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rabrooks

Front Suspension Swap? Anybody done one

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Posted (edited)

I'm looking for ideas for a better front suspension for my 75 280z track car build. I can buy an aftermarket K member or modify something from the bone yard. I expect I'll end up fabbing something of my own. But I'd like ideas and /or see what others have done.

I want to do some version of the double a arm setup. to get rid of the McPherson strut. The strut setup has limitations on the track.

Thanks

Roger

Edited by rabrooks

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The Z car's have one of the best suspensions for handling out there and with improvements like a quality adjustable coil over setup they are great to race.  Just with the common suspension upgrades for the McPherson strut Nissan setup, which is what Frank Leary's Giant killer Z car basically used that dominated racing and was national champion 8 years straight.  It is a great design and with minor upgrades it will out handle most everything out there.  You can get many upgraded parts to give you more unlimited suspension adjustment from Techno Toys, Arizona Z car, and if you really want to get fancy check out Apex engineering options,

www.apexengineered.com/store/c3/240z.html

 

 

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The strut setup on these cars is ok, but there's a reason they aren't competitive anymore. No camber gain in roll and the nightmare front hubs (hello, scrub radius called...) are challenges that can't be solved with this arrangement.

 

The Apex Engineering is in my opinion the kit to get. It lets you lower the car and raise the inner arm pickup point to correct your roll center. I've drilled out my stock sub-frame, and that mod combined with the outboard roll center adjuster blocks make for a wizard handling car. 

 

You MIGHT be able to graft in a Miata front subframe, but you'll undoubtedly run into some hilarious issues with this. I say go for it, particularly if you've already exhausted the adjustments in the stock configuration! And post photos if you do.

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Agree with Ben. Struts can be fast, but it's harder to get them there. The other issue with struts is the dearth of racing quality struts. Race quality shocks are readily available and much cheaper if you compare like for like to struts. I wouldn't do a Miata front end. The suspension geometry is great, but they have weak bearings and racers have to replace them a lot. Maybe a RX8 or something bigger. Mazda really does build awesome handling and painfully underpowered cars... 

If you're going to fab it up, I'd suggest looking at circle track parts. They have everything you need from prebuilt control arms, hubs, uprights, all the way down to weld on bosses for shock mounts.

The problem is that the angles of the arms and length of the tie rods and all the particulars have an effect, and just because it's SLA suspension doesn't mean it's done right with camber gain and bumpsteer that is better than what you started with. Takes more math and geometry skill than I have to figure all that out, which is why I'm still on struts. I'd avoid the Mustang II prebuilt subframes that you see on drag racer sites. My understanding is that they usually have terrible geometry.

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Camber gain, shmamber gain. Just dial in your static and send it. It'll be fine. ;) I would not place the entire blame of a car being non-competitive on the fact that it has a strut suspension. Are M3s non-competitive? How about Porsche 911s and Caymans? Yeah, they have other crap in the rear but you get the point.

 

OP, what limitations of the strut are you planning on eliminating with your double-wishbone setup? Have you driven the car on track and gone through the process of dialing in the chassis? I'm not saying that the S30 has the most optimal geometry but to think you can just graft a double-wishbone setup into a car and have it be better is a bit silly. Why not just spend the time and money on dialing in what you have? Unless the real reason for the question is that you just want to play around and make something different, in which case as you were...

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Many newer strut suspensions use dual ball joints. I know BMW uses them on some of their vehicles, new Mustangs, etc. Not sure about Porsche. You still have to take into account that the Z was designed for a 175mm tire and when you put wide enough rubber on it to compete with today's cars they have issues with scrub radius and the more modern cars aren't running the same caster, ackerman, camber gain, etc that you'd find on a 1970 Datsun.

Grafting on a SLA setup that has better geometry should actually produce gains in performance. Not sure why you would argue to the contrary. 

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1 hour ago, JMortensen said:

Many newer strut suspensions use dual ball joints. I know BMW uses them on some of their vehicles, new Mustangs, etc. Not sure about Porsche. You still have to take into account that the Z was designed for a 175mm tire and when you put wide enough rubber on it to compete with today's cars they have issues with scrub radius and the more modern cars aren't running the same caster, ackerman, camber gain, etc that you'd find on a 1970 Datsun.

