When to change gear RPM's.

[chrisphysics]

After reading "d_jones"'s thread about loss of power above 5500k rpm it got me thinking about when I should be changing gear.

My firsts thoughts would be to change at the red line, but if I'm in 3rd or 4th gear the engine seems to be up in the 5500-6500 zone for so long. I also believed on the smaller turbos (K03s) they lose boost higher up in the range so often it's faster to change up slightly early.

On a standard 180 petrol (AUQ) is the power at the wheels going to be more at 6000k in 3rd or the same wheel speed in 4th?

 

[chrisphysics]

It seems there is no set point when it's best to change gears as this can change from gear to gear. See the below pulled from different forums.

I already knew this to some extent. It would be good if someone had a power / rpm graph for a standard AUQ engine, then I note down the rpm differences between the gears and work out the best points to change or gear.



"Power accelerates cars. Basically you want to change gear to maximise the amount of power the car is producing, so you want to change gear once you're past the car's power peak at the point where the engine would be producing more power at the revs it'll drop to when you change up*. There is no set point; if the ratio between the gears differs there'll be a different optimum change point for each gear. The maximum torque point is a red herring (unless it happens to coincide with maximum power, which is unlikely). Power is what matters."

 

[Muttley]

There's no point in going above the max power revs, and no point in dropping below max torque after the change. From reading the spec sheets, max power is about 5500 and max torque just above 2K, although the curve seems pretty flat between 2K and 4K. So change at or before 5500 rpm would be my advice

 

[traumapat]

There's no point in going above the max power revs, and no point in dropping below max torque after the change. From reading the spec sheets, max power is about 5500 and max torque just above 2K, although the curve seems pretty flat between 2K and 4K. So change at or before 5500 rpm would be my advice

id agree looking at my old print out which is remapped but tells the same story. your no longer gaining power after 5500rpm.

 

[d_jones]

"There's no point in going above the max power revs, and no point in dropping below max torque after the change. From reading the spec sheets, max power is about 5500 and max torque just above 2K, although the curve seems pretty flat between 2K and 4K. So change at or before 5500 rpm would be my advice "

I would have to strongly disagree.

You are not taking into account power loss through gear ratios.

To work out the optimum shift points you need to plot G in each gear to the rev limiter. Line them up in a graph and the point where the lines cross for each gear is optimum.

You will find each gear is different but in general 1st gear is a fraction of a second before the limiter and 2nd is not far off. I did this once on a TDI which is virtually dead after 4000 but the optimum shift point from 1st was like 4500. 2nd was about 4300 then they sort of leveled off at about 4000.

If you were to change at 5500 in each gear your 1.8t you will be loosing a lot of time!!

 

[PhilW]

http://forums.audiworld.com/vag/msgs/861.phtml

 

[Muttley]

Interesting graphs. They are from a four-speed box, of course. A six-speed box would generate two more curves and they would be closer.

His first point is key: "Your acceleration (change in speed over change in time) is greatest at the torque peak, and tapers off after the torque peak." So the aim, in simple terms, is to change so that your revs drop back to the torque peak, which for the sake of argument we can say is anything between 2000 and 4000 rpm.

I haven't got dyno figures to work with, but I do have the gear ratios for the six-speed boxes used in LC and LCR's (ERR, FML, FZQ). I also have a spreadsheet and I'm not afraid to use it

I've taken the assumption that the aim is to change up so that the next gear is engaged at 4000rpm. The gearbox build specs give me the ratios so I can get the ratio of engine rpm to wheel rpm between adjacent gears, this is in column 2. From that it's easy to get the rpm you need to get to in the lower gear to get 4000 on change up (column 3).

Column 4 shows what happens to rpm if you rev to the power peak and then change up. In no case do you drop below the torque peak, in fact you stay in high-torque region in the lower gears.

ERR gearbox (type 02ML, six-speed)
	
	Ratio	rpm to get 4000 	rpm after change
		on change up	at 5500
		
1-2	1.62	6500		3400
2-3	1.42	5700		3900
3-4	1.29	5100		4300
4-5	1.23	4900		4500
5-6	1.20	4800		4600

It's interesting that 1st-2nd is a big jump, and results in a need to go well past the power peak. As you go up the box the ratios get closer, and mean you don't need to rev so high.

All this is just ink on paper of course, only engineering figures and not real road performance. Actual drag strip times will vary depending on many other factors a well as optimum shift point. However, for road use, I think it's safe to say that changing up at or a bit below 5500 will get you close to optimum acceleration in the traffic light drag race The winner is likely to be the one with the best tyres.

