When to change gear - max acceleration
Discussion
Discussing this point with another colleague
To get max acceleration from a car, is it best to change gear close to the red line - i.e max out the revs?
and does the same apply with a diesel car as a petrol
When watching pros in rally cars they have a quick start - so what revs do they move the engine to before releasing the clutch!
To get max acceleration from a car, is it best to change gear close to the red line - i.e max out the revs?
and does the same apply with a diesel car as a petrol
When watching pros in rally cars they have a quick start - so what revs do they move the engine to before releasing the clutch!
mawallace said:
When watching pros in rally cars they have a quick start - so what revs do they move the engine to before releasing the clutch!
if you've ever played Gran Turismo and done the licenses you'll know it's a case of finding the maximum possible revs without spinning the wheels.It will depend on the gearing of the individual car; Many people would say shift up at peak torque (Or where it drops off), however, this fails to accounts for the fact that if you do rev to redline, you reach the next gear in-powerband.
https://www.youtube.com/watch?v=zZBqb0ZJSwU
It's also more fun to rev to the bitter end
https://www.youtube.com/watch?v=zZBqb0ZJSwU
It's also more fun to rev to the bitter end
Depends from car to car.
With my 126 it's max revs then quickly feed in the clutch (not dump the clutch) then take it to the max before ramming it in second. I'll still get left behind from anything bar cyclists but found its the way to get the most from it and doesn't seem to affect economy however its driven.
More entertaining to drive than anything else I have..
With my 126 it's max revs then quickly feed in the clutch (not dump the clutch) then take it to the max before ramming it in second. I'll still get left behind from anything bar cyclists but found its the way to get the most from it and doesn't seem to affect economy however its driven.
More entertaining to drive than anything else I have..
RDMcG said:
I hate to redline anything. Not sure I ever get maximum acceleration but I don’t enjoy abusing a car.
You are missing out! Well, maybe not. In my old cars the redline was well beyond the point the power noticeably tailed off. Getting to 8250rpm is now something to savour for me.ambuletz said:
if you've ever played Gran Turismo and done the licenses you'll know it's a case of finding the maximum possible revs without spinning the wheels.
And with that reference a good chunk of my adolescent years came flooding back...Just gone from 330d auto (2016) to 120d auto (2019) and noticed a big difference in where the car thinks it should be changing gear. The 330d relied on the torque much more when you put your foot down and it down shifted to usually 3-4k rpm. The 120d relies far more on revs and will down shift to 5-6k rpm to get that acceleration.
it's weird as I think it down shifts to much and misses the torque (but I suppose they know better then me). I know it's a different variant in each (8HP70 and 8HP45) but do they alter the brains for different fuels and torque within each variant?
it's weird as I think it down shifts to much and misses the torque (but I suppose they know better then me). I know it's a different variant in each (8HP70 and 8HP45) but do they alter the brains for different fuels and torque within each variant?
TheDrownedApe said:
Just gone from 330d auto (2016) to 120d auto (2019) and noticed a big difference in where the car thinks it should be changing gear. The 330d relied on the torque much more when you put your foot down and it down shifted to usually 3-4k rpm. The 120d relies far more on revs and will down shift to 5-6k rpm to get that acceleration.
it's weird as I think it down shifts to much and misses the torque (but I suppose they know better then me). I know it's a different variant in each (8HP70 and 8HP45) but do they alter the brains for different fuels and torque within each variant?
I imagine the specific engine characteristics of the i6 in the 330d mean it just has more low down torque than the 4 pot in the 120d. It might have more volumetric efficiency, it’ll probably have completely different piston bore and stroke as well as a million other things. Keeping revs low will mean less parasitic losses overall so it probably helps out mpg figures.it's weird as I think it down shifts to much and misses the torque (but I suppose they know better then me). I know it's a different variant in each (8HP70 and 8HP45) but do they alter the brains for different fuels and torque within each variant?
For the majority of cars max acceleration is achieved by changing gear just before you hit the red line.
There might be some exceptions for certain turbo-engined cars, but as a rule of thumb, red line it.
There's a good video explaining this by youtuber Engineering Explained. Something to do with torque x revs = work done.
There might be some exceptions for certain turbo-engined cars, but as a rule of thumb, red line it.
There's a good video explaining this by youtuber Engineering Explained. Something to do with torque x revs = work done.
You simply need to review a graph of BHP v rpm. Then ensure that when you change up, the area above the graph between current and next gear rev point gives a minimum. So for a 335d diesel, this means changing up at 5000 rpm (cut-out is at 5300), which drops the next gear back to 3500, 3500, 4000, when moving into 2nd, 3rd, and 4th gear. The same applies in the top four gears too, but you are above 70mph.
In the graph below, the power output is shown by the white line, so keep the peak area to the minimum (that shows the ‘take it to 5000, drop back to 3500/4000’ principle)
Peak power in blue area
In the graph below, the power output is shown by the white line, so keep the peak area to the minimum (that shows the ‘take it to 5000, drop back to 3500/4000’ principle)
Peak power in blue area
Edited by Pica-Pica on Tuesday 10th December 18:41
Edited by Pica-Pica on Tuesday 10th December 18:42
LeoSayer said:
For the majority of cars max acceleration is achieved by changing gear just before you hit the red line.
There might be some exceptions for certain turbo-engined cars, but as a rule of thumb, red line it.
There's a good video explaining this by youtuber Engineering Explained. Something to do with torque x revs = work done.
Yes, torque(at any specific revs) x that rev value = powerThere might be some exceptions for certain turbo-engined cars, but as a rule of thumb, red line it.
There's a good video explaining this by youtuber Engineering Explained. Something to do with torque x revs = work done.
SAS Tom said:
RDMcG said:
I hate to redline anything. Not sure I ever get maximum acceleration but I don’t enjoy abusing a car.
Why do you think redlining a car is abusing it? Surely if you’re using it anywhere before the limiter then it was designed to do that?meatballs said:
RDMcG said:
I hate to redline anything. Not sure I ever get maximum acceleration but I don’t enjoy abusing a car.
Don't get an e92 M3 then. The V8 is a joy, but max power at 8300 rpm with the redline at 8400 so you really need to drive it hard for maximum enjoyment.
Have a read of this: http://www.fjr1300.info/misc/torque-power.html
I'm pretty sure it's accurate but happy for the Pistonheads engineering types to debunk.
I'm pretty sure it's accurate but happy for the Pistonheads engineering types to debunk.
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