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 Post subject: Sunpension Calculations
PostPosted: September 10, 2009, 10:18 pm 
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All right, I've made some more progress, but my documentation is lagging, so I'll try to get some pictures up in the next couple of days. In the mean time I've been getting ready to tackle the front suspension. I had read about the suspension calculators, and tried to understand all of the different terms, read through the Staniforth book. I am pretty sure I've understood almost every major section about suspension geometry at one time or another, but each new term seems to push the old one out of my head. Also I had not downloaded the actual program, so most of the discussions I read didn't make too much sense to me. The other day I finally got a windows computer working and downloaded the Wishbone software and tried to make a little sense out of it. Well today I worked on my suspension calculations all day, I read through all of the posts I had read time and time before. The information is out there, but its not set out in a step by step fashion to go from nothing to designed suspension easily. Everyone has a different level coming in, and different goals, and like they say its all a compromise even with the "best" suspension. I read several times that your calculations can have a lot more accuracy than most (me) can hold in the actual building process. I'll try to go through the steps I took, and document as well as possible, so someone else could follow all of the steps, but I'm writing this after I've spent a lot of time researching, and I'll probably skip over some stuff along the way. This is not a entirely to teach, especially since I'm not at all confident that I've done this "right". I'm hoping some people will step in and either confirm or critique what I've done to help me build some confidence, or enough knowledge to do it again hopefully better.

Extremely condensed quick and dirty solution:
1: Make both your lower mounting height on your chassis the same as your lower balljoint
2: Spread out your lower locations on the bottom of the framerail at the same distance from the centerline say about 1 foot apart
3: Make your upper arm length 2/3 of your lower arm
4: mount your upper arm locations where they fit with that arm length on the up/down rails at the front of your frame.
5: rotate your upright so that the lower ball joint is 7.5 deg in front of the wheel centerline (caster)
6: lean your tire in .5-1 deg (static camber)
With little/no calculations this should give you a decent suspension

Long version (detailed explanations, maybe not too much better thought out)
I read Allan Staniforth's Competition Car Suspension a Practical Handbook 4th edition It was a good book and I got some of my suspension targets from it, but I think you could design your suspension without it if you don;t want to get a copy, but its a good book, and I'll be keeping my copy. :)

I downloaded the Wishbone analysis program by McDermott (its in a link in the post below)
viewtopic.php?f=5&t=1438
I had been paranoid about viruses, and my computers weren't running well, so I hadn't tried it before, but since so many people had used it, it is apparently not a virus, so I gave it a shot, and it was fairly painless. It doesn't want to run on Linux Ubuntu, so I had to install it on my non-internet windows machine I keep around for just such occasions, but supposedly if you are smarter/care more than me you can find linux workarounds further down the link above.

The file you downloaded is a setup file. Go ahead and click through its installation and you get the executable file.

When you open Wishbone you start with their example file and edit it. Do not type example.wsh it won't open, just type example.

People rightly complain about screen resolution, but if you hit enter get a starting set of results then hit F6 and enter a couple more times the input screen comes up full screen, and is much easer to see.


Starting in Wishbone you need the following measurements for input in your file.

Tire Height
Track Width (can be changed, but take a guess by starting with the same as the rear)
Wheelbase (can be changed, but take a guess by measuring where you think things will go)
upper and lower ball joint
(locations height from ground, distance from centerline of chassis, distance in front/behind the center of the wheel)
"ball-joint" on steering arm, same format.
measure the height of your frame off of the ground as a point of reference
-Remember when you are taking measurements you are measuring to the center of the ball-joint where the bend is really happening)

You will be adjusting the following inputs to design your suspension.
upper and lower front and back mounting locations
toe control location
static camber
static toe

Inputs that you probably won't actually know, but will just leave filled in or make a guess
CG height (maybe just assume its half way up the height of your engine?)
CG long (if you can put your car on scales take the weight ratio and multiply it by the length of your car)

