Car traction question

[Rubycon]

If a front drive car pulls the car forward and a rear drive car pushes etc.

Is the reason that a rear drive car does worse in bad weather because the weight distro puts more weight up front? If two vehicles one rwd and one fwd both had 50/50 would there still be any advantage?

I don't drive and was just wondering what this is all about as I read more about fwd is better for snow and such.

 

[Demon-Xanth]

The FWD car does better because of both the weight on the drive wheels and the fact that it does "drag" the car. Though VW Beetles have been known to be pretty good and decidedly RWD because their weight is on the wheels.

 

[thirdeye]

That's general jist of it. FWD cars will generally have more weight over the front wheels providing more traction in snow for example. Also FWD is "easier" to drive for the common person. When you lose traction due to acceleration in a FWD car you're generally just spinning the front tires, in RWD, the rear of the car will tend to rotate. This then requires more control/skill to keep the car on the intended path.

 

[Zenmervolt]

Originally posted by: Rubycon
If a front drive car pulls the car forward and a rear drive car pushes etc.

Is the reason that a rear drive car does worse in bad weather because the weight distro puts more weight up front? If two vehicles one rwd and one fwd both had 50/50 would there still be any advantage?

I don't drive and was just wondering what this is all about as I read more about fwd is better for snow and such.

That's pretty much it. RWD tends to slip more just because there's less weight over the wheels. FWD cars are usually between 60/40 and 65/35 in weight distribution, while RWD cars are (with the exception of some very purpose-designed sporty cars and some older rear-engine cars) usually between 50/50 and 55/45. The other advantage of FWD is more weight over the steering wheels, which can help with low-speed directional control in bad conditions.

Oddly enough, the Porsche 911 is an excellent car in the snow because even though its RWD, it has a huge rear weight bias (between 40/60 and 35/65). Granted, the newer ones have enough power to easily negate that, and the wide tires don't help, but those are different issues.

Thirdeye is completely correct about handling characteristics as well.

ZV

 

[mooseracing]

Originally posted by: thirdeye
Also FWD is "easier" to drive for the common person. When you lose traction due to acceleration in a FWD car you're generally just spinning the front tires, in RWD, the rear of the car will tend to rotate. This then requires more control/skill to keep the car on the intended path.

I can't drive FWD for shit. The front ends all push in the snow while acceling when turning. I acel when i turn with my truck and steer with the rear, I go where I planned on going.

In theory A rear shouldn't rotate side to side if its an open rear end, 3 tires still have leteral traction. Now if a locker like I have, and loose rear traction i go right around.

 

[Rubycon]

So this is why those with pickup trucks put sand in the bed?

 

[thirdeye]

Originally posted by: mooseracing

Originally posted by: thirdeye
Also FWD is "easier" to drive for the common person. When you lose traction due to acceleration in a FWD car you're generally just spinning the front tires, in RWD, the rear of the car will tend to rotate. This then requires more control/skill to keep the car on the intended path.

I can't drive FWD for shit. The front ends all push in the snow while acceling when turning. I acel when i turn with my truck and steer with the rear, I go where I planned on going.

In theory A rear shouldn't rotate side to side if its an open rear end, 3 tires still have leteral traction. Now if a locker like I have, and loose rear traction i go right around.

That's because you know how to drive.

Once you learn RWD in the snow, FWD becomes complete crap because it doesn't do anything but push.

Originally posted by: Rubycon
So this is why those with pickup trucks put sand in the bed?

Yes, more weigh over the rear tires helps a lot, especially since there isn't much weight over the rear in a pickup truck.

 

[exdeath]

It's mostly an issue when you lose traction in a corner and you have an angle between the steering wheels and the direction the power is applied.

FWD cars tend to pull the front end in the direction you want to go and if there is no traction you'll just under steer and slide sideways off the road. The back of the car is simply dragged along and power is ALWAYS applied in the direction the steering wheels. No net rotation on the car.

RWD though when you change the direction of the front of the car, instead of being dragged and following in line with the front, the powered rear wheels may continue to kick the rear out because the power is not applied in the same direction as the steering wheels. This makes RWD cars tail happy, and easier to rotate and spin out of control in poor traction conditions.

