HybridZ custom suspension design thread

[e_racer1999]

Why don't we (the members of HybridZ) undertake the design of a front suspension that utilizes the factory front frame rails. We have several members on the forum with some expertise in this area and several like myself who wish to know more.

 

As a start, I propose that the front frame dimensions (just the frame rails not the strut towers), front crossmember, and rack be retained (to the inner tie rod only). By holding a few things constant, we can reduce the number of variables in the design.

 

The design should use upper and lower control arms and a readily available spindle assembly. Things that should be considered are bumpsteer, roll center, camber gain, scrub radius, etc...

 

Is anyone interested in playing?

Who has suspension design software to try out various proposals?

 

 

 

nobody else made it from the other thread, so i figured i would lol

 

anyway, i was thinking: what parts beside the spindle would it be possible to source from other cars?

[thehelix112]

An OEM single would be a bad idea for me. A main motivation for double wishbones (assuming thats what this thread/project will be about) is the ability to run wider wheels and tyres, and improve cornering. I am much more interested in a spindle designed to deal with the loads hot 12" slicks produce, than one designed to cope with warm 8" hard road tyre loads.

 

First of all, does anyone have a recommendation for a good/authoritative book on chassis/suspension design? Please don't say Milliken & Milliken as then I really will have to go continue reading it.

 

Dave

[74_5.0L_Z]

I'm sorry but "Milliken & Milliken ".

 

"Hot 12" slicks" is a start. Be more specific. Provide us with a tire from Hoosier or Goodyear.

Do you want to build the car around a 15", 16", 17" or 18" wheel?

Do you want to minimize scrub radius or minimize KPI?

What overall track width do you want?

 

I think it would be cool to try and maximize the length of the control arms and design around wheels with a large back space.

[JMortensen]

Jason, your post is exceedingly vague. What are you trying to do? Are you actually building something or do you just want to bench race different systems?

 

Personally I feel that the stock-ish strut system can be built up to a pretty impressive level of competency if you take the time and effort to do it right. I would not choose a strut style suspension if I were designing something from scratch, but why some feel a need to get rid of it and replace with 5 link rear setups is a bit beyond me. And it seems that not too many pay attention to the front end which is the really lacking end in my experience.

 

Competition Car Suspensions by Alan Staniforth is a good book. It mostly concerns itself with formula cars, but still a good resource with particularly good Ackermann info. Race Car Vehicle Dynamics by Milliken & Milliken is extremely technical and although I felt that I learned a lot from reading it I think I got more info about tires and aero out of it than I did about suspension. The "X" To Win series by Carroll Smith is another good series of books but they're getting a little long in the tooth.

[thehelix112]

Dammit.

 

I just don't get the time required to study and understand the things in there. Took me over a month to get through the Tyre chapter. I don't like skimming, I read it over and over until I understand it. Perhaps I'm just dense.

 

I'm not entirely sure if you're being sarcastic regarding the tyre specifity, but I'll assume not. I don't have an answer, but would hope to build in enough adjustability to have freedom of tyre choice.

 

The brakes I have planned will fit under 15s, so once again, wheel size will be a tuning factor.

 

I guess what I'm getting at is I don't have a good start point, nor do I really know how to go about picking one. So perhaps I'll just observe this thread for a while.

 

I am curious now as to the pros and cons of scrub vs KPI, will go look that up.

 

Long control arms makes sense.

 

 

Dave

[74_5.0L_Z]

Jon this all got started because boostedh23a1 is building a tube chassis similar to mine and has some strut questions. He was asked why he was going to the trouble of building a tube chassis front end but still keeping the strut suspension.

 

As part of my reply, I posed the following challenge:

 

Why don't we (the members of HybridZ) undertake the design of a front suspension that utilizes the factory front frame rails. We have several members on the forum with some expertise in this area and several like myself who wish to know more.

 

As a start, I propose that the front frame dimensions (just the frame rails not the strut towers), front crossmember, and rack be retained (to the inner tie rod only). By holding a few things constant, we can reduce the number of variables in the design.

 

The design should use upper and lower control arms and a readily available spindle assembly. Things that should be considered are bumpsteer, roll center, camber gain, scrub radius, etc...

 

Is anyone interested in playing?

Who has suspension design software to try out various proposals?

