Suspension Thread.

fastx19

fastx19

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In another post, @Steve Hoelscher and @Rupunzell were both commenting on not using the Miata suspension as there are much better choices. So, I thought it might be interesting to discuss what other options might exist out there for a custom setup. Note, this is not intended to be a bolt on product, instead, it would take quite a bit of fabrication to make it work.

Years ago, I was looking at the suspension from an RX7 or RX8 as well. If I remember correctly the reason was theirs was all aluminum and very light.

If anyone else has suggestions, please chip in.

Thanks!
 
Having just finished (well, 95% done) a suspension refurb on my car, it seems to me to cut unsprung weight, the most weight savings could be realized in the hub carriers/pillars themselves. They are cast iron or cast steel and crazy-heavy duty for a 2,100 lb car. But that would require very expensive fabrication or purpose built aluminum casting and machining, not cheap. Probably would not survive a realistic cost-benefit analysis.

Something that "should" be a lot less $$ than recasting the hub carriers would be to fabricate replacement rear control arms. Not only should some weight savings be realized, it would also provide an opportunity to upgrade or modernize the ball joint at the hub carrier end, a welcome option since replacing these ball joints requires a lot of effort and the replacement parts are pretty costly and are subject to whether or not whomever made the existing batch of replacements would want to be bothered to make another batch when this supply runs out. To a lesser extent the bushings at the chassis mounting points could also be re-evaluated, but these are under-stressed and replacements are plentiful.

Speaking of rear control arms, I read somewhere that early in the development of the X1/9 chassis and suspension, the engineers originally thought to simply graft the 128 front suspension lock stock and barrel into the rear of the X. From a production point of view you can see the attraction of using things already in the parts bin. However, road testing showed that the 128 front components simply were not up to the task of controlling the rear tires like the engineers thought they should to deliver the required road manners and stability, so they went with the stamped open c-channel arms with the welded and riveted ball joint.
 
Alternate suspensions on strut cars is a popular modification subject. We all know that cost savings was the McPhearson Strut design goal. Its easier to manufacture, package and assemble than most other independent suspension designs. However, the design limitations compromise its performance potential. It was the cost savings that made it popular in the economic duldrums of the late '70s and early '80s. So when people start talking about improving the performance of these cars the subject of improved suspension designs always surfaces. As with any engineering project the cost(effort)/benefit analysis should drive the effort to improve performance.

The first question that should be asked and answered is the end results desired. The answers can range from a slightly improved road car to a pure track weapon. The next quesiton is the scope. How extensively you are willing to modify the car and how much time/effort/cost are you willing to invest in the project.

To answer these questions we should evaluate the OE suspension and its capabilities and limitations. I will start by quoting myself: "the X1/9 is the best driving racing car I have ever driven". That was a bold statement at the time I made it (years ago) and one that is still relevant today. However, in the time since racecars have gotten better and I have driven quite a few more including things like the McLaren GT3 to a Radical RXC. Clearly the GT3 McLaren and Radical RXC are faster than the my DSP X1/9 but are they "better". The answer is difficult to quality but my brain and heart say "no". As a driver, my DSP X1/9 never failed to deliver if I was capable of executing.

Given the above, unless you are well down the path of building a custom chassis, with custom driveline, the need for something beyond the X1/9 struts suspension is pointless. The X1/9 strut suspension is about as good as you will find and remember no less than Porsche used McPhearson strut front suspension on their (996/997/991) GT3 factory racecars. So the strut suspension can be made to work exceedingly well. I have proved that myself with both my DSP X1/9 and my MP Toyota MR2.

If you want to build something beyond the capabilities of the OE strut design then using some other OE, double A-arm, design comes with its own limitations. In my experience the Miata suspension is pretty good but, like any OE suspension, is compromised by its intended use (street car, low cost, packaging and ease of manufacture). The RX8 and Lotus Elise are better but come with their own limitations.

Because I am now directly involved with the design and manufacturing of modern racing cars, and do thousands of laps in development testing, I have a much deeper frame of reference on great racecar design. We (Fields Auto Works) design and build a track car called the Cardinal. It incorporates a unique pull-rod suspension design that meets all of the criteria for an effective design. Its simple, light, functional, easy to manufacture and neatly packaged.