Now you know what's required to input into the computer program to get your output, but what kind of output are you looking for?
Goals
Caster 5-9 deg (I shot for 7.5) This will make your steering wheel self center when you let go of it/makes your steering heavier
You control this by rotating your upright so the lower ball-joint leads the upper. (you could do it backwards, but that the wrong way, you are supposed to have the lower in front.
KPI 5-9 deg (mine has 10.xx) this is built in to your upright and is not adjustable, so although you might want to, you can't change it without changing your uprights, which would be cheating :)
Camber .8-1 deg of additional camber per deg of roll (your tires will have an ideal amount of camber they are designed for, but if you don't know, or don't even know what compound you will be using, you are just left with the initial rule of thumb. Initial camber will pretty much add that much throughout the range of roll +/- a little.
Roll Center you want this from 1 - 4 above the ground, maybe lower, but this is the range I was looking at for a performance not race car. The main thing you want is to see the roll center height stay in the same location as you change the roll on the car.
upper
Its at this point while I'm looking for the documentation of where I found these "rules" that I found the following link which is appropriately stickied in the suspension section. It has most of the thoughts I have above.
viewtopic.php?f=5&t=1227
These were a few goal that I found looking through the forum, and reading Staniforth's book.

To meet these parameters you can change:
Track Width (apparently Caterhams are a little narrower in the front)
Suspension inboard mounting points
Location angle of the upright
also you will need to mount steering rack which will affect bump steer, but that wil come later (since I haven't dealt with it in my design yet)

Where to start when you are plugging in to Wishbone?
Go back to my quick and dirty solution and use it to set up your initial mounting points.
Change the height and width of your upper mounting locations to control your outputs.

You don't want to start messing with the steering rack locations (toe control) till you finish locating the arm mounting points.
The steering rack location will determine bump steer, or your goal of lack of bump steer :)
Staniforth's rules are (I am using a forward mount steering rack)
Bump Droop Rack Adjustment
toe in toe out raise forward
lower rear
toe out toe in lower forward
lower rear
toe out toe out lengthen rack
shorten rack
toe in toe in shorten rack
lengthen rack
remember you can also add some static toe to change your outputs

I think that is the best I have gathered.
Here are some of my outputs, please let me know what you think and why so I can either add some more goals or change my process in some other way.

I'll try to keep updating this post with additional information as I change my design
Sorry it got so long
Thanks,
Sam


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PostPosted: September 10, 2009, 10:21 pm 
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It looks like I posed the pictures in the exact opposite order that I was hoping to.
If I ever fix it this post won't make much sense :)
Here is the last screen shot it wouldn't fit in the upper post.
This one has roll, bump and steering, and I really don't know what I am supposed to shoot for under these conditions, so if you know, let me know.
Thanks,
Sam


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PostPosted: February 22, 2010, 8:58 pm 
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So, I've basically been doing a whole lot of nothing, but I have sold a few more parts, so hopefully I'll be able to order the fiberglass and heims before long. I did get a manual miata rack I plan to shorten. I guess I'll get/make an adaptor to go from the miata threads on the end to the s2000 female threads on the ball joints. (Of course they are not the same.)
If anyone has a chance to look through my suspension calculations above I'd appreciate it, I might post a link to them over in the suspension section some time.

Sam


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PostPosted: February 22, 2010, 10:18 pm 
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Great write up - Thanx!

I have the rear subframe out of an '02 S2000 sitting in my shop just looking for a home. I'm glad you are a bit ahead of me.

I disconnected the subframe connectors and the engine connectors and then just lifted the car off the rolling assembly with an engine hoist which made it (relatively) easy to do.

Sure wish the car had come with a power plant frame to keep everything aligned and looking purty on the ground. It would have also made moving it around in the shop a lot easier.

I'm fragile so I'm waiting till it warms up some to begin building. We've had more snow and cold weather here than we've had in 50 years.

