Major Suspension Issues [Archive]

Big Bird

05-10-2005, 02:51 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mike T.:
When first rolling our chassis out, we've noticed that our rear suspension is a lot stiffer than expected with 1:1 IR and 120 lb/in springs. It's getting close to competition and we still haven't sorted the issue out, and are beginning to worry. Anybody have any ideas as to what the problem could be? </div></BLOCKQUOTE>

Thats really funny. Would give a bit of a bumpy ride I'm sure.

We assume you are mounting the shocks to the engine? OK, time to remove the cloth and reveal all.....

Cheers,

XtremeDream

05-10-2005, 05:29 AM

Man, it does look like you are pulling the damper when you go into bump hence you flipped the purpose of the damper. You usually see twice (about that) the force in rebound than in bump with dampers hence the stiffer surprise.

Psychosis

05-10-2005, 11:08 AM

Oh, and if you got a somewhat extra harsh scrutineer, you'll fail for having a jacking point that is not 1" tubing. It got a (pretty big) dent in it http://fsae.com/groupee_common/emoticons/icon_razz.gif

Denny Trimble

05-10-2005, 11:10 AM

Yup, that's what comes with free stress relieving services, apparently... http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif

Steve Yao

05-10-2005, 04:28 PM

GG, guys and gal. ;-P

05-11-2005, 12:13 AM

Oh, yes... dear, dear... too much showboating...

As suspected, the designers have made it far too complicated and the poor old spanner twirlers have got confused and put the rockers in back to front...

But why? WHY??

Why mount those heavy coilovers so high (as high as is practically possible, it seems) and so far from the CG? Why the high CG and large yaw inertia?

Tsk, tsk, mutter, mutter....

Z

PS. I do like that "floating toe-link" concept on the left though. Should reduce uncomfortable G-loading on the driver during righthanders...

Denny Trimble

05-11-2005, 01:32 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:
Oh, yes... dear, dear... too much showboating...

As suspected, the designers have made it far too complicated and the poor old spanner twirlers have got confused and put the rockers in back to front...

But why? WHY??

Why mount those heavy coilovers so high (as high as is practically possible, it seems) and so far from the CG? Why the high CG and large yaw inertia?
</div></BLOCKQUOTE>

Actually, the shocks were flipped back when we pulled the engine, and we thought it looked funny, so here it is on the forum.

Have a look at the real configuration here:
http://students.washington.edu/auto/DesignReportImages/2005/images/Isometric.jpg

Why are the shocks mounted there? Mike T spent a lot of time looking at various options, and arrived at this one for a few reasons:

1) Chassis torsional stiffness through the shock linkages; the rear rockers are mounted as far forward as possible, and the fronts mounted as far rear as possible, to make the length of chassis loaded in torsion shorter. The load paths are very efficient in this design.

2) Suspension member and balljoint strenghts, stiffnesses, and weights; the pushrod force "helps" the lower control arm resist cornering forces. Attaching a pullrod would require heavier upper and lower control arms than in this design.

3) Overall packaging; It's difficult to fit low-mounted shocks in such a tight rear-end, while meeting the above goals and accommodating an anti-roll bar and chain / tensioning space. Our 2002 and 2003 cars had pullrods, with less than optimal performance characteristics in all of the above areas. The CG for the shock system might have been lower, but installed stiffness and anti roll bar functionality were issues.

I'd be very pleased to see a great pullrod system, I've studied the competition closely. I'd also be very interested in seeing suspension stiffness numbers of these "ideal" pullrod systems.

Z, you keep criticizing, but I haven't seen any images of the great cars you must have built. I make an effort to share a lot of information with everyone here on the forum. Care to take a break from telling us what we should build, and show us what you have built?

http://fsae.com/groupee_common/emoticons/icon_smile.gif

XtremeDream

05-11-2005, 05:26 AM

Well, you are right about the pushrods theoretically being better but we run a pull rod system in the front and we never had any issues with stiffness values. I do not have the actual number for you but we do run a 0.5''x0.028'' steel pull rod which is very light. But as you said Denny, the antirollbar is a lot harder to package and it is even harder to make it as efficient. Pushrods in my opinion are huge in serious racing like F1 and heavier cars but with a car that weighs in the 400's I don't think it is as big an issue.

-MGizzle

UofM-Ann Arbor MRacing

Daves

05-11-2005, 08:42 AM

Denny Trimble

05-11-2005, 10:45 AM

Dave,
That looks pretty well-done, good work.

