MKII Suspension Analysis: Front Suspension - Page 2 - MR2 Owners Club Message Board
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post #21 of 98 (permalink) Old December 31st, 2007, 11:35
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traffic,

#4 is pretty darned close to the ideal autox setup for stock class. I don't doubt it worked the best. It has the stiffest front v rear ratio. All of the others were probably too soft up front relative to rear.

I'd guess #2 probably felt stiffer, but at the limit #4 was probably more neutral and predictable.

Jim brings up a good point, anyone have a suspension analysis of a late model 911?
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post #22 of 98 (permalink) Old December 31st, 2007, 13:31
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I'll check with Owen. He might have one.

Ask yourself how much the front suspension design matters once the inside front wheel is off the ground. e.g. Where is the front RC?
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post #23 of 98 (permalink) Old December 31st, 2007, 13:34
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is hiking a wheel up "good" though? yeah you can be fast but some times you're fast in spite of your setup, no because of it
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post #24 of 98 (permalink) Old December 31st, 2007, 13:39
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One of the benefits of hiking up the inside front wheel is that it distributes the load it would have normally born to the other three corners. In a RWD car, this helps with motive traction by putting more force on the rear inside wheels.

One of the benefits of running a monster rsb on FWD cars is that it uses the force of the rear inside wheel (behing hiked up) to put more force down on the front inside wheel for accelerating out of corners.

You'll often times see cars like BMWs and such accelerating out of corners with the inside front off the ground.
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post #25 of 98 (permalink) Old December 31st, 2007, 13:53 Thread Starter
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Quote:
Originally Posted by jreyenga
Alex, I really think IC height has more of an impact on 'funny handling' than roll-center migration. I spent A LOT of time mulling over all this stuff and trying to justify it during my FSAE days.

It depends on what your final goal is. If you are just trying to get a better understanding of suspension design to apply some of that knowledge to FSAE you're probably learning a fair amount. FSAE is a huge daunting project, and with suspension design/vehicle dynamics, the more you learn the more complicated it gets. In the end, there is no perfect suspension. If you can get simulations that look ok or good, you can gain a lot more by testing the car than running in circles with the analysis trying to approach 'perfect.'

Toyota honestly probably didn't spend much time perfecting the stock geometry. They were probably more concerned with packaging and using off the shelf components. Study a modern porsche 911 if you want to see a less compromised MacStrut suspension. There have been millions of dollars of smarts put to trying to make stock-ish 911s go around a track as fast as possible, and they seem to do a good job of it.
I am actually done with school (just graduated this december). I will be honest, my SAE suspension design was pretty basic, it was really just throw in some points, tweak it a bit till it seemed deacent and go with it. We only just found Optimum K in the last few weeks of the semester. Before that we were basically trying to design in working model (2d motion program). Its only the 3rd year of the program at my school, so I'm really just hoping to have made a suspension thats better than the previous two

My main goals are basically to try to make my car handle better, and hopefully help out the community in the process. Randy is probably going to take this much farther than I ever well, basically I am coming away from this with a general idea of "don't lower it too much, and get some stiff-ass sway bars". Of course, if a I could get my hands on a set of RCAs and bumpsteer spacers I would definetly go for it

"the more you learn the more complicated it gets": Yeah, tell me about it
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post #26 of 98 (permalink) Old December 31st, 2007, 14:11
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Quote:
Originally Posted by twoina2
I'll check with Owen. He might have one.

Ask yourself how much the front suspension design matters once the inside front wheel is off the ground. e.g. Where is the front RC?
While the RC is useless, I think the IC length and camber curve for the outside wheel may still have meaning. I think what I'm doing is correct, but it would be nice to know that it's close to what someone like Porsche came up with.
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post #27 of 98 (permalink) Old December 31st, 2007, 14:18
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Quote:
Originally Posted by kbrew8991
is hiking a wheel up "good" though? yeah you can be fast but some times you're fast in spite of your setup, no because of it
I ragged on Owen about that when he was autoxing his Neon.

Unloading an inside tire is one thing. Hiking it up is another. So, I ragged on him about how he was raising his CG.

