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trackrat79
06-01-2006, 03:22 PM
Has anyone used a cambered non-independent rear end? Nascar uses them and some road racing teams use them but I don't know anyone personaly that has expieriance with them.

RobM
06-01-2006, 07:32 PM
for a street driven vehicle you would wear tires like a sum of a bitch. but most of our cars do that any way. my question is how much maintenance does a rear end like this need? i assume it would have to be a full floater? how much camber is usualy built in? how much would it take for the tire to wear flat enough to cancle this out? I need to concentrate on making the front of my car hook up harder in corners...

Norm Peterson
06-02-2006, 03:46 AM
Tire wear isn't necessarily bad - that depends on how much camber exists (and also on how much toe). I suspect that the harder (on average) and more frequently you take corners the more a slight amount of negative camber might actually be beneficial.

The axle on my '79 has about -0.5* camber and some toe-in, and I don't have any unreasonable rear tire wear rate. I have no idea how much of it came as OE and how much occurred over time and loading. Anyway, aside from a pinion nut that came loose, a pinion that started shedding teeth and one dead posi, it has required no maintenance other than checks for fluid level since 1986. As I understand it, you can go up to about one degree of combined toe and camber before the splines need a special profile to accommodate the angular misalignment.

Keep in mind that under cornering, a stick axle does move such that the wheels change their camber relative to the road. Just how much depends on the amount of lateral load transfer across the rear axle and on the spring rates of your rear tires. A rough guess might be about one degree per lateral g. Optimum cornering camber may differ slightly from that, as most tires develop their best lateral grip at some slight amount of negative camber. But carried too far, it starts interfering with straight line acceleration and braking.

Norm

RobM
06-02-2006, 04:07 AM
i think tires with some side wall would work well. my theory is the camber would compensate for some of the side wall deflection. i didnt know the splines could ride at an angle in the carrier.

wendell
06-02-2006, 04:59 AM
Some where around 0.75 is the limit for traditional axels. After that the loads will start to shorten the life span of the rear. Crowned splines allow for the missalinement and return the axel to it's prefered "floating" state.

trackrat79
06-02-2006, 08:20 AM
I don't put a lot miles on the vehicle and at some point I would like to make it a track ready vehicle. At this time the car is riding on 295 50 15 all around and I plan on sticking with the 15" wheels. I want to go wider in the back but wheel diameter will stay the same.

funcars
06-06-2006, 05:37 PM
I've run one with 1.5 neg each side. It had to come out and I put a regular non-cambered floater back in until I have my torque arm in the car to keep the pinion angle under control. You get soem pretty nasty toe changes in a bad direction unless you have a link type of suspension. They wear tires but so what. You need to get crowned axles and hardened drive plates. Make sure to get the toe dialed in by stock car products or speedway engineering or someone that knows how to do it properly.

It's pretty durable stuff. Street only use doesn't make sense, but if you run it hard on the track too it helps. You will also need to change roll stiffness to get everything working right because you will have more grip in the rear.

Hope this helps.

trackrat79
06-07-2006, 08:09 AM
Finaly someone that has actually used it. I am not worried about toe to much. 68 chevy shortbed pickup is the project vehicle. Long arm suspension, adjustable anit sway bars, adjustable spring pirches, all the fun stuff.

Norm Peterson
06-07-2006, 08:22 AM
You want just enough static toe-in to keep the outside tire from toeing out as the pinion angle varies. Too much static toe-in will add a separate understeer effect (and toe-out will tend to make it loose).

Norm

RobM
06-07-2006, 04:53 PM
verrrry interesting.

trackrat79
06-08-2006, 09:10 AM
:confused: How does the toe change on a solid axle during suspension travel?

Damn True
06-08-2006, 09:23 AM
If it's straight it dosent. If there is toe built in though it can change as to the degree of pinion angle change.

TLWiltman
06-08-2006, 10:26 AM
I think you'll be able to visualize this...

Let's say you have a cambered rear end... 1* @ 0* pinion angle.

As the pinion angle becomes more negative (pinion down), some of the negative camber becomes toe-in. The extreme of this would be at 90* pinion down, at which point there would be NO negative camber. There would, however, be 2* of toe-in (1* per wheel).

As the pinion angle becomes more positive (pinion up), some of the camber becomes-toe out (this is VERY BAD!).

When I bought my cambered rear axle I had the camber set at 0 pinion angle. When the pinion angle gets set at 2-3* down, I'll have a bit of toe-in without getting into toe-out under acceleration.

IOW camber+rotation=toe.
Yes, you are worried about toe.

trackrat79
06-09-2006, 12:46 AM
I get that if you camber the top of the tire in that the camber starts to add toe as the vertical center line of the tire mores with the pinion angle. But with the limited amount of suspension travel a streat car has is this realy a worry. The only time I could see the tires going to toe out is under heavy deceleration and thats not a bad thing as it will help the rear end rotate around the corner better.

Norm Peterson
06-09-2006, 02:43 AM
Using oversteer effects at the rear is more appropriate for auto-x than either higher speed track stuff or out on the public streets. In the latter two cases, it only has to get away from you once to make for a rather bad day.

Note too, that you can get several degrees of pinion angle change just due to bushing compliance, and this would be a toe-out effect during acceleration.

