question on what it means to rotate and how

[2013kAB]

what is "rotate" while cornering - i understand it as the feeling of and actual rear of the car following a radius or describing a radius. is it like all wheel steering?

when a car is said to "rotate" while cornering, is that a result of the rear differential allowing the tires to spin at different rates (outside faster, inside slower)?

 

[SoundGuyDave]

Nope. When a car is said to "rotate" through a corner, it's actually describing VERY mild oversteer. Essentially, it allows the axis of the chassis (not the front wheels) to point in more towards the center of the corner, and since the chassis is pointing in the right direction sooner, you can get back on the gas sooner...

It's usually achieved by a chassis tuning that is slightly biased towards oversteer in the corner entry phase, and/or is assisted/created by trailbraking. NOT something to try to accomplish on your first visit or two to a track...

 

[2013kAB]

got it. thanks.

 

[Gray Ghost GT]

"Mustang and oversteer".... two words not normally said in the same sentence. LOL Ways to get you there to better rotate the car:

(1) Aggressive alignment (negative camber, lots of caster and little toe) suspension geometry

(2) Stiffer front sway bar and spring vs. the rear to increase lateral load transfer at the rear

(3) Tires and tire air pressure: mark and check the wear area of the outer section of your tires

(4) Driver technique - managing the "traction circle"; car control practice on the wet skid pad

(5) Weight reduction and increase rear down force (aerodynamics) - reason for APR GTC-200

(6) Reduce bushing deflection so your suspension settings "don't walk" under hard cornering, etc.

(7) You will become very familiar with trailbraking the more time you spend tracking the Mustang.

(8) Balance of cornering speed, braking, throttle (oversteer), steering inputs and weight transfer

 

[2013kAB]

i think i've been too worried about oversteer since this is a high-power rwd car. not pushing hard enough to see that the mustang plows rather than oversteers in stock form. but i have definitely noticed it's quite easy to get oversteer with the throttle in the wet and the snow we've gotten.

 

[csamsh]

Just an observation that may or may not be related...somebody more knowledgeable can perhaps chime in. I've seen "it's not the differential" but I think my differential helped? Perhaps I'm not interpreting this correctly, but whatever.

When I switched from the stock T-Lok to the Torsen T2R, the car seemed to turn in much easier/quicker, and was much more stable/controllable under power in a turn, perhaps because one wheel wasn't lighting up. Oversteering into a turn, especially in an autox setting, became much easier and much more manageable as well. Much easier to add throttle/steering and correct without getting wheelspin.

 

[dontlifttoshift]

"

(2) Stiffer front sway bar and spring vs. the rear to increase lateral load transfer at the rear


(5) Weight reduction and increase rear down force (aerodynamics) - reason for APR GTC-200

Those both = understeer

 

[sheizasosay]

Yeah I agree with that ^^

 

[Gray Ghost GT]

The list I provided above addresses both the natural tendencies of the Mustang to understeer while improving its ability to "rotate" while cornering; creating more balance in the suspension with the right steering input from the driver. The Mustang has more weight in the front over the tires. How does reducing or equalizing that weight help create more understeer?

 

[sheizasosay]

The list I provided above addresses both the natural tendencies of the Mustang to understeer while improving its ability to "rotate" while cornering; creating more balance in the suspension with the right steering input from the driver. The Mustang has more weight in the front over the tires. How does reducing that weight help create more understeer?

I thought you were listing ways to increase oversteer. That was the mindset when I looked at it.

Stiffer front springs *usually* will bias towards getting rid of oversteer. I would say the majority of the time unless you want to talk about the platypus. No need though.

Adding a rear spoiler says more rear traction though. I wouldn't imagine a better ability to rotate. Speed would be factor too.

 

[SoundGuyDave]

Agreed. Biasing spring and bar rates (AKA wheel rate) forward tends to promote understeer, any way you look at it. If you're trying to bias your setup towards oversteer, that's not really the way to go about it.

