Transmission made simple

Discussion in 'GT6 Tuning' started by jblackrevo9, Apr 23, 2014.

  1. jblackrevo9

    jblackrevo9

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    How many of you guys out there always wonder why other drivers pass you with ease?

    Most of the time,well actually your problem is that your gears are not set with in the bandwidth of the engine's horsepower and torque!!!

    [​IMG]

    (From Google.)

    Look at the chart above...

    You have a scale of 0 to 7000 rpm. Notice that most of the power is near/at 7000 rpm with a slight decrease at 7000 rpm. Your goal is to set your gear close to the maximum revolutions per minute (rpm).
    In this example, the FIT RS 2010 puts out 117 hp and 107 pounds or torque.

    To achieve the this vehicle's most potential. Look at the graph and divide it into 4 equal sections.

    7000rpm / 4 = 1750


    Now you know that 1/4 of 7000 rpm is 1750.

    Look at the graph again. Pay close attention. To make it easier, take a pencil and use that to have a good guide of the four equal sections.

    Again, most of the engine's power is near 7000,therefore you need to have your gear within its power. Pay attention to where your engine's hp and torque meet. That should be your minimum for the lowest point for any gear you prefer to be long or short enough to shift into. Anything below this point and you can severely disturb your momentum.

    (These are just numbers just as example.)


    Take the 1750 you have and subtract it by 7000rpm

    7000 rpm - 1750 = 5250 rpm (Yes I know of the torque/hp meeting but I'm not talking about that.)

    Look at your graph again.

    I hope you guys remember the 4 equally divided sections. If you did this right, you should know that 5250 rpm is almost exactly where the hp and torque intercept. This is the lowest point in the rpm bandwidth. Again, anything lower than this and you will lose your momentum.



    Now that you figured this out, now we can begin set gears.

    [​IMG]
    (From Google.)

    (Notice that in the graph above, the lines are longer. Since they are long, your gear range will be too.)
    [​IMG]

    (From google.)

    (Notice in this graph, the lines are shorter and since they are shorter, your gear range will be shorter.)


    I'm going to make this simple for ya'll.

    The lines above, represent the range for your gears. For example, if the lines are really short, your gears will be in a higher bandwidth.

    Example.

    You have a rpm range of 0 to 10,300 rpm (Rx8 concept bandwidth)

    Shorter gear (short lines) will have you between 8,000 rpm and 10,300.

    Compared to longer ranges (longer lines) that will have you between 5,000 rpm to 10,300.


    For the Fit, your lines need to be shorter in order to be with in the vehicle's peak performance.

    [​IMG]

    Look at the example above.

    Look at the tachometer. You see the number 5 and 7 (which is in the red line). That is your bandwidth and where your gears need to shift within. Again, anything below 5, will have you shifting below, causing the car to under perform when accelerating.

    When you have your gears set, you can increase the car's acceleration by moving the Final gear ratio to the right when your gears are set.


    Do not change gear after increasing acceleration or decreasing ( unless you car's peak performance has changed, then you will need to find the bandwidth again), if you do this, you can mess up your vehicle's momentum.


    I hope I made this simple for you guys.

    Feel free to shoot me some questions.

    You know the name....Jblackrevo9 (see you online)
     
    Last edited: Apr 24, 2014
  2. SiNS3V3N

    SiNS3V3N (Banned)

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    5252rpm is the crossover on all cars. It's a product of how hp is calculated.

    (TQxRPM)/5252 = hp

    It's not clearly marked in GT6 but it's the same on all cars hp and tq cross at 5252rpm

    I think your thinking of peak torque instead. That's what you don't want to fall under when shifting.
     
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  3. jblackrevo9

    jblackrevo9

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    That's not what I've explained. I talking having the gears shifting within the bandwidth.

    5250 is just a coincidence, I do apologize if I mislead you.

    All cars do not cross at 5250 rpm. They cross at various rpm.

    Example: Take a look at the graph of a tuned nissan skyline, the torque and horsepower crossover way before 5250rpm.
     
