Saintor

Stupid and dead wrong.

Purpose of LSD is the same as AWD; to limit the loss of traction. And I owned an AWD car with a locking diff. Mind blown?

SamDoe1

And yes, given your lack of understanding, I am surprised that you owned such a car.

TacoBello

Why do you always come off with such "my way or the highway" posts? People would easily get along with you, if you didn't purposely try to antagonize time and again. How you still don't understand this, after being banned and being on various forums is beyond me. It's not that complicated.

And for the record, you are incredibly wrong. An LSD does not help in the way you are suggesting. I have one in my car and it never ever helps in getting going from a standing stop, if the ground is sloppy or icy. It just doesn't. The car behaves like any other non-lsd fwd car. I'm not sure why you are having a hard time understanding this. No one is trying to mislead you here.

wackjum

Couple of different concepts being thrown around here. This might not be super technical, but generally here are the various different things discussed to get us all on the same page:

Differential - A gearset required to allow different wheels on the same axle to spin at different rates. Because all 4 wheels on a car will take different paths while driving around, they will be required to turn at different rates in respect to one another. The drive wheels (front, rear, or all) need to be able to get the power together, but apportion the power differently as necessary.

Open Differential (or standard or unlocked) - The default differential. The design of this differential will distribute the same torque to each wheel on the axle. This also means that if one wheel does not have any traction at all, the other wheel will get negligible power and the end result is there is no forward travel of the vehicle. This is because the wheel without traction will spin very easily, getting very little torque but high spin. The open differential distributes the same amount of torque to the other wheel.

Limited Slip Differential - The differential, through different techniques, will not allow the above scenario to happen. As one wheel slips, the differential limits the slip (hence the name) and transfers this power to the slower moving wheel. This preserves some forward movement ability even if one wheel is slipping. This can also be accomplished electronically by individually actuating the brake of the slipping wheel. The slipping wheel now takes more power to turn (due to the brake being applied) and the open differential then gives more power to the other wheel.

The reason why LSDs are found on a Civic Si or TL 6MT is because those are performance biased front wheel drive cars. By its nature, FWD cars lose drive wheel grip more easily than RWD. Now that RWD cars no longer have solid beam rear axles, they tend to maintain traction over their rear wheels easier than FWD cars. Performance oriented RWD cars will also have LSD as standard or an option, but it it is not as important to them as in the FWD unless you're doing some VERY spirited driving (like a track). For commuter level cars, the more common thing now is to implement a brake LSD type thing.


All-Wheel Drive - There is a center differential that apportions power between the front and the rear wheels as necessary. Much like the differential discussion above, there are different ways to apportion the power. I don't think anybody uses a simple open differential to split power between the front and rear axles because that would be useless. Instead, there's going to be various forms of what is essentially a limited slip differential that is splitting power between the front and rear axles as needed. Some cars are usually FWD and send power to the rear during slip (cheaper to build on a front engine car), and then some cars are RWD and send power to the front in slip. This is what's called the "front" or "rear" bias.

On more sophisticated systems, there may also be limited slip differentials between each wheel on each axle. What this means is not only can power be sent front or rear as needed, it can also be sent side to side as needed. This is what the mechanical version of SH-AWD did.

Locking differential - A differential that can be locked to move as one unit. Power will be split regardless of wheel spin. This is a problem if used on road so this is reserved for off-road vehicles. A locking differential can be found at the center differential and/or one or both of the axles. In other words, a center locking diff will send power 50/50 F/R and then some cars have a rear locking diff that will send the power 50/50 L/R. And then there are some that have a front locking diff too (Jeeps, Humvees, other hardcore offroaders).

Nowhere is all of this stuff more apparent than when you go off-roading (or I suppose driving in snow).

2WD car (FWD, RWD doesn't matter) with open differential - If any one of the two drive tires slip, no forward movement of the car.

AWD with open differentials on the axles - If any one of the main drive tires slip, power is sent to the other axle. If any one of those slip too, there is no forward movement of the car.

