Rear suspension - Toyota conversion...

[johnl]

I've just completed my latest 147 project, namely to be rid of the horrid soft and squishy rubber bushes in the rear lateral control arms. Note that this is not a description of old knackered bushes, but relatively new ones on good crack-free condition.

The softness of these bushes is responsible for a very significant lack of lateral stiffness in the rear suspension, as well as excessive dynamic toe change as lateral force rises. The lack of lateral stiffness causes vague and relatively unresponsive handling, as well as degrading steering precision and directional stability. The excessive dynamic rear toe change (i.e. toe-in gain under lateral load) is intended to create rear stability when cornering, but adds to understeer (as does the lateral softness, probably). Both the lateral softness and the dynamic toe change cause erratic geometry changes, affecting stability both when cornering and when travelling in a straight line, especially on uneven surfaces.

The issue isn't so bad when the ambient temperature is fairly low, because the low temp causes the rubber in the Alfa bushes to harden up, and the car will tend to steer and handle a lot better when it's very cold outside. However, the underlying problem still exists, and the car is still not as good as it could be regardless of ambient temp (i.e. bush rubber temp). When the ambient temperature rises, the rubber softens up even more, so on hot days the problem becomes much worse (at least this is my experience).

Note that the bushes in the front arms are significantly softer than the bushes in the rear arms (which nevertheless are still quite soft). This is so additional dynamic toe change can occur under lateral load, i.e. the bushes in the front arms deflect more than the bushes in the rear arms, so under lateral load the toe gains more toe-in.

So, what to do? Hard poly bushes would be worth a shot, but can be problematic. By chance I discovered that some Toyota Camrys use rear suspension control arms that feature spherical bearings at each end. These are in effect the same kind of joint found in 'Rose' joints (aka 'Heim' joints or 'spherical rod ends') often found used on racing cars and it seems increasingly in some road cars. Unlike the ones used on racing cars, the Camry items are very well sealed against dirt and water, and are already attached to metal rods. The genesis of an idea. 

So, I bought some from a wrecker ($45). It turns out that I could use them for the outer ends of my proposed custom made control arms, but the (spherical bearings) are too wide to use on the inner end (and cannot be modified to make them fit). Modified plan; use half of a Toyota Corolla rubber bushed control arm (AE112, though other Corollas seem to use the same arms) on the inner end of each new arm (another $45 for a set of Corolla arms). I knew from a past project (my old Honda) that the Corolla control arm rubber bushes are much much stiffer than the Alfa control arm bushes, though again they are too wide, so they need to be narrowed to fit (fundamentally a careful hacksaw and file job).

Note that the Corolla arms also use softer bushes in the front arms, but they are still stiffer than any of the Alfa control arm bushes. I decided not to use them, and bought another set of Corolla rear arms (another $45...) so I could use the stiffer rear bushes in all my custom arms. Also note that the front Corolla arms do not have a length adjuster, but using four of the rear Corolla arms gave me length adjusters for all four of my custom arms.

Because they are all Toyota parts the Camry and Corolla arms use the same length adjustment (rear toe adjusters), so it was possible to just screw the Camry and Corolla arms together to form a complete control arm having a spherical bearing at one end and a fairly stiff rubber bush at the other end. The resulting custom arm is 'infinitely' adjustable for length using the Toyota adjuster, but even so are too short for the 147, so needed to be lengthened by means of welding in a tubular extension (the Toyota parts are tubular and solid bar construction, much better – i.e. less likely to flex with compressive loadings - than the folded tinfoil that Alfa uses).

I now have four rear control arms each with a spherical bearing at the outer end and a much stiffer rubber bush at the inner end. All four arms are adjustable for length, so not only is rear toe adjustable using the adjuster in the arm (or the Alfa cam toe adjuster if you wish), camber is as well.

