FWD SUVs, why do they exist?

[agent00f]

I'm quite confident you're the only person on this forum who thinks you're the incredibly smart one. It's simply not worth anyone's time to discuss anything with you.

No, I'd say there used to be more people who thought they knew a few things about cars.

 

[JCH13]

Yaw control only needs brake distribution.


All other things equal as stipulated the rwd is simply smaller. Even disregarding this most buyers here clearly don't care much about fuel economy, and rightly so given gas is relatively cheap.


Under the physics of dynamic friction conditions, corner performance is predicated on maximizing weight (as opposed to balance) over the outside front and then drive wheel, which works out best for fwd. This translates to the basic rally or wet driving technique.



The ladder frame is only strong in very limited directions, thus a frame stronger in most directions is stronger overall.

Yaw control benefits immensely from torque vectoring differentials. Torque vectoring is more effective on AWD than any 2WD because it has ~2x as much traction to work with. Yes, selective braking can control yaw, but torque vectoring with AWD can improve ultimate cornering capacity. Again, this is a small incremental improvement, but it is a thing.

RWD is not smaller than FWD. RWD generally adds a transmission tunnel and possibly a differential hump. Many of the secondary benefits of FWD are derived from its great packaging, yes, but to dismiss cost and fuel economy from buyer consideration is to be blatantly ignorant of market forces. See: http://www.nydailynews.com/autos/bu...ns-people-buy-specific-cars-article-1.2552707 where fuel economy and price rank in the top 10 reasons why people buy a new car, and interior comfort (which is on the JDPA survey) isn't.

In the dynamic traction situation you outline it may be possible for FWD to out perform RWD. However, your situation is based on the unspoken assumption that weight transfer under acceleration won't lift too much weight off of the front axle. I think your thought has some validity, but I don't think it applies broadly to all vehicles and conditions.

Strength should not be confused with stiffness, which it often is, and one should not forget that some chassis strength is derived from the cab and bed bodies. If we assume that unibodies and ladder frames are made with the same type of material, it is possible, if not likely, that unibodies would be stronger. However, unibodies are generally constructed with lower-strength steels (such as EDDS) in order to facilitate the large strains associated with their formation. They also do not benefit from heat-treatments because of the spot and seam welds used in their construction (welding removes heat treatments in a localized area, generally where stress concentrations occur). Ladder frames, on the other hand, can be more readily manufactured from significantly stronger steels and are small enough in height to be heat-treated if that is desired. The new F150 boasts about 70ksi strength steel in its frame, whereas EDDS steel used in the automotive panel forming operations I'm familiar with has a yield strength as low as 14ksi. Thus it is entirely possible for a ladder frame to be stronger than a similarly-sized unibody because ladder frame construction allows the practical use of stronger materials and heat treatments where unibody does not, and it receives reinforcement from the bed and cab, which possess unibody construction. It is also possible for the pendulum to swing the other way, so we should not assume one or the other.

Unibody is almost unarguably stiffer for vehicles of the same interior volume than ladder frames. But we must not confuse stiffness (deflection per unit force or torque) with strength (amount of force or torque sustained without permanent deformation) in the extremely dynamic loading situations a vehicle (where a lack of stiffness can prevent damage).

For your own sake, next time try for a retort that won't do well on r/iamverysmart.

I only base my retort on empirical evidence from my interactions with you.

Lets keep the discussion and differing of opinions civil and stop with the subtle insults -- DaTT

 

[agent00f]

Yaw control benefits immensely from torque vectoring differentials. Torque vectoring is more effective on AWD than any 2WD because it has ~2x as much traction to work with. Yes, selective braking can control yaw, but torque vectoring with AWD can improve ultimate cornering capacity. Again, this is a small incremental improvement, but it is a thing.

As first mentioned whatever performance improvement is limited to additional traction on throttle, and from what I've seen of typical driving, throttling early out of corners when there's much yaw still expected is uncommon in any case. In fact I can safely say I've pretty much never seen anyone else drive like that on the street.

RWD is not smaller than FWD. RWD generally adds a transmission tunnel and possibly a differential hump. Many of the secondary benefits of FWD are derived from its great packaging, yes, but to dismiss cost and fuel economy from buyer consideration is to be blatantly ignorant of market forces. See: http://www.nydailynews.com/autos/bu...ns-people-buy-specific-cars-article-1.2552707 where fuel economy and price rank in the top 10 reasons why people buy a new car, and interior comfort (which is on the JDPA survey) isn't.

Buyers principally shop on price category, ie people getting mercedes are going to get mercedes/bmw/lexus/etc and not a camry. Within that category fwd drive cars are simply going to be bigger inside, both because of some cost saving, and lack of drivetrain structure behind the firewall (rather significant diff on smaller cars). The difference is almost a whole size step up.

You can see how serious americans are about fuel economy by the size of cars they buy and the ratio of hybrids sold when that's available on a model.

In the dynamic traction situation you outline it may be possible for FWD to out perform RWD. However, your situation is based on the unspoken assumption that weight transfer under acceleration won't lift too much weight off of the front axle. I think your thought has some validity, but I don't think it applies broadly to all vehicles and conditions.

It applies to the performance case under limited traction conditions as mentioned. I brought it up because it's not well known.

Strength should not be confused with stiffness, which it often is, and one should not forget that some chassis strength is derived from the cab and bed bodies. If we assume that unibodies and ladder frames are made with the same type of material, it is possible, if not likely, that unibodies would be stronger. However, unibodies are generally constructed with lower-strength steels (such as EDDS) in order to facilitate the large strains associated with their formation. They also do not benefit from heat-treatments because of the spot and seam welds used in their construction (welding removes heat treatments in a localized area, generally where stress concentrations occur). Ladder frames, on the other hand, can be more readily manufactured from significantly stronger steels and are small enough in height to be heat-treated if that is desired. The new F150 boasts about 70ksi strength steel in its frame, whereas EDDS steel used in the automotive panel forming operations I'm familiar with has a yield strength as low as 14ksi. Thus it is entirely possible for a ladder frame to be stronger than a similarly-sized unibody because ladder frame construction allows the practical use of stronger materials and heat treatments where unibody does not, and it receives reinforcement from the bed and cab, which possess unibody construction. It is also possible for the pendulum to swing the other way, so we should not assume one or the other.

Unibody is almost unarguably stiffer for vehicles of the same interior volume than ladder frames. But we must not confuse stiffness (deflection per unit force or torque) with strength (amount of force or torque sustained without permanent deformation) in the extremely dynamic loading situations a vehicle (where a lack of stiffness can prevent damage).

The original point here is that all else equal like weight, a structure with substantial reinforcement along certain directions is going to be overall weaker than a generally strong alternative.

Also not sure what the value of the stiffness/strength semantics are other than to demonstrate you took that class in school, it's not like we're talking materials with differing yield curves.

I only base my retort on empirical evidence from my interactions with you.

That would explain why your retorts aren't any better than your empirical judgement.

As stated above, let's keep this civil -- DaTT

 

[npaladin-2000]

Guys, let me know when you're done and I'll come back.

Sent from my mobile device.

 

[OverVolt]

Brb changing title to "The forum posters on page 4, why do they exist?"

 

[Tormac]

Most of the SUV drivers I know are women who drive them because the SUV is tall and it lets them look around and see over traffic.

They never do any type of driving that would require more than front wheel drive. The fwd version gets better gas mileage on average, less maintenance and less to go wrong.

Lets face it, almost no SUV's ever get driven off-road, and almost no one needs 4wd. But I know a lot of people who either like the look/feel/height of suv's.