Norm

trackrat79
06-09-2006, 09:00 AM
Bushing compliance. The only way the pinion angle is going to change is if the welds break on the axle perches. I don't have leaf springs or a four link for suspension to have to worry about axle rap distorting bushings.

Norm Peterson
06-09-2006, 01:35 PM
It was a general comment. If you have a truckarm, particularly one with a hard or solid chassis side attachment, or a completely rod-ended link arrangement it isn't really applicable. But in the absence of any such information I really have to assume that bushing compliance and its geometric consequences are present, and address the issue accordingly.

Norm

trackrat79
06-09-2006, 10:27 PM
I thaught I had mensioned that this is for a 68 1/2 ton pickup. All solid bushings. So some of your info may not aply but it is still good to know for other vehicles I may be involved in further down the road.

chicane67
06-10-2006, 12:43 PM
I have done quite a few cambered rear's...

But on a street chassis that isnt going to spend the majority of its life on a track.... 0.50* is max without using cambered snouts or bevel cut splines on the axles. You will find that you will go thru side gears and clutch packs more than anything. Tire wear isnt really an issue unless you do a lot of straight line driving and never turn.

The truck arm suspension in your 68 will still toe-in the outside tire under compression due to the fact that your IC will change. Your upper link is pretty short if I remember correctly. I did a 68 about 10 years ago that had a DANA60 in it with lots-o-cubes and found that it was almost a set requirement to run a bushing with some compliance.... as soild bushings would bind, even in very limited travel.

Planting your IC is going to be very key. Not only to control any unwanted IC change, but because it concurrently changes the toe at the same time.

trackrat79
06-12-2006, 02:27 PM
WHat is IC .and ther are no upper links on a truck arm unless you are refering to the track bar that centers the rear end between the fraim rails. If you are I don't have a stock track bar. I fabd up my own fully adjustable full width one that has very little side movement. I stll don't see how the toe can change when the axle is locked in place front to back.:hmm:

Damn True
06-12-2006, 02:48 PM
IC = Instant Center

Norm Peterson
06-12-2006, 06:04 PM
It still rotates about its side view IC, though perhaps not a whole lot. Then again, there isn't a whole lot of difference between a 50" side view virtual swing arm and a 50" real swing arm (with a physical arm and pivot) . . .

Norm

RobM
06-12-2006, 06:56 PM
with sour suspension having not much more then 3-4 inches of travel max, i cant see the toe changing a noticable amount

wendell
06-13-2006, 04:19 AM
rat,

TLWiltman did a pretty good of explaining the relationship between rear camber and toe. To recap...

With the pinion angle at 0 and 1 degree of negative camber,the top of the tire is pointing towards the center line of the car in the verticle plane. If the pinion angle is at 90 degrees the pinion is pointing straight up your 1 degree of camber is now 1 degree of toe out(the rear edge of the tire is pointing at the center line of the car in the horizontal plane). If the pinion is further rotated to 180 degrees (pinion pointing at the rear of the car) your degree of negative camber is now 1 degree of posstive camber.

Because your truck arm rigidly mounts the axel, pinion angle will change as the suspension moves the axel up and down. Any change in pinion anlge will correspond to a change in the camber /toe relationship. Hope that helps.
edit: three new posts by the time I was finished

TLWiltman
06-14-2006, 01:02 AM
Basically, if you have 0 toe at 0 pinion angle, and then add some negative pinion angle you should be perfectly OK. The big thing is that you NEVER have toe out. Also, with a T/A rear suspension, the pinion will rotate upwards a bit under acceleration due to the rubber bushings at the front.

trackrat79
06-14-2006, 01:41 PM
I don't have rubber bushings in the trailing arms. With the length of the arms the dagree change from travel is about 15-20. Is that really enough for me to be worried about toe out and what would you recomend I have the pinion angle set at to minimize that possability. Given a 1 dagree camber set for each wheel.

RobM
06-14-2006, 07:52 PM
are you running solid bushings or just somthing harder then rubber? im building a rear suspension and im trying to decide what to do with that.

TLWiltman
06-16-2006, 12:45 PM
are you running solid bushings or just somthing harder then rubber? im building a rear suspension and im trying to decide what to do with that.
Options for truck-arm mounts...
-Rubber
-Speedthane-compounds range from hard to soft. Often used for tuning by NASCAR teams.
-monoballs

Pinion angle. If your 1 degree camber is at 0 pinion angle, I would think... -3 to -4* pinion angle should work. With monoballs, you might be able to reduce that to 2-3*

cagedruss
08-02-2006, 01:36 PM
I would not suggest it. Puts abnormal wear and force on the factory Axle bearings. Generally we use about 1-2 degrees neg. Camber on the axle tubes. But we are using floater housings with a rather large wheel bearing and they are easier to inspect and change.

Norm Peterson
08-03-2006, 02:56 AM
More than 1 and you do need to do things a bit differently.

But I'd rather have about -0.75 than zero, and absolutely do not want to see any static positive camber back there. Having it go slightly positive dynamically due to axle roll means that you're already giving up some grip on the end that you have no direct control over - with this occurring at the time you need all the grip you can find.


Norm