Problems; other than the need to narrow the Corolla rubber bushes, the Toyota bushes and bearings use 14mm bolts, Alfa uses 12mm. So, it's necessary to sleeve the ID of the Toyota parts down to 12mm. The Camry spherical bearings are wider than the Alfa bushes, so the long bolt at the hub is a bit too short. I cut about 14mm off the spacer tubes and all is good (this does not significantly affect the stock distance between the centres of the outer bearings / bushes, if the tube were not shortened this distance would increase due to the extra width of the Camry bearings vs the Alfa bushes, i.e. the distance between centres remains about the same for the Alfa bushes and the Camry bearings, so leverages and geometry are more or less unaffected).
While I was at it, I decided to take the opportunity to make all four arms of equal length, instead of the front pair of arms being 32mm shorter. This meant pulling the subframe in order to drill (and file) new less widely spaced mounting holes in the subframe (for the front pair of control arms).

Many (most?) cars with a multilink rear suspension do use shorter front arms to create bump / rebound toe gain, but not all. For example the arms on both the Camry and the Corolla are all four equal length. This might not sound like much of an endorsement, but consider that the Lancia Delta Integrale also uses equal length rear control arms...

The idea behind the front arms being shorter is to create toe-in with bump and rebound motion. I did the drawing (CorelDraw) which tells me that for the 147 this equates to 0.4mm of toe gain at each rear wheel per 10mm of suspension travel. It's not really necessary to eliminate this, but it does create a 'non-linearity' in the geometry behaviour.

So, was it worth it? A definite yes. After the obligatory wheel alignment, the handling is now much 'tighter' and more responsive, the steering more precise, the car more directionally stable on uneven surfaces, and when cornering (i.e. much less need for steering 'corrections' to hold the line). Subjectively it seems like quite a lot less steering input is required for any given corner or direction change. The car seems to corner significantly 'flatter', with less body roll (at least in the initial phase of the corner).

Downsides? Well, the rear suspension is a bit harsher, but not nearly as much as I feared it might be. On smooth roads it's just 'firmer', it feels a bit like the damper rate has been increased somewhat. On coarse surfaces (such as dirt roads) it is definitely significantly harsher, but not drastically so (subjectivity warning, others may disagree...). The car is just a bit more 'skatey' on loose dirt surfaces. Keep in mind too that my car has a substantial (20mm) rear anti roll bar. Cars with a less stiff rear end may not be affected to the same degree...?

Regards,
John.

[Citroënbender]

A cracking read, and good for tickling the brain - thanks!

[johnl]

Glad someone is interested...

More k's with the modified rear suspension linkages, and the more I drive the car the more I like the result.

This is a major improvement in how the car drives. The steering and handling are now so much more 'competent' and confidence inspiring than it was with the stock control arms and bushes, it's very significantly better. The car now feels like a proper 'sports car' to drive, whereas previously it only really felt like it was trying to be one...

Words that come to mind; sharper, tauter, tighter, dare I say more go-kart like? Steering is much improved, with better 'on centre' feel, more immediate response to even small inputs. The steering wheel now feels quite a bit more 'connected' to the road, as does the chassis in general.

The car now tracks very true even on quite bumpy roads, i.e. directional stability is substantially improved. Tramlining is largely gone, where before it was significant. I presume most of the tramlining behaviour was due to poorly controlled rear wheel camber and toe deflections every time a wheel encountered any irregularity in the road surface, i.e. excessive rear steer and changeable camber thrust effects (likely more of the former and less of the latter).

Understeer is significantly less. The car is more predictable. There is a section of uneven surface backroad nearby where the car used to start feeling unstable and frankly a bit unsafe at speeds approaching 100kmh. Yesterday I found myself driving on the same stretch of road at 120kmh before realising how fast I was really going (easier if the speedo were more visible...). The car felt fine and quite composed (unlike before...).

I do think most of this is due to reducing flexure in the arm bushes, i.e. eliminating any deflection in four of the bushes (by replacing them with deflection free spherical bearings), and substantially lessening deflection in the remaining four bushes (by using stiffer bushes).