What are you going to do to correct the rear bumpsteer issue? Stiff springs so it doesn't move as much or will you relocate the rear toe link (I think it needs to be lengthened).

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PostPosted: February 23, 2010, 1:20 am 
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carguy123 wrote:
Great write up - Thanx!

x2



Out of curiosity, where did you get your donor?


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PostPosted: February 23, 2010, 8:57 pm 
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carguy123 wrote:
Great write up - Thanx!

Thanks! I hope its accurate :)

What are you going to do to correct the rear bumpsteer issue? Stiff springs so it doesn't move as much or will you relocate the rear toe link (I think it needs to be lengthened).


I was not thinking about rear bumpsteer, and was not planning on doing anything about it. My plan is to use the stock rear springs and weld in some brackets to support them at the top, around the gas tank/roll bar area. I think I can probably get different springs for the rear if that seems necessary, but maybe I will need to make changes in the future. Maybe you can hurry up and get ahead of me so I can have someone to solve some problems for me :P It will probably happen anyway because I'm building a new house this year, so all of the metal fun slows down, and the wood fun ramps up.

I got the wrecked car from Jay's (rebuildable cars/junkyard) in KY about 20 miles from where 71 and 75 split. He's got a web site that lists what he's got. I think his prices are pretty good, although he said he'd never buy another s2000 at auction again, I think he had it almost a year before he sold it. He told me he sold it for what he paid at auction, but who knows if its true or not. I'd still recommend buying a newer wrecked car and parting it out if you have some money to start with and want to keep your costs really low. It takes a loooong time though, I'm still selling parts, and I think I've been doing it for almost 2 years now. It was a lot of fun taking the car apart and seeing how everything was designed, I was really impressed with the quality of the s2k, but posting stuff for sale on the internet is really just work. I'd probably be better off just getting a part time job and saving the money. I would personally suggest just being rich and not worry about selling the stuff you don't need :D :) :lol: :wink: It seems like that would be easier.


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PostPosted: February 23, 2010, 9:09 pm 
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Right now I am kind of stuck on what to do with the bottom balljoint on the front wheels. Its kind of hard to see in the picture, but it connects to the hub in 2 places with 2 bolts. Of course the balljoint is tapered, so I don't want to just put it through a straight hole and leave a bunch of wobble room, but I'm not sure what the taper is and how much a tapered tool will cost. I think I saw a couple of sizes in my southwest speed catalog, so I bet they are out there. I wish the bottom a-arm was mild steel, so I could cut it off and weld on, but I think its cast, so I'm going to try something more acceptable, whatever that ends up being. I was planning on drilling the top hole out on the hub, and using a studded rodend like keith did in his book. I might just get a hunk of steel and bolt it to the hub on the bottom and do the same thing if I can get it to clear, but I'd like to use the balljoint if possible. Let me know if this makes any sense, and if you have ideas, especially if anyone has used the s2k hubs before!
Thanks,
Sam


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PostPosted: February 23, 2010, 9:22 pm 
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I built my house a year or so ago so I totally understand. I'm just now getting back to actually doing car things.

What year model was your car?

The bumpsteer issue in the rear really isn't an issue until or unless you have a lowered car & are tracking it, which I'd presume you'll do with your new baby.

They make a bumpsteer kit to get rid of it, but I've not been able to get my hands on one to see what they really did. When I took my subframe out it appeared to me that all the rear toe bar needed was to be lengthened. It sits in there like a steering arm but the pivot point is at the bottom arm but the link is only about as long as the upper arm hence some bumpsteer when the suspension is compressed. Unfortunately the link attaches to the subframe and you can't really move it back enough to match the length of the lower arm so it means some sort of new attachment point.

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PostPosted: February 23, 2010, 9:50 pm 
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carguy123 wrote:
What year model was your car?

I've got an '02 its the newest (and until recently most expensive) car I've ever owned, and its in 1000 pieces :D


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PostPosted: February 23, 2010, 11:44 pm 
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You did keep the key/transponder/ecu together didn't you? It won't start if you didn't.

