The Lotus Cars Community banner

1 - 15 of 15 Posts

·
Registered
Joined
·
5 Posts
Discussion Starter #1
Right so over the winter I've refurbished my suspension. Finally now getting to the sharp end of things and I'm doing the alignment.

I've set up the car with ballast, fitted the husbands, levelled the floor plates, corrected the for the rear wheel size difference etc. However this evening I've been measuring camber. I can get the car to within spec, however I'm looking for to get to nominal (its the perfectionist in me).

So I've measured the camber on all for wheels worked out the adjustments required and added the required shims. However after jacking, fitting, and dropping one side at a time then bounce with my weight on the sill I get readings which don't match what I'm expecting. I can only assume its because the car requires settling. However I can't role it back and forth on hub stands only side to side.

Any tips for resettling the car to get a truer reading.
 

·
Registered
2008 Lotus Exige S240
Joined
·
55 Posts
What hub stands are you using? Do they only slide in the “X” or “Y” plane? Is so, would some sort of slip plate (e.g. greased plastic sheeting between metal plates) on a single side or single axle of the car help to let things move to their neutral location after your adjustments?

Cheers,
Bryan
 

·
Registered
Joined
·
5 Posts
Discussion Starter #3
Each plate has two bearing so they glide in Y perfectly. Large X movements are constrained by the bearings. Movements around the Z axis are ok with the bearings so starting can be centred and caster checked for instance.
 

·
He's on fire!
Joined
·
3,292 Posts
maybe a picture or link to your hubstands would help. A lot of hubstands are designed to allow some movement, but I'd still have slip plates or a garbage bag with silicone sprayed in it to aid with settling.

I also open the doors and stand on/jump on the side sills right where the black plastic ends and the aluminum is exposed on both sides. For my hubstands there is a limit to their travel so afterward I check and make sure I have not reached the limit on any corner and make sure each hubstand is still centered on the scales. I don't have any fences on my scales so I keep an eye on the scales to make sure I'm not going to bounce the car clean off them.

With this method I typically observe differences of a couple hundredths of a degree, which begs the next questions-

How accurate are you trying to get (ie do you expect to measure -1.71*, lift/lower the car, and expect to still get -1.71*? If so I think your expectation might be too high and that a range from -1.65* -1.74* is probably accurate enough.

What are you using to measure and how?

If you take measurements from different points on the same hubstand, do your measurements change? (is there any reason to believe there is some flex in the hubstands themselves)
 

·
Registered
Joined
·
5 Posts
Discussion Starter #5
Here is a link to the Hubstands

I guess what I’m expecting is when I measure 2.1 degrees of rear camber lift and insert a 1mm shim that I get something less than 2.1mm rather than 2.15 degrees.
I’m using a b&g digital caster camber gauge (more easily available in the UK) which is similar to the longacre one.

Done the bouncing on the sill and trying to rock the car as much as possible to settle it.

Suspension has been rebuilt with rose joints so I’d expect the numbers to be a bit more stable than with OE bushes.
 

·
Premium Member
Joined
·
1,339 Posts
Most camber gauges only repeat to +/- 0.1 degrees. A 1mm shim should have gotten you a couple of tenths of a degree. Also, if you have single or double adjustable shocks, you should open the settings way up so the shocks don't effect the settling.

Later,
Eldon
 

·
Registered
Joined
·
5 Posts
Discussion Starter #7
Gauge is apparently accurate to 0.02 degrees. Shock are fixed ride height and fixed damping so can’t play that trick unfortunately.
 

·
He's on fire!
Joined
·
3,292 Posts
so a couple of things. First, you should lift/lower the car, changing nothing, and verify you have an approach/equipment that is consistent. If you didn't do this first, there's pretty much no way of knowing if your first measurement of -2.1* was accurate... for all we know the inaccurate measurement is the first one (or perhaps both). I go around the car and check the camber once, then repeat to verify my initial measurements, then make a change, then go around the car twice more measuring camber. I measure in the same pattern, same measurement point, same everything I can think of to keep my approach consistent from one time to the next.

On the hubstands you linked I'd definitely be looking to spray the base with silicone spray so that those little wheels could slide around wherever they needed to. When you say you've leveled the floor plates, that means they are not only individually leveled, but all four of them are at the same height relative to each other? I use a self leveling laser line to make sure all 4 of my scales are the same height relative to each other.

