Dangle_kt
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| posted on 25/1/09 at 02:25 PM |
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CEC vs. BEC power to weight = track time question
I have just been re-watching the fantastic display of the r500 round the top gear track, and was interested that during the review it was mentioned it
has the same power to weight ratio as a veyron.
Impressive. But when the stop watch came out the caterham was quicker, and on a very cold track too.
Also take into account the veyron is a million pound supercar and so will have exquiste handling it got me thinking.
Is the advantage the caterham has down to weight, not power to weight ratio - but just plain old weight?
E.g. no amount of electronic wizardry and investment can make a car that weighs more (even with comparible power) go round a track as fast.
I was thinking about corners, and the fact that each extra KG is going to be pulling the car back to going in a straight line - therefore making a
heavy car handle as well as a lighter car is exponentially (or maybe just more) more difficult?
This brings me onto the main thrust of my post:
The whole BEC vs CEC thing, and the fact that CEC cars can make equivilent power to weight ratio as a BEC (admittedly with significant more cost) - is
it all pointless if they wont handle as well?
Imagine a BEC weighing 450kgs, and CEC weighing 550kgs, both pumping out the same power to weight through a bigger engine in the CEC - they are both
set up by the same company, corner weighted etc, same tyres, same suspension design and general chassis design, and same driver - the BEC will be
quicker.
DISCUSS
*pulls pin* clink clink clink...... 
[Edited on 25/1/09 by Dangle_kt]
[Edited on 25/1/09 by Dangle_kt]
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JoelP
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| posted on 25/1/09 at 02:28 PM |
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dead cert to me, but most people wouldnt argue about track performance.
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nstrug
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| posted on 25/1/09 at 02:37 PM |
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The Veyron has 485 bhp/tonne, the R500 has 526 bhp/tonne.
Lighter cars will usually outbrake heavier ones (not sure what the brakes are like on the Veyron), leading to better lap times for the same
power/weight.
Imagine the tyre and brakes bill after tracking a Veyron...
Nick
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oldtimer
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| posted on 25/1/09 at 02:42 PM |
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Not sure I agree, but not sure I can explain why O don't.
I would have thought the reason that the Veyron and Caterham had different lap times woild be because they were entirely different cars.
Surely 2 near identical locosts with the same power/weight ratio would have near identical lap times? why wouldn't they?
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JoelP
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| posted on 25/1/09 at 02:51 PM |
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quote:
Originally posted by oldtimer
Not sure I agree, but not sure I can explain why O don't.
I would have thought the reason that the Veyron and Caterham had different lap times woild be because they were entirely different cars.
Surely 2 near identical locosts with the same power/weight ratio would have near identical lap times? why wouldn't they?
because assuming they are on the same tyres, the bec has 50-100kgs less to pull through the corners - as a percentage thats a significant difference.
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mark chandler
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| posted on 25/1/09 at 02:54 PM |
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Easy answer, look at race lap times, 893 blade will be as fast as tinkered Rv8 pushing out twice the power.
Small tight circuits BEC wins, long ones CEC wins.
Bec should go around bends better as its the lighter the car the less force trying to throw it off the track, thats why its pointless fitting huge
wheels and tyres on one.
But if you wanted to drive freestyle hanging the back out on bends etc I suspect you would have a lot more fun in a CEC.
Are you trying to beat other people or just out to have a good time? okay its hurts to be slower. On the road I cannot get close to driving my little
car near the limit as you would just end up going far to fast so in reality behaving like a 'cock' in one of these irrespective of speed
will make you the fastest thing out there until you strike something
I have now come to the conclusion the best place for these is the track so may not bother tax/MOT/insurance this year and put the money towards a
couple of track days or an ARDS course.
my three pennies worth
Regards Mark
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MkII
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| posted on 25/1/09 at 03:07 PM |
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what were the lap times for the veyron and the R500.m.
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zilspeed
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| posted on 25/1/09 at 03:07 PM |
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I'm no expert, so ignore everything that I say.
Discount power and acceleration (an unpopular, thought, but stick with me anyway). If you do this you can assume that all cars being compared have
identical power to weight and can accelerate equally.
What are we left with ?
Braking and cornering are the only two variables left.
What brakes better ?
A lighter car.
Less weight = less kinetic energy to dissipate throught heat and noise (with a tiny bit of light because if you're really on it you might get
your brake discs to glow a bit.)
Cornering.
First part of the corner after blending out of the braking zone is the turn in point.
A heavy car due to inertia cannot turn in as well as a light car (Especially if all of that weight is up the front - see SpeedyXJS for details).
Drag race - if the heavy car has enough grunt and good traction it can win.
Really twisty course with hairpins and lots of changes of direction it won't win.
Fast course with no slow corners - somewhere in between.
