Mounting the engine without subframe spacers, and without tilt.

[The Dark Side of Will]

I think that some of you guys have been over-thinking the subframe spacer affects... Bumpsteer is changed by changing the mounted height of the rack relative to where the tie rod ends are connected to the steering knuckle, correct?
If that is correct, then the reason Jonsku is saying that there is no discernible difference in a car running spacers to one that doesn't, is because there is no difference in bumpsteer! There is a difference in roll center height, but not bumpsteer... the reason? You have not made any changes in the geometry between the mounted height of the rack and the attachment points of the tie rod ends to the knuckle. The whole assembly is being moved, or more accurately, the body is being raised, relative to the whole assembly. All of the components that could affect bumpsteer by moving them independently of each other, are all being moved together. The wishbones and the rack are both mounted to the subframe in the same relationship to each other, whether the subframe is bolted against the frame rail or bolted to a spacer which is 20mm thick. Nothing in the geometry of the rack height, to the tie rod ends, to the mounting of the wishbones, to the location of the knuckle changes, no matter where you locate the height of the subframe, relative to the frame rail... within reason. A large change in space between the frame rail and subframe will result in a change in geometry of the rear of the wishbone mount and the inner wishbone ball mount, I'll concede that.
For a track car, the roll center change, by using the spacers on the subframe is not a good thing... on a street car, not so much of a bad thing. Think about it and you'll reach the same conclusion... all things being equal, raising the body 20mm, relative to stock, by using a spacer between the subframe and the frame rail, will not change any geometry of the rack to the knuckle. It can't, they're mounted in the same plane, you've just raised the body, relative to that plane...

Garey

Exactly.

As I've said before, lowering the car doesn't change the shape of the suspension's bumpsteer curve. It just puts the suspension at a different point on that curve. The bumpsteer curve of the suspension is determined by the relationship of the arcs tracked by the tie rods and control arms through the suspension's motion.

However, moving the rack up or down relative to the crossmember, even as little as 2 mm WILL change the bumpsteer curve of the suspension. If you change the shape of the curve without knowing what your before and after curves look like, you're just shooting in the dark. You might as well try to fix a no-start condition by replacing random lightbulbs.

You can use parts like the below to replace a tie rod end with a rod end and threaded stud. This lets you move the rod end up and down to change the bump steer curve of the suspension. This is how race cars adjust bumpsteer.

http://www.speedwaymotors.com/Adjustable-Tie-Rod-Adapter-Stud-to-Heim,3333.html

You can make VERY small adjustments with this setup and small adjustments ARE very important.

[The Dark Side of Will]

I agree with what you're saying Garey, but you're also forgetting that the top of the strut stays with the body. So in reality, it is the same as a 20mm drop as far as the subframe is concerned. The vehicle and bottom of the struts will stay the same height while the subframe drops down.

And when people talk of bumpsteer on here, I believe they're speaking of the extra force you get acting on the tie rod after it passes horizontal rather than changing its plane relative to the control arm.

He's not forgetting that at all.
Spacing the subframe down is very very similar to lowering the car by the same amount. The only difference is that the length of the strut doesn't change with subframe spacers.

There is only one definition of bumpsteer:

"The change in toe a wheel demonstrates as its suspension traverses its travel."

There is no other definition of bumpsteer.

[tttoon]

What about spacing both the subframe and the control arm bushing mounts the same amount? That would change caster to a degree too, but if the level change of the bushing center and the subframe are the same this should not be an issue right?

[The Dark Side of Will]

This page has the brutally simple diagrams that I hope will explain the topic of bumpsteer:

http://www.quadratec.com/jeep_knowledgebase/article-68.htm

Here's a simple DIY setup for measuring bumpsteer:

http://www.roclife.org/forums/showthread.php?72343-Started-some-bump-steer-measurements

No more excuses.

[The Dark Side of Will]

What about spacing both the subframe and the control arm bushing mounts the same amount? That would change caster to a degree too, but if the level change of the bushing center and the subframe are the same this should not be an issue right?

Not significant.
What matters is the axis from the center of the inner ball joint to the center of the outer ball joint.

[bmwmech1]

I've said my peace...:)

Garey

[Jonsku]

However, moving the rack up or down relative to the crossmember, even as little as 2 mm WILL change the bumpsteer curve of the suspension. If you change the shape of the curve without knowing what your before and after curves look like, you're just shooting in the dark. You might as well try to fix a no-start condition by replacing random lightbulbs.

If you're concerned with such small change, be my guest. However, it would be very beneficial to the people to understand that such a change does NOT have ~any effect on the drivability of the car.

