Straight Axle Camber

[Zachalanche]

I'm interested in possibly putting .5 -1 degrees of negative cambur in my 9 in rear housing. has anyone done something similar? what were your methods, and what potential problems could I run into (premature bearing wear, axle failure etc.) thanks in advance for your input.

[DynoDon]

The NASCAR boys run rear end camber on the Ovals. On banked tracks I think they will run somewhere in the area of 1.5-2 degrees positive on the left and 1.5-2.0 degrees negative on the right. On Flat track some teams will go to Zero Camber and on Road Race courses anywhere from zero to 1.8 degrees negative.
But that is with full floating axles and that helps to relieve some of the wear issues at the splines. On a non floating axles, I would not consider more than 3/4 degree or I think you will have wear issues with both the axle spline and the diff spline.

[Zachalanche]

I am running non floating axles. your recommendation lines up with my idea of staying under an 1 degree. should I be trying to add any toe?

Also more info: this is for a car that will be set up mainly for open road racing and used occasionally on track days at millermotorsports park.

[exwestracer]

With non-floating axles, you are really going to put some strain on the outer bearing seat radius area. We normally try to tweak the housing as far out as possible, but that is using a floating axle shaft. With non-floaters, you would want to bend the housing IN as far as possible, but that ends up turning the housing into a giant banana... Dead splines will end your day, but breaking the flange off the end of the axle could end your life...

Open road racing? Are you sure it's worth the risk? Mark Donohue tested the idea on his 1969 Trans Am Camaro (to the point of using CV joints at the ends of the axle shafts) and found out it wasn't one bit faster, even on the tires of the day. With modern low-profile tires, the need for counteracting sidewall flex is greatly reduced. The NASCAR guys did it (I believe they are now limited to 1deg) because they run right on the ragged edge of traction ALL the time, and it added a little life span to the right rear tire.

I'm sure there will be all sorts of conflicting opinions and examples of it being done, but non-floating axle shafts are designed NOT to bend, and that's exactly what you are asking it to do. Just my $.02 from having been there.

[DynoDon]

Ray, I think the current rules for Cup limit them to 1.8 degrees, WITH full floaters. And I agree, it's not worth the effort. I ran .5 degree in my Tiger and could never tell the difference, on old Bias Ply Race Tires. I thought about this just last week as I was prepping the rear end for the Falcon and I stayed at Zero. Putting enough strain on the little 8" 28 spline as it is - but I do like the light weight!

[silver69camaro]

It's not too hard, but you have to know what you are doing.

First you'll have to start with a housing with no ends on it and the center section installed. Install the housing ends onto the axles (Ford 9" here), and mock up the axles to your camber and toe and tack the ends to the tubes. If you're good, you can fully weld the ends with minimal alignment change. I've found this method to be more accurate then bending the tubes. Also, because of the slop in the splines, it doesn't stress out the bearing because the axle is perpendicular to the bearing surface. It works really well.

On a stock width housing, you'll have to move the axle vertically about 3/8" of an inch for about 1/2 degree of camber, so you may have to increase the weld area on the tubes. Add some toe as well, about 1/8" total. Doing this really closes the gap between solid axle suspensions and independent.

[Nessumsar]

CV joints at the ends of the axle shafts

I have always wanted to try this. So much so I have been looking around for an axle in junkyards. It seems like the eaisiest, and most practical way to add camber/toe to the rear of our cars. I also like the idea of it being adjustable by use of tie-rods.

[Zachalanche]

It's not too hard, but you have to know what you are doing.

First you'll have to start with a housing with no ends on it and the center section installed. Install the housing ends onto the axles (Ford 9" here), and mock up the axles to your camber and toe and tack the ends to the tubes. If you're good, you can fully weld the ends with minimal alignment change. I've found this method to be more accurate then bending the tubes. Also, because of the slop in the splines, it doesn't stress out the bearing because the axle is perpendicular to the bearing surface. It works really well.

On a stock width housing, you'll have to move the axle vertically about 3/8" of an inch for about 1/2 degree of camber, so you may have to increase the weld area on the tubes. Add some toe as well, about 1/8" total. Doing this really closes the gap between solid axle suspensions and independent.

from what I can tell griggs racing does it the way you described
http://picasaweb.google.com/griggsra...36531229244434

[Zachalanche]

With non-floating axles, you are really going to put some strain on the outer bearing seat radius area. We normally try to tweak the housing as far out as possible, but that is using a floating axle shaft. With non-floaters, you would want to bend the housing IN as far as possible, but that ends up turning the housing into a giant banana... Dead splines will end your day, but breaking the flange off the end of the axle could end your life...

Open road racing? Are you sure it's worth the risk? Mark Donohue tested the idea on his 1969 Trans Am Camaro (to the point of using CV joints at the ends of the axle shafts) and found out it wasn't one bit faster, even on the tires of the day. With modern low-profile tires, the need for counteracting sidewall flex is greatly reduced. The NASCAR guys did it (I believe they are now limited to 1deg) because they run right on the ragged edge of traction ALL the time, and it added a little life span to the right rear tire.

