I remember when I was developing my own sets for XRG (drifting on VHP), that there was an optimal shifting point (lets say 5600 RPM) which would be displayed on the dashboard with a shifting indicator light. Nowadays, this shift light is no longer here (on road going cars anyways). So, as a general rule, where would I shift? Before the rev - limiter, on the rev - limiter? How much?

I'm talking in regards to the XFG, where I am trying to get as much outta the thing. I see people shifting on 8k, where myself, I shift at around 7500 - ish. Will dynocharts help? I've lost my share of the S2 car dynocharts...

Anyways, TYIA

XFG had a shift light at about 8000 rpm. Just check older versions to see it.

before the engine explodes

depends where you are at which track with which gear-ratios :P
But shift when you feel you should.

I shift at abound 7800RPM, because after that it feels like it kind of looses power

Quote from Flame CZE :

XFG had a shift light at about 8000 rpm. Just check older versions to see it.

The old shift indicators in LFS used to calculate the amount of power available in the next gear and compare it to the current output, and obviously when more power was available by shifting, the light would come on.
It's generally a very easy calculation to do for your setup, given the car's torque and power-curves as well as the gear ratios of your setup, but it's not going to gain you tenths, so I would just shift just before the redline and then concentrate on my driving instead.

When it feels slow... That's how you would simply do it.
If you REALLY want to make sure - put auto gearbox on and drive. When the auto shifts, that's the ideal point (for this gearing). And yes, the auto gearbox calculates torque in the current gear and the next gear.
Another option is to press F9 or F10 and look at the acceleration force.. Compare it by shifting up and down.

Quote from evans :

The old shift indicators in LFS used to calculate the amount of power available in the next gear and compare it to the current output, and obviously when more power was available by shifting, the light would come on.

Quote from RasmusL :

Another option is to press F9 or F10 and look at the acceleration force.. Compare it by shifting up and down.

Agreed.

i wish the cars in LFS have those dyno maps :S

Normally shift at the redline, because a car pulls harder in a lower gear than it would in the next, even when the torque curve is going downwards.


@ NXS_Freedom
They are here somewhere on the forum

Whenever I feel I need the next gear

sometimes an early shift will really help with traction, sometimes its better to hold in lower gear to the redline/limiter before a brake point.

every gear is adjustable in the garage

SD.

If you have a graph of rear wheel torque versus rpm for all gears, you'll see the lines intersect on the right side of the lines (except perhaps between 1st and 2nd). If shift were instant, you'd shift where these lines intersect. Since shift times are not instant, you shift at a bit higher rpm. The idea is to maximize the rear wheel torque for the speed near a shift point. This assumes a normal torque curve where the torque peak is significantly less than redline.

In most cars you won't be too far off the optimum by hitting or nearly hitting the red line.
The MRT however, is another thing entirely! (But luckily it does still have a shift light.)

Quote from GenesisX :

I remember when I was developing my own sets for XRG (drifting on VHP), that there was an optimal shifting point (lets say 5600 RPM) which would be displayed on the dashboard with a shifting indicator light. Nowadays, this shift light is no longer here (on road going cars anyways). So, as a general rule, where would I shift? Before the rev - limiter, on the rev - limiter? How much?

I'm talking in regards to the XFG, where I am trying to get as much outta the thing. I see people shifting on 8k, where myself, I shift at around 7500 - ish. Will dynocharts help? I've lost my share of the S2 car dynocharts...

Anyways, TYIA

heh, just the same the car havent changed if you want to be superaccurate get replay analyzer to see max torque vs. rpm. The indicator was nothing else but this rpm.

Quote from AndRand :

heh, just the same the car havent changed if you want to be superaccurate get replay analyzer to see max torque vs. rpm. The indicator was nothing else but this rpm.

If you mean torque at the crankshaft then no, the shift point is massively higher than this.

The power peak in the XFG is about 7000 rpm, while the torque peak is more like 5400 rpm. (Straight from the info screen, I don't have the torque/power curves either.)

But the shift point depends on the gear you are changing up to, so an accurate shift light is NOT simply rpm-dependent.

I was driving a close-ratio set earlier, where the 3rd to 4th and 4th to 5th shift points were (in my opinion) not very high at all - maybe 7500 rpm or even less. The basis I use is to try to match the power in the gears (basically the same as the torque to the wheels * wheel speed), so that if I change from 4th gear 7300 rpm to 5th gear 6700 rpm, I'm probably vaguely matching the power I had in 4th to the power I will have in 5th. But without a torque curve, you can't get it spot-on...

