MKII Suspension Analysis: Front Suspension - Page 5 - MR2 Owners Club Message Board
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post #81 of 98 (permalink) Old October 18th, 2010, 07:19
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Very good read fellows.
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post #82 of 98 (permalink) Old December 5th, 2011, 08:09
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After reading through this thread, I didn't see any mentioning of traction bars for the front. Are these legitimately beneficial to the MKII front suspension? Full Race makes/made a set. There was discussion by Fazio on this product when he bought it.

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post #83 of 98 (permalink) Old December 5th, 2011, 17:37 Thread Starter
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Generally speaking, traction bars won't change the suspension geometry, which is why they don't get a mention here. Now, the full race ones replace the front mount brackets with their own bar and bracket arangement, so they may have an effect, particularly on the anti dive character of the front end. But I don't know for sure how much change they make in that area. Be careful with these, as depending on what if any racing you do, they may put you in a class you don't want to be in.

Now, if you consider any spherical bearing front (or rear for that matter) strut rod to be a "traction bar", then yes, they will make a difference. They will reduce slop in the suspension, while still allowing the suspension to move freely.


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post #84 of 98 (permalink) Old December 5th, 2011, 21:43
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LOL. I shoulda followed this thread more closely. I was on a '95 FSAE team and I got RIPPED for using a force based analysis and giving up the kinematic. Good to see Bill came around.

O
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post #85 of 98 (permalink) Old December 6th, 2011, 04:44
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Quote:
Originally Posted by Alex W
If you add spacers at the steering rack (the inner end of the tie rod) you will want to space it UP, not down. Remember, the goal is to space down the ball joint, and then after you do that you need to return the tie rod to parallel with the control arm. If you increase the droop on the control arm you need to do the same on the tie rod, but if you space it down at the rack it will point up more, not down.

Spacing both the ball joint and the outer rod end down equally will return you to stock geometry. Slightly different spacings may be useful to reduce bumpsteer, but the primary goal is to just get back to stock on a lowered car. I don't know exactly what you would want for spacers if you were to space the rack end up, but I believe you would still want the same ammount of spacer as you have on the ball joint. I haven't analysed this case however, since I don't see any point in moving the rack end up when its so much simpler to move the outer end down.
I have limited knowledge on geomoetry but do fiddle with my car trying to work out the right tune for it. One of the little tests I did was as you have mentioned here with parallel LCA and tie rods. I simply assumed this was the correct way, had some cromo drop links made up, then fitted these to the car. They ended up being 3+ inches long but a few things happened once fitted, measurements made and tested on the car. First, is the test in race conditions ended in one link snapping at 80mph through a left hand sweeper due to the link being stressed and too long( no damage, just a some air time and a trip to the sand trap). Before I left for the weekend, I took measurements. Although the two were parallel when plotting the bump steer there was a variance of 20mm toe out on compression and 12mm on extension due to the links. Massive mistake..I dialed some of it out with caster adjustment but still hade 10mm out under compression. I have a new set but yet to plot data.
Also would like to know if people have played with rear caster settings to dial out rear bump steer. I did manage to dial some of it out but will it effect anti dive/anti squat?
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post #86 of 98 (permalink) Old December 6th, 2011, 14:12 Thread Starter
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Quote:
Originally Posted by B24nsw
I have limited knowledge on geomoetry but do fiddle with my car trying to work out the right tune for it. One of the little tests I did was as you have mentioned here with parallel LCA and tie rods. I simply assumed this was the correct way, had some cromo drop links made up, then fitted these to the car. They ended up being 3+ inches long but a few things happened once fitted, measurements made and tested on the car. First, is the test in race conditions ended in one link snapping at 80mph through a left hand sweeper due to the link being stressed and too long( no damage, just a some air time and a trip to the sand trap). Before I left for the weekend, I took measurements. Although the two were parallel when plotting the bump steer there was a variance of 20mm toe out on compression and 12mm on extension due to the links. Massive mistake..I dialed some of it out with caster adjustment but still hade 10mm out under compression. I have a new set but yet to plot data.
Also would like to know if people have played with rear caster settings to dial out rear bump steer. I did manage to dial some of it out but will it effect anti dive/anti squat?
Ouch, gotta be careful of that sort of thing. There is a reason I make my studs out of 4340 steel, and also design the spacers to help support the studs bending load by putting compression loads into the knuckle.

