Gearing calculation
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Compare your gear-ratio
In order to determine the right gearing in relation to the choosen pignon and tyre-height fill out this form and check the percentage.
  Select pignon Select main gear Select tyre diameter
Reference ratio
Your ratio
       
Percentage
0.00%
 Fill out the form and press calculate  

General
Normally, within the standard package of every Plafit assembly kit a pignon with 10 teeth and a main gear with 34 teeth is delivered.
When you want to setup your car for a particular race or track obviously the gearing ratio is major important.

Impact of changing the gear-ratio
Changing the gear-ratio as well as the tyre-height do have impact on the following variables:

  • Straightline speed
  • Acceleration
  • Response of the car
    • (This is closely related to the power-band of the engine. Just as a normal gasoline engine has a specific torque range where the engine delivers the most torque/power.)

    Which gear-ratio do I need?
    This depends on a lot of things but let's try to get an idea of what happens here.
    First you have to drive the car round the circuit to get a good look and feel of the car. If the car feels slow coming out of the corner hitting full throttle, you might consider increasing the main gear with 1 or 2 teeth.

    On the straights it's important that the engine has time enough to rev up to it's maximum. Just listen to the sound. If you feel it's not getting there, again increase your main gear with 1 or perhaps 2 teeth and test again.

    If the car is really nervous and reving up fairly quick hitting topspeed halfway the straight, you might consider selecting another pignon. For instance from 12 to 13 or even 14. (Be aware of the fact that the change in ratio is much higher when you switch to another pignon!!).

    Power-band
    Every engine has a specific RPM range in which it delivers the most torque.
    Let's say the maximum torque of an engine is 20 NM (Newton Meter).
    The power-band could be described as the RPM range (let's say: between 12.000 and 18.000 rpm) where the engine delivers 90% of it's maximum torque, with the maximum situated at 16.000 rpm.
    Obviously you will need the exact specs of the engine to make sure what you're doing.

    In pratice it comes down to the general response of the car during 1 complete lap. Any given track consists of straights and corners.
    Obviously the more and longer straights a circuit has, the longer the gearing ratio should be.
    A short track with not that many straights requires a more responsive car to the throttle, therefor needing a shorter gearing ratio.
    It also the depends on the levels of grip you've got. Basically it all comes down to the driver and his car feeling happy with each other.

    Conclusion
    The changes merely describe an indication of how to handle and choose the gearing ratio. Obviously the truth is on the track itself....When the flag drops.............the Bullshit stops!!

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    Presentation
    Short Introduction to the LMS Cars
    Chassis
    Building a Plafit chassis
    Lights
    How to keep 'm burning in the dark
    Gearing
    Calculating the right gear ratio
    Wheels & tires
    Getting grip on the LMS tracks
    Bodies
    Shaping an LMS car