The end of the car that looses traction first has the least resistance to movement and leads the car, and naturally the part of the car that is powered will be more likely to break traction. In a FWD car the front wheels break loose first and the front of the car leads, while the rear still maintains traction with nothing else to cause otherwise. When RWD breaks traction, the front has more grip and the rear wants to swing around and lead, since it faces less resistance.

In icy conditions with RWD, people tend to loose traction with the front wheels first, trying to turn too fast, while the rear is still gripping. In response they panic and feed more throttle to the still gripping rear wheels (to try to "turn faster"?) which starts to push the back of the car momentarily before the added power also breaks the rear loose, and now the car is both sliding AND rotating.

In my RWD car in ideal conditions, I can blip the throttle on a turn and swing the rear around right where I want it. Brief throttle breaks traction for an instant, swings the rear around, and when throttle is let off, the tires grip again. But on ice, the static friction that would otherwise cause the tires to regain grip after you let off, is much lower and the car continues to slide rear end first under inertia.

It's easy to see if you play with a toy car on a table, or even your cordless mouse right now. If you pull the front end and make rapid changes in direction, handling is predictable and you don't "lose" the car. But push it from the rear while making a sudden change of direction on the front and you'll likely rotate the car 180 degrees. Also your pushing finger may have trouble staying on the car depending on how far and how fast it rotates, etc. because the orientation of the car is less predicable, directly reflecting real driving conditions.

 

[Pacfanweb]

Originally posted by: Rubycon
So this is why those with pickup trucks put sand in the bed?

Yes. The main reason FWD goes better in the snow is all the weight on the wheels.

Weigh the rear of an RWD down the same amount and it'll go just about as well. FWD gets a slight advantage of the drive wheels being able to turn, but the weight is the main thing.

 

[OrganizedChaos]

Accountant: We need this vehicle to be $1000 cheaper to build
Engineer: Well we could convert it to FWD but the weight distribution will be screwed up.
Marketing guy: We'll tell people its a feature, that we designed the car to be front heavy for safety reasons.
Management: $1000 cheaper and we get to pass off a poor design as a feature? Brilliant, lets do it!

 

[Demo24]

Originally posted by: Rubycon
So this is why those with pickup trucks put sand in the bed?

yep, trucks generally have lower geared ratios for torque. So when starting off the rear wheels have lots of torque but little weight above holding them down. On some light trucks with manuals it can be pretty tricky to not spin the wheels in the rain

 

[Demon-Xanth]

I'll attest to the fact that unless heavily modified, 4WD, or loaded/towing, trucks hook up like Urkel in a lesbian bar. The Durango which shared many parts with the Dakota was always known for hooking up good on even on crappy tires while my 230/295 is enough that I have to launch like a Lingenfelter Corvette otherwise the same thing happens. idle=bog, 1200RPM=hook, 2000RPM=spin for a long time. And this is with a set of mats made to go in horse stalls in the bed and traction bars attached. Though the latter only helps with wheel hop, not so much hooking up. A pair of slicks would probably drop my 60' time by about a third of a second.

I actually got stuck on wet grass that had a small slope because with the combination of my spring angle, complete lack of traction from GT-II tires, and no weight in the bed, every time I tried to back up I slid forward.

 

[Zenmervolt]

Originally posted by: OrganizedChaos
Accountant: We need this vehicle to be $1000 cheaper to build
Engineer: Well we could convert it to FWD but the weight distribution will be screwed up.
Marketing guy: We'll tell people its a feature, that we designed the car to be front heavy for safety reasons.
Management: $1000 cheaper and we get to pass off a poor design as a feature? Brilliant, lets do it!

For 95% of driving by 95% of people on public roads at legal speeds, FWD is superior. There's simply no debating that.

The only practical advantage of RWD in street situations is for towing.

Now, do I prefer the "feel" of RWD? Yes. Do I prefer to drive RWD? Yes. But it's ridiculous to call it a "poor design". It allows cars to be lighter and roomier and for the vast majority of drivers it is significantly safer in poor conditions.

If you ask me which I like more, the answer is RWD.

If you ask me which is more practical, the answer is FWD.

ZV

 

[JulesMaximus]

Originally posted by: Rubycon
If a front drive car pulls the car forward and a rear drive car pushes etc.

Is the reason that a rear drive car does worse in bad weather because the weight distro puts more weight up front? If two vehicles one rwd and one fwd both had 50/50 would there still be any advantage?

