AE86/XE7X with RA40/60 struts bump steer 3D explanation

[beerhead]

Yes the diagrams don't show the bump actually happening, not sure how I could even do that with Sketchup. Use some imagination All they show the base setup of the steering arm geometry with and without the RCA with the stub axle sitting at the same camber point.

Look at the steering arms, if they aren't parallel to the steering rack, as the strut compresses the pin for the tie rod end becomes closer to vertical and causes the wheel to toe in. This crap can't be explained in words, but its obvious the closer you are to factory geometry the better the car will perform

All steering systems have an element of bump steer, its just life. But there is no real way to fix the RA40 strut issue in a corolla, apart from not running them in the first place.

[RobertoX]

Sorry I disagree, if you have the same height strut as original that just happens to be an RA40 one but the LCA and steering are remain the same then the bumpsteer will be the same. The problems start when you lower your car, this affect will happen regardless of the strut that you use.
Running an RCA puts all the geometry back to factory.

You don't necessarily need to have the steering arm parallel to the steering rack either. because it's all ball joints the 'plane' (I assume you are referring to the flat part of the steering arm) is irrelevant. The movement is defined by the location of the tie rod outer ball joint, the LCA ball joint and the upper support. You can get rid off all of the planes and what not in there and use wireframe geometry to show bumpsteer.


When looking at the geometry In front view the LCA, tie rod, steering arm and chassis create a simple 4 bar linkage. As the 4 bar linkage moves around (suspension bump) you want the steering arm to remain at the same angle (no toe change). This does not necessarily translate into having the steering arm parallel to the rack.

You're right in that it is difficult to describe and you also make a good point:

its obvious the closer you are to factory geometry the better the car will perform

So many people mess with their geometry without thinking about this sort of stuff, this is the best advice in regards to bumpsteer.

[RobertoX]

So I got bored and put together some short vids of what it looks like:
http://duivesteyn.net/rob/Bumpsteer/demo_0002.wmv
You can't really see the bump steer in this one but it gives you an idea of the geometry.


If you look at it in front view you can see the wheel toeing a bit.
http://duivesteyn.net/rob/Bumpsteer/Standard.wmv

Toe change is more pronounced when it is lowered:
http://duivesteyn.net/rob/Bumpsteer/...20no%20RCA.wmv

It is corrected back to the same amount as the second video with the addition of an RCA (represented by a gap between the steering arm and the strut )
http://duivesteyn.net/rob/Bumpsteer/...50mm%20RCA.wmv

It's a bit hard to see because the video is slightly poor quality and there is something going on with my stupid video driver. The toe change is stubtle so possibly hard to see, I might try to play with the geometry a bit to make it more pronounced and obvious on the video.
The geometry in this is made up generic mac strut but you get the idea I hope, I don't know the hard points for corolla etc.

[beerhead]

I couldn't make out your vids too well, but I know what you're trying to explain. Essentially Image 1 vs image 3 in my diagrams. But, I'm not talking about generic bump steer from lowered vehicles, hence the title, RA40/60 Struts bump steer explanation for corolla's.

The king pin angle is wrong on a RA strut, it induces positive camber. The stub axle points further down. Did you notice that the 2 struts have stub axles at different king pin angles in my animations? Fitting them does the same to your steering geometry as cutting around 20mm of length from your LCA in an AE86 with standard struts, sounds like a sweet mod Even adding absurdly large RCA's does not return the steering geometry to anywhere near as good as factory (clearly shown in image 1 vs image 4)

When you run some sigma arms to widen the track and repair the camber you also change the 3D arc which the wheel follows while steering, I don't know exactly what it does, but if its not the same as factory it can't be good.

RA40 struts in a corolla / AE86 should be frowned upon, this is all I want to convey. It seems like a nice cheap brake upgrade, but it's such a serious downgrade to handling that it shouldn't even be considered as an option.

[love ke70]

im sorry, but you can make anything work, and with 400 hp i wouldnt be suggesting going back to smaller brakes to get some nicer handling, let alone the ridiculous prices on ke70 power steering gear.

im gonna have a serious play with this setup and see if it can be made to work, which i strongly believe it can

[RobertoX]

Does anybody have a definitive answer for the angle between the spindle and the strut for RA60, RA40, KE70, AE71, AE86?

I have heard that the angle on the RA60 strut is a fair bit more than AE86 which results in positive camber but that the angle on the RA40 strut is not so bad.

[love ke70]

ra60 angle is definately more, but its not a problem that cant be fixed.

[beerhead]

Robertox: Wth an RA40 or a RA60 strut when you extend the lines of the kingpin inclination , and the strut tube to their intersection, the point does not correspond to the contact point of the wheel on the car, one of the fundamentals of suspension design.

I didn't say don't upgrade your brakes, I said if you're doing an upgrade don't use RA struts, if you've got 400hp in a sub tonne car, you really need the handling to be spot on, and there are many other options available. You bought your car with the 1GGTE and the RA60 struts fitted, so you can't really be blamed for the setup Andrew

You can make it work perfectly, and I'll tell you how. But if the car is street registered these kind of mods shouldn't be done, in all states it's illegal to modify cast parts!

