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Old 01-15-2003, 12:19 AM   #1
AWD987
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Default Difference between AWD and 4WD? And other questions...

What is the difference between AWD and 4WD?

On my tires it says max load 44 psi. Does this mean that the tires should be at 44 psi? And if I upgraded to 17in tires would my car ride smoother or would it be harsh? Also would bigger tires have any effect on my speedometer reading?

If i'm driving downhill and just hold in my clutch and coast down the hill for long periods of time, am I doing any damage to anything in my car? Usually when going downhill I just put the car in neutral, hold the clutch and brake when needed until I start loosing speed and just put it into whatever gear I need. Does it hurt my car to let the transmission slow me down? Like If I'm doing 25 in 3rd, and know I'm going to have to slow down, does it hurt the car to put it into 2nd and let the transmission slow me down?

I have heard stories about alot of people damaging the cars transmission, or clutch, is this due to driver abuse, or an actual problem with WRX's?
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Old 01-15-2003, 01:49 AM   #2
Sean
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4WD: Front and rear wheels are locked together. If you drive a "real" 4WD vehicle on the highway at speed for any extended period of time the transfer case will more than likely explode.

AWD: There's lots of expensive stuff between the front and rear wheels to keep the above from happening.

Tire Pressure: Tires should say max load and max PSI. The max PSI is cold pressure. If you're still on the stock RE92s then you should probably run a max of 35 or 38 (if you had to ask what your pressures should be, don't mess with them until you read up on what changing pressures actually does). Increasing tire pressure increases the snappiness of the car to a point and then you start losing traction. Much harsher ride. Go to www.tirerack.com and go to the Tire Tech section to read up on what changing tire pressures does.

Tire Size: Go to www.trunkmonkey.com and click on Tire Size Calculator. You can move up to a larger wheel and tire and still keep your rolling diameter the same so the speedo stays accurate. For example, the 205/60R15 (15") tires that came stock on my Impreza were replaced with 215/45R17 (17") wheels without changing the speedo at all. The first number is the tire width, the second number is the sidewall ratio and the third number is the wheel size. So, a 205/50R17 is almost the same as a 215/45R17.

Holding in the Clutch: Don't hold in the cluch. It doesn't do much damage but it still puts unnecessary wear on the throwout bearing. Just keep it in gear...performance drivers almost never use neutral or hold in the clutch for more than a second or two (except in emergencies when you're, well, spinning around in circles trying to keep the car from stalling).

Engine Braking: Use engine braking (use the tranny to slow you down) if you are performance driving. Keeping the car in gear at all times and selecting the gear that you'll need ahead of time gives you better control of the car. For normal street driving, just use your brakes. Engine braking puts unnecessary wear on the transmission.

Damaging Transmissions: If you beat on the tranny, it will explode. Period. Use common sense. If you rev to 5k RPM and dump the clutch, you'll break something. If you powershift and grind gears while your foot is to the floor on the gas pedal, you'll break something. The old gen and new gen transmissions are quite sturdy but don't take kindly to abuse. You can drive fast and push the car hard and, if you revmatch and blip and use common sense when shifting, you won't have any issues.

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Old 01-15-2003, 03:27 AM   #3
ldivinag
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Quote:
Originally posted by Sean
[b]4WD: Front and rear wheels are locked together. If you drive a "real" 4WD vehicle on the highway at speed for any extended period of time the transfer case will more than likely explode.
ummm why would the t-case explode? when in 4wd, the front output is now working. so that is taking the load and spreading it between the rear output and the front...

now other parts may explode. for example, my 90 toyota 4runner doesnt really have a speed limit when in 4wd but i think the front driveline isnt as balanced as the rear and i think the whole car will shake to pieces...
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Old 01-15-2003, 05:23 AM   #4
supermarkus
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My Jeep Cherokee with Selectrac did perfectly fine at highway speeds even in part time 4x4, it's the turning that gets ya if your drive shafts are locked all the time.
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Old 01-15-2003, 11:33 AM   #5
Jack
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Sean is spot on with his explanations. I'd only replace "explode" with "make really bad metalic noises and no longer function as expected".

With many truck type 4 wheel drive systems, they will indeed warn not to run on dry pavement at all. These are gear locked, so any speed difference at all will at best cause tremendous wear on gears in the system and at worse, break teeth. I've had these systems on plow trucks. That's what they are for. Zero slip at zero speed to push snow out of the way.

Max load AT xx PSI is telling you that if you inflate to this pressure, the tire will hold that load. There may be a different max (cold) pressure listed on the tire, but they are often the same, since you can put the most load on with the highest pressure.

Going to any different size wheel/tire can usually be done by choosing a combo with the correct aspect ratio, so your overall diameter (circumference) is the same. There are lots of tire calculators to figure this out, but going to the manufacturers site and looking for an actual circumference or rev/mile will be more accurate. A 205-55 Azenis will NOT be exactly the same width as a 205-55 RE-92.

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Old 01-15-2003, 10:33 PM   #6
SUPER RAD
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Because I am also curious, I am wondering if someone will answer the question of why going to a bigger wheel such as 17 or 18 in. makes a chnage in "ride quality". Please explain.
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Old 01-15-2003, 10:39 PM   #7
Mike Wevrick
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Default Re: Difference between AWD and 4WD? And other questions...

Quote:
Originally posted by AWD987
On my tires it says max load 44 psi. Does this mean that the tires should be at 44 psi?
The recommended tire pressure is on a metal plate near the door; also in the manual. I like to go a few lbs higher; say 35 front and 32 rear.
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Old 01-15-2003, 11:00 PM   #8
Mike Wevrick
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Quote:
Originally posted by SUPER RAD
Because I am also curious, I am wondering if someone will answer the question of why going to a bigger wheel such as 17 or 18 in. makes a chnage in "ride quality". Please explain.
Basically if you increase the size of the rim without increasing the overall diameter of the tire the amount of rubber and air between the rim and the ground decreases. This means there is less of a "cushion" to absorb bumps from potholes etc and the ride will feel firmer/harsher.
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