Soarer Wheels, Tyres & Suspension|
There is only thing that is constant no matter what car you drive, you only have tiny points of
contact with the road; your Tyres, and they are so crucial that Companies will spend 10's of
millions of pounds on development. 9/10ths will see no end product, but the other 1/10th is what
lets us drive with hardly a thought or care knowing full well that whichever manufacturer made our
tyres they will do their job better than we can, as drivers, do ours.
The fact is most drivers [for 99.999% of their driving time] don't give them a second thought. Only
after an incident do we suddenly not take them for granted. The most common incident is the
breakaway around a favourite bend, we get out check that there is still some tread, reassure
ourselves all is well, promise to check the pressures at the weekend and proceed with a little
circumspection, 'til the next time. But being Soarer drivers you're a cut above the norm and you
want to know why, and how, this happens.
The key words here are Slip Angles and Hysteresis. You will be familiar with the terms Toe-in and
Toe-out [look at your own feet], and understand perfectly well that if all four wheels on your car
pointed straight ahead any undulation in the road would send it off course and the first bend you
took at even quite slow speeds would feel very awkward. You need to point the wheels to oppose
one another on each axle, think of it as like an arrow without the pointed end, instead just butt
ended, its flight would loose its accuracy, that accuracy comes from the opposing forces working
the entire surface of the pointed head because the arrow travels in 3D, we need toe-in and toe-
out to do the same for us on tarmac.
It's a tribute to modern Tyre and Suspension design that so much sure-footedness is delivered
with such a tiny amount of opposition, this has come about because of the increasing accuracy of
the Suspension manufacturers machinery which meant more design specific tyres could be
made. This thanks largely to the efforts of Citroen and Michelin. Previous attempts at front wheel
drive [e.g. Cord of USA] were vastly expensive due to this necessary accuracy, and were
[usually] not intended for high production numbers.
So now we have a stable motorcar, able to travel in a straight line very nicely, then the road
curves away. Round you go and it is at this point the Slip angle and Hysteresis come in to play,
[they were there even when we were moving straight ahead, but to a much lesser degree]. If the
tyre gripped the road perfectly then you would come to a dead stop, the tyre has to give up its
grip for you to go somewhere so it must not stick to the road like glue! Now just as the tyre gives
up its grip to go forward it has to give up some of its grip when we corner we call the difference
between the perfect theoretical line and the actual line travelled the slip angle and how it lets go is
the Hysteresis. The latter is the bit that can mean life or death for any driver.
Imagine if you will a tyre that had fantastic amounts of grip and in a particular corner could get
you round at 90mph but at 91mph lets go with no warning. You just crash. I know that my speed
would always be well below the 90mph limit. Now, if I used a tyre that could go round at 85mph
but started telling me that it is losing grip from 70mph and did it in such a way that it inspired
confidence I know I would be a better, safer driver with that tyre fitted to my car! I have to say that
some tyres, namely the top grade Yokohama's, Goodyear's and Bridgestone's have such high
levels of grip in the dry that it is very difficult to gain any experience of their final slip angles until
sometimes its too late and you are in a ditch wondering what the Hell happened.
For many drivers these tyres are too like the first of the above examples. By necessity these very
grippy tyres have a subtle Hysteresis loop, which only shows itself at quite remarkable levels of
adhesion in the dry, but when its wet or damp things happen much quicker than with an ordinary
tyre. Having recently very nearly 'lost it' in a good friends R34 Skyline running the grippiest tyres a
have ever experienced I can say from terrifying experience, they me gve no warning that they
were at or even near their limit.
REMEMBER A LAW OF PHYSICS, THE HIGHER THE LATERAL LOAD, WHEN SHE GOES,
THE QUICKER AND MORE FORCEFULLY IT WILL HAPPEN.
So, lets see if we can avoid these 'brown underpants' moments.
