ideal shift rpm
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ideal shift rpm
any mathmaticians or physicists out there that can give a scientific explantion of the ideal shift point?
There is a lot of debate whether to shift at peak rpm, because otherwise power is dropping per rpm, or to change half-the-rpm-gear-change past the peak power point (i.e. peak at 6k, changing gear drops 1.5k, so change gear 750 rpm past peak power) to give the highest average power?
views are welcome, but there must be a scientific point to change and since i only have an "E" in A-level physiscs 5 yrs ago i dont think im qualified
There is a lot of debate whether to shift at peak rpm, because otherwise power is dropping per rpm, or to change half-the-rpm-gear-change past the peak power point (i.e. peak at 6k, changing gear drops 1.5k, so change gear 750 rpm past peak power) to give the highest average power?
views are welcome, but there must be a scientific point to change and since i only have an "E" in A-level physiscs 5 yrs ago i dont think im qualified
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From: Here, There, Everywhere
Have always been told, it's best to shift up once your torque starts to drop, as torque is acceleration. Evo did a STi tune test, and they said the same. No point in hanging onto a gear once the Torque drops.
I might be wrong though
I might be wrong though
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From: Old Codgers Home
You would have thought they would have installed an idiot light to tell you when to change, wouldn't you?? In this day and age 
Or you could just use the good old fashioned ear and brain system which has stood many real drivers in good stead over the years!!
All this useless Mass debating about nowt!!
Pete
Or you could just use the good old fashioned ear and brain system which has stood many real drivers in good stead over the years!!
All this useless Mass debating about nowt!!
Pete
What you need to do is look at the power/torque curves for the engine, and also the overall gear ratios. What you can then do, is work out the torque at the wheels along the rev range for each gear. The gearbox etc is effectively a torque multiplier. Plot these together on a graph, and when the torque at the wheels in a lower gear drops below that of the torque at the wheels in the next gear up, it's time to change up a gear.
What you will find, is that unless the torque plummets at higher revs (e.g. WRC cars with the 32/34mm restrictor), invariably for the absolute fastest acceleration (ignoring things like available traction etc) you will take the car to the red-line in each of the lower gears. For higher gears (ie 4th/5th/6th), you may find that due to the overall gearing that you are better changing up closer to peak power, or at a point where you hit peak torque in the next gear when changing up.
Cars that can produce useable torque at higher revs can take advantage of lower/closer gearing, hence multiplying the torque from the engine more and getting better acceleration. Think of 2nd gear in a typical Impreza, which is capable of getting the car up to the 60 - 70mph range. If the engine could rev to say 19krpm (like an F1 car), then 2nd gear would be good for something like 180mph, and first gear would be good for something like 100mph. In an F1 car, 1st gear is probably good for 80 - 90mph at peak revs, and at most circuits 6th/7th gear would be good for around 200mph. This means they have roughly 5 or 6 gears between 1st and 2nd gear on a normal road car! Even though an F1 car only produces around 300 lb/ft of torque, it can do so at high revs, and take advantage of much lower gearing so the effective torque at the driven wheels is many times that of a road car with the same sort of torque produced at lower revs.
John
What you will find, is that unless the torque plummets at higher revs (e.g. WRC cars with the 32/34mm restrictor), invariably for the absolute fastest acceleration (ignoring things like available traction etc) you will take the car to the red-line in each of the lower gears. For higher gears (ie 4th/5th/6th), you may find that due to the overall gearing that you are better changing up closer to peak power, or at a point where you hit peak torque in the next gear when changing up.
Cars that can produce useable torque at higher revs can take advantage of lower/closer gearing, hence multiplying the torque from the engine more and getting better acceleration. Think of 2nd gear in a typical Impreza, which is capable of getting the car up to the 60 - 70mph range. If the engine could rev to say 19krpm (like an F1 car), then 2nd gear would be good for something like 180mph, and first gear would be good for something like 100mph. In an F1 car, 1st gear is probably good for 80 - 90mph at peak revs, and at most circuits 6th/7th gear would be good for around 200mph. This means they have roughly 5 or 6 gears between 1st and 2nd gear on a normal road car! Even though an F1 car only produces around 300 lb/ft of torque, it can do so at high revs, and take advantage of much lower gearing so the effective torque at the driven wheels is many times that of a road car with the same sort of torque produced at lower revs.
John
Last edited by JohnS; Jul 19, 2005 at 09:48 AM.
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Originally Posted by pslewis
You would have thought they would have installed an idiot light to tell you when to change, wouldn't you?? In this day and age
Or you could just use the good old fashioned ear and brain system which has stood many real drivers in good stead over the years!!
All this useless Mass debating about nowt!!
Pete
Or you could just use the good old fashioned ear and brain system which has stood many real drivers in good stead over the years!!
All this useless Mass debating about nowt!!
Pete
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Originally Posted by JohnS
What you need to do is look at the power/torque curves for the engine, and also the overall gear ratios. What you can then do, is work out the torque at the wheels along the rev range for each gear. The gearbox etc is effectively a torque multiplier. Plot these together on a graph, and when the torque at the wheels in a lower gear drops below that of the torque at the wheels in the next gear up, it's time to change up a gear.