Find someone with a strut bending machine and have the strut bent to create negative camber. Have the base plate of the strut machined flat so that its square with the strut tube. Machine the base of the steering arms where the bolts are to allow a square mating surface for the bolts and re-drill at the offset angle for the dowels and the strut to match up.

[RobertoX]

Robertox: Wth an RA40 or a RA60 strut when you extend the lines of the kingpin inclination , and the strut tube to their intersection, the point does not correspond to the contact point of the wheel on the car, one of the fundamentals of suspension design.

You are saying that the axis of the strut (damper central axis) and the king pin axis are not the same? This is true for a lot of strut designs but has nothing to do with bump steer.
What is the "contact point of the wheel on the car"? The car and the wheel shouldn't be touching, this is a fundamental of suspension design
Maybe you mean tyre contact patch? Then unless you have 0 scrub radius and 0 mechanical trail, yes, the KPI wont go through the centre of the tyre contact patch.

Bending the strut to fix the poor camber is fairly common but you shouldn''t need to do all of that milling and re-drilling. Like I said, the 'plane' of the steering arm is totally irrelevant to bump steer. The only reason I can see why you would need to do such a mod is if the steering tie rod fouled on the steering arm after bending the strut, there is enough clearance for this not to happen though.
If you were to do this you would also need to fill in the old holes with something (weld I suppose) before re drilling otherwise the you will have an elongated hole. And you would need to mill the bottom of the arm where the bolt head mates up against to be parallel to the newly milled top surface. Sounds like a lot of dicking around for no gain to me.

[love ke70]

Robertox: Wth an RA40 or a RA60 strut when you extend the lines of the kingpin inclination , and the strut tube to their intersection, the point does not correspond to the contact point of the wheel on the car, one of the fundamentals of suspension design.

I didn't say don't upgrade your brakes, I said if you're doing an upgrade don't use RA struts, if you've got 400hp in a sub tonne car, you really need the handling to be spot on, and there are many other options available. You bought your car with the 1GGTE and the RA60 struts fitted, so you can't really be blamed for the setup Andrew

You can make it work perfectly, and I'll tell you how. But if the car is street registered these kind of mods shouldn't be done, in all states it's illegal to modify cast parts!

Find someone with a strut bending machine and have the strut bent to create negative camber. Have the base plate of the strut machined flat so that its square with the strut tube. Machine the base of the steering arms where the bolts are to allow a square mating surface for the bolts and re-drill at the offset angle for the dowels and the strut to match up.

still probably isnt what i would ahve done in the beginning, but with the ra60 powersteering rack going in, which means new mounting, i think i can move the rack to make it work better, and either bend the strut or run some adjustable LCA's. will see how much i can get blue plated
i do want it to stick better, and its gonna take some effort with the 1g, which is why this thread is of interest to me.

[beerhead]

The only variable changed between the 2 struts is the KPI. Running massive RCA's to get the camber back, regaining close to factory geometry leaves only the plane which the steering arm works on as a modified component. By the process of elimination this can be the only reason that RA40 struts handle like rubbish. What else has really changed?

Have you tried RA40 struts in your car? There isn't a corolla driver on any forum who didn't notice a handling loss using these struts, most of them go back to a factory strut, but not all drivers are pushing the edge and don't notice the issue.

Bump steer to me is an inclination for a wheel to toe in and out. Which is exaggerated by a non perpendicular tie rod pin. This is a form of bump steer that no body has ever even tried to explain.

[RobertoX]

Bump steer is the change in toe angle as the suspension goes into bump. It is usually measured and quoted in the straight ahead position (ie rack centeralised). It's not really open to interperetation.

I have used RA40 struts before (for supra brake upgrade) and I would use them again. There was a big handling improvement but its a little hard to compare as it was going from a standard strut to coilovers. There was no problem with camber.
I have also used sigma lower control arms and I would never use them again, handling didn't improve and there seemed to be increased bump steer but I didn't measure it.

Does anyone know the mounting point locations for a ke70/ae71 corolla? I'd like to make a correct model of the geometry, I could make some graphs of bumpsteer, it'd be nice to actually quantify this

[beerhead]

Sounds good robertoX, I'll measure it all up sometime soon. I'd love to see a model of whats going on with the steering arms with RA40 struts, there's something bad going on for sure, and it'd be good to know the complete answer rather than us arguing about technicalities. BTW what simulator are you using for the bump steer vids? You'll have to work out how to make them into gifs so people can view them easily.

[RobertoX]

Awesome, that'd be good if you could. And I agree, arguing about what will happen without anything solid to back it up is a bit pointless.
I don't have a car to measure at the moment. I do have some ra40 struts in the shed that I'll try to measure and I also have a ae71 cross member and steering rack, but I need to know the relative position of the upper support centre and also the castor control rod body pivot.

The videos were done with solid edge, and it only puts out avi, I don't know how to do a gif...