power in the Sport map, even I have to tell myself it doesn't.So diesels feel faster because they have a higher jerk value.
Actually best not to try and find an owner, it might take a while
kambites said:
It's not even the low rev power, quite. I think it's more the rate of change of torque as they come on boost. The human body is very poor at judging constant forces, however it's very good at judging rate of change of force. So the perception of speed comes not from the second derivative of position with respect to time (acceleration) but the third (apparently called jerk).
So diesels feel faster because they have a higher jerk value.
Now that makes a lot of sense!So diesels feel faster because they have a higher jerk value.
I don't think they do feel fast, personally.
My experience of modern diesels spreads from the generic manual gearbox commonrails up to the 3.0 V6s and ZF autoboxes in JLR stuff. I've also had various 5-series diesels as courtesy cars etc.
Sure, they produce a slug of torque, but I always found the way diesels seem to really piss about in the upper end of their rev ranges before changing up a gear (on "premium" car autos) more than offsets any feeling of "fast" from the initial torque, and conspires to make the car feel rather slow.
On a manual of course you can accelerate with the foot hard down and change gear early to avoid the frustrating lack of acceleration higher up, but the car still doesn't actually go anywhere quickly.
I appreciate that some people like diesel power delivery, but personally, I hate it so much that I prefer petrol for all my driving.
My experience of modern diesels spreads from the generic manual gearbox commonrails up to the 3.0 V6s and ZF autoboxes in JLR stuff. I've also had various 5-series diesels as courtesy cars etc.
Sure, they produce a slug of torque, but I always found the way diesels seem to really piss about in the upper end of their rev ranges before changing up a gear (on "premium" car autos) more than offsets any feeling of "fast" from the initial torque, and conspires to make the car feel rather slow.
On a manual of course you can accelerate with the foot hard down and change gear early to avoid the frustrating lack of acceleration higher up, but the car still doesn't actually go anywhere quickly.
I appreciate that some people like diesel power delivery, but personally, I hate it so much that I prefer petrol for all my driving.
kambites said:
It's not even the low rev power, quite. I think it's more the rate of change of torque as they come on boost. The human body is very poor at judging constant forces, however it's very good at judging rate of change of force. So the perception of speed comes not from the second derivative of position with respect to time (acceleration) but the third (apparently called jerk).
So diesels feel faster because they have a higher jerk value.
Exactly this !So diesels feel faster because they have a higher jerk value.
Look at a curve for a bmw 2.0l diesel:
Its very steep to the left of 1700rpm, and drops of quite significantly pretty quickly. It feels much faster than it is as per above post. But its rubbish to live with every day, at least with a manual trans in lots of traffic (I have a 318d).
Curve from a BMW M3, much smoother..
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