This is why big heavy engines in suppsosedly light and nimble cars does not make any sense at all.
My old sylva may be low tech, but they're known race winners and my bike engine is as near the bulkhead as I can get it and as far over to the
left as I can get it.
Seeing as I sit on the right. I'm around 80kg nowaday, so is the engine.
All the way through the conversion, my over riding thought has been the hairpins at Forrestburn. If your LSIS can't do tight corners then you
got it wrong.
That's my theory and I'm sticking to it.
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v8kid
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| posted on 25/1/09 at 03:10 PM |
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Why place such an artificial restraint as assuming the tyres are the same width? The CEC as it is heavier can stand a higher unsprung weight thus
wider tyres. The limit is the widest tyres available which will limit the highest comparable weight.
I guess this is why the Bugatti made a poor show - relative to its weight the tyres were not wide or soft enough.
Regarding braking its all down to the c of g height and the weight distribution. Under braking the weight is transferred forwards - the higher the
cofg the more weight is transferred. In practice this means to share the braking equally the static weight distribution has to be rearwards.
Crunching numbers a 60/40 r/f distribution with a 12 inch cofg height will give 50/50 weight distribution at approx 1.4g - but not at any other g of
course.
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dinosaurjuice
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| posted on 25/1/09 at 03:17 PM |
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the power weight ratio is less crucial when you start thinking about resistance, particularly air resistance.
at speeds above about 65mph (when air resistance out proprotions the rolling resitance of tyres and transmission) the maximum HP is more important
rather than the hp/tonne.
the key part of air resistance is the velocity SQUARED!! a car will need 4 times the power to double its speed, plus the power needed to over come the
constant retarding force from drivetrain.
hence why a 485hp/tonne bugatti can do 250mph, but a 526bhp/tonne caterham can only do 140ish???
going around corners is even more complicated, and even more of a compromise...
i like BEC's and CEC's, but CEC's and more importantly DEC's suit my driving style.
will
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MkII
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| posted on 25/1/09 at 03:28 PM |
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while i dont dispute that lighter is faster when it comes to handling braking the R500 beat the veyron by 0.4 of a second but the veyron is more tha
1500kg heavier than the caterham. so the difference in times between a 550kg cec and a 450kg bec would be very little.m.
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dhutch
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| posted on 25/1/09 at 03:51 PM |
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The way i would look at it is, ignoreing how non-linearly proberbly most of it scales.
- Then ultimatly if you have a car thats 2/3 times the weight, and conrespondingly 2/3 times the power. Surely it then needs a track thats 2/3 times
as big, and to take 2/3 times as long.
Ie, while the car may be bigger all over evenly, the track and time are still the same size!
Daniel
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turboben
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| posted on 25/1/09 at 04:06 PM |
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Maybe the r500 can take better lines on the track because its narrower?
Surely more weight makes more grip to deal with the veyrons bulk in the turns and braking.
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andylancaster3000
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| posted on 25/1/09 at 04:08 PM |
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Have a look at the practice times from the 750mc Kits and RGBs this year. Take donington for example, which has a fair mix of both fast and twisty
stuff. The top half of both grids have a pretty similar spread of times, from about 1:18-1:22 in similar conditions.
A fair chunk of the kits in this half are 1800 zetecs 175-180bhp, and maybe nearer 160-170 on average for that half of RGB grid. The chassis are
pretty much the same spec in these classes, the RGB's are in the order of 80-90Kg lighter in general and both on the same tyres. It just shows
overall that there really isn't much in it .
I guess the bike engine boys/girls might be better off in the braking and twisty sections but they lack the torque for the faster stuff.
(probably the first and last time I comment in a CEC/BEC debate . Both have their advantages/disadvantages and I'm somewhat undecided as to
which I prefer!)
[Edited on 25/1/09 by andylancaster3000]
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MikeR
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| posted on 25/1/09 at 04:15 PM |
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We're also not including the fact the cec cars will have a more neutral balance front rear.
From what i've read on here, due to the light weight of the bike engine the bec's tend to be rear heavy.
This will affect the braking and cornering of the cars (although may slightly improve acceleration).
The best test is whats already been said - how do they perform on a track (or even better variety of tracks).
And once that debate is over, which do you prefer to drive. Given the choice of the fastest car in the world or the most enjoyable, i'll take
the enjoyment (i must be getting old).
