Hi all, after a bit of searching, here and over the net, i tried to gather to information about gear ratio calibration. I'm using bob's project3 tool(it can't do goods without knowledge) to create my sets. However, i'm overwhelmed by the topic and i need a little help.

First, here's what i think i gathered.

• Final drive ratio
  You setup this last. This set your top speed.
  
• Torque is what gets you going at low speed
  You need to be at the top of the curve after a shift(ex from 3rd to 4th)
  
• Power is what you need at high speed
  You need to push your rev past the top of the power curve
  
• The higher the gears, shorter the shifts will get
  
  

So if i'm right, there's a powerband you always want to be in i guess? So would it be between max torque and max power? Or Shoud it "bleed" from both sides?

So i guess i need to set the final gear to 1, set the first one to the lowest value that don't make me stall at first, then set the gear in between to stay in that powerband?

Thanx a bunch guys
Feel free to correct me!

On a side note - I know there are guides out there for that but i'm sure that a couple stikies in the setups section about differents aspects of a car setups would really help some guys that want to get into setups. I think this section is too often aimed at 1 car with 1 specific setup instead of general concept.

We could exchange about those topic instead "only reading them"

Quote from poirqc :

Hi all, after a bit of searching, here and over the net, i tried to gather to information about gear ratio calibration. I'm using bob's project3 tool(it can't do goods without knowledge) to create my sets. However, i'm overwhelmed by the topic and i need a little help.

First, here's what i think i gathered.

• Final drive ratio
  You setup this last. This set your top speed.
  
• Torque is what gets you going at low speed
  You need to be at the top of the curve after a shift(ex from 3rd to 4th)
  
• Power is what you need at high speed
  You need to push your rev past the top of the power curve
  
• The higher the gears, shorter the shifts will get

So if i'm right, there's a powerband you always want to be in i guess? So would it be between max torque and max power? Or Shoud it "bleed" from both sides?

So i guess i need to set the final gear to 1, set the first one to the lowest value that don't make me stall at first, then set the gear in between to stay in that powerband?

Thanx a bunch guys
Feel free to correct me!

On a side note - I know there are guides out there for that but i'm sure that a couple stikies in the setups section about differents aspects of a car setups would really help some guys that want to get into setups. I think this section is too often aimed at 1 car with 1 specific setup instead of general concept.

We could exchange about those topic instead "only reading them"

Wow, you overcomplicated things a bunch. Let me try and help point you in the right direction..

As far as racing with standard manual transmissions is concerned, focus on peak horsepower.

Ideally, you'd want the engine to run at peak horsepower at all times. Such operation could be made possible with a constantly variable transmission, which lets you rev to peak HP and holds it there indefinitely until you remove your foot from the skinny pedal.

On an engine with a bell curve on the horsepower graph, you'd want to shift so that you'd be at the same power before and after the shift. That is, you want the engine RPM to straddle the max horsepower RPM. On some cars, horsepower falls off quickly after peak horsepower, so you'd want to skew the gear ratio so that it favors the area before peak horsepower.

And it's better that you don't set the final drive ratio to 1. Most cars have final drives between 2.5 and 4.5 in real life, so a good starting point would be 3.5 or 3.75. Set it to that, then fix the gear ratios so that acceleration is ideal, and adjust FD after that to max the speed out on particular tracks.

But realistically, Bob Smith's Proj3 sets up gear ratios just fine. I always use the Auto Space Gearing button, and fiddle with the Adjustable Progressive setting (drop into top gear), depending on how peaky the car I'm tuning is.

Adjust the highest gear to max out at the end of the fastest straight, adjust the gears in between to give optimum acceleration out of the most crucial corners.

Final drive ratio

• You setup this last. This set your top speed No, you set this early on, along with top gear, so that top speed (which is dependent on drag and power, simply) occurs at around peak power.
  
