Honda suspension comparison.

[JohnL]

LOL

was waiting for your post

I couldn't let that statement stand. I just don't like Mac Struts, they aren't 'nice' engineering. If it weren't nearly impossible to design a beam axle with a low enough roll centre, a front beam axle might even be a better bet than a Mac Strut.

but you didn't make much comment of the two suspension designs compared in this thread

That's because I'm not all that familiar with the detail of these different suspensions.

I have to assume that one basic design is similar to that of my CB7 Accord, in having a radius rod forming the forward part of the lower 'wishbone', and the other is like that in my nephew's EG Civic, having a lower control arm rigidly attached to and in front of another substantial forging, these two forged components forming the lower 'wishbone'??

If so then as a matter of principle I prefer the radius rod design because the radius rod is loaded only in tension / compression and as a result is reasonably light (less unsprung mass, always good). On the other hand the heavier forged leading arm of the EG Civic style wishbone (from memory) seems to be largely loaded in 'bend', and relies upon it's rigidity in bend to resist deflection of the wishbone (which will be most highly loaded under heavy braking).

This is because the second forging is shaped to allow clearance of the tyre when the inside wheel is turned to it's fullest extent. To make a steel component rigid in bend requires it to be rather substantially massive, or of a rather substanially proportioned hollow section. I suspect that despite it's size, this forging possibly won't be stiff enough to give as high a resistance to deflection as the radius rod probably will...

The problem is that it's hard to package a simple and lightweight radius rod behind the LCA because it will interfere with the amount of steering lock that is possible when the inside wheel is turned, i.e. before it's been steered all that far the inside front wheel will come into contact with a straight radius rod located behind the LCA because the inside wheel needs to turn much more than then outside wheel (because of Ackermann geometry).

The only ways to avoid this are to minimise the Ackermann geometry, minimise steering lock (and thus maximise the turning circle), to attach the radius rod to the LCA half way along it's length instead of nearer the outer end of the LCA (which will massively increase loadings on both the LCA and the radius rod), to reduce the distance between the points at which the LCA and radius rod attaches to the chassis (which will increase loadings on the radius rod), or most practically to use a substantially robust forging shaped to clear the fully turned inside wheel as a substitute for a radius rod.

When using a lightweight straight radius rod, it's easier for steering clearance if the radius rod is located in front of the LCA. The only downside is that a substantially rigid location must be provided for the attachment of the front ends of the radius rods, meaning that a more robust front cross member must be fitted.

[chargeR]

Any of the SLA ('double wishbone') front suspensions will in principle be superior to the Mac Strut. Having said this, a sensibly modded Mac Strut will be superior to a poorly modded (or designed) SLA suspension, but all else being equal the SLA will be better out of the box (typically, but the Devil is in the detail), and have more scope for improvement, especially for a FWD car.

Mac Struts are a very compromised design, but do have advantages in that they are compact (easier to package into the chassis due to lack of upper wishbone), they are robust, they are lightweight, and they are relatively cheap to make.

Did I say they were cheap?

On the other hand Mac Struts don't change camber enough with suspension motion (which makes them very sensitive to body roll causing substantial unwanted camber change relative to the road surface), the caster angle unavoidably changes with suspension motion, the damper is subject to quite substantial internal loadings that are the result of lateral forces and braking forces being reacted within the damper body (between the piston and the damper tube wall).

This latter problem isn't an issue for SLA suspensions because all forces (other than vertical ones which the damper is well suited to dealing with) are reacted through the upper part of the suspension 'upright' (aka 'knuckle' etc) and in the upper wishbone (not in the damper), but with a Mac Strut the damper body and rod are forced to act as if they were the suspension upright....

Mac Struts are not well suited to wider tyres due to the limited camber change, and tend to require excessive static neg camber angles to compensate for this (more so with wider rubber), but this causes other problems...

Even with substantial static neg camber this does not really make up for the geometric deficiencies of a Mac Strut, just alleviates them somewhat by maximising the lateral grip of the outside front contact patch (i.e. pre existing static neg camber helping to keep the OF wheel near vertical when cornering hard) at the expense of the inside front contact patch, which ends up being very small with a very substantial dynamic camber causing the tyre to be running on it's very inner edge.

Sure, Porsche use Mac Struts on the 911, but on these cars not much is really asked of the front end, all (most of) the lateral and longitudinal traction action occurs at the back end due to the heavily rearward weight bias and the need for rear traction dictating a relatively very roll stiff front end that unloads the inside front wheel very substantially when cornering (thus the dynamic camber angle and grip of the IF is laregely irrelevant...).

Now for a FWD car we need to keep the inside front contact patch planted heavily on the ground (i.e. low front roll stiffness relative to rear roll stiffness) and presented as 'squarely' to the road as we can manage in order to maximise it's grip in order to minimise understeer and maximise traction exiting corners. This is not acheived if we allow the IF to lean over at drunken angles with only it's inner edge in road contact, yet this is what we are more or less forced to do when setting up a Mac Strut for 'high performance' applications.

