Why Front Wheel Drive Sucks (And Why Rear Wheel Drive Is Coming Back)

[Thorin]

There's several types of limited slip differentials available.  Funny enough, the one that's used on the HMMWV (or Hummer in it's civilian guise) is the Torsen system.  The manual for the HMMWV actually suggests applying the brake lightly to keep a wheel that's off the ground from spinning so that all its torque can be transferred to the other wheel.

Applying the brake on one wheel so that it doesn't take any of the torque the engine is producing is an excellent concept, in my mind.  That's not to say it hasn't been implemented poorly in some vehicles, though.

(Hah hah, Lazy and I both read the same LSD article, although I knew about the HMMWV using Torsen before I read that article).

[Melbosa]

Traction Control should be superior to common limited slip differentials. In most cases the differentials will reduce over all power to reduce wheel speed, where as Traction Control only reduces the speed of the free wheel, transferring all of the power to the other wheel. The negatives I can see for traction control are two fold as I have had a far amount of driving time on cars equipped with it. 1. It can be loud, just like some ABS systems. On my car it makes a GRRR GRRR noise when it engages. 2. It will at will at extra wear on your break system. 3. Don't try and do a burn out with it engaged.... it is counter productive.

Traction Control is superior to standard differentials.  Limited Slip diffs, even according to your article do, the transfer of power that you are talking about in your line about Tranction Control.  Traction Control limits the speed of the tire it is working on, but does not by definition cause any power to be transferred anywhere else as a mechanic. It may happen as a result, but that is more the mechanics of other parts of the car, not the Traction Control system itself.  Limited slip on the other hand does this as a design:

A limited-slip dif' is a type of differential which uses either fluid or mechanical mechanisms to control the amount of power being directed to a particular wheel. When a wheel loses contact with the ground a standard differential will transfer all power to this wheel and none to the wheel which remains in contact with the ground. This means this axle is no longer effective in driving the vehicle. The limited slip dif' reduces the amount of power going to the wheel which is no longer in contact with the ground. This allows the other wheel to retain a varying degree of efficiency depending on the type of limited slip dif'.

Source: http://www.fronteraowners.co.uk/info/using4wdfaq.htm

The solution to these problems is the limited slip differential (LSD), sometimes called positraction. Limited slip differentials use various mechanisms to allow normal differential action when going around turns. When a wheel slips, they allow more torque to be transferred to the non-slipping wheel.

Source: Link from Lazy

[Melbosa]

In any case, I think we've covered most of this stuff on this thread.  There is a lot of helpful information posted here for the average driver, and a lot of help on how to handle our winter roads.  Good luck out there and drive safe.

[Melbosa]

As a side note:  Here is a nice tool for determining changes in size tires (for what the tire will look like at that size):

http://www.miata.net/garage/tirecalc.html

And a good link for tire sizes themselves:

http://www.nationaltire.com/basics/default.asp

[Thorin]

the larger diameter tires do help with clearance [...] The downside is burning some rubber on hitting bumps when I have heavier passengers in my back seat and a full load in the trunk

If your tires are contacting *any* part of the body of your car, you might as well be juggling a couple of hand grenades with the pins pulled.  In this scenario, tires will wear prematurely in weird ways and fail *spectacularly* at the most inopportune times, possibly causing collisions, roll-overs, and injury.  For instance, tires that come into contact with the top of the wheel well repeatedly have a much higher chance of having the steel belts break, at which point the tire will try to re-form itself from looking like a car tire  (flat tread) to looking like a bicycle tire (round tread).  If the belts break without the tire bursting, you're vehicle will now have little traction on that corner of the vehicle because so little of the tire is still touching the ground (as opposed to a flat tire where lots of your tread is touching the ground).  If this happens at highway speed, you're likely to careen off the road in a random direction.

Vehicles are designed (and they were in 1985 as well) to never have contact between tires and car-body.  Even if your springs are completely compressed and hitting the bump-stops, the correct size tires for the vehicle will not touch any part of the body of the car.

The rims that came with the car were 195 70 R14, so that's what I got when I replaced the old tires on buying the vehicle, since they were nice rims and I didn't want to buy new ones.

