a4: drive vs overdrive
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Joined: May 2009
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a4: drive vs overdrive I got a 99 z28, mostly stock despite a few bolt ons including exhaust and lid. Gears are stock. I have the stock a4 tranny, and never thought twice about using D opposed to [D]. I read in the manual the drive provides more power; perhaps if someone is towing or traveling uphill. I have been driving in regular drive recently and noticed a nice increase in performance, and a lot more power in any gear, especially at low RPMs. There have been times when I punched my car in overdrive, and watched the RPMS slowly rise instead of exploding and the car throwing me down the road. However, in regular drive, I have more power at the command of my foot. Is this normal? I know the only downside of driving in regular drive is lower fuel economy, but its just more fun. When i descend down hills my exhaust rumbles, and it sounds sick! So whats the difference? Is overdrive simply an extra gear for the car to travel in, because i feel like in regular drive my car doesnt downshift as much. Please discuss how you drive your a4
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
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From: So.Cal.
In OD or [D] the available gears are: 1st, 2nd, 3rd, 4th.
In D the available gears are 1st, 2nd, 3rd.
4th gear has ratio 0.696 (keeps engine RPM lower for a given MPH).
3rd gear has ratio 1.000 (keeps engine RPM higher for a given MPH).
3rd gear usually keeps engine RPM in the engine's torquey region, that's why 3rd gives quicker acceleration than 4th.
When in [D] you punch the throttle, there are two situations (keeping it simple):
- your MPH is sufficiently low to allow the PCM to shift the trans from 4th to 3rd (the RPM should jump up and your MPH should rise quickly);
- your MPH is above the downshift threshold, so the PCM keeps the trans in 4th (your RPM rise slowly as does your MPH).
In D the available gears are 1st, 2nd, 3rd.
4th gear has ratio 0.696 (keeps engine RPM lower for a given MPH).
3rd gear has ratio 1.000 (keeps engine RPM higher for a given MPH).
3rd gear usually keeps engine RPM in the engine's torquey region, that's why 3rd gives quicker acceleration than 4th.
When in [D] you punch the throttle, there are two situations (keeping it simple):
- your MPH is sufficiently low to allow the PCM to shift the trans from 4th to 3rd (the RPM should jump up and your MPH should rise quickly);
- your MPH is above the downshift threshold, so the PCM keeps the trans in 4th (your RPM rise slowly as does your MPH).
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Launching!
Joined: Oct 2008
Posts: 294
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From: Bowling Green, KY
In manual 3rd the overrun frictions are applied (but only in 3rd) that's why your getting compression braking. (That rumble you hear when you let off the gas).
Why is racing in 3rd bad? Bringing on the overrun frictions adds support to the input sprag.
Why is racing in 3rd bad? Bringing on the overrun frictions adds support to the input sprag.
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TECH Enthusiast
Joined: Jan 2008
Posts: 509
Likes: 1
From: North Chicagoland
I was told by many in a previous thread that when I hit the strip to race in D. I leave it in D around town as well since I cruise around 45mph and that's about the speed the tranny can't decide between 3rd and 4th. If I'm gonna be on the highway then I'll pop it in OD but that's about it.
As far as what the OP has posted, I wonder if what is stated on the owners manual has something to do with the computer programming. Basically making reference to things like TQ management and timing here. Might be something to consider. Vince B
