The REAL reason for C8 understeer
10-22-2019, 10:06 PM
#61
Instructor
I also think that the understeer was intentionally baked in by GM as a safety measure. I don't fault GM for doing this. I don't have any experience with a mid engine car, but from what I have read, the ME configuration reduces the polar moment of inertia, which means when the car does start to spin, it will be harder to for the driver to catch. Assuming that is a true statement, then I believe GM did the right thing. If people don't like it, they can buy another car or adjust the suspension or perhaps wait for the higher performing corvette models that will be coming out the the future. I currently have a 2005 C6 which I've had since it was new, and I've enjoyed auto crossing it. It's been a lot of fun learning how to control that car. I look forward to doing the same when I get a C8 hopefully in 2021. If I ever get to the point, that I think the car is holding me back (doubtful), then I will look into adjusting the suspension. I'm sure I will get years and years of enjoyment out of it before that happens though.
10-22-2019, 10:34 PM
#63
Le Mans Master
Everyone should be happy it understeers. We wouldn't be able to afford the insurance if it didn't.
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Phil1098 (10-22-2019)
10-22-2019, 10:40 PM
#64
Team Owner
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St. Jude Donor '05
I dont follow all these threads how do we know for a fact it understeers? Somethings gotta give at some point when you get past a g.
Id love to see these new cars with no nannies at all...put the fun factor back in.
Id love to see these new cars with no nannies at all...put the fun factor back in.
10-22-2019, 10:52 PM
#65
Instructor
There is nothing to prevent you from turning off the various electronic nannies.
On my C6, I generally only do that when I am auto crossing, but that is my choice, others are free to do as they see fit
10-23-2019, 06:59 PM
#66
I'm not aware of ANY new car you can buy today that is not going to Understeer at neutral or maintenance throttle - at the LIMIT. The real question is where does the understeer get to be problematic - is it at 80% of max grip or 97% of max grip, and what is that Max Grip level...
As several previous posts have stated - the C6, C7 & now the C8 are more than capable of cornering at over 1g (heck the C4 was the first one to hit the 1G mark - and that was back in 1984). Not very many people have the skill / guts to push their car to those levels, specially on the street - and GM is well aware of that.
So - let's talk about why mid engine (and by that I mean engine behind passenger compartment) cars can turn faster laps than cars with the engine mounted up front. Part of the "magic" is that you have more load on the rear wheels as you accelerate out of a corner. If you look at the weight distribution - the rear wheels are probably going to have more than 50% of the static weight distribution, and when you accelerate - you shift weight backward - so even more load goes on the rear tires. Now - there are some things engineers can do with suspension geometry to help the situation even further under acceleration, but the fact is that as you come out of a corner there will be more weight on the rear tires (this might just be one reason why almost all the mid engine cars out there run wider rear rubber than front rubber). Now let's think about the lower polar moment of inertia - basically that means that less force will be required to change the car's momentum (read direction). So - the talented drivers will be able to apply power sooner, and will be able to apply more power at a given point int he corner exit than with a car that has the engine in the front. They will also need to use less total front tire angle to generate the required force to change direction...
Bottom line - the reviews do say the C8 understeers. That's FAR from a surprise !!! The degree of understeering that's being reported seems to be varying depending on which review you read. Also perfectly understandable - some car reviewers are probably far less skilled drivers than others, and some reviewers were probably expecting the same tuning in the base C8, as they see in a McLaren that sells for 8 time the price of a base C8 Coupe. Sorry guys - different market !!! The guys who work on suspension calibrations all day know that the customers who really want hardcore handling are probably going to be waiting for the Z06 (or better) to be released. Many of the people who say they want a Z51 package really don't want those kinds of spring rates or those nice hard suspension bushings, and the engineers know that as well.
Oh - just one last thing. Cornering force (in G's) is proportional the the Square of the velocity. (The equation is that G Force = Velocity ^2 / (14.97 * r) {where r is the radius in feet}. So - say you toodle through an off ramp at 50 MPH and generate 0.5 G. Go in 20 MPH hotter and you're now at just a hair under 1G.
