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Old 04-28-2004, 10:07 PM   #1
Pakin
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Question The WRC 4WD System

I'm wondering if the WRC cars uses the 4WD system on the tarmac stages?

I understand back in the Group B days, the cars would spin and slide like crazy (controlled) on the corner because of thier lock.

Are the 4WD systems the traditional ones we see today on SUVs? Or are they designed differently and allow the system to differentiate speeds via driver control (maybe like DCCD?)?

Thanks,

-paK +1
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Old 04-28-2004, 10:20 PM   #2
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They still use 4wd on tarmac. The differentials are very advanced and Electro-hydraulically controlled. Not anyting at all like an SUV

They slide around hairpins by pulling the handbrake which then locks rear wheels and opens center diff.
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Old 04-28-2004, 10:35 PM   #3
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Ford built their belated Group B RS200 with a shift on the fly 2WD/4WD system. The concept was that they'd use 2WD on tarmac events, and 4WD on gravel/snow.

The cars were just as fast in 4WD on tarmac as they were in 2WD, so most of the cars had the levers removed.

Glenn
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Old 04-29-2004, 01:59 AM   #4
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Yup, the AWD system works just as well on tarmac as on gravel.

The system is way more advanced then almost anything available on a production car. Every WRCar (except the new Lancer WRC) uses active differentials, which can actively send power to the wheels that need it before any major slippage occurs.

In fact, the only reason F1 doesn't use AWD is because it is banned (it was banned due to saftey issues IIRC... driveshaft being literally inches away from drivers butt and spinning up to 12k rpm).
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Old 04-29-2004, 09:33 AM   #5
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Quote:
Originally posted by DonA
They still use 4wd on tarmac. The differentials are very advanced and Electro-hydraulically controlled. Not anyting at all like an SUV

They slide around hairpins by pulling the handbrake which then locks rear wheels and opens center diff.

do they?
you have seen this?
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Old 04-29-2004, 09:35 AM   #6
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Don't you get Speed Channel? If not, bitch to your local cable company...
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Old 04-29-2004, 01:55 PM   #7
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Quote:
Originally posted by jmott
do they?
you have seen this?
Yeah, WRC drivers do it all the time. If you watch any of the tarmac rallies, you'll notice from time to time the rear wheels will lock up and the front ones will keep spinning while sliding around a hairpin. The only way to do this is to disconnect the center diff, otherwise it would be utterly destroyed with the back wheels locked up and the front wheels spinning.
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Old 04-29-2004, 02:02 PM   #8
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Quote:
Originally posted by nKoan
Yeah, WRC drivers do it all the time. If you watch any of the tarmac rallies, you'll notice from time to time the rear wheels will lock up and the front ones will keep spinning while sliding around a hairpin. The only way to do this is to disconnect the center diff, otherwise it would be utterly destroyed with the back wheels locked up and the front wheels spinning.
This I can acknowledge. Sounds valid.

Thanks for the replies everyone.

-paK +3
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Old 04-29-2004, 02:18 PM   #9
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they did have some AWD F1 cars in the late 60's early 70's. The werent fast enough, but one almost won a race in the rain before crashing.

i love this website
http://www.ddavid.com/formula1/story...0Wheel%20Drive
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Old 04-29-2004, 02:56 PM   #10
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Here is some video of the 2002 season that shows a little tarmac fun http://www.rallyplanet.com/media/mov...wrc-2002-1.wmv

BTW - The Citroen Xsara was once a 2wd entry only run in select tarmac events. They domated so much they outraged the World Rally teams to the point that the FIA made rules more rigid for the F2 cars. Citroen built a new turbo charged 4wd WRC the Xsara T4.
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Old 04-29-2004, 06:41 PM   #11
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Quote:
Originally posted by AndyRoo
they did have some AWD F1 cars in the late 60's early 70's. The werent fast enough, but one almost won a race in the rain before crashing.

i love this website
http://www.ddavid.com/formula1/story...0Wheel%20Drive
The AWD cars were technically banned due to a saftey argument IIRC. I think it was because of a driveshaft being literally inches away from a drivers butt, and spinning at 12k rpms.

I really wonder if the AWD F1 cars could have ever become as competitive as the RWD ones.
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Old 04-29-2004, 08:01 PM   #12
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Quote:
Originally posted by nKoan
Yeah, WRC drivers do it all the time. If you watch any of the tarmac rallies, you'll notice from time to time the rear wheels will lock up and the front ones will keep spinning while sliding around a hairpin. The only way to do this is to disconnect the center diff, otherwise it would be utterly destroyed with the back wheels locked up and the front wheels spinning.
You can also see occasional shots of them pulling the handbrake on tarmac hairpins, just like on gravel.
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Old 04-29-2004, 08:21 PM   #13
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once utech was talking about driving a car with the totally active centerdiff, he said on corner entry it felt like a rx-7 (i'm fairly sure he said rx-7). i'd assume they actually open the centerdiff under heavy braking (or even engine decel?) to promote oversteer. on doug's #88 car i made a (crappy) bracket for the ebrake microswitch so the computer knows when the brake is on, but i believe he said it still didn't work (sorry doug).

a person could have the computer know when the brakes are on, ebrake is on, clutch is in, individual wheel speed, and the throttle %, so those are all imputs that could be used to decide how to control the center diff.
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Old 04-29-2004, 08:39 PM   #14
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Quote:
Originally posted by digitalpimp
a person could have the computer know when the brakes are on, ebrake is on, clutch is in, individual wheel speed, and the throttle %, so those are all imputs that could be used to decide how to control the center diff.
adding to yours...

