proper drive ratio

[hoba]

i want to know how to determine the proper drive ratio that wont make the rear wheel spinning to avoid losing time in the events
http://fsae.com/groupee_common/emoticons/icon_confused.gif

[hoba]

i want to know how to determine the proper drive ratio that wont make the rear wheel spinning to avoid losing time in the events
http://fsae.com/groupee_common/emoticons/icon_confused.gif

[Xeilos]

Calculation. Its pronounced calculations.

[dbsharp]

I used tire the data to estimate the amount tractable torque the tires would produce. If you know how much torque the engine produces, it is a simple calculation to find what ratios will not exceed the tractable torque of the tires.

That said, I expect to spin the tires in first gear with the sprocket ratio I selected.

I'm on a first year team, a lot of what I have determined is based off speculation, and my collective experience in motor sports up to this point..... don't rely on my "guess"

[Xeilos]

Carroll Smith provides a good treatsie (in TUne to Win if my memory serves correctly) for gear ratio calculation albeit at a very un-technical level. It is one place to start and do gear ratio calculations if you are short on time or are lacking technical expertise.

If you want to get more technical, you can do create a tractive force diagram from your torque curve, rolling radius and wheel speed. RET-Monitor has a short two article blurb on this and should get you started in addition to the usual Google search. If you have tyre data, you can estimate (with appropriate coefficient scaling factors) the maximimum tractive force you can generate at the wheels. Lastly, you will need to estimate your top speed (in which event, I will leave up to you) to determine a lower limit on you final drive ratio.

[Sormaz]

If you don't want the rear wheel spinning, I would suggest a final drive of 0.

That way, you won't lose any time, in fact you will get it all!

[hoba]

thx alot

[JDS]

The proper ratio to avoid spinning the rear wheels is traction and launch control. http://fsae.com/groupee_common/emoticons/icon_wink.gif In all seriousness though, if you are trying to design your gear ratios such that your rear wheels cannot spin, then you will have no chance at achieving maximum acceleration.

[hoba]

then how i design it to have the maximum acceleration

[Edward M. Kasprzak]

hoba, you're coming at this from the wrong direction. It's not the gear ratio that makes a tire "spin". Instead, it's an unbalanced torque at the rear wheels. In its simplest form, the torque balance compares engine torque at the wheels with the torque produced by longitudinal tire force acting at a distance from the wheel center.

I suggest understanding what your (or any) engine torque vs. engine speed curve looks like, and then do the calculations to transfer this torque to the wheels. Be sure to use several different gear ratios to see the gearing effect. To learn more about what tires can do, research "tire friction coefficient" and "slip ratio". Note that you seldom directly control the slip ratio of a tire.

For more help, follow the advice given by dbsharp and Xelios above.