Mighty MMI (man machine interface)
What makes a race
car go faster? More specifically, a cheap road car based racer, not dissimilar
to hundreds that get campaigned round our fair land by enthusiastic club-persons
Power is a good thing, obviously. Suspension and brakes all help, of course.
How about seat mounts?
What, I hear you say, is he mad? Well, quite possibly, however here we
will go over how to tune your driving environment so you can get the best
out of your car, feel comfortable and be in control.
There is something very important here and it involves your arse. When
you have a car on the limit round a corner, you sense the onset of slip
etc by relating what you see to what you feel. The more isolated you are
from the car the more difficult it is to be precise, and I speak as someone
who has spent some time drifting splendidly isolated Bentleys (but that’s
another story, maybe later)
Having a very firm seat that is rigidly bolted to the car gives you the
best possible feel for what is going on. When you turn the steering wheel
on a road car, there can be a lag before the car moves and then the seat
moves. This give a feeling of uncertainty and if its really bad (worn
bushes etc) your ability to place the car precisely all goes to pot.
Now this is an important fact, your confidence and precision depends on
the feedback you get through the seat and through your eyes. It also depends
on the car doing exactly what you expect it to, but we will come on to
By the way, don’t get confused if you see compliant seat mounts
on a GT LeMans car, they need some isolation because of the rigidly mounted
engine and rose jointed suspension, over a two hour stint that would rattle
By comparison, our compliant mounted engine and suspension means we are
quite well isolated to start with, so the seat gets nailed to the floor.
By ‘nailing’ I am of course referring to the MSA compliant
3mm steel or 5mm ally mounting plates described in the Blue Book.
The mounts need to be able to take huge forces in case of a crash where
accelerations of over 10g could have you bouncing round the car like a
Nomex covered tomato in a blunt blender. 10g, that’s like expecting
the supports to hold up the best part of a ton, the Blue Book spec (section
Q) for seat belt mounts is 1.8 tonnes and for seat mounts it is 1.5 tonnes.
The word ‘gosh’ springs to mind.
On the subject of seats, it is worth making sure your arse cant slide
about and also that your shoulders are given a bit of support. That means
you can feel the car moving directly and can concentrate on moving your
feet and hands without also trying to stay upright and located in the
Having said that, you must make sure you can move your arms freely to
fully rotate the wheel in a mad panic (just try rotating the wheel whilst
flapping your elbows like a manic chicken impersonator, you will be amazed
how many bits of car are in the way).
Right then, that’s your arse out of the way, lets move on to thighs
(which reminds me of a party near Turin, but again that’s another
Your thighs should be supported so that your feet rest naturally on the
pedals with very little effort. Try relaxing your legs completely and
see where they flop, if its in a reasonably good driving position then
the job is done, if its with your feet under the pedals, you have some
adjustments to make. The more natural it feels then the less likely you
are to miss the pedal when it all gets exciting in a spin on the track.
Next we must look at the rest of your new office furniture. To get the
max from the car and yourself all the controls need to be in just the
right place, falling to hand naturally where you expect them to be.
The steering wheel should be at a comfortable (but safe) distance, elbows
slightly bent but everyone has there own preference, whatever works for
you is the key here. The dash and stalks, if used, should be clear of
the wheel, I once span at Cadwell in an SD1, the frantic twirling of the
wheel resulted in me bending the indicator and wiper stalks. They seemed
fine during normal driving, when I had time to work round them, but in
the heat of a spin they were in the way.
The gear stick should fall to hand easily and your elbow should not encounter
any obstacles when shifting. If you need to modify it then make sure any
welds are strong enough to cope with an angry driver putting their full
force on it. The throw should be short enough for quick changes but long
enough so you don’t get the wrong gear. Often with production based
cars, replacing rubber linkage joints with Rose type joints helps quicken
gear shifts because it feels better and gives you more confidence.
3. The view.
The seat is not only responsible for your arse, but also for your head,
oh yes. With the seat in your chosen location, you must be able to have
a clear view of the road. I know its obvious but it is surprisingly easy
to forget whilst working late in the confines of your garage, you loose
perspective in there. And 13mm spanners as well, odd really.
I built my first racer on the driveway and the view forwards seemed fine
until I got to my first race, then I discovered I couldn’t see the
apexes or the grid lines, with comedy results as you might expect.
Importantly, the gauges should be easy to read even when you are not looking
at them. In the good old days gauges had needles and they were arranged
so that all the needles were vertical when all was ok. We are very good
at detecting horizontal and vertical lines, which may go some way to explaining
tartan. If the engine overheats or oil pressure drops the needle deviates
from the perpendicular and it is easily noticeable. These days we have
simple warning lights, shift lights, oil pressure warning light etc These
are excellent and work well using your peripheral vision, and lets face
it, in the heat of the battle you wont be looking at the dash board.
