2014 C7 Chevrolet Corvette

[serialk11r]

Originally Posted by totopo

I vaguely recall interviews about it back when it was JGTC and allowed both FMR and MR. IIRC being MR had a weight penalty associated with it, so all the top cars were FMR, but i'm not sure how much the weight penalty it was. Was it so they were heavier than the FMR cars because they didn't like honda? or just to make the weights equal?

I wish real professional engineers shared their mathematical models and would answer these types of questions.

? There is not much to model. MR moves the center of gravity back for more grip at the rear and decreases the polar moment so the tires have to do less work. I'm pretty sure a race prepped MR2 will outperform a race prepped Miata. Like the F1 cars you mentioned, race cars will often have a huge rear bias.

I'm pretty sure FMR is not inherently heavier than MR, at least with the torque tube setups you find on the higher performance cars. The torque tube only barely adds any mass. Having the engine at the front makes cooling a bit simpler.

The reason why FMR is popular is because the low polar moment of a MR car can bite you in the ass in the form of snap oversteer. A rear engined car like the 911 will also rotate easily because the light front end can change direction much faster than the rear. MR2s and 911s alike are known for losing control easily when pushed past the limit.

[totopo]

Originally Posted by serialk11r

? There is not much to model. MR moves the center of gravity back for more grip at the rear and decreases the polar moment so the tires have to do less work. I'm pretty sure a race prepped MR2 will outperform a race prepped Miata. Like the F1 cars you mentioned, race cars will often have a huge rear bias.

I'm pretty sure FMR is not inherently heavier than MR, at least with the torque tube setups you find on the higher performance cars. The torque tube only barely adds any mass. Having the engine at the front makes cooling a bit simpler.

The reason why FMR is popular is because the low polar moment of a MR car can bite you in the ass in the form of snap oversteer. A rear engined car like the 911 will also rotate easily because the light front end can change direction much faster than the rear. MR2s and 911s alike are known for losing control easily when pushed past the limit.

what if you made the mr2 and miata have the same weight and same engine and same tires?

why would an MR car have a lower polar moment? a 50/50 transaxle has much lower polar moment compared to the CG. But that's some imaginary CG, not how the car actually turns in most instances. If a car is over-rotating, like at corner entry, it is actually probably rotating more over its front wheels. So an MR car will have MUCH higher polar moment, and that is exactly why they have a tendancy of snap oversteer in corner entry.

i recall hearing an interview with a JGTC engineer saying that actually slight front bias is better for a race car, mostly because on track, when you let go of the brakes, you get on the gas almost immediately. He said basically you want close to 50/50 balance for the driver when you are mid corner, and to do this you actually need slight front weight bias since the driver is on the gas mid corner.

It kind of makes intuitive sense to me too, because to be fast you want to be at the traction circle on all your tires. in a RWD car, if you have extra traction on your front at corner exit, it does nothing for you.

FMR definitely has more weight by packaging.

[Sideways&Smiling]

Originally Posted by totopo

what if you made the mr2 and miata have the same weight and same engine and same tires?

why would an MR car have a lower polar moment? a 50/50 transaxle has much lower polar moment compared to the CG. But that's some imaginary CG, not how the car actually turns in most instances. If a car is over-rotating, like at corner entry, it is actually probably rotating more over its front wheels. So an MR car will have MUCH higher polar moment, and that is exactly why they have a tendancy of snap oversteer in corner entry.

i recall hearing an interview with a JGTC engineer saying that actually slight front bias is better for a race car, mostly because on track, when you let go of the brakes, you get on the gas almost immediately. He said basically you want close to 50/50 balance for the driver when you are mid corner, and to do this you actually need slight front weight bias since the driver is on the gas mid corner.

It kind of makes intuitive sense to me too, because to be fast you want to be at the traction circle on all your tires. in a RWD car, if you have extra traction on your front at corner exit, it does nothing for you.

FMR definitely has more weight by packaging.

You sure that was JGTC and not Nissan? Because I remember Nissan making this argument about the 350z when it came out... Toyota also tried to spew the same thing about the FRS/BRZ/86, and they say that's why they made it front-biased instead of 50/50.... but, in reality, we all know the reason they did this is the same reason they gave it a quite long wheelbase... the car was made for drifting. They wanted the driver to have more time to control a slide. It doesn't necessarily handle better for racing. It handles better for drifting.

I'll always be on the rear-mid being superior for grip driving side of this argument. There's a reason F1 is the way it is.

[strat61caster]

Originally Posted by totopo

I wish real professional engineers shared their mathematical models and would answer these types of questions.

Here was my textbook, might be able to find a pdf from a less than reputable source:

[ame="http://www.amazon.com/Engineering-Applications-Dynamics-Dean-Karnopp/dp/0470112662/ref=sr_1_2?ie=UTF8&qid=1418245441&sr=8-2&keywords=vehicle+dynamics+karnopp"]Engineering Applications of Dynamics: Dean C. Karnopp, Donald L. Margolis: 9780470112663: Amazon.com: Books[/ame]

Yes a true mid-engined layout reduces the vehicles moment of inertia vs. engine up front transaxle in back, think about rotating a long rod around the center vs. a short rod, the short rod will spin faster with the same applied force, quicker response, quicker handling.

Originally Posted by totopo

i recall hearing an interview with a JGTC engineer saying that actually slight front bias is better for a race car, mostly because on track, when you let go of the brakes, you get on the gas almost immediately. He said basically you want close to 50/50 balance for the driver when you are mid corner, and to do this you actually need slight front weight bias since the driver is on the gas mid corner.