• Torque is what gets you going at low speed Torque applies at all speeds. To say torque is low speed and power is high speed is very simplistic, and not usable for car preparation really.
  You need to be at the top of the curve after a shift(ex from 3rd to 4th) No, this is the wrong way of thinking. You want to shift so that you have more power or wheel torque in the next gear than if you stayed in the original gear. This almost certainly means shifting after peak power, and almost certainly (unless you have really close ratios) puts you below peak torque after the shift.
  
• Power is what you need at high speed
  You need to push your rev past the top of the power curve You can't "push your revs". Your revs are what they are, defined by gearing and road speed. But you want peak speeds to occur at peak power (ish, as drag varies, through inclines, wind variations or slipstreams), and the power figures only real use is to estimate top speed (imo).
  
• The higher the gears, shorter the shifts will get What? The greater the difference in numerical ratio the greater the drop in revs between each gear. If you can get away with close ratios (which usually means a very tall 1st gear, which might sacrifice a bit at the starts) then you still have the same top gear, but closer gaps inbetween gears. If you don't have close ratios (i.e. the engine needs torque multiplication to get it 'off the line', then your ratios will be more widely spread, and hence give a bigger rev drop.

So if i'm right, there's a powerband you always want to be in i guess? Yes, there is a powerband, but it is independant of your gearing. You set the gearing to suit the power band, and not set the power band via the gearing.
So would it be between max torque and max power? Or Shoud it "bleed" from both sides? Hmm, not sure what you mean here. It's very difficult to define 'powerband' from the power/torque curves on most engines, as most are relatively smooth curves. Obviously some have sudden peaks, which can point to a narrow powerband. But mostly it comes from driving the car and seeing how peaky it is - i.e. how low the revs can go before performance is drastically reduced.

So i guess i need to set the final gear to 1, set the first one to the lowest value that don't make me stall at first, then set the gear in between to stay in that powerband? Final drive ratio affects all the gears. Best bet is to set the final drive ratio to a middle, sensible value. Then choose a top gear ratio that gives a good top speed, and the highest 1st gear ratio you can get away with without sacrificing starts. Then adjust the other gears to give a nice spread (higher gears will be closer than lower gears, so it is not a linear spread). This might mean you have to readjust top gear if you are now way past peak power at the end of the longest straight, and you might want to tweak the other gears to better suit certain corners or the starts (no point having a critical corner where you are sitting just off the shift point in 3rd but way below the powerband in 4th - much better to set the gearing so you in the middle of the powerband in one of the gears - which one is up to you!).

I hope this helps you. Gearing is both REALLY simple and quite complicated at the same time, depending on the depths you want to go to over it. Have a look at Inferno site setup ratios and see if you can spot patterns, and see if you can see a few areas where they can be improved.

The language barrier cause me some problems as english is'nt my native one.

I've understand most of what is explained here. I'll re read this after i get back from work and ill ask some more questions after.

No problem - take your time reading, ask questions if you don't understand, and ask questions about other stuff, and I'll/we'll try to help!

bloody hell, talk about overcomplicating things.

Basically, forget about torque - it's irrelevant. You want to maximise your engines power output. The red shift light is a magical happy happy shift light that comes on when you could be making more power in the next gear, so change when it goes red. Set the gears up so they are nice to drive, usually rev out top gear on the straight but on some tracks not needed.

I wouldn't forget about torque, rightly or wrongly, I tend to set the final and top gear to give me maximum speed on a given track, then set everything inbetween , with gear changes to just before peak torque.

You'll never shift before peak torque, or peak power. In both cases (power and torque) you will shift AFTER the peak (quite a while after peak torque in most cases). So Dan, you are doing something funny with your gearing...

I'd never forget about torque - with the wheel torque and gearing data, and a few educated guesses on drag, you can quickly work out in gear accelerations, top speeds (and how gearing changes that) etc etc. The power curve is relatively useless (but will come up with the same shift point information, so in this case alone is acceptable).

Wrong wording by myself, I meant that AFTER a gearshift has taken place, the engine is just before peak torque

Okay then - I'll let you off

Quote from tristancliffe :

I'd never forget about torque - with the wheel torque and gearing data, and a few educated guesses on drag, you can quickly work out in gear accelerations, top speeds (and how gearing changes that) etc etc.