A point about torque peak: in a normally aspirated engine this is well defined and happens at comparatively low rpm. The key difference for the LC/LCR is the turbo, which gives you the effect of a variable compression ratio and flattens out the torque curve, gets it high earlier and keeps it at the limits set by the engines construction.

 

[chrisphysics]

Interesting graphs. They are from a four-speed box, of course. A six-speed box would generate two more curves and they would be closer.

His first point is key: "Your acceleration (change in speed over change in time) is greatest at the torque peak, and tapers off after the torque peak." So the aim, in simple terms, is to change so that your revs drop back to the torque peak, which for the sake of argument we can say is anything between 2000 and 4000 rpm.

I haven't got dyno figures to work with, but I do have the gear ratios for the six-speed boxes used in LC and LCR's (ERR, FML, FZQ). I also have a spreadsheet and I'm not afraid to use it

I've taken the assumption that the aim is to change up so that the next gear is engaged at 4000rpm. The gearbox build specs give me the ratios so I can get the ratio of engine rpm to wheel rpm between adjacent gears, this is in column 2. From that it's easy to get the rpm you need to get to in the lower gear to get 4000 on change up (column 3).

Column 4 shows what happens to rpm if you rev to the power peak and then change up. In no case do you drop below the torque peak, in fact you stay in high-torque region in the lower gears.

ERR gearbox (type 02ML, six-speed)
	
	Ratio	rpm to get 4000 	rpm after change
		on change up	at 5500
		
1-2	1.62	6500		3400
2-3	1.42	5700		3900
3-4	1.29	5100		4300
4-5	1.23	4900		4500
5-6	1.20	4800		4600

It's interesting that 1st-2nd is a big jump, and results in a need to go well past the power peak. As you go up the box the ratios get closer, and mean you don't need to rev so high.

All this is just ink on paper of course, only engineering figures and not real road performance. Actual drag strip times will vary depending on many other factors a well as optimum shift point. However, for road use, I think it's safe to say that changing up at or a bit below 5500 will get you close to optimum acceleration in the traffic light drag race The winner is likely to be the one with the best tyres.

A point about torque peak: in a normally aspirated engine this is well defined and happens at comparatively low rpm. The key difference for the LC/LCR is the turbo, which gives you the effect of a variable compression ratio and flattens out the torque curve, gets it high earlier and keeps it at the limits set by the engines construction.

I disagree again. Read the other comments acceleration has nothing to do with peak torque, it's all about power. If you look at the audiworld graph acceleration in 3rd is faster than 4th all the way to 6200rpm. If you changed to 4th any sooner you'd be losing out.
It's also not a 4 speed box they've just not bothered to log 5th and maybe 6th.

 

[traumapat]

interesting thread guys.

been thinking. if the optimum torque comes it at 4k max power is acheived at 6k.

if say in 2nd gear thats not optimum.. and peak power for this gear is 7k. you change up but instead of hitting 3rd at the ideal 4k i now get 5k. according to my graph thats a loss of 20lbs/ft.

isnt it just as important to set up the next change as opposed to getting every snip of power out of 2nd gear?

 

[Willie]

"There's no point in going above the max power revs, and no point in dropping below max torque after the change. From reading the spec sheets, max power is about 5500 and max torque just above 2K, although the curve seems pretty flat between 2K and 4K. So change at or before 5500 rpm would be my advice "

I would have to strongly disagree.

You are not taking into account power loss through gear ratios.

To work out the optimum shift points you need to plot G in each gear to the rev limiter. Line them up in a graph and the point where the lines cross for each gear is optimum.

You will find each gear is different but in general 1st gear is a fraction of a second before the limiter and 2nd is not far off. I did this once on a TDI which is virtually dead after 4000 but the optimum shift point from 1st was like 4500. 2nd was about 4300 then they sort of leveled off at about 4000.

If you were to change at 5500 in each gear your 1.8t you will be loosing a lot of time!!

Are you really going to be able to tell the difference when totally going for it between 4300 and 4500 RPM.
I couldn't do it, infact I change gear about 5800 but no way could I say accurately as I'm paying more attention to not crashing. even if you do dip the clutch at RPM indicated 4300, what is the actual RPM?? Because your engine will over run a bit due to the Flywheel's rotational mass and momentum.
I've allways changed at 5800 and have quite easily walked away from an identical LCR.
As above stick in your cars high torque range and don't worry about it too much.