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mr henderson
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| posted on 25/1/09 at 04:29 PM |
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quote:
Originally posted by dinosaurjuice
the power weight ratio is less crucial when you start thinking about resistance, particularly air resistance.
at speeds above about 65mph (when air resistance out proprotions the rolling resitance of tyres and transmission) the maximum HP is more important
rather than the hp/tonne.
the key part of air resistance is the velocity SQUARED!! a car will need 4 times the power to double its speed, plus the power needed to over come the
constant retarding force from drivetrain.
hence why a 485hp/tonne bugatti can do 250mph, but a 526bhp/tonne caterham can only do 140ish???
going around corners is even more complicated, and even more of a compromise...
i like BEC's and CEC's, but CEC's and more importantly DEC's suit my driving style.
will
Some very goopd points there, the air resistance is crucial. It all depends on the track. A BEC 7 would get laughed at at Le Mans (except it
would be dangerously slow, so wouldn't be allowed on the track in the first place)
John
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dinosaurjuice
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| posted on 25/1/09 at 05:20 PM |
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quote:
Originally posted by mr henderson
Some very goopd points there, the air resistance is crucial. It all depends on the track. A BEC 7 would get laughed at at Le Mans (except it
would be dangerously slow, so wouldn't be allowed on the track in the first place)
John
EXXXACTLY!!
a bugatti would be NO match to a well set up BEC on a twisty and rapid speed changing course.
in the same way a BEC would be no match to a bugatti on the le mans circuit (as mentioned).
IMO the Topgear track is an excellent combination of speed and agility - and gives quite a good comparison between cars. its obvious that those which
satisfy both of these excel, (zondas, keonigsezccxxss etc)
coming back down to earth again, i love to drive a torquey and relaxed car that goes well when i want it to. likewise some people adore the immense
scream of a bike engine at 14thou.
horses for courses/ courses for horses.
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C10CoryM
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| posted on 25/1/09 at 06:02 PM |
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I'm not sure I understand how comparing a Veyron to a Seven makes any sense.
The Veyron is a luxury car built for top speed. Meaning a heavy, high powered car that is not going to handle well.
The Seven is.... well exactly the opposite.
It's like comparing a jetliner to a bi-plane in performance.
End of the day, the only reason low power/light weight cars are fast is because they are light. As soon as you have other forces at play, such as
aero drag, the 100-300bhp of the typical seven is nothing.
"Our watchword evermore shall be: The Maple Leaf Forever!"
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DIY Si
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| posted on 25/1/09 at 06:36 PM |
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Anyone know what the top speed of an R500 could be, given different gearing? IE, is it's top speed set at roughly 140-150 by its gearing, or is
it a limit of power?
As for the original discussion, it would depend on the track. The BEC, being lighter will brake later and turn faster. However, the CEC is likely to
be able to pull a higher top speed. Or if not a higher top speed, then it may well get to it's top speed quicker.
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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Volvorsport
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| posted on 25/1/09 at 06:37 PM |
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all other things being equal , the car with the lowest centre of gravity will win - gordon murray .
BEC being lighter has less inertia , so is easier to accelerate ,corner and brake , it may also be easier on its tyres .
power to weight is only half the story .
a BEC generally has its weight lower down and its bias is more favourable than a pinto and type9 upfront .
i do remember some setup data that with a person aboard a westie has a rear bias , which is gonna be better with less overall weight up front .
question is why did i pick a volvo engine
Adrian Newey prefers his weight distribution at 60/40 for the rear
www.dbsmotorsport.co.uk
getting dirty under a bus
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rf900rush
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| posted on 25/1/09 at 07:23 PM |
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Dax Rush Busa turbo was quoted as 777bhp / ton way back when I first look to build.
Top Gear lap record was matched by Duncan a while back at 1min 17, although unofficial.
Linky here
For unbeatable track times a Turbo Busa 7 will be hard to beat for the cost.
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AdrianH
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| posted on 25/1/09 at 07:59 PM |
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A question not wanting to go off track, but does the weight of the car and therefore the force it puts down on the ground not have something to do
with acceleration and braking as well.
The lighter the car the less friction it can put down to either move or stop. The heavier the more.
I guess there must be a balance but not sure how to work it out!
Adrian
Why do I have to make the tools to finish the job? More time then money.
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Dangle_kt
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| posted on 25/1/09 at 09:19 PM |
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Sorry to have stirred up the old arguement, but I hope you all agree there was at least some science and logic to my question/discussion rather than
just a "mines bigger than yours" type comment.
I was genuinly interested in the replies.
Thanks fellas
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alistairolsen
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| posted on 26/1/09 at 10:48 AM |
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for a given tyre adding twice as much weight over it willnot give twice as much grip, so a heavier car is always a disadvatage in cornering and
braking.
As said, se7ens excel below 100mph where air resistance isnt a huge issue, above this the body shape and lack of outright power tend to hurt them.
Its worth remembering also that one shouldnt look to peak torque and bhp figures, but rather the area under the curve. This is where some engines are
referred to as peaky and other people prefer a wide spread of torque.
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livelee
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| posted on 26/1/09 at 11:54 AM |
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The post on the previous pages with the lap times tell the story. Does the 750mc have a history of fastest laps by each type of car at the circuits
they race on?
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