Measuring Camber on an uneven surface

Hello,

It's clear in the course how to level out the entire car, corner to corner, using tiles. However, what if the surface has inconsistency in the angle of the floor beneath each tire? (Since we won't all have perfect working surfaces. ☺️) I have to assume this will throw off your camber measurement on each corner.

If you have a digital camber gauge that allows you to zero out the angle to a reference angle, is it best practice to do that first? Or would you just take the camber measurement as the car sits, without a reference angle?

My situation was on the rear wheels. Left under tire surface measured 1 deg and right was 1.5 deg.

I find a flat surface (reference surface) on the chassis of the car, and re-zero the camber gauge for each side. Sometimes easier with race cars.

Oscar,

Great job checking that out, and trying to do things just right!

Hopefully the tile itself is rigid and flat, and the tire sits within a single tile. If that's the case, you can measure the angle across the tile, specifically across where the lateral contact patch of the tire is. Then you can then measure camber at the wheel and offset it by the angle you measured across the tile. You'd have to do that per corner.

I any tile is over 2 degree, then I'd be more worried about weight transfer impacting camber etc. Do the best you can with the situation you have.

Thank you both for the replies!

I've followed that exact methodology when measuring! Ridged tiles and measuring at the contact patch. So that's great to have confirmed.

I wanted to make sure I was getting as close as I could with the area I have to work with.

I just realized what you meant by potentially being more worried about weight transfer.

The car itself is level laterally. Using tiles on the left and right sides to ensure this. However, there are variations in the floor that make the contact patch of the tires not level. So there's no real reason to worry about weight transfer since the car was leveled first. Only the angle the wheel would sit at while under load.

Sounds good Oscar!

I haven't watched this module yet, so I apologize if the following is redundant. This mostly applies to modified vehicles that started life on the road.

As you're looking to improve your results, a significant factor I see during alignments of vehicles that require being jacked/lifted to adjust things, is the vehicle not fully settling after jacking/lifting it up and setting it back down. For this reason I like to drive the car in, check all alignment settings before ever lifting it. Then I lift and drop it without making any adjustments, measure again, and see how much the alignment readings change. Then I jounce the car and try to settle it, and again check how different the readings are from how the car drove in, fully settled.

That helps me understand either what it's going to take to settle the car fully between changes, or I'll see that I can't get it to fully settle, but at least I know how far off I'll be and in what directions so I can adjust the settings I shoot for accordingly. Then when I'm basically done, I drive the car around, take some turns, do some acceleration and braking, get the car to actually settle, then recheck and confirm where things ended up.

Hang on, seems to be some confusion - the angle of the surface the tyre is on DOESN'T affect the camber! Camber is a fixed relationship between the wheel hub assembly and the chassis/frame. Do NOT "correct" the camber for it!

What an uneven surface will do is alter the way the tyre tread is loaded, and in most instances the important point is making sure the mid-point of the tyre loads is "flat" relative to the other three tyres' points, with at least one exception being for beam axles.

Assuming the ride heights are correct, David's suggestion of referencing the camber to the chassis should work perfectly well.

OP, I'd suggest using four flat blocks, with shims/packing/wedges being used to set the surfaces to exactly the same height and flatness, so any doubts are removed.

I should clarify I'm not disagreeing with David, just trying to help find a compromise. Factory race cars generally make reference to chassis simple, but sorting that out on a modified road car often leaves people confused or with worse results.

For discussion, what if the tires were inflated a bit more than typical road race pressure, so the impact of tile angle is negligible, and then perform the alignment just by taking typical wheel camber measurements?

Thanks all for diving in on this one!

Please correct me if I'm understanding this incorrectly. What I'm gathering from the conversation is:

Camber is a fixed relationship between the wheel hub assembly and the chassis/frame. (This is why David F suggested taking a reference angle from the chassis, rather than from the floor.)

The reference angle should not be taken at the floor beneath the tire. (I believe Mike M made his suggestion thinking the car itself was not level laterally.)

Therefore, assuming the car / chassis is leveled laterally before measuring camber angles, a measurement can be taken without using a reference angle.

Any inconsistencies in the floors surface will be negated by tire deformation. (Reducing the PSI in the tires slightly may help in this case?)

As a last question / confirmation after taking this all in. Assuming the car / chassis is level, the main variable that would affect camber angle would be vertical travel of the wheel / suspension, correct?

Yes, if the car is truly level with the ground then you can reference camber at the hub vs. the ground.

And yes I touched on testing camber with the chassis fully vs. partially settled because it is a factor in not just camber, but also toe.

I've verified on a number of cars that changing air pressure in the tires while the car is on slip plates on an alignment rack, did change the alignment readings on the rack software, so my usual suggestion is to set the alignment up with the tires at operating pressure.

On race teams using setup pads, setup is always done at the same tire pressure for consistency.

With that in mind, and because your adjustments will ultimately be relative and I don't think your absolute values will be far from accurate, I'd just use normal tire pressure. Align the car in the same spot, on the same tires, at the same pressure each time and you'll be able to make accurate adjustments. Just be super mindful about what I said regarding how much the vehicle settles. That's likely the biggest variable out of what we've discussed so far.

Thanks for the confirmation and additional detail. All of this help in understanding the mechanics is appreciated.

Awesome. It's great to strive for perfection, while understanding the real world often isn't quite perfect, but you can have great results the way you'll be doing things.