What I mean about stiffness, and I've talked about it on all the "chassis torsional stiffness" threads, is:

-Install dummy shocks (steel bars)
-Fix the front or rear hubs, and twist by the hubs at the other end
-Record angle of twist at the hubs, and also at the frame.

From this, you can get chassis torsional stiffness (torque / frame twist), and also "installed" torsional stiffness (torque / angle of twist at hubs). You can then use the serial spring equation and get the stiffness of the suspension system in chassis torsion loading.

If you haven't done this test, you might be in for a surprise at how much chassis stiffness you lose in your suspension, due to bellcrank loading, etc.

It's another good reason not to do your chassis torsion tests / FEA by restraining the frame at nodes.

XtremeDream

05-11-2005, 12:45 PM

Dang Dave, that is some pretty cool stuff man. I like the way you mount those dampers. You mind me asking what motion ratios you are running on the car??

And Denny, you mind if I ask what stifness do you guys get when you do the test with the suspension on the car? And yes, we got the surprise too hehehe.

Daves

05-11-2005, 01:08 PM

I am a powertrain guy, so I do not know the motion ratios. However, feel free to ask us if you are at competition in a few days.

Denny, thanks for explaining suspension stiffness. We have had inconsistent results when trying to test the torsional rigidity a couple different times. Hopefully we'll figure it out by competition time.

JadgPzIV

05-11-2005, 04:02 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">I'd be very pleased to see a great pullrod system, I've studied the competition closely. I'd also be very interested in seeing suspension stiffness numbers of these "ideal" pullrod systems. </div></BLOCKQUOTE>

Denny,

For our 2004 car, we decided to used "ideal pullrod package" influenced by the Woolongong 2003 front suspension. Like you, we tried to reduced the lenght of the frame in torsion. We used the same configuration ( shock and bellcrank orientation) at the front and at the rear, even the front-end triangulation of the frame is very similar to the rear-end.

This allowed us to mount easily the rocker in double-shear and to 'fully-triangulated' the rocker mounting.

BUT, it was very diffucult to package the anti-roll bar at the front and at the rear. We used a wide rear-end, it simplify the packaging. In a tight setup like your's, it's impossible to orient the shock/rocker in this way.

Another disadvantage of our 2004 setup, is the angle of the pull-rod. This angle is 'too much horizontal' and it increased the load in the pull-rod and rocker mounting. We had difficutly to find Brass or Bronze bushing for AN6 Bolt strong enough to resist to the load.

This design is at it's second iteration (car 2004 and car 2005) and I hope the guys will be able to demonstrate the advantages of this setup in the next days in Detroit!

Unfortunatly, we don't have any physical testing on this chassis. But, by FEA the frame have 2000 Lbf*ft/deg 'upright to upright' and 67 lbs.

http://www.gmc.ulaval.ca/fsae/pics/car_2005/hauteurCG2004/PB200041.jpg

Sorry for my mediocre english writing skills!

Mike T.

05-11-2005, 04:03 PM

Z, I'll take your comments as sarcasm and a continuation of the joke. I had figured you'd be one to appreciate the humor in this. For anyone still wondering, we are retarded, just not to this extentent. Early one morning, after far to many days with little sleep, I though it'd be amusing to post these pics from our motor swap to see how people would react and how long it'd take for people to catch on.

On another note, we've just updated our website with some photos, so check out the galleries if you'd like to see some actual pics of the back end.

fade

05-11-2005, 05:02 PM

mike i noticed that the pushrod ball joints are different than in the design drawings you posted. It looks like you had planned on using sphericals at the a arms with a tapped threaded rod on the rocker for length adjustment. did you have problems with that method? i designed a similar set up that used a female rod end on the rocker side.

Mike T.

05-11-2005, 06:19 PM

No Problems, and we kept that type of differential pitch adjustment for the toe rods since it provides small length changes per turn of the bushing and thereby precise and repeatable toe adjustment. When in the manufacturing stage, it was decided to go with the LH/RH threaded rod ends for the pushrods since we don't need that fine of adjustment for ride height, and wanted more adjustment than we could get from what you saw in the design report drawings.

Denny Trimble

05-11-2005, 07:01 PM

XtremeDream,
You'll have to look at our design boards in Pontiac to get those numbers... http://fsae.com/groupee_common/emoticons/icon_smile.gif

05-11-2005, 08:19 PM

Quote from Denny; "Z, you keep criticizing..."
-------------------------------------------

Dear, dear... I've done it again...

