412 virtues

[lansdownplace]

Principly because of a lowered center of gravitydue to the bodywork
and the reinforcement in the chassis and a lower stance on the
front. They dig into corners better. I notice the difference
compared to my Brigand but the guys at BCL all say the same thing.

[Peter.Kent]

I'd be surprised if there was that much difference in handling due to
differences in chassis and body. Sure, there is no solid roof on the 412
but there is a darned great targa arrangement. There is a little more
overhang at the back but it's only an empty boot. Overhang at the front is
surely about the same. The one change there might be significant to
handling is the 360 engine in the s2 which I believe to be considerably
lighter than the earlier units in the 411 (and first few 412s). P

[lansdownplace]

Hi Peter. The 360 engine is a lot lighter than the 400 but the
reduction in power is compensated by the drop in weight. The engine
is set lower I believe but there a lot of additional steel in the
chassis. There are two large reinforcing plates under the driver and
passenger which sit on the polar moment of the car which also shift
the weight from above the roll axis to below it which reduces body
roll to a degree by reducing the roll center and concentrating mass
inside the wheelbase. The shift of weight towards the lower half of
the car and the fact that the 412 S1 (400 engine) weighs in at 1714
kg as opposed to 1783 for a 603 with the lighter 360 engine gives
some indication of the difference in total mass reduction.

As I am not an engineer so I can't explain further, I can only report
that my S2 is very well balanced, especially with the front shocks on
a hard setting and the rear set quite soft. Perhaps some other 412
drivers can elaborate?

Paul

[Peter.Kent]

Having delved about under the thing, I didn`t see enormous weight in
"plates".

Replacement of exhaust manifolds (did`nt weigh them but they are seriously
heavy) plus heads (weight even more ditto) and inlet mainifold more relevant
as they are all at the top of the engine. I think my new gearbox is supposed
to be lighter but that is lower down. My s2 certainly handles better than
ever.

I think some later models have the engine lower between the chassis rails.
That would be a benefit. As to suspension, I run a compromise .... exhaust
scrapes if I`m careless but generally OK. P

[TLF799R]

[quote]
How come?

The 412 has exactly the same chassis, suspension, steering etc as the 411,
so why would it handle any better?

(Should I move these later posts to a new "412 love-in" thread?)
[End Quote]

Kevin,
There's no need to feel bad about having a lesser model- you too could own
a 412 one day - just don't give up on your dream!

As far as handling is concerned it is simple, just look how aerodynamic the
412 is!

Philippa

[penman]

Hi Phillipa
to make a quote box

How come?

The 412 has exactly the same chassis, suspension, steering etc as the 411,
so why would it handle any better?

(Should I move these later posts to a new "412 love-in" thread?)

I have put a [/quote] where you have the put [ End Quote]

[lansdownplace]

removed email artefacts

[Kevin H]

Originally Posted by lansdownplace

Principly because of a lowered center of gravitydue to the bodywork and the reinforcement in the chassis and a lower stance on the front. They dig into corners better. I notice the difference compared to my Brigand but the guys at BCL all say the same thing.

Okay, firstly I was talking about the 412 (as in the original 412), but I can't imagine the 412 S2 or S3 to be much different where it matters.

A slight change in centre of gravity, and a slight change is all that is achievable, will make no material difference to the car's cornering abilities.

Any gains would be far outweighed by changes fitting wider wheels and tyres.

If the chassis has been reinforced in later 412s it would only mean that BCL came to the conclusion that chassis rigidity had been compromised in the first place by losing the roof!

It is in the tyres, wheels and suspension set up where the big cornering gains can be made. But between the 411 and 412 (s1) there are no differences here, (I don't know if later 412 s2/3 differ in the suspension, but I doubt it).

Both 411 and 412 s1 will benefit from replacing the steel wheels with the lighter Avon Safety wheels and wider tyres. I noticed a marked improvement in my 411 with this change.

As for weight reduction, simply reducing sprung weight (engine, transmission, body etc will mainly affect straight line acceleration and stopping distance. To improve cornering through weight changes you need to reduce the sprung/unsprung weight ratio by reducing the unsprung weight (not the sprung weight). In fact reducing this ratio by reducing sprung weight can have a detrimental affect. Although the weight changes between the 400 and 360 engines would not have very much affect either way given the overall weight of these cars.

[lansdownplace]

A couple of points, all of the 412s were reinforced underneath as
this was required by the authorities at the time to avoid having to
re-crash the cars rather than for need. There is no noticeable
scuttle shake on my S2, I can't speak for the earlier cars although
I am told there is a very small degree of chassis flex in extremis
on the all cars from the 407 to the 412, which is absent in the
later 603/Blenheim series which are more rigid due to the amount and
location of steel in the roof and upper structure. I can't agree
with your dismissal of the effects of lowering weight, especially
lowering the center of gravity and the roll axis. Try driving any
car with a full roof box for a practical demonstration of the
effects of this. My old BMW handled significantly differently with
four passengers than two, and the shift infront/rear weight balance
from that was small but it affected the cornering and roll. Sprung
weight does affect cornering dependent on where it is, due to
increased/decreased lateral momentum and the effects of roll.
Aerodynamics have an effect over about 70 mph on cars but who knows
what the positive or negative theoretic effects of this are between
different Bristols other than by observation. As I previously noted
I am not an engineer, but I do appreciate the accumulated effects of
small changes in practice. That is, after all, why manufacturers are
always tweaking their cars. The 411 has the engine set back further
than a 407 for example which changes the yaw axis and transforms the
handling between the two cars. The 407 was 'disappointing', although
I can't personally verify that as I haven't driven a 407 so I rely
on the reports in the media and Mr Setright on that one.

Set up does matter greatly but it is the sprung weight that you are
supporting and that does affect the dynamics.

Paul

[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

[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!