QUOTE(Tech @ Feb 11 2005, 08:53 AM)I thought they came with limited slip from the factory and some older ones had posi as an option.
Positraction is sort of a GM term for a limited slip differential -- the terms are synonymous. "Locking" differential is similar but not exactly the same, as the former use friction (clutch) packs, whereas a locker uses a cam that forcefully locks the shafts without any slippage.
And no Volvo 240 came from the factory with it, ever (though I believe certain limited edition 140's, in the 1960's, may have). But it was, and is still, an available dealer-installed option (i.e., the warehouse still has them, I believe).
QUOTE(bloodyvolvodriver @ Feb 11 2005, 08:04 AM)hello every one can you help me please i believe the 144s + 244s could be optioned with LSD's for better traction in wet or icy conditions does anyone own one or have any info?
I forgot to add that I don't think it's a good idea for snow and ice, actually. It's really best for a racetrack. Here's why...
An open differential, the normal type, lets one or the other wheel spin, and while that's not good for getting going, the fact that there's one wheel that isn't slipping (the one with more traction) means that this wheel will hold your rear end of the car in line, avoiding a skid.
You have to remember a corollary of the cardinal rule (friction circle) of tire traction -- a tire that is spinning (or locked, as in braking) has no lateral traction, which means that it cannot resist sliding sideways.
Now, if you install a LSD, both of your rear tires might break loose and spin when you try to get going on ice. Now, with both of your rear tires spinning, your car will helplessly fishtail, either back and forth if you're lucky, or else you'll wind up spinning around and skid 180 (or even 360 degrees), like the idiot kids in parking lots doing "doughnuts", because the rear end of your car has no resistance to slewing sideways. At least, with an open differential, one back tire was less apt to spin, and could hold your car's rear in place.
Volvos, by their weight (over the rear wheels), are generally very good in snow and ice. But that assumes that you've put appropriate tires on the car. I use studded snows (currently, Nokian Hakka-2's) on all four corners on all my cars, and I never have any problems (we vacation in New England snow country regularly). If you're having traction problems, your problem isn't the open differential, but the tires you're using. By the way, it will probably cost far more to properly install a LSD in your differential (given that it's not new, the installation will require all sorts of additional pieces to get everything adjusted right) than to buy a set of four wheels and good studded snow tires.
Newbie, I'd like to add my 2 cents.......
Ken C's physics lesson is fairly accurate, but his logic is lacking. In the ice or snow scenario, you're trying to get moving, presumably straight ahead. If your car starts to "helplessly fishtail", the average driver will let up on the gas pedal. At some point, the tires will regain traction, and you'll move ahead. And the more tires that are actually trying to move the weight of the car forward, the better chance that one of them will maintain traction. Once the car starts moving, the easier it becomes to keep it moving, and so on. ( Hence, the popularity of four wheel drive.)
I do agree with Ken about the expense of adding limited slip verses a good set of snow tires. Rear- wheel drive Volvos are famously good at getting around in the snow, if you have the right tires. I have an '83 240 with generic, private label snows on the rear ($45 bucks a piece), and the car never gets stuck. (When you shop for tires, resist the urge to get wide tires; the taller and skinnier the tire is , the better the traction in snow will be.)
re: "...resist the urge to get wide tires; the taller and skinnier the tire is , the better the traction in snow will be...."
I couldn't agree more, and I'm sorry I didn't think to add that myself.
More physics , if interested:
Going in sand and even most consistencies of mud benefit from a wide, "high floatation" sort of tire, as well as lowered air pressure! In contrast, going in snow benefits most from the narrowest tread (and therefore tallest sidewalls, or high apsect ratio). Here's why:
Sand and mud have a generally uniform density through their depths -- because neither sand nor mud (i.e., the water in mud) are compressible. Therefore, the best solution is to stay out of those materials and remain above them. Also, they have a certain amount of resistance to being "pushed around" (for lack of a better term) and the tires' treads can generate some force against them, and in reaction push the car forward.
A broad tire advancing (not stationary) through sand and mud, presents a somewhat harder to sink frontal area -- lowered air pressure also helps, because it increases the area of the contact patch and spreads the car's weight over a larger area, with less pounds per square inch downward pressure pushing the tires into the sand or mud.
Snow, on the other hand, consists of ice crystals that tends to deform due to repeated cycles of compression and melting-refreezing as traffic moves over it. Very quickly, the "snow" pack becomes a material of varying density, loosest on top and densist on the bottom. Thus, there is some advantage to enabling the tread (assuming you've got appropriate snow tire lugs -- and somewhat better*, studs) to reach deep enough to "push" against the deepest, and densist part of the snow pack which best resists the tread and provides a forward reaction. Thus, you "go" better when your tires are pushing against the deep, hard packed snow at the bottom instead of the loosest "fluff" on the top [assuming your snow tires are tall enough to reach it]....
[ * studs are really of greatest advantage on glare ice, not snow, but if the material at the bottom is icy (or the snow is covering ice), it could help a bit.]
... And narrow tires reach deepest, tending to cut through the snow like a "deep V" displacement boat hull rather than a broad, "planing" boat hull that tends to rise above its substrate.
Also, increasing tire pressure helps here, lessening the area of the contact patches and increasing the downward pressure (pounds per square inch), making the tires sink better.
And, in any amount of inevitable sinkage of the tire into the snow as it is rolling forward (not stationary), the front area of the narrow tire is less than the wider tire, and there will be less snow-plow effect and therefore less resistance to advancing through the snow.
1 - 6 of 6 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.