Dirt road and AWD...

[TeeLoo]

First let me tell you that I'm not a particularly skillful driver (I like to think I am but I'm not...), I have limited technical knowledge and this is my first experience with an AWD car. OK, so last weekend I'm following my wife's cousin on a dirt road, we're going relatively fast and having fun. He is in front and drives a 10 year-old stock Volvo 850 turbo wagon (with 4 season tires that looked like they had one year left). I was driving as fast as he was and I could sense the rear of my car going (and he noticed it in his rear view) yet the Volvo (fwd) was handling the curve in a very stable fashion. I am wondering, driving an AWD especially a Subaru, why in the heck does the rear of the car begins going when under the same circumstances a fwd vehicle seems to be in better control then I was. That being said I wasn't affraid of loosing control of the car. He told me that if the Volvo would start going he probably wouldn't be able to keep control of it. Still, this leaves me perplex. Can anyone provide me some explanations/insights on this? Could it be that a stiffer Subaru chassis vs. a softer Volvo chassis that would absorb additional centrifugal force?

[Ken S]

Hard to say since lots of things could be contributing to the differences in dynamics. Tire pressures, sway bar stiffness, weight distribution, torque distribution, throttle inputs, ESP vs. no ESP, etc, etc... In an grossly oversimplified explanation, stay on the gas in turns with AWD vehicles. Since you have power going to the rear wheels, you don't want to induce any power on/off oversteer, which it sounds like was happening to you. Ken

[ta2tony]

the legacy gt is reported to behave much like a rear wheel drive vehicle. so next time the rear slides around on you, smile real big, punch the accelorator, and steer into it. have fun! ps-the FWD car doesn't have the rear wheels spinning to pull the rear end around like that, but understear is worse than overstear, so consider yourself lucky.

[NicoGamine]

[quote name='TeeLoo']Can anyone provide me some explanations/insights on this? Could it be that a stiffer Subaru chassis vs. a softer Volvo chassis that would absorb additional centrifugal force?[/quote] Hello Teeloo The GTs have a central differential which sends a minimum of 55% of torque to the back wheels, which means that it will behave like a RWD car (to a point, like getting stuck in snow... :) ). As ta2tony mentions, oversteer is easier to manage than understeer. Your GT has about the same weight distribution as the Volvo (front heavy, somewhere around 60/40) so the GT's rear wheels will loose traction before the Volvo's or your GT's front wheels but when the front wheels start loosing traction the Volvo will start sliding straight through corners while your GT can slide around corners. FWIW, my 2000 L wagon with automatic transmission (not the same differential) does a similar thing: The car first understeers then oversteers (the back comes out) if driven fast enough :twisted: on gravel and snow. For fun and safety have a good practice session in a snowy parking lot, nothing too fast, just to get an impression of how it feels when the back end goes. Nicolas (in Montreal, too... :) )

[axis008]

NicoGamine is right about the 45/55 F/R... but that is for the 5EAT. Is that what you have? The manual GT has 50/50 F/R power distribution.

[TeeLoo]

[quote name='axis008']NicoGamine is right about the 45/55 F/R... but that is for the 5EAT. Is that what you have? The manual GT has 50/50 F/R power distribution.[/quote] Yup, Wagon GT Limited 5EAT. So I guess the car was oversteering since there was traction on the rear wheels while turning in order to negotiate the dirt road curve...

[Throttlejockey]

[quote name='TeeLoo'][quote name='axis008']NicoGamine is right about the 45/55 F/R... but that is for the 5EAT. Is that what you have? The manual GT has 50/50 F/R power distribution.[/quote] Yup, Wagon GT Limited 5EAT. So I guess the car was oversteering since there was traction on the rear wheels while turning in order to negotiate the dirt road curve...[/quote] Umm..........let's see....you have the brand new car and you're behind him letting him throw dirt at your car? With AWD stay on the throttle in the corners and it will pull you out. When in doubt....gas it. :D

[scubie02]

yeah, I wouldn't be following anybody very closely with my new car--good way to get dings. Part of the problem is probably the re-92's, they really do suck. The volvo is also probably much heavier than the subie. Tires make a big difference though.

[Nick]

I would suggest reading a good book on handling dynamics...something that explains weight transfer and under and oversteer. In an AWD or RWD car, oversteer like you were getting can be provoked in one of two ways: Lift throttle or power-on. In lift throttle, you enter a turn on the gas and lift off in mid-corner. This transfers weight forward (off the rear wheels) causing them to have less traction and thus slide easier. The solution for this is to get back on the gas and even out the weight between the front and rear wheels. The opposite of this is power-on oversteer, where in the middle of a corner you mash the gas causing the rear wheels to spin and break free. The solution is to reduce throttle slightly and stop the rears from spinning, but not lifting completely or else you will be in scenario 1. In all cases, oversteer requires quick opposite lock steering to "catch" the rear end. As others have said, your car's power distribution starts at 50/50 or 45/55 depending on what transmission you have, but remember that that ratio constantly changes depending on which end has more grip. Ah, the beauty of AWD. -Nick