Denny, calm down, cheer up, err, maybe these will help http://fsae.com/groupee_common/emoticons/icon_smile.gif http://fsae.com/groupee_common/emoticons/icon_smile.gif http://fsae.com/groupee_common/emoticons/icon_smile.gif http://fsae.com/groupee_common/emoticons/icon_smile.gif http://fsae.com/groupee_common/emoticons/icon_smile.gif Have you had a few allnighters? Mike picked up my angle ("floating toe-link", etc...). Anyway, I'm trying to help and I can't do that by saying "very pretty", etc. That's why teachers use red pencils - to point out what's wrong, not what's right.

Re: Photos of what I have built. I should point out that the last circuit racecar I was directly involved with was about 25 years ago. Since then mostly rally cars and off-roaders (much more fun). I think I have a few photos of them but they are mostly of the cars upside down in a ditch! I'm not big on "studio" photos...

Re: Sharing. Perhaps you could send Bryan P. (of High school car thread) some of that ackermann/steering-geometry info?

(to be continued..)
Z

05-11-2005, 08:51 PM

(Continuation of previous post. These "photo threads" are hard to post on (me???) and I keep getting cut-off (phone!!))

Critique of Mike/Denny's UW car.
--------------------------------

Racecar design is primarily a packaging exercise - like Tetris, or packing the family wagon for summer holidays. The main rule is "all heavy masses down low and towards the centre of the car".

The UW car has the ARBs as high and as far from the CG as possible. Likewise, the coilovers are almost as high as possible, but fractionally closer to the car centre. These components are relatively easy to move around and could be positioned much better.

As Denny pointed out, taking suspension loads towards the centre of the car gives an effectively shorter and stiffer chassis. Also correct is that the pushrod/rockers introduce a lot of extra (unwanted) torsional flexibility into the hub-to-hub load path.

So, as an example, leave the coilover chassis mounts where they are, and mount the "bottom" end of the coilovers direct to the lower wishbones, possibly via short struts. This will give a stiffer overall installation, lower overall weight, lower CG height, and lower yaw inertia. And best of all, it will be less work and cheaper.

The problems with this last example are:
1. Lower motion ratio. (Solution: Fit stiffer springs and a few extra cliks on the dampers.)
2. What about the ARBs? (Solution: Use "U-bars" at the bottom of the chassis and towards centre of car - same advantages as before.)
3. Doesn't look like a "real" modern racecar. (Solution: Nope, I can't solve that...)

Sorry guys!

Now, into the fall-out shelter...

Z

Just in case - http://fsae.com/groupee_common/emoticons/icon_smile.gif http://fsae.com/groupee_common/emoticons/icon_smile.gif http://fsae.com/groupee_common/emoticons/icon_smile.gif

Mike T.

05-11-2005, 09:53 PM

If you're expecting an empassioned and inflamed response, you won't get it.

We never actually did any analysis on any of this stuff, never looked at these different concepts in CAD with respect to CoG location, MoI, or enything else for that matter. We never based our design decisions on any of this analysis that we didn't do, and came up with this car by simply wishing it to look like a 'real' modern racecar. How do you think we ended up with our dampers backwards?

I'd have to say, judging by your response, that we been successful. Glad to see that you like it.

05-11-2005, 10:26 PM

Okay, Mike, that wasn't an empassioned and inflamed response, but is was pretty sarcastic.

I was at a recent off-road race meeting and there was a young guy there who had recently built (and was still developing) his car. It was a good job and he was winning a lot of races. I asked a bit about the car, including "Why have you mounted those big coilovers in front of the front wheels, and with the tops leaning even further forwards like that?" Off-road coilovers are BIG. There is a good reason for having high pitch inertia on off-road cars, but I was curious for his response.

He looked at his team-mates, kind of laughed, and said "We're not sure ourselves, but some of the other cars have it and we reckon it looks cool - real fast", or words to that effect. Anyway, he knew a bit about what makes a car fast, his car was successful, but he didn't kid himself on everything. He gave a very honest, open response.

I was just wondering why you reckon your solution is better than the (simpler) coilover-direct-to-lower-wishbone method. Aero-drag? That's why F1, Indy, etc. stopped doing it.

I realize you guys are busy and somewhat tense now, so you don't have to answer.

Z

jack

05-11-2005, 10:45 PM

Z,

This year we went with a bottom mounted damper / pull rod setup. After having actually designed (and soon to build) this setup, I can tell you being an armchair critique is much easier. If our chassis allowed for it, I much rather would of gone with a design similar to UW. You really can't just sit there and say that they could of done it better, without actually trying it.

