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Old 02-10-2008, 05:47 PM   #1
OZY-323
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shifting method?

here's a query,
going on the straight, what are the best times to shift from one gear to the next, does it differ from cars, and by that i mean at what RPM is best to shift?

Oz
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Old 02-10-2008, 05:52 PM   #2
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Depends on what you're trying to do... Drive smoothly? Or drag someone? :-P
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Old 02-10-2008, 06:08 PM   #3
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Originally Posted by OZY-323 View Post
does it differ from cars
yes
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Originally Posted by OZY-323 View Post
at what RPM is best to shift?
max accelleration = 6,000rpm
normal shift = 3,000rpm

and then it also changes with wheels, mods, clutches installed.

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Old 02-10-2008, 06:09 PM   #4
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Originally Posted by OZY-323 View Post
here's a query,
going on the straight, what are the best times to shift from one gear to the next, does it differ from cars, and by that i mean at what RPM is best to shift?

Oz
for going as fast as possible in a straight line:

Usually the shift point will be wherever the geared torque (gear ratios effectively multiply torque from the engine) in one gear dips below what the geared torque would be in the following gear, even if the engine power is already dropping off by that point (this is because the rotational force at the wheels will STILL be higher, and the higher this rotational force, the greater the acceleration. Usually this is redline, unless your engine spins to some unholy RPM, or you are using specially selected gear ratios to maximize geared torque for your powerband.

To work it out, you need to plot your power curve, then work out the torque curve, then multiply out your effective road torque for each gear...then graph the whole lot together... you can then quite easilly see where the maximum force is being applied to the road (you can also take this one step further and with a little more information such as weight of the car, COD and a guestimate on friction and get a reasonably accurate picture of how fast the car will accelerate in an "ideal" situation).

On some cars, the shift point will be different for EACH GEAR....but usually the cross over is so far past the redline, that redline is the best you can do... if i have time later i might do up a spreadsheet you can play with to show you whats what...

for going fast around corners:

This gets a little more complicated - the reality that waiting for the "crossover" point is going to provide maximum acceleration, you also need to take into account what gear you will be hitting a corner in, and exiting in. Playing around with shift points etc on a circuit is probably less of an exact science, but shifting gears mid corner should probably be avoided to lessen the chance of unsettling the car.... I'm not a circuit racing expert, so someone like Ryan, or Greg from GSL will probably have a better take on how to optimize shift points on a circuit....
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Old 02-10-2008, 08:08 PM   #5
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I usually shift where power peaks.

my car's power peaks at ~5500rpm, and drops off from there

my car's torque peaks at ~4000rpm


when I shift at 5500rpm it drops me to about 4000rpm right at the torque peak, I think this is similar to what Lordworm is saying.



but depending on the situation I may hold a gear longer or shortshift.
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Old 02-10-2008, 08:09 PM   #6
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for going fast around corners:

This gets a little more complicated - the reality that waiting for the "crossover" point is going to provide maximum acceleration, you also need to take into account what gear you will be hitting a corner in, and exiting in. Playing around with shift points etc on a circuit is probably less of an exact science, but shifting gears mid corner should probably be avoided to lessen the chance of unsettling the car.... I'm not a circuit racing expert, so someone like Ryan, or Greg from GSL will probably have a better take on how to optimize shift points on a circuit....

from what I've read, it's usually best and faster to enter a corner in the correct gear to exit, but leaving plenty or headroom in the gear (IE: not belting the redline, use torque)
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Old 02-10-2008, 08:14 PM   #7
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I usually shift where power peaks.

my car's power peaks at ~5500rpm, and drops off from there

my car's torque peaks at ~4000rpm


when I shift at 5500rpm it drops me to about 4000rpm right at the torque peak, I think this is similar to what Lordworm is saying.



but depending on the situation I may hold a gear longer or shortshift.
kind of but not...

you're shifting according to the engine's torque and power curves...I'm saying you should be shifting (for a given gear) at the point where geared torque for the gear you are in crosses over with what the geared torque for the next gear would be, or if you can't do that because the cross over is past your red line, you shift at red line. Engine torque still has a lot to do with it, but by considering ONLY engine power, you are only looking at half the picture....

Its a bit to get your head around - and without plotting it all out and actually seeing what the impact of gearing does to the force applied to the road its hard to understand...however, you can achieve a greater gearing advantage (and superior acceleration) by shifting according to your gear ratios.

I'll do up a spreadsheet...wont really have time tonight....but i'll try an do something over the weekend.....might explain it a little better.....
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Old 02-10-2008, 09:10 PM   #8
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I can shift accurate to 3 decimal places
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Old 02-10-2008, 10:03 PM   #9
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The quickest way is to leave it in "D"
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Old 02-10-2008, 11:24 PM   #10
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The quickest way is to leave it in "D"
shouldn't that be 'G'? for granny
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Understeer is when you hit the wall with the front of the car and oversteer is when you hit the wall with the rear of the car. Horsepower is how fast you hit the wall, torque is how far you take the wall with you.