I'm sure there will be all sorts of conflicting opinions and examples of it being done, but non-floating axle shafts are designed NOT to bend, and that's exactly what you are asking it to do. Just my $.02 from having been there.

point well taken. This does however leave me curious how much there is to be gained with this. and perhaps if I determine at some point that lack of rear camber is limiting perfromance then maybe it is time to build a floating rear end.

I am also curious how much camber is possible before the non floating axle begins to bend.

[silver69camaro]

from what I can tell griggs racing does it the way you described
http://picasaweb.google.com/griggsra...36531229244434

Yep, that would be the same concept.

[exwestracer]

I am also curious how much camber is possible before the non floating axle begins to bend.

If you attempt to relocate the housing end to gain camber, you are bending the axle and putting side load (down) on the diff side gears. Remember there are no bearings in there. If you bend the axle tube at the center, you get a banana but you are only loading the splines. Either way, at 3/8" offset for .5deg as Matt has suggested(or more), something is going to be unhappy....

[exwestracer]

I have built a system to "split" the axle in half, using a splined coupler and floating inner axle shaft. I'm running a floating outer end as well, but this would elimnate a lot of the bind; as the offset is split between 3 sets of splines and the axle bend is minimized. PM me if you're interested in how it works.

Having said that, I still don't think it's worth it in the OPs application...

[rentedmule]

Couldn't you just run camber tires rather than modifying the axle?

[Wicked]

I agree, trying to run a camber rear axle is asking for trouble as far as wear goes.

The point of negative camber is so that after the car has taken a set/rolled in a corner, that the tire is still flat on the ground for maximum contact patch. On a front engine car and considering the height of the COG and proximity to the front axle, camber is required to ensure a good contact patch during roll. With a live axle, the tires surface and axle will always remain parallel to the ground. Not as much to be gained on the rear.

The other issue with camber in the rear is you significantly reduce your tire patch during forward acceleration.

[Gitter Dun]

I just came across this thread this morning and I find it funny because I was looking at some recent track photos of my car in the corners yesterday and my front tires look flat but my rear tires show alot of side load and I was thinking of a way to remedy this. The first thing that came to mind was IRS but I am interested in hearing more about adding neg. camber to straight axle set ups. I think the first thing to do would be to talk to John Griggs and ask him if he has had any issues with his housing set up. Griggs does alot of road racing so I'm sure he would know of any issues by now. Anybody here know John very well?

[Wicked]

post the pics...just curious to see them.

[Gitter Dun]

post the pics...just curious to see them.

Here are a couple of picks showing lateral loads on rear tires. Not sure if it would be worth building neg. camber into rear axle but that is one idea I am thinking about.

[Wicked]

Here are a couple of picks showing lateral loads on rear tires. Not sure if it would be worth building neg. camber into rear axle but that is one idea I am thinking about.

Generally if your wearing the front more than the rears, you need more rear sway bar. That would increase the load on the rear tires and reduce the load on the fronts. I have built a rear sway bar for a front drive car in the past. Before the rear bar, the front were doing all the work. With the rear bar added(and adjustable) we can make the rear tires wear faster and do more work than the fronts in the corner. This is especially handy on a fwd car making 532whp.

In your case, your car appears to be doing the opposite. This is probably because you have not only the lateral load but also the motive force from the rear wheel drive. Perhaps you need a larger front bar(smaller rear bar would effectively do the same thing but would allow for more total body roll) to make your fronts work harder. If would also reduce the load on your rears and allow for better out of corner acceleration.

How do your tires wear after a track session? Does it push or is it loose in corners? What about under braking?

[Gitter Dun]

Tire wear is fine but I notice the rear tires getting hotter than the fronts when I'm checking tire pressures. Car handles great until the rear tires get hot and then the car starts to get loose. The loose condition typically happens during the late afternoon sessions when the track temps are there highest. So far the car has been behaving well under braking but I should probably up grade soon. Reason I say this is because I noticed the brakes starting to fade during my fastest sessions. Once again, seems to be happening when track temperatures are the highest.

You make a good point though, I going to see who makes a bigger front bar.

[Wicked]

Tire wear is fine but I notice the rear tires getting hotter than the fronts when I'm checking tire pressures. Car handles great until the rear tires get hot and then the car starts to get loose. The loose condition typically happens during the late afternoon sessions when the track temps are there highest. So far the car has been behaving well under braking but I should probably up grade soon. Reason I say this is because I noticed the brakes starting to fade during my fastest sessions. Once again, seems to be happening when track temperatures are the highest.

You make a good point though, I going to see who makes a bigger front bar.

Reason I ask about the brakes is to understand the handling bias.