Grafting on a SLA setup that has better geometry should actually produce gains in performance. Not sure why you would argue to the contrary. 


I can see where this is going and I'm not interested in getting sucked into another tedious, head-banging, never-ending straw man argument. In fact, I'll bet the OP never returns or follows through so this is likely to turn into another pissing contest...

 

Sure, there are some modern strut suspensions that use split-lower arms but not all of them do, the E30/E36/E46 M3 for example.

 

I used Ben's statement as a jumping-off point as he decried struts as the sole reason the Z isn't competitive anymore which I don't agree with. It could be (is) a myriad of factors that all add up. It's not a malicious jab but a friendly argument, and he redeemed himself afterwards saying that in spite of the apparently non-competitive struts, his car handles fine, wizard-like even. And this is coming from someone that is actively competing.

 

You're getting things twisted, Jon. I like how you threw in "better geometry" into the argument when what I really said was, "thinking you can just graft a double-wishbone setup into a car and have it be better is a bit silly". Obtaining better geometry is not at all a trivial task, which is precisely what I had meant if you look back at the previous sentence, and most people don't have the knowledge and/or skills to pull it off. Maybe you can agree, considering the last paragraph in your first reply essentially argues the same exact point which you've then gone and contradicted in your reply:

 

Quote

The problem is that the angles of the arms and length of the tie rods and all the particulars have an effect, and just because it's SLA suspension doesn't mean it's done right with camber gain and bumpsteer that is better than what you started with. Takes more math and geometry skill than I have to figure all that out, which is why I'm still on struts

 

 

 

Quote

You still have to take into account that the Z was designed for a 175mm tire and when you put wide enough rubber on it to compete with today's cars they have issues with scrub radius and the more modern cars aren't running the same caster, ackerman, camber gain, etc that you'd find on a 1970 Datsun.

 

I run 225mm rubber on my Z and it's fine. Camber plates give me about -2.5° of camber. I'm not competing with anyone but it's not a bad handling car by any means. Ackerman doesn't matter as much as you think it does and caster/camber gain don't matter much either if you dial in enough static camber.

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Not really suspension swap, but something. Strut suspension is´t so bad, in fact it is like double whisbone with infinity long upper arm.

 

 

Roll center ~60mm above ground, caster ~7 deg, KPI ~15 deg, near zero scrub radius, and ofc. abjustable camber.

 

What kind of better geometry you have in mind? 

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3 hours ago, Neverdone said:

That last sentence literally caused every engineer who designs suspension for a living to have a simultaneous aneurysm.

 

So that's great, they're all dead now. I hope you're happy.

 

 

 

:lmao: The irony is tantalizing...

 

People, especially "internet experts", love to fixate on one attribute that they may or may not understand very well and always miss the big picture. I'm sure you can dig up endless amounts of convincing information on the great importance of Ackermann, or camber gain, or front toe settings, or rod/stroke ratio, or backpressure, ad nauseam.

 

What's lacking is looking at the system as a whole.

 

What is the use-case for the car? In this thread, we seem to be talking about a track car.

 

What's your maximum steering input on a road course? Maybe 120 degrees? Even with 100% Ackermann, you're going to see negligible differences between L/R slip angles. To quote an excerpt from page 545 in "The Multibody Systems Approach to Vehicle Dynamics" by Blundell and Harty (my emphasis in bold):

 

Quote

There exists some confusion over the significance of Ackermann geometry at speed. For ride and handling work, the significance is sometimes overstated. (...) The lateral forces to achieve 0.4g at 50mph are over 5900N for a typical 1500kg vehicle, so the Ackermann effect amounts for lateral forces of some 0.4% of the total - a small modifier on the vehicle as a whole.

 

It's the same story with caster angle, it's effects are also dependent on steer. Steer angles on the track are low and thus caster effects are minimized. It's a slightly different story at an autocross, depending on how tight the course is, but lack of caster can be mitigated with adjustments to static camber, camber compliance, and roll stiffness.

 

The solution to lack of camber gain is, you guessed it, static camber.

 

The various suspensions that have been put into cars were all invented for a reason. There is no best.

 

I hope I've done my part in resuscitating said dead engineers. 

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I have no idea why you took that turn Leon, I was simply trying to continue the discussion by pointing out that strut suspensions have evolved since 1970, not starting a pissing match. If you're happy with your static camber setting, more power to you. Have a nice day.