I don't drive and was just wondering what this is all about as I read more about fwd is better for snow and such.

A car that is 60/40 biased toward the front in a FWD car would be excellent in the snow. The trouble with a comparably weighted RWD car is that when the rear wheels do break traction it induces oversteer which is not easy to control. A FWD car is much more predictable in the snow for this reason.

Honestly though, a good set of snow tires and adding some weight to the trunk of a RWD car will have a dramatic effect on improving the cars winter driveability.

 

[zerocool84]

Originally posted by: Zenmervolt

Originally posted by: OrganizedChaos
Accountant: We need this vehicle to be $1000 cheaper to build
Engineer: Well we could convert it to FWD but the weight distribution will be screwed up.
Marketing guy: We'll tell people its a feature, that we designed the car to be front heavy for safety reasons.
Management: $1000 cheaper and we get to pass off a poor design as a feature? Brilliant, lets do it!

For 95% of driving by 95% of people on public roads at legal speeds, FWD is superior. There's simply no debating that.

The only practical advantage of RWD in street situations is for towing.

Now, do I prefer the "feel" of RWD? Yes. Do I prefer to drive RWD? Yes. But it's ridiculous to call it a "poor design". It allows cars to be lighter and roomier and for the vast majority of drivers it is significantly safer in poor conditions.

If you ask me which I like more, the answer is RWD.

If you ask me which is more practical, the answer is FWD.

ZV

Honestly FWD has gotten a horrible rap cus of The Fast and Furious

 

[Demon-Xanth]

Originally posted by: zerocool84
Honestly FWD has gotten a horrible rap cus of The Fast and Furious

Nah, FWD got a bad rap because RWD got the image of being higher class while RWD was lower class

ie: BMW's are all RWD/AWD in the US while cars like the Corolla are FWD

Most people buy an image, not a car.

 

[PandaBear]

In addition to all the above:

FWD is also more fuel efficient, but not as sharp of a turning radius due to the drive axles. FWD also has a tendency to torque steer if you have more than 300HP (V6 3.2+), and an additional axles that take up leg room front and back. Transmission in RWD usually last longer due to more room for its space (Auto), easier to change spark plugs and exhaust works. U-joints in RWD usually last longer than the FWD's CV joint.

I'd say for non sport car 4 cylinders or under, FWD is better. RWD for fun and high power but not for cost or fuel economy. Auto industry usually build car based on this rule, so unless you are buying a V6 3.0+ entry level Luxury/Sport Car in America, you usually don't have much of a choice one way or the other.

 

[Zenmervolt]

Originally posted by: PandaBear
In addition to all the above:

FWD is also more fuel efficient,

No. In terms of overall drivetrain loss FWD is not significantly different from RWD.

Originally posted by: PandaBear
but not as sharp of a turning radius due to the drive axles.

Also no. Tire width and fender clearance become issues long before the amount of flexibility in the CV joints is used up.

Originally posted by: PandaBear
FWD also has a tendency to torque steer if you have more than 300HP (V6 3.2+)

Correct.

Originally posted by: PandaBear
and an additional axles that take up leg room front and back.

No, wrong again. For a given wheelbase, FWD will offer more interior room, including legroom, than RWD. Since FWD cars can use simple spindles in the rear, the rear axle is eliminated, which frees up far more passenger space than the front axle removes.

Originally posted by: PandaBear
Transmission in RWD usually last longer due to more room for its space (Auto)

Now that's just ridiculous.

Originally posted by: PandaBear
easier to change spark plugs and exhaust works.

Depends more on the car than on the layout. It was much more difficult to reach the spark plugs on my V8, RWD cars than it was to reach them on my I4 and I5 FWD cars. Ditto for exhaust. Granted, V6 and FWD can be a pain to work on.

Originally posted by: PandaBear
U-joints in RWD usually last longer than the FWD's CV joint.

Again, ridiculous. Unless you damage a CV joint by hitting something an tearing the boot, allowing the grease to escape, they will last just as long as a U-joint. Additionally, almost all RWD cars built today use CV joints instead of U-joints. Any RWD car with IRS will use CV joints, the only cars using U-joints now are cars with live axles. At 165,000 miles, the CV joints in the rear drive axles of my 951 are original and showing no signs of wearing out.

ZV