First, do you need all that grip? Simply put, it all depends on your driving style and ability and how
deep your pockets are! Also are you getting the best out of what you already have? Go out to
your car with a pen and pad and get some info off the Tyre sidewalls and the Wheelrims, the size
[225/55×R16], the Uniform Tyre Quality Grade [Treadwear XX[X], Traction X[X], Temperature X],
Plies [Sidewall [X], Tread [X],[X],[X] , rims 16×7JJ (50) with the X's filled in by you. If you have
different makes all round your car then you may need a bigger pad you may also be running
different rim sizes and tyres make a note of the lot. Oh, and remember to look for the words
'ROTATION' with a little half arrow.
That was fun wasn't it!, some info isn't there is it!, did you look on the inner wall?
OK, lets start, tyre size the '225' bit means the overall width of the tyre is 225 mm at its maximum
and you should, at least, have the same size on the same axle! The '/55' is the Aspect Ratio and
is represented as a percentage of the width as the height of the sidewall in this instance, 55% of
225=123.75 mm, again, you should have the same A/R on the same axle!
The 'R' bit means it's a Radial Ply tyre (more of that later) next up the '16' means the tyre fits a
16" rim, by the way, ever wondered why we have mixed units? I mean mm & Inches. When all
tyres were Crossplies they were measured in the Sopwith decimal inch system i.e. 5.90×13 etc.,
I've not a damn clue why the Sopwith system apart from the fact that Tommy Sopwith was a fine
Engineer, but so it goes. Then there was the collaboration between Citroen and Michelin and you
guessed it, they're unit of measurement was, and still is, Metric and the Michelin was the first
proper Radial and it was so superior that it took the World by storm. So all radials are measured
Metric except of course the Diameter.
The UTQG is very useful, don't listen to those who say 'it means nothing' they are, in almost
every way, incorrect. The first number relates to how hard wearing the Tyre is, 100 means 30,000
miles of normal use by a 100 HP, 22 Cwt motorcar, this translates to about 9,000 miles in our
Lexii. (d'yer fink dat's the plurus fer Lexus.) So when you see '95' as the first number on a £250
tyre you know they're gonna cost you 3p. per mile per tyre!!!! My own tyres are rated 200 (18,000
miles) and set me back £125 ea. 'all-in' less than 0.7p. per mile per tyre. That's a 4 fold difference
so what do we each get for our money, are those 'specials' 4 times better? Well actually, errrrr,
No! They are better but not by that much, for all the reasons mentioned above. Next is traction,
the best (for road use) available is AA, followed by A, B and C the minimum for us must be A, but
bear in mind that the AA rating was introduced in '97 and some of the tyres at present rated A
would be re-rated as AA. This is a WET BRAKING traction value NOT lateral or radial
acceleration. There is a corollary between these but it is difficult to explain without the use of
formulae. The next part of the UTQG is temperature and this relates to the your tyres ability to run
at sustained high speed and the A rating means that they have passed the 145mph for ½hour in
near desert conditions without sustaining any failure. But the real trick is the interpretation of this
raw data with the next bit.
Plies, if you thought it was clever getting the right mix of rubber compound then the contradictions
in designing the belts that give strength and suppleness to the tyre carcass has reduced grown
men to gibbering, dishevelled and tearful individuals sitting in padded cells wearing a 'cuddle-me-
self' coat. It is so complex that I know of no Computer Program that can do it! Even Formula One
tyres are human engineered, I think it is the last part of a F1 car that is! It has always been this
way at the top and with each new generation of tyre design the older design gets used by a less
well-known producer usually (now) in Taiwan or Korea. So those budget tyres were 'state of the
art' 3 or 4 years ago and trust me there have only been tiny incremental improvements since
then, so I think the premium is not really worth paying. Just get the highest Treadware number
with 2 A's and make sure you have 5 plies on the tread, 2 outer polyester, the middle 2 of steel
and the innermost Nylon, and at least 2 plies in the sidewall, I think now all side walls are
synthetic and Rayon seems to give the best flexure control with polyester not far behind.
