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I'm curious to hear of any experience in an autocross application of a solid rear axle that has been cut/torched/welded/etc. to give a small amount of negative camber (looking for about -1°). I don't really have specific questions at the moment, so I'm just looking for general input that might be helpful as to whether it's worth doing it or not. My car will use DOT r-comps and it's a Dana 30 axle with a high-preload truetrac. It's not my daily driver, but it will still be doing some street miles so it's not an autoX-only car by any means.

It's easy to do, not so easy to do well. First, do you have tire temp data that shows higher outside edge temps on your current setup? In not, cambering the rear is a waste.

Second, you will quickly destroy axles if you camber beyond that magic angle, as the splines will bind and fail.That magic angle varies by make.

Third, to do it right, you should have some sort of jig to control and measure angles as you work on the tubes. It is real easy to overdo it.

Fourth, if you need camber beyond that magic angle, you can get a machine shop to crown the OD of the splines, so they live longer.

Best of luck!

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I need a stupidity filter for the internet!

thanks for the tips. I have taken tire temps on the rear, but not frequently, and only for curiousity. I tend to focus on the front tires simply because it is a solid rear axle with pretty even temps. but I do notice a variation. maybe 2° - 5° from inside to outside. I know I get a lot more outside edge wear on the rear though. My R3S04's were nearly corded on the inner edges but had rubber on the outer edge, yet the outer edge corded first and the inner edge never rolled over enough to even touch the ground (225/45/15 pinched on a 7" wheel). That's why I think I could see some benefit. I think the plan is to first check how much the axles hang down when in a differential, then use a homemade jig, cut the axle housings, bend, measure camber after tacking the axle housings, then check half-shaft fit, and weld it up slowly. I'm not doing the work myself, and I may not even have it done to my axle. It will be tested on another car just like mine, so if it works, then I may give it a try.

The outside edge wear may be from the whole rear suspension tipping in the fast corners. Do you have a big rear bar? Can you sometimes see daylight under the inside rear tire? A solid axle can put a lot of stress on that outside edge if you are getting that much roll. I drive rwd Volvos, I know about roll. A more compliant rear may be the solution.

You may not even need to cut the tubes if you are only shooting for 1 degree. With the right press, you can often just bend one degree into the tubes.

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I need a stupidity filter for the internet!

I've used a cambered rear end for a long time in my CP car.  -1degree.  It is a full floating setup with crowned axles.   This is all pretty standard stock car stuff...they make them with up to 1.75 degrees in either direction.

You have to be VERY careful of your pinion angle and how it changes throughout suspension travel.  Camber at static can become toe, which really screws up traction in the rear.

Do you have pictures of your car in turns?  Before going to the full floater axle, the stock axle flanges used to bend a ton....I don't think a degree of negative would have kept them at 0 in turns.  This might only be a CP and Mustang issue.

HTH,

DaveW

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FSPvolvo:

I'm curious to hear of any experience in an autocross application of a solid rear axle that has been cut/torched/welded/etc. to give a small amount of negative camber (looking for about -1°). I don't really have specific questions at the moment, so I'm just looking for general input that might be helpful as to whether it's worth doing it or not. My car will use DOT r-comps and it's a Dana 30 axle with a high-preload truetrac. It's not my daily driver, but it will still be doing some street miles so it's not an autoX-only car by any means.

The details of decambering a stick axle have been discussed over at www.FRRAX.com - as I recall, if you simply heat the tubes it's been a bit more difficult than anticipated.  If it matters, F-bodies run 7.5" ring gears as OE.

 Have you actually measured the rear for camber and toe yet?  I'm betting that neither is precisely zero. 

 Another question that comes to mind deals with the width of the rear wheels vs the tire size/tread width.

FWIW, my semi-retired stick axle car has lived with about 0.5° negative camber and about the same amount of toe-in for over 20 years now, and that car was/is entirely liveable as a daily driver.  There has never been unusually rapid or uneven tire wear except for the one time I didn't keep the tires properly inflated.  No problems with splines binding at a total angular misalignment of just over 0.7°.  A little twist in the left axle splines that I suspect is connected to my son's greater interest in drag racing has been the only axle/side gear issue.

Norm

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seat time is where you find it (semi-retired) weenie CP '79 Malibu, (no longer ST/SP legal) '95 626

BigJon:

The outside edge wear may be from the whole rear suspension tipping in the fast corners. Do you have a big rear bar? Can you sometimes see daylight under the inside rear tire? A solid axle can put a lot of stress on that outside edge if you are getting that much roll. I drive rwd Volvos, I know about roll. A more compliant rear may be the solution.

You may not even need to cut the tubes if you are only shooting for 1 degree. With the right press, you can often just bend one degree into the tubes.

I've used a BRB (1"), but more recently I've decided that BFB is the way to go. Right now I'm running a truetrac for a Dana 30 jeep front axle. It's low-preload, so it will spin the inside tire in tight corners when enough weight comes off the inside tire. Last year I used the 225/45 Hoosier on 15x7. Next year I'm using 245/45 A6 or 265/45 V710 on 16x9.5. If I do the cambered axle thing, it won't be until after I have more events & data on the new wheel/tire setup. I want to run no rear bar or maybe a really small stock rear bar along with my 325lb springs. With a change to the high preload truetrac, I think I'll have plenty of traction.

It's nice to know that there are people using cambered axles in autocross. Whether or not I NEED it is another question. Thanks to all for the info and links.

I do have car pics. I'll post some up later. I'm using 475lb on struts in the front with custom valved bilsteins all around and a 1" front bar with a 3/4" rear bar. It's pretty flat...for a volvo. :)