Learn Me: suspension types pros and cons

While pondering my next car project (which will be stuffing a LS into something that small that can turn) I've come to realize just how little I know about the various types of suspension of various cars. I'm confident in my ability to stick an engine in, but I want the suspension to be as issue free as possible.

Front Suspension: - the e36 has mac strut front, I THINK this is not considered as good as double A arm, but I'm not sure why. Everyone raves about the handling of the e36, so how big of a deal is this? what are the draw backs for a sports car?

Rear Suspension - the z4, 944 and others have a rear trailing arm. same question, what are the drawbacks?

The big advantage to MacPherson struts is that they're compact, because there's no upper arm. This gives designers a lot more space in which to mount a transverse engine for a FWD car, which is why 90% of the cars on the road today have MacPherson struts. BMW doesn't use transverse engines or FWD, so I have no idea why they use struts...

The big disadvantage to MacPherson struts (aside from being relatively heavy) is that the camber doesn't change much as the suspension compresses. In an ideal world, you'd want the tire to have close to zero camber when traveling straight (thus delivering good straight-line traction if it's a drive wheel, and minimizing tire wear), but gain a lot of camber when cornering (so as to keep the tire relatively flat as the weight transfers and body rolls) to maximize lateral grip. MacPherson struts do a pretty terrible job at this.

Double a-arms are the reverse -- they take up a lot of inboard space with the upper arm, but that arm is what enables the camber gain.

I'm not sure what the back end of a z4 or a 944 looks like. I think pure trailing arms are usually used with live axles, they have no camber gain at all. In a car with IRS, you might have a trailing arm in conjunction with additional links.

Z3s used "semi-trailing arms", which is an arm that is mounted on a diagonal relative to the axis of the car. These were popular in the 60s & 70s (fewer moving parts than double a-arms), but they often have undesirable characteristics in terms of dynamic toe change and suspension binding due to arms in conflicting arcs. AFAIK they're basically obsolete these days.

One other historical advantage to double a-arms is that they are relatively easy to analyze mathematically, thus making the suspension designer's job easier. This is one big reason why they have been popular in purpose-built race cars pretty much forever. Modern computers make this kind of analysis & simulation a lot easier, so OEMs have been moving to systems with lots of single-point links ("multi-link" suspensions) which let them tweak the behaviour of the wheel much more closely to deliver the handling that they are targeting.

If you want a car to turn well and you can choose any kind of suspension you want, then it's double wishbone suspension for you, as used on possibly every purpose-built race car made in the last 50 years, and most midrange to high-end sports cars and supercars.

The reasons manufacturers don't put double A-arms on every single thing are packaging (they're one of the most space-hogging suspension types), cost (macstruts have one less arm so they're cheaper) and sometimes strength (for offroad use, 3-link/4-link or Hotchkiss leaf spring setups are stronger, but you often still see double A-arms especially on the front). Also their bias-free nature is a bit of a disadvantage in circle-track racing.

The only questions should be if you want a bellcrank setup or whether to go with super-tall or conventional uprights.

What does that last paragraph mean?

If you are putting a big v8 into a small car, I would think the space saving advantages of a MacStrut would work well for you.

Another added "disadvantage" to the strut set up.. lack of suspension travel. Porsche, BMW, VW and like limit the travel on their suspensions to keep the tyre from gaining or losing camber in corners. A car with little suspension travel does not lean much (I think the A1 rabbit had all of 4 inches of travel)

The Z4 has a relatively complex suspension, not unlike that of the E36 coupe/sedan (but not the Z3 or 318ti) and the E46. It is a well designed system with few inherent flaws other than needing a basketful of bushings when it comes time to replace them. The Semi-trailing arm system used in the E30, 318ti, Z3, and air cooled Porsches does weird things with lifting the centre of gravity and potentially tucking in a hard corner. This is a design that does not like weight shift when cornering. Once you commit, do not lift, and it will usually power you through well. If you lose your nerve and lift or touch the brakes, it will snap the car around before you know what happened.

