carguy123
carguy123 SuperDork
1/31/11 10:25 p.m.

For those of you who's attention span doesn't last more than 4 paragraphs, once again you'll be left out. For those wanting to learn there's some info to be taken away.

http://rejsa.nu/forum/viewtopic.php?t=60154

Hasbro
Hasbro HalfDork
2/1/11 12:19 a.m.

Nice. Pretty easy to understand. I'm going to throw this at some Honda guys on another forum. Thanks.

I also like teh pretty colors on teh pictures.

unevolved
unevolved HalfDork
2/1/11 12:36 a.m.
Hasbro wrote: I'm going to throw this at some Honda guys on another forum. Thanks.

Werd. Just did the same.

Dr. Hess
Dr. Hess SuperDork
2/1/11 7:12 a.m.

Nice MK2 MR2.

nderwater
nderwater HalfDork
2/1/11 8:27 a.m.

Awesome write up. This is exactly the kind of info I've been looking for while wondering, 'What would it take to make my Miata handle like a Ferrari?' Both cars are fitted with double wishbones with coil-over shocks, and in photos the suspension geometry doesn't appear to be that different.

I had the chance to flog a number of exotic cars last year (R8, Gallardo, 997 Turbo, Vantage, others) and the experience really changed my perception of how a car can (should?) handle at the limit. The most impressive of the bunch was the Ferrari 360 I had to chance to autocross. Even though the ride was compliant over uneven pavement, when pushed the car exhibited nearly no brake dive or body roll and slid through corners with what really felt like even grip from all four contact patches. While I'm used to cars which steer with the throttle, I'd never driven anything so neutral. It was exhilerating to drive, and that's not even counting the amazing engine.

The first time I drove an S2000 in anger I thought "Wow, this is what a well tuned Miata must feel like." Flogging a 911 was even better - it's as if a talented shop tweaked an S2000, then gave it more balls. But unlike even a 911, the Ferrari didn't feel heavy on the front tires under breaking, and on turn-in didn't seem to rotate around a planted front tire. What is it that makes this car so different?

Utimately, I'd like to learn what combination of factors mix to create a ride which is streetable, yet neutral at the limit - and whether or not that feeling could be replicated on a miata without exotic components. My thought was that if I better understood the mechanics of the suspension I would like to replicate, the easier it would be to make decisions about the specifics of the suspension setup I'm looking for.

carguy123
carguy123 SuperDork
2/1/11 9:27 a.m.

You can see the attention to detail, or is it lack of compromises, that combine to give you that totally in control feel of the Ferrari.

nderwater
nderwater HalfDork
2/1/11 10:34 a.m.

I know I can’t get Ferrari style or a Ferrari engine without spending Ferrari money. But can I get Ferrari handling without breaking the bank?

imirk
imirk New Reader
2/1/11 10:54 a.m.

In reply to nderwater:

Locost/midlana? because then you design all the parameters discussed in that essay.

Sidenote: the 355 is one sexy bitch

ransom
ransom GRM+ Memberand New Reader
2/1/11 10:56 a.m.
carguy123 wrote: For those of you who's attention span doesn't last more than 4 paragraphs, once again you'll be left out. For those wanting to learn there's some info to be taken away. http://rejsa.nu/forum/viewtopic.php?t=60154

I haven't read the whole thing yet, but I did immediately hit a couple of items which concerned me... While no conclusions were immediately drawn from it, the fact that the "spring and shock assembly (blue line) pointing just inside the center of the contact patch" seems like a red herring. But more worrying is this:

Notice, also, that the brake rotors are on the centerline of the contact patch so that braking forces are not directly coupled into the steering.

Huh? How is the location of the brake rotor within the hub package supposed to influence steering?

I'm going to shut up 'til I get a chance to read the whole thing; I was just struck by those pieces, and it gave me pause with respect to the quality of the article...

scardeal
scardeal HalfDork
2/1/11 11:43 a.m.

My head asplode! But eventually, I'm sure I could wrap my head around it.

GameboyRMH
GameboyRMH GRM+ Memberand SuperDork
2/4/11 9:07 a.m.

Wow I'm glad I ran into this thread.

scardeal
scardeal HalfDork
2/4/11 9:16 a.m.

Does anyone know of any good books/websites that prime someone on suspension design and analysis?

It'll define things like roll centers, ackerman, etc. That is, it's more than just definitions of camber and spring rate.

carguy123
carguy123 SuperDork
2/4/11 9:20 a.m.

I'm currently reading Competition Car Suspension by Allan Staniforth soon to be followed by Chassis Engineering by Herb Adams and then by Engineering to Win - Understanding Race Car Dynamics by Carroll Smith.

I'm learning a lot or should I say I'm understanding a lot.

ransom
ransom GRM+ Memberand New Reader
2/4/11 10:15 a.m.

In reply to carguy123:

Those are great books. I also like Staniforth's "Race and Rally Car Sourcebook" and Smith's "Tune to Win" (which IIRC contains more suspension info than "Engineer to Win", which focuses more on structures?). I also dig Neil Roberts' "Think Fast".

Going back to the article from the original post, I'm dubious. I'm not an experienced chassis engineer myself, so you should probably take at least as much salt with my gripes as with the article, but it just felt frequently as through the author were looking at the example to reinforce his assumptions, as opposed to the apparent intent to simply dissect what's going on with the Ferrari.

A more worrying example, similar to the one I noted earlier, but related to the rear suspension, and this time with conclusion drawn:

The spring and shock are aimed directly at the center of the contact patch, and thus have excellent control over it.