The whole parallel thing is kinda a "perfect world" sort of situation. In reality, there are a lot of other things that effect it. The angle, the height, the angle fwd/aft, the angle of the strut, the amount of caster, etc. All can play a roll in bump steer. Measure and adjust untill you have it dialed down to essentially zero and you should be good.
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post #87 of 98 (permalink) Old December 6th, 2011, 16:10
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Quote:
Originally Posted by Alex W
Ouch, gotta be careful of that sort of thing. There is a reason I make my studs out of 4340 steel, and also design the spacers to help support the studs bending load by putting compression loads into the knuckle.

The whole parallel thing is kinda a "perfect world" sort of situation. In reality, there are a lot of other things that effect it. The angle, the height, the angle fwd/aft, the angle of the strut, the amount of caster, etc. All can play a roll in bump steer. Measure and adjust untill you have it dialed down to essentially zero and you should be good.
Yes was lucky there wasnt a wall in the way.. I did use a very hard steel but when talking with a engineer next door to the track who actually made me a new set in two hours so I could make the last session of the day( still pleased as punch about that!), he stated not to go too hard with the steel as it will snap instead of simply bending. So I have a new set made from a lower tensile material so it bends instead of snapping. I also made the first set very similar to your units as pictured.


As you have said there is a lot to it, for the perfect set up. The more I analyse the less I know! I have also been reading suspension books but there isvery little on strut suspension. Another point with the extra long links is the ackermann effect. Im sure it causes this effect but didnt have the time to check before the race meet. It would be great to lift the rack up higher but there is a fair amount of work to do this.This as you know will reduce the need for longer links,ackermann,bump steer etc.
Have you conducted studies on the anti dive of the SW20? What it is set up to do, how to change the settings to suit your required application. I have lowered my front location points inline with RCA's but unsure if this is the correct way. It was really a educated guess. Also didnt do this to the rear so the anti dive/squat characteristics are set differently for front and rear.
Here is a pic of the front unit. Thanks. Steve
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post #88 of 98 (permalink) Old November 9th, 2012, 18:36
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I spent some time on the car a few weeks back. The time was spent making a bump steer tool. You would have seen these in "How to make your car handle" by Fred Pune(I think that?s his name).
It?s a very useful tool for seeing exactly what is happening with bump steer and caster movements through the range of suspension travel (springs removed of course). Turns out, the longer front links were a complete waste of time.
Front end: I reduced the front RCA's to 25mm then fitted the original adjustable toe links where with a little bit of work, I found zero bump steer through the range.
Rear end: Even with the 32mm RCA's, there was still 6mm of toe-in but with some work, I managed to get it down to 3mm. From what I can see, the only way to get it to zero, is to have a pivot point for the rear toe link located close to 15mm from the centre of it original position.
Another point is the location of the trailing arm pivot point after making RCA fitment. From what I can see, this should really be adjusted too for a 'as close to perfect as possible' suspension path.

I altered the front which resulted in a more consistent arc of travel but the rear is different. The rear is the standard pivot location with a different arc. The rear arc of travel moves front to rear unlike the front. It could be caused by the front running way more caster due to steering but that?s another guess..
Having a bracket made up with multiple locations holes for the rear trailing arm, then welded into place is an option to solving the problem. Chances are, I will make a jig then I can bolt on to the rear trailing arm pivot to see if there are any real changes.
If I?m looking at anti squat and dive characteristics being varied, what is changing with new location points for the trailing arms?
Is it anti squat/anti dive?
With variation to RCA?s what?s happening with AS/AD. Is it affected?
Would it cause front diving and the rear jacking up under brakes or load?
Or, front jacking up and the rear diving under brakes or load?
Or, one of a 100 other possibilities..
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post #90 of 98 (permalink) Old November 10th, 2012, 11:40
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I use scale model to analyze suspension adjustments. The pic above showed a perfectly parallel tie-rod and link alignment which should reduce bump and torque steer to a minimum by keeping set camber.
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post #91 of 98 (permalink) Old November 10th, 2012, 17:04
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Which picture is that? The one in my post?
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post #92 of 98 (permalink) Old November 11th, 2012, 11:42 Thread Starter
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Quote:
Originally Posted by B24nsw
I spent some time on the car a few weeks back. The time was spent making a bump steer tool. You would have seen these in "How to make your car handle" by Fred Pune(I think that?s his name).
It?s a very useful tool for seeing exactly what is happening with bump steer and caster movements through the range of suspension travel (springs removed of course). Turns out, the longer front links were a complete waste of time.
Front end: I reduced the front RCA's to 25mm then fitted the original adjustable toe links where with a little bit of work, I found zero bump steer through the range.
Rear end: Even with the 32mm RCA's, there was still 6mm of toe-in but with some work, I managed to get it down to 3mm. From what I can see, the only way to get it to zero, is to have a pivot point for the rear toe link located close to 15mm from the centre of it original position.
Another point is the location of the trailing arm pivot point after making RCA fitment. From what I can see, this should really be adjusted too for a 'as close to perfect as possible' suspension path.