His answer was that the rear CG didn't matter because his car was going to under steer at the limit anyway. He chose the monster rear bar to get better turn-in. I countered that he might be better off with a "somewhat smaller" monster rear bar. He countered with how the under/over steer dynamic changed when the tire lifted and the dynamic was better if he lifted the inside rear tire right away.

Guess its true. The more you know, the more complicated it gets.
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post #28 of 98 (permalink) Old January 2nd, 2008, 23:41
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I don't have anything on Porsches. I can tell you that the neon has very low camber compensation and virtually no roll center migration by comparison. The roll center moved about 8" horizontally when the tire lifted off. Pretty undramatic. Camber compensation does matter but in the grand scheme of things is not terribly important and IC's matter only in the affect that they have on camber compensation.

As to whether it's fast or not.. no doubt on the neon. Or a GTI. Or civic or CRX or blah blah blah. Fundementally the problem is that one end is really heavy and the other light but the tires do not have similar size splits. That means that in order to get such a car to have semi-neutral handling requires the light end have extra weight transfer. Extra weight transfer plus less weight to transfer = liftoff. It's fundemental, and there is not much you can do about it.

Moreover, once you realize that you can't keep it down anyway, you find that increaseing the roll stiffness on the hiking end results in no change to handling balance, but typically results in a substantial improvement in post apex (I got about 10% improvement on the neon).

So, it's faster to let it go up. If you are racing, you pretty much gotta do it. If you want something fun however and aren't too interested in lap times....

O
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post #29 of 98 (permalink) Old March 5th, 2008, 15:20
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Im all a bit confused in this thread... but what would be the results of converting a 91 front suspension to 93 spec, using adjustible tein/tanabe/etc traction rods while keeping the rear 91 suspension the same?
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post #30 of 98 (permalink) Old March 12th, 2008, 19:31
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Quote:
Originally Posted by Ultra Optimus
Im all a bit confused in this thread... but what would be the results of converting a 91 front suspension to 93 spec, using adjustible tein/tanabe/etc traction rods while keeping the rear 91 suspension the same?
The only difference is that the front strut rod mount is beefier on the '93 and has no caster adjustment. That and running a tad lower spring with different bumpstops.

But I didn't see any difference in ball joint placement between the two.
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post #31 of 98 (permalink) Old March 29th, 2008, 16:15
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post #32 of 98 (permalink) Old April 6th, 2008, 15:40
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Does anyone have some numbers that they measured for their input on optimum K? I'd like to have something to compare to when I measure mine to see if we're on the same page. 91 Front mr2 suspension, any ride height, just no measurements with after market arms (Assuming they exist). I'm wanna make a macro for excel to get the initial geometry based on ride height (height of chassis mounting points above the ground).

I also started a post about relocation of the LBJ, I wanna see how much difference a few inches makes. If it proves well (which I do believe it will) I'll draw up something for machining and try it out.

Thanks guys,
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post #33 of 98 (permalink) Old April 7th, 2008, 07:39 Thread Starter
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I can give you a screen shot of the inputs I used for optimum K (its a demo, but the only limitation is no saving, so I "save" by taking a screen shot). Unfortunately, I'm in Pennsylvania for the next month for work, and my screen shots are on my computer at home in Montana. However, once I get back I would be happy to provide the data.

My only request is that you make your own measurements and compare to mine, just to double check I think most of mine are pretty accurate, but having someone else make the measurements would be nice as well.
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post #34 of 98 (permalink) Old April 7th, 2008, 11:32
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Quote:
Originally Posted by buzz1167
I also started a post about relocation of the LBJ, I wanna see how much difference a few inches makes. If it proves well (which I do believe it will) I'll draw up something for machining and try it out.
You're talking about moving the ball joint downward, right? I know we've had this discussion in this forum. My charts in post #11 assume the LBJ is moved downward 1" along with a dramatic movement inboard of the strut top.
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post #35 of 98 (permalink) Old April 7th, 2008, 22:24
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Yea, I think it can be moved farther than that though, I was wondering how much more you could get. I was hoping for a more ideal case that would involve not needing lots of static camber.