Denny Trimble

05-11-2005, 11:35 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:

I was just wondering why you reckon your solution is better than the (simpler) coilover-direct-to-lower-wishbone method. Aero-drag? That's why F1, Indy, etc. stopped doing it.

I realize you guys are busy and somewhat tense now, so you don't have to answer.

Z </div></BLOCKQUOTE>

Well, the lower installation ratio, and falling rate, of the direct-mounted shocks you mentioned are pretty large disadvantages in my opinion.

The springs would have to be heavier, and the dampers would have to work at lower speeds, which is not beneficial to their ability to control the car.

And, to be honest, I think a "u-bar" connected to the outside ball joints would be very long, heavy, and not very structurally efficient. If you mounted it low, you'd have to either support it near the lower inner pickups (narrow), or add extra structure to support it at a wider location.

I guess we could mount the coilover directly to the middle of the lower control arm. One team did this last year in Detroit; you could see more deflection in their control arms than in their shocks! The structure would have to be much heavier to keep installed stiffness reasonable.

We don't have the aero considerations of F1 / Champcar to require inboard shocks, but the other benefits I noted previously still make them worthwhile in my opinion.

I don't think many people in FSAE fully understand rising and falling rates, so we tune our bellcrank linkages to be linear for spring and anti roll bar motion.

I think the falling rate nature of direct-mounted coilovers will have significant effects on a narrow-track car in roll. But, that might be a price some are willing to pay for a simpler car.

Oh, and I'll PM Bryan with that info you sent me. Any guidelines on redistributing it?

Jarrod

05-11-2005, 11:40 PM

Z - if you are talking about a coilover mounted direct to the lower wishbone by the outer balljoint, the major issues are motion ratios, you suggested simply using a stiffer spring and damping, but it is more than that. If you reduce your motion ratio, you are using less and less shock travel, less shock velocity, so hysteresis issues are more dominant, resolution in damper tuning is reduced. This also increases the forces into the shock mounts as does the pullrods with very shallow angles. We have a 1:1 motion ratio, so use every mm of shock travel available, I'm sure many are trying to do the same, we also have linear rates within 1% for the full travel, and can quite easily bolt on a new bellcrank with a rising rate if we so desire. Structural issues also play a role, i have never seen an FSAE car that has suitable structure to hold a shock directly off a lower wishbone, as our dampers are all too short (UCA about 200 mm long, damper 260mm long at full extension (we are using the penskes, MTB even shorter), the geometry alone suggests it is not a great option. In the last three years I have looked at a lot of arrangements for dampers, the versatility of a bellcrank system always wins out over the simple solution and its inherent drawbacks each time i look at it. The compliance can be an issue if you let it, but it doesn't need to be. also a damper weighs about 1kg with spring(overestimate), assuming 280mmCGH, 600 mm shock CGH height(overestimate), 300 kg car and driver, 4 shocks

(1x4x600 + 300*280)/(304) = 284 mm cgh

lay your driver down another 2 degrees and you get your CGH back to 280. Depends how hard you want to chase it.
I certainly believe in lowering CG, reducing inertias, but sometimes commonsense must prevail, in terms of structure, dynamics and packaging.
I prefer the damping control. (BTW we run pullrods at the rear, and the ARB is a nightmare)

I go to great lengths to ensure every design and packaging decsision is thouroughly thought out on our car, to be certain we can answer these type of questions, because I often ask them of myself.

The short answer after all of this rambling is the simple solution has a drawback in damping control, and in our case and most others structural reasons.

05-12-2005, 03:01 AM

Ah, good, some calm, rational interchange of ideas http://fsae.com/groupee_common/emoticons/icon_smile.gif .

Denny, Jarrod,

1. There is nothing very wrong with falling rate. If rising rate was so good everyone would be using it. Almost nobody does, at least not to the extent seen on the back of MotoX bikes - it doesn't work well on cars (not for the "corner springs" - ok for "third spring"). The rising rate for severe bump control can come from the bump-rubber. Falling rate can be a benefit - see Zero-droop thread for more info.

2. Springs with lower motion ratio are the same weight. They are stiffer, so heavier wire, but they only need shorter travel. Basically, the same amount of strain energy to absorb = same weight springs (except for minor difference due to "dead" coils).

3. U-bar should be a pipe. The arms can have flexibilty (as "blades") but this is not necessary.

4. Dampers. There are countless racecars with total mass 3-6+ times FSAE, much stiffer springs, and maybe 1" total suspension travel, so much harder work for the dampers. I doubt that the dampers will be challenged in FSAE (probably the easiest formula for dampers).

