412 virtues

[Kevin H]

Paul,
I was talking about handling differences between the 411 and 412 - I am not at all surprised that a 407 doesn't handle as well. Apparently incremental improvements were made between the 407 and 411/412 due to increasingly more subtle changes in steering and suspension geometry and spring rates (devised by Mr Sevier if my memory is correct).

Of course a car handles differently if you put a carrier on the roof, or if it's full of people. However, my comments were in the context of what you said about engine position, and weight, centre of gravity and cornering.

I still maintain that the differences you mentioned, between the 411 and 412, would not create any material difference between the handling of the two cars, all other things such as wheels/tyres etc being equal.

Kevin

PS. We are allowed to disagree

[lansdownplace]

Hi Kevin, We are indeed!

[lansdownplace]

Hi Kevin, I started with my own experience on the relative
difference, but as 'why' was asked I thought I should go off and
check for myself.

I have now managed to lay my hands on some facts and figures on this
handling issue, which do explain my thesis.

The 412 S1 has 32% more torsional rigidity than the 411 although the
beam rigidity is the same, The 412 S2 has the bars at the top of the
windows connecting the A and B pillars and other chassis modifications
so the torsional rigidity rises to 45% more than the 411 with 25%
stiffening in beam rigidity. The effect of this is to make the car
respond more readily to steering input as it maintains the alignment
of the the suspension better, reduces the oscillating effect of
flexion in the chassis. It explains why it hunkers down in corners
more readily.

The other data to hand now is that the center of gravity is 8 mm lower
in the 412 than the 411, which I thought sounded small, but the effect
is magnified because the center of gravity on a 411 is 80mm above the
roll axis, whereas it is 72mm on the 412 ( and lower again on the
Beaufighter).That represents a 10% improvement in the roll couple
ratio which does make a difference to the balance of the car. In a
perfect world the center of gravity would sit on the roll axis, but
there you are.

Some other interesting technical stuff I picked up is that the
Blenheim is three times stiffer than the 411 and the Blenheim had the
highest torsional rigidity of any passenger car up until '98. It is
stiffer than the McLaren F1. The reason is that the chassis is further
reinforced, but the body skeleton acts as a monocoque in it's own
right, but in addition the panels are rigidly fixed to the skeleton
and provide further stiffness an they they are thicker than normal.

Anyway, yes we are free to disagree, but I am happy in my own mind
that I understand the reasons behind the claims for the 412 handling
and having observed them in the wild I am going to take by 412 out for
a bit of a thrashing this afternoon!

regards

Paul

[TLF799R]

Blimey Paul,

What a lot of facts!

You see I usually just rely on my unshakeable belief that the 412s are superior but you can even explain why - most impressive!

Interestingly when Jeff from the factory popped by to see Bertie at the Italian car day he specifically mentioned the handling of the 412 and said that it had always been his favourite to drive from that point of view.

Philippa

[lansdownplace]

Hi Phillipa i will have to reluctantly conceed that the Blenheim
probably handles better. It does look like I swallowed a
dictionary. Anyway I spent a very pleasant couple of hours this
afternoon refining my driving technique on high speed curves and
balancing the car with the throttle. I feel cofident enough to take
her up over twenty tomorrow.

Paul

[Kevin H]

Originally Posted by lansdownplace

Hi Kevin, I started with my own experience on the relative difference, but as 'why' was asked I thought I should go off and check for myself.

I have now managed to lay my hands on some facts and figures on this
handling issue, which do explain my thesis.

The 412 S1 has 32% more torsional rigidity than the 411 although the beam rigidity is the same, The 412 S2 has the bars at the top of the windows connecting the A and B pillars and other chassis modifications so the torsional rigidity rises to 45% more than the 411 with 25% stiffening in beam rigidity.

Paul, it's always interesting to get more information about our cars, but I'm sure you won't be surprised if I ask where these facts and figures come from?

It's worth pointing out that differences expressed only in percentages are all relational, and the 411 was reckoned to handle very well indeed, and not just by Setright.

There is probably an optimal point for chassis rigidity, and increasing it past that point doesn't necessarily translate into better handling because it also depends upon the suspension (spring rates, damping), roll axis. C of G, wheels and tyres, tyre pressure, anti roll bar, weight distribution and probably one or two other things we haven't thought of!

The other data to hand now is that the center of gravity is 8 mm lower in the 412 than the 411, which I thought sounded small, but the effect is magnified because the center of gravity on a 411 is 80mm above the roll axis, whereas it is 72mm on the 412 ( and lower again on the Beaufighter).That represents a 10% improvement in the roll couple ratio which does make a difference to the balance of the car. In a perfect world the center of gravity would sit on the roll axis, but there you are.

Surely it depends where the roll axis is? This would also induce jacking effect would it not?

I would be keen to know just how the C of G has been lowered, and if the weight distribution differs between the cars.

Some other interesting technical stuff I picked up is that the
Blenheim is three times stiffer than the 411 and the Blenheim had the
highest torsional rigidity of any passenger car up until '98. It is
stiffer than the McLaren F1.

