RUCAs for camber better for toe curve? (or, why noone using trailing arms?)

[prj3ctm4yh3m]

too long to post in the Q&A thread....

i came over from s2000's which had both the burden and blessing of a double a-arm in the rear-the car was a handful anyway, so maybe the multilink here affords more opportunity for fine-tuning camber and toe curves.

my questions:

1) it seems like shortening the LCA to correct camber, and adjusting the toe arm accordingly, puts unnecessary off-axis tension on the trailing arm pivot at the knuckle [see pic below - use your mental travel simulator]. it SEEMS like lengthening the UPPER control arm in lieu of the LOWER to correct camber would have less effect on the trailing arm curve. i.e. its not rotating as much around the vertical axis. is this accurate? what am i missing?

2) i see a ton of trailing arms for sale lol. Why does noone use them here? (i know the standard explanation for them - they just adjust caster/thrust bblabla) it SEEMS like NOT shortening them can drastically affect the toe curve, which is a REALLY important thing in a car with no weight over the rear end. is there a general consensus on any beneficial affect it has on the toe curve at say 25mm drop (adjusting either the LCA and/or UCA)?



http://www.edmunds.com/car-reviews/t...alkaround.html

Please learn me.

[solidONE]

1. Ease of adjustment/installation.

2. Cost.

[prj3ctm4yh3m]

Originally Posted by solidONE

1. Ease of adjustment/installation.

2. Cost.

that's obvious and doesn't really answer the inquiry. thank you though.

[gramicci101]

Most people try to get more negative camber, not less. So they're lengthening the LCA or shortening the UCA. But unless they're trying to stance the car, which has its own requirements, they're not changing it by a lot. A few millimeters, probably. While yes, that does put a little bit of tension on the trailing arm, it's not that much, and that's what bushings are for. As far as why LCAs are used vs. UCAs, it's because the LCA is easily adjustable and doesn't require you to disassemble the suspension, even if it does require a toe adjustment as well. RacerX makes an adjustable UCA if you want one.

As far as why trailing arms are available, it's because people will spend money for them. The OEM trailing arm is fine for most usage; it just doesn't look cool. I would love to swap all my rear suspension bits for Cusco or SPL so they'd all match and be pretty, but that's a lot of money spent unnecessarily. If you're doing something where the OEM arms are no longer sufficient, like airing out your car to sit on the ground, then there are plenty of options to choose from.

[solidONE]

Originally Posted by prj3ctm4yh3m

that's obvious and doesn't really answer the inquiry. thank you though.

NP

Seemed like you had a good handle on what each of the links do. LCA is just easy, cheap and effective. With 25mm drop you're probably looking at about -2.0~2.5 degree of camber in the rear without other adjustments, which is about the amount of camber people shoot for on this car for better handling. Only minor adjustment is required in the LCA's length. Not too many people are interested or feel the need to make the kind of adjustments to the different curves. Dial in the camber and toe then call it a day.

This thread might interest you: http://www.ft86club.com/forums/showthread.php?t=26661

[prj3ctm4yh3m]

Originally Posted by solidONE

NP

Seemed like you had a good handle on what each of the links do. LCA is just easy, cheap and effective. With 25mm drop you're probably looking at about -2.0~2.5 degree of camber in the rear without other adjustments, which is about the amount of camber people shoot for on this car for better handling. Only minor adjustment is required in the LCA's length. Not too many people are interested or feel the need to make the kind of adjustments to the different curves. Dial in the camber and toe then call it a day.

This thread might interest you: http://www.ft86club.com/forums/showthread.php?t=26661

i just didn't want to mess up the toe curve unnecessarily, after a bad experience with the S2k. Thanks!

[mav1178]

The vast majority of users, much like guys on 240SX/Z32 platforms, end up going with camber and toe adjustment.

For what I did with my car (50% track 50% street), all I did was rear lower adjustable arms and SPC toe arm inserts (so rear toe can be adjusted properly after camber is added)

Drove like a dream everywhere I went.

-alex

[strat61caster]

Measure your own toe curve, on this car it's really predictable, linear, and not extreme.

