Nohachi's suspension ramblings thread

[SekiguchiUeno]

I was probably tired yesterday so have not payed atention how i write, and maybe made some mistakes, i mean it at horizontal LCA position. My post is corrected now. Probably i have not understand you the first time. Thought that at the 7.7degree strut angle the wheel camber is +1.
But it is probably so if i see this another post. When the strut-hub angle is 9degree, at 7.7 degree strut angle the camber should be +1,3 which is in the tolerance.
At -0,3 camber i have 9,3strut angle and subframe LCA pivot is lower than the balljoint 10mm.
But then again LCA on my car are almost horizontaly under static load. So that changes nothing on bad rch independent on the camber value.


Later i change the measurements to your original, because the beanbandits one manipulate the strut lenght and lca position little bit, main problem is in the hub-strut angle, is it not only 8degre probably? At 8,3degre strut i have +0,7camber.

[NoHachi]

Time to give this one a bump. The maths model is more or less ready, so I'll slap those results on the forums soon.

Some more data points for people interested in this stuff:

REAR AE86 unsprung weight: ~100kg total
FRONT unsprung weight: ~35kg/side

AE86 camber curve :

[img name=]http://www.aeu86.org/files/86/86_camber_curve_162.jpg[/img]

NOTICE: These results were gathered using the idiot measuring method, using my iphone and a tape measure. It does give a good indication of the relative amount of camber gain you can expect and also of the shape of the curve. This is for a short stroked ae86 at a reasonable ride height (not slammed atm) and using 2.5cm rca's. The line seams pretty linear throughout its range. So I don't expect many surprises for the slammed amongst us.

[roman]

A few random thoughts....

People always want to run short steering arms for maximum lock, BUT shorter arms will give you more bumpsteer.

Running the longest arms possible that give you the required amount of lock will be best for minimising bump steer.

Also there are two distinct types of 80s RWD cars:

narrow body and wide body.

Narrow body cars generally had smaller lighter engines like 4AGE etc, and sometimes no power steer.

Wide body cars like MA61 generally had heavier engines, power steer, etc etc.

The narrow body cars have their struts quite upright, where as wide body ones have the struts tipped further inwards towards the centre of the car.

Doing so raises the roll centre, my theory is to account for the larger mass in the engine bay and higher centre of gravity from the big engines.

More castor is required when tipping the struts over, but because most/all of these cars had power steer, there are no issues with increased steering effort. The narrow body cars keep the struts tipped upright to minimise castor required, which minimises steering effort when the cars do not have power steer. With the lighter mass in the front of the car, the roll centre position does not need to be as high to give the same amount of roll, so this works fine.

Most people put narrow body struts into the widebody cars, to give increased camber.

If you put widebody struts in a narrow body car, you get positive camber.

However!

If you had ajustable top hats, you could use the wide body struts in a narrow body car, tip them over as far as required to get the right amount of camber, and you'll have raised your roll centre compared to using narrow body struts adjusted to the same camber angle.

Any of that make sense to anyone?

[NoHachi]

There is too little adjustment range in camber plates to make this worthwhile. Also, why would you want a higher roll centre?
I'm not sure about the relationship between steering arms and bump steer. The tie rod and lca are still in the same plane. You'll have to convincme on that issue.

[roman]

you get more lock with shorter steering arms, because for each mm of side to side movement of the steering rack, you get more degrees of turning on the strut.

Bump steer is the steering rack arm... end things... (tie rods?) moving through a seperate arc to the lower arm, causing it to pull or push on the end of the steering arm... non volountary steering inputs.

The amount (side to side) that the steering arm pulls or pushes via bump steer is fixed, but the degrees of movement that this causes is relative to the steering arm length.

People dial in shite loads of camber at the front, but is the increase in grip partially due to improved roll centre distributing load more evenly to the inside tire?

When you lower Mcpherson strut, the roll centre drops a hell of a lot lower than the COG, mostly because of the lower arm angle.
The goal of RCAs for mac struts is only ever move the roll centre back UP.
Closer to the centre of gravity.

looking at the diagram of what determines roll centre position, lower arm angle has the biggest influence, however angle of the strut, and also lower arm length (by virtue of tipping the strut over) will increase roll centre height also.

Getting the struts tipped over even just a few degrees more, for the same amount of camber, will give a better roll centre position.

Roll centre migration is interesting, because when your car rolls, the roll centre moves (drops!) further from the COG, causing more roll, causing further drop, causing more roll etc etc. So you need to run very hard springs.

A high roll centre allows softer springs for the same amount of roll resistance, so good in cornering and also bumps.

I doubt its possible to actually raise the roll centre higher than the COG, so any tricks to pull to raise it as high as possible should be good.

I'll need to check some actual measurements to find out what actual affect different configurations could have though, I dont know what the kingpin inclination angle is on widebody/narrow body struts. I just know that you end up with a few degrees of positive camber with MA61 etc struts in an AE86/carina/etc.

[NoHachi]

Hi Roman,

You're absolutely right about the steering arms and bump steer effect. They don't cause bump steer by them selves, but any bumpsteer already present will be more noticeable.