  4. oppositelock

    oppositelock

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    This is actually false. Horsepower = torque * RPM / 5252. Assuming we're using horsepower and pound-feet as our measurements, it is mathematically impossible for them to cross at anything other than 5252. If they don't, then either the torque and power curves are being graphed at different scales or they're using different measurements such as kilowatts and newton meters.

    Back to the main subject, the chosen "powerbands" in your examples seem kinda arbitrary. Why is it the top fourth of the rev range, rather than the the top third or top fifth? Why is the optimim rev range for a Honda Fit between 5000 and 7000? I understand that you're saying you want close gear ratios to keep the revs up, which is true, but there's no actual mathematical calculations going on here. This could confuse people more than it helps, unfortunately.
     
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  5. Motor City Hami

    Motor City Hami

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    That wasn't all that simple. I am still lost on transmissions. I have read all of the transmission guides and still don't quite get it. I have always used the flip trick and tried to optimize launch vs. wheel spin off of 2nd and 3rd gear corners.

    When I see explanations like this or @praiano63 I feel like I may be leaving some speed on the table, but can never quite figure out how to get there.

    Can someone make this really simple and tell us how to set each gear within the rev range. And, maybe show some results? How much time gain can you get with this method over others? I honestly have not studied the transmission too much other than trying to get 2nd and 3rd gear right.
     
  6. jblackrevo9

    jblackrevo9

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    I agree with you, that is true but I'm pretty sure you took the 5250 and thought I was talking about that, the numbers were just examples. Yes not all cars will be able to start at that shiftpoint. It is supposed to be used as a guide so that you that within the perimeters of the torque and horsepower bandwidth.


    Use test course. When shortening the gears or making them longer, pay attention to where the gears are shifting.

    Trust me, this works, I always watch other driver's car jolt because one of their gears shift out of the bandwidth or powerband as other may call it.

    Having dividing it in to 4 equal parts help me stay focused on where my gears need to be.

    Like I said, cars will perform best depending on where their curves are.Here is an example.

    (Again I apologize about that 5252 or 5250 is a coincidence. I happened to calculate that when substracting, and never talked about these formula with this set of numbers but I just happened to get this as a result.)

    "Horsepower = speed (RPM) x torque (ft-lbs) / 5252

    To find the horsepower at any given RPM, multiply the torque at that RPM by the RPM, then divide by 5252. This will generate a horsepower curve by calculating the horsepower at various RPMs. Find the peak of this curve (the highest horsepower number), and that is the horsepower rating of the engine. Depending upon the torque curve of the motor, maximum horsepower may occur at low or high RPM. Generally it is near the maximum RPM of the engine."
     
  7. killerjimbag

    killerjimbag

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    What?
     
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  8. DolHaus

    DolHaus

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    I'm still not entirely sure what horsepower does lol I understand the basic principals and how its worked out, but how it applies baffles me.
     
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  9. jblackrevo9

    jblackrevo9

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    [​IMG]

    Look at the tachometer. Lets say redline is at 8100 rpm, your torque and hp meet at 5900rpm. Have your gears shift between 6000 and 8100rpm. To do this, your gears must be short ( shorter lines in the transmission graph).
     
  10. rams1de

    rams1de

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    From what I gleaned reading the stickied torque thread, the aim should be to achieve the highest average bhp (or whatever power unit your game shows) from your power band.

    What that amounts to depends on the power curve, the torque curve being redundant at this point. A typical power curve will increase steadily through the rev range until reaching a peak before falling off, like the FIT in the OP which peaks at 6500rpm and falls away thereafter.

    I have an RX-7 which has a slightly different power curve, reaching 404 bhp at 7100rpm, looking at the graph it falls away to something like 325 bhp at the redline, 8100rpm.

    You get an idea from the pic

    [​IMG]

    Because it forms a relatively constant umbrella like shape towards the peak, it's a good example to make a few guesstimations of numbers from the graph to go with the figures provided by PD in the garage and on the speedo.