When trying to get the most out of a Mac Strut design, we can't really make a silk purse out of a pig's ear (Mac Strut = pig's ear), at best we can make a purse that looks a lot less pig's ear-like than it actually is...

Note that for all purpose designed modern race cars (not racers made out of modded road cars), SLA is the suspension of choice at every corner of every car...

Great post! "You must spread some Reputation around before giving it to JohnL again." . It is good to read an accurate comment on the Macpherson strut suspension not simply the "New hondas have Mcstrut suspension so they are automatically crap" mentality that seems to be prevalent.

yeah, just cos you have a dc5

DC5 front suspension works okay despite being Mcpherson strut and a quite poorly designed one at that. Care to come to the track to compare the relative merits of each suspension architecture?

[Bludger]

I couldn't let that statement stand. I just don't like Mac Struts, they aren't 'nice' engineering. If it weren't nearly impossible to design a beam axle with a low enough roll centre, a front beam axle might even be a better bet than a Mac Strut.

I agree totally, Macpherson struts are just a cost cutting thing.


Interesting points you pointed out there John, my assumptions have always been that the A arms were a better design from Honda solely because they just appeared to be more beefier and stronger than the counterpart. Taking into consideration the forces applied to the LCA's when accelerating & braking, I still would have thought that the A arms would be able to handle the forward/rearward forces better. But I think someone with your background would have a more credible point of view than one coming from me. So I'll take your word for it that the Radius rod design is better.

Would love to be able to see a scientific experiment testing and deciding conclusively which is better.

Thanks

[JohnL]

It is good to read an accurate comment on the Macpherson strut suspension not simply the "New hondas have Mcstrut suspension so they are automatically crap" mentality that seems to be prevalent.

Not "crap", just compromised, and a pity considering that older Hondas were fitted with a superior / more sophisticated design, so the cruder Mac Strut represents a backward step from Honda.

It is always surprising that Mac Struts can be made to work as well as they can be made to work, but I suspect much of this is down to the ability of modern high performance tyres to overcome suspension deficiencies (up to a point).

DC5 front suspension works okay despite being Mcpherson strut and a quite poorly designed one at that.

You said it; "works okay despite being Mcpherson strut". All else being equal, if it were an equally well sorted SLA it would be better.

Care to come to the track to compare the relative merits of each suspension architecture?

Who would we get to ensure that all the other pieces of string were equally long?

[chargeR]

Not "crap", just compromised, and a pity considering that older Hondas were fitted with a superior / more sophisticated design, so the cruder Mac Strut represents a backward step from Honda.

It is always surprising that Mac Struts can be made to work as well as they can be made to work, but I suspect much of this is down to the ability of modern high performance tyres to overcome suspension deficiencies (up to a point).

I think the issue is that the earlier double wishbone hondas have a great, well developed suspension design compared to most other FWD cars. The sector of the car market that FWD hondas seem to occupy is generally filled with cheap and easy Macpherson struts and torsion beams and the EGs and their like seem like a bit of an oddity. Now that Honda has begun cheaping out and blessing us with simpler and cheaper suspension structures, the performance of which the general consumer will be unable to seperate from the earlier designs, we are right to complain .

You said it; "works okay despite being Mcpherson strut". All else being equal, if it were an equally well sorted SLA it would be better.

Undoubtedly. But all cars have their flaws for performance use, but particularly production cars. And if one is forced to use a production car, who is to say whether the advantages of some of the platforms fitted with McStrut suspension will or will not outweight the disadvantage inherent in the suspension?

Who would we get to ensure that all the other pieces of string were equally long?

Why try to make the competition fair, I am already at a significant disadvantage .

[tseesinngwailo]

Awesome info JohnL , what is your background?

And is this the reason why my DA Integra doesnt have the turning circle of my Wife's EG?

The really big money question is though, when I sell my DA and upgrade, is a DC2R going to be a better handling car than an EP3R Civic (my two choices)

Cheers
Chris

[Bludger]

Awesome info JohnL , what is your background?

And is this the reason why my DA Integra doesnt have the turning circle of my Wife's EG?

The really big money question is though, when I sell my DA and upgrade, is a DC2R going to be a better handling car than an EP3R Civic (my two choices)

Cheers
Chris

according to what John has just said, the radius rod design would have more ability to have a greater turning circle than the A arm.

so DA should have more than the EG.

might not be the case in practise.

Also as said, if all being equal, double wishbone setup over Macpherson struts.

so dc2r > ep3r

[JohnL]

I agree totally, Macpherson struts are just a cost cutting thing.

Sad but true. Not that Mac Struts are necessarily a bad thing for the average shopping trolley, a perfectly suitable design for such an application...

my assumptions have always been that the A arms were a better design from Honda solely because they just appeared to be more beefier and stronger than the counterpart. Taking into consideration the forces applied to the LCA's when accelerating & braking, I still would have thought that the A arms would be able to handle the forward/rearward forces better.

The problem is the shape of the forging, i.e. it's effectively bent, forces can't pass through it in a straight line. Any time a member has a bend in it, it needs to be much more substantial in order to adequately resist forces as they 'negotiate' that bend, i.e. any bend creates a weakness that will often require a very large increase in the mass or size of that member to match the rigidity of a straight member.