... but we're working through a linkage. Not a full pullrod or pushrod arrangement, but fundamentally the relationship between the movement of the wheel and that of the shock are not well defined by this factoid. The shock could be mounted at several similar locations which resulted in having it "aimed directly at the center of the contact patch" and which had wildly differing motion ratios.

Anyhow, there's probably some good information in there, I just get worried when there's stuff that looks inaccurate to me mixed in...

triumph5
triumph5 Dork
2/4/11 1:12 p.m.
ransom wrote:
carguy123 wrote: For those of you who's attention span doesn't last more than 4 paragraphs, once again you'll be left out. For those wanting to learn there's some info to be taken away. http://rejsa.nu/forum/viewtopic.php?t=60154
I haven't read the whole thing yet, but I did immediately hit a couple of items which concerned me... While no conclusions were immediately drawn from it, the fact that the "spring and shock assembly (blue line) pointing just inside the center of the contact patch" seems like a red herring. But more worrying is this:
Notice, also, that the brake rotors are on the centerline of the contact patch so that braking forces are not directly coupled into the steering.
Huh? How is the location of the brake rotor within the hub package supposed to influence steering? I'm going to shut up 'til I get a chance to read the whole thing; I was just struck by those pieces, and it gave me pause with respect to the quality of the article...

I believe what it means is that with the brake rotor directly in line with the "kingpin" angle, that when the brake is applied it won't act like a lever arm at a fulcrum,-- in this case the fulcrum being the kingpin. If the rotor were not in line with the kingpin, and in turn in the center of the contact patch, then application of the brake would make it effect the steering by acting as a lever arm on the kingpin and in turn the steering.

In other words, if the rotor were offset from the center of the contact patch, and you applied the brakes, the rotors would "steer" the wheels due to the lever action of the offset rotors. To exaggerate, put the rotor a foot outboard of the wheel, put on the brakes, and you'd have your hands full trying to keep the car braking in a straight line.

ransom
ransom GRM+ Memberand New Reader
2/4/11 2:01 p.m.

In reply to triumph5:

In other words, if the rotor were offset from the center of the contact patch, and you applied the brakes, the rotors would "steer" the wheels due to the lever action of the offset rotors.

I think you're mistaken on that point: For the brake to cause a steering torque around the kingpin, the caliper would need to be mounted on the opposite half of the "hinge" created by the kingpin from where the rotor is mounted. The wheel, spindle, rotor, and caliper are all rigidly mounted to the upright. The only force that the caliper applies directly is that torque is applied to the entire upright in the direction of wheel rotation when the brake is applied.

The steering axis (kingpin) is a pivot, or hinge. There is nothing you can do to cause a hinge to move by applying force to only one side.

I believe the only steering torque resulting from braking is due to the portion of the contact patch outboard of the steering axis' intersection with the ground applying a force different from the inboard part. This can be due to camber, dirt, bumps, or simply having a nonzero scrub radius. If both sides of the car are symmetrical, this balances (except for bumps, etc).

Actually, I have to amend that slightly. I think kingpin inclination (KPI) could theoretically feed braking torque into steering. As the kingpin inclines further and further, taken to the logical extreme, it becomes parallel to the spindle, at which point braking torque is on a parallel axis to steering torque (at this point steering wouldn't actually steer, it would just rotate the upright around the spindle's axis). It seems like at normal KPIs of 5-10 deg, this would be a very small factor.

triumph5
triumph5 Dork
2/4/11 2:26 p.m.

Well put. I think some of what I was trying to say got lost, and you expressed it better. It is an interesting discussion. The one point that I would take up is , "There is nothing you can do to cause a hinge to move by applying force to only one side." I thought of opening a door. But, are you talking of moving the entire hinge?

You last two graphs sum up your point exactly as I was thinking, with steering being effected by the contact patch outboard of the steering axis.

ransom
ransom GRM+ Memberand New Reader
2/4/11 3:27 p.m.

In reply to triumph5:

Perzackly: I would say that in our examples, a steering motion at the kingpin is analogous to opening or shutting a door. When you open a door, you're applying force to both parts of the hinge: You've got your hand on the door, which is on one side of the hinge, and you're moving your hand relative to your feet, which are attached to the other side of the hinge by way of the floor and the doorjamb. So you're pushing the hinge halves away from or toward one another.

Continuing that tortured example, applying force to only one side of the hinge is like trying to shut a door while you are hanging from that door with your feet off the floor.

Because I can't seem to leave a tortured analogy alone, I'm going to turn our door into the upright, the hinge at the edge of the door into our kingpin, you yourself (still hanging from the door with your feet off the floor) into our caliper, and the doorknob into the wheel and rotor. It's not a complete model, but I think it's enough to demonstrate that no amount of torque applied between the door (upright) and doorknob (rotor) by way of the caliper (you) will cause the door to move (steer).

I can't decide whether that last paragraph is in any way useful, but I kinda think it's funny, so I guess I'll hit 'post' :)

triumph5
triumph5 Dork
2/5/11 12:15 p.m.

Well the last graph did leave me hanging!! Where is Shekky Green (sp?) when you need him? I am going to sit down this weekend with the OP, and go through the article, if anything it does prod me into deeper thinking than the usual junk from day to day.

I'd be interested in hearing what keith thinks about the OP.

mike
mike Reader
2/5/11 11:13 p.m.

I agree with ransom, the two things he points out also jumped out at me. The brake rotor comment, in particular, is in error, I think. If the caliper bracket and rotor hat were stiff, then the rotor could be way inboard or way outboard without causing a different steering torque. The brake system at any one corner of the car causes a moment couple to be generated between the upright and the hub, oriented along the spindle axis.

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