Rims are measured in diameter and width.  Most likely, they were 14" x 6", with a J lip (less common is a JJ lip).  Tires are measured as 195/70R14, which means 195mm wide tread, sidewall height is 70% of tread width (195mm x 70% = 136.5mm sidewall height), the tires are Radial tires, and the tires fit on 14" wheels.  According to The Tire Rack Online, your Celica is supposed to have 185/70R14 tires on it.  The 195/70R14 tires that you have are 10mm (5%) wider and 14mm (2.3%) taller, with 44mm (2.3%) more circumference.  This may be just enough to allow rubbing against the car body, which really shouldn't happen.  It also means that your speedometer is 2.3% slow (100km/h on the speedo is really 102.3km/h).  There should be a metal plate attached to one of the door jambs, the inside of the glove box, or the inside of the gas filler door that specifies the correct size of tire for the vehicle, if you want to double-check what The Tire Rack lists.

[Shayne]

Nice post Thorin

[Thorin]

Thanks.  Was it the deft use of quotations, or the sexy mathematics that made you like it?

[Ustauk]

the larger diameter tires do help with clearance [...] The downside is burning some rubber on hitting bumps when I have heavier passengers in my back seat and a full load in the trunk

If your tires are contacting *any* part of the body of your car, you might as well be juggling a couple of hand grenades with the pins pulled.  In this scenario, tires will wear prematurely in weird ways and fail *spectacularly* at the most inopportune times, possibly causing collisions, roll-overs, and injury.  For instance, tires that come into contact with the top of the wheel well repeatedly have a much higher chance of having the steel belts break, at which point the tire will try to re-form itself from looking like a car tire  (flat tread) to looking like a bicycle tire (round tread).  If the belts break without the tire bursting, you're vehicle will now have little traction on that corner of the vehicle because so little of the tire is still touching the ground (as opposed to a flat tire where lots of your tread is touching the ground).  If this happens at highway speed, you're likely to careen off the road in a random direction.

Vehicles are designed (and they were in 1985 as well) to never have contact between tires and car-body.  Even if your springs are completely compressed and hitting the bump-stops, the correct size tires for the vehicle will not touch any part of the body of the car.

The rims that came with the car were 195 70 R14, so that's what I got when I replaced the old tires on buying the vehicle, since they were nice rims and I didn't want to buy new ones.

Rims are measured in diameter and width.  Most likely, they were 14" x 6", with a J lip (less common is a JJ lip).  Tires are measured as 195/70R14, which means 195mm wide tread, sidewall height is 70% of tread width (195mm x 70% = 136.5mm sidewall height), the tires are Radial tires, and the tires fit on 14" wheels.  According to The Tire Rack Online, your Celica is supposed to have 185/70R14 tires on it.  The 195/70R14 tires that you have are 10mm (5%) wider and 14mm (2.3%) taller, with 44mm (2.3%) more circumference.  This may be just enough to allow rubbing against the car body, which really shouldn't happen.  It also means that your speedometer is 2.3% slow (100km/h on the speedo is really 102.3km/h).  There should be a metal plate attached to one of the door jambs, the inside of the glove box, or the inside of the gas filler door that specifies the correct size of tire for the vehicle, if you want to double-check what The Tire Rack lists.

Thanks for the info.  I've always known my speedometer's been off.  As for the rubbing, this only happens in the few instances when I'm running a full passenger load and a full cargo load in the trunk, or when I'm making a really sharp turn.  If it was doing it all the time, I'd be worried given what you have said, but I think it'lls be ok given how its only infrequently I've had this trouble.  The only time I smelled rubber over a good deal of the trip was with four people in the car and a full load in the trunk on the way to and from Lazy's house warming, and even then it was only happening when I hit bumps along the road, mostly by Tom's place.  I'll probably get my tires rotated in the spring, so I'll ask for them to look for odd wear then.  Thanks.

[Thorin]

As a side note:  Here is a nice tool for determining changes in size tires (for what the tire will look like at that size):

http://www.miata.net/garage/tirecalc.html

Thank you!  Now I can tell my wife that we need 215/40R20s for the new minivan, when we buy it (up from 215/65R16s).  Just so we can say we've got 20" rims...

