Gear Ratios

Discussion in 'GT2 Settings & Tunings' started by Talentless, Apr 23, 2002.

  1. Talentless

    Talentless Staff Emeritus

    Messages:
    10,081
  2. troy1

    troy1

    Messages:
    306
    Very nice explaination
     
  3. Shemsi

    Shemsi

    Messages:
    48
    goood job!
     
  4. Monouk

    Monouk

    Messages:
    130
    this stupid comute wont let me load that page for the gears. If someone can get a different host, or post it here or somthng it would help me alot.
     
  5. Option2

    Option2

    Messages:
    786
    Talentless
    Racing Line passer by


    Joined: 10 Aug 2001
    Posts: 9

    Posted: Fri Aug 10, 2001 6:13 pm Post subject:

    --------------------------------------------------------------------------------

    One of the common tips is to have the first two gears close in numbers and shorter and the rest wider apart, but that oversimplifies and is worthless if your car is already more powerful and you are not worried about a good start, plus you may not need 2nd or 1st for the remainder of a race, but if you spin out it is good.

    Now the biggest factor with acceleration is how short the gearing is, but, if I am not mistaken, too short of gears tends to multiply too much torgue to the drive wheels.

    If your gearing reads as the following:

    3.098
    2.004
    1.766
    1.453
    Final Drive: 3.009

    Then changing the final drive ratio to 3.6 would be changing that gear, at least to a shorter gear.

    That change would potentially improve acceleration and definitely decrease top speed.

    The positives of shorter gearing our acceleration and that they tend to restrict how far back the needle travels which means there is less time until the needle gets back to the next shift point.

    The disadvantage is top speed and that it may not do well for torgue, torgue peak may be below the lowest mark the needle goes to.

    Top speed is acheived when gearing is numerically lower all around, but in some cars there is not sufficient power to accelerate to a speed, so compromise is needed.

    A balance between short and tall gearing is the key.

    Now the advantage to tall gearing is that it tends to increase the range you can adjust your gears to and may be better for some low speed corners where you want to be able to take advantage of low-end torgue. But the time waiting for the needle to travel costs time.

    I think the gearing can effect handling, cars tend to have handling problems with some final drive ratios.

    I prefer tall gearing myself.


    You can calculate how far back approximately the tach needle will travel by dividing the previous gear ratio into the current gear and multiplying that by the shift rpm. So if you shift from 1st to 2nd, 2 and 1 respectively: 1/2=0.5 times 8000 (the rpm you upshifted at)= 4000, which is about how far back the needle will go.

    You can also estimate your tire size.

    1. Choose a car.

    2. Choose a course with a level straight.

    2. Choose a gear that will allow you to accelerate but slowly.

    3. Choose an rpm and not the rpm, speed at that rpm and the gear you are in.

    4. Now do the following.

    Multiply the the final drive ratio, top speed, gear you were in together and times that by 88. Divide the total by the rpm, this will give you the tires circumference, save that number.

    Let's say you want gearing that will give you 150 mph in 6th gear at 5000 rpm.

    To do this you need to know the tire size, final drive ratio and 6th gear ratio

    Final drive: 4
    6th gear: 0.8
    Tire: 6.75 cu ft (I think it's in cubic ft?)

    Multiply 6.75 by the rpm

    6.75 times 5000

    33750

    divide that number by the sum of the speed you want times 88

    150 times 88

    33750/ (150 * 88 )= approx. 2.557

    If you divide 2.557 by the final drive ratio, it will tell you what 6th gear needs to be, if by 6th gear it will tell you want the final d needs to be.

    2.557/4=0.63925
    2.557/0.8=3.19625

    It is also a good idea to try to set the gears so that you will be in the power range with the speed you are at.

    You do not want to be taking a turn at 90 mph and have the optimum range be, say from 5000=7500 rpm, and you are either at 8000 or 4000 and the power is too low.

    Of course experiment.

    I hope this helps you out, Fox.