5. Damper rod can be extended by short strut to reach lower outer ball-joint (or other solutions...).

6. CG and yaw inertia calculations should also include ARBs, rockers with extra bearings etc., and the extra chassis structure to carry the loads between rocker and coilover chassis mount, etc.

7. So the old goat's suggestion still has that lighter, stiffer chassis, with lower overall weight/CG/yaw inertia, less cost, quicker build time, more time for driving, etc., etc, ...

http://fsae.com/groupee_common/emoticons/icon_smile.gif

Z

PS. Denny, distribution is free.

James Waltman

05-12-2005, 03:09 AM

Denny, I stumbled across another critique of your car and figured it would set everyone straight. Below is a condensed version.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">
From random crazy old machinist:
hi Denny T - some very nice work there, but (don't you love that "but" thing ? http://fsae.com/groupee_common/emoticons/icon_smile.gif) - if I were a driver I wouldn't get in that car for love nor money. And if I were a track official I wouldn't let the thing out of the pits... For the rest, do you race that car or is it for shows? If it's for shows it's really nice. If you plan to race it, throw it away and start fresh. It's not practical for any kind of real racing and possibly dangerous to boot. You guys need to spend a lot more time at the track if you wanna do this stuff http://fsae.com/groupee_common/emoticons/icon_smile.gif
</div></BLOCKQUOTE>

Denny Trimble

05-12-2005, 03:26 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by James Waltman:
Denny, I stumbled across another critique of your car and figured it would set everyone straight. Below is a condensed version.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">
From random crazy old machinist:
hi Denny T - some very nice work there, but (don't you love that "but" thing ? http://fsae.com/groupee_common/emoticons/icon_smile.gif) - if I were a driver I wouldn't get in that car for love nor money. And if I were a track official I wouldn't let the thing out of the pits... For the rest, do you race that car or is it for shows? If it's for shows it's really nice. If you plan to race it, throw it away and start fresh. It's not practical for any kind of real racing and possibly dangerous to boot. You guys need to spend a lot more time at the track if you wanna do this stuff http://fsae.com/groupee_common/emoticons/icon_smile.gif
</div></BLOCKQUOTE> </div></BLOCKQUOTE>

Yup, those cranky old machinists can get a little fiesty sometimes... James, you are a true information junkie.

OK then, if anyone would like to peruse the originals of Z's articles in Racecar Engineering, they're on my website at:
http://students.washington.edu/dennyt/fsae/zapletal/

05-12-2005, 10:44 PM

Some further points regarding Push/pullrod&rockers vs coilover-direct-to-lower-wishbone. (My previous comments were written late at night and I forgot these, so just for the record...)

1. Coilover-direct-to-wishbone doesn't necessarily have a falling rate. It is, in fact, easy to give it a rising rate. In practice the rate doesn't change much either way (a few %) so the whole rising/falling rate argument is a moot one.

2. Damper control. As noted by others in the above posts a push/pullrod&rocker introduces unwanted flexibility into the suspension linkage. Furthermore, the two extra push/pullrod balljoints, and the rocker pivot, which in some cases is a bronze bush (!), adds extra "stiction" into the linkage. The combination of flex and stiction between the damper and the wheel (that the damper is trying to control) diminishes the damper's effectiveness. A well detailed system (ie. good quality BJs, rolling element rocker bearings, stiff rocker mount structure, etc.) can minimise these effects but not totally eliminate them. So on the one hand there is extra flex/stiction between damper and wheel, and on the other there is a bit less damper velocity. Take your pick...

I mention these points because, of all the features on FSAE cars, I see the push/pullrod&rocker as the least justifiable. I really see very few, if any, significant, rationally justifiable arguments for "rockers". I see lots of significant reasons not to have them.