[Mr. Analog]

Thanks for the info.  I've always known my speedometer's been off.  As for the rubbing, this only happens in the few instances when I'm running a full passenger load and a full cargo load in the trunk, or when I'm making a really sharp turn.  If it was doing it all the time, I'd be worried given what you have said, but I think it'lls be ok given how its only infrequently I've had this trouble.  The only time I smelled rubber over a good deal of the trip was with four people in the car and a full load in the trunk on the way to and from Lazy's house warming, and even then it was only happening when I hit bumps along the road, mostly by Tom's place.  I'll probably get my tires rotated in the spring, so I'll ask for them to look for odd wear then.  Thanks.

Actually, from what I've heard any scraping is typically a bad sign, under load or not.

[Shayne]

Thanks.  Was it the deft use of quotations, or the sexy mathematics that made you like it?

Well thought out I guess.  I read it, understood it all.

[Melbosa]

As a side note:  Here is a nice tool for determining changes in size tires (for what the tire will look like at that size):

http://www.miata.net/garage/tirecalc.html

Thank you!  Now I can tell my wife that we need 215/40R20s for the new minivan, when we buy it (up from 215/65R16s).  Just so we can say we've got 20" rims...

You and the escalades

[Melbosa]

Thanks for the info.  I've always known my speedometer's been off.  As for the rubbing, this only happens in the few instances when I'm running a full passenger load and a full cargo load in the trunk, or when I'm making a really sharp turn.  If it was doing it all the time, I'd be worried given what you have said, but I think it'lls be ok given how its only infrequently I've had this trouble.  The only time I smelled rubber over a good deal of the trip was with four people in the car and a full load in the trunk on the way to and from Lazy's house warming, and even then it was only happening when I hit bumps along the road, mostly by Tom's place.  I'll probably get my tires rotated in the spring, so I'll ask for them to look for odd wear then.  Thanks.

Actually, from what I've heard any scraping is typically a bad sign, under load or not.

Ust's are from the tires. I know Ray told him when he bought it that they were bigger that should be on the car.  The previous owner thought they looked kewl.

[Ustauk]

Thanks for the info.  I've always known my speedometer's been off.  As for the rubbing, this only happens in the few instances when I'm running a full passenger load and a full cargo load in the trunk, or when I'm making a really sharp turn.  If it was doing it all the time, I'd be worried given what you have said, but I think it'lls be ok given how its only infrequently I've had this trouble.  The only time I smelled rubber over a good deal of the trip was with four people in the car and a full load in the trunk on the way to and from Lazy's house warming, and even then it was only happening when I hit bumps along the road, mostly by Tom's place.  I'll probably get my tires rotated in the spring, so I'll ask for them to look for odd wear then.  Thanks.

Actually, from what I've heard any scraping is typically a bad sign, under load or not.

Ust's are from the tires. I know Ray told him when he bought it that they were bigger that should be on the car.  The previous owner thought they looked kewl.

Yup, I knew going in they were oversized, but I was too cheap to buy smaller rims, and I did like the way they looked as well.  The tires were brand new when I bought them, and I haven't put that many kilometres on them, so I think it should be ok.

[Cova]

I haven't posted in here yet, cause I don't even know where to start with this thread...

As for the original subject, I didn't bother to read the article, but yes RWD is ALWAYS better than FWD in all situations (except stupid examples designed to make it bad eg. stopped with only rear-wheels in an icy hole).

As to other points...

Tire diameter is really irrelevant as far as traction is concerned - ground clearance is the only thing affected.

In the summer on wet/dry surfaces you typically want a wider tire.  On snow/ice you typically want a narrower tire.

When stuck, you do NOT want the wheels to be spinning - you get maximum friction (traction) when there is no spinning/slipping, once you break friction it will continue to slide/spin easily.  It doesn't matter how your specific traction control works, if your tires are turning at least as fast as the car is moving forward it won't hurt anyone trying to push the vehicle - preferably though the tires are spinning as slowly as possible, such that if the car starts to move forward the tire will grip and stop spinning, thereby actually pulling the car instead of a person pushing it.  Yes - 99% of people who get stuck are idiots who don't know better than to floor it.