[brentpicasso]

As you may remember I've been working on bump-steer correction on the MR2.

I've installed roll center adjusters, and relocated the steering tie rods to the bottom of the knuckle. Suspension consists of ground control coil over shocks with ground control camber plates.

So I'm doing my bumpsteer measurements. I've removed the springs and brought the suspension up to normal ride height. I then 'compress' the suspension 2.5" to check the bump steer,which is how much the wheel steers itself when going over bumps or cornering.

- with the steering tie rods mounted to the bottom of the knuckle, I see a fair amount of toe in during compression.
- with the steering tie rod mounted to the top of the knuckle (stock configuration) I see a large amount of toe-out during compression.

Based on my research, in the front, you absolutely do not want toe in in the front, since it'll make the car steer more sharply (in effect) when going into corners. Toe out is bad too, resulting in less bite/grip and less responsive feel.

As an experiment, I dropped the steering rack down by 1.5". With the tie rod ends mounted to the bottom of the steering arm, I measured almost zero toe!

Now I need to drop the location of the rack. I can make some spacer blocks for mounting it, but that causes a problem with the steering column shaft reaching the steering box. Looks like I need to come up with some way of extending it.

That's it for now.

 

[rnoll98]

Hrmmm. Time to put this in while you've got the space
http://store.summitracing.com/partd...=110&Ntk=KeywordSearch&Ntt=steering+quickener

A little toe out is actually good, we use it in autox to give better initial grip going into a corner. But, as you said, you'd rather have no bump steer. Then you can dial in a little static toe out in the front if you want. There appears to be a little room to play with in the u-joint on the steering rack, but probably not the 1.5" you're looking for. I forget what the steering column shaft looks like north of the u-joint. Maybe someone sells stock splined shaft that you can cut to fit?

 

[brentpicasso]

LOL I've been thinking the same thing. Here's what I've found:

(scroll down)
http://poske.com/cgi-bin/shop.pl/file=Coleman/page=index.htm/SID=129592499

The one you listed is a bit heavier but might fit better if I don't have enough length to work with.

After I drop the rack I will be able to adjust it to bump in, bump out, or near zero depending on how I adjust the connecting point of the outer tie rod.

Brent

Brent

 

[rnoll98]

That quickener looks a lot nicer than the one i found.

Quick thought on geometry. I would definitely watch the movement both on bump and rebound. It'd be very easy to set the car to have nearly zero change under bump, and some wacky change under rebound. From what I've read, you want to set it up so that the angle of your tie rod is parallel to the angle created by the imaginary line that passes through the ball joint and the control arm inboard pivot. This will give you zero toe change under bump and rebound IF your tie rod and control arms are the same length. That's a whole other issue.

 

[erwendell]

Hmm, now that's something I hadn't considered before. The RCA solve the increased roll couple problem but in the process, because the steering/toe links are no longer parallel with the lower control arm, bump steer/toe increases. And some people still think that the more parts you throw at the car the faster it gets. Placebo effect of cars.

 

[MACE]

Once you get bump steer down, you can start on roll steer.

In other words, do you still have zero "bump" steer with the wheels cranked into cornering position?

Speaking from total igornance, I would think you would like a bit of toe-in when the nose dives under braking (for added braking stability) and you would battle roll steer with stiff anti roll bars. Isn't toe out more skittery and toe in more stable?

As an armchair suspension teck sic I kind of like the softish spring / shock with stiff bar theory.

 

[erwendell]

Bump steer and roll steer are the same motion because they both result from movement of the suspension in league with steering (front) and toe link (rear) design. Bump steer is always undesirable while roll steer can be beneficial. To answer your question, yes, bump steer is still zero with the wheels turned because the relative lengths of the steering and lower control arms hasn't changed and their angles are still parallel. There is a slight length change due to the fact that the outer tie rod moves on a radius centered on the steering axis while the inner tie rod moves in a purely linear fashion. Not having measured it I don't know for certain but given the range of motion I would imagine the effect is minor and there's nothing to be done about it in any case. The only way steering input occurs with suspension movement is if the lengths were different (different radius of swing = different movement in x plane for given movement in y) or if the angles were different (different starting points on the sine curve = the outer joint on one arm could be moving inward while the other is moving out). Hmm, hope that makes sense.

 

[MACE]

yes, bump steer is still zero with the wheels turned because the relative lengths of the steering and lower control arms hasn't changed and their angles are still parallel. There is a slight length change due to the fact that the outer tie rod moves on a radius centered on the steering axis while the inner tie rod moves in a purely linear fashion. Not having measured it I don't know for certain but given the range of motion I would imagine the effect is minor and there's nothing to be done about it in any case.

