Weight Distribution?
Discussion
21TonyK said:
Thanks Tony. I'm interested to compare the car that everyone hails as the ultimate handling car (the Elise) with that other car that everyone says doesn't handle well because it has its engine in the wrong place... I only have one source on the latter's weight distribution, but it seems that it's the Elise has the greater rear bias...
Not all down to fornt/rear distribution, it depends on the position of the CoM within the width and height of the car as well as the length and the actual weight, but I'm sure you know that 
50/50 for example with the CoM higher up isn't going to be so great, but 32/68 with low down CoM could be better for example.
50/50 for example with the CoM higher up isn't going to be so great, but 32/68 with low down CoM could be better for example.LivinLaVidaLotus said:
Not all down to fornt/rear distribution, it depends on the position of the CoM within the width and height of the car as well as the length and the actual weight, but I'm sure you know that 50/50 for example with the CoM higher up isn't going to be so great, but 32/68 with low down CoM could be better for example.
Yes, you're right. How else could we compare the Elise and 911?.. Surely the other masses in the car are distributed in a similar manner front:rear? Does this mean the Elise is more of a pendulum to drive than a 911? 50/50 for example with the CoM higher up isn't going to be so great, but 32/68 with low down CoM could be better for example.Thinking of the height of the CofM, the Elise engine's CoM must be much higher than that in a Porsche! The top of the engine on a 911 is level with your knees, yet on the Elise it's up near your middle (flat six vs in line four).
The Elise has most of its weight very near the centre of mass, giving it an extremely low polar moment of inertia, whereas the 911 has its mass pushed more towards the extremes. This means that the Elise needs far less rotational force to turn the car (I mean to change its orientation not direction of travel) which makes it far more responsive, especially in low-speed corners.
I think the idea that 50/50 weight distribution is "perfect" was invented by BMW's marketing department. Friction is a coefficient with respect to weight so all things being equal, the front and rear of a car that's cornering neutrally will break traction at the same time regardless of weight distribution (although behaviour after traction has broken is different). Of course in reality things like relative tyre temperatures will be affected by weight distribution so it does make a difference, but not as much as you might think. Rear biased weight is good (in a RWD car) for accelerative grip too.
I think the idea that 50/50 weight distribution is "perfect" was invented by BMW's marketing department. Friction is a coefficient with respect to weight so all things being equal, the front and rear of a car that's cornering neutrally will break traction at the same time regardless of weight distribution (although behaviour after traction has broken is different). Of course in reality things like relative tyre temperatures will be affected by weight distribution so it does make a difference, but not as much as you might think. Rear biased weight is good (in a RWD car) for accelerative grip too.
Sam_68 said:
RobM77 said:
How else could we compare the Elise and 911?.. Surely the other masses in the car are distributed in a similar manner front:rear? Does this mean the Elise is more of a pendulum to drive than a 911?
But you're forgetting the magic words: 'Polar Moment' 
It seems that yesterday afternoon I did forget about that I'd love to know how the Polar moments of the two cars work out. More to the point, if the 911 engine is behind the rear axle, how on earth does it manage 60R/40F weight distribution?!?!21TonyK said:
If you take the average kerb weight plus driver you're getting closer to a 40/60 distribution. Combined with a very low mass and low CoM I reckon the Elise is pretty damn good. Certainly "feels" better than the BMW "50/50" weight distribution!
Interesting. I've got an Elise S2 111S and have had a BMW E36 325i and a BMW E46 330ci in the past and the BMWs were definitely better balanced - no question at all.RobM77 said:
Interesting. I've got an Elise S2 111S and have had a BMW E36 325i and a BMW E46 330ci in the past and the BMWs were definitely better balanced - no question at all.
I don't think "better balanced" has any kind of common definition. Some people seem to use it to mean that a car has a high polar moment of inertia, making it more reluctant to change orientation and hence less "twitchy"; some people use it to mean exactly the opposite, ie capable of changing direction quickly; yet another group of people mean tending towards 4-wheel-drift when it breaks grip (which tends to come from a high polar moment of inertia). I think the most common definition is probably that a car is "well balanced" if you can easily and predictably adjust its cornering attitude with the throttle. I suppose the "easily" bit comes from a relative lack of grip and the "predictably" bit comes, again, from a higher polar moment of inertia.
Edited by kambites on Tuesday 18th September 09:04
kambites said:
RobM77 said:
Interesting. I've got an Elise S2 111S and have had a BMW E36 325i and a BMW E46 330ci in the past and the BMWs were definitely better balanced - no question at all.
