Rear toe link and toe changes

[Suberman]

Does anybody know, or knows a link, describing the changes in rear toe through the range of suspension travel?

Another way to ask this is what do you have to do to rear toe static settings if you drop your car by an inch or so?

That upper forward toe link in the rear suspension looks quite short to me and suggests there's quite a lot of rear toe change through the suspension movement range.

[OrbitalEllipses]

Lowering the car changes the position of the lower control arm, which changes camber. This arm's effect on camber dynamically effects toe. In short, you'll find out when you get on the alignment rack.

I'd imagine Googling multi-link rear toe would be fruitful.

Yes, I unhid your post to see it.
@CSG Mike @CSG David @Racecomp Engineering

[Racecomp Engineering]

This is a good link:
http://www.iwsti.com/forums/gr-suspe...bumpsteer.html

In short, yes there is some dynamic toe change and more of it when you start lower.

- Andy

[Suberman]

Exactly what I was looking for. Thanks v. much.

It appears this link is to a WRX site and the posts are about the WRX rather than the BRZ? Is the toe link horizontal also on the BRZ? Ok found pics on the Internet and looks like the BRZ uses the WRX STI rear suspension which is pretty cool actually. Or am I looking at photos of some Japanese only STI BRZ components? Hmmm. More photos from whitelin.au shows the STI uses the same rear suspension as the BRZ.

It would seem that this car might benefit from setting static rear toe as far out as permissible.

I recall the Weissach axle Porsche was so pleased with themselves about had a floating link that toed the outside rear wheel out in compression.

If memory serves, BMW tried something similar with their otherwise quite old fashioned semi trailing arm rear suspension used up until around 1990 when they finally switched over to multi link.

Has anybody tried zero rear toe or toe out?

Does it work or does it just make the rear axle twitchy when running straight?

[wparsons]

Zeroing out the rear toe in, or adding toe out will make the car much more eager to rotate at turn in and also less stable in a straight line... so probably the exact opposite of what you want to do.

If you're just looking to keep the alignment in check with a drop of about 1" the stock toe links are adjustable, but if you drop it too much and correct the camber with adjustable LCA's then you'll need a bigger adjustment range than the stock toe links provide.

[Suberman]

Well, no, it should improve cornering because any suspension movement either way will still toe in the rear wheels, just from an initial setting that is neutral. Looking at the edmunds walk around article I notice no lower ball joint on the bottom of the hub carrier upright at the rear so that toe link can only twist the hub in the toe rubber bushings on the outer ends of the lower control arms. There's an upper ball joint. There can't be very much toe change purely from that toe link.

The idea is to reduce the slip angle generated at the rear axle to get it closer to the slip angle generated at the front as cornering loads increase (suspension deflects). This should produce more civilized handling.

The more initial rear toe in you have the sooner the rear axle will reach maximum possible slip angle and slide.

As you say, setting rear toe at zero would enhance turn in but it will also increase maximum cornering grip as the suspension compressed because the tire won't be forced to run at an additional slip angle beyond what the lateral g forces produce.

The disadvantage would be a higher tendency to step out if you lifted off abruptly but this also can be advantageous if the rear axle is going to toe in on rebound anyway. You generally want the front to tuck in if you've overcooked your entry. As I understand the arc of the toe link ( assuming it is horizontal on this car when the car is at rest, which I still don't know) lifting off will reduce rear toe in, tightening the line but if you really overdo it and enough weight transfer occurs the rear will toe in again as the rear axle begins to droop. I mean this car is exceptionally easy to hold at pretty large drift angles on snow, but that isn't very fast.

What I would really be interested in is someone who knows whether zero toe or toe out makes this car twitchier in a straight line. The rear wheels will toe in under squat or dive so braking and cornering should be good.

The other part of this set of articles, albeit about the WRX, points out the trouble with the bump stops. Somewhere in this forum is a really useful thread on the lack of damper travel before the bump stops are engaged. The bump stops do not have a linear rate. That can be quite annoying if you know how to drive. Just as you think the car is taking a nice set you run over a small bump or undulation and the spring rate changes on you.

I've said before that the BRZ is too twitchy for a serious driver, hard work to drive compared to how it could and should be. I don't dispute it is a hoot to drive and mildly challenges you on a weekend run. But, really, I'm past all that. I'd like this car to handle more like the poor man's Cayman it could so easily be.

If Toyota ever gets around to releasing a supercharger kit, so easy for them to do, it's going into my BRZ. Then I really must find a better solution to the twitchy rear axle. Another 80 bhp or so and a big snack of mid range torque will change this car from the beginner special it is at 200 bhp and 151 lb ft I to a car that will really get your attention. It will likely be way too expensive to try and change the geometry. I like the factory spring rates. The factory dampers are nothing to write home about but they are good for the price bracket of the car. Changing bump stops would be easy while upgrading the dampers.

If tweaking the alignment would work I'd do that right away.

[wparsons]

Despite your giant diatribe, zeroing out toe or running toe out will most definitely make the car more eager to rotate and also less stable in a straight line.

