Rearend camber

[Count]

Starting to set up the rearend for my corvette, and I am wondering if anybody has any thoughts on camber and toe in the rearend.  I'm working up a ford 9" full floater housing and I need to decide if I'm going to add anything or run 0 camber and toe.

[Blue]

Just an odd question here.  On the Breedlove/Fossett/Ahlstrom car the original designers set it up to have (supposedly) 1 degree of camber and toe in on the rear wheels.  We actually measured it across the range of suspension travel and it varied quite a bit.  What is typical in LSR and 300+ mph drag racing?

Granted we are comparing wheel-driven to thrust-driven;  I'm just curious.

[doug odom]

You camber and toe the rear end for cornering. For LSR you want it straight and flat.

[maguromic]

On the rear engine roadster I am working on we designed it with ½ degree of camber and zero toe in the rear. We tried to get a balance of the least amount of drag with stability. A lot also have to do with the type of tire you are running and its construction. Our rear suspension is built around the 28” Good Year LSR tire. Tony

[Count]

Thanks guys, I'll be running the goodyear 28's also.  I've been considering .5 deg. camber, just not sure if that will help or hurt things.

[jimmy six]

Tony!  Does camber on a non-independant rear housing cause drag? The concept for LSR doesn't sound right but what works is more important.............JD

[maguromic]

JD,  Both the independent and non independent rears with camber causes some drag.  But the benefits of stability gained by being on the borderline of drag outweigh the negatives. In the case of our roadster ½” of camber was the boarder line. As I stated in my earlier post a lot also has to do with the tire your running and the construction of the tire. What works with a Good Year may or may not work with a M/T and visa versa. With 30 plus years of suspension design from Indy cars to prototypes under his belt, Steve Conover designed the suspension on our car along with consultation with the Good Year engineers and the Koni engineers.  It took about three months to finalize everything.  Even though with the many-ply construction of the Good Year LSR tire doesn’t contribute as much to pneumatic trail as a standard racing tire, it was taken into consideration (Before everyone jumps on me saying this only maters in a car turning, it dose mater going straight not as much, but still maters.  Just ask a tire engineer).  It’s all built around the 28” Good Year LSR tire in the rear and the 21” Good Year LSR tire in the front and there unique characteristics and will not work with the M/T tires. This wont work on every car as there is no cookie cutter approach to all of this. Tony

[jimmy six]

     Thanks Tony for the explanation. Putting an axle without u-joints in a calculated bind is a step way above my knowledge. I believe the first any layman knew about camber in a passenger car style rear end was from listening to NACSAR on Sunday and having competitors go out of the race with problems. I can see lees of a "strain" with axle width of 55 to 60"; narrow ones may cause more problems.
     For a guy like me who uses 4 different rear tire combinations (brands too) for diameter this would be impossible. I don't want to give up that Pontiac pinion angle and with only so many ratios available for them I need the tire diameter choice.
     Thanks you've enlightned me again...............JD

[maguromic]

JD, After reading my post it may sound like only the tire characteristics were taken into account.  But other things that are also taken into consideration, suspension design, weight of car, speed objective, length of car and many more other factors.  It’s the whole package, and sometimes compromises have to be taken.  Tony

[Rex Schimmer]

The NASCAR guys can run camber becasue they have crowned splines on their axles and run full floating style hubs and axles. The crowned splines allow them to bend some camber into their rear end. Even with crowned splines you still have friction when you add camber. Friction equals horse power. If you are running a tubo 500 inch+ engine maybe it won't matter. Tony's setup uses CV joints which have considerably less friction when angled. If the tire can run with some small degree of camber I don't think that there is any doubt that it will add a certain amount of stability to the car, the real question is "is it worth all of the hassel on a straight axle"?? On an independent design like Tony is using it is just a matter of screwing some rod ends until you have the camber you want.

Rex

[John Burk]

In maybe '65 Pete Robinson had normal rear tread width with his top fueler but had a wider than normal rear and turned his Halibrands backwards for negative offset to put the wheel bearings at the center of the tread . He lost several final rounds due to having to lift because of handling problems . It then became obvious that the standard combination with the wheel bearing farther inward was bowing the axle and toeing the wheels in under acceleration and improving handling . My friend said with their Formula 5000 Lola they always ran rear toe in . Trailers sway less with the wheels toed out .

[saltfever]

(edited). . . The crowned splines allow them to bend some camber into their rear end. Even with crowned splines you still have friction when you add camber.  . . . If the tire can run with some small degree of camber I don't think that there is any doubt that it will add a certain amount of stability to the car,

Rex I'm trying to understand your post . . . sorry for all the questions. If you bend the housing to get camber, but use crowned splines, then the tire could run flat (zero camber). Or are you saying they bend the housing and add even more camber which the crown splines will allow. If wheel camber is equal to the bent housing why would you need to crown the splines? The axel centerline is exactly perpendicular to the wheel plane and there would be no relative motion between them. Or are you indicating the crown splines are in the third member where the misalignment motion takes place?

Also, we are talking very small values here (one degree)! How do you manufacture that into the housing with any accuracy? Is the housing bent, the bearing-end flanges machined that way, or the ends welded on with 1 degree misalignment?

Another thought. Could you shim the lower part of the bearing flanges to "tilt" the flange to get camber?

Very interesting thread and thanks to all.

[maguromic]

I have one 1” cambered and one ½ “ cambered 9” floater left over from my IMSA car.  Both housings came from Speedway Engineering and are both spot on in accuracy. For LSR the floater 9" seems like a lot of bearing drag.  Though I have heard some guys running ceramic bearings in floater hubs along with axle seals in the tubes to cut down on the drag.  Tony

[Rex Schimmer]

Saltfever,
You have to remember that the NASCAR guys are running "full floating axle" rear ends which is means the wheel is not mounted to an axle flange like your street car. The wheel is actually mounted to a hub that has a set of typically Timken style bearings that run on a stub that is welded to the rearend housing. Part of this hub is a drive flange that is splined and the actual drive axle is a straight shaft that is splined on both ends, one end runs in the differential and the other end engages the splines in the drive flange. If you bend the axle housing on a floater you will angle the wheel mounting hub and drive flange the amount of the bend now the straight splines on the drive axle will not fit into the drive flange without binding so they "crown" the splines on the drive axle outer end to allow it to engage the drive flange with out bind. There is still friction generated by the crown spline rotating in the drive hub but there is not binding.

If you bend a standard style housing to get camber you will actually bend the drive axle and put large stresses in the outer wheel bearing and cause bearing failure. Bearings are extremely "stiff" so any miss alignment even what we may consider small, 1/2 degree?, will cause very high stresses on the bearing and cause failure.

Rex

[saltfever]

Thanks, Rex.
I have seen full floating hubs and they seem to protrude out quite far. I think the recommended rim width for the 28" Goodyear is either 4.5' or 5". That is not a very wide rim. Isn't the floater hub likely to stick out past the rim? Can you get shorter hubs so they can be covered up?

Both you and Tony mentioned the drag caused by camber. What values are we talking about here? Assuming the pumpkin is removed (to eliminate it's drag) can the axles be turned over by hand? Are we talking inch pounds or foot lbs of torque here?
TIA