'02-03 were the best years for powerbands.

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PostPosted: February 24, 2010, 7:29 am 
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Although I am not exactly sure what/where the transponder is, I know I still have it in one of the tubs, because if I sold it, I would know what/where it is :)

I am pretty sure that power will not really be a concern since 150 would probably be screaming fast, but more is better right :twisted: , plus a wider range would be nice.
Thanks for the tips
Sam


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PostPosted: February 24, 2010, 10:46 am 
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The transponder is in the key module and it's VERY important. Your key won't talk to the ecu if you don't have it. You need a complete, running S2000 for the dealer to be able to match them up.

It's part of the factory immobilizer system.

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PostPosted: February 24, 2010, 4:25 pm 
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S27sam wrote:
Right now I am kind of stuck on what to do with the bottom balljoint on the front wheels. Its kind of hard to see in the picture, but it connects to the hub in 2 places with 2 bolts. Of course the balljoint is tapered, so I don't want to just put it through a straight hole and leave a bunch of wobble room, but I'm not sure what the taper is and how much a tapered tool will cost. I think I saw a couple of sizes in my southwest speed catalog, so I bet they are out there. I wish the bottom a-arm was mild steel, so I could cut it off and weld on, but I think its cast, so I'm going to try something more acceptable, whatever that ends up being. I was planning on drilling the top hole out on the hub, and using a studded rodend like keith did in his book. I might just get a hunk of steel and bolt it to the hub on the bottom and do the same thing if I can get it to clear, but I'd like to use the balljoint if possible. Let me know if this makes any sense, and if you have ideas, especially if anyone has used the s2k hubs before!
Thanks,
Sam


The inverted balljoints caused me some grief too. I couldn't decide how best to handle them. First I tried buying some weldable shock eyes, but by the time you increase the taper size to accept the balljoint there isn't much material left. So what I finally ended up doing was using a piece of 1/4" plate, cut out a triangulated pattern for the lower control arm, and in my case shock mount. Then I cut another smaller piece that just supported the balljoint and welded the two together all around. Basically just make a backer to give it some more depth. It worked out ok. The one thing you need to be aware of though is the balljoint angle. If you make your control arm straight and make the tapered hole 90* to the arm, you’ll limit the suspension travel in droop significantly. The arm really needs to kick up at the end where the balljoint meets. I didn’t do this on mine, but I’m willing to live with it for the time being. I may redo these in the future though…it was a dumb mistake on my part.

For the balljoint hole just use a 7* tapered ream that you can get from Speedway for $80. http://www.speedwaymotors.com/Tapered-Ball-Joint-Reamers-7-Degree,2918.html or try to borrow one from someone in the forums. I'd offer you mine, but I'm in Canada and the duty to ship it there and back would be more than the tool.

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PostPosted: February 24, 2010, 6:10 pm 
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Hey Thanks Mike, it makes sense to me, do you have a build log, or some pictures, you could either post a link here, or just put the picture in for reference . Although at $80 for the reamer I might be cheaper to just switch over to studded rod ends and just drill a straight hole. Let me know if anyone thinks one has an advantage over the other. I really appreciate you knowing the angle of the correct reamer, I was just going to find the callipers and my geometry skills :)

CarGuy123, I know I've got it all so it shouldn't be a problem, but what do all of the people that buy an ebay combo do? I've never seen one come with a key or immobilizer, even though most do come with an ecu. I'm sure there's some way of getting it running, but it may take a trip to the dealer and undoubtedly more $$$


Thanks guys!


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PostPosted: February 24, 2010, 6:16 pm 
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My car has served as the set up mule for Brian @ Ultralite more times than I can count. I take it in and have them program 8-10 keys at a time. IIRC it's about $100 a pop for reprograming.

Without a working car you are pretty much out of luck unless you buy a JDM ecu or know how to bypass the immobilizer which requires soldering.

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