I don't think "better balanced" has any kind of common definition. Some people seem to use it to mean that a car has a high polar moment of inertia, making it more reluctant to change orientation and hence less "twitchy"; some people use it to mean exactly the opposite, ie capable of changing direction quickly; yet another group of people mean tending towards 4-wheel-drift when it breaks grip (which tends to come from a high polar moment of inertia). I think the most common definition is probably that a car is "well balanced" if you can easily and predictably adjust its cornering attitude with the throttle. I suppose the "easily" bit comes from a relative lack of grip and the "predictably" bit comes, again, from a higher polar moment of inertia.
Edited by kambites on Tuesday 18th September 09:04
What I was referring to was the provocation that the cars needed when turning into a bend to attain a neutral stance, the general feel of the car mid corner, and the shift of weight and rear traction when exiting the bend.
Both BMWs needed less provocation to be neutral on turn in, and if you got things wrong you were never far off a 50:50 grip balance front:rear. On corner exit, traction wasn't as good as the Elise.
In contrast, my Elise needs a fair bit of provocation to be neutral on turn in, and has masses of grip on corner exit. Without that all important good turn in, mid corner my Elise feels light at the front and heavy at the rear (like the Clio V6, for instance), although with a good turn-in the car is amazingly adjustable mid corner (moreso than the BMW), which results in very pleasing handling. Thankfully, the turn-in is easy to get right, unlike a FWD car for instance (e.g. my old Metro race car). On corner exit the Elise really digs down at the back and finds masses of traction.
A big difference between the BMWs and the Elise is during oversteer. The BMWs felt balanced during oversteer, in fact with an LSD I reckon I could hold one sideways for a long time without too much trouble (neither of my cars had LSDs). The Elise oversteers progressively and lucidly, but once out to a certain angle, you can really feel the weight at the back - I mean this in two senses: firstly, if you don't stay on the power it goes out very quicky indeed, and secondly when you're oversteering there is more a feeling of driving a pendulum than in the BMW, where everything felt balanced, even at large angles of oversteer.
Phil-CH said:
RobM77,
Don't you drive a Caterham? If so, why not use that to compare the weight distribution to the Elise? AFAIK, most Caterhams have a 50:50 weight distribution (probably including driver)...
Cheers Phil
Don't you drive a Caterham? If so, why not use that to compare the weight distribution to the Elise? AFAIK, most Caterhams have a 50:50 weight distribution (probably including driver)...
Cheers Phil
It's a full on racing car, so it's very tricky to compare with road cars as it has full racing suspension and a racing focused setup.I can look up the weight distribution of mine when I get home. I know it's not bang on 50:50.
If you're interested though, the balance feels very good, it's incredibly quick witted when it comes to moving in and out of oversteer and understeer, although once it's there it is actually very stable and doesn't want to spin that easily. Interestingly, mine is currently set up to be very edgy indeed, and I probably need to calm the rear end down a bit before the next race (I had massive problems with understeer in my first race, and the guy that set it up went a little too far in removing it!), although you can always feel the weight of the engine up front. One of the most alarming features is the front end lift at speed. Much above about 80-90mph, the front end feels like it's lifting off the ground when you corner. It's weird - like understeer with no feeling. I'm taking the Craners at Donny at about 110mph, and you can really feel it there.
Edited by RobM77 on Tuesday 18th September 09:55
RobM77 said:
It's a full on racing car, so it's very tricky to compare with road cars as it has full racing suspension and a racing focused setup.
I would think comparing an Elise to a race-setup caterham with close to 50:50 weight distribution is a lot closer than using a large and soft BMW (with CoM rather high) with also 50:50 - which is why I brought it up. RobM77 said:
I can look up the weight distribution of mine when I get home. I know it's not bang on 50:50.
I know the Superlights come close to 50:50. Doing a search on Google confirms that. Wikipedia states a 49:51 for the Caterham CSR as well...Well, anyway - I do know that the traction is a bit better in the Elise. That weight at the back really helps to get the power down. On the other hand, I have a bit more respect in the corners simply because I know that once the weight at the back starts to shift, it *can* bite you. In the Caterham however, it seems to take an awful lot to lose complete control of the back end. At least in my (somewhat limited) experience...
Cheers Phil
Edited by Phil-CH on Tuesday 18th September 10:18
Phil-CH said:
RobM77 said:
It's a full on racing car, so it's very tricky to compare with road cars as it has full racing suspension and a racing focused setup.
I would think comparing an Elise to a race-setup caterham with close to 50:50 weight distribution is a lot closer than using a large and soft BMW (with CoM rather high) with also 50:50 - which is why I brought it up. Phil-CH said:
RobM77 said:
I can look up the weight distribution of mine when I get home. I know it's not bang on 50:50.