At full droop I measured 1mm of toe-in, at full compression (no spring, car sitting on bump stops, w/ LCA's installed and adjusted) I measured that the car toed-in further to a total toe of 7mm over >3.5" of suspension travel. From 1/2" above OE height to fully slammed it's super flat changing only 2mm going from 5mm-7mm, camber was in the -2.65 degree region when slammed.

Maybe that's not true when it's lengthened to reduce camber, but the only time I could see that happening is when you slam it and want to reduce tire wear which means grip isn't a priority and you probably don't give a fuck about toe curves.

UCA's may be academically better, but practically speaking I can wing a camber change in a dirt parking lot on my LCA's, the right wrenches and a jack, some string and jack stands if I want to be fancy about it. Not sure I could do that on UCA's, add in the cost and for me I don't think I'll be changing anytime soon.

'Mental travel simulator' I'm stealing that.
Although I rely on the 'hand visualization plugin' far more than most.

[Racecomp Engineering]

We've been saying since before the car came out that the upper control arm is the better place to adjust camber. It's just a pain in the ass.

Whiteline makes an adjustable bushing for the upper arm that is a nice piece and the poly bushing alone makes a nice difference that can be felt. But many shops can't or won't install and it's not easy to adjust.

- Andrew

[prj3ctm4yh3m]

Originally Posted by strat61caster

Measure your own toe curve, on this car it's really predictable, linear, and not extreme.

At full droop I measured 1mm of toe-in, at full compression (no spring, car sitting on bump stops, w/ LCA's installed and adjusted) I measured that the car toed-in further to a total toe of 7mm over >3.5" of suspension travel. From 1/2" above OE height to fully slammed it's super flat changing only 2mm going from 5mm-7mm, camber was in the -2.65 degree region when slammed.

Maybe that's not true when it's lengthened to reduce camber, but the only time I could see that happening is when you slam it and want to reduce tire wear which means grip isn't a priority and you probably don't give a fuck about toe curves.

UCA's may be academically better, but practically speaking I can wing a camber change in a dirt parking lot on my LCA's, the right wrenches and a jack, some string and jack stands if I want to be fancy about it. Not sure I could do that on UCA's, add in the cost and for me I don't think I'll be changing anytime soon.

'Mental travel simulator' I'm stealing that.
Although I rely on the 'hand visualization plugin' far more than most.

Lol you're welcome to it. thank thank you. super helpful. exactly what im looking for.

one question - practically speaking, do you think changing static camber at the LCA has a statistically greater effect on static toe than changing camber at the UCA?

[prj3ctm4yh3m]

Originally Posted by Racecomp Engineering

We've been saying since before the car came out that the upper control arm is the better place to adjust camber. It's just a pain in the ass.

Whiteline makes an adjustable bushing for the upper arm that is a nice piece and the poly bushing alone makes a nice difference that can be felt. But many shops can't or won't install and it's not easy to adjust.

- Andrew

at what point does it make sense to make tension arm adjustments?

[wparsons]

Originally Posted by Racecomp Engineering

We've been saying since before the car came out that the upper control arm is the better place to adjust camber. It's just a pain in the ass.

Whiteline makes an adjustable bushing for the upper arm that is a nice piece and the poly bushing alone makes a nice difference that can be felt. But many shops can't or won't install and it's not easy to adjust.

- Andrew

The MSI UCA is the only one that's adjustable on the car, but they're like $1500/pair. Not quite as easy to adjust as the LCA, but not nearly as hard as the bushings or Racer X UCA.

[strat61caster]

Originally Posted by prj3ctm4yh3m

one question - practically speaking, do you think changing static camber at the LCA has a statistically greater effect on static toe than changing camber at the UCA?

I would assume so given there's only one link up top and the hub orientation is controlled by the lower links.

The toe link mechanism is remarkably repeatable imo, like I said I could wing an adjustment in the dirt and not be too far off.

[Racecomp Engineering]

Originally Posted by prj3ctm4yh3m

at what point does it make sense to make tension arm adjustments?

I assume you mean toe and not tension.

Our car used the whiteline rear adjustable upper control arm bushing and we did not need any toe adjustment beyond what the stock arms allowed us. This is true for cars with adjustable lower control arms in most cases.

- Andrew