Do you seriously sit around calculating any of that when making a set?? Top speed is rarely seen in the combo's available, and it seems more straightforward to adjust top gear after a basic test drive, to me. Whatever works for you I guess

No of course I don't - this is more of a real life thing, and was added to improve the discussion on gearing.

I see a top speed on EVERY combo in EVERY car. It is the highest speed I achieve on that combo. You gear the car so you are at peak power at this speed - hence gearing for 'top speed'.

However, in real life, as well as gearing for the circuits top speed, you sometimes need to know the top 'theoretical' speed of your car - there is never any point gearing for a higher speed than this, so you can easily work out the highest potential gear you'll ever need.

In LFS we do not have either power or torque curves visible (easily), so all calculations are either done by speedo feedback, lap time feedback, or with Bob's setup tool.

You see top speed on every track? If you had a longer straight, the car just wouldn't accelerate any more? You're gearing must be a long way out

No, no, no. You misunderstand me.

I gear for THE TOP SPEED at that track. The highest speed on the course. Let's say the UF1 has a maximum theoretical top speed of 90mph, but at FE1 can only reach 75mph. The Top Speed of the UF1 at FE1 is, therefore, 75mph, and you gear the car to be at peak power at this speed. You cannot go faster than that (because the straights aren't long enough), so you don't need to gear for the remaining theoretical 15mph.

Do you see? It's really quite simple. You are confusing Maximum Speed the car can ever reach versus the maximum speed a car can reach on a config (which might change as your gearing improves, or as the handling/grip gives you more speed out of the corners, or your own driving improves, so sometimes your top speed will increase with track/development time, hence you gear slightly longer (top speed equates to less than peak hp revs) so that car improvements 'correct' your gearing.

No, you misunderstand me
I hear you loud and clear about top speed for a config. Top speed is not reached at peak power though - top speed is reached either at the rev limiter, or closer to it than peak power.

I also don't believe you want to hit peak power in top gear just as you start braking either - you're wasting all the high end power just the other side of the peak if you do that, and spending more time in the pre-peak portion.

Yeah, I suppose that's true actually. All the racing/technical books, and advice given over the years is gear for peak hp at peak speed, and I must confess I never actually considered that part of it (although I have spent a while thinking about the other elements of gearing) much. I shall apply some brain cells to that thought, and see what happens.

Quote from Blowtus :

No, you misunderstand me
I hear you loud and clear about top speed for a config. Top speed is not reached at peak power though - top speed is reached either at the rev limiter, or closer to it than peak power.

I also don't believe you want to hit peak power in top gear just as you start braking either - you're wasting all the high end power just the other side of the peak if you do that, and spending more time in the pre-peak portion.

Not if you don't have enough power after the curve to overcome aerodynamic drag.

Top speed SHOULD be geared for peak power unless that speed is well below maximum theoretical speed. Otherwise it's going to take a while to accelerate that last bit.

Don't forget that as well as using shorter gearing for using the part of the power curve above peak power in top gear, you benefit with additional acceleration throughout all gears (assuming you are altering final drive here), and thus for the majority of the straight, so a little less acceleration at the end of the straight is pretty irrelevant.

I think Tristan is still correct, because the torque curve mathematically has to be decreasing by this point, therefore going past peak power is still producing less torque at the wheels than staying in the portion before before peak power. There is no next gear to worry about.

I'm starting to understand what all everybody's adding, but i'd like to go a little off-topic, since good on topic things have been told.

What's are the pro/cons of a close ratio transmission.

I think you stay closer to peak power around most of your shifts but you could lose some time shifting?

Quote from Secondaries :

Not if you don't have enough power after the curve to overcome aerodynamic drag.

Top speed SHOULD be geared for peak power unless that speed is well below maximum theoretical speed. Otherwise it's going to take a while to accelerate that last bit.

That's the point - on the vast majority of combos top speed reached is below the speed the car is capable of given sufficient gearing and straight road, so you continue to accelerate beyond peak power.