Some of it may be due eliminating - at least in theory - any toe change with bump / rebound (by making all four control arms the same length).

Some may be due to eliminating toe change caused by unequal compressive bush stiffness in the front vs rear arms (by ensuring front and rear arms use bushes etc of the same stiffness, i.e. not softer in the front arms).

Some may be due to replacing the bent tin 'U' section arms for more compressively rigid tubular / rod constructed arms. I'm not at all sure on this last point, but it wouldn't surprise me if the stock Alfa arms had a tendency to elastically 'bow' to some degree when subjected to a significant lateral compressive load. If so then this would not be a good thing to occur.

Surprisingly, the rear end feels not just laterally stiffer, but also vertically stiffer. It's now much easier to feel road irregularities with the rear wheel encounter them (than it was before). I suspect this may be due to the fact that the control arms angle slightly upward from the outer to the inner ends, so, a bump pushes the wheel upward which then has to also move slightly outward because the outer end of the control arm must move in an arc.

Due to the tyre having lateral grip this imparts a compressive force into the control arm, which previously was more 'absorbed' by the softer bushes (and any other incidental deflection in the arm, which may act like a spring of sorts), but now is more directly imparted into the subframe because deflection is substantially reduced. This equates to an effective increase in vertical stiffness because of the slight upward angle of the control arm, i.e. most of the bump force is absorbed vertically by the strut, but some is imparted into the arm both laterally and vertically (i.e. most of the compressive force imparted into the arm pushes the chassis laterally, but some pushes it upward, more so the more upwardly oriented the arms may be).

This is also felt in other ways. Today I had three people in the car (including driver). Previously this would make the rear of the car feel quite 'wallowy' over undulations in the road (like the dampers were way too soft), but with the new stiffer arms this effect seemed noticeably quite a lot less than with the original arms (and didn't hit the bump stops once, instead of several times as used to occur with three on board...).

The car definitely corners with significantly less body roll than before. I have a theory on the why's of that too, but that's more than enough typing for now...

Regards,
John.

[johnl]

Just in case anyone is interested,

From memory, the Camry rear suspension lateral control arms that I used were from an XV20 model (1997 to 2001).

The front pair of control arms from this car don't have a length adjuster, and I can't recall whether they have a spherical bearing at both ends, or whether it's a spherical bearing at one end and a rubber bush at the other (didn't look closely because I was interested in the rear arms, not the front).

The rearward arms do have a spherical bearing at both ends, and do have adjusters, but are not exactly identical. One rear arm has its adjuster in the middle, the other has it near one end, which makes no practical difference (but might be an issue if you are obsessed with symmetry...).

The Corolla arms are from an AE112, but as I said other Corollas seem to use similar arms. Front arms again have no adjuster, and in any case the front arm bushes are relatively soft vs the rear arm bushes, so it's better not to use them (still stiffer than any of the Alfa bushes). The rear arms do have adjusters that are compatible with the Camry adjusters, so half a Camry arm can be used with half a Corolla arm to make a complete arm with a spherical bearing at one end and a rubber bush at the other end.

So, two rear Camry arms and two rear Corolla arms give the parts needed to make four hybrid arms with a spherical bearing and rubber bush at each end (four spherical bearings, four rubber bushes, four adjusters). There is no reason why the spherical bearings from the Camry front arms couldn't be used, other than you don't get an adjuster with them so you will end up with a fixed length arm. It's useful to have adjusters in all four arms because this allows camber as well as toe adjustment.

All four resulting hybrid arms will be too short, so an extension tube must be welded in. The Corolla bushes must be narrowed to fit the subframe. From memory the original width is 43mm, and what you need them to be is 30 to 31mm (mine are 31, a bit of a squeeze to get them into position). As mentioned all four bush / bearing ID are 14mm, and need to be sleeved down to 12mm (this is only to do with positioning the arm relative to the hole, once the bolts are tight the spacer sleeves don't secure the arm in place, the bolt tightness does).