I did some tests yesterday, just playing about (in FXO mostly), and it really didn't make much difference to the drag-race timing (a tenth or two) if I used shift-up points differing by 500 rpm or more

Quote from Neilser :

I did some tests yesterday, just playing about (in FXO mostly), and it really didn't make much difference to the drag-race timing (a tenth or two) if I used shift-up points differing by 500 rpm or more

Those 1-2 tenths of a second makes all the diference. Just think of how many upshifts you do on a track, let's say FE4, or AS5. Even 0.05 sec in each upshift makes quite a lot on a whole lap.

Quote from RevengeR :

Those 1-2 tenths of a second makes all the diference. Just think of how many upshifts you do on a track, let's say FE4, or AS5. Even 0.05 sec in each upshift makes quite a lot on a whole lap.

Ah, sorry, wasn't clear enough - I meant only a tenth or two over the entire drag run (4 upshifts in a 5-speed box). And a tenth or two is probably similar to the error margin anyway, since I didn't do very many runs; I was simply trying to reassure the OP that the variation would be pretty modest in general terms. But yes, in the right places on certain tracks, I'm not at all sure that the effect would be entirely negligible for a full 500 rpm variation in shift-point.
If I could work out a really easy way to do a more precise test, I'd do it. Maybe a replay analyser (haven't downloaded any yet) would be the right way to do it...

One thing I did notice while replaying various replays carefully to see what the acceleration was in the various gears before and after a shift - if you don't get too close to the redline and shift with your foot kept flat to the board, the engine revs keep rising while the clutch (auto or other) is down, and then when the clutch is released the extra energy the engine has built up while the car was decelerating compensates somewhat for the slight speed reduction during the shift. (Of course, even if you do hit the redline, the revs will still have to drop significantly when the higher gear is hooked up by the clutch, but the gain is a bit smaller then...)
You can clearly see a couple of MPH increase as the clutch engages, with much higher (like 1.5x or even 2x) acceleration than when the revs have fallen back and the clutch is no longer slipping. (Of course, this does warm your clutch up! )

Quote from Neilser :

One thing I did notice while replaying various replays carefully to see what the acceleration was in the various gears before and after a shift

your acceleration comes from torque, not the power which enables to deal with growing opposite forces (ie. air drag), so in proper gearing you should change gears as soon as torque is diminishing as torque on higher gear should be higher.

Quote :

if you don't get too close to the redline and shift with your foot kept flat to the board, the engine revs keep rising while the clutch (auto or other) is down, and then when the clutch is released the extra energy the engine has built up while the car was decelerating compensates somewhat for the slight speed reduction during the shift. (Of course, even if you do hit the redline, the revs will still have to drop significantly when the higher gear is hooked up by the clutch, but the gain is a bit smaller then...)
You can clearly see a couple of MPH increase as the clutch engages, with much higher (like 1.5x or even 2x) acceleration than when the revs have fallen back and the clutch is no longer slipping. (Of course, this does warm your clutch up! )

creating more slip afterwards

Quote from AndRand :

your acceleration comes from torque, not the power which enables to deal with growing opposite forces (ie. air drag), so in proper gearing you should change gears as soon as torque is diminishing as torque on higher gear should be higher.

Well, torque and power are intimately related, but it would be a grotesque understatement to say that they are often misunderstood

Again I'm unsure here if you are talking about engine torque or torque at the wheels.

The peak acceleration in a given gear would happen at peak engine torque if it weren't for air resistance (which increases with road speed). However, the peak acceleration at a given engine speed [edit: argh, no, I meant road speed!] if you have a choice of gears will be in the gear which maximises the engine power.

Since power = torque * angular speed, the engine power peak is always at higher RPM than the torque peak. Depending on the engine, it can be slightly higher, or much much higher - it depends entirely on how steeply the torque curve falls above peak torque.

So if (as I suspect) you meant that you should change gear after the engine torque peaks, then I'm afraid you're wrong - this will be dramatically too early, so early in fact that for most cars you should be trivially able to prove it to yourself on a drag strip by reference to the "Info" tab's engine torque peak RPM value... Only if peak torque and peak power are really close together does this point become moot (don't know for sure if any LFS car has that property).