The computer that controls the AWD system is quite advanced to a degree that is unknown to me. It collects data from various sensors around the vehicle such as yaw, g's, steering, wheel speed, and a few others and it electronically applies it's hydralic system and power the wheels that is designated to with those calculations from the sensors.

Ex.
Steering right, applying throttle will send 50% of torque to the rear outside tire and 25% to inside and 12.5% to both front wheels. Steering straight after the turn may then distribrute 65%rear and 35% front.

Ex.
If sliding/overteering out of a corner after the turn from the previous example, the yaw and G sensors will take those calculations and go from 50% of torque to the rear outside tire and 25% to inside and 12.5% to both front wheels to 25% all around OR 12.5% rear tires and 50% outside front and 25% inside front tire to pull out of the drift/slide.

This is done with the hydralic diffs.

That's my knowledge of this AWD system. Someone can correct or comment if wanting to.
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Old 04-30-2004, 11:43 AM   #15
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FYI - STI center diff opens when ebrake is pulled. I discovered that this winter.

Don
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Old 04-30-2004, 12:26 PM   #16
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Quote:
Originally posted by nKoan
If you watch any of the tarmac rallies, you'll notice from time to time the rear wheels will lock up and the front ones will keep spinning while sliding around a hairpin. The only way to do this is to disconnect the center diff, otherwise it would be utterly destroyed with the back wheels locked up and the front wheels spinning.
You can pull the ebrake to lock up the rear wheels on a WRX and it doesn't lock up the front wheels. Yes this is bad for the diff...but its not impossible...and I've done it dozens of times. Something prolonged like towing the car on 2 wheels would of course destroy the center diff.
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Old 04-30-2004, 02:52 PM   #17
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Quote:
Originally posted by jmott
do they?
you have seen this?
Last year Carlos Sainz did one and followed it through with a dual 360 on tarmac in a Focus.....
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Old 04-30-2004, 03:50 PM   #18
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Quote:
Originally posted by Calimoxo2
Last year Carlos Sainz did one and followed it through with a dual 360 on tarmac in a Focus.....
What event was that? Are you thinking about Gilles Panizzi's little spin show at the 2002 Rally Catalunya in the Peugeot 206?
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Old 04-30-2004, 05:13 PM   #19
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Quote:
Originally posted by Calimoxo2
Last year Carlos Sainz did one and followed it through with a dual 360 on tarmac in a Focus.....
Carlos drove for Citroen last year. I think you are thinking of Panizi at Catalunya in 2002 in a Peugeot 206.
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Old 04-30-2004, 06:36 PM   #20
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Quote:
Originally posted by SleeperWRX
You can pull the ebrake to lock up the rear wheels on a WRX and it doesn't lock up the front wheels. Yes this is bad for the diff...but its not impossible...and I've done it dozens of times. Something prolonged like towing the car on 2 wheels would of course destroy the center diff.
I hate to be the person who buys your car when you sell it.
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Old 05-01-2004, 12:48 AM   #21
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So what exactly is the benefit of the rally cars using 4WD over AWD? Correct me if I'm wrong, but from the things I've read, 4WD locks all 4 wheels at the same speed where as AWD varries them.
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Old 05-01-2004, 04:49 AM   #22
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If you want to draw that distinction, I believe that WR cars use AWD because the power to each wheel is constantly changing.
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Old 05-01-2004, 08:55 AM   #23
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Right but in the sport it is generally referred to as 4wd when I guess you could technically call it AWD
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Old 05-01-2004, 09:20 AM   #24
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center diff < transfer case... but essentially the same thing. Both divert power to the other set of wheels. Most AWD cars are FWD layouts with center diffs sending power to the rear, most 4WD cars are rwd with a transfer case external to the tranny sending power to the front via a separate external driveshaft at a set (locked) ratio. Again, basically the same thing... its more semantics.
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Old 05-01-2004, 06:53 PM   #25
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Quote:
Originally posted by nKoan
I really wonder if the AWD F1 cars could have ever become as competitive as the RWD ones.
I bet it would be today... but the big teams simply won't put the R&D in it i would say. It would take time for it to be competitive... simply because of the advancements of the RWD cars today...
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