The width of the Corolla bushes must 30 to 31mm at the inner crush tube, but the outer tube needs to be a bit narrower by at least 2mm each side of the bush. This gives the outer sleeve some clearance to the subframe, to allow for unhindered motion.

The long hub bolt that secures the outer ends of both control arms is too short for the Camry spherical bearing width (too little protruding thread to tighten the nut on), so the spacer tube must be shortened as needed (about 15mm).

If you decide to make all four arms the same length, the subframe must be taken out to make new inner control arm mounting holes. Taking the subframe out is surprisingly easy...

Did I say that this modification is a HUGE improvement over the standard Alfa arms...?

Regards,
John.

[johnl]

I'm surprised this project hasn't generated more interest / questions.

Did I say that this modification has TRANSFORMED the handling of my car? Really, the more I drive it the more pleased I am. I doubt I've ever made a single suspension modification (to any car) that has had a more beneficial impact on the way in which the car steers, handles, and most importantly feels to drive. Maybe fitting Koni or Bilstein dampers, hard to say, close thing, in different ways.

I'm sure this would be translatable to the 156, GT, or any car using a vaguely similar rear suspension with overly soft stock control arm bushes.

IMO these Camry spherical bearings / control arms are a real find. All the benefits of 'spherical rod ends' but properly weather and dirt sealed. They are robust enough to be a standard fitment on a mass produced road car, so rapid wear shouldn't be an issue (as it tends to be with other spherical bearings, i.e. the kind typically used on racing cars). That, and they are already attached to rods that make it fairly easy to adapt them for use in other than Camry applications...

Regards,
John.

[ugame]

It's had 278 views worth of interest

I read it with interest, but as I had nothing to add to the post, I didn't comment. Others may be the same.

Keep up the great work. It's always good to be aware of alternative setups so that if the time comes and you're staring down the barrel of costly OEM parts, you can make an informed decision.

I dont have any issues with the handling on my 147 but then it's "only" the 2.0 TS and is the daily family car, and does that job just fine. Even when on a spirited drive through the hills.

....and on the Motorkharna day when I stole it from the carpark after my wife turned up.
In fact, that day it felt like it had the power and handling of a Ferrari. You get that feeling when the car you've just been tracking is a 1974 Beetle though

[johnl]

I didn't notice the 'views' number, just the lack of feedback. Nice to know someone is reading it.

If I'd posted something similar on the Honda site that I used to frequent I suspect I'd probably have generated a couple of pages of responses, from those lauding me as a genius to those condemning me as a heretical fool for questioning and corrupting the fundamental engineering choices made by Honda which would obviously make my car a death trap...

Yes, the 147 is a bit 'sporty', but personally I think the 147 (and 156, GT?) rear suspension is very compromised by Alfas choice to fit such soft rear control arm bushes. I suspect this is a product of Alfa trying to make the 147 (et al?) too many things for too many people, i.e. 'sporty' but not so 'sporty' as to put off the mainstream demographic.

I might say the same thing re Alfas choice of front damping rates. I might say the same thing about Alfas choice re the pathetically weak rear anti-roll bar (during my rear ARB conversion I had a few days where I had no rear ARB at all, and could feel no difference in the handling...).

Do the GTA versions use different bushes? I don't think they do, and if not then Alfa missed an easy way to make these variants much better handling and more focused cars, after all these were supposed to be the 'red hot' versions....

Regards,
John.

[Fetta GTV]

How do u go with registration inspection and insurance when you modify suspension components?
Does it require engineer approval when changing major components?

[johnl]

That is a rather, awkward, question.

To the best of my understanding, some suspension modifications don't require a certified engineers report (i.e. from a 'recognised signatory') or approval from the relevant authorities. This would include things like fitting 'uprated' bushes (such as polyurethane), fitting uprated dampers, changes in spring and anti roll bar stiffness, changes in ride height less than 50mm down or up. This doesn't mean that there aren't many cars on the road with such modifications that have been achieved in a less than desirable or competent manner...

