corner exit traction

[strat61caster]

Originally Posted by Porsche

I don't think so.

Obviously, your personal experience has convinced you that this is true. I cannot argue with your personal experience, nor would I.

But your general assertion that modern cars suffer increased final oversteer as the speeds increase is simply false. You are mistaken.

It would be a disservice to the readers of these forums to allow this to go unchallenged.

I ask you to produce authoritative proof of your assertion on a broad, general scale.

Hey look my vehicle dynamics textbook is online!
Vehicle Stability

Basically in the section linked Figure 6.11 illustrates that a car setup for oversteer (like the FRS) will likely be more unstable at high speeds and a vehicle set up for undeersteer is stable at higher speeds. It's why 911's are so successful in racing but have a reputation for being hard to control for everyone else. It also explicitly states in the paragraph below the figure that a car that understeers will understeer MORE at higher speeds when comparing similar steering inputs (the graph shows the understeer line dropping off, representing unresponsiveness).

This is simplified and doesn't delve into specifics but I think it shows nicely that depending on the setup, some cars are stable, some aren't, depends on the car. And like you explained, not many people are willing to test this, much less journalists borrowing cars.

Don't you just love it when everybody is right?

[CSG Mike]

Originally Posted by autobrz

The front needs more camber. The front tire is probably rolling over and riding on the sidewall. Once you give the front more negative camber though, you will experience way more grip and way more oversteer

I believe the fr-s is more oversteery than the brz and that is at lower speeds. I've never seen a car that becomes more understeery at higher speeds. It always becomes looser as the speeds increase. Can't explain why though.. as far as lawsuits, the vsc does a pretty good job of keeping the car on the road and going in the intended direction.

That's most cars....

[GTM_Challenge]

Interesting thread. Subscribed.

[CSG Mike]

Originally Posted by strat61caster

Hey look my vehicle dynamics textbook is online!
Vehicle Stability

Basically in the section linked Figure 6.11 illustrates that a car setup for oversteer (like the FRS) will likely be more unstable at high speeds and a vehicle set up for undeersteer is stable at higher speeds. It's why 911's are so successful in racing but have a reputation for being hard to control for everyone else. It also explicitly states in the paragraph below the figure that a car that understeers will understeer MORE at higher speeds when comparing similar steering inputs (the graph shows the understeer line dropping off, representing unresponsiveness).

This is simplified and doesn't delve into specifics but I think it shows nicely that depending on the setup, some cars are stable, some aren't, depends on the car. And like you explained, not many people are willing to test this, much less journalists borrowing cars.

Don't you just love it when everybody is right?

The FRS doesn't oversteer by itself. It oversteers due to driver input. It will understeer at static turns.

[Porsche]

Originally Posted by strat61caster

Hey look my vehicle dynamics textbook is online!
Vehicle Stability

You're the author?

[Porsche]

Originally Posted by CSG Mike

The FRS doesn't oversteer by itself. It oversteers due to driver input. It will understeer at static turns.

Thank you!

Final understeer in high speed bends, a stable and relatively safe status, setup that way by the auto manufacturer for keeping the public safe. Anything less is bordering on insanity for a street car being sold to the general public.

This is NOT to say, however, that a determined driver cannot send it off the road tail first with sufficient provocation. I expect the aforementioned Scandinavian Flick should do the trick. (Again, video, please, @autobrz)

[strat61caster]

Originally Posted by Porsche

You're the author?

I wish, he is a cool guy. He taught the class I took.

[Porsche]

Originally Posted by strat61caster

I wish, he is a cool guy. He taught the class I took.

Cool!

[Bravo Romeo Zulu]

My first car was a Mk1 MR2 which I drove almost 30 years ago. I'd say that the BRZ has similar rotation characteristics on turn-in but the biggest difference is of course that the MR2 was quite a handful in an oversteer situation whereas the BRZ is easy to catch (VSC off). On corner exit, the MR2 was more hooked up under acceleration due to the extra weight on the rear.

On a related note, I just replaced the stock tires with Michelin Pilot Super Sports in the stock size. They are pretty close to R compound tires like the Hoosiers and Kumhos I used to autocross on, in terms of grip and steering feel. I am super impressed. FYI, the wear rating is misleading because while the stock tires have a rating of 240, the PSS rating is 300. However, Michelin has a 35,000 mile wear warranty on the stock tires vs. 30,000 for the PSS. Anyway, highly recommend the PSS -- and there is a $70 rebate right now.

[CSG Mike]

Originally Posted by Bravo Romeo Zulu

My first car was a Mk1 MR2 which I drove almost 30 years ago. I'd say that the BRZ has similar rotation characteristics on turn-in but the biggest difference is of course that the MR2 was quite a handful in an oversteer situation whereas the BRZ is easy to catch (VSC off). On corner exit, the MR2 was more hooked up under acceleration due to the extra weight on the rear.

On a related note, I just replaced the stock tires with Michelin Pilot Super Sports in the stock size. They are pretty close to R compound tires like the Hoosiers and Kumhos I used to autocross on, in terms of grip and steering feel. I am super impressed. FYI, the wear rating is misleading because while the stock tires have a rating of 240, the PSS rating is 300. However, Michelin has a 35,000 mile wear warranty on the stock tires vs. 30,000 for the PSS. Anyway, highly recommend the PSS -- and there is a $70 rebate right now.

If you think the PSS is good.... try something a bit stickier, but still a street tire.

[robispec]

yeah EVERYTHING starts at the road contact patch!

[autobrz]

Most of my experience has been in a autoX. It's been my experience that when I set-up the car to rotate for slower corners, the car suffers looseness in high speed transitions. In order to set-up the car for high-speed transitions, the car will feel tight and want to push in lower speed stuff.

I guess there are two differences in what we're talking about: transitions are not steady state cornering and the high speed I'm used to in autoX is not top speed for the vehicle.

Maybe you're completely right most vehicles will have terminal steady state understeer but I argue most vehicles will also become more loose in transitions as speeds increase.

I also didn't take into account aerodynamic lift of the front...

[Porsche]

Originally Posted by robispec

yeah EVERYTHING starts at the road contact patch!

Stops there, too.

Those four, fist-sized, rubber, contact patches are the only thing standing between me and St. Peter. I take good care of them, sometimes altering tire pressures daily, as needed.

[Porsche]

Originally Posted by autobrz

I also didn't take into account aerodynamic lift of the front...

According to German auto mags, there's lift at the rear as well.

So far, I haven't noticed my hood trying to lift up; I'm not keen on carefully scrutinizing my hood, though ... at 100+ mph.

I've got my eyes on other things, not least of which is watching out for the stray Enforcer out cruising around the back country roads.