I actually prefer the suspension from the E30/318ti/ It is simple, very robust, and as long as you remember it's limitations, without drama or surprise.

The don't lift or touch the brakes sounds worrisome in a light high hp car and me tendency to be stupid

icaneat50eggs wrote: What does that last paragraph mean?

(assuming you mean mine)

A bellcrank setup is where instead of the coilover being attached directly to an A-arm or upright, it's mounted inside the car and connected through a bellcrank to a push-rod or pull-rod that connects to an A-arm or upright. This reduces unsprung weight, gives the suspension more adjustability and saves space in the wheel wells, and it's good for aero if the suspension is exposed. The downsides are expense, complexity and overall bulk. Still, it's a fairly common setup on race cars and supercars.

Supertall uprights are just what they sound like - they've been used in the past on a lot of Hondas for example for packaging reasons, but more recently they're being used to reduce weight and make room for huge wheels. In this design the upright extends up and out of the wheel and the upper A-arm sits completely above the wheel, vs. a conventional upright where both A-arms sit inside the wheel. It takes a lot of design effort to save weight with them, but they're being used on a lot of supercars and high-end sports cars these days.

Macstruts tend to gain positive camber in roll and even just through their range of travel. This is why so many people who race cars with strut suspension run a lot of static negative camber. They also suffer greatly from bumpsteer and generally you can really only get them to work ok in a very narrow range of travel.

Trailing arm suspension can have decent camber curves, but that can cause issues when lowered as the lower the suspension, the more of a "jacking" situation can occur under braking and the more static negative camber you tend to have which can cause traction issues for driven rear wheels.

For production built cars where it is nearly impossible to relocate the suspension pickup points to where they should be after lowering a vehicle, these issues can become very worrisome. Look at some of the slammed or hella flush rides to get an idea of the issues at a macro level.

For a car you're designing from scratch, you can locate the pickup points where you want them, so whichever solution you use, you can maximize their potential to some extent.

A double a-arm solution tends to be the best compromise for all uses when looking at keeping the tires in contact with the ground with a decent camber curve, little bumpsteer and decent forward bite for drive use. It does take up a bit more room and it is a bit more expensive and difficult to implement.

It should be noted that on a light car with very sticky rubber, ideal suspension design gets a little less important as long as it doesn't have any overly nasty traits. This is especially true with hugely stiff shocks and springs as the amount of suspension movement is fairly small and you're relying more on mechanical and any aero assistance you might have to provide grip.

I should have said I'm not building anything from scratch, I want a good platform that has a well developed kit for the ls swap

As has been said, double wishbone fronts are the bees knees if set up properly. Some are terrible. GM A and G body for example. They were short spindles with a terrible UCA angle that caused negative camber during compression. Its pretty easily fixed, but not cheap to do it right. The "right" way is an aftermarket taller spindle. The cheap way is B-body spindles, but that will add track width and bump steer; the latter not being necessarily a big issue if you don't have much travel.

The other thing is mount points. No amount of good arms, springs, or simple changes to static geometry can fix a double wishbone with poorly engineered mount points.

My point is, I don't think it necessarily matters if you're building on someone else's existing engineering. Double wishbone > Strut for the range of possible engineering, but BMW has managed to make excellent handling with struts and GM managed to completely berkeley up a double wishbone. If you find something that has been engineered to handle well, I wouldn't stress on how they did it, just take advantage of it.

Well then, you'll be stuck having to maximize whatever you end up with. Which generally means sticking as much tire as you can under it and stiffening it up so that it doesn't move too much.

This is pretty much the exact same project I'm planning right now. The two front runners for me right now are the E36 and FC RX7, as they're both good handling cars with pretty well developed LS swap options that should be doable in my budget. I think the trade-off between the two is a better rear suspension design, newer platform, and more plentiful parts supply in the e36 vs lower weight and a somewhat easier and potentially cheaper swap into the RX7. Probably depends on what I can find in good condition and suitable spec first.