Its a finer point beyond the problem you've mentioned, but I've found that 1mm shims clearly have manufacturing tolerances. Before I had 0.5mm shim I used to use the ones that were on the higher end of tolerance on the drivers side and those on the lower end on the passenger side.
 

·
Registered
Joined
·
5 Posts
Discussion Starter #9
That’s a good point on the measure lift, settle measure again and verify.

On the levelling i did the first pad vs the floor then all the other pads were set level to that first pad to create a level “floor”. I then measured and lift the rear pads to account for the difference in wheel diameter front to rear and keep the attitude of the car correct as the hubstands are a fixed length.
 

·
Registered
Joined
·
4 Posts
IMO, the problem is in using hub stands. I tested a set of hub stands for doing alignments on a spec miata for a company that was bringing them to market. I was never able to repeat what I saw on the stands with what I saw with the car ON THE WHEELS.

I believe this is what is going on and why it is not repeatable: hubstands are usually a plate that is probably about a half inch thick that drops to the floor directly below the flat plane of the rotors. So basically it is replicating a tire that is only a half inch thick or so. Our tires are not a half inch thick. The car rests on a much wider contact patch than the hubstands when the wheels are on and it changes the camber, which changes the toe (at least in the front).

What I have been wanting to try is to weld a perpendicular plate at the base of the hubstands that are the same width of the tires to see if I can get repeatable results. The hubstands that I was using did have bearing rollers on the bottom so bind was not the issue.
 

·
He's on fire!
Joined
·
3,292 Posts
I disagree with the above and it is not my experience. The hubstands take out an inconsistency (the wheels themselves), and are easier to get repeatable results, at least with camber and toe, and also with scale measurements if you have the right setup (either hubstands with a wider base or a dual load cell scale).
 

·
Registered
Joined
·
4 Posts
You misunderstand me and I don't think we actually disagree on anything yet because we are talking about two different things when I said repeatability.

Im talking about repeatabilty between the numbers I get on the stands and the numbers I see on the ground and with the wheels on. I am not talking about repeatability of obtaining numbers only on the stands. I agree with you that you can get better ( by better I mean easier ) repeatability on the stands but what you get on the stands is not hitting the road!!! I care about what I am driving, not what the setup is when the car is on stands. As you pointed out and as I mentioned, the wheel and tire changes things. The problem you have with repeatability using the wheels is that you have to take your time and great care to get repeatability. But the end result is that you have setup numbers that are reflective of what you are actually driving.

You certainly could use the stand numbers as a baseline and correlate that to what you are experiencing in the car to make changes that are generated and measured back on the stands. I just prefer to have the actual number that the car is seeing when making contact with the asphalt. It is also a fairly consistent method and baseline of numbers when talking to others as they are more than likely setting up the cars and taking measurements with wheels on.

You can absolutely get repeatable numbers on the stands and usually faster and more consistently than when using your wheels. Just don't expect your camber or toe number to be the actual camber or toe as when you lower it off the stands.
 

·
He's on fire!
Joined
·
3,292 Posts
I'm curious - do you remember how far off are your hubstand vs wheel measurements where? Given that the wheel is in plane with the hub I find no change in toe, and found no significant change in camber... like least significant digit different (hundredths position)

Cross weights, that is a different story. Can't remember exact number, but I think I found the car gains about 0.6% from hubs -> wheels, so I shoot for 49.4% or whatever and verify I end up with 50.0% +/- 0.2% with wheels on.
 

·
Registered
Joined
·
4 Posts
Im sorry I don't recall the exact delta. Im now trying to figure out why your cross would be changing so much or at all.
 

·
He's on fire!
Joined
·
3,292 Posts
Yea I thought it was unexpected as well, but wanted the cross weight to be right with the wheels on. I had a few hypothesis:

1 - Not all wheels weight the same. Manufacturing tolerances on the tires, different wheel weights, etc
2 - Slightly different rake "created" on the hubstands vs actual
3 - Slightly different positioning of the hubstands vs wheels on the scales

0.6% of 2,000 lb is 12 lb

I proved I was able to consistently repeat what I observed, because I was as surprised as you the first time it happened. Took the wheels off, cross went down, put them back on, cross went up (by the same pct). Ran out of time to troubleshoot further and decided that for HPDE I was splitting hairs.
 
1 - 15 of 15 Posts
Top