Btw, some E36 / Z3 steering racks are already lower in mounting point height than the E30 units and thus need couple 2mm spacers in order to mount properly. I've NEVER heard any complaints / comments related to bad bump-steer behaviour due to the spacers (which can of course be used in two ways - up or down).

Two V8 projects here have used E36 rack with spacers on the top-side, thus lowering the rack. Neither of them used subframe spacers, and worked very well.

[The Dark Side of Will]

We can go back and forth about what's significant and what's not all day, but in the end ONLY the measurements matter.

Apparently no one has ever done any...

[E30SPDFRK]

Why don't you do some yourself then and stop arguing with people that have first hand experience?

[The Dark Side of Will]

Driving is not measurement.

For example, if the car feels nervous braking for a bumpy corner, is it bumpsteer or toe?

When I buy a body for my project, it will be an iX.
If I find I have the desire to change the stock bump steer curve, I will take a measurement. I'll probably snag the setup pictured above to adjust the factory curve.

Right now I'm still making sure I can package everything in the engine bay, get the gear ratios I want, etc.

[dirty30]

Anyone looking to perfect the suspension geometry of an E30 is wasting thier time when there is that snap oversteering, non-adjustable, unsprung heavy trailing arm mess out back! Save the serious track nerd geometry stuff for the E36 guys!








Semi j/k fellas.

[The Dark Side of Will]

I challenge you to replace the E30 rear suspension with something lighter... ;)

And if you think E30's have a snap oversteer problem, go drive a Pontiac Fiero to 10/10ths! :woowoo:

[noid]

I'm with you Dark side (how ironic), there are many ways to skin a cat, and as far as I am concerned there is the right way and the 'it works' way of doing things. Very German like of you.

Call me crazy, but if we are messing with suspension geometry to accommodate the m60/2, what is the point in choosing an e30 as a base over another car? For me the reason I want to do it in an e30 is to have an e30 feeling factory-esque car, with ~280-300hp, and a V8 sound (which i have grown to love with my x5 4.4). If we start messing with geometry even a bit, as far as I am concerned it is not the same car.

[E30SPDFRK]

I'm with you Dark side (how ironic), there are many ways to skin a cat, and as far as I am concerned there is the right way and the 'it works' way of doing things. Very German like of you.

Call me crazy, but if we are messing with suspension geometry to accommodate the m60/2, what is the point in choosing an e30 as a base over another car? For me the reason I want to do it in an e30 is to have an e30 feeling factory-esque car, with ~280-300hp, and a V8 sound (which i have grown to love with my x5 4.4). If we start messing with geometry even a bit, as far as I am concerned it is not the same car.

As has been said but completely overlooked, there is no need to mess with anything during the swap. It fits perfectly fine without any modifications to the subframe/steering/suspension/etc..

[The Dark Side of Will]

I'm with you Dark side (how ironic), there are many ways to skin a cat, and as far as I am concerned there is the right way and the 'it works' way of doing things. Very German like of you.

Call me crazy, but if we are messing with suspension geometry to accommodate the m60/2, what is the point in choosing an e30 as a base over another car? For me the reason I want to do it in an e30 is to have an e30 feeling factory-esque car, with ~280-300hp, and a V8 sound (which i have grown to love with my x5 4.4). If we start messing with geometry even a bit, as far as I am concerned it is not the same car.

Thanks!
Spirited discussions lead to the best learning. It always hurts when our deeply held beliefs are challenged, but the learning process.
No hard feelings should result because we all end up better for it afterward!

As has been said but completely overlooked, there is no need to mess with anything during the swap. It fits perfectly fine without any modifications to the subframe/steering/suspension/etc..

I think this whole thread was started to discuss a way of installing the V8 with zero angle across the guibo. Apparently, with the V8 "dropped in", there's an angle across the guibo that's greater than stock.

My take on it is that you need to know three things:
1. You need to what you have now. (IE, what your design parameter is in the initial configuration and where it is relative to optimal.)
2. You need to know what you're going to change (How much and in which direction you need to change your design parameter, which parts you'll change to get there and what side effects those modifications will have.
3. You need to know what you end up with. (What your design parameter is after the modification, what it is relative to expectation, and whether it's better or worse than it was)

For the driveline angle topic, item three has been partially adressed. (This Post)
None of the above have been addressed on the bump steer topic.

What I've described above is the basics of the process of deliberate engineering development. In this case, it's of a vehicle from a normal street car into a hot lapping demon. :twisted: :borg:

If you're just after "the stance" or "the sound" or want to cruise around and only make a few shakedown trips down the 1320, then disregard everything I've posted in this thread. :p