With the wing, I can kinda see that. Bias the "natural" tendency of the car towards oversteer, then correct that with the wing for higher-speed corners, like fast sweepers and big carousels. That way, when you hit a slow-speed corner, you get more oversteer bias, and still keep a neutral or understeer bias for the high-speed stuff. I haven't played around with aero enough to really comment there, but in theory it works.

 

[Whiskey11]

Just an observation that may or may not be related...somebody more knowledgeable can perhaps chime in. I've seen "it's not the differential" but I think my differential helped? Perhaps I'm not interpreting this correctly, but whatever.

When I switched from the stock T-Lok to the Torsen T2R, the car seemed to turn in much easier/quicker, and was much more stable/controllable under power in a turn, perhaps because one wheel wasn't lighting up. Oversteering into a turn, especially in an autox setting, became much easier and much more manageable as well. Much easier to add throttle/steering and correct without getting wheelspin.

Ooo Ooo! I can chime in!

This is because a clutch based differential has a drive (on power) and coast (off power) differentiating power. We are very familiar with the effect on power and how it pushes the car to the outside of a turn rather than turning the car but the off power is important too. If you could set the coast lock up to 100% you'd basically lock the rear axle off power and accomplish terrible corner entry understeer.


A Torsen by contrast only biases under power and is "open" when off power. Someone will have to correct me if I'm wrong but there has to be some torque on a Torsen for it to differentiate like we think it does and that doesn't happen while coasting. It's one of the major reasons why guys running full on race cars on roadcourses don't like Torsens nearly as much as there is a sudden loosening of the chassis during the transition between gas and brake that can unsettle the car. For autocross, we don't care (thankfully we aren't driving Cadillacs) because a slightly looser car helps get the car rotated through a corner. Obviously a Torsen allows the car to rotate under power too through it's torque biasing throwing power to the outside tire which helps push the car around the corner.

Dave, I think what Gray Ghost is saying that on a strut based car you can increase front wheel rate to a point where the car stays in a more favorable part of the camber curve and that can increase front end grip to push the car towards oversteer. After that point though (somewhere around 350lbs/in with the off the shelf adjustable 35mm front bars) adding more without addressing rear spring rates will push it back towards the conventional wisdom of stiffer front = understeer.

 

[sheizasosay]

The platypus is alive.

 

[csamsh]

Ooo Ooo! I can chime in!

This is because a clutch based differential has a drive (on power) and coast (off power) differentiating power. We are very familiar with the effect on power and how it pushes the car to the outside of a turn rather than turning the car but the off power is important too. If you could set the coast lock up to 100% you'd basically lock the rear axle off power and accomplish terrible corner entry understeer.


A Torsen by contrast only biases under power and is "open" when off power. Someone will have to correct me if I'm wrong but there has to be some torque on a Torsen for it to differentiate like we think it does and that doesn't happen while coasting. It's one of the major reasons why guys running full on race cars on roadcourses don't like Torsens nearly as much as there is a sudden loosening of the chassis during the transition between gas and brake that can unsettle the car. For autocross, we don't care (thankfully we aren't driving Cadillacs) because a slightly looser car helps get the car rotated through a corner. Obviously a Torsen allows the car to rotate under power too through it's torque biasing throwing power to the outside tire which helps push the car around the corner.

Dave, I think what Gray Ghost is saying that on a strut based car you can increase front wheel rate to a point where the car stays in a more favorable part of the camber curve and that can increase front end grip to push the car towards oversteer. After that point though (somewhere around 350lbs/in with the off the shelf adjustable 35mm front bars) adding more without addressing rear spring rates will push it back towards the conventional wisdom of stiffer front = understeer.

that....actually makes sense. Torque sensing and all

 

[Roadracer350]

Just pull a Jeremy Clarkson and yell "MORE POWA" and gas it! You will be fine!