[xrad]

How well balanced is the 968 with full tank vs empty tank?

100lbs difference?

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[flash]

depending on how you set the front and rear ride height, but at factory spec (i found this once, but cannot remember where, and i'm searching to find the source again):

full:
hardtop is 66lbs tail heavy
as i remember, the cab is about the same amount nose heavy, but that may just be my car - i'm checking

gas weighs about 6 lbs/gallon for a total of about 120 lbs, all over the rear axle

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[Torbjorn968]

<!--quoteo(post=74900:date=Jul 2 2009, 11:35 PM:name=flash)-->QUOTE (flash @ Jul 2 2009, 11:35 PM) <{POST_SNAPBACK}><!--quotec-->depending on how you set the front and rear ride height, but at factory spec (i found this once, but cannot remember where, and i'm searching to find the source again):

full:
hardtop is 66lbs tail heavy
as i remember, the cab is about the same amount nose heavy, but that may just be my car - i'm checking

gas weighs about 6 lbs/gallon for a total of about 120 lbs, all over the rear axle<!--QuoteEnd--><!--QuoteEEnd-->

Then there is the definition of well balanced. Most chassis engineers seem to favour a distribution of weight about 40/60 forward/rear. At least when optimizing for racing, else you would see no tail heavy cars racing. Most of them are.

//TL

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[flash]

that is a factor of increased braking requirement - a slight rear bias is good for that, as it facilitates transfer - 40/60 is pretty heavy, and is not the "norm", but it does happen

that's too much for these cars though 2-3% is about it, even on the biggest of tracks - less on smaller ones - a very slight inside bias is good too - you'll have to change that depending on the direction of the rotation of the track

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[Torbjorn968]

I believe it is also a factor of allowing more rubber at the rear without understeer which helps accellerating out of the corners. A Cayman as one reference is 45/55. 40/60 as a "norm" was from an article in a Swedish mag written by a chassis engineer and seem to be about right if you look at cars such as Lotus Elise (38/62), Ferrari F 430 (43/57). When it comes to race cars or the most extreeme street cars somethin more tail heavy than 50/50 appears to be the aim. You very seldom see a dedicated race car desighed with a front engine. So light weight battery and a GRP hood seems a good idea for our cars!

//TL

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[Cloud9...68]

Yes, that's what makes weight reduction something of a challenging proposition in these cars, since the easiest means to reduce weight (remove the spare tire, pump, and tool kit, replace the stock exhaust with a lightweight cat back system, lightweight seats, plexiglass rear hatch window, etc.) remove it from behind the midline.

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[Torbjorn968]

Optimal is always a relative matter. Optimal in terms of laptimes seems to be slightly tail heavy. Still cars like the 944/968 and BMW E 30 M3 are described as being among the most well balanced cars around which may be that a car with 50/50 in weight distribution is easier to drive fast than the mid or rear engined cars. From what I hear they change direction quicker but they also spin quicker on the limit. So perhaps the 968 concept is about accessible performance?

But in reference to the original question in this thread I think that one do not need to slavishly try to get exaclty at 50/50. And lighter is always better even if removed from the rear, balance can be adjusted to compensate for small changes in weight distribution.

T

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[flash]

the other cars you mention are all mid engine cars - that is why the balance is what it is - it would be nearly impossible to get much closer to 50/50 without the cars being ridiculously heavy

but yes, adjustments can be made, and balance is relative - still, starting off fairly balanced helps make the job of tuning easier

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[Cloud9...68]

It's always amazed and intrigued me that despite the fact that in the ultimate forms of racing (F1, Indycar, Can Am, etc.), the clear advantages of the mid-engine layout have led to its universal adoption, there is still plenty of room on the podium in the more down-to-earth classes for every conceivable layout (front engine/transaxle, rear drive, front engine, rear transaxle, rear drive, mid engine, the seemingly absurd rear engine/rear drive, and even the occasional even more absurd front engine/front drive). It just goes to show that with the right preparation, and a driver with the skill to exploit his or her car's configuration's relative strengths, minute issues like a fraction of a percent more weight in the front or rear than may be considered "ideal," can be ovecome.

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[flash]

absolutely - obviously a mid engine layout makes for the lightest cars, and are therefore easier to build to go fast, but they do race everything - heck, you can even race your lawnmower

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[Torbjorn968]

<!--quoteo(post=74970:date=Jul 5 2009, 07:01 PM:name=flash)-->QUOTE (flash @ Jul 5 2009, 07:01 PM) <{POST_SNAPBACK}><!--quotec-->the other cars you mention are all mid engine cars - that is why the balance is what it is - it would be nearly impossible to get much closer to 50/50 without the cars being ridiculously heavy

but yes, adjustments can be made, and balance is relative - still, starting off fairly balanced helps make the job of tuning easier<!--QuoteEnd--><!--QuoteEEnd-->

I am assuming they are mid engined since this gives the balance the chassis engineers wants as are all mid engined formula racers. Very few performance trackday oriented cars are rear engined, most mid engined and a few front engined.

I also mention this because the original poster had thoughts about balance with the reference of 50/50 as an ideal. Moving a couple of percent away from a perceived ideal to which you are close will seem more dramatic than adjusments a fair way away from what seems to be actually ideal, a decent amount of tail heavyness.

//TL

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[flash]

the largest majority of racecars in this country by sheer numbers are all front engined - i'm not talking about club racing either

hint - it's also the single biggest spectator sport in the country

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[LuJac]

I feel balance is relative to the driver. With a team of open wheelers with two drivers, each car can have very differant setups. More weight in the rear will help rotation, but can't stand as much trail on braking. Trailing is saftey valve when racing. Brake bias has a great effect on this too. A car that is loose is more difficult to drive, but is slightly quicked than one that that understeers.Getting off throttle will bring the nose in (sometimes !!). Understeer is easier to drive, but is slow. I feel unexperiaced drivers usually favor more forward bias as it is usually is easier to control. As experiance grows and they get quicker they look for better turn in. Then again, there is not much you can do with a relativly stock Porsche. The factory did a VERY good job with the compromises that are needed for a dayly driver. I've driven Porsches for almost 40 years each has a differant approach to handling and balance. Just my thoughts !!!
lujac

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[flash]

all valid - i generally prefer a tail heavy car myself, but i like a touch of controllable oversteer - i have had to work hard to get that in this car, particularly since most of the weight loss has been in the rear

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[biotechee]

NASCAR - yuk.

Sorry, no offense to any NASCAR fans intended....

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[flash]

lol - yeah - i didn't say i liked it, only that it was HUGELY popular here, and dominates racing

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