Most pure race cars (open wheel, open ruleset: F1, Indy, Karts, Sprint cars) and super cars have rear bias, with a pendulum effect you can get quick rotation, also covered in the book linked above. Front engined is preferred for many other reasons, but pure speed is not one of them, the 911 has been so incredibly successful for a reason.

[Ultramaroon]

Originally Posted by strat61caster

Here was my textbook,...

Only one?
[ame="http://www.amazon.com/Engineering-Mechanics-Dynamics-4th-v/dp/0133569160/ref=sr_1_102?s=books&ie=UTF8&qid=1418250665&sr=1-102&keywords=engineering+dynamics"]http://amzn.com/013356916[/ame]
http://amzn.com/0137099819

The problem is none of this stuff is accessible to the casual reader. There's still quite a bit that can be demonstrated and understood intuitively without doing the math. Even just thought experiments with mentally assembling sticks and bricks can help.

[strat61caster]

Originally Posted by Ultramaroon

Only one?

The problem is none of this stuff is accessible to the casual reader. There's still quite a bit that can be demonstrated and understood intuitively without doing the math. Even just thought experiments with mentally assembling sticks and bricks.

For a ten week class with 3 prerequisite classes (and a dozen prerequisites for those), yes only one textbook

Guy asked for engineering formulas and equations, I delivered where I would get mine. It's not like the book is solely proofs, there is enough background and thought experiments to guide the casual reader, a solid knowledge of algebra should be able to get you through most engineering textbooks as you skip over the calculus and more obtuse dynamics principles.

[serialk11r]

Originally Posted by totopo

what if you made the mr2 and miata have the same weight and same engine and same tires?

why would an MR car have a lower polar moment? a 50/50 transaxle has much lower polar moment compared to the CG. But that's some imaginary CG, not how the car actually turns in most instances. If a car is over-rotating, like at corner entry, it is actually probably rotating more over its front wheels. So an MR car will have MUCH higher polar moment, and that is exactly why they have a tendancy of snap oversteer in corner entry.

The NB Miata and MR2 Spyder are very close specs wise. Miata weighs a little more and has a smidge more power I think. Tires is easy to make equal, they have the same wheel sizes. This isn't a discussion, the cars are similar, and the MR2 has more grip if you optimize the suspension because the weight distribution is more favorable. In fact it has more grip stock despite a pretty bad suspension setup that's not adjustable.

The polar moment is lower because the mass is concentrated near the center of gravity. Polar moment is a scalar quantity, center of gravity is a point in space, there's no "compared to" lol. Someone needs to go back to high school physics :P

Snap oversteer happens because the center of gravity is far back and so if the rear breaks loose it'll slide around quickly for the exact same reason an FF car tends to understeer.

[Ultramaroon]

Originally Posted by strat61caster

For a ten week class with 3 prerequisite classes (and a dozen prerequisites for those), yes only one textbook

Guy asked for engineering formulas and equations, I delivered where I would get mine. It's not like the book is solely proofs, there is enough background and thought experiments to guide the casual reader, a solid knowledge of algebra should be able to get you through most engineering textbooks as you skip over the calculus and more obtuse dynamics principles.

I kid! I misinterpreted your response and proceeded to agree with it

I just think his question was misguided altogether.

[totopo]

Originally Posted by serialk11r

The NB Miata and MR2 Spyder are very close specs wise. Miata weighs a little more and has a smidge more power I think. Tires is easy to make equal, they have the same wheel sizes. This isn't a discussion, the cars are similar, and the MR2 has more grip if you optimize the suspension because the weight distribution is more favorable. In fact it has more grip stock despite a pretty bad suspension setup that's not adjustable.

The polar moment is lower because the mass is concentrated near the center of gravity. Polar moment is a scalar quantity, center of gravity is a point in space, there's no "compared to" lol. Someone needs to go back to high school physics :P

Snap oversteer happens because the center of gravity is far back and so if the rear breaks loose it'll slide around quickly for the exact same reason an FF car tends to understeer.

ops, thanks, brainfart

[Noble713]

Vengeance Racing 660rwhp with minor mods, 48hrs after delivery of their Z06:
http://www.corvetteforum.com/article...60-hp-new-z06/

It's a shame GM as a corporate conglomerate is such a bureaucratic and inept mess, because they've clearly got some very competent automotive engineers.

[dcreason86]

Originally Posted by jsimon7777

Gods do I hate Jonny Lieberman. That guy writes like me at 16 at acts like Lincoln at Disneyland.

Thought I was the only one. Annoying as hell! They should have Lagos do all his segments.

[EAGLE5]

Originally Posted by dcreason86

Thought I was the only one. Annoying as hell! They should have Lagos do all his segments.

Well, he acts 1000 times better than he writes. When he wrote for Autoblog, I wrote them a letter of complaint. When he left for Motor Trend, I figured he'd fit right in with the rest of their bad writers. He actually got a bit better once he went under their editing: from excretory to just plain awful.

[themadscientist]

I like the shape.



I liked it the first time I saw it, when it was a Ferrari.

[Joakim3]

Originally Posted by DarkSunrise

Just saw this video yesterday. Phenomenal car! I don't particularly like the way the C7 looks, but the performance of the C7 Z06 (w/s3 aero package) in Randy Pobst's hands is incredible, especially considering it's a stock street car. The 1:30 laptime at RA matches the Evasive FR-S, which was on better tires and purpose built for the track. Very impressive.

The evasive FR-S also has 200whp less than C7 Z06 lol, so it kind of lessons the impact of the Z06's time. Plus it's apple vs. oranges comparing a race car to road spec track car

But either way is damn impressive that for ~100k, you can have a car that literally nothing short of a P1, Laferrari, 918 or dedicated race car can outrun you on track







...... Except a 25k build LS1/2 powered Miata enging swap