I can't find the thread(s) with the specs with the search (ignores words with 3 or less letters), but I remember reading in a few places that the BRZ's run more rear toe-in stock than the FRS'.

If you don't believe me, scan the CSG/RCE suspension thread to see what others are saying about front and rear toe settings.

The more toe you run (either in or out) the more you'll wear your tires as well, from a wear standpoint 0 toe all around is ideal and any handling balance needs should be addressed by spring/shock rates, other alignment settings or tire changes if possible.

Not knocking the theory, but without actual numbers it doesn't hold too much weight. Are we talking about a toe change of 1/32" for 2" of suspension movement, is it more, is it less? If it takes the full droop or full compression to change the toe by 1/16" you're seeing far less change in corners. If it's changing by 1/16" just by getting in or out of the car then it will make a huge difference in a corner.

If anyone has an alignment rack this would be easy to test by supporting the car and removing one of the rear shocks and seeing how much the toe changes throughout the range of suspension movement.

[Suberman]

The specified toe settings have a very small range. However, toe has a disproportionately significant effect on handling, particularly tracking. It is made adjustable for this reason, when other settings remain fixed.

I seriously doubt that adding rear toe in would be of any value. Reducing it to the minimum spec would, in theory, help.

I'd be very surprised indeed if Subaru specified more rear toe in than Toyota.

The capacity for that toe link to induce significant toe in changes is severely limited by the two lower arms unless the precise geometry of those links also induces toe in. You can't tell from photos or diagrams, you need to watch the suspension in motion, preferably without the spring or roll bar attached. Nobody's done that yet as far as I know, and really why would you since it can't be changed economically.

[wparsons]

Did you go read the suspension thread like I suggested? If you had, you would see that what you're suggesting is contradictory to what people that actually track their cars (and work at shops for a living) are suggesting.

You're the first person I've seen bring this up as a problem on this platform, does that tell you anything Mr. Arm Chair driver?

[solma]

There seem to be a lot of theory on the subject, I have mesure toe movement vs travel(in REAR only), the fact is that on decompression(underbracking) it toeing in and on compression its toeing out up to almost the end of travel after its start to toe in again.

By changing the mounting point of the toe arm on the subframe you can play with the curve, and there enought place on the U bracket to have a large range of ajustment by drilling new holes.

I think the discussion on have to be split in 2 category, first the racing setup, there no point of playing with the dynamic curve as the suspension setup is normally so stiff that it does move much during cornering, so you ajust the toe statically to your linking and go from there. The second case, like mine, is street/weekend track setup, because I want softer suspension for the road it cause a lot of traveling on the track that means a lot of toe change during cornering, making important to understand dynamic toe.

But there and other big player in our case, the rear upper arm, subframe side as 2 different rubber(for stiffness) making the upper arm inegal movement(to the front) possible when appling torque to the wheel(giving gas), when the suspension is compress, the toe arm will go up, by twisting the hub clockwise(giving gas), the toe arm start going down pushing the hub outward(toe out), I think that why the frs is so prone/easy to driffing at low speed.

[solidONE]

Originally Posted by solma

There seem to be a lot of theory on the subject, I have mesure toe movement vs travel(in REAR only), the fact is that on decompression(underbracking) it toeing in and on compression its toeing out up to almost the end of travel after its start to toe in again.

By changing the mounting point of the toe arm on the subframe you can play with the curve, and there enought place on the U bracket to have a large range of ajustment by drilling new holes.

I think the discussion on have to be split in 2 category, first the racing setup, there no point of playing with the dynamic curve as the suspension setup is normally so stiff that it does move much during cornering, so you ajust the toe statically to your linking and go from there. The second case, like mine, is street/weekend track setup, because I want softer suspension for the road it cause a lot of traveling on the track that means a lot of toe change during cornering, making important to understand dynamic toe.

But there and other big player in our case, the rear upper arm, subframe side as 2 different rubber(for stiffness) making the upper arm inegal movement(to the front) possible when appling torque to the wheel(giving gas), when the suspension is compress, the toe arm will go up, by twisting the hub clockwise(giving gas), the toe arm start going down pushing the hub outward(toe out), I think that why the frs is so prone/easy to driffing at low speed.

Has anyone taken measurement or made calculations as to how much and how the toe changes. According to some of my rough measurements and complimentary alignment checks done Sears Auto I seem to have the opposite result as your finding. With the rear of the car fully weighed with full tank of gas, spare tire and stock muffler in place I measured 1/8" toe in using 24" long wooden blocks and measuring tapes. With the stock muffler removed and a track pipe in it's place, quarter tank of gas, I measured about 1/16" of toe out using the same method. It seems excessive... improbable, but the change to toe out from decompression by removing weight from the rear was confirmed by laser alignment rigs. Up until then the toe adjustment was untouched from the day I bought it from the dealership and likely the day it rolled off of the assembly line.

Stock + Camber bolts front and rear, little more than 3/4 tank of gas, no driver


Removed factory muffler and installed track pipe, zeroed front toe, little more than 1/4 tank of gas, 150lbs driver in seat, no other adjustments made

Got out of the car and remeasured after I saw the toe out.


Muy confusing