    <font size=-1>[ This Message was edited by: Talentless on 2001-08-10 18:16 ]</font>

    food for thought.

    let's assume you have an imaginary gearbox. 6 spd. lessay the #s are ::

    1st - 5.000
    2nd - 3.000
    3rd - 2.000
    4th - 1.500
    5th - 1.250
    6th - 1.000

    with a final of 4.000

    i want to keep the mph-per-gear the same, and adjust the final drive both of two ways. i want one to have a final of 2.500 and the other to have 5.500.

    so my other two gearboxes will be ::

    2.500=8.000, 6.000, 3.200, 2.400, 2.000, 1.600
    5.500=3.636, 2.182, 1.455, 1.091, 0.909, 0.727

    if you take these three gearboxes into the 0-400m/0-1000m tests, it is likely that you will find the 2.500 gearbox beats them - more likely in 0-1000.

    there're two factors to consider for the 'why' - as each gear can produce identically the same mph per gear.

    1 - the 2.500 gearbox , during acceleration , gives more responsibility to each RPM for mph. said better: there is a great difference in MPH for a subtle difference in RPM. -- the 5.500 gearbox , for each gear in accel , has to traverse much more RPM than the 2.500 does - for precisely the same range of MPH. this is all important due to powerbands, and their general trend to want to be narrow, rather than broad and universal. thus, with a 2.500 gearbox, you're spreading out the time you're in a narrow range of RPM, thus the potential exists to 'stay' in the powerband, whereas with the 5.500 gearbox the potential exists to need to first get into the powerband, and then you end up passing right out of it again ( due to the traversal of RPM happening quickly ).

    2 - same basic point, but from a different angle. GT2 doesn't *really* seem to care about this, but if you think of your car and its manual transmission, it can be clear to you. consider again the 2.500 and 5.500 gearboxes in the same car. redlight. there's a yellow mustang GT convertable next to you, and some panama jack wearin' barbeque master is smiling from behind his $2.oo walmart shades as his girlfriend gets wet to the bark-tearing thunder of his purpose-crafted four-point-six litre v8 as he instigates the throttle. you're next to him in your car of choice. he wants to run, he feels that it will at least earn him a bj if he can smoke everything he encounters on his way to dropping her off at the bookstore. greenlight. ok, you're in first, you're on the gas, traa la la.... ok, you're now at 6500 rpm. ok, goto 2nd gear. in the 2.500 gearbox, good chance that 2nd gear wants to spin at ~4000 rpm for the current MPH, but the 5.500 gearbox would want to spin at ~2300 rpm for precisely the same MPH. this is going to not only suck for your powerbandness, but will also make your car buck like a fiend as you obliterate 4000 rpm the engine was used to with a single twitch of the heel. if you were being *polite* to the transmission assembly at large, and waited for the tach to indicate a fall down to said 'correct' 2300 rpm, you'll be waiting a *lot* longer than if the tranny only had to fall down to 4000, eh?.

    so there're two arguments for using the *lowest* possible final drive for any given transmission setup ( given the overall total engine:to:wheel ratio is retained ).

    you might find that many times in GT2, it favours a low final drive. one example that you can feel quite easily is with the LSD. it's always good fortune to have that result.... anyhoo, with a low final drive, the LSD seems *much* more proactive at high RPM - whereas with the high final drive, said high RPM will deliver a much more relaxed LSD. so basically, don't forget to adjust your LSD after your severely adjust your gear ratios.

    the LSD takes a good few years to really 'master' in GT2, or even simply get the hang of, but it's well worth experimenting with, as long as you keep your eyes open for the empirical data to come wafting by.
     
  6. Talentless

    Talentless Staff Emeritus

    Messages:
    10,081
    not all of those comments are mine.
     
  7. Talentless

    Talentless Staff Emeritus

    Messages:
    10,081
    this much is mine.


    One of the common tips is to have the first two gears close in numbers and shorter and the rest wider apart, but that oversimplifies and is worthless if your car is already more powerful and you are not worried about a good start, plus you may not need 2nd or 1st for the remainder of a race, but if you spin out it is good.

    Now the biggest factor with acceleration is how short the gearing is, but, if I am not mistaken, too short of gears tends to multiply too much torgue to the drive wheels.

