Your Perfect Shift Point (by Red94Vette)
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Racer
Joined: Aug 2000
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From: Houston, Texas
Your Perfect Shift Point (by Red94Vette)
I will try to make this as simple as possible to understand. Here we go.
Forget about the "whole area under the curve" and forget about horsepower peak for this little short discussion.
What are we trying to do when we race? Bottom line, we are trying to maximize our acceleration at any point in time. Period. It can't get any simpler than that.
We have several gears to select from while we race, do you think we start in 1st just because it's the 1st gear? No, 1st happens to give us the most acceleration at the start of the race. So, when is the right time to abandon 1st gear and jam it into second?
The answer is simple. When 1st gear fails to give us the most acceleration at a point in time.
The point when to shift is when the combination of the gearing in the next gear plus a raise in engine torque output out accelerates your current gearing with a falling torque curve (lower torque).
Pretty simple really. But when is that point exactly? Is it at your HP peak? Is it 500 RPM or 1000 RPM after HP peak?
The answer is, it depends on your gear ratio spacing and the shape of your [b]torque curve[b/]. That's it.
Here is a graph of the acceleration in a high 11 second M6 vette.
The perfect shift point is when the acceleration in the current gear equals the same acceleration in the next gear. If you keep accelerating in the current gear, you will notice the line falls below the acceleration of the next gear. Well, that defeats our whole purpose of trying to accelerate the hardest at any time.
The shift point in this case is 6400 RPM from 1st to 2nd gear. The motor makes max Hp at 5500 RPM.
Here's a simple way to determine your shift point.
Take your current engine torque at an RPM and multiply it by the 1st gear ratio and save that answer.
Now take that RPM and multiply it by the 2nd gear ratio and divide it by the 1st, that is your new RPM if you shift. Now, look up on your torque curve the torque at that new RPM. Multiply that new torque value by the 2nd gear ratio. If that value is equal or greater than your first value that you saved previous then you should have shifted, meaning you would accelerate faster in 2nd gear vs 1st gear.
Remember it all falls back on trying to accelerate at your maximum rate at any time during the race.
I'm sure some of you already knew this or knew it but couldn’t explain it, but I wanted to help the others that are confused on this issue of shift points. You usually shift past your HP peak but it ultimately depends on two things, the shape of your torque curve and gear ratio spacing not peak power.
The End.
Forget about the "whole area under the curve" and forget about horsepower peak for this little short discussion.
What are we trying to do when we race? Bottom line, we are trying to maximize our acceleration at any point in time. Period. It can't get any simpler than that.
We have several gears to select from while we race, do you think we start in 1st just because it's the 1st gear? No, 1st happens to give us the most acceleration at the start of the race. So, when is the right time to abandon 1st gear and jam it into second?
The answer is simple. When 1st gear fails to give us the most acceleration at a point in time.
The point when to shift is when the combination of the gearing in the next gear plus a raise in engine torque output out accelerates your current gearing with a falling torque curve (lower torque).
Pretty simple really. But when is that point exactly? Is it at your HP peak? Is it 500 RPM or 1000 RPM after HP peak?
The answer is, it depends on your gear ratio spacing and the shape of your [b]torque curve[b/]. That's it.
Here is a graph of the acceleration in a high 11 second M6 vette.
The perfect shift point is when the acceleration in the current gear equals the same acceleration in the next gear. If you keep accelerating in the current gear, you will notice the line falls below the acceleration of the next gear. Well, that defeats our whole purpose of trying to accelerate the hardest at any time.
The shift point in this case is 6400 RPM from 1st to 2nd gear. The motor makes max Hp at 5500 RPM.
Here's a simple way to determine your shift point.
Take your current engine torque at an RPM and multiply it by the 1st gear ratio and save that answer.
Now take that RPM and multiply it by the 2nd gear ratio and divide it by the 1st, that is your new RPM if you shift. Now, look up on your torque curve the torque at that new RPM. Multiply that new torque value by the 2nd gear ratio. If that value is equal or greater than your first value that you saved previous then you should have shifted, meaning you would accelerate faster in 2nd gear vs 1st gear.
Remember it all falls back on trying to accelerate at your maximum rate at any time during the race.
I'm sure some of you already knew this or knew it but couldn’t explain it, but I wanted to help the others that are confused on this issue of shift points. You usually shift past your HP peak but it ultimately depends on two things, the shape of your torque curve and gear ratio spacing not peak power.
The End.