4WD with locked center differential - Power is sent 50/50 to the front and rear axles regardless of slip. If any one tire slips on each axle, there is no forward movement of the car.

4WD with "locking differential" - This actually means one or both of the axles also have a locking differential. So power is sent 50/50 to F and R, and then if "locked" power is additionally split 50/50 L and R. So as long as a single tire on the locked axle gets grip, the car can continue to move forward.

wackjum

Before somebody jumps in to correct me, technically a 4WD vehicle has a transfer case and not a differential. But for me it has been easier to visualize and explain the concepts if you think of them in the same vein as differentials.

wackjum

Second addition - Apparently some companies do use an open center differential in AWD applications but then compensate for this inherent uselessness by throwing in electronic brake "limited slip."

The reason is cost. This would be the cheapest and mechanically simplest way to get AWD.

YeuEmMaiMai

please put down the crack pipe....you have no idea what you are talking about....

Climbing that hill in a SUBARU WITH ALL SEASONS.... I passed a row of 30+ FWD/RWD cars that were all on the side trying to go up.... tell me again how RWD is better in the snow?

AWD provides MORE TRACTIVE EFFORT AS IT CAN USE ALL 4 WHEELS to move the car forward instead of 2 at the front of rear of the car...

horseshoez

iTrader: (2)

Clearly you are reading challenged. Where have I written AWD cars do not have the advantage in acceleration?

Maybe you're the one who needs to put the crack pipe down.

SamDoe1

Good post. The unfortunate downside is that the majority of the crossovers you see on the market today use such a system with an open center diff (it's more of a PTO system but same-ish) and fix any issues with brake based traction control systems. The upside is that it's cheap to design and implement, the downside is that it's pretty useless when the going actually gets tough. This is why Subarus tend to do so well in rough conditions because they don't have an open center diff.


You've said that RWD is better than AWD and are now backpedalling when shown all the evidence that it's not.

To recap:
- RWD is better than AWD!
- Except for in the snow
- And for acceleration
- And for handling
- Doesn't make a difference for braking

horseshoez

iTrader: (2)

Incorrect, you said I said that, I didn't. Please stop putting words in my mouth, either that or quote the post where I stated RWD was superior in all aspects to AWD.

YeuEmMaiMai

uhh, is that the best retort you got? for a minute there I thought I was going to get a well thought out reply....not.. There is absolutely no scenario where RWD is better in the snow, all other things being equal

horseshoez

iTrader: (2)

Well then you really don't understand physics. In an "all else being equal" scenario, there is no question a lighter RWD car (say 330i vs. 330xi) will stop shorter in slippery conditions; simple physics.

The other most common area where a RWD car will out perform an AWD car is when rounding a bend while climbing a grade; if you understand the "friction circle" concept (posted above) you'll see every ounce of forward tractive energy put into the front wheels will cause a commensurate reduction in lateral grip.

ttribe

In each of the cases I've bolded, the additional words did nothing but act as fuel on a fire. If you want to discuss the issue, even passionately, please do so. But, quit with the insults. You've been warned.

JS + XES

iTrader: (1)

Seriously. Kids are acting like they are in junior high.

Saintor

You are definitely fuel to the fire, no mistake.

ttribe

That's enough. No more.

Chief F1 Fan

horseshoez wins because of age. Everyone else stop trying to win.

YeuEmMaiMai

No it won't, in the picture I posted I was stopped (not moving) while waiting for that civic to turn.. I mean slide down that hill... as soon as they were out of the way, away I went.... again there is absolutely no scenario where RWD outperforms AWD in the snow. not a single one. No one driving on unplowed roads gives a rat's ass about a car's dry weather performance... if you are concerned about braking performance by saying if RWD was lightew, etc, again who cares? if you are that concerned about stopping distance, do not over drive conditions...

mrmako

I never heard of an advantage braking with any type of drive. Braking is braking, unless you are letting the transmission do the braking, then AWD might slow you down a little bit more because the transmission regressive force is going to all four wheels. Now, saying a RWD car brakes better? Um, you'll have to produce some test results that show this (ie. cars with somewhat equal weight, weight distribution, and brake setup). The tyre type / contact patch and braking system plus the initial speed / road conditions are what set up your braking forces (along with vehicle weight dynamics.