Now to rim size I know of 2 standard fitments for a Soarer 15×6½ and 16×7 and the standard
tyres are 215/60R15 VR and 225/55R16 VR resp'y. What we get from this is the height of the
Sidewall and their Rolling Radii, 129mm & 124mm resp'y and 639mm & 654mm resp'y. The
former set tells us that that the 16" rim is the sportier, the lower the A/R the lower the amount of
potential flexure there is in the side wall and as the A/R lowers, higher grades of sidewall material
have to be used. The latter is necessary to maintain a reasonably accurate speedo although as a
rule ±1% will not be too bad.
Another factor to bear in mind is the ratio of the rim width and the tyre width. There are certain
ways to affect how a tyre will behave after you have selected a suitable candidate, one very
interesting way is with the rim width. It used to be a guideline that if the rim was approximately
75% the tread width the tyre would be at its best, then the figure went up to 80% then 85% and
now even 90% is used to provide very sharp responses as the sidewalls are nearer to the
theoretical ideal. For example I run 17×8 at the Front and 17×9½ at the Rear with 235/45 (86%)
on the Front and 265/40 (91%) on the Rear. By the way the rims are from a Supra, just find a
local Supra specialist and he will have replaced at least half a dozen standard wheel sets for
expensive showy rims for some unthinking rich kids, (a little bit of cynicism crept in there, sorry).
Slap £300 down on the table and drive off with a set.
Experience on our site shows this set-up to be fine for the V8.
Offset, if you change the size of your rims then you must look at this so as to avoid fouling of the
wheel arches. So what does it mean? When we only had crossplys the interface between the rim
and the hub was central to the rim width, this was a hand-me-down from how wire wheels and
even cartwheels had been made and it seemed 'right'. Ah, but those guys at Citroen had a
problem, we know it now as 'torque steer' but back then it seemed quite insurmountable, the
lighter the car the more prone it was to this phenomenon. The wheel became a huge dumb-bell
which was OK when the wheels movement was confined either to just steering or power
transmission but not both. Worse still, at the start, the radials were more wayward than the
crossplys! Michelin half sorted that by changing the internal belting sequence. The problem still
persisted and does to this day but the other simple solution found at the time by Michelin/Citroen
was to set that interface closer to the outside edge of the tyre. This seemed to 'equalise' some of
the more high level inertial forces acting on the wheel. So that is why we have offsets and, again,
they used mm to describe it, so we have on our rims a number like 40,50 or 60. As our motorcars
bodywork became enclosed and more aerodynamic and speeds increased it helped again with
high speed Steering and Braking so you mess about with it only with sufficient knowledge. This
you are well on the way to possessing. With my Supra 17" rims I have a 50mm O/S with no
fouling, the wheels are still very 'set in' to the bodywork.
Do you remember I asked if you would note if you saw the word 'ROTATION' with a little arrow
pointing (hopefully) the right way to describe a forward motion? Well, if you did I hope they were
on the same axle and always in pairs! People who really ought to know better very often tell me
that this does not matter, but on every car I have driven when this has been tested, the wet
braking performance is degraded to a point where it is simply damned dangerous.
Tyre types. That 'ROTATION' sign tells you this is a 'directional' tyre. This is a fairly recent
innovation for Road going tyres, if you look at the tyre you will see that the blocks of rubber that
make up the tread pattern form an arrow shape it may be broad and 'broken' or very pointed and
look like a series of 'V's. It's the introduction of a special sort of silica with a high valence polymer
that has made this and other newer designs viable. The other newish tyre type is the Asymmetric
and generally these seem to be best on the rear axle of a rear wheel drive motor. They perform
well on the front only when its dry, in the rain especially summer deluges they can aquaplane
badly, i.e. lift off the Tarmac! They simply cannot bail out the standing water if they are too wide
and for any given width the Directional will be better at clearing the water. For our Soarers,
because of their weight distribution Directional is by far the best for us.