About roll centre position. If I understand you correctly, your idea is to use struts with a larger inlination angle instead of RCA's to get roll centre back to OEM? Interesting idea, but you end up changing more things then roll centre.

Increasing KPI increases jacking loads when cornering.. transferring weight from the rear of the car to the front with any kind of steering angle. Much like caster does on the diagonals. Picture a line perpendicular to the strut (in essence the hub of the car) that the wheel attaches to. For any kind of rotation, the outer end of the hub has to move down. That means you have to "lift" the car up with the steering wheel. This is called jacking.

Increased KPI also has some effects on scrubradius. But this might turn out to be better rather then worse when running negative offset rims.

Last effects is that you have a tiny reduction in the motion ratio. Probably nothing worth worrying about.

I'd be interested to take a drive and see how this would feels.

[SekiguchiUeno]

Roman thanks for new insights.
Newer thought about that, how much degree could the difference between MA61 and AE86 hubs on the strut be?
Would the camber adjustment be enough, i think not and longer LCA needs to be used. With more lean struts the front outer tire will be put more on their outer edge while steer so it will be needed to compensate with even more caster? This also opens like Nohachi said troublefree using of lower offset wheels.

My intention was to let me make custom springs that put the car on stock offroad position again and are stiffer about 3kg/mm. And then if not enough use RCAs and longer LCAs to put the roll centre higher while maintain also better camber management that longer LCA ofer(thanks nohachi for graphs and measurements again).

btw: where to get MA61... struts and how they differ in other aspects.

[roman]

NoHachi Wrote:About roll centre position. If I understand you correctly, your idea is to use struts with a larger inlination angle instead of RCA's to get roll centre back to OEM? Interesting idea, but you end up changing more things then roll centre.

RCAs would definitely be used as well, as big as can fit under the wheels.

But even when you do that, you cant get the lower arms back to the factory angles, so roll centre has still moved in relation to the COG, compared to factory. This would just be another trick to raise the roll centre higher, the very same trick that Toyota uses to raise the roll centre on their cars with heavier factory engines.

I'm aware of the side effects of kingpin inclination angle. buuuuuuuttt, what I propose just mimicks the OEM setup of the 'widebody' cars anyway... If there were any disasterous handling consequences, it would be evident by 75% of the 80s Toyota fleet of RWD cars.

It would be quite easy to see how this suspension configuration drives... Drive an MA61! haha... or Cressida.

SekiguchiUeno Wrote:Roman thanks for new insights.
Newer thought about that, how much degree could the difference between MA61 and AE86 hubs on the strut be?

I cant remember... But I remember hearing that if you use them, you end up with 2-3 degrees of positive camber, if with standard top plates.

So it's not a MASSIVE difference... But just another trick to use to help bring the roll centre back up. I'll have to sketch it up to see how much difference it actually makes.

Quote:Would the camber adjustment be enough, i think not and longer LCA needs to be used. With more lean struts the front outer tire will be put more on their outer edge while steer so it will be needed to compensate with even more caster?

Yep there's enough camber adjustment, it's been done before, I know someone with MA61 struts in their '86. Dont need to use a longer LCA, just adjustable camber tops.

But acheiving the same thing with a longer LCA would probably be better in terms of camber gain, so long as your wheels still fit under the gaurds more or less

Quote:btw: where to get MA61... struts and how they differ in other aspects.

There are pretty much identical struts in MA61, cressida, soarer, etc etc.
Cressida struts are likely easiest to find.
I've currently got the exact same type of struts, but 'narrow body' ones from a TA63 Carina. With the plan to change to the ones with more kinpin inclination angle some time down the track, as I can adjust camber to suit.

The end goal of all of this, would be to use the suspension geometry for roll resistance rather than spring rate, so I could run as soft a spring as possible without having the car tip over through the corners.

[NoHachi]

Quote: The end goal of all of this, would be to use the suspension geometry for roll resistance rather than spring rate, so I could run as soft a spring as possible without having the car tip over through the corners.

I don't understand roll centres fully..but enough to know that my simple model of roll couple based on the distance between the geometrical roll centre and the COG is too simple. If tried doing some stuff based on force based roll centres but decided it was over my head. So these days, I just don't worry about it too much.

Another thing that changes is the relationship between the strut and the LCA which will change your camber curve. Any effect here will have a lot of impact on overal performance.

[roman]

One of the posters here 'Rick' with the red supercharged AE85 is running MA61 front struts in his car, might have to dig up his project thread and have a look again.

edit:



Should give him a chase up about how his car is going, he lives nearish to me at last check.

Although I guess the total amount they've moved isnt huge. edit: Aaahhh I see he's running NCRCAs at the bottom too, you'd need to tip them over more with out them... Or run longer LCAs, which would be a good thing.

Yeah I've just been having a rethink of some established 'facts' about suspension setups for the older toyotas.

A few years ago, NCRCAs were all the rage, now people arent keen on them at all.

Or running short as possible steering arms has always been in favour.

I've just been trying to rethink a few of the established ideas, and decide whether they're good or whether there's scope for improvement perhaps.
Although, I need to get my car running first, that would help hahahaha