Keep in mind too that the greatest loading these members will ever see (short of a crash loading) are going to be the forces created by heavy braking. Due to being in front of the contact patch, the radius rod will 'see' this force as a tensile force attempting to stretch it, and will be able to resist such a force very easily (how much weight could hang from a bar that thick, with effectively zero stretching of that bar? quite a substantial amount I'd suggest).

Due to being behind the contact patch, the forged component of the other design will 'see' a braking force as a compression that is attempting to increase the bend which already exists in the forging. It may well be strong enough to not flex a great deal under this loading, but it will inevitably flex to some degree.

The forging may possibly be nearly as rigid under heavy braking as the radius rod, but if so then it's much heavier to achieve it (which isn't likely to be a significant issue for a road car, and only a minor one for a racer). I doubt there's actually much to choose between the two different approaches to the lower wishbone design, until braking forces start becoming very substantial...

[JohnL]

I think the issue is that the earlier double wishbone hondas have a great, well developed suspension design compared to most other FWD cars.

A well designed suspension compared to most other cars period, FWD / RWD or 4WD, better than BMW for instance. Honda really pioneered this style of SLA suspension (with the very tall upright), it has been copied since.

The sector of the car market that FWD hondas seem to occupy is generally filled with cheap and easy Macpherson struts and torsion beams and the EGs and their like seem like a bit of an oddity. Now that Honda has begun cheaping out and blessing us with simpler and cheaper suspension structures, the performance of which the general consumer will be unable to seperate from the earlier designs, we are right to complain .

That's the problem, Honda was competing on price against other more or less similar cars (at least similar to those who don't appreciate or care about the finer points of Honda engineering) that had cheaper suspensions. Honda had a better suspension but this meant nothing to 99% of their potential customers.

Even the typical more 'sporting' driver has little understanding of the superiority of the SLA over the Mac Strut, which are now so ubiquitous that most expect no better. Frankly, with modern tyres at relatively moderate speeds, most of the time it would be hard to tell the difference between an SLA and a Mac Strut suspension, at least you'd be hard pressed to tell any difference on the typical test drive.

Undoubtedly. But all cars have their flaws for performance use, but particularly production cars.

My experience of Hondas with SLA suspensions (other than the more sporting variants such as the various Type Rs of which I have no experience) is that while the basic suspension design is terrific, the affect is somewhat spoiled by the very soft spring / damper rates, and the tiresome understeery not very responsive set up. They are however an exceptional basis for improvement.

There are some hidden weaknesses in some, e.g. the rear anti roll bar attachments (chassis and suspension) on my CB7 are (were) unacceptably flexible and have had to be replaced with stiffer items or other wise modified.

And if one is forced to use a production car, who is to say whether the advantages of some of the platforms fitted with McStrut suspension will or will not outweight the disadvantage inherent in the suspension?

From a performance perspective, any chassis needs to be only two things; light and rigid. A light / rigid chassis with Mac Struts may well be a better choice than a car with SLA suspension but is heavy and not so rigid. It's all a compromise, picking the best compromise is the challenge.

[JohnL]

Awesome info JohnL , what is your background?

Chris,
My interest in chassis dynamics started when I was racing karts and also designing kart chassis (from first principles) that were in detail not quite like any other kart chassis (project abandoned due to lack of funds).

And yes, karts do have suspensions, it's just that they lack discreetly defined articulations as cars conveniently have. The laws of physics apply in exactly the same manner with karts as they do with cars (or trucks...etc), it's just that the manner in which car and kart design exploit the physics varies in detail. Other than this I'm just an amatuer who's read widely and given this sort of stuff a lot of thought...

And is this the reason why my DA Integra doesnt have the turning circle of my Wife's EG?

There could be clearance issues other than the exact stlye of LCA longitudinal location.

The really big money question is though, when I sell my DA and upgrade, is a DC2R going to be a better handling car than an EP3R Civic (my two choices)

I can't possibly say, I have no familiarity with these particular cars.

I will say that just because car A has an SLA suspension and car B has Mac Struts, it doesn't necessarily follow that car A is the better handling car, there are too many variables involved to make such a prediction. It would however IMO be reasonably safe to assume that car B has the greatest potential to be made into the best handling car, if it isn't already...

[JohnL]

according to what John has just said, the radius rod design would have more ability to have a greater turning circle than the A arm.

so DA should have more than the EG.

might not be the case in practise.

The fact that the EG has the longitudinal locating member behind the LCA in principle tends to limit how far the inside wheel can be steered, but, it also depends on just how much clearance is built into any effective 'bend' in this forging.

It also depends on the inward angle of the radius rod for the other design, and whether or not there are other unrelated clearance issues. The devil is always in the detail, but steering lock is very often limited by clearance of the tyre sidewall to other parts of the car at the inside wheel because Ackermann geometry causes the inside wheel to be steered substantially more than the outside wheel.

[SHOGUNOVDDRK]

And is this the reason why my DA Integra doesnt have the turning circle of my Wife's EG?

Chris, not forgetting lowering and Rim/Tyre size does affect handling aswell.