I altered the front which resulted in a more consistent arc of travel but the rear is different. The rear is the standard pivot location with a different arc. The rear arc of travel moves front to rear unlike the front. It could be caused by the front running way more caster due to steering but that?s another guess..
Having a bracket made up with multiple locations holes for the rear trailing arm, then welded into place is an option to solving the problem. Chances are, I will make a jig then I can bolt on to the rear trailing arm pivot to see if there are any real changes.
If I?m looking at anti squat and dive characteristics being varied, what is changing with new location points for the trailing arms?
Is it anti squat/anti dive?
With variation to RCA?s what?s happening with AS/AD. Is it affected?
Would it cause front diving and the rear jacking up under brakes or load?
Or, front jacking up and the rear diving under brakes or load?
Or, one of a 100 other possibilities..
Indeed, one thing that I have found (and I think you have too) is that, while models are great for a lot of things, if you really want to eliminate bump steer you have to actually measure it directly and make adjustments. Regarding rear bump steer, I have found this to make a significant difference:
https://mr2oc.com/showthread.php?t=455693

Here is my cheap DIY bumpsteer gauge:
https://mr2oc.com/showthread.php?t=452807

Regarding Anti-squat/dive, I don't think RCA's will have much of an impact on that. Anti-squat/dive are primarily related to the line between the two chassis side pivot points and the fwd/aft angle of the strut. Changing caster has an effect, as does swapping to the 93+ front strut rod brackets, but RCA shouldn't.
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post #93 of 98 (permalink) Old November 11th, 2012, 15:51
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Yes, that the guage I made up. A little more basic (no guage and had the car on it wheels with no spring)but I end up with the same result.

Looks like we are on the same track with the anit squat/dive as I have adjusted the front caster rod mounting points to a lower point but not the rear which I suspect, effects the balance/pitching of the car. The mod is in the picture above.

Did you do a back to back test with the changing of the rod brackets?
Did you take measurements and look for variations in changes to wheelbase?
Would be great to see a graph of comparison or just a note to say 'yes it reduced wheel base by..or change the travel arc by..I only have the modded version on the front, so I can not do a test.

I wonder if Toyota set the car with this dynamic geometry to create a balance of sorts. With a 2mm toe in on the rear you will get good economy from your tyres but when you go for a fun drive on regular road tyres, it would improve turn in with the rear toeing out a little then help with corner exit when it will toe in again. The problem is high speed stability but that should not be a issue in day to day drives or a weekend drive.

If you up the tyre rating, power and brakes, I guess it exceeds the factory expection of the car then requires a different approach as we are experiencing but this is only a theory I came up with, not an answer as it is more than likey wrong.

93rdgtsam: Unfortunately the geometry does not work like that. I built those units, they broke as they were too long(while flying through a corner..) then measured after the experience, only to find they were way of the mark. The longer links cause the steering ratio to increase too. Toe out under ackerman(turning) was also terrible. It must have cost me two seconds a lap on a 3km road course. So bigger is not always better..
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post #94 of 98 (permalink) Old November 13th, 2016, 17:59
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After having another read through this discussion last week, I just thought of an idea that I haven't seen mentioned anywhere else. It could be that this is just a silly idea and that I'm overlooking something important, but I hope I'm onto something.

In order to obtain his Optimum-K simulation results, Alex had to accurately measure the dimensions of various suspension components, of which many would be quite awkward to measure, if not impossible without removing some of the components from the car or having spares of those components.

