Fully locked diffs in RWD front engined live axled cars.

[Al Weyman]

I was surprised to discover that when the IROC NASCAR race cars were used on a road course they used a fully locked diff not a slipper but used a slipper on an oval course. I am having trouble getting power down to the ground on my reasonably powerful front engined RWD car and wondered if I should go the same route. I have spoken with a friend who raced a powerful SDI and he recon he locked the diff up so tight it may as well be fully locked so i wondered if anyone else has had any experience circuit racing (road racing in the US) with a fully locked diff and what were your impressions of the set up. I would imagine with a FWD car it would be undriveable and with an IRS car unneccessary which is why I am asking about a front engined rear wheel drive car with solid live rear axle which by its very nature will tend to lift a rear wheel at high cornering speed and loose traction.

[bdwoody]

al we in the xsport racing stable have a couple of cars in this configuration .RS500 x thunder saloon and a ford falcon aussie v8 both run with what they call a spool diff which is a bit miss leading as there is no diff just the cwp.it does tend to push on a little but this can be dialed out and if you do lift a wheel you dont lose traction.if you hoof it the tail will step out which is always good for a picture or 2..

[Al Weyman]

Thats interesting, If i decide to go this route I would fit a spool as they are available for the axles, in my old HotRodding days I would have reached for the arc welder. :-)

[1200Datto27]

The V8Supercars have the pivot point for the watts link setup on a nut with a threaded rod on it attached to a external adjuster, to allow for the rear roll center to be adjusted mid race, depending on whether the driver wants more front end bite, or grip from the rear. The way that this affects the car is that by raising the rear roll center, the roll action during cornering lifts the inside wheel off of the ground, allowing for the car to turn better. Conversely, if the driver wants to get the car to drive off of the corner better, the rear roll center gets lowered, resulting in less weight transfer and keeping the inside wheel on the ground.

[Al Weyman]

Don't they have Independant Rear Suspention like the Holden Commadore?

[1200Datto27]

Nope, both the Holden and Ford V8Supercars run a Ford 9" live rear axle, the road cars that they are based loosely on have IRS. The Bathurst 24 Holden Monaro had an IRS system in it however.

[coln72]

Go for the spool. Used to run an early Corolla with a welded diff (I know its not in your power leauge) and yes it would understeer if you tried to corner with any power on. This was dialed out mostly by playing with spring rates and front end settings.

Driving style also had to be changed to suit the characteristics of the car. Had to get off the throttle, get the car turned in and then get back on it (in my case usually looking through the side windows )

[Al Weyman]

I think if I go for it I will also go for some uprate Strange or similiar axle shafts as well as the standard ones look a bit puny.

[bdwoody]

al take a looksee at a falcon 9" rear axel if you get the chance it has fully floating hubs and ball ended halfshafts so you can adjust camber and toe in/out, all pretty trick realy...

[Al Weyman]

Rules say I have to use what came with the car externally at least, I have a full house 9" in the Penske IROC Racer in my garage.

[watty]

Last season I used both a TRD slipper, and a locked (welded) after I fizzed the some teeth off the crownwheel of my slipper. It was very different to drive, but certainly not undriveable - the car was only 3/10ths of a second slower best lap vs best lap.
I certainly wouldn't hesitate to use one again - the only real down side was higher tyre wear on the front due to the a higher level of intial understeer on high speed corners.