I used to own an 84 Audi 5000S Wagon manual in southern Bavaria (actually Norther Austria. The weight distribution on that thing was horrible (40/60). And if anything was in the hatch, oh, boy. Winter driving in that car was a neat trick.

I'm not ancient, but I've lived a fairly long life in a lot of countries to have some experience. And FTR, I'd never drive in Russia. No f-#$%*&^ way.

horseshoez

iTrader: (2)

You folks continue to miss the point; take two otherwise identical cars, but with one lighter than the other, the lighter car will ALWAYS stop shorter, all else being equal.

Consider the following:

• 2018 BMW 330i -- 3,541 pounds
• 2018 BMW 330xi - 3,706 pounds -- 165 pounds heavier

• 2018 Mercedes-Benz C300 ---------- 3,417 pounds
• 2018 Mercedes-Benz C300 4MATIC - 3,594 pounds -- 177 pounds heavier

• 2018 Infiniti Q70 5.6 LUXE ------- 4,043 pounds
• 2018 Infiniti Q70 5.6 LUXE AWD - 4,239 pounds -- 196 pounds heavier

• 2018 Chrysler 300 Limited ------- 4,013 pounds
• 2018 Chrysler 300 Limited AWD - 4,267 pounds -- 254 pounds heavier

So, given the AWD drivetrain imbues zero braking benefit, the lighter RWD car will always stop shorter. Are we now on the same page?

mrmako

This does not answer the braking question, but explains FWD/AWD/RWD pretty well:

https://www.digitaltrends.com/cars/fwd-vs-awd-vs-rwd/

horseshoez

iTrader: (2)

The article says:

"Honda’s long list of affordable performance models, with the exception of its NSX, have been built exclusively on front-wheel drive platforms."

Hmmm, maybe they've never heard of the S2000.

wackjum

First of all, a lot of these arguments I've been seeing are very clinical or academic. There's also been a lot of focus on snow driving, but that's not really relevant to 00TL who lives in Houston with me. I say clinical or academic because it has to do with paper statistics. Have you guys actually driven all of these different cars?

We've been saying RWD is more fun. Seems everybody, including myself, have been guilty of just kind of glossing over the basics but we haven't said why RWD is more fun. Legend2TL did provide some explanation, but I think we need something that covers the fundamentals and translates to real world experience for the uninitiated.

Right now in my driveway, I have FWD (Acura CL-S 6MT), RWD (Acura NSX, SL55 AMG), and AWD (911 Turbo). So I've driven them all. In plain words, this is how they are different.

Like I said previously, AWD helps manage power. Tires have a finite amount of grip. If you have RWD, you're splitting the power by half. If you have AWD, you're splitting the power 4 ways. Since tires can only generate so much grip, as power gets higher, having power split among more tires means that an individual tire doesn't get overwhelmed. The easier it is to overwhelm the tires, the more skill it takes to make sure the tires don't get overwhelmed and result in a total loss of control that the driver is not skilled enough to recover from. This is why high horsepower cars tend to have AWD.

The reason why RWD "is more fun" is because of rotation. When you go into a turn, you have to get the front facing where you want to go. This rate of turn is usually influenced by the steering wheel. But if you can get the rear tires to slide laterally a little, you can "rotate" the front of the car around quicker. In a RWD car, this can be accomplished by giving a little gas. The power overwhelms the rear tire's grip and they slide a little. This is called power induced oversteer. A little bit of of slide is called rotation. A lot of slide is drifting. This takes a bit of skill (and I'm not very good) but when you get it, it is thrilling. This is also not really reproducible on the street. Maybe on some back roads, but don't slide into the ditch!

