Weight as a factor

  • Thread starter Thread starter halfracedrift
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halfracedrift

halfracedrift

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Hey people, as some of you know, i'm doing a science project on comparing the FF drivetrain and the MR drivetrain and i was wondering

just about how much weight affects a car's balance? like.. what %

my dad said it was ~ 5%, but i'm not sure, which is why i'm asking :p
 
Look at the lotus elise... It has much less hp than a Honda S2000 but accellerates almost as good becouse of it lightness. But i saw a program here (I even think you posted it) called CarTest, maybe it can help...
 
What do you mean? Do you mean balance front/rear or side/side? Or do you mean how much does weight factor in to performance in general?
 
What are you getting at? How much weight makes a significant difference in performance?

I would say about 2% more on either front or back is noticeable. Especially on the back.
 
In terms of cornering.. sorry left that out...
and, yeah i know cartest can help.. but i'm not sure how acurrate <-- spell check
it is... so.. yeah
and 12 sec, thats what i meant...
 
Originally posted by halfracedrift
In terms of cornering.. sorry left that out...
and, yeah i know cartest can help.. but i'm not sure how acurrate <-- spell check
it is... so.. yeah
and 12 sec, thats what i meant...
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If you mean whether changing a car's balance makes a difference, then it does. The threshold for what's noticeable will vary from car to car. For example, 2% on a track-prepared Lotus Elise could be the difference between spinning on turn 1 and pulling through it like a champ.

If you mean what a car's balance should be, then -- again --it depends on the car. Porsche 911's are almost 70% rear biased (30% front), with the engine and most of the drivetrain above or behind the rear wheels. BMW's M3 aims for a "perfect" 50-50 balance, front to back. The M3 and 911 are both great cars, and take turns quite well at the limit, but require different techniques because of that difference in weight balance. Mid-engine cars are different still. The car you use doesn't matter, so long as the balance is set for the car you have, and you know the proper technique for that car (FR, MR, etc.).

Lateral balance should always be 50-50. Anything else would cause uneven tire wear, unless the suspension was set to compensate...in which case cornering could be...interesting.
 
Originally posted by Hooligan
Lateral balance should always be 50-50. Anything else would cause uneven tire wear, unless the suspension was set to compensate...in which case cornering could be...interesting.
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Unfortunately, this is almost impossible, because engineers have to account for the weight of a passenger on one side of the vehicle. Lateral balance is rarely 50/50. The BMW M roadster actually has a 50/50 weight split front to rear AND left to right with equal weight passenger and driver.

Anyway, the original question needs to be more specific. Some cars would have more of a noticeable difference than others. It would need to be "What effect would losing Y pounds have on X car".
 
Well a TV show in the UK took an old Jaguar XJS V12, and ran it 0-60. It scored 8.6 seconds. Then they stripped out everything they could, and ran it again. 220KGs lighter, it ran 7.4s to 60. They also said the lighter car was FIVE SECONDS faster to 100, but did not quote times for that.

Weight is everything. As the great Colin Chapman said "To make a good car great, just add lightness"
 
Originally posted by B Campbell
Unfortunately, this is almost impossible, because engineers have to account for the weight of a passenger on one side of the vehicle. Lateral balance is rarely 50/50. The BMW M roadster actually has a 50/50 weight split front to rear AND left to right with equal weight passenger and driver.
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I meant NASCAR-imbalanced, where all you can really do is curve to the left.... ;)

Anyway, the original question needs to be more specific. Some cars would have more of a noticeable difference than others. It would need to be "What effect would losing Y pounds have on X car".
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Exactly. Losing 50kg from the front of an S2000 would be drastically different than 50kg from the front of an NSX, for example. It all depends on the specific car.
 
As a guy that drives a car with an empty weight of under 2100 pounds, I can tell you that some cars are VERY sensitive to small changes in weight distribution; i.e. passengers, fuel level, thinking heavy thoughts, etcetera.

Also, there are some cars that are notoriously unbalanced. For instance, some Mustangs are more nose-heavy than some FWD cars at 57/43 F/R. That might explain why no New Englander with more than three brain cells would ever own one, except possibly as a summer toy.

And then there are well-balanced cars that are just too heavy to handle quick manuevers. While a Subaru WRX has decent lateral grip on a skidpad, a 124 HP Saturn outshines it on the slalom simply because it's ~600 pounds lighter.
 
I've got cartest. ver. 4.5. had it for a few years. there's a cartest 2000. i'm not sure if there are both free and pay versions of ver. 4.5
 
Originally posted by jervinator
As a guy that drives a car with an empty weight of under 2100 pounds, I can tell you that some cars are VERY sensitive to small changes in weight distribution; i.e. passengers, fuel level, thinking heavy thoughts, etcetera.


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:eek:

Yap.. 5-10% fuel load weight increase does a LOT to a car.
 
If a car has perfect 50/50, when it accelerates doesnt some of that shift to the back? So would it be better to have a little weight bias in the front while not in motion? i dunno i confused myself.
 
Originally posted by alikax
If a car has perfect 50/50, when it accelerates doesnt some of that shift to the back? So would it be better to have a little weight bias in the front while not in motion? i dunno i confused myself.
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your thinking of momentum. The weight of the car doesn't move when you accelerate/decelerate (sp?).
 
Originally posted by mark2080
your thinking of momentum. The weight of the car doesn't move when you accelerate/decelerate (sp?).
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Well, yes and no. Momentum is the energy of an object in motion. While it is dependant upon the weight of that object, it doesn't determine the weight, or its distribution.

At rest, the car's momentum is 0. As the car starts to move, that momentum slowly builds in the form of kinetic energy. Since the car is not a solid block, but a complex machine, parts of it have trouble keeping up. (However, it can be shown with quantum mechanics that even a solid block experiences a weight shift.) If you were to somehow manage to keep scales under the car's wheels as the car is accelerating, you would notice a "change" in weight balance. That is, the car would increase its load on the rear tires, while decreasing its load on the front tires (the "hunching back" that softly-sprung cars like the Mustang do).

This shifting of weight balance is useful when manuvering at high speeds. The Porsche 911, for example, is quite rear-biased at standstill (with the engine over the rear wheels). However, this is very helpful taking turns at moderat to high speeds. In a braking situation, the rear-engine setup keeps a substantial amount of the car's total weight on the rear wheels, helping to keep them planted on the road. If the engine were in the front, there would be even more weight up front, and less in the back, reducing friction on the rear wheels. If you reduce rear tire friction too much, the car can spin out (oversteer) on a turn, or under heavy braking.

As for a car at rest, the weight balance doesn't matter...up to a point. A 13.6L V16 rear-engined 911 would have its front wheels off the ground before you even got in the car. ;)
 

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