Autocross straight axle front suspension camber question

So a friend of mine is building a 1998 ZJ Grand Cherokee 5.9L Limited for autocrossing in CAM-T. I'll wait for that to sink in.  He is running 225 width 200tw tires and has the vehicle extremely low.  He also has absurd spring rates, via 2 diesel F-350 Super Duty  front springs cut in half and installed at each corner. He messaged me asking if I thought  -5.5 degrees of camber (I guess he's running adjustable upper and lower ball joints) was excessive. Problem is, I have no clue on straight axle stuff. Does he need more or less camber than on a suspension where camber changes with suspension travel?

That's a few orders of magnitude more camber than he needs most likely.  My ZJ is at about -3/4* up front.  For full out autocross type use, I'd figure somewhere in the -1 to -1.5* range should be about right, depending on what the tires need.  There's no camber loss due to body roll on a solid axle, so camber needs are lower.  

Also, 225s seem a bit narrow for the amount of weight he's dealing with.  I'd think it would benefit (a lot) from more tire.  

Wait, you mean solid DRIVE axle up front????? Not straight axle?

In reply to Dusterbd13-michael :

Depends on if he is using it as an AWD like it was originally, or not.

Dusterbd13-michael said:

Wait, you mean solid DRIVE axle up front????? Not straight axle?

Unless the guy swapped in the dummy beam from a 2wd ZJ or XJ, then yeah, it's a driven straight axle up front.  

But still a 4wd style azle, not a streetrod drop axle style, right?

Edit: thanks. Didnt know there was zuch a 2wd axle. Thought they were all double a arm like the dakotas by that point in 2wd

Dusterbd13-michael said:

But still a 4wd style azle, not a streetrod drop axle style, right?

Yeah.  The stock 2wd beam setup is basically the same as the 4wd axle just without the diff and with just outer stub shafts in the unit bearings and not full axle shafts.  No extra drop in it or anything.  The XJ-R guys did notch it for clearance to get lower without hitting the oil pan though.   

rslifkin said:

Dusterbd13-michael said:

Wait, you mean solid DRIVE axle up front????? Not straight axle?

Unless the guy swapped in the dummy beam from a 2wd ZJ or XJ, then yeah, it's a driven straight axle up front.  

He's converting it to 2WD so that he can run CAM-T. Otherwise he would have had to run in E/Street Prepared with AWD. At one point he was considering leaving the transfer case and front drive axle in and then could bounce between CAM and E/SP by pulling the t-case fuse

NickD said:  

He's converting it to 2WD so that he can run CAM-T. Otherwise he would have had to run in E/Street Prepared with AWD. At one point he was considering leaving the transfer case and front drive axle in and then could bounce between CAM and E/SP by pulling the t-case fuse

No t-case fuse on those, they're mechanically shifted (although the stock case is fulltime 4wd anyway).  Only way to truly disable 4wd is to just pull the front shaft (which won't hurt the stock fulltime case on a 96 - 98 ZJ).  

Also, I feel like I need to see this thing at some point.  And I need to get by butt in gear and start fixing stuff on my ZJ.  I've put a whopping 50 miles on it in the last 6 months...

Id say that 5.5 would be extreme in this case. 2-3 should be plenty.

rslifkin said:

NickD said:  

He's converting it to 2WD so that he can run CAM-T. Otherwise he would have had to run in E/Street Prepared with AWD. At one point he was considering leaving the transfer case and front drive axle in and then could bounce between CAM and E/SP by pulling the t-case fuse

No t-case fuse on those, they're mechanically shifted (although the stock case is fulltime 4wd anyway).  Only way to truly disable 4wd is to just pull the front shaft (which won't hurt the stock fulltime case on a 96 - 98 ZJ).  

Also, I feel like I need to see this thing at some point.  And I need to get by butt in gear and start fixing stuff on my ZJ.  I've put a whopping 50 miles on it in the last 6 months...

Its very GRM. I've been offered an opportunity to do-drive it at an event once its up and running. If nothing else, it should be amusing

I'm not sure a ZJ fits in CAM*T*. Maybe C but I don't know. Either way I approve of the project.

5.5* does sound a bit excessive, but for how little tire he's running, I wouldn't be surprised to see  3-4* be optimal. If you can call anything about what he's doing optimal. You're right that it shouldn't need as much camber as a traditional suspension, but it'll still need all the front grip it can get and as long as the front wheels aren't driven a little extra camber won't hurt anything except tire wear in most cases. Also does seem like it's CAMC since the body style originated after 1989.

tires will be very unhappy in braking at anything more than about -3.5 deg.

I would go 2-2.5 tops as a solid axle will actually have good camber control.  Think about it, the axle will remain parallel to the ground unless you are lifting the inside wheel, so you only have lateral force on the tire moving the carcass, unlike a MacP strut car that will have a net camber loss due to body roll.  (bad tradeoff of the solid front is that it will transfer upsets from bumps to both front tires and unsprung weight reactivity over bumps)

You primarily see big camber numbers to compensate for loss of camber due to body roll which is taken out of the equation here. 

Apexcarver said:

I would go 1.5-2 tops as a solid axle will actually have good camber control.  Think about it, the axle will remain parallel to the ground unless you are lifting the inside wheel, so you only have lateral force on the tire moving the carcass, unlike a MacP strut car that will have a net camber loss due to body roll.  (bad tradeoff of the solid front is that it will transfer upsets from bumps to both front tires and unsprung weight reactivity over bumps)

 

You primarily see big camber numbers to compensate for loss of camber due to body roll which is taken out of the equation here. 

Exactly this.  You only need as much camber as the tires need to handle the lateral loads (which will depend on the tire and the sidewall height).  

Relevant solid axle notching for camber

Jeep XJ-R build thread

I guess he was shooting for 3 degrees with 2 degree upper ball joints and 1 degree lower ball joints and somehow got 5.5 from them. Also, just learned he is running 275s, not 225s. The 225s on from his STS Maxima were just on to see how much going from a truck-size to a car size tire would drop it

I agree about 5.5 being excessive.  All he needs to compensate for is tire flex, and however much it lifts the inside front tire.  A degree or so, and then adjust based on tire wear and lap time.

This looks like a job for TIRE PYROMETER! [/cartoon announcer voice]

Seriously, I think the tire temps will tell the tale here. He'll be able to benefit from running the minimum camber the tires like, which will increase braking performance. 

On edit: If he can build in lots of droop travel and run a very light/not run a swaybar, it should do a fine job of keeping the front tires down. 

I'm confuse on ball joints on a straight axle.

Please enlighten me.

Never mind, I figured it out

I agree with others, since there is no camber change with body roll, 1 or 2 neg.  would be enough.

Tire temps helped me get the right set up on my ZX2SR

5.5deg is excessive in any case. More than 2.5 is lots, more than 3.5 is asking for trouble. When the amount of negative camber becomes huge, a car with really awful suspension geometry may corner well with all that camber, but you'll start to get problems in a straight line like a loss of braking performance and uneven tire wear. There is an absolute range you want to stay inside with static camber.

In reply to GameboyRMH :

Only time I saw somebody run 5 degrees was a '67 Camaro in a restricted autocross class that didn't allow changes in geometry. He set it up for 5 degrees so when it leaned over and lost camber the outside tire would have around 2 degrees. 

The tube notched and cut to 5° in the center would give 2.5° per side, ala the Archer Brothers Comanches PettyCashRacing, and the XJ-R

Best way to set camber which is only needed in a turn.  Turn the wheel about 15 or 20 degrees. Measure the camber on the outside wheel.    This take in effect of caster adding camber .