I think we agree that roll steer still exists even when bump steer is zero due to the differences of travel of the steering arm as you describe. Like you, I don't know if the additional increment of toe is significant. I disagree that nothing can be done about it. You can optimize roll steer if you do your bump steer modifications checking with the wheels turned.

None of us know if zero toe change is the optimum solution.

Do you think OEM suspension engineers have it all down to science or is it trial and error even in the big leagues? Probably still 50/50 but with instrumentation they can eliminate a lot of the fuzzy data.

 

[erwendell]

Actually what I was referring to nothing to be done about was the fact that the outer tie rod end swings in an arc. I didn't mean to imply that that bump steer was unsolvable or that roll steer was necessarily bad. Roll steer as a matter of fact can be quite good and more than a few manufacturers have gone to great lengths with respect to rear suspensions in order to optimize it. As far as I know, the changes in placement and lengths of the rear suspension links in the 87-89 cars was to change the roll steer characteristics.

As far as whether or not it's a science, I would say yes for the most part because all of these motions can be easily modeled in a computer. They may not know exactly how much they want until the test drives but they have no problems figuring out how to achieve it.

The only thing that nags me about roll steer characteristics is that they were calibrated to the slip angle range of the stock tires. The FC RX7 people have found that putting big sticky tires on their cars cause the roll steer characteristics to become downright scary. Granted, that's a system that relied on compliance of the stock rubber bushings whereas the mk1 system uses ball jointed links and depends for the most part solely on geometry.

 

[tksmr2]

http://www.kcn.ne.jp/~nabeck/apntr.htm


Todd
87sc
www.cardomain.com/id/tksmr2

 

[JimKing]

Interesting. Is there a translation of that anywhere? Relocating the tie rod end to the other side of the arm lowers it's pivot point 60mm, acording to their diagram. And the RCA they are using looks like 30mm. So they are suggesting that it is ok, or even beneficial, to have the tie rod and LCA in a different relationship than stock.

 

[tksmr2]

Jim, don't know. I'll have to contact Nabeck, the owner or OOashii, a friend of Nabeck to see if they can translate it for me. Nabeck is the most popular AW11 owner in Japan so I would think he would know what he is doing with his own car. Plus I have seen pictures of his AW11 on an autocross course. I don't think Nabeck speaks much if any English but I do know OOashii does.

I do know that Nabeck got those front tie rod parts from http://www.apn-jp.net/parts.html He has 23mm rear RCA's I think and 30mm front RCA's.


Todd
87sc
www.cardomain.com/id/tksmr2

 

[verno-dub]

Hey, this might me a little off topic, but would you guys know the size of the steering rack mounting bolts, including pitch and lenght?

 

[brentpicasso]

Those are interesting links.

What I don't see is what the ride height is of the mr2 being depicted. Those RCAs and dropped tie rods may not be appropriate for different setups.

For example, that setup would not work well for my mr2's ride height- I've measured that already.

Oh- and one more thing- we don't know if they tuned it for minimal bump steer or if they dialed in some bump in or bump out.

In any case a translation would be nice.


Brent

Verno- I'm looking to drop the steering rack too. I think I may be going with an aftermarket rack instead....

 

[verno-dub]

Verno- I'm looking to drop the steering rack too. I think I may be going with an aftermarket rack instead....

Im thinking the biggest limiting factor in dropping the rack would be the "tunnels" the rack inner tierods pass through. I had my car in the air today and although the mod to put the tie rod ends under the knuckle will leave a comfortable amount of room for suspension articulation, dropping the rack 1.5" might cause the inner tie rods to hit the bottom of the tunnels.

Brent, would you know what the rack mounting bolt size is, as well as the length and pitch?

Vern

 

[tksmr2]

Those are interesting links.

What I don't see is what the ride height is of the mr2 being depicted. Those RCAs and dropped tie rods may not be appropriate for different setups.

For example, that setup would not work well for my mr2's ride height- I've measured that already.

Oh- and one more thing- we don't know if they tuned it for minimal bump steer or if they dialed in some bump in or bump out.

In any case a translation would be nice.





Brent

Verno- I'm looking to drop the steering rack too. I think I may be going with an aftermarket rack instead....

I'll see what I can do about the translation.

Todd
87sc
www.cardomain.com/id/tksmr2

 

[tksmr2]

I got a few more websites with parts.


front and rear bumpsteer correction modifications
http://www.sunlogisco.com/cgi-bin/ebn/cgi-bin/list.cgi?ctg_id=e-AW-001

>with the tie rod ends
http://www.apn-jp.net/parts.html

> Roll Center Adjusters (RCA's)
http://www.ko-wa.ne.jp/car/part.htm

Todd
87sc
www.cardomain.com/id/tksmr2

 

[rnoll98]

I got a few more websites with parts.
> Roll Center Adjusters (RCA's)
http://www.ko-wa.ne.jp/car/part.htm

Interesting that the thickest they offer for the SW20 is 25mm. I was thinking of making some in the 45-50mm range for myself, but still need to see what is optimal.