I must be doing something wrong in my Excel Macro because although it has similar the same shape the numbers are all wrong. Apparently I'm not really familiar with the macphearson system and how it moves or I'm being stupid somewhere... Probably a combination of both.

Yea, the idea was that I could make measurements at whatever height my car is at right now, get measurements from you guys at whatever height you are at, and make sure that I can at least believe our measurements. I've got poly bushings coming in this week and I'll measure it when I install them.

Thanks so much,
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post #36 of 98 (permalink) Old April 7th, 2008, 22:31
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A hint: the wheel does not move directly toward the upper shock mount. It's offset because the strut shaft isn't on the same line as the SAI. This was something I had to think about a while before I made the leap.
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post #37 of 98 (permalink) Old April 7th, 2008, 22:39
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Ok, Now that I went back a read very carefully i see that this acronym RCA is what you guys are calling a roll center adjuster... Sorry I haven't heard of anything being called that before.

With regards to the movement. I have it setup so that the upper fixture moves at an angle that is parallel to the strut axis and with a magnitude that equals the vertical displacement. Sorry, that sounds weird... heres what I mean.

I pick the point that is the center of the mount for the strut (Upper Spindle Point). Its offset upwards and inboard of the LBJ. Then I draw a line from there (the upper point) to the strut mount. Then I translate the LBJ along its circular motion. Then I figure out how much vertical movement has occurred from the LBJ. I say that the upper point moves that far up and its moves towards the car by - Tan(strutangle)*upwardmotion. Of course this is recalculated for every position...

Edit...
What do you think about the fact that I'm neglecting a Delta Camber from changing the vertical displacement of the Upper point WRT to LBJ? I figure, Cos(0) or cos(10deg) pretty much =1. I've also made the rigid assumption up front, but I think the demo version of Op.K does too.

I'm also deriving camber from the difference between the LBJ and the upper spindle point. Taking the static position (some big degree value) and making it my static camber value by simple subtraction from all derived camber values. Seemed relevant at the time.

Last edited by buzz1167; April 7th, 2008 at 22:57.
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post #38 of 98 (permalink) Old April 7th, 2008, 22:56
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I think that makes sense. Understand that the strut shaft both moves and tilts as the suspension compresses. It basically swings as it compresses.
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post #39 of 98 (permalink) Old April 7th, 2008, 22:59
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Yea, ok. I don't really know how thats accounted for... At every point I simply draw a line (really I just get the slope) between the Upper spindle point and the chassis mount for the strut. So if that changes then my program allows for it b/c it calculates a new slope every iteration.

Anyway, I think I'm just gonna wait until I can make some hard measurements, I might just have measured something awkward.
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post #40 of 98 (permalink) Old February 8th, 2009, 17:03 Thread Starter
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The reacent posting of reasonably priced RCA's in the vendor for sale forum has gotten me thinking about this problem again. I remembered finding last year (posted earlier in this thread) and an RCA in the front only should provide some benefit.

I re-ran the analysis with a 3/4" RCA and matching tie-rod spacer on the front only. The graph below shows the lateral movement of the roll center, front as a solid line, rear as a dashed line. Red is for a car lowered 1" with no other change, blue is for a car lowered 1" with a 3/4" RCA on the front.

Two things to note:
I re-measured the front geometry late last fall, and came up with slightly different numbers on some of the points. These new numbers actually made things worse, which is why the red line goes so totally nuts on this graph compared to the front roll center movements I had reported previously. I think these new numbers are more accurate than the old ones, but it means this graph isn't really comparable with the old ones.

Second, the rear shows different movement on the red vs blue graphs, even though nothing changed on the rear. I don't know why this is, other than that the front and rear, when analysed together, must have some impact on each other. However, when I analyse the rear alone I get a curve more like the blue one, so I think for some reason the front going wacky is making the rear look better than it actually is.



Has anyone here built a custom front tie rod setup? Any info on where to get a metric taper pin to attach a rod end to? Also, I have found pleanty of sources for metric female rod ends, but none are as long as the stock tie rod, I think an extension would be needed.

Last edited by Alex W; November 9th, 2018 at 09:01.
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