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Quote

Grafting on a SLA setup that has better geometry should actually produce gains in performance. Not sure why you would argue to the contrary.

 

You took what you said and what I corroborated and then completely contradicted it in your response to me, seemingly just to start an argument. That's the only way that statement could be taken, no matter what your intentions were. Point taken on the struts but the conclusion to your post was that statement above which certainly seemed like trolling for a pissing match.

 

Anyway...

 

If you're going to graft a double-wishbone suspension onto your Z, more power to you! I enjoy seeing cool fabrication projects. But when the premise involves just tossing something in because it might theoretically be "better", that doesn't fly around here and is the reason HBZ used to be great. This would've been thrown in the Shed long ago...

 

Image result for old shed

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Regardless of OP's likelihood of execution I think the spirit of discussion is quite useful. 

 

I'm not sure the motivation in trying to kill the discussion. The question was vague, yes, but the replies were interesting. We're no strangers to swapping parts here especially from other makes, and I also think we have members who have shown we don't just stick on components with bubble gum and duct tape. The scope of the suspension as a whole may not be executed perfectly given we don't know much about the OP, but a discussion of alternative setups I imagine would be useful. Mark's corvette or sc300? I forget which, but that conversion comes to mind as a well executed example.

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Like most discussions on the internet, I'm sure this would've went much better if it were done in person. I'm passionate about taking a data-driven approach to problem solving and it's frustrating when people don't read and process what's been written. Especially when we're having a technical discussion which involves carefully chosen wording and little riff-raff.

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On 6/6/2018 at 11:59 PM, Leon said:

Camber gain, shmamber gain.

 

If camber gain, shmamber gain isn't trolly, then what is?  Certainly doesn't look like carefully chosen wording.  Looks like fight picking.

 

Bad blood from the past?  JM seems very reasonable.

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14 minutes ago, NewZed said:

 

If camber gain, shmamber gain isn't trolly, then what is?  Certainly doesn't look like carefully chosen wording.  Looks like fight picking.

 

Bad blood from the past?  JM seems very reasonable.

 

No, it's not trolling and is indeed carefully chosen. Read the thread.

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Posted (edited)

The inevitable question is whether the effort in doing something ambitious (research, sourcing components, fabrication, testing and adjusting) is justified by the eventual benefits.  My personal feeling is that for those who have the skills and resources to do this successfully, the question no longer needs to be asked.  For the rest of us, it's too easy to get seduced by impressive theoretical options, that end up only causing frustration and dejection.

 

That said, my preference would be to start with some kind of suspension modeling software.  The more sophisticated ones are doubtless expensive, but there should be a basic one available as freeware.

 

A swap that used at one time to be popular, or at least occasionally encountered, was the front suspension from the C5 Corvette.

Edited by Michael

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I think with the modern trend of "I know what I am doing" by maybe some that are not as knowledgeable taking over the land scape asking questions are a good measure to check yourself. Whether there is merit in the response, or the questioner will follow solid advice will always be determined. 

 

Chances are people have different perspectives, priorities, and experiences, the benefit of the forum is that it brings people together. Some might have extensive track experience, others may have extensive autocross experience, others may know the intricacies of stance, and others may know the world of drifting. Suspension/steering for these activities are quite different depending on the course and layout. 

 

The caveat is always how much do you let the information influence your decision. Some may be bench racing, others may be suspension engineers, everyone is going to have an opinion. 

 

I think a good exercise is to entertain the options, that usually helps lay out your priority. Like maybe a double wishbone setup is the most stable with great camber characteristics and adjustability, but if adding additional suspension pickup points is out of your time/budget/etc then the priority obviously falls into limiting to something of a similar nature ala strut with single lower control arm. You don't have to act on every suggestion, but looking into it can help focus your own goals. 

 

 

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On 6/7/2018 at 3:34 PM, Leon said:

I used Ben's statement as a jumping-off point as he decried struts as the sole reason the Z isn't competitive anymore which I don't agree with. It could be (is) a myriad of factors that all add up. It's not a malicious jab but a friendly argument, and he redeemed himself afterwards saying that in spite of the apparently non-competitive struts, his car handles fine, wizard-like even. And this is coming from someone that is actively competing

 

Leon, you are correct and I would be remise to claim that the only reason for the Z's not being on par with newer cars is its strut suspension. All that is meant to imply is that at peak driver performance, a SLA front end WILL outperform a strut front end. Can mere mortals get to that point in driving? That remains to be seen. 

