1st gen celica susp. and steer and struts (strut tops - are ta22 and ra28 the same?)

[o_man_ra23]

Those roll centre adjusters look to do nothing about bumpsteer... as bumpsteer is caused by a difference in the length/angle between the tie rods and the lower control arm. The RCAs wont do anything about changing that, it will just give negative camber, and increase track. It will also increase your ride height. So it seems that these RCAs give neg camber and increased track as improvements, and increased ride height as a depreciation.

Anyone able to explain to me how these will eliminate bumpsteer as T3 claims??

Cheers, Owen

[Zerko]

I don't think they increase ride height as they go UNDER the hub/axle. they will only push your control arm down. Your wheel and strut assembly (and compressed distance between strut top and hub)remain unchanged.

[o_man_ra23]

I don't think they increase ride height as they go UNDER the hub/axle. they will only push your control arm down. Your wheel and strut assembly (and compressed distance between strut top and hub)remain unchanged.

Therein lies the problem with 10Hr work days, you dont quite think properly at the end of them. Still doesnt explain the bumpsteer corrections tho.

Cheers, Owen

[LeeRoy]

Therein lies the problem with 10Hr work days, you dont quite think properly at the end of them. Still doesnt explain the bumpsteer corrections tho.
Cheers, Owen

As Zerko said about pushing control arm down is right.

When you lower your car you make the control arm sit closer to horizontal than it was originally in which case it would have pointed down. So since it is now at a different angle when you hit bumps it is able to have a greater lateral movement of the tierods and exert more force creating bumpsteer.

So by lowering this control arm closer to what it was you reduce the bumpsteer.

- LeeRoy

[o_man_ra23]

But if the suspension is setup correctly in the first place, the ackerman angles will be correct for all suspension travel and steering, and then you wont have bumpsteer no matter how you raise or lower the suspension. bumpsteer is all about getting the lower control arm and tie rod to move the same vectoral distance, and rotate through the same angle when moved. They should be parallel at all times. So as the RCA doesnt alter the angles between the control arm and tie rod, as they sit above the outer tie rod end and lower ball joint holder, then they dont eliminate the bumpsteer as advertised, they just alter how it affects the car.

Cheers, Owen

[WDE_BDY]

Macpherson strut is a compromise though in terms of bump steer, the factory setup is optimised for a set range of movement. Once you lower the car too far it goes outside this range, the RCA restore the correct angle to the lower arm.

Callum

[o_man_ra23]

Righto, so when I convert to rack and pinion, I need to resize and position the rack such that the distance between the centre of the rack end ball and the centre of the tie rod end ball is identical to the distance between the centre of the LCA inner bush and the centre of the lower ball joint ball when the toe is set correctly. By doing this, and then making the LCA and tie rod parallel, then I will have eliminated bumpsteer from my car completely as the relative lenghts and angles between those two items wont change during suspension travel. In practice the tyre will actually try to toe in more due to the rolling outward (relatively compared with the LCA) of the balljoint and outer tierod end holder. Perhaps I should do a computer model of this, and work out the lenght and positioning of the rack to eliminate bumpsteer...

Hmm... If I do this, i could sell the model (or the program i write to do the model) couldnt I?? Any buyers?? Might do it in Visual basic.

Cheers, Owen

[Norbie]

RCA's are about minimising camber changes, not bump steer. To acheive minimum camber change through the arc of the control arm, you need to have the control arm horizontal when the car is stationary on flat ground. If you lower your car the control arm will no longer be horizontal, and that's where RCA's come in.

[o_man_ra23]

RCA's are about minimising camber changes, not bump steer.

Sounds right, but read the T3 website... they claim that their neg camber RCAs eliminate bumpsteer... so thats where my argument came from. Thanx for comfirming my query tho.

Cheers, Owen

[WDE_BDY]

I would have to disagree there Norbie. I have not seen many strut front ends where the LCA's are horizontal, they all seem to angle down to the wheel from factory. By lowering outside of the factory planned range of normal travel you end up with all sorts of nasty effects including bump steer and odd roll centre changes. Part of the job of RCA's is to bring you back to the factory range not just for the LCA but also for the steering arm (which is a fixed distance from the LCA). Other methods include dropping the attachment point to the steering arm with something like this -


Callum

[TA-022]

i always thought minimal bumsteer setup by factory; is thrown out of wack when you lower your car due to the angle change of the steering components - which bear a direct correlation to the change in control arm angles from said lowering.

if what i believe is true then the RCA's should help to correct the lower control arm angles and hence help rectify increased bumpsteer caused by lowering of the vehicle.

[TurboRA28]

bumpsteer is often built in from factory.. peoples normal reaction in emergency is jump on brakes.. so bumpsteer causes wheels to toe in, more stable braking.

but the idea is right if you setup the control arms and steering arms in a paralelogram then it doesn't matter what height the car is at, there wont be bumpsteer

if you look at the front end of say an ae86, it is far from a paralelogram hence the large amounts of bump steer when you lower it.

[barned01]

what's your setup like joel (in the 28)
You put in the ae86 crossmember.
I assume you kept the ae86 controll arms and steering rods from the rack.
Does that mean your setup is pretty much the same (ie not the parallelogram setup)?
What about when compared to your ta23 crossmember and ke70 rack, what were the angles like on that?

Obviously the camber top if you had one (i can't remember) would have fixed the camber issue with the increased track, but was bump steer affected?
was it at standard ride hight or lowered?

and are we all getting off track of the original question and should start another thread?

[WDE_BDY]

Be good if a mod could split this so we don't lose the current discussion or the strut top info.

Callum

[Toy77]

title changed to represent changed, but worthy, direction of thread.

Stew