 

I posed it as both an exercise with hopes of producing a real product. Call me weird but it sounds like fun.

 

The original thread is here:

http://forums.hybridz.org/showthread.php?p=818359#post818359

[ZT-R]

aww i feel loved

[JMortensen]

All right then, why don't we start with boosted's requirements. We don't really know what he wants or is capable of building yet. A suspension modeling program is going to be pretty important when things start to get specific, so that might be something that he wants to acquire once we pin things down a bit.

[e_racer1999]

sorry about that jon! i should have referenced the original thread in my first post. i have edited the first post so that future looker-ons will know what is being discussed

[tube80z]

I have susprog3 and that can be used to model these. Really all it spits out are the coordinates and then there are easily graphed in excel or something similar.

 

I have a lot of thoughts on what matters but little in the way of answers. Unfortunately you're going to find that once you nail down the constraints you're not left with a lot of options.

 

I think one of the first things to do is to start with the tires and intended use of the car because these will have influence when you get to item 6 below.

 

Here's a basic list of what to look at to get started.

1. Lower arm should be close to horizontal (when in use)

2. Longer arms are better than shorter arms

3. Don't get carried away with antis (things should move free and easy)

4. Decide on spindles/knuckles/struts.

5. Decide on halfshafts (for RWD)

6. Now decide on camber gain, roll center height, aim for zero bump steer, and don't forget to the ARB.

 

Now that you have "designed" a suspension you must learn to "tune" it. I guess that will a different topic altogether.

 

Cary

[Dragonfly]

I was at the vintage races recently and I took a few pictures of things that you normally do not get to see... I felt this one would be good in this thread.

 

 

I realize this is a rear engined car with a transaxle but the suspension setup should get some brains going on here. This is the car that this suspension shot came from.

 

 

As a side note... take a look at the angle of that radiator.

 

Dragonfly

[heavy85]

I was at the vintage races recently and I took a few pictures of things that you normally do not get to see... I felt this one would be good in this thread.

 

 

That looks like a semi-trailing arm set-up. May be hard or impossible to package into a Z rear suspension.

 

Cameron

[thehelix112]

Doesn't look like semi-trailing arm to me. Looks like a typical uneven-length double wishbone setup.

 

Impossible? Please.

 

Dave

[wheelman]

I agree with Jon, we should actually be concentrating on the front suspension not the rear.

 

Here is the link I posted in the other thread to a SLA suspension setup for an SN95 Mustang. I think this would be a good starting point to design a similar setup for an S30 Z.

http://www.agentfortyseven.com/racing/suspension01.html

 

Wheelman

[bjhines]

Hmmm...

 

I have a few comments on this approach,

 

I might do a few things while retaining the stock struts.

 

1. convert the front end to rear-steer:

This would allow small dia tire and wheel packages(If you could buy them anymore). The problem comes from the fact that the steering knuckles interfere with big-brakes and wide wheels when combined with typical lowering mods. This forces the use of 16"-18" wheels depending on the mods. The larger dia. wheel packages weigh more and raise the overall ride height.

The rear steer fix would allow the steering arms to angle away from the inside lip of the wheels and away from the brake disk. While maintaining proper ??ackerman.

Unfortunately the rear steer idea might not work with the rearward facing TC rods. The frame rails might also have to be cut to allow the rear rack placement. The other issue comes from the fact that there is no where to put the rack while keeping the longitudinal engine tranny in place. You could weld a transverse front end onto the car.

 

TC RODS:

The TC-rods also need the pickup points raised to maintain anti dive properties. Unfortunately they hit the frame rails if they are raised much at all. Again we need to look at cutting the frame rails.

The strut towers could be widened and moved slightly rearward to allow easier adjustments and increase caster without pushing the front wheels into the front lips of the fenders.

 

 

Rear suspension:

For the rear and I like the horizontal arrangement of the rear control arms. many of the retro-fit rear ends have used a trailling arm design. I don't like it.

The problem comes from the driveshaft angles and the work involved to relocate the lower-control-arm pivot points to correct geometry when lowered. Most fixes I have seen involve cutting, extending, and rewelding the rear spindle castings. I have also seen a milled aluminum block that was used to lower the rear outer pivots. The inner pivots would again involve cutting into the chassis to raise them.