Cardinal Chassis Front.jpg


It takes more than just great suspension to make a great racecar and the Cardinal hits on all of the key points. Thus I can say it has surpassed what I was able to achieve with the X1/9. But then the Cardinal is a purpose build trackcar and not a modified production car. It has proven to be the best driving racecar I have ever driven. Now I can't wait to drive out new Scioto which should be ready for testing in a couple of months.
 
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McPhearson Strut suspension designs are not inherently poor, they are a given set of trade offs like any other suspension design. What makes them SO undrerdesiable for a track car.. they are SO tall.. due to geometry. Bit of McPhearson Strut and Lancia Stratos trivia, there were two versions of the Stratos chassis, one for Tarmac centric stages another for off road-dirt centric stages. The Tarmac centric stages got the all double A-arm suspension due to optimization lower need for suspension travel allowing the geometry of the all double A-arm suspension to have an advantage. For dirt-off road centric stages the strut suspension chassis was used due to increase suspension travel which was an advantage on those dirt-off road stages...

Point being, it is all a trade off with the decider being what the goals and needs are.

Back in the days of doing several LeMons races each year, much time was shared with Dave Coleman (that Mazda USA chassis/suspension guy) we share lots about suspension design and what the general public demands and needs. Mazda (and likely every other car brand) is well aware of what the average driver/customer wants and their capabilities as drivers. Due to legal liabilities, driver abilities and much more, car brands design, set up and "tune" any given suspension/chassis to meet these customer expectations.. which is very often extremely different than demands and expectations of enthusiast. Essentially before being overly critical of any suspension/chassis design, consider the audience it was designed and produced for..

Motor sports being what it is today is vast, it can range from production based cars to off road buggies and much more. Each specialty places specific demands on chassis, suspension and more.

Add to this modern aero cars with some being capable of generating 3-4 G peak due to aero, this adds another crinkle to chassis/suspension design. This also places very specific demands on the driver and how aero cars must be driven.. Tires become curious too as they are now required to work over a very broad load range due the dynamic range from no aero to full aero.. or a 1200 pound race car suddenly becomes an effectively well over 1200 pound car due to aero.

Or off road buggies where tightly controlled wheel travel is a premium. 2-3 feet of tightly controlled wheel travel is a very good thing..
This puts remarkable forces and energy dissipation on the dampers.. and the suspension bits take an absolute pounding in ways no track or road car will ever be subjected to..


Bernice
 
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Dan Sarandrea (Phila) said:
Having just finished (well, 95% done) a suspension refurb on my car, it seems to me to cut unsprung weight, the most weight savings could be realized in the hub carriers/pillars themselves. They are cast iron or cast steel and crazy-heavy duty for a 2,100 lb car. But that would require very expensive fabrication or purpose built aluminum casting and machining, not cheap. Probably would not survive a realistic cost-benefit analysis.

Something that "should" be a lot less $$ than recasting the hub carriers would be to fabricate replacement rear control arms. Not only should some weight savings be realized, it would also provide an opportunity to upgrade or modernize the ball joint at the hub carrier end, a welcome option since replacing these ball joints requires a lot of effort and the replacement parts are pretty costly and are subject to whether or not whomever made the existing batch of replacements would want to be bothered to make another batch when this supply runs out. To a lesser extent the bushings at the chassis mounting points could also be re-evaluated, but these are under-stressed and replacements are plentiful.

Speaking of rear control arms, I read somewhere that early in the development of the X1/9 chassis and suspension, the engineers originally thought to simply graft the 128 front suspension lock stock and barrel into the rear of the X. From a production point of view you can see the attraction of using things already in the parts bin. However, road testing showed that the 128 front components simply were not up to the task of controlling the rear tires like the engineers thought they should to deliver the required road manners and stability, so they went with the stamped open c-channel arms with the welded and riveted ball joint.
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A thought that might be added to Dan's excellent comments is in regard to the front suspension. If you were to build custom, lightweight hub carriers (uprights), then perhaps making new front suspension arms (similar to the ones he suggested for the rear) could be done. Not that the stock front arms are excessively heavy - as Dan pointed out - but in order to improve the design of the trailing arm / radius rod. More specifically the leading pivot / bushing affair. Another advantage to making new front arms is to utilize readily available components that will match whatever you want to use for the uprights / carriers.

