Engine Drag Control
Thread Starter
Le Mans Master
Joined: May 2000
Posts: 8,729
Likes: 1,508
From: Redmond WA
Engine Drag Control
Back in my C6Z if I let off the gas at a higher RPM in a lower gear the computer would intervene to add throttle a little so that your rear tires don't drag and yaw you around.
"Engine drag can occur on low and high coefficient surfaces when the driver suddenly releases the throttle.If the engine drag force becomes larger than the frictional force between the tire and the road, the tires will break loose from the surface and slip. This could induce vehicle instability especially with rear drive vehicles on low-coefficient surfaces.
The EDC algorithm has been developed to provide accurate control of the wheels. EDC will help reduce the yaw rate of the vehicle and thus achieve greater vehicle stability."
Has anyone thought they experienced this on the C7Z? With or without a DIC message?
The symptom would be you let off the gas, you decel, then right away it seems like someone hits the gas a little and you decel less than you were.
I'm also curious as to whether this could only occur in the M7. Seems like, especially with a locked converter, it could happen with both.
"Engine drag can occur on low and high coefficient surfaces when the driver suddenly releases the throttle.If the engine drag force becomes larger than the frictional force between the tire and the road, the tires will break loose from the surface and slip. This could induce vehicle instability especially with rear drive vehicles on low-coefficient surfaces.
The EDC algorithm has been developed to provide accurate control of the wheels. EDC will help reduce the yaw rate of the vehicle and thus achieve greater vehicle stability."
Has anyone thought they experienced this on the C7Z? With or without a DIC message?
The symptom would be you let off the gas, you decel, then right away it seems like someone hits the gas a little and you decel less than you were.
I'm also curious as to whether this could only occur in the M7. Seems like, especially with a locked converter, it could happen with both.
Last edited by davepl; May 27, 2016 at 11:04 AM.
Race Director
Joined: Jan 2005
Posts: 10,924
Likes: 854
From: Daytona Beach FL
Were your C6 tires different sizes than stock tires?? 
The quote you have above indicates that if the rear tires are sensed to be going slower than they should be when you let off the throttle, the engine thinks that is due to the tire losing traction so a little bit of throttle is added to keep them from slipping. The system knows how fast the rear wheels should rotate compared to the front wheels, and if the ratio isn't correct it figures the rear wheels are losing traction on a slippery surface, so it adds some power to get the rear wheels turning at the rotational speed the system is expecting to see.
However, with the C6 I used to see posts about this all the time, and owners were invariably getting the message due to having tires that were different sizes than stock.
Typically it was with a larger tire in the rear. A tire with a greater diameter than the stock size rotates more slowly than the stock one would. With a larger than stock rear tire, when you let off the accelerator the system thinks the rear tire/wheel is turning too slowly and is probably losing traction on a slippery road surface, so it adds some throttle to keep the wheel rotating at the proper ratio of speed compared to the front wheel.
I don't know if the C7 has that feature - but I would imagine it does.
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The quote you have above indicates that if the rear tires are sensed to be going slower than they should be when you let off the throttle, the engine thinks that is due to the tire losing traction so a little bit of throttle is added to keep them from slipping. The system knows how fast the rear wheels should rotate compared to the front wheels, and if the ratio isn't correct it figures the rear wheels are losing traction on a slippery surface, so it adds some power to get the rear wheels turning at the rotational speed the system is expecting to see.
However, with the C6 I used to see posts about this all the time, and owners were invariably getting the message due to having tires that were different sizes than stock.
Typically it was with a larger tire in the rear. A tire with a greater diameter than the stock size rotates more slowly than the stock one would. With a larger than stock rear tire, when you let off the accelerator the system thinks the rear tire/wheel is turning too slowly and is probably losing traction on a slippery road surface, so it adds some throttle to keep the wheel rotating at the proper ratio of speed compared to the front wheel.
I don't know if the C7 has that feature - but I would imagine it does.
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Track Rat
Joined: Oct 2006
Posts: 6,466
Likes: 3,464
I've never seen that message but when I first started tracking the call I noted that it feels like when you let off the gas the car keeps going for a 1/2 second or so. It was very disconcerting at the time but strangely I no longer notice it.
Given what you just posted about engine drag control I wonder if I was coming off the gas too quickly and the ECU was doing this to module the speed with which the rear times slowed.
Given what you just posted about engine drag control I wonder if I was coming off the gas too quickly and the ECU was doing this to module the speed with which the rear times slowed.
Race Director
Joined: Jan 2005
Posts: 10,924
Likes: 854
From: Daytona Beach FL
Here's a post with links to a "couple" of threads in the C6 section about it - and I think every one of them is about the "drag control" message coming on after larger rear tires were put on:
https://www.corvetteforum.com/forums...post1570072072
I took a quick look in the C7 Owner's Manual but don't see any reference to drag control mentioned - but I imagine it probably has pretty much the same control systems as the C6.
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https://www.corvetteforum.com/forums...post1570072072
I took a quick look in the C7 Owner's Manual but don't see any reference to drag control mentioned - but I imagine it probably has pretty much the same control systems as the C6.
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Thread Starter
Le Mans Master
Joined: May 2000
Posts: 8,729
Likes: 1,508
From: Redmond WA
Yes, in my case I'd added drag radials. I updated the computer to reflect the tire size, but that didn't seem to fix it.
That said, this "feature" still exists and works even if your tires are the right size, but having "different" sized tire will fool it into kicking in sooner because it -thinks- the size difference is a speed difference. At least that's how I think it works.
I presume it's to avoid downshifting, the rear tires drag from compression, and the rear end wants to yaw around. With different sized tire the computer gets fooled into thinking its happening, but it still can -actually- happen is what I mean, I suppose.
That said, this "feature" still exists and works even if your tires are the right size, but having "different" sized tire will fool it into kicking in sooner because it -thinks- the size difference is a speed difference. At least that's how I think it works.
I presume it's to avoid downshifting, the rear tires drag from compression, and the rear end wants to yaw around. With different sized tire the computer gets fooled into thinking its happening, but it still can -actually- happen is what I mean, I suppose.