 

Those are just a few ideas. There is one overreaching factor that keeps popping up. The chassis must be heavily modified to allow the fitment of fat wheels and lower the ride height. Even then we are still using the old school/cheap strut type suspension. Just getting that to work on a lowered car means cutting it up, you might as well just buy/build a kit car that uses common/modern parts.

[ZT-R]

im not buildng a full out race car. mainly street, some strip, maybe 1 or 2 autox. ill probably run 17" rims with street slicks. and 13" rotors in the front.

[bjhines]

Then you can just build the standard S-30 set up.

 

The S-30 chassis IS NOT your typical unibody. We have a front engine, rear wheel drive, longitudinal driveline, with the cockpit in the back of the chassis. You cannot just slap a newer/different suspension on the car. The front end is ESPECIALLY different than most modern cars.

 

The front frame rails are lower than most cars. The driveline is not mounted using subframes. The strut towers are WAYYYYYYYYYYYYYYYYYYY out in front of the firewall. We have a front steer set up. The overall spacing of the components is suited to Zero offset wheels. This is totally different than modern set ups.

 

If you want a different car, buy a different car. The BMW Z-3 is very close to the Z in overall layout with a much more modern design.

[74_5.0L_Z]

bjhines,

 

 

"If you want a different car, buy a different car." I'm sorry, but that is not the HybridZ way. I look at my Z as a blank slate upon which I can spew my wildest ideas (limited of couse by time and money). I know that I am not alone in this sentiment.

 

There are some aspects of the stock front suspension that can be improved by converting to a SLA type front suspension. Mainly, camber gain can be greatly improved.

 

His stated purpose for the car does suggest that a strut suspension based on the existing components will suffice. However, he is already in the process of building a tube chassis, so many of the constraints of the original chassis do not apply.

 

I, on the other hand will probably pursue building an SLA front suspension. I already have my tube chassis complete, and it would be a simple task to add mounting points for upper control arms. My lower control arms are currently stock length (but utilize sperical bearings). My idea is to lengthen the lower control arms by two inches. At the same time I would increase the backspace of the front wheels by the same two inches.

 

For an upright there are several options: First, I could cut off a strut housing and add provisions for an upper ball joint. I dont know if this option will provide an acceptable KPI. Another option is to acquire a front spindle set-up from another car (perhaps a C4 vette). This option is attractive because the spindle could be purchased complete with five lug hubs and big brakes.

 

Whichever upright I end up with, it will be necessary to make some custom upper control arms. The same is true for the outer tie rod ends. The stock ones will nt be long enough. These would be constructed by sourcing the parts available through Coleman racing, Afcoracing and others.

 

Regardless, on HybridZ I rarely expect to hear, "If you want a different car, buy a different car." For better or for worse, that is not the way we operate.

 

Dan McGrath

[e_racer1999]

what i see as our biggest project is an upper control arm (after reading Dan's post). once we source an appropriate spindle (C4 vette sounds good, has to be pretty durable), the trick will be making an upper and mounting it. well, then we have the suspension to take care of. i'm not too knowledgeable on suspension geometry, but i would think that having the strut/shock as far inboard as possible would be beneficial, so that wheels with larger backspacing would be possible.

[bjhines]

bjhines,

 

 

"If you want a different car, buy a different car." I'm sorry, but that is not the HybridZ way. I look at my Z as a blank slate upon which I can spew my wildest ideas (limited of couse by time and money). I know that I am not alone in this sentiment.

 

.......

 

Regardless, on HybridZ I rarely expect to hear, "If you want a different car, buy a different car." For better or for worse, that is not the way we operate.

 

Dan McGrath

 

 

The original poster seemed to desire a "bolt-on" modern suspension.

I pointed out quite clearly that you are not going to make any drastic improvements without cutting up the car.

 

I have an extensively modified chassis(with struts), that has involved hundreds of hours of chassis modification. It would have been equally difficult to hack off the front end and tube frame it in the process.

 

For the sake of sanity I will repeat... Buy a Z-3. There are too many things wrong with the S-30 design to expect major improvements with minimal effort and cutting.

 

Ohhh.. and please read what I wrote before you get offended. There are some MAJOR problems with your proposal.

For ONE!!!!! we need a rear steer set up, retaining the original rack and crossmember pretty much cuts that out. In fact, retaining the longitudinal driveline pretty much rules that out.