merchauser

I have all new front end components, including rack, bushes, A arms, and ALL related parts; no issues and all good.
car is lower than spec at 166mm. front end alignment specs are good, EXCEPT cannot get caster spot on; slightly off.




my car seems to want to travel where I point it, and if I am on a road crown, will drift a bit, in the respective direction.

can someone shed light on whether that is a result of caster being out of spec? and is my inability to get the correct
caster measurements, a result of the lowered ride height?

FredR

No real problem with those alignment numbers- side to side caster could be improved a little but I doubt you would notice that difference.

I take it you understand that your original caster spec limit was 4 degrees and later models were specified up to 5 degrees and that can be applied to earlier models.

Lowering the car post alignment will increase camber and cause some degree of toe out but that is of no consequence to you unless that is what you plan to do. My front ride height is about 160mm and never had any issues but then I have stiffer springs.

Modern tyres with higher levels of grip can easily support 1 degree of camber with stock rubber, with wider rubber I run 1.5 degrees of camber.

Speedtoys

What wheels do you have?

merchauser

I have Carrera lll 18" wheels 245 up front and 295 in the rear

dr bob

That small amount to difference in caster --might-- cause the car to tend towards the left. If you are noticing that road crown is causing it to go right, then the settings you have are about perfect. Most drive-tests after adjustment include a slight imbalance in caster to keep the car pointing straight on the roads you drive on.

Camber and caster together will cause the car to tend left or right. Your car will tend towards the side with less negative camber. In your case, the settings for camber and caster are somewhat offsetting. Not ideal as camber changes with body roll while turning, while caster is constant.

Your toe settings are a little light. Spec is 1/4 of a degree (15 minutes) of toe-in on each side, with a +5 -0 tolerance. So toe-in will be between 15 and 20 minutes, or 0.5 to 0.6 total toe. Especially with your car sagging on the springs, you will want to get those settings right. Else risk scrubbing the inner ribs off.


Fred correctly points out that modern tires like a little more camber. If ou notice scrubbing or even chunking of the outer tread blocks, more camber will help. With more camber comes the need to be more precise in the adjustments, as camber will be steering the car more inroad imperfections. Where we live now, downwind of the old volcanoes, the roadbeds are all volcanic cinders. That stuff fractures over time allowing the paved surface to sag under the abuse of all those tires pressing down. Results is grooves or troughs in the surface that like to steer the car a bit. Mine is much more sensitive to the camber in the road when the camber settings on the car are more negative. Getting the camber and caster balanced perfectly is time-consuming, a practice not important with the average tech. The settings show a tolerance which they are happy to use; that tolerance is OK, except that the settings from side to side still need to be exactly the same. Since caster and camber are so closely related in how you adjust and measure, getting both settings correct and the same on both sides can take a lot of fiddling. It takes me the better part of an hour, plus there's always some "trimming" after some drive time. It's a very iterative process. Plus every caster/camber adjustment futzes with the toe-in.

Better race shops may be willing to work with you to get things better than what you get from the local tire store. But the extra time deserves extra compensation. Be ready for that.

Speedtoys

The additional positive scrub radius over stock will do that some too.

FredR

When you say your caster is "maxxed out" I noted that comment to be a bit puzzling in that you appear to be going for a more or less stock alignment and that being the case the values should have been in the range 3.5 to 4 degrees to get a green traffic light on the print out. I consider caster maxxed out when the adjustment hits about 5.5 degrees but one should also note that the amount of camber set impacts the amount of caster that can be attained thus why the lower ball joint has that peculiar shaped adjustment aperture. You should have been able to get a figure of 4 degrees for caster [had you wanted such] with no problem so I am left wondering why you are in the range you are not that it is a problem- far from it as I consider such numbers desirable.

When it comes to accuracy of the numbers I take those with a pinch of salt. I have considerable experience using the Hunter machines and mostly do the alignment myself with the machine attendant acting in assistance [they know me that well]. Whereas I try to get the camber and caster numbers exactly the same both sides in practice it is nigh on impossible to get both sides with the same output value considering the sensitivity of the adjusters and the fact that changing one parameter often changes something elsewhere and it becomes an iterative chase- something that would probably **** off the machine operator in your part of the world. In practice when it comes to camber and caster getting the numbers to line up side to side I find it possible to get it so with one of the two parameters so try to get the camber numbers the same and tolerate caster being different by 0.1 degrees [6 minutes]. Even if you look at your numbers you will see that at minus 0.7 degrees of camber on the left front the traffic light shows red even though it is in the factory specified range. Even a gust of wind can change the indicated values such is the sensitivity and hysteresis of the system. Getting the toe in numbers the same on the front wheels to two significant figures is easy- no excuse for that difference not that it will impact steering performance any.

As Dr Bob notes, we drive around on roads that normally have a crown to assist drainage and this naturally tends to pull the car gently to one side slightly so perfectly normal to have a slight yaw as the car naturally wants to go to the side of the road. As Dr Bob notes one can even tune for that but personally I would not even dream of it. Similarly as Jeff notes the offset can play a part. I have lost count of the number of times I have cautioned those wanting to fit wheels with incorrect offsets. To be fair in dry conditions I doubt you would notice a difference but in the wet, the crown is there to permit drainage and thus as the rain drains the depth of water on the surface changes as the water ponds on the side of the road. At some point this difference in depth of water creates a yaw effect and the whole point of the NSR is to help counter such conditions as the steering then self corrects.

Finally if you are running with 245's up front if yo want to get the full potential of the cornering capability on track days or whatever you will need more front and rear camber. If all you do is drive on long straight roads do not bother.