 

Going off topic, but the bigger issue for competition (for my case at least) is the lack of power. I'm at minimum class weight and with a 8.5/10 motor build, about 9lbs/whp, with the guys at the pointy end of the field closer to 6-6.5 lbs/whp. 

 

For auto-x the Z has a lot going for it; light weight, excellent weight distribution, narrow even with monster tires on it, and lots of space to modify and add parts. The class I race in allows for most of the foils in the suspension to be fixed, and the excellent aftermarket support these cars have found recently makes it easy to get the adjustable parts. I'm getting closer with the car, and still believe that the nut behind the wheel is the limiting factor. Once that ceases to be the case, I'll be sure to post pics of my front suspension conversion. 

 

I will say that doing a front end conversion like this is a fabulous way to add years of development to a car, if not well thought out, or completely ruin a good car if it's not thought out at all.

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OP is back. Thanks for all the input. I wasn't expecting so much discussion and diversity. So let me try to explain my purpose for the thread and my idea of a suspension swap. 

 

The strut arrangement is a good setup when all the geometry is right. My problem is I don't like the fact that the spindle is fixed to the strut. So the suspension will always be at an angle based on the rotating position of the lower control arm. If the suspension is a double a arm setup I feel like I will have  more adjustability. I like the idea of setting camber and having built in geometry that the camber remains under compression. So the shorter upper a arm, attached to the chassis at a more outboard point allows negative camber  to remain and can be better dialed in. Also, I feel like the suspension will move around less as a double a arm setup.

My previous track car was an 09 c6 z06. It was an awesome track car. I found the car to be unparalleled in high speed corners and of course the straights because of the power. Slow corners, I was unable to hang with the good Porsche's. Since I started this thread, I found something in the aftermarket that is for the Z and it is an awesome setup. I can't share anymore than that because I promised I wouldn't share the information. Keep your eye on Apex Engineering.

 

After looking more closely at the rear suspension and fender well of the car, it appears I will have to cut out the inner fender well and move it inward in order to create an attachment point for the upper a arm. The lower one is fine as is. Please share your thoughts on this. I want to do this because of my comfort in double a arms and because of the statement below about roll centers.

 

On a different tangent. I have some roll center questions. Determining roll center is easy enough for front and rear. It seems most cars are set up with a lower roll center in the front and the rear is typically higher. So that puts a roll center axis thru the car front to back not being level. So is that the best set up or is the best setup for cornering and tire wear to have the roll center level. Keep in mind, I realize roll center is dynamic. But is seems if the roll centers were more level it would be a better setup. Having said that, maybe a good cage  and stiff chassis with a roll center high in the rear would put alot of pressure on the front outside tire. maybe too much causing a huge push

 

Thanks

Roger

Edited by rabrooks

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6 hours ago, rabrooks said:

So is that the best set up or is the best setup for cornering and tire wear to have the roll center level

 

You used the b-word...

 

If I may summarize your post, you want to convert the front and rear suspension in your 280Z from struts to dual A-arms because you feel like you'll have "more adjustability" and "the suspension will move around less"? And because your Corvette couldn't keep up with Porsches in slow corners? Then some stuff about roll centers that showed a fundamental lack misunderstanding of what roll centers do.

 

Quote

But is seems if the roll centers were more level it would be a better setup.

 

You might as well say, "if your anti-roll bar rates were more equal, it would be a better setup". Roll centers are just one component of anti-roll which itself is just one component of vehicle handling.

 

It's all a system. You will be frustrated and lost if you're only looking at single characteristics in isolation.

 

You have to understand the problem first, ask yourself the right questions, research and execute. In reality, that's an iterative loop. Currently, there is a lack of understanding and lack of clarity as to your wants and therefore needs. I've seen the Apex kit and while nicely crafted, it represents the above statement.

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The z can have camber change under compression as well with the factory struts. Use roll center spacers to keep the control arm at a downward angle. The arc of the arm will have camber gain until you are past the level point of the arm, then will start loosing negative camber.

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