Please don't take this as an insult of anyone's car. I really believe that building an FSAE car could be a lot easier, and that would be a lot more fun for all involved! http://fsae.com/groupee_common/emoticons/icon_smile.gif http://fsae.com/groupee_common/emoticons/icon_smile.gif http://fsae.com/groupee_common/emoticons/icon_smile.gif

Z

Pavan Dendi

05-13-2005, 12:37 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:
...good quality BJs... </div></BLOCKQUOTE>

These are usually really hard to come by if you're an engineer. http://fsae.com/groupee_common/emoticons/icon_frown.gif

omg i'm so sorry for posting this

Jarrod

05-13-2005, 02:32 AM

Z - after some quick analysis, I am beginning to see that this solution could indeed be viable, IF the chassis and suspension layouts were suitable. This would require quite a wide chassis, and either very narrow track, in which case the falling rate issue would need to be carefully managed, or with the wheel a long way outside the upright. This wouldn't work very well on the front, but may work on the rear, with a lot of cars now running trailing arm setups. The motion ratio issue is still there, but it is workable, and given the damping available in the FOX RCs in particular, we have run similar motion ratios in the past anyway. (0.65 is easily acheivable, probably better if you wanted to really work it). Making a new end for the damper shaft would certainly not be the hardest job we have ever done.

Unfortunately we are too late into design and starting build, or our rear suspension could have gone very old school.

Do you have any sauce for my humble pie?

Mark Bacchetti

05-13-2005, 10:07 AM

Has anyone see the front rocker package on the Stohr C Sports Racer? The rocker has a 180deg pivot with the shock mounted to the pushrod. What do you guys think?

-Mark
Cal Poly Pomona

http://www.csupomona.edu/~mdbacchetti/stohr_rocker.jpg

05-13-2005, 06:57 PM

The above (Stohr) system was common on the rear of many Ducati bikes some years ago (don't know if they've changed recently).

This approach is often used to increase the motion ratio (or install. ratio, depending on definition) of a coilover whilst using the original coilover mounts. In my opinion it only makes sense if the damper can't be made stiff enough for the direct mount case (springs are easy to make stiff). If the car has very stiff springs then it needs stiff damping, hence this system. But on a more softly sprung car most dampers can cope, hence this is just extra weight, friction, flex, cost, etc. Incidently, on the Ducati it is used to give the rising rate that is good on bikes, but doesn't work on cars as previously noted (rising rate "corner springs" change handling balance with body pitch, and jack the car up during cornering).

If the lower wishbone chassis mounts (above) are directly under the top coilover mount, then a direct mount coilover would have a small rising rate, but decreasing to constant rate with upward wheel movement.

Z

PS. A system similar to above, but with a direct mount coilover with its top mount near, or pehaps just behind, the upper wishbone rear chassis mount (for lower yaw inertia and more direct load path) is roughly what I was suggesting for a "simplified double wishbone" layout.

PPS. Note that Stohr's car doesn't seem to have any front ARB. Apparently these cars are winning lots of races...

Lyn Labahn UW-Madison

05-14-2005, 06:11 PM

Is that a rod end in bending at the top of the upright? Carroll must be rolling in his grave.....

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mark B:
Has anyone see the front rocker package on the Stohr C Sports Racer? The rocker has a 180deg pivot with the shock mounted to the pushrod. What do you guys think?

-Mark
Cal Poly Pomona

http://www.csupomona.edu/~mdbacchetti/stohr_rocker.jpg </div></BLOCKQUOTE>

Denny Trimble

05-14-2005, 08:15 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Lyn Labahn UW-Madison:
Is that a rod end in bending at the top of the upright? Carroll must be rolling in his grave.....

</div></BLOCKQUOTE>

Better yet, did you notice the lower ball joint is bolted through a 1/4" aluminum plate with no washer under the nut? Seems like it's just begging for deflection, with that large of an offset from the balljoint center to the mounting plate.

And how did they mill the box-shaped pocket in the upright, with a 1/8" x 1-1/2" endmill?

Daves

05-14-2005, 08:35 PM

But wait -- if you make the rod ends in bending really big and heavy, they won't break. At least that was our FSAE team's philosophy 3 years ago, as well as our mini-baja's current philosophy. So go ahead and use a 1/4" O.D. pullrod with some 3/8" rod ends.

Actually, our school's first FSAE attempt (2001-02) had Koni shocks mounted between the A-arms. The car weighed 780 pounds, but it took 12th place overall.

Also, did you notice the RRPF's (Rapid Retension Polymer Fasteners) holding the brake lines to the A-arm? That's something I wouldn't expect to see in an expensive car.

ben

05-17-2005, 03:41 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:
The above (Stohr) system was common on the rear of many Ducati bikes some years ago (don't know if they've changed recently).
</div></BLOCKQUOTE>

'04 Ducati MotoGP rear end has a swing arm mount and a rocker mount on the engine. The rocker is operated by a pullrod off the swingarm and the coilover is mounted between the rocker and the swingarm and therefore has no direct mount on either then engine or the frame. Haven't had a close look at the '05 Duke.

Ben