What you will find, is that unless the torque plummets at higher revs (e.g. WRC cars with the 32/34mm restrictor), invariably for the absolute fastest acceleration (ignoring things like available traction etc) you will take the car to the red-line in each of the lower gears. For higher gears (ie 4th/5th/6th), you may find that due to the overall gearing that you are better changing up closer to peak power, or at a point where you hit peak torque in the next gear when changing up.
Cars that can produce useable torque at higher revs can take advantage of lower/closer gearing, hence multiplying the torque from the engine more and getting better acceleration. Think of 2nd gear in a typical Impreza, which is capable of getting the car up to the 60 - 70mph range. If the engine could rev to say 19krpm (like an F1 car), then 2nd gear would be good for something like 180mph, and first gear would be good for something like 100mph. In an F1 car, 1st gear is probably good for 80 - 90mph at peak revs, and at most circuits 6th/7th gear would be good for around 200mph. This means they have roughly 5 or 6 gears between 1st and 2nd gear on a normal road car! Even though an F1 car only produces around 300 lb/ft of torque, it can do so at high revs, and take advantage of much lower gearing so the effective torque at the driven wheels is many times that of a road car with the same sort of torque produced at lower revs.
John
What you will find, is that unless the torque plummets at higher revs (e.g. WRC cars with the 32/34mm restrictor), invariably for the absolute fastest acceleration (ignoring things like available traction etc) you will take the car to the red-line in each of the lower gears. For higher gears (ie 4th/5th/6th), you may find that due to the overall gearing that you are better changing up closer to peak power, or at a point where you hit peak torque in the next gear when changing up.
Cars that can produce useable torque at higher revs can take advantage of lower/closer gearing, hence multiplying the torque from the engine more and getting better acceleration. Think of 2nd gear in a typical Impreza, which is capable of getting the car up to the 60 - 70mph range. If the engine could rev to say 19krpm (like an F1 car), then 2nd gear would be good for something like 180mph, and first gear would be good for something like 100mph. In an F1 car, 1st gear is probably good for 80 - 90mph at peak revs, and at most circuits 6th/7th gear would be good for around 200mph. This means they have roughly 5 or 6 gears between 1st and 2nd gear on a normal road car! Even though an F1 car only produces around 300 lb/ft of torque, it can do so at high revs, and take advantage of much lower gearing so the effective torque at the driven wheels is many times that of a road car with the same sort of torque produced at lower revs.
John
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From: Sheffield; Rome of the North
Originally Posted by JohnS
What you need to do is look at the power/torque curves for the engine, and also the overall gear ratios. What you can then do, is work out the torque at the wheels along the rev range for each gear. The gearbox etc is effectively a torque multiplier. Plot these together on a graph, and when the torque at the wheels in a lower gear drops below that of the torque at the wheels in the next gear up, it's time to change up a gear.
What you will find, is that unless the torque plummets at higher revs (e.g. WRC cars with the 32/34mm restrictor), invariably for the absolute fastest acceleration (ignoring things like available traction etc) you will take the car to the red-line in each of the lower gears. For higher gears (ie 4th/5th/6th), you may find that due to the overall gearing that you are better changing up closer to peak power, or at a point where you hit peak torque in the next gear when changing up.
Cars that can produce useable torque at higher revs can take advantage of lower/closer gearing, hence multiplying the torque from the engine more and getting better acceleration. Think of 2nd gear in a typical Impreza, which is capable of getting the car up to the 60 - 70mph range. If the engine could rev to say 19krpm (like an F1 car), then 2nd gear would be good for something like 180mph, and first gear would be good for something like 100mph. In an F1 car, 1st gear is probably good for 80 - 90mph at peak revs, and at most circuits 6th/7th gear would be good for around 200mph. This means they have roughly 5 or 6 gears between 1st and 2nd gear on a normal road car! Even though an F1 car only produces around 300 lb/ft of torque, it can do so at high revs, and take advantage of much lower gearing so the effective torque at the driven wheels is many times that of a road car with the same sort of torque produced at lower revs.
John
What you will find, is that unless the torque plummets at higher revs (e.g. WRC cars with the 32/34mm restrictor), invariably for the absolute fastest acceleration (ignoring things like available traction etc) you will take the car to the red-line in each of the lower gears. For higher gears (ie 4th/5th/6th), you may find that due to the overall gearing that you are better changing up closer to peak power, or at a point where you hit peak torque in the next gear when changing up.
Cars that can produce useable torque at higher revs can take advantage of lower/closer gearing, hence multiplying the torque from the engine more and getting better acceleration. Think of 2nd gear in a typical Impreza, which is capable of getting the car up to the 60 - 70mph range. If the engine could rev to say 19krpm (like an F1 car), then 2nd gear would be good for something like 180mph, and first gear would be good for something like 100mph. In an F1 car, 1st gear is probably good for 80 - 90mph at peak revs, and at most circuits 6th/7th gear would be good for around 200mph. This means they have roughly 5 or 6 gears between 1st and 2nd gear on a normal road car! Even though an F1 car only produces around 300 lb/ft of torque, it can do so at high revs, and take advantage of much lower gearing so the effective torque at the driven wheels is many times that of a road car with the same sort of torque produced at lower revs.
John
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