If you meant wheel torque in what you wrote, then your first statement was correct, that acceleration comes from wheel torque, but you still don't change gear when the wheel torque diminishes, as the wheel torque in any given gear is simply proportional to the engine torque.

Hope that was mostly clear

I had this derived from feel-in-pants, that I didnt bother to look at closely. And I have no experience with manual to feel acceleration kick-in compared at gear change at torque peak and redline, as auto does it auto

And now I am convinced It even shows that gear change should occur at redline as torque is always higher on lower gear.

Quote from Neilser :

However, the peak acceleration at a given engine speed if you have a choice of gears will be in the gear which maximises the engine power.

That doesn't make much sense to me. At a given engine speed you have a given engine power, and since transmission doesn't change power only rpm and torque (except for the transmission losses, but that's not the point here) you always have the same power at the wheels for a given engine speed, no matter which gear you are in. Perhaps you meant wheel speed.

Quote from Iron :

That doesn't make much sense to me. At a given engine speed you have a given engine power, and since transmission doesn't change power only rpm and torque (except for the transmission losses, but that's not the point here) you always have the same power at the wheels for a given engine speed, no matter which gear you are in. Perhaps you meant wheel speed.

Basically theres optimal ranges for every gear.

On the street 1st goes about 30-40 and you'd wanna shift roughly, 2nd goes... you get the point.

Thats why YOU change the gear ratios and final drive, it's your toy. My 744ti volvo will light them up in 1st and 2nd, sometimes 3rd. If I'm in 1st I shift before 4-5k, otherwise it hits the rev limiter even with half throttle (darn turbo engines ) when I throw a LSD in I want a lower final drive ratio, not sure if 5th is working yet (overdrive/manual tranny, weird one) seems to not be as when I push the button in 4th like i used to do it dont shift....

anyways 5th wasnt much lower as I remembered, 4th i guess i have is 3 or 3.5k rpm at around 80 or so, which always leaves me boosting too much

And how is that correlates to my post?

Link to image of rear wheel force (in g's) versus speed for a old ZX11 motorcycle. If shift time was instant, you'd shift where the lines cross, since shifts take some amount of time, you'd shift at slightly higher speed. 1st to 2nd gear shift is at red line, then the rpm for ideal shift point decreases with the gear.

http://rcgldr.net/misc/shiftpoint.jpg

Quote from AndRand :

And now I am convinced It even shows that gear change should occur at redline as torque is always higher on lower gear.

Nice graph, though the horizontal axis only seems to be RPM for the engine curve, and the others appear to use road speed. And indeed, for this engine, the curves don't cross so I agree that all shifts would be optimal at the redline.

Quote from Iron :

That doesn't make much sense to me. [...]
Perhaps you meant wheel speed.

Oh damn Yes, I meant road speed, argh, can't believe I checked that and still missed it. Argh and double argh Thanks for spotting the nonsensical bit!

Quote from JeffR :

Link to image of rear wheel force (in g's) versus speed for a old ZX11 motorcycle. If shift time was instant, you'd shift where the lines cross, since shifts take some amount of time, you'd shift at slightly higher speed. 1st to 2nd gear shift is at red line, then the rpm for ideal shift point decreases with the gear.
http://rcgldr.net/misc/shiftpoint.jpg

Yup, a nicer case than AndRand's, as the gearbox in his example needed a few extra cogs in it This is the situation in most LFS cars, with most setups, I think.

One thing these curves conceal btw is that the amount of time spent in each gear is dramatically different. So when tuning a box (while you need to think about the track of course) it's much more important to get it right for the higher gears, where you spend much much longer than in 1st or 2nd. So in a long straight run to max speed in a 6-speed box, you might spend a reasonably short time in 3rd, and it doesn't matter so much that you spend quite a big fraction of that time way off the power peak (i.e. big rev range, corresponding to a big fractional increase in speed while in the gear) but in 5th, you want to spend most of your time as close as poss to the power peak (either side of it, naturally) and that will correspond to a much more limited rev range, and a much smaller fractional speed increase while in the gear...
(I've never actually done the sums to compare the average engine power output over a whole acceleration run with different box setups though - must play with it sometime. Anybody recommend a good replay analyser? I think though that the setup which maximises average power will result in both the highest final speed and the fastest time over a set distance...)