    From the graph let's assume the following power figures:

    325bhp at 8100 redline
    365bhp at 7600
    404bhp at 7100
    365bhp at 6600
    325bhp at 6100
    285bhp at 5500

    Without calculations but from looking at those numbers the car will produce higher average power between 7100 and 8100rpm than with a power band from 5500 to 8100rpm. Similarly, it will produce higher average power if the band falls between 6600 and 7600rpm and if the power band is between 7100 and 7600rpm.

    The pic shows the gear ratios of a FC Transmission with only max speed adjusted. Changing through the gears, the RPM drops to create the lower end of your power band, the top being your chosen shift point. I think we've established that shifting at 7600rpm (365 bhp) will mean the engine is operating at higher average power than if continuing to redline (325bhp) where the power is falling off.

    This table shows the RPM after each gear shift on the above transmission

    1-2 5500 (giving power band 5500-7600 shift point)
    2-3 6100
    3-5 6100
    4-5 6500
    5-6 7000

    Using the same final gear as the starting point and applying the tranny trick to produce a close ratio transmission produces the following table

    1-2 7000 (power band 7000-7600 shift point)
    2-3 7000
    3-5 7000
    4-5 7000
    5-6 7000

    You can see the second transmission will provide more average power throughout the lower gears resulting in faster acceleration without reducing top speed.

    On a rolling start this method could easily equate to over a second per lap (haven't done a comparison on this car, sorry). For online racing the first gear may be too long causing the car to bog down and that advantage can be lost on the grid.

    I think this is the point the OP is trying to get across.
     
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  11. jblackrevo9

    jblackrevo9

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    I'm glad that you understand what I'm talking about.

    Yes I am but I hope they understand this too.
     
  12. jblackrevo9

    jblackrevo9

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    "Horsepower is what pushes, pulls, shoves, or drags our rides through the friction-filled world. If we want to go faster, it takes more horsepower. If we want to go slower, it takes less horsepower." - Harold Bettes, SuperFlow

    Read more: http://www.hotrod.com/techarticles/hrdp_0401_torque_horsepower_guide/#ixzz2zp6yYkTX


    Check out this link to understand torque and horsepower

    http://www.youtube.com/watch?v=fgLNO3ThGD4
     
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  13. killerjimbag

    killerjimbag

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    Don't believe what PD programmed into tranny's and equation to HP.
     
  14. Motor City Hami

    Motor City Hami

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    I'm sorry. I still don't understand what to do. The title of this thread is "Transmission Made Simple." Posts containing 460+ words is not looking all that simple to me.

    I will be honest. I know how to make a car go around a corner fast, but I kind of have a set it and forget it mentality to the transmission. I am always willing to learn more about going faster, but you've lost me.

    So what is step 1? Finding these numbers?

    How did you get to this list of numbers? Did you try to estimate the distance across the graph in the lower left corner to get to approximate bhp and rpm intersections? So there is a bit of guesswork and estimation in there, right?
     
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  15. DolHaus

    DolHaus

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    Yeah I knew that stuff but I just find it hard to figure out what HP actually does. Torque is easy to understand, its just twisting force essentially, bigger the number harder it turns. What I struggle to quantify is how HP affects things, a motor works by way of rotation (torque) so what other forces is it producing?
    (both of your links go to the Hotrod page btw)
     
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  16. rams1de

    rams1de

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    Yes thought I'd explained, the bhp and rpm figures are guesses taken from the graph to help illustrate what average power might be.

    The RPM figures for gear changes were taken from a couple of brief runs through the gears on Route X while watching the rev counter. Rounded for simplicity.
     
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  17. jblackrevo9

    jblackrevo9

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    Yes, and this is why I asked that you go to test course or route X to watch the rev counter like rams1de said. So that you will know the powerband or bandwidth of where the gears need to shift.
     
  18. jblackrevo9

    jblackrevo9

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    I apologize, the second one was suppose to show you video:

    here:


    A car with a lot of torque doesn't necessarily have difficulty in turns. It depends on how you tune your LSD that will affect the ability to turn.

