All wheel drive vs. front wheel drive SUV's

When comparing AWD vs. FWD:

An AWD vehicle will get better traction and handle better in the rain, snow, and other slippery surfaces like leaf-covered streets. In a climate like CA where it doesn't rain all summer, the first few rains of the season make the oils rise off of the road surface, making them very slippery. An AWD vehicle will also be slightly more stable in conditions where hydroplaning occurs.

On the negative side, the AWD hardware weighs more and has more drag on the drivetrain so it will get poorer fuel economy, and there are 2 extra differentials to maintain.

AWD vehicles are driven by all four tires, so they are inherently more stable and predictable in adverse conditions. Having said that, there is not a car on the road that can overcome sheer stupidity.

False.

A two wheel drive car with snow tires (or tires otherwise appropriate for conditions) will, on the road, always be more capable than an all wheel drive vehicle with all-season or otherwise inappropriate tires.

That last statement sure is true. Several years back I had a 91 camry and was in a town about 30 miles away when it was snowing. The 4WDs were passing me on the interstate, but about 5 miles down the road I was passing them back as they were in the ditch. They thought just casue they could go it was fine to go fast, they did not realise they could not turn or stop much if any beter than a 2 wheel car.

One advantage to AWD over FWD is the torque is biased to the rear in most AWD versions, (although some are 50/50) thus reducing the dangerous tendency to loose steering control upon deceleration that is common with FWD.

mike

Talk about stating the obvious :)

I concur with Ralph Mowery. Years ago I was constantly driving over a snowy mountain pass in a FWD Honda. Both AWD and 4WD SUV’s would pass me, only to end up on in the median or on their tops some time down the road.

Improved car traction does not translate in the ability to drive faster safely under slippery road conditions, or increase the cars ability to stop Just because these cars can go in the snow, does not mean the can stop any better or will not slid of the road just like any other car. Something the cars owners ending up learning the hard way.

This being said, having the capability of getting in to 4WD from 2WD in a car with some ground clearance can come in handy for extreme conditions. I have never needed it when driving on the highway. If things get real bad, there are always cable chains. A 10-minute job to put them on and take them off.

Not true -- it depends on the conditions!

In about 76 I lived in Mt Shasta, Ca where it does snow - we had an Audi fox wagon (FWD) and I drove an International P/U with studed rear tires and positraction. I usually in tose days carried a few hundred lbs of ballast in the bed. One day, I had a heck of a time getting into the drive and garage. (We had to pull and back in because it did snow a lot) I probably spent 15 minutes slipping/slidding on a bit of pack and maybe 18" of fresh. My wife drove in with the Audi - continental all season tires - pushing the loose stuff up on to the hood, backed in and asked me "what t he heck you been doing?"

With that said, because I have to drive in the crap at times, am 68 and have had 2 strokes, I drive an AWD Highlander. BUT I always pack the cable chains with me!

Not in my experience. I've had plenty of examples of all of them, and yes, I buy good snow tires.

Also, snow is not the only "adverse" condition.

Unless one has to drive REGULARLY in a rural area, snow tires are marketed for suckers. For most URBAN people, you do NOT need snow tires--GOOD all season tires are adequate. I've lived in Edmonton Alberta, Canada..in the great white north for SIXTY years and have been driving for 46 years.....in all sorts of snow and ice conditions. Yeah, I've had to use a shovel the odd time but that was usually when I insisted on parking in a spot that had 2 feet of snow.

Actually, no, where torque bias exists, its generally to the front wheels. I don't know of any NORMALLY FWD car that has an AWD variant that biases torque to the rear. There's lots of RWD vehicles with AWD/4WD variants that runs to the front (most SUVs).

Examples are

- Honda CRV which is about 65/35 front rear (look at the diff ratios and the rear diff hydro lock system)

- Chrysler "AWD" minivans are about 75/25 when its actually working, and maybe 10% rear when its not, due to the rear drive being derived from the RH front axle. Its an expensive system that only works because there's an ABS/Traction system that gives limited AWD. Lose the ABS system and the "AWD" becomes just excess weight.

- Early Mitsibishi Lancer GSR / EVO 1, EVO 2 with the W5M31 transmission with about 65/35 bias to the front. The rear diff ratio was numerically lower on the rear. Mitsu found this was unsuitable (and fragile) and switched to the W5M33 series, see below.

Examples of 50/50 in normal operation are

- Mitsubishi Eclipse/Expo/Outlander/EVO 3+ Series with the center diff/viscous coupler (W5M33 and W5M40 series transmissions and variants). Front / Rear diff ratios are (almost) the same. Torque can vary somewhat automatically FR. In extreme situations the center viscous coupler locks and you get back to 50-50.

-Audi Quatro uses an automaticlly controlled center diff that can be progressively locked. Competition versions use (AFAIK) a Torsen diff.

- Subaru. Depending on one of at least three types of AWD (std, automatic and WRX-std). The most capable is the WRX type with a Torsen center diff, the less capable is the hydro clutch system in cars with the automatic transmission.

Then do a bit more research, WBMA ;)

mike hunt

AWD is not really a safety feature, AWD helps you get going in the mud/snow, the treads on your tires are a much more important safety feature overall for stopping power and cornering

I'm not familiar with the WBMA acronym ...

I stand by my description of the Honda CRV, Mitsubishi and Subaru AWD systems. Torque split is easy to decide simply by looking at the diff ratios. Assuming the same size wheel, the normal operation torque split is the ratio of front_diff/rear_diff ratios.

Please give us all the benefit of your superior knowledge, and tell us specifically which AWD variants of a FWD vehicle bias the torque to the rear wheels under normal operation conditions.

SD

A minor problem (particularly in a vehicle with a moderately-sized engine) that is easily overcome by shifting to neutral and/or stepping on the clutch, a practice I've also found useful in RWD vehicles.

IMHO, the safety advantage of AWD, for the majority of drivers, is less than that afforded by good tires. There is considerable advantage to a vehicle with a low center of gravity (car) vs. high center of gravity (SUV/light truck) in slippery conditions.

These days AWD systems vary from vehicle to vehicle. Most are not full time AWD; the second set of wheels is powered only when they start to slip. Know what you are buying. If you live in the mountains where it snows your neighbors will be happy to tell you all about AWD and 4WD systems.

It's nice to have, but not that necessary. Winter tires are best for new dry snow, something we seldom have on Canada's urban and main highways. With salting slush is the norm. So IMO under these conditions All season tires are best. ABS brakes are very important, should be a legal requirement on new cars.

What is more important is common sense and a feel for driving on very slippery roads. Although I've driven all my life in Canadian snowy conditions, the 40 yrs going to the western Canadian ski hills in all conditions, I still practice my winter driving driving skills with the first snow each season, including always driving slower than the slip point. This has meant I get there before many AWD, 4WD, etc. vehicles which often are in the ditch on their roofs.

Unfortunately recent vehicle design is often not desirable on snowy roads, this includes excessively low profile tires which float on the snow at speed.

You are correct, that is why most FWD vehicles can be bumped into neutral without pressing a button or such. The difference is with RWD when that happens, even a novice driver can detect what is happens when the rear loses traction, while FWD drivers generally do not realize it is the cause of the steering loss then does what is necessary to disengage the tranny. It becomes even more pronounced with an automatic tranny, as it automatic drops to a lower gear as speed decreases.

One of my homes is located on the outside of a curve at the bottom of a long grade in northeast Pa. Whenever it gets sloppy I have FWD cars in my yard as they apply brake, when the car losses steering control, rather than disengages and riding through the turn ;)

mike hunt