So I got to thinking, what if there's a way of observing the dynamic changes to the suspension geometry (at least in compression) while the car is just sitting on the garage floor? My idea would still be quite fiddly, but not too bad

Assuming that you already have your ride height set, here are the steps that I had in mind:

1) Disconnect the sway bar (this could be done around steps 4-6 instead, but it may be easier to do it first).
2) Make sure the car is on a level surface.
3) Measure and write down the height from the ground up to a suitable reference point near the wheel for which you want to analyze the suspension geometry.
4) Jack up the car using the nearest jacking point, then remove the wheel.
5) Attach a spring compressor to the suspension coil spring.
6) Undo the top nut for the suspension strut, then drop and swivel the suspension strut outwards and completely remove the suspension coil spring from the strut.
7) Re-install the suspension strut into the strut tower and put the top nut back on.
8) Re-install the wheel.
9) Lower the jack until that corner of the car is at exactly the same height that was measured in step 3.
10) It should now be possible to freely move the suspension upwards as far as you want, with the true geometry being maintained. This is the key to this idea!
11) Once you reach this step, you can use your preferred DIY procedure (or an adaptation of it) to measure various alignment variables at different levels of suspension compression on that wheel. Dynamic camber should be quite straight forward to measure in this way. It would be much more time-consuming to measure the dynamic toe (bump-steer), but possible nonetheless.

I'd like to hear people's thoughts on this. Feel free to criticize, or make suggestions on how to improve upon this idea.
I know that this idea would only be suitable for checking some basic stuff, but I think it would be quite valuable for observing exactly what happens as the suspension compresses, without having to worry about slightly inaccurate measurements leading to imperfect software simulation results.

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post #95 of 98 (permalink) Old November 15th, 2016, 20:11 Thread Starter
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Totally possible to do that. In fact, that's a pretty basic race-car setup procedure, usually used to measure / adjust bump steer (aka, dynamic toe). It's actually not too hard, just need a bump steer gauge (pretty easy / cheap to make yourself). And actually, it's not just bump, you can do the full range if you want, just leave the car on jack stands and use a floor jack to run the suspension through it's full range of motion.

It won't get you any info about the roll centers, but you could certainly use it as a check on camber curve and bump steer calculations.

You are right that many of the points are quite awkward to measure, and I will admit that the accuracy of my measurements wasn't perfect. But, it was close enough to get a good idea of what was going on. But to really fine tune bump steer, you just have to measure it directly. And in case you are wondering, the results of those direct bump steer measurements are included in my geometry adjustment kit
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post #96 of 98 (permalink) Old March 6th, 2017, 20:12
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Quote:
Originally Posted by Alex W View Post
Totally possible to do that. In fact, that's a pretty basic race-car setup procedure, usually used to measure / adjust bump steer (aka, dynamic toe). It's actually not too hard, just need a bump steer gauge (pretty easy / cheap to make yourself). And actually, it's not just bump, you can do the full range if you want, just leave the car on jack stands and use a floor jack to run the suspension through it's full range of motion.

It won't get you any info about the roll centers, but you could certainly use it as a check on camber curve and bump steer calculations.

You are right that many of the points are quite awkward to measure, and I will admit that the accuracy of my measurements wasn't perfect. But, it was close enough to get a good idea of what was going on. But to really fine tune bump steer, you just have to measure it directly. And in case you are wondering, the results of those direct bump steer measurements are included in my geometry adjustment kit
Only quoting the above hoping it triggers a notification for you.

Is the bolt pattern on the front strut mount square? Instead of increasing caster (for manual steering), could we decrease caster by rotating the shock to point at the front inner strut mount bolt hole? Or would there be a clearance issue underneath?
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post #97 of 98 (permalink) Old March 6th, 2017, 21:55 Thread Starter
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Is the bolt pattern on the front strut mount square? Instead of increasing caster (for manual steering), could we decrease caster by rotating the shock to point at the front inner strut mount bolt hole? Or would there be a clearance issue underneath?
The pattern is rectangular, but you could still do what you suggest by swapping the mounts left to right and then rotating each 180. However, this would probably leave you with near zero caster, or possibly even negative caster, which would probably give you some pretty weird / bad steering feel with no self centering effect. I wouldn't recommend it.


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post #98 of 98 (permalink) Old March 11th, 2017, 00:41
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The pattern is rectangular, but you could still do what you suggest by swapping the mounts left to right and then rotating each 180. However, this would probably leave you with near zero caster, or possibly even negative caster, which would probably give you some pretty weird / bad steering feel with no self centering effect. I wouldn't recommend it.
Sorry for not getting back earlier, but thank you for your response.
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