    Horsepower get your car accelerating, moving around. The more horsepower the faster you will move but a vehicle with more torque will move faster with horsepower.
     
  19. DolHaus

    DolHaus

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    Interesting video, makes sense as far as I understand things.

    Slight misunderstanding, when I said "the harder it turns" I meant it rotates (the flywheel) with more force.

    I understand the maths of it but I just don't understand how HP applies terms of force. Does it do the same thing as torque (rotational force)? Does it allow the engine to Rev higher somehow?

    You don't have to answer if you don't want to, I'm just curious is all
     
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  20. SiNS3V3N

    SiNS3V3N (Banned)

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    @DolHaus

    Torque is the power moving the car

    Hp is a representation of the torque being used over a period of time (rpm)

    Acceleration is greatest at highest torque, slowest after highest hp.

    Modern engines with variable valve timing and digitally controlled boost can flatline torque. Example the Bugatti Veyron has 900ft-lb flat from peak to fall. It's Acceleration is steady.
     
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  21. GTP_CargoRatt

    GTP_CargoRatt

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    I am with Hami here. Several people have tried to explain it to me but I am still not getting it completely. A step by step guide, with illustrations, would really help. Maybe if I gave you the specs of the car I am working on now and you walk me through the trans setup, I might be able to wrap my head around it.

    Just quoted you Keith as I am looking for the same answers as you.
     
  22. killerjimbag

    killerjimbag

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    What car are you setting up? Give me the setup your driving I'll make you a tranny.
     
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  23. GTP_CargoRatt

    GTP_CargoRatt

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    Ok, give me a few hours and I'll post it in Jordans tuning database as its for the Seasonal TT at Eiger. No hurry Killer, just whenever you get a minute. I might even have it right, who knows. :dunce: I'm sitting in 11th place atm on the leaderboards so maybe this monkey got something right, Lord knows its not my driving that got me there. :lol: Even a blind squirrel finds a nut once in awhile. :lol:
     
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  24. SiNS3V3N

    SiNS3V3N (Banned)

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    @rams1de

    You seem like your looking for optimum shift points with your post, not actually tuning gears. You're looking to find a shift RPM which brings you back to the same point on the power curve (power is the same before and after shift, called "straddling" the curve), and shifting so that you maintain the maximum area under the curve.

    It's better done with the torque curve as your acceleration curve mirrors the torque curve. This is stuff we do for drag racing to keep the car accelerating at the highest rate.

    That okay for calculating shift points, but the torque data needs much more details and without it being VERY precise it is near impossible to do guestimating the exit and entry power figures. Especially with the graphs PD gave us. We can roughly get an idea, just not very precise and the point being precise power matching.

    That is the right idea for shift point calculating, once done correctly it usually has each gears shift point at a different rpm.

    Your calculations are incorrect finding the rpm you arrive at when shifting, I'm not sure where you get those numbers maybe watching the tach while you drive ? Here is the equation that will get you the exact numbers.

    """This table shows the RPM after each gear shift on the above transmission"""

    CORRECTED

    (7600shift)

    1-2 5119rpm
    2-3 5550rpm
    3-4 5822rpm
    4-5 6100rpm
    5-6 6408rpm

    These are the actual rpm you will grab at if shifting at 7600rpm, using the gears in the pic. I would need the gears to figure out your second set, but doubtfully all gears grab at 7000rpm from a 7600rpm shift.

    This might help

    To figure out what rpm the next gear grabs after a shift here is the formula.

    ( New Gear / Old Gear ) x shift rpm = entry rpm

    ( 2.002 / 2.972 ) x 7600 = entry rpm

    0.67362 x 7600 = entry rpm

    Entry rpm = 5120

    Repeat for all gear shifts.


    To jblackrevo, (is that Traxxas Revo? I have 3 Revo's) very sorry but your "method" is NOT talking on what rams1de's post is bringing up. His post touching on optimizing shift points and I guess trying to tune the gears to shift points?? Please don't get offended. Your method makes no sense to me, your math is incorrect and you use values that are not relevant.