DON'T EVER BUY REMOULDS OR PART-WORN TYRES, PLEASE, DON'T, EVER.
Tyre pressures it may seem obvious but it is not the tyre that keeps you rolling and supports the
car ,it's the air inside and pressures are really important. In the testers world there is only one
way to get the perfect pressure. Take your car, a 'trident' tyre temperature gauge (it records the
temperature in the centre and both shoulders of the tyre), a foot-pump with a very accurate
pressure gauge, a Dictaphone, some sandwiches, don some overalls and hit the A44 between
Oxford and Mid-Wales. Throw in a couple twisty roads in the marches of Wales and after a day
(providing it rains) you emerge with the correct result. This was the case up to about the mid-
seventies, (except very early on the 'trident' was the testers own hand) but as the roads filled up
most of the testing was done behind gates on 'fake' roads. Although even now real road
experience is still used, but really as confirmation of the 'closed' results. I fervently believe if one
of the 'old boys' could be persuaded to get hold an XK8 and went through the old routine it would
be a vastly better car, but to be fair I think the questions being asked are different now, from then.
Still, nostalgia's not as good as it used to be.
So in 3500 words we have covered the little bit of rubber that touches the road. Now lets deal with
SPRINGING TO ATTENTION
The Soarer has 3 different types of suspension Coil & Damper, Air and Active. All 3 use steel
components and the black art of smithying is intrinsic to their performance. It used to a very
voodoo rich subject dealing with Spring Rates, Damping Valves, Bushing, Lever Arms and on and
on and on. To short-circuit all of this, the complexity eventually boiled down to 25 formulae and
any competent Engineer can access them; some are even on the net! Briefly, what does each
The wheel is mounted by 5 chamfered studs to (at the front) the Kingpin, (at the rear) The Stub
axle (except the Active which has another Kingpin) these items are connected to the upper
wishbone and the lower wishbone and is nearly vertical. It is tilted over slightly to the front of the
car and this is the Castor Angle and it is also tilted slightly at the top either in toward the body or
the other way and this is the Camber Angle. The castor angle is what used to bring the steering
back to 'centre' after taking a corner. Citroen used this as another way of controlling the dreaded
'torque steer' on FWD cars, the Kingpin was tilted quite far forward at the top, making the weight
of the car bear down on the centring. That is why some quite small cars have Power Steering. If
you think about it you are 'jacking' the car up with the steering. Soarers have a very slight castor
angle (more of a 'failsafe' really) and self-centring power steering, this is good as the further
forward this component is tilted the more it affects (adversely) the handling. We are off on a
tangent, there are certain words bandied about by 'TV pundits' about 'handling' and 'roadholding'
and for the most part they talk out of their -, this is what the terms really mean.
Handling is Hysteresis. Seat of the pants stuff (subjective).
Roadholding is Quotient. Measurable (Lateral 'G' etc.).
The 2 pairs of wishbones are attached to a partially cast, exceptionally rigid cross-member with
very hard bushing. The locating points are carefully judged to allow for anti-dive & anti-squat
effects, this is done by tilting their axis lines, analogous to the Castor, Camber and Toe-in
mentioned earlier, the shocker is fixed to the lower wishbone (bottom) and the monocoque (top).
The sprung force is achieved by; 1, A coil (helix) of steel, effectively a torsion bar wound up into a
confined space. 2, Air or Gas filled units.
The sub-frame assemblies mean you can isolate unwanted reactions, one of the most difficult
items in this respect is the anti-roll bar, always been the perpetrator of many knotty problems,
setting it to react within a sub-frame whilst still working effectively on the monocoque was the
solution on the Soarer. This requires great accuracy, go out to your car get on the floor and look
up at the mounting points of the wishbones, and marvel at the vernier discs fitted to each point of
attachment, this is truly bloody marvellous. Not even the legendary Mercedes 'S' class build
quality could take this scrutiny.