Id be curious to hear where you head is at the moment, as your goals and criteria seem very similar to mine.

icaneat50eggs wrote: I should have said I'm not building anything from scratch, I want a good platform that has a well developed kit for the ls swap

"stuff an LS3 into something small that can turn with a well-developed kit". Sounds like you need to call Keith.

Furious, Your thread really got my head churning. It sounds like our goals are similar. My one additional one is I'd love it if the car would be nice enough and big enough my wife and I could use it for weekend trips for the two of us.

My heart says miata since I lived my last one (RIP). I loved how light it felt compared to my dads s2000. However even with a hard top and extra sound proofing the wide didn't love riding in it.

My leading three right now are Miata, rx8 and e36. Need to look more into the rx7

For my money, I'd be looking at 928s as well.

In reply to icaneat50eggs:

Sounds like a NC is what you want as it s more roomy inside than the older ones.

That or an RX-8

The only Porsche ones I've found are renegade. They seem slightly sketchy and leave you a lot of stuff to figure out

Is there another company making Porsche swap kits? A boxster would be sweet

curtis73 wrote: For my money, I'd be looking at 928s as well.

take out the problematic Porsche lump and drop in a bigger more powerful LS? sounds like a win to me

In reply to icaneat50eggs:

Texas Performance Concepts, much better for the 924/944/968 Chassis. They have a forum where there are details for doing it yourself with a variety of engines and even the 928.

The drawback is that the suspension parts are expensive compared to a BMW and the chassis is quite a bit older than some of the BMWs.

I like the RX7 for a few reasons. For one, it accommodates the V8 very well, the tranny tunnel is apparently huge due to the position of the eccentric shaft on the rotary. The brake booster and steering shaft aren't a concern, as they can be on the E36 with certain kits, and it seems the stock f body manifolds can be used. There are stock drivetrain options that are robust enough to handle the torque. The swap has been done a zillion times and seems even better developed and supported than even the E36 or Miata. The Granny's kits are dirt cheap and I think this would be the lowest cost option by a fair margin.

I've ruled out the 944 based on docwyte's input on cooling and gearing, plus Porsche parts prices.

I like the RX8, good suspension design, much newer, but don't think i wanna deal with trying to get one to pass emissions. I'm pretty much set on staying OBD 1 I think. Plus, I'm not keen on relocating the steering rack.

The Miata is obviously great, but I think would end up being out of my budget. The need to buy (or build) a complete subframe plus upgrade the entire drivetrain puts it into another price bracket, from what ive seen.

928 would be cool, but I don't think is quite what I'm looking for right now. And again, Porsche tax.

What kind of budget? Are you doing this swap to end up with an LS swap in a unique vehicle or do you just want a RWD 2 seat sports car with an LS?

What I'm getting at, is you can probably get a used C5 for around the same money you'd spend getting your swapped ride to meet all of your requirements. If the Internet can be trusted, a C5 weighs within a hundred lbs or so of a stock Rx-8, seems to check all of your size/weight/drivetrain/wife's comfort boxes, and would be a heck of a lot faster and easier than going through the swap.

If the journey of an LS swap is the goal more than the end result, then I saw a sweet Z3/ 5.3L combo the other day. That particular swap had never occurred to me, but it seemed to work. A Solstice/Sky would be cool too. Fox Body LS swap kits grow on trees for a reason too. Could end up being the lightest option.

Struts tend to suck less when you're not trying to put both steer and put power though them, e.g. the 911 got along fine with them up front for a long time, and a lot of well liked mid engine cars used them in the rear.

The uniqueness is a big selling point. My first build was very unique and I enjoyed it much more than other cars that were faster.

But I don't want to reinvent the wheel. Been there done that. I used to have more time than money, now I've switched those and can pay for a well thought out kit

Furious, what drivetrain parts are reused with the fc Swap?

Furious I think the v8roadsters kit doesn't need to relocate the rack