If you really want to find out go to Santa Pod or the like and you'll soon find out

 

[chrisphysics]

interesting thread guys.

been thinking. if the optimum torque comes it at 4k max power is acheived at 6k.

if say in 2nd gear thats not optimum.. and peak power for this gear is 7k. you change up but instead of hitting 3rd at the ideal 4k i now get 5k. according to my graph thats a loss of 20lbs/ft.

isnt it just as important to set up the next change as opposed to getting every snip of power out of 2nd gear?

If you change up early you'll lose out on acceleration, that means two seconds later you'll be going slower than you could be. Then when you hit the next gear you're behind in rpms. and thus speed. It might be a loss of torque at the engine to change later but torque at the wheels well always be higher in the the lower gear until the torque really starts to drop off. (ie 6000 /6500 rpm).

 

[traumapat]

If you change up early you'll lose out on acceleration, that means two seconds later you'll be going slower than you could be. Then when you hit the next gear you're behind in rpms. and thus speed. It might be a loss of torque at the engine to change later but torque at the wheels well always be higher in the the lower gear until the torque really starts to drop off. (ie 6000 /6500 rpm).

yes see what your saying but dosnt the same apply changing late? your hitting 3rd gear at 5k wheras my way im starting 3rd gear at 4k... longer usable powerband. dosnt this equal out in real terms?

 

[Muttley]

To get back to the original question (which I'd certainly lost sight of), changing up at 6000 rpm from 3rd to 4th will drop you to 4700 rpm. Now we need a dyno curve, which I don't have to hand. My guess would be that power would be about equal, going from the falling side of the curve in 3rd to the rising side in 4th.

The thread title is when to change gear: but the original poster didn't say if this was for daily driving or drag-race performance. The two cases will give different answers, not least because in daily driving you have to balance absolute acceleration against the noise, aggravation and general wear and tear on hardware and the driver My answers are more to do with daily driving, not absolute performance, partly at least because I don't have dyno curves to work with. The differences in performance that win races are not generally significant in daily driving.

So I still say that, for daily driving, there is no point in going over peak power rpm and you want to stay above peak torque.

Pat, my choice of 4K rpm as a change-up target is not from precise measurement, it is just that at 4k the torque is starting to drop off noticably.

Now, torque and power. The two have a fixed relationship, so you can't talk about them in isolation.

Power(bhp)=Torque(lb-ft) x rpm/5252

So the shape of the torque curve affects the power curve: as rpm rises torque starts to drop off above maybe 2000 rpm. so the power only continues to rise as long as the torque curve doesn't drop too fast.

In basic terms: torque is about how big a bang you can make in the combustion chamber, power is about how soon you can make the next one, how many you can make in a second. In a petrol car, higher rpm is always better, right up to the point where the engine falls to bits, although there are lots of things that have to be just right to keep performance rising at higher revs.

In terms of acceleration, flat-out maximum performance will be got by revving past the power peak so that the change up comes where power at the lower revs (rising) is similar to the power at the higher revs (falling) This is why racers spend all their time at high rpm. That's also what the acceleration curves produced above have shown, and there's no arguing with real-world results.

For daily driving, the gains are minimal, and the consequences need to be kept in mind - principally poor mpg. It simply isn't practical to drive all the time as if you were on a racetrack.

So, then, a generalisation to finish with: in daily driving, provided you aren't interested in the last few percent of acceleration, change up at or before the power peak but make sure that you are above the torque peak after the change. This will give a fairly wide range of change options - often referred to as "drivability" - which means you can adapt your driving to road conditions. It can be easy to fixate on performance targets (acceleration, top speed or mpg, say) which is fine until life throws an oil slick, or a wandering child, in your way.

 

[chrisphysics]

yes see what your saying but dosnt the same apply changing late? your hitting 3rd gear at 5k wheras my way im starting 3rd gear at 4k... longer usable powerband. dosnt this equal out in real terms?

The same does apply if you change too late and the power and dropped off to such an extent that the lower hear ratio no longer makes up for this.

The point is while you're in 3rd at 4k accelerating hard i'll still be in 2nd accelerating harder and pulling away. When I change to 3rd we'll both in the 3rd but i'll be going faster and you'd never catch.

If you're changing up early the longer power band point doesn't work as by changing early you're reducing the size of thatpower band.

 

[chrisphysics]

To get back to the original question (which I'd certainly lost sight of), changing up at 6000 rpm from 3rd to 4th will drop you to 4700 rpm. Now we need a dyno curve, which I don't have to hand. My guess would be that power would be about equal, going from the falling side of the curve in 3rd to the rising side in 4th.