As several previous posts have stated - the C6, C7 & now the C8 are more than capable of cornering at over 1g (heck the C4 was the first one to hit the 1G mark - and that was back in 1984). Not very many people have the skill / guts to push their car to those levels, specially on the street - and GM is well aware of that.
So - let's talk about why mid engine (and by that I mean engine behind passenger compartment) cars can turn faster laps than cars with the engine mounted up front. Part of the "magic" is that you have more load on the rear wheels as you accelerate out of a corner. If you look at the weight distribution - the rear wheels are probably going to have more than 50% of the static weight distribution, and when you accelerate - you shift weight backward - so even more load goes on the rear tires. Now - there are some things engineers can do with suspension geometry to help the situation even further under acceleration, but the fact is that as you come out of a corner there will be more weight on the rear tires (this might just be one reason why almost all the mid engine cars out there run wider rear rubber than front rubber). Now let's think about the lower polar moment of inertia - basically that means that less force will be required to change the car's momentum (read direction). So - the talented drivers will be able to apply power sooner, and will be able to apply more power at a given point int he corner exit than with a car that has the engine in the front. They will also need to use less total front tire angle to generate the required force to change direction...
Bottom line - the reviews do say the C8 understeers. That's FAR from a surprise !!! The degree of understeering that's being reported seems to be varying depending on which review you read. Also perfectly understandable - some car reviewers are probably far less skilled drivers than others, and some reviewers were probably expecting the same tuning in the base C8, as they see in a McLaren that sells for 8 time the price of a base C8 Coupe. Sorry guys - different market !!! The guys who work on suspension calibrations all day know that the customers who really want hardcore handling are probably going to be waiting for the Z06 (or better) to be released. Many of the people who say they want a Z51 package really don't want those kinds of spring rates or those nice hard suspension bushings, and the engineers know that as well.
Oh - just one last thing. Cornering force (in G's) is proportional the the Square of the velocity. (The equation is that G Force = Velocity ^2 / (14.97 * r) {where r is the radius in feet}. So - say you toodle through an off ramp at 50 MPH and generate 0.5 G. Go in 20 MPH hotter and you're now at just a hair under 1G.
Last edited by Purple92; 10-23-2019 at 07:43 PM.
10-23-2019, 07:08 PM
#67
Race Director
Understeer means the front ends pushes or plows, easy to see with a front wheel drive car. Neutral means both ends let go at the same time and never provided any warning you were near the limit. You don't want oversteer because when it lets go you slide off rear end first. Old 911 Porsches were known for trailing throttle oversteer. Which means the driver missed his brake point, said oh **** I'm going too fast, turns the wheel and gets off the gas unloading the rear of the car and off the road he goes back end first.
Understeer is always the safety net of OK bub, your just about done, better back off if you don't want to crash.
Understeer is always the safety net of OK bub, your just about done, better back off if you don't want to crash.
11-06-2019, 08:53 PM
#68
Your reply is spot on
This is correct, when a car is understeering, the common reaction is to lift throttle and apply brakes, both of which improves the situation by reducing G forces and putting more weight on the front tires increasing grip, causing you to turn in as desired.
On a Oversteering car, the reaction is the same the result is terrible. Lifting throttle only shifts weight off the rear tires reducing grip making it oversteer more (known as lift throttle oversteer) Appling the brakes does the same thing less grip at the rear increasing the over steer, more grip at the front, so the front turns in harder and the back lets go, Now you are spinning with the tires pointed in the wrong direct to correct for the skid. So the correct thing for a mass produced car is to deliver it with an alignment and tire specs that understeers. The trackers know they need to adjust the alignment and tire pressures.
On a Oversteering car, the reaction is the same the result is terrible. Lifting throttle only shifts weight off the rear tires reducing grip making it oversteer more (known as lift throttle oversteer) Appling the brakes does the same thing less grip at the rear increasing the over steer, more grip at the front, so the front turns in harder and the back lets go, Now you are spinning with the tires pointed in the wrong direct to correct for the skid. So the correct thing for a mass produced car is to deliver it with an alignment and tire specs that understeers. The trackers know they need to adjust the alignment and tire pressures.