Both front and rear tubular, redesigned suspension arms have been made by a couple of companies (not sure if they are still available):
Front....
Ft arms - Copy.jpg

Rear....
Rr arms - Copy.jpg
 
Aero changed track race cars and suspension design ... in remarkable ways since then..
~Gordon Murrary's Brabham BT46B



Bernice
 
and remember - aluminium always fatigues - always. Every alloy, every application. It is a fundamental aspect of aluminium. Then we have lack of stiffness. Ally is one third the stiffness of steel. In general terms, redesigning a steel part in ally gives a 50% weight reduction although ally is one third the density of steel. This is due to beneficial geometric effects - the ally part must be larger due to low material stiffness and as you increase size, your geometric stiffness rises [non-linear]. The product of material and geometric stiffness usually allows 50% weight reduction. But - ally is not good at temperature and the stronger alloys suffer more. The summary is that if you want to use ally in highly stressed and or hot areas, the design is non trivial and the new part will look very different from the original steel part. I have not looked, but I suspect that advice for improving the various production cars that come will ally arms is to replace them with steel to improve stiffness :)
 
Steve Thomas said:
and remember - aluminium always fatigues - always. Every alloy, every application. It is a fundamental aspect of aluminium. Then we have lack of stiffness. Ally is one third the stiffness of steel. In general terms, redesigning a steel part in ally gives a 50% weight reduction although ally is one third the density of steel. This is due to beneficial geometric effects - the ally part must be larger due to low material stiffness and as you increase size, your geometric stiffness rises [non-linear]. The product of material and geometric stiffness usually allows 50% weight reduction. But - ally is not good at temperature and the stronger alloys suffer more. The summary is that if you want to use ally in highly stressed and or hot areas, the design is non trivial and the new part will look very different from the original steel part. I have not looked, but I suspect that advice for improving the various production cars that come will ally arms is to replace them with steel to improve stiffness :)
Click to expand...

The entire suspension of my Giulia is Aluminium. As are the subframes, as it is in Ferrari's as well. Just sayin'.

1696982411662.png


1696982209282.png


1696981939463.png
 
SuperTopo said:
The entire suspension of my Giulia is Aluminium. As are the subframes, as it is in Ferrari's as well. Just sayin'.

View attachment 77927

View attachment 77926

View attachment 77925
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I aint't saying you can't, I am saying its a high end design task supported by lots of development etc - and still, is fatiguing but will have been designed so that failure should be beyond anticipated life of car and or a very expensive service lies in the future if the individual components have been lifed.

It is pretty :)
 
Rupunzell said:
One more item...

Often not to never considered, improving the driver.. instead of "improving" the car..


Bernice
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Exactly put a good driver in a poorly set up car and they can usually drive it better than a crappy driver is a well set up car. Its like I used to tell my girls, if you cant hit with a $30 bat, a $400 isnt going to help.

Odie
 
Aluminum suspension components are common in modern vehicles. These are typically cast aluminum alloy that has been extensively modeled using FEA to ensure it meets the required lifecycle standard of the manufacturers. Aluminum alloy suspension components reduce unsprung weight and therefore improve ride quality. Also, the reduced weight improves fuel efficiency.

Back on the alternate X1/9 suspension subject; some years after retiring my X1/9 racecar I built a 1st generation (AW11) MR2 for entry in the "Prepared" category (D Prepared to be specific). The Prepared category allows extensive modificiation to the original suspension type. So a strut car must retain the strut suspension but the components and mounts are unrestricted.

The AW11 chassis is remarkably similar in architecture to the X1/9, the front suspension is virtually a direct copy. The rear is similar but is where Toyota made some mistakes. Using the lessons learned from the X1/9 I redesigned the MR2 geometry and fabricated simple tubular components with rod ends replacing the bushings. The revised geometry put the roll centers where I wanted them, corrected bump steer problems and improved the typically bad strut camber curve.

Front suspension (shown in full compression for range of motion study):

SAM_3150.JPG


Rear suspension shown at static ride height:

0329161317a.jpg


Note how low the car sits. Static ride height for the new suspension is below the point where the stock suspension bottomed. Yet adequate suspension travel is maintained and geometry is optimized.