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Old 03-10-2008, 12:17 AM   #11
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As lordworm says it's not just peck power torque it's also gearing

My best example is my own mx-6

6K redline.

1st to 2nd - best is 5400rpm or 5600rpm vary.
Reason is 1st ot 2nd is close and the engine is still on boost when it drops back to 3200rpm any more at 6000rpm change is waste.

but 2nd to 3rd. you need to rev 2nd out to at least 5700rpm if not 6K. because the gap in 2nd to 3rd gear is larger. It won't put oyu off boost it drops you just below the cross over of torque and power.
On stock motor it's unnoticable. But on a mildly worked and retuned engine or Hi-flow turbo as mine. It's very noticable. It's like 500rpm of turbo lag. Yet boost does not drop. Even flat shfit

One thing I'd note is D - in drive is the BEST shift.
car makers do there best to work out best for both economy and WOT shift point.

very comom in the 4 speed era of 3 speed auto with over drive.
was to see either.
gap 1 to 2nd so 1st is quick getaway gear
or gap 2nd to 3rd.
And then again depending on the engine.
you would some cars
change redline 1st to 2nd change and always 500rpm or 300rpm before redline on the next.

Then come the 5speeds and I remember closely the SLK 230K 5 speed auto had very vety short 1st gear - rocket gear I called it. engine would not hit redline in that gear unless you forced it. about 800- 1200rpm off redline but gap to 2nd was so close it was in effect to get the car going motor spun up hard and Bang 2nd gear you were gone. 2nd gear was right in the meet.
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Old 05-10-2008, 11:32 PM   #12
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If your doing circuit or racing someone through twisties, make sure to be in the gear you want to be exiting the corner, try to make sure its not short stint on the exit.

It may take awhile but you get a kind of sense of what your exit speed will be and can pick what gear would be best suited.

In my car (BJII) I dont let the revs drop anywhere below 3k when im driving.
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Old 06-10-2008, 08:51 AM   #13
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under 3K for spirited driving? cos i never touch 3K unless i'm on the highways with normal driving.
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Old 06-10-2008, 09:09 AM   #14
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under 3K for spirited driving? cos i never touch 3K unless i'm on the highways with normal driving.
x2 i ysyally shift at about 4.5k for everyday driving?
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Old 06-10-2008, 10:07 AM   #15
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In my car (BJII) I dont let the revs drop anywhere below 3k when im driving.

he means they dont go under 3k, not dont go over 3k.

ie: keep revving above 3k.
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Old 06-10-2008, 06:33 PM   #16
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he means they dont go under 3k, not dont go over 3k.

ie: keep revving above 3k.
i hit about 3.5k during normal driving. highest i had mine up to was around 8.5k (don't ask). spun the big end bearings but didn't know until the next day. the sound it made was unreal though.
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Understeer is when you hit the wall with the front of the car and oversteer is when you hit the wall with the rear of the car. Horsepower is how fast you hit the wall, torque is how far you take the wall with you.

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Old 06-10-2008, 07:48 PM   #17
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I usually don't push past 3.5 - 4k while normal driving.

If i push mildly i still aim to keep it below 5k but when im out to belt the pants of the thing then i push to 6.8k or so. Don't really go to redline any more, the motors not too fond of it.

Ive also been miles past 8k, but i got lucky and didn't do any damage. It probably got close to 9 before i realized to back of the throttle - flat shift gone bad . Wasn't in gear as the throttle was wide open. 7k - 9k takes a very short time when the engine is unloaded.
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Old 06-10-2008, 08:22 PM   #18
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Ive also been miles past 8k, but i got lucky and didn't do any damage. It probably got close to 9 before i realized to back of the throttle - flat shift gone bad . Wasn't in gear as the throttle was wide open. 7k - 9k takes a very short time when the engine is unloaded.
i think it only damaged the bearings as i was trying to dodge a truck and didn't think to shift. it was only when i actually heard the engine screaming and backed off i looked down and it was at 8.5 dropping. dunno how far up it went. a few seconds of not thinking
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Understeer is when you hit the wall with the front of the car and oversteer is when you hit the wall with the rear of the car. Horsepower is how fast you hit the wall, torque is how far you take the wall with you.

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Old 06-10-2008, 11:11 PM   #19
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Quote:
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here's a query,
going on the straight, what are the best times to shift from one gear to the next?
Oz
usually when the clutch is depressed
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Old 07-10-2008, 06:46 AM   #20
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Quote:
Originally Posted by OZY-323
here's a query,
going on the straight, what are the best times to shift from one gear to the next?
Oz
Quote:
Originally Posted by Cincinnatus
usually when the clutch is depressed
I lol'ed.
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