I know the Superlights come close to 50:50. Doing a search on Google confirms that. Wikipedia states a 49:51 for the Caterham CSR as well...Phil-CH said:
Well, anyway - I do know that the traction is a bit better in the Elise. That weight at the back really helps to get the power down. On the other hand, I have a bit more respect in the corners simply because I know that once the weight at the back starts to shift, it *can* bite you. In the Caterham however, it seems to take an awful lot to lose complete control of the back end. At least in my (somewhat limited) experience...
Cheers Phil
Yes, that's true. I'm not sure if I'm allowed to post on-track footage for copyright reasons, but I got two massive oversteer moments on video whilst testing the other week at Brands (I carry an in-car bullet cam). The back went unbelievably quickly just after turn-in to Druids. I flicked on half a turn of opposite lock (I'm running a quick rack, so that's probably equivalent to a full turn of lock in an Elise!). The oppo lock then just stays on for the entire bend, gets wound on even more just after the apex, and then gently wound on during the exit. It snaps quickly, but doesn't want to spin - in the dry, at least!Cheers Phil
the words "an elise" and "a 911"
dum de dum.
elises are generally quite different between cars.
same with 911's, might just say "carrera" on the boot but can you tell if its sport chassis, sport suspension, X51, etc etc etc, just from looking at it from the outside?
most 911's are specced differently from another, like most elise owners buy add ons to improve their elise porsches seem to add options from the word go and apart from the switchable exuast rarely seem to add anything else on once its out the showroom (no one will touch it come resale if you do)
having owned "a 911" and "a s1 elise" and having spent a month everyday use in a S2 i can tell you the 911 felt more grippy, stuck to the ground better and not that much heavier.
the elise was more "chuckable" as in you can duck around corners "ass out" and catch it easily, although across bumpy roads is alot more skittish and feels less stable.
the S2 was somwhere in the middle, I didnt go chucking it about as it wasnt my car but the ride felt more like the porsche, it was an S but didnt feel as fast as my std S1 . . . . .
on a tight twisty track without a long straight im sure the S1 would keep with the porsche, just about but that would be quite the opposite if there was a straight run, the 911 would leave it for dust.
dum de dum.
elises are generally quite different between cars.
same with 911's, might just say "carrera" on the boot but can you tell if its sport chassis, sport suspension, X51, etc etc etc, just from looking at it from the outside?
most 911's are specced differently from another, like most elise owners buy add ons to improve their elise porsches seem to add options from the word go and apart from the switchable exuast rarely seem to add anything else on once its out the showroom (no one will touch it come resale if you do)
having owned "a 911" and "a s1 elise" and having spent a month everyday use in a S2 i can tell you the 911 felt more grippy, stuck to the ground better and not that much heavier.
the elise was more "chuckable" as in you can duck around corners "ass out" and catch it easily, although across bumpy roads is alot more skittish and feels less stable.
the S2 was somwhere in the middle, I didnt go chucking it about as it wasnt my car but the ride felt more like the porsche, it was an S but didnt feel as fast as my std S1 . . . . .
on a tight twisty track without a long straight im sure the S1 would keep with the porsche, just about but that would be quite the opposite if there was a straight run, the 911 would leave it for dust.
Sorry I wasn't trying to compare the performance of the two cars, that'd be down to spec etc,, as you rightly say. I was, however, interested in the fact that the 911 has a reputation for being a pendulum and therefore difficult to drive, when in fact that Elise has slightly more rear weight bias!! The key, as Kambites and others have pointed out, is clearly polar moment of inertia. I'd love to know how that compares between the cars.
I wasn't trying to compare the performance of the two cars, that'd be down to spec etc,, as you rightly say. I was, however, interested in the fact that the 911 has a reputation for being a pendulum and therefore difficult to drive, when in fact that Elise has slightly more rear weight bias!! The key, as Kambites and others have pointed out, is clearly polar moment of inertia. I'd love to know how that compares between the cars.RobM77 said:
the 911 has a reputation for being a pendulum and therefore difficult to drive
lolits all rubbish mate.
anyone can drive a RWD 911 quickly, thats what they are designed for.
if anything the elise is harder to drive becuase its lighter and doesnt have the massive amount of rear wheel grip that the 911 has thus can jump about a bit when pushing on.
DucatiGary said:
RobM77 said:
the 911 has a reputation for being a pendulum and therefore difficult to drive
lolits all rubbish mate.
anyone can drive a RWD 911 quickly, thats what they are designed for.
if anything the elise is harder to drive becuase its lighter and doesnt have the massive amount of rear wheel grip that the 911 has thus can jump about a bit when pushing on.
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