Only an idiot would think it would. Unless you were way beyond the peak BHP in the low gear. Which few engines would allow anyway.
Does it come as surprise to you that changing up results in less torque at the rear wheels? And it's the maximum torque which produces the best acceleration. ;-)
I've been trying to get that point across for some weeks now. But it is obviously beyond many. ;-)
Peak torque is always at lower RPM than peak BHP.
I agree. So to make the car go the fastest, even though you can feel the acceleration dropping off, it's still worth staying in the lower gear past peak power. Ie aiming for peak power where possible, same as I've been saying for quite a long time.
Funnily enough I've been arguing that for quite a long time...
It has to be :-)
It's rather irrelevant, but with a decent set of ratios, you'd change up around peak BHP and plonk things close to the peak torque in the next higher gear. Unless you just like making a lot of noise and wasting fuel, of course.
Then why do you keep on mentioning BHP?
Just waiting for Turnip to come along and disagree. ;-)
Faster compared to what?
Compared to being in the lower gear.
(the answer I'd expect would be "no", hence even though you're feeling the acceleration drop off, it's still worth staying in the lower gear and using max power if you want to carry on accelerating as fast as possible)
I'm beginning to lose the will to live!
Yesterday, you you agreed with my two propositions. Please re-read the second one and then explain why you are contradicting yourself by what you are now saying.
Supposing that you had an infinitely variable transmission (with an upper and lower limit, of course) and could program it to maintain the engine speed constant as the car accelerated. If I understand you correctly, you would argue that in order to maximise acceleration, you would need to hold the engine at its max torque speed. Most other people here would say that was nonsense, because you could get more power to the wheels - and hence acceleration - by running the engine at its maximum power speed instead. So where do you stand on this?
Yes, it would. But you'd still have less thrust at the wheels because of the higher gearing.
That's what you'd expect. The torque - and hence the acceleration in that gear drops off. But it will almost certainly drop even more when you change to the next gear up even though the engine is producing more torque.
Next time, take an accelerometer with you, and tell us what happens in the higher gear.
IN A GIVEN GEAR. I've come to the conclusion that you're trying to view a 3-dimensional problem in 2 dimensions!
I did the math earlier. Peak power is at higher revs, so you can use a lower gear. This means that the torque at the output of the gearbox is higher at peak torque.
Like this:
2000 RPM, 400nM, geared down 2:1 to 1000 RPM gives you 400nM. 5000 RPM, 200nM, geared down 5:1 to 1000 RPM gives you 1000nM.Dave refuses to admit that this means you get better acceleration at peak power than at peak torque.
The only exception is when you are in 1st gear and cannot change down.
Andy
Yes.
(Well - almost. You want the gear that gives you the highest possible power output for that road speed. It's not likely to be exactly peak except for CVTs.)
Andy
No, it isn't. Its probably past peak torque for most rad car engines, but not that far past ot.
For the best 0-60, standing quarter, or whatever you would
No, you would change up *after* you reached it.
You are in fact confusing torque with power.
No, they dont. Not is the confused and simplistic way that you do.
No, in fact it doesn't.
But it would be a weird sort of engine where it wasn't
Some engines can be made to deliver both at the same point. At the point where the engine is revving itself to imminent destruction.
I agree peak torque can't be BEYOND peak BHP in rev terms. ;-)
Notice how he has changed the goalposts "That an *engine* accelerates at its best at peak BHP".
That is of course incorrect, but we are not talking about the engine, we are talking about the *CAR*. Which includes a gear box.
The optimal point to change up is beyond peak bhp, such that at the road speed the car is doing, the BHP that results after you have changed up is less than peak bhp by the same amount as the bhp when you changed up, was before. That keeps the average BHP as high as possible, and thus the overall acceleration as high as possible.
If BHP doesn't make cars accelerate why the F*CK do we bother with it, since a million to one gearbox on an elastic band will give you more torque than a formula one car engine.
Leftybrain thinking is like that. Its the curse of the almost-intelligent. Thinking you understand what you actually don't.
Have something to add? Share your thoughts — no account required.
Ask the community — no account required