This photo is of the car at max lateral g (approximiately 1.6g). Note the tires are virtually square with the pavement and the limited body roll. This is the result of all of the development work on geometry and re-engineeing the strut suspension to work as desired. Notice too the ride height. The car cannot reasonably be any lower as it will drag the bellypans and differentical housing if any lower. Note the rocker panel's pinch weld is below the hight of the wheel rim.

shoelscher-2.jpg


The point here is that this car's primary competitor is the Miata, with its double A-arm suspension, and yet this MR2 is as quick or quicker than any of the Miatas it competes agains. It as won 3 SCCA National Championships and would have won 3 more if not for cone penalties.

This demonstrates what can be accomplished, fairly easily, with the X1/9s existing strut suspension if a little thought and effort is applied. One of the benefits of using a fabricated tubular lower control arm is the option of using an alternate upright (hub carrier). The AW11 MR2 uprights are lighter than the X1/9s, more robust wheel bearings, upgraded brakes and a 4x100 wheel lug pattern. With this in mind it would be very easy to convert the X1/9 to MR2 uprights, realize all of those benefits and improve the X1/9s suspension geometry for performance applications without the effort required to convert to double A-arm.
 
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Steve Thomas said:
and remember - aluminium always fatigues - always. Every alloy, every application. It is a fundamental aspect of aluminium. Then we have lack of stiffness. Ally is one third the stiffness of steel. In general terms, redesigning a steel part in ally gives a 50% weight reduction although ally is one third the density of steel. This is due to beneficial geometric effects - the ally part must be larger due to low material stiffness and as you increase size, your geometric stiffness rises [non-linear]. The product of material and geometric stiffness usually allows 50% weight reduction. But - ally is not good at temperature and the stronger alloys suffer more. The summary is that if you want to use ally in highly stressed and or hot areas, the design is non trivial and the new part will look very different from the original steel part. I have not looked, but I suspect that advice for improving the various production cars that come will ally arms is to replace them with steel to improve stiffness :)
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Sorry for the nitpick, but loss of stiffness and strength is a function of temperature, chemical environment, load/type of load and number of load cycles. Happens to all metals.

Also, the vast majority of metals including steels and aluminum/aluminum alloys have pretty much the same specific stiffness. Examples of outliers are copper/copper alloys which have low specific stiffness and beryllium/beryllium alloys which have much higher specific stiffness that exceeds most carbon fibers. Stiffness based designs are usually driven by minimum part thicknesses that are functions of manufacturability, stress, buckling, damage resistance and/or other processes such as corrosion protection. In summary, other factors other than stiffness would determine choosing one metal versus another.
 
bruinbro said:
Happens to all metals.
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yes but no but. If most steels are kept to reasonable stress levels, then their fatigue life is effectivly infinite. Fancy steels and high stress not so much. All aluminium, from pure to alloyed to hell and back has finite fatigue life at any stress level.

Same with temperatures - most steels are good to quite high temperatures but aluminium loses strength very quickly with rising temperature.

Specific stiffness is not the whole picture [a bit abstract] - You actually get better than specific stiffness would suggest if you redesign from steel to ally. The ally part has to be bigger in section to meet the stiffness of the original design but not in proportion to the relative difference in modulus. As the part gets larger, geometric stiffness help. Hence, generally, an ally redesign will be 50% of the weight of the original steel. Specific stiffness woul;d suggest that redesign from steel to ally would not save any weight - not the case. Except if we are talking say, a simple tension member in which case, no geometric benefit and the ally part will weigh the same as the steel part for the same stiffness.

Sadly, ease of manufacture and lowest cost/price drive most material choices.
 
Steve Hoelscher said:
Aluminum suspension components are common in modern vehicles. These are typically cast aluminum alloy that has been extensively modeled using FEA to ensure it meets the required lifecycle standard of the manufacturers. Aluminum alloy suspension components reduce unsprung weight and therefore improve ride quality. Also, the reduced weight improves fuel efficiency
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Absolutly - and they are cheap to mass produce. Ally is a very nice production material but do not try and do ally suspension parts at home children!
 
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