With FWD, the technique to get around a turn quickly is different. You can't simply add power to step the rear out a little. The rears in a FWD car will almost always have more grip than the fronts so there's no rotation. Instead, the technique with FWD is to get a little bit of trail braking (because braking transfers weight to the front and presses down in the power wheels) and then power your way out of the turn. Point the car's front where you want to go and get on the throttle and have the front tires claw your car out of the turn (this is why FWD cars need an LSD. If either of the two tires lose grip, you're not going to go anywhere with an open diff).

With AWD, you're splitting the power to all wheels so it is a lot harder to overwhelm the tires. Driving AWD fast around turns is closer to FWD than it is to RWD. Go into turns a little hotter than with a RWD car and use weight transfer and some throttle to slide the rears and get some rotation (if you have a RWD biased system), and then nail the gas once your front is pointed where you want to go. The 4 tires will grab and push you out of the turn.

As you can see, FWD and AWD technique is more noob friendly. A lot of it is "point and squirt" whereas RWD takes more finesse. But in the hands of a better driver, being able to rotate the rear is going to get you around a turn faster than steering inputs alone. This is why the 911 Turbo is AWD and the GT3 is RWD.

mrmako

And what I found concerning snow braking:

https://www.youtube.com/watch?v=fMHSBXjiyac

horseshoez

iTrader: (2)

Same link as before; do you have a new one? I'd like to review the article.

RDX10

mrmako

fixed. refresh your screen.

1killercls

Kill me now.

SamDoe1

You are absolutely right that FWD and AWD is more noob friendly on a track. On the road, FWD and AWD are more manageable on a daily basis and FWD is lighter, easier to build, and more fuel efficient. For a daily, AWD is for those few days a year when you really need it...and on those days you're glad you have it.

If you toss in the caveat of "everything equal" then yes, you are right. But often times, things are not all equal. For example, the E46 AWD 325xi had the larger brake calipers from the 330i/xi instead of the normal ones from the RWD 325i in order to manage the issue of weight. It's not the same as just pointing from one to another and say "hey! they're the same!" as that's probably not true.

horseshoez

iTrader: (2)

I've been saying "all else being equal" since this thread started.

SamDoe1

But that's not a correct assumption to make.

horseshoez

iTrader: (2)

Sorry, not buying. Your example of the E46 is very much the exception.

Regardless, the E46 325i will still stop shorter than the 325xi.

TacoBello

You're seriously splitting hairs here. Yes, a car that weighs 200 pounds less will marginally brake better than one that weighs 200 pounds more. But... you're over simplifying it kind of. In my experience, in snow, it's better to have that extra 200 pounds when trying to get traction. But there's also so much more that can play into it- you simply change the tires, or wheel size, and numbers start changing all over the place. It's not unusual to move down a size or two when it comes to winter wheels (width and diameter). A narrower tire sinks deeper into the snow, giving more traction, as opposed to a wider wheel that will float more on the snow.

Either way... sure... you win. a RWD may marginally brake better than an AWD car... under certain conditions. I really wonder if anyone would actually notice the 4 feet they would stop sooner, or not.... unless that 4 feet results in someone being in another person's back bumper But again... this is assuming the cars are 110% identical in every way, save for drivetrain... which isn't always the case.

horseshoez

iTrader: (2)

Forgive me for splitting the hairs. On more than one occasion folks in this thread have maintained AWD was superior in all aspects in winter conditions; all I've been trying to do is to point out the flaw in that logic.

Regarding the extra weight; sorry, a heavier car, all else being equal, will always stop in a longer distance in the snow.

SamDoe1

Come on over, we can find a snowy road and see if your car stops faster than my Jeep. Well provided it makes it to the snowy road to begin with and then can actually get up to 60mph before stopping in the distance we have that is.

horseshoez

iTrader: (2)

Not sure what you're getting at; you're proposing an apples to grapes comparison; no benefit in that at all.

SamDoe1

Well no, by your logic your lightweight RWD car should stop miles ahead of my heavy AF Jeep. Any car to car differences should be a wash given the vast divide in weight right?

horseshoez

iTrader: (2)

Where is the "all else being equal" element of comparing my TL to your Jeep?

1killercls

SamDoe1

There isn't but again, by your logic, you should stop miles ahead of the Jeep right?