This is quite amazing, if it's true. And if it is true, it clearly demonstrates that chassis stiffness or torsional rigidity does not dictate handling (because a Blenheim does not handle as well as a McLaren F1).

There is another point to consider here. Any figures that come out of BCL refer to original specification cars as they left the factory. There aren't many like that any more, especially when we are talking about 412 or earlier.

For example the 412 S2 had wider, lower profile tyres than the 411, but I now have the same wheels and tyres on my 411, as do many other 411 owners. This in itself lowers the 411 slightly, lowers the roll centres, roll axis and C of G, although it doesn't reduce the roll couple value. But it does makes a very noticeable improvement to how the car handles over the standard steel wheels and tyres. Stick an uprated anti roll bar on it and it improves it further.

Having completely dismantled the front end on my 411 it became clear that what appeared to be a reasonably good and standard condition suspension, was nothing of the sort. And I suspect this is the case with many of the cars that haven't been restored, in which case this all becomes theoretical!

[TLF799R]

I give up!

Has anyone else ever noticed how Kevin only ever likes facts and figures that support his theories!!!

Philippa

[lansdownplace]

Kevin, I have presented the facts,to back my argument, I disagree
with many of your points, but politeness has prevented me from
pointing out some inconsistencies in your argument. For example you
simultaneously argue that lowering the center of gravity by moving
mass downwards in the car and lightening it have no effect whatever,
whilst acknowledging in the next breath that putting weight on the
roof(in a roof box) or by adding passengers will obviously affect
handling. You can't have both sides of the argument.

I scoured all the available sources for this data and when I
couldn't find the information I wanted I rang the factory and asked
then very nicely. Rather than answer my question I was invited out
to examine the information myself, which I did yesterday, I live
five miles away. I suppose it is one of the benefits of buying/
rebuilding and maintaining your car with BCL and being politely if
enthusiastically interested in what they do out there. Also having
the same people (individuals that is) work on the car as built it
the first time around helps. The figures I quoted are figures I have
seen personally from original documentation before anyone asks.

Phillipa mentioned Jeff saying that his view is that the 412 was the
best handling of their cars, and he has said the same to me. However
unlike Philippa or I, Jeff isn't a die hard 412 fan, he loves the 411s
which is what he was building when he started with the company.

Yes they do refer to original spec, but fortunately for me, my own 412
which was pretty unmolested, was recently rebuilt from the ground up
by the factory to the original spec so apart from 7 inch Blenheim
Alloys, my car rides as built. I drove lot of V8s before buying my
first Bristol, the most memorably awful was a 410 that someone in the
car business had rebuilt themselves, he was proudly telling me how he
had used bushes from a ford and done the front suspension himself as I
plowed straight on at a roundabout at about 10 miles and hour with the
most astonishing understeer ever. I didn't conclude that 410s were
bad, merely that you have to be very careful where you get them from.
You can get a good version or a bad version of any car, the best bet
is to get one from BCL that they have rebuilt or converted to a Series
6, or better still a brand new car. I can't imagine any aftermarket
version of the cars being better, or at least I haven't seen one. You
get what you pay for in life I guess.

I choose a 412 over a 411 although the latter has been reckoned to be
more of a safe bet financially in the past because I like the styling
more, it handles better (IMHO) and I can drive with the wind in (what
very little is left) of my hair. It is personal choice and enjoying
the car is all that matters. If it was just a financial decision I
would have bought a smart car.

One final point, I haven't checked the McLaren F1 figures yet. but it
has completely different suspension set up, for racing and not
cruising so they are not apples and apples. I am at McLaren in a
couple of weeks so I will ask them for the figures. Also lack of
torsional stiffness is one of the major problems in handling that no
amount of suspension tweaking will overcome. A good example is the
Aston Martin DB7 coupe got rave reviews for handling, whilst the rag
top with exactly the same suspension gets panned. It has to be set
soft because the torsional rigidity so so impaired it won't ride
properly.

Anyway, If the facts are with you, you can argue the facts, if
principle is with you, you can argue the principle, or you can just
argue.

I am off to the races.

Regards

Paul

[UK6]

Hello Paul, Kevin and other Technophiles,
A relatively easy way to compare one car's cornering ability with respect to another's is to compare their respective maximum lateral accelerations around a fixed radius bend.

Acceleration values can be obtained by attaching a relatively inexpensive accelerometer to the cockpit of each car in turn and drive each test car in turn at max speed (point of breaking traction) around a, say, 100m diameter "track" defined by witches hats on a safe, deserted car park or airfield. The higher lateral 'g'reading gives an indication of superior road holding.

One could swap wheel/tyres from one test vehicle to the other (if they fit!) to determine the effect of tyre selection.

"G Tech" offer a 3 axis accelerometer for ~ $110 US at...
http://www.gtechprostore.com/cgi-bin...on&key=0400452

As a point of comparison, a 1998 Lexus SC 400 attains ~ 0.8g on a 300ft skid pan.

The more advanced accelerometers can also give one a fair estimate of linear acceleration and horsepower output values - useful for other arguements!!

Regards,

Brett