What I really want is the billet aluminum A/T shift knob. Uber-bling! :thumbup

 

[tksmr2]

http://www.kcn.ne.jp/~nabeck/apntr.htm

APN bump measures Piro tie rod end

It is Piro ball tie rod end used together with the roll center adjuster to correct the arm corner that has gone mad by having lowered height.

The setting to aim cause the Toe change when the corner ring inside rolls in Piro tie rod end's for the reception desk made in auto paddock Nakagawa this daring to give the difference to the thickness of the adaptor in the roll center adjuster and the tie rod end by the structure installed through the adaptor is given to HIGH-GEARed AW11 though rear is equipped with the tie rod end matched to the thickness of the roll center adjuster of TBS.

Because the reception desk is a piercing method while it is a method that a rear Tie rod of AW11 pierces from the upright under when a Tie rod that lowers this installation position is installed, it is necessary to process the taper part of upright from the lower side by relate by lowering the Tie rod position.

It is necessary to give the taper processing from the upright lower side to install a Tie rod that lowers such an installation position below though a pure reception desk Tie rod of AW11 becomes an installed method on upright.

It seems to have seen the Tie rod installation part of upright on.
Purely it cuts down from the under from among the taper that has been
undergone plastic operation and a crowded taper is seen on though it is not easy to understand. It is also possible to return Zagri from the under to a pure, Tie rod of the piercing type by suppressing it half. (Because the accuracy of the unit of ..Sn.. No 1 milli ..such processing.. is demanded, it is safe to leave the processing with DIY to the pro shop difficultly.

This upright processing was obstructed directly to auto paddock
Nakagawa in Aichi Prefecture, HIGH-GEARed was done, it sent because
parts were stockouts, and it installed it for myself.

The adaptor rod is the one that strength was put out with Hitasmiyakihai on the assumption of running in the circuit, and Piro ball bearing is a structure of sticking to that can be oiled.

Difference of APN Tie rod of Tie rod of piercing method (on) and of
thorn in the under method (under) of purity supra.

It is understood that a Tie rod height and angle are quite different. When height is lowered, I think that the advantage in which of the thorn in the under is changed is large of a Tie rod because the arm corner gives cheers by lowering height and the load rests upon the ball joint.

Because the setting to aim at the corner ring performance improvement
by the roll center adjuster installation of 23mm is given as for a set
value in APN, the corner ring performance that Onzaral is pleasant can
be experienced by the roll center adjuster use for a thickness near it.


However, stability also has the decreasing disadvantage at the bump etc. under straight advancement because it is an arm designed by the setting that moves Toe when rolling.

This working is working that the difference of the thickness of the adaptor of a roll center adjuster and a Tie rod brings, it makes to the setting that adjusts the difference of the angle of a Tie rod and Roaarm by changing the thickness of the roll center adjuster and values the straight advancement stability or it makes to the setting that values the corner ring or it is also possible to adjust it freely.

(30mm is recommended from 20mm in the setting data of APN. )

The setting is possible also in the squid way by changing the difference measuring the distance that moved from the Tie rod position of normality like this and the distance that moved from the Roaarm position of normality though this is an image of AW11 of the friend who installed the same Tie rod. This friend has changed to the setting to value the straight advancement stability by using the roll center adjuster with a considerable thickness.

It might be also interesting to own some adjusters and to change the setting according to the stage. (Because the performance cannot be demonstrated in not taking heart the alignment of course in every case though attention is necessary. )

Because it can do nothing but find it repeating make-up & trial because
Various items like the damping force, the freedom length, the spring rate of shock,the camber, the caster, Toe, and the running condition, etc. twine round a best setting in implications, it is not to have a mind to work on the setting of the leg considerably seriously after the movement of Sas and the arm is understood well if an opposite expression is done, the expression called parts that remain in the hand can be likely to be done.

However, I do not think that this easily has parts worth when the one
requested from foot surroundings of AW11 is a lot of.

 

[tksmr2]

A Tie rod that uses the rod of the long type that can be used according to the stroke on the Ribamp side of the shock absorber of a super-short type has been released from APN besides a Tie rod through this short adaptor. It might be more effective in AW11 etc. that are united the set for the race.


(Over 5000 charaters, above is the end of the 1st part).

I have two more pages that are somewhat translated at best, haha. I will post them later on. If someone wants the original email I got form OOHashi about the three pages on Nabeck's site I can forward it to them. It's a very bad translation but I guess it's better than Altavista. OOHashi told me his Homepage is very difficult to translate.

Todd
87sc
www.cardomain.com/id/tksmr2