Replacing things like complete control arms, as I have done, is I suspect more likely to require such a report and approval. That I have used components from another fully approved vehicle may negate this. That I have modified their length may have the opposite effect, mostly because it involves welding (if a cracked standard arm were repaired by welding, would that then be illegal?).

For me to engage a recognised signatory who is qualified to sign off on suspension modifications to 'light vehicles' (not all signatories are) is not easy. The nearest such person is hundreds of km away. I don't have the time. So, technically my car may be in breach, as for many reasons will be thousands of others I strongly suspect.

I am completely confident that my control arms are entirely safe. They are well constructed and certainly more robust than the (IMO) relatively flimsy stock Alfa control arms. They have the appearance of a 'stock' component. I am sure they will raise no eyebrows at the annual inspection. The cars handling (and therefore primary safety) is certainly significantly more stable with the replacement arms than with the stock arms.

Are there insurance implications if this modification is ever detected, quite possibly. Is this likely, I very much doubt it.

Move along, nothing to see here...

Regards,
John.

[Divano Veloce]

John, I'll let you know what I think of this mod next week...

[johnl]

John, I'll let you know what I think of this mod next week...

DV,
Those are some familiar looking parts, at least the control arms. Looks like each of those arms is half a Camry arm and half a Corolla arm, if I'm not mistaken?

Looks like you have narrowed the rubber 'silentbloc' style bushes (which would be the Corolla parts I assume), as I had to do with mine. I think it might be possible to fit the (wider) Camry spherical bushes into the 147 subframe, but the frame would have to come out for significant modification, i.e. some cutting, bending / widening to suit the wider spherical bushes, and welding shut.

Having both the joints in each arm being spherical bushes would mean zero complaince, which for handling would be somewhat better than one bush in each arm being rubber (at the expense of some additional increase in harshness, don't know how much but I suspect not a great deal). Not to worry, the Corolla rubber bushes are much stiffer than the jelly like Alfa bushes, and should be a big improvement along with the Camry spherical bushes (and at least a little bit of compliance is probably not all that unwise...).

If you had the subframe out (which is quite easy), might as well make new holes for the forward control arms so that all four arms could be made to be more or less equal length (i.e. forward two arms not shorter than rearward two arms, but very close to same length). This will reduce a roll oversteer geometry in the rear suspension (where with roll motion, the outside suspension going 'up' gains some toe-in and the inside suspension going 'down' gains some toe-out, creating an understeer promoting toe geometry as chassis roll occurs). Having all four arms more equal in length will reduce this tendency.

I don't recognise the anti roll bar? Looks Alfa, but appears thicker than the stock 14mm rear ARB. I don't think it looks thick enough...

Regards,
John.

[Divano Veloce]

Another option is the GTA alloy rear subframe. It has the the pin for the inner arm ends in single shear so the wider camry rod ends should fit (just with longer bolts). The GTA alloy frame may not be amenable to the equal length arm mod though.

The sway bar is 17mm GTA rear bar.

[johnl]

I didn't know the GTA had an alloy subframe (casting I assume), never looked at a GTA up that close. It does sound like a single shear attachment would suit the Toyota spherical bushes.

I don't know how much of a difference the equal length rear control arm modification makes. There is a theoretical roll understeer reduction, which may be significant, but may be minimal. My arm length modification occuured at the same time as getting rid of the soft bushes, so the effect of one change clouds the water re the other change.

If roll motion is greatly reduced (stiff ARB, springs etc.) then the understeer affect of the stock unequal length control arm geometry will also be reduced. My rear ARB is 20mm, but it's not an off the shelf / bolt on kit. It's quite stiff, but I see no reason why I'd want it any softer. The stock 14mm bar is so soft I couldn't feel any difference when I took it off in preparation for fitting the custom ARB.