    I couldn't find anything on his second set of gears using the "tranny trick" because he said with the same final gear. I like to see them before talking on them. I don't believe gears all grab at the stated rpm, the math of the second example I have to question as it was incorrect in the first example.

    @rams1de
    What are the gears ratios of the second set you used the tranny trick to get? I can calculate the actual rpm after a shift and to speak on your example they are required
     
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  25. alexamenos

    alexamenos

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    I'm with Hami and CargoRatt.

    I think a practical and sensible way to test gearing is to run IMS and clock 60-120 times (or 80-160....something that takes you from 2nd into 5th) for various transmission setups each with the same 6th gear ratio. I'd suggest a good benchmark would be to set the gears via the max speed slider and then attempt to beat that setup. Point being if you can't beat times from a gear setup that takes no thought or effort, you ought to be putting thought and effort into something other than gear tuning.

    I've done exactly this with a couple of cars and so far I've only been able to find very very modest gains and those gains have come simply by setting all gears via max speed and then reducing gears 1 & 2 and maybe 3 just a tad, strictly by sight and feel.
     
  26. alexamenos

    alexamenos

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    So...new gear = Old Gear x Entry RPM / Shift RPM...

    ...if I'm shifting at about 8250 rpm, my 2nd gear is 2.100, and I want my entry RPM for 3rd gear to be 6500 rpm, then...

    3rd Gear = 2.100 x (6500*8250) = 1.655

    Correct?
     
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  27. SiNS3V3N

    SiNS3V3N (Banned)

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    Sorry, yes your reversing the equation, that is correct. Nicely done.

    To reverse the equation (as it appears that is what your doing)

    ( Entry rpm / shift rpm ) x old gear = new gear
     
    Last edited: Apr 25, 2014
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  28. rams1de

    rams1de

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    @SiNS3V3N thanks for the explanation how to calculate entry RPM.

    I think you've missed the point of my post, my fault for not being clear enough.
     
  29. SiNS3V3N

    SiNS3V3N (Banned)

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    I think your point is clear and as far as calculating optimum shift points your right there, our prob is PD with those near useless graphs. Makes it hard for us to see figures that are not peak numbers.

    Don't ignore torque

    The rate of acceleration across the rpm's mirrors the torque curve, so highest acceleration is at peak torque, not peak hp. Important factoid.

    I can't speak on your second set of gears as they are not posted, that would be helpful.
     
  30. alexamenos

    alexamenos

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    OK....I think what we're talking about here is a conservation of momentum kinda thing.

    The teeth on gear two (for instance) are moving at a speed proportional to the RPMs x circumference of Gear 2. When we shift into Gear 3, the teeth on Gear 3 must be moving at the same speed as they were on Gear 2 (because the drive gear hasn't changed speeds notably).

    So,

    Circ (2nd Gear) x RPM (2nd Gear) = Circ (3rd) x RPM (3rd)

    This equation must be true....except for when its not like when you accidentally shift down into first gear while going 95 mph. But this conservation of momentum is going to hold true anytime we have a reasonably well timed shift. (all this is in fact confirmed by wikipedia, which means it must be true)

    Allowing for a little algebra...

    Circ (2nd) / Circ (3rd) = RPM (2nd) / RPM (3rd)

    Now I can go out on a track and fool around in 3rd gear for a bit and get a good feel for when 3rd gear really kicks in...let's say, 6k rpm. If I'm redlining at 8k rpm, then I know my ratio of 3rd gear to 2nd gear ought to be about 6k / 8k, or 0.75. If on the other hand acceleration doesn't kick in until around 7000 rpms, then I want my 3rd gear to be 7k / 8k, or about 0.875 x 2nd gear circumference.

    One question remaining is whether gear in GT represents a diameter or circumference, but I think I can figure this out by playing with it a bit. This will change the math a bit but the principle is the same.
    --------------------------
    on further reflection this ^^^ isn't quite right...but on the right track for using desired rpm to set gears rather than setting gears to try to hit desired rpm
     
    Last edited: Apr 25, 2014