Quote from Ball Bearing Turbo :

I think Tristan is still correct, because the torque curve mathematically has to be decreasing by this point, therefore going past peak power is still producing less torque at the wheels than staying in the portion before before peak power. There is no next gear to worry about.

It doesn't matter what the torque curve is doing. Power is just a combination of the frequency torque is applied, and the intensity of it.
The torque curve always starts to decrease substantially before peak power is reached.

Quote from Blowtus :

It doesn't matter what the torque curve is doing. Power is just a combination of the frequency torque is applied, and the intensity of it.The torque curve always starts to decrease substantially before peak power is reached.

It doesn't? Guess what dynos measure, and where power is calculated from - not the other way around.

Power is a product of RPM and torque (which I assume you meant by "frequency and intensity")

Torque is torque (force is force), period. If I exert a particular force on any given object, I impose an acceleration upon said object which is completely related to the mass of the object, and the strength of the force applied. More force = a greater moment of acceleration for a given mass.

Less torque means less acceleration, period - and unfortunately there's no way around that. I would never say either the torque curve or the power curve is irrelevant since one can be derived from the other easily.

I've beaten this topic to death with Tristan before and it's not pretty. There are some things I think I'll never full understand, unless someone one day can precisely articulate for me an answer to the following question I posed to Todd ages ago. He gave me a long reply with math, which makes sense - and I take it for granted but admit I still can't visualize fully the reasoning; even though the math is dreadfully easy and logical in and of itself:

Snippet of a PM sent to Todd/Tristan ages ago:
****
Really the only thing that still perplexes me about the whole issue is the fact that the definitions for power and torque cause contradictions... F=MA is so simple, and as pointed out in the thread applies to a theoretical instant. However, acceleration takes place over time. You said in the thread that the greatest rate of instantaneous acceleration (in any GIVEN gear) takes places at the torque peak (simple F=MA, makes perfect sense to me). However if that was completely true in practice - then how is it possible that greater acceleration over time (a whole bunch of "instants" of which the previous theory is comprised) does not cooincide with higer torque values, but rather higher power values?
****

Note that the very definition of horsepower is stated as force over time; ie 33000 lb.ft/min, so to me, more horsepower means more force is being applied per unit of time, meaning object x should have had more force applied to it after x time passes.. Therefore object x is farther away. However, that does not jive with F=MA and I have no idea why.

gearing multiplies torque though - you don't get as much acceleration at 4000rpm in 5th gear as you do in 4th.

More force does equal greater instantaneous acceleration - but if you apply a slightly smaller force much more often in a given time period, you accelerate the object more.

edit: good question! I suspect the answer lies in the fact that as the car is accelerated to higher speeds, it requires more applications of force to get the same acceleration. It's easier to accelerate something from a standstill than it is at 200kmh. I don't see that anything is changed because of the query you pose though, acceleration in the next gear is still lower than current gear at same rpm, so even though current gear is not accelerating as fast as it's 'peak' it can still be more than the next gears 'peak'.

Quote from Blowtus :

gearing multiplies torque though - you don't get as much acceleration at 4000rpm in 5th gear as you do in 4th.

I realize that, which is why I noted originially that there is no "next gear" so the fact remains the max acceleration for the given gear occurs at peak torque, and the acceleration in top gear will follow the torque curve. I can't stress this enough - for the GIVEN ratio this is true. Changing the final gearing changes the torque multiplication just as you said. edit: so it really might depend on the engine's characteristics after all...

Quote :

More force does equal greater instantaneous acceleration - but if you apply a slightly smaller force much more often in a given time period, you accelerate the object more.

I pondered this too, and still do, but the problem is that a dyno for example is not measuring each combustion and giving you sum of the generated forceS (plural), it's taking the net total force acting on the dyno - which is essentially the difference between the sum of all the explosions, and the timespan where no force is applied between each firing. Subtle difference, but still true - it's therefore giving you the value of a theoretical constant torque. At least that's the way I see it; could be total crap I guess.