I'm interested to hear your experience with this modification.

Regards,
John.

[Divano Veloce]

I've installed the rear arms and performed the equal length mod as well.

The handling has been transformed, as John has described - with no increase in harshness that i could feel.
This is a great hack using commonly available parts - well done John for sharing this with the community.

The factory Alfa bushes are quite soft, especially the front arm bushes. If one were reluctant to do the camry/corolla mod (which is a reasonable amount of work) a set of rear arm bushes installed in the front arms would help. But if I had another 147 the camry/corolla mod would be the FIRST thing I did to it.

[johnl]

Quite a difference isn't it. Goes to show just how important 'lateral stiffness' is at the rear of the car, if not stiff enough then it really takes the edge off the steering and handling response, not to mention causing that little rear end wiggle as the corner straightens out (more obvious on hot days when the rubber is warmer and softer). Pity Alfa uses such mashmellow bushes in the rear lateral control arms.

The bushes in the front Alfa arms are somewhat softer than the bushes in the rear arms, which is a common thing with this style of twin lateral control arm set up. It is deliberate, and is done so as to increase toe-in gain with lateral force acting on the outside wheel, i.e. the softer bushes in the forward control arms deflect more than the somewhat harder bushes in the rearward control arms, and this creates a tendency to increase toe-in and understeer under lateral loading. Car makers do so many things to intentionally induce understeer, this is but one of them.

This is also why the rearward lateral control arm is fitted so far behind an 'imaginary' line drawn between the contact patch and the upper strut mount, compared to how far less forward of this line the forward control arms are fitted. The further away from the 'line' the control arm is (to the front or to the rear of the line), the less compressive lateral force is leveraged into the arm, and the less the bushes will be compressed. The rearward arm is farther behind the 'line' than the forward arm is in front of the line, so the front arm becomes more heavily loaded with compressive force than does the reaward arm, so the forward arm bushes compress more (even if they were not softer) than the rearward arm bushes. This causes a gain of toe-in (and understeer) with lateral force acting on the control arms.

So in stock form, at the rear suspension alone we have several understeer inducing 'strategies' deployed by the suspension engineers. There is the shorter length of the forward control arms relative to the rearward control arms (creates toe change with roll motion, regardless of bushing stiffness). There is the use of softer bushes in the forward control arms and stiffer bushes in the rearward control arms (creates toe change with lateral force). There is the position of each control arm relative to a line drawn between the contact patch and upper strut mount (also causes toe change with lateral force). This is not to mention such obvious things as a puny rear ARB (which add understeer due to its puniness relative to the front ARB). There may well be other things that I have missed, wouldn't surprise me at all.

If using the Corrola rubber bushes it should be noted that the forward arm bushes are also softer than the reaward arm bushes (similar to the difference with the Alfa bushes, except that even the softer Corrola bushes are stiffer than any of the Alfa ones), and the rear Corrola arm bushes are the better ones to use.

Understeer may be a 'good thing' for the 'average driver' (who can't really drive very well), but it does not add to the fun at all. Having said that, understeer in some degree is rather essential...

Your next experiment might be increasing rear tyre pressure substantially (which increases lateral stiffness in the tyre casing). At present I have PS4 Michelins on the front, and these have quite a stiff casing and don't seem to like higher psi. I'm currently running 32psi in them, much more and the ride does get rather harsh, the inate stiffness seems not to need higher pressures to steer and handle well. I have some Maxxis tyres on the back, and these cases are not nearly as stiff, but respond well to higher psi without incurring excessive harshness. The higher the psi in my Maxxis tyres (when fitted on the rear) the better the handling becomes, and I kept increasing pressure until I'm now at 50psi (flame resistant suit is folded neatly next to my computer). I haven't gone higher, but there has to be a sane limit somewhere, and point of diminishing return. I'm not sure if the stiffer PS4s would respond as well to much higher pressures if fitted on the rear, haven't gone there yet.

Regards,
John.