The thread title is when to change gear: but the original poster didn't say if this was for daily driving or drag-race performance. The two cases will give different answers, not least because in daily driving you have to balance absolute acceleration against the noise, aggravation and general wear and tear on hardware and the driver My answers are more to do with daily driving, not absolute performance, partly at least because I don't have dyno curves to work with. The differences in performance that win races are not generally significant in daily driving.

So I still say that, for daily driving, there is no point in going over peak power rpm and you want to stay above peak torque.

Pat, my choice of 4K rpm as a change-up target is not from precise measurement, it is just that at 4k the torque is starting to drop off noticably.

Now, torque and power. The two have a fixed relationship, so you can't talk about them in isolation.

Power(bhp)=Torque(lb-ft) x rpm/5252

So the shape of the torque curve affects the power curve: as rpm rises torque starts to drop off above maybe 2000 rpm. so the power only continues to rise as long as the torque curve doesn't drop too fast.

In basic terms: torque is about how big a bang you can make in the combustion chamber, power is about how soon you can make the next one, how many you can make in a second. In a petrol car, higher rpm is always better, right up to the point where the engine falls to bits, although there are lots of things that have to be just right to keep performance rising at higher revs.

In terms of acceleration, flat-out maximum performance will be got by revving past the power peak so that the change up comes where power at the lower revs (rising) is similar to the power at the higher revs (falling) This is why racers spend all their time at high rpm. That's also what the acceleration curves produced above have shown, and there's no arguing with real-world results.

For daily driving, the gains are minimal, and the consequences need to be kept in mind - principally poor mpg. It simply isn't practical to drive all the time as if you were on a racetrack.

So, then, a generalisation to finish with: in daily driving, provided you aren't interested in the last few percent of acceleration, change up at or before the power peak but make sure that you are above the torque peak after the change. This will give a fairly wide range of change options - often referred to as "drivability" - which means you can adapt your driving to road conditions. It can be easy to fixate on performance targets (acceleration, top speed or mpg, say) which is fine until life throws an oil slick, or a wandering child, in your way.

I think that about sums it up perfectly. Certainly in real world driving a do change before 5000rpm to improve mpg, give less engine wear etc.

 

[Willie]

n normal drivng your changing at 5,000 RPM, really, even in first.......

Wow very different driving styles going on here
I go to 4,000 RPM max on daily driving or up a steep hill maybe 5,000 PRM
But then I am getting 42 MPG

 

[chrisphysics]

I didn't say normal driving a said real world. That's on the road nailing it. (in other words while on the road I don't brother reving much past 5000rpm as that's often enough to beat Mr "i've got a TDI with torques i'm fast." (obviously excluding Mk1 Leons here. They're all fast even when standing still.)
While while going down a busy city road i'll change at a more normal 2000rpm? sometimes more sometimes less depending on the situation.

 

[traumapat]

The same does apply if you change too late and the power and dropped off to such an extent that the lower hear ratio no longer makes up for this.

The point is while you're in 3rd at 4k accelerating hard i'll still be in 2nd accelerating harder and pulling away. When I change to 3rd we'll both in the 3rd but i'll be going faster and you'd never catch.

If you're changing up early the longer power band point doesn't work as by changing early you're reducing the size of thatpower band.

but you wouldnt be accellerating harder in second as at 4k in 3rd ive my max torque running and increasing engine power. whereas youve little torque at the high end of 2nd?

change gear and whereas im using all availible torque your coming in 1k rpm later so conitue this through the gears and youve not actually hit your full torque in any gear? (im looking at a graph as we speak albeit ihi)

ihi may be different as you cant use all the power in 1st & 2nd anyway due to traction... so its struggle to feed the exact amount before slipping... hence the rush to hit 3rd and relax.

i think your point is valid... but wonder if it amounts to much in practice

need to get down to pod and try it out

 

[traumapat]

Pat, my choice of 4K rpm as a change-up target is not from precise measurement, it is just that at 4k the torque is starting to drop off noticably.

.

lol. mine has little torque/power before 4k!

 

[chrisphysics]

but you wouldnt be accellerating harder in second as at 4k in 3rd ive my max torque running and increasing engine power. whereas youve little torque at the high end of 2nd?

change gear and whereas im using all availible torque your coming in 1k rpm later so conitue this through the gears and youve not actually hit your full torque in any gear? (im looking at a graph as we speak albeit ihi)

Look at that graph from the audi world forums. The acceleration provided in 2nd is higher than 3rd at every point right up until 6800 or something. That's prove as far as i'm concerned. Even more so considering the car measured is a 1.8T