F15 oversteer or understeer?

[artem123]

Question is in title. I searched all over and cannot find a definite answer. So, by design, does F15 oversteer or understeer? Thank you)))

[r33_RGSport]

artem123 , most of the street car are aligned for Understeer since it is much2 easier to control by novice driver.
So, the answer would be understeer.

[artem123]

Originally Posted by r33_RGSport

artem123 , most of the street car are aligned for Understeer since it is much2 easier to control by novice driver.
So, the answer would be understeer.

Thank you r33_RGSport. That what i though.

[lowlevelhell]

The vehicle understeers by design. This is a function of weight, body roll, and the negative camber of the rear wheels.

[artem123]

Originally Posted by lowlevelhell

The vehicle understeers by design. This is a function of weight, body roll, and the negative camber of the rear wheels.

Thank you.

[42pilot]

I'm going to research this one. Neither makes sense and both equally dangerous. Lawyers would love to get hold of a manufacturer who states their vehicle is biased one way or another. The correct answer, I would bet, is neutral or balanced. Environmental factors will dictate whether you have under or oversteer.

I spent 11 years at Road Atlanta teaching people how to get out of both situations in their Porsches. Hell, in an older 911/930, you had both conditions inherent in one car, depending if you were accelerating or decelerating. One of the reasons Porsche went back to 4WD and put an engine in the middle of a car (Cayman) was to get proper balance. That thing is on rails. Panamerica - balanced. Cayenne - balanced. Boxster - balanced. M3/M5 - balanced.

I've pushed my X5 and it's balanced - the front does not push and the rear does not step out. I cannot imagine BMW designing an X5 to push (understeer - keep going straight losing all input from the steering). Imagine coming to a decreasing radius turn on a hillside or mountainside road. You enter too fast, turn the car - bang - understeer and off the edge you go.

If anyone has proof (and comments from forums don't count), I would like to read it. I googled it quickly and found comments in popular car magazines state that cars are designed to be balanced, but either condition can happen given poor tire tread, road conditions, road camber, tire temp, and so on. I always set my cars up to be 100% balanced by corner balancing the weight of the car and using adjustable sway and coil-overs.

Anyway, please let me know what you find.

[artem123]

Originally Posted by 42pilot

I'm going to research this one. Neither makes sense and both equally dangerous. Lawyers would love to get hold of a manufacturer who states their vehicle is biased one way or another. The correct answer, I would bet, is neutral or balanced. Environmental factors will dictate whether you have under or oversteer.

I spent 11 years at Road Atlanta teaching people how to get out of both situations in their Porsches. Hell, in an older 911/930, you had both conditions inherent in one car, depending if you were accelerating or decelerating. One of the reasons Porsche went back to 4WD and put an engine in the middle of a car (Cayman) was to get proper balance. That thing is on rails. Panamerica - balanced. Cayenne - balanced. Boxster - balanced. M3/M5 - balanced.

I've pushed my X5 and it's balanced - the front does not push and the rear does not step out. I cannot imagine BMW designing an X5 to push (understeer - keep going straight losing all input from the steering). Imagine coming to a decreasing radius turn on a hillside or mountainside road. You enter too fast, turn the car - bang - understeer and off the edge you go.

If anyone has proof (and comments from forums don't count), I would like to read it. I googled it quickly and found comments in popular car magazines state that cars are designed to be balanced, but either condition can happen given poor tire tread, road conditions, road camber, tire temp, and so on. I always set my cars up to be 100% balanced by corner balancing the weight of the car and using adjustable sway and coil-overs.

Anyway, please let me know what you find.

Thank you for such in-dept post. It took me countless ours to research for my previous ride ( VW Touareg T-2), i called VW of America and at some point had a conference call with "top hand german engineer" via translator just to find out which way Treg was build, and it turned out, according to german guy, car was "balanced with touch of understeer" which played well with my own feeling. Not sure if i am up to the same venture as i got much busier with family. If i hear something i will post.
PS. Another "top tier" engineer from the same company told me that Treg's transmission is sealed and never needs a oil change in it, while Bentley publishers manual clearly stated that 60K or 6 years transmission fluid change is a must...

[42pilot]

Originally Posted by artem123

Thank you for such in-dept post. It took me countless ours to research for my previous ride ( VW Touareg T-2), i called VW of America and at some point had a conference call with "top hand german engineer" via translator just to find out which way Treg was build, and it turned out, according to german guy, car was "balanced with touch of understeer" which played well with my own feeling. Not sure if i am up to the same venture as i got much busier with family. If i hear something i will post.
PS. Another "top tier" engineer from the same company told me that Treg's transmission is sealed and never needs a oil change in it, while Bentley publishers manual clearly stated that 60K or 6 years transmission fluid change is a must...

Nice.

I've been reading some of my suspension books and on-line articles and best I can tell, nearly every passenger vehicle (no brands were mentioned) is designed to be neutral (or balanced), but because there are so many variables, and handling is not linear, some cars will have slight understeer and some will have oversteer. As I stated earlier, environmental factors will dictate which way the car breaks - front or rear. So as far as I am concerned, these are neutral.

As for the tranny, one of my customers is ZF in Gray Court, SC. At this facility, they make trannies for Ranger Rover, VW and Honda. I know some of the people at ZF in Germany as well, and all of the "car guys" in each of the factories state, ALWAYS change the fluid at 30,000 miles - full stop, period. These are the same people who see the returns that come back from dealers and are disassembled for analysis. So, when the majority of employees who work at ZF tell me to change the fluid, regardless of what BMW states, I'm doing it. For some reason, 30,000 miles seems to be a magic number, including my Ford Powerstroke and my SL550. Every 30k, Merc and Ford recommend flush and fluid replacement. The X5 will get the same, keeping in mind, I own, not lease.

[lowlevelhell]

Originally Posted by artem123

Thank you for such in-dept post. It took me countless ours to research for my previous ride ( VW Touareg T-2), i called VW of America and at some point had a conference call with "top hand german engineer" via translator just to find out which way Treg was build, and it turned out, according to german guy, car was "balanced with touch of understeer" which played well with my own feeling. Not sure if i am up to the same venture as i got much busier with family. If i hear something i will post.
PS. Another "top tier" engineer from the same company told me that Treg's transmission is sealed and never needs a oil change in it, while Bentley publishers manual clearly stated that 60K or 6 years transmission fluid change is a must...

I think we're talking about different aspects of handling. In daily driving, almost every passenger car will be neutral in its handling, even what we consider sports cars. Where the characteristics of over and understeer appear is when you exceed the boundaries of the traction circle. In the case of most large vehicles and especially those with AWD and staggered tires like the X5, the exceedence will manifest as understeer. The front tires will lose traction first and exhibit sideslip through the curve. On the X5, the negative rear camber exacerbates this by setting the rear wheels up for better biased grip in a corner. In the case of a small, light, RWD car like the Subaru BRZ, the exceedence of the traction circle will manifest as oversteer. The rear driving wheels will lose grip first, walking the tail out.

In normal daily driving, you should experience neither out of your X5, though if you were to overcook a flat corner by a large margin, you might notice it a touch.