If the view is good you then need to check for clearance, during this
check anyone walking into the garage will think your are a sad git, hey
ho. Sit in the seat, preferably with the harness on. Have your crash helmet
on. Wave your fist around your helmet. Now you look really silly. There
should be a fist size gap between your helmet and the padding on the roll
cage and any other bit of car.
Try doing this whilst moving your head about. If you find anything hard
which cant be moved, it needs padding, not soft B&Q foam which instantly
crushes, oh no, you need high density rubbery stuff, roll cage padding
is a good example.
If you have a crash, your neck will stretch, side impacts are the ones
most likely to send you into a coma. Check there is nothing hard for you
noggin to smash into. Also check for clearance to the steering wheel,
whilst strapped in and you skid lid on, try to head butt the steering
wheel, if you get within a fists width then you will hit it in a crash.
I had a crash a couple of years ago on a Comp Safari, I skidded and hit
a tree at about 40 or 50 mph which shortened the car by a foot. Sitting
in the remains of the car afterwards it tried the above test and could
not get any part of my lid within 4 inches of the wheel, yet in the accident
I hit it with enough force to smash the visor.
This is serious stuff, we want serious fun, but to do that we must survive.
Now you are comfortable, well secured, the controls fall easily to hand
and your warning lights are sorted, we need to give you some air.
You need fresh air to your lungs to keep you awake and also you need to
be at a comfortable temperature. Give some though for where the cabin
air comes from, make sure there is no chance of engine bay fumes or exhaust
getting anywhere near it. Remember that the air coming into the cabin
must also leave it at some point, otherwise the flow slows down and any
farts will make your eyes water for fifteen laps. Or is that just me?
Of course this theory is all very well and good, but some cars present
a ‘challenge’. As an example lets see how this fine theory
relates to my fine motor car, a Jaguar XJS.
Well, to tell the truth, badly. Sitting in the car as standard, my head
hits the roof and cant rail. Add to this a crash helmet and a roll cage
and I will have to remove four vertebrae!
In the standard seat, my arse is about six inches off the floor. If I
mount the race seat base touching the floor my head will still hit the
roll cage, this is not good.
It gets worse however, there is a large box section cross member on the
floor that joins the transmission tunnel to the sill, its about 4 inches
The best solution is obviously a compromise, which is quite often the
case with club level motorsport, and benefits from a bit of lateral thinking.
In this example I decided to use a high back seat usually used in off
road racing, it has a near vertical back which means I can fit it with
the rear mounts on the floor and the front mounts on the cross member.
This gives a steep recline which I prefer and gives me a tad more clearance.
The steering wheel is replaced with a lighter weight racing item that
has a sensible rim width, not the spindly rim of the standard Jag wheel.
Its also a smaller diameter which improves the steering feel remarkably,
this is because the same movement of my arm now has a greater effect on
the car. I also lowered it by putting spacer blocks and longer bolts on
the column mounts which made a huge difference in steering feel.
Now that I am sitting on the floor, the gear stick it a little high. Also,
it wobbles too much due to the compliant rubber mounts it is on, again
this relates to the need to have things fall to hand and behaving as expected,
the wobble introduces uncertainty which reduces my performance (and it
really is a performance). Removing the mounting plate and bolting the
selector directly to the trans tunnel improves things no end.
Next issue is the gauges. There is a small rev counter which is not too
easy to see in my peripheral vision. Just as importantly, the temperature
gauge (these cars are renown for overheating) is a particularly useless
linear bar graph type affair, as are the oil pressure, fuel and battery
indicators. Not only that, but they are also wrong and have a very small
movement between ‘normal’ and catastrophe. When the temperature
gauge reads just above cold, but below normal, the radiator is at 90 C.
That means that a reading of Normal would only be reached when the engine
has seized and caught fire.
New gauges are in order but beyond my tight budget. So to make use of
our horizontal line recognition I put a piece of thin red tape across
the gauge, at the max temp that I was happy with in a race. When the needle
reaches this point it makes a continuous line and is easy to see at a
glance. Now the whole lot works quite well together. Most Autograss racers
simplify things further by fitting a fog light on the dash as an oil pressure
warning and leaving it at that.
I like my race cars, they are very individual and any other driver would
hate it, but they are built for my own needs, and that’s the key.
Everything is where I expect it to be and does what I expect it to do.
Even in an emergency. The way you do things in your own racer may be completely
at odds to convention, but if it feels right then it is right. And of
course conversely, that £2000 carbon fibre seat may look the dogs,
bit if it is uncomfortable then to you then its worthless.
Well there you have it, the interface between this man and his machine
was sorted, and lap times fell.
The next big performance gain will come from practice.