    If your gearing reads as the following:

    3.098
    2.004
    1.766
    1.453
    Final Drive: 3.009

    Then changing the final drive ratio to 3.6 would be changing that gear, at least to a shorter gear.

    That change would potentially improve acceleration and definitely decrease top speed.

    The positives of shorter gearing our acceleration and that they tend to restrict how far back the needle travels which means there is less time until the needle gets back to the next shift point.

    The disadvantage is top speed and that it may not do well for torgue, torgue peak may be below the lowest mark the needle goes to.

    Top speed is acheived when gearing is numerically lower all around, but in some cars there is not sufficient power to accelerate to a speed, so compromise is needed.

    A balance between short and tall gearing is the key.

    Now the advantage to tall gearing is that it tends to increase the range you can adjust your gears to and may be better for some low speed corners where you want to be able to take advantage of low-end torgue. But the time waiting for the needle to travel costs time.

    I think the gearing can effect handling, cars tend to have handling problems with some final drive ratios.

    I prefer tall gearing myself.


    You can calculate how far back approximately the tach needle will travel by dividing the previous gear ratio into the current gear and multiplying that by the shift rpm. So if you shift from 1st to 2nd, 2 and 1 respectively: 1/2=0.5 times 8000 (the rpm you upshifted at)= 4000, which is about how far back the needle will go.

    You can also estimate your tire size.

    1. Choose a car.

    2. Choose a course with a level straight.

    2. Choose a gear that will allow you to accelerate but slowly.

    3. Choose an rpm and not the rpm, speed at that rpm and the gear you are in.

    4. Now do the following.

    Multiply the the final drive ratio, top speed, gear you were in together and times that by 88. Divide the total by the rpm, this will give you the tires circumference, save that number.

    Let's say you want gearing that will give you 150 mph in 6th gear at 5000 rpm.

    To do this you need to know the tire size, final drive ratio and 6th gear ratio

    Final drive: 4
    6th gear: 0.8
    Tire: 6.75 cu ft (I think it's in cubic ft?)

    Multiply 6.75 by the rpm

    6.75 times 5000

    33750

    divide that number by the sum of the speed you want times 88

    150 times 88

    33750/ (150 * 88 )= approx. 2.557

    If you divide 2.557 by the final drive ratio, it will tell you what 6th gear needs to be, if by 6th gear it will tell you want the final d needs to be.

    2.557/4=0.63925
    2.557/0.8=3.19625

    It is also a good idea to try to set the gears so that you will be in the power range with the speed you are at.

    You do not want to be taking a turn at 90 mph and have the optimum range be, say from 5000=7500 rpm, and you are either at 8000 or 4000 and the power is too low.

    Of course experiment.

    I hope this helps you out, Fox.
     
  8. misnblu

    misnblu Staff Emeritus

    Messages:
    2,312
    As Ive said many times in the past two years, thank you Talentless for your genius.
    :)
    Misnblu
     
  9. Talentless

    Talentless Staff Emeritus

    Messages:
    10,081
    Nice of you to say, but that was not genius. It's knowledge.
     
  10. hsrdragger

    hsrdragger

    Messages:
    469
    Hail, Talentless!
    The Allmighty GearHead!:lol:
     
  11. orpheusd0wn

    orpheusd0wn

    Messages:
    94
    bump
     
  12. Korndawg

    Korndawg

    Messages:
    380
    ooh i love tech info like this. :dopey:
    might take me an hour or so to fully understand it tho lol :dunce:
     
  13. TMM

    TMM

    Messages:
    1,203
    Location:
    England
    You and me both...
     
  14. sucahyo

    sucahyo

    Messages:
    2,171
    I notice that using lighter flywheel can increase acceleration time, and using lower final gear have the same effect as using lighter flywheel
    and using short gear (i don't care if the wheel spinning in low speed) I can easily win any race with lower power to weight ratio cars.
    winning using Nissan skyline GTS4 in tuned turbo no1 cup race 1 or 3 is fairly easy.
     
  15. Jmac279

    Jmac279

    Messages:
    960
    Location:
    Canada
    It's needlessly complex, IMO, but whatever works ...

    Physics suggests a much simpler approach that makes a little more sense ...