The truth is, no modern car should deal with the road badly. The only thing is cost cutting before
the production starts deals the deadly blow. Take a simple thing like the bushes, which keep the
metal components of the suspension from touching. Good Manufacturers spend a lot of time and
money getting them made well, taking care to specify the right rubber and tolerances and it pays
off, I am not an admirer of BMW but in the 70's they upped the quality on these components just
as Jaguar lowered theirs. This simple thing meant that when Tony Dron drove the XJ6 and the
528 the latter had a consistency of handling, which made it the better car, and I think he said so,
and many other Motoring Writers agreed with him.
The fact that the Jaguar had better intrinsic designs in most parts of the car shows just how
important detail is. That's how to fall down on the small scale, how about on the grand scale. A
little known (to the general public) piece of suspension creed is that the front and rear suspension
assemblies have a base resonance. It's the low frequency actuation of all the components as
apiece, and a good Engineer would work out the frequencies and ensure that the front and rear
are not reciprocal. Sounds simple, but low frequencies interact and the ideal of the front base
resonance being at a higher frequency than the rear is hard to achieve. The only recent cars that
have failed have been engineered in America, where the desire for tight control of suspension
has only recently taken hold. I know, I know, the Soarer was designed in America, but it was
ENGINEERED in Japan, had it been the other way round, I doubt if I would own one.
We have precision made all round independent, dual wishbone suspension with progressive rate
coil springs, a front and rear anti-roll bar and top and bottom wishbone angle attachments to stop
diving and dipping at the front. This is the best form of road car suspension you can get and
provides the most effective control of the wheels. The best companions to this set-up are gas-
valved shockers. The reasons are simple the older, oil filled, units needed to be set very stiff
when cold, so as the car warmed to its task the warm shockers were 'just right'. On high
performance cars this used to mean a bone-jarring ride for the first few miles. For a Lexus this
would be no good, so gas-valved it was. But why stop there? While we are at it, give the car 2
separate settings, and why not have rapid-reaction adjustable valving (TEMS) so as to allow the
steering inputs (via an accelerometer) to stiffen the side under the most load and soften the
lighter side? Don't believe me? On my car, if you are in PWR/ECT mode and turn late and very
sharply in a bend the car hardly seems to roll at all, it leans of course but it does not roll!
I'm filled with admiration for the Toyota Engineers who did this, in my experience no one has ever
done it better or even equalled this magnificent feat of suspension magic, its that damn good!I
think some of you are saying what's the difference between the car 'leaning over' in a corner and
rolling? Look at it this way, after a couple of drinks I may lean on the Bar of my favourite Pub
(Alcohol is a muscle relaxant) but after a lot more drink I become rolling drunk, miss the Bar, and
fall flat on my face, that's the difference, its all about control. All-in-all an impressive list but to
crown it all, put the front and rear assemblies on their own sub-frames so as to ensure different
resonance frequencies and a near vibrationless ride. So is the suspension faultless? No, not for
me at least. The springs could be just a little bit more progressive.I want the PWR/ECT shocker
settings all of the time. The original toe-in settings were more suited to the asphalt of Japan more
than the undulating English Country lanes. I posted a more performance-orientated set in the
Club Forum earlier this year. I have changed them again this new set are really only suited to my
style of driving and not published for general use.
A word or 2 about Air suspended cars, stick to the published settings, all of them, don't mess with
them. Fit the bigger rims and the even the spacers, adjust the toe-in to those posted on the
Forum but that's it.
A word or 2 about Active Suspended cars, stick to the published settings, all of them, don't mess
with them. Fit the bigger rims and the even the spacers but that's it.
Iain Wiltshire - Newbury, Berkshire, England. 2 December 2001
©The Lexus Soarer Owners Club