Discussion about car weight, weight distribution and turning

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Having so many brilliant minds here I wanted to open the floor for discussion on the topic of weight distribution.

  • First of all, what is the approximate weight distribution of our cars? Whatever it is, it is probably far from 50/50.
  • In theory the lighter the car the fastest it would be able to change directions, thus turn faster.
  • Although a very generic statement, a 50/50 bias is a "good" goal, maybe a little more rear bias is better, but at least close to 50/50. I understand there are many variables involved here.

The above aspects brings me to a thought. Assuming I can't change weight bias by removing weight, as in our cars unless you change to aluminum block or make some more drastic changes in the front, it would be hard to move the bias to the rear. If you add weight to the rear you can probably come closer to 50/50, but you will be adding weight to the car, which will make it harder to change directions. So the question would be, what is the balance between increasing weight, and changing bias when you can only add weight? As you can see, it is an interesting conundrum so I want to hear your thoughts.

PS: I also understand that there are other options to lighten the front beyond an aluminum block, but I expect the changes would need to be dramatic to make a significant difference in the bias. Yes, you can go to an aluminum intake, remove the A/C compressor and some small change here/and there, but that probably will make too little of an impact, or maybe I am wrong and it would be more important.

 

mjlan

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According to this vintage road test, weight distribution of a Boss 351 is listed as 57.1 / 42.9

https://www.curbsideclassic.com/blog/vintage-reviews/vintage-reviews-1971-ford-mustang-boss-351-its-possible-that-stylist-cant-work-in-a-sporty-medium/

If I'm remembering my vehicle dynamics classes (argh memory test), the feeling of crisp response and nimble handling comes from having a low CG and keeping all of the heavy parts as close to that CG as possible.

As far as the traditional muscle car front weight bias issue is concerned,  battery relocation is your best bang for buck. Weight reduction in front of the CG (aluminum engine parts etc.) will shift the bias rearward.

 
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Don C

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Using the 1971 AMA Specifications I came up with this:

Coupe with 302 and automatic 57.0%/43.0% front/rear

Mach I with 302 and automatic 57.2%/42.8% front/rear

Mach I with 351 Cleveland 4V and 4-speed - 58.0%/42.0% front/rear

Mach I with 429SCJ and 4-speed - 60.1%/39.9% front/rear

I'm out of space, so couldn't post the chart.

 
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Using the 1971 AMA Specifications I came up with this:

Coupe with 302 and automatic 57.0%/43.0% front/rear

Mach I with 302 and automatic 57.2%/42.8% front/rear

Mach I with 351 Cleveland 4V and 4-speed - 58.0%/42.0% front/rear

Mach I with 429SCJ and 4-speed - 60.1%/39.9% front/rear

I'm out of space, so couldn't post the chart.
Thanks. Depending of the configuration, it is a little better than 60/40. With some of the aluminum part replacements and mods I may be close to 57.5/43.5 - I still have the battery on front, which in should be about 40lbs. The Boss has the battery in the back so it looks like it is close to 57/43.

I agree that a low CG is critical, but would a car with a light rear tend to oversteer? Traction aside we would need wider tires in the front than the rear, but that's silly because we need wider rear tires to transfer that V8 power to the ground.

I am just wondering if you add a ballast to the rear end of the car, would that improve cornering ability, or not really because now the car is much heavier.

 

rvrtrash

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As far as front weight bias, you can replace the Mach 1 urethane bumper with a chrome, or even fiberglass, version and save at least 100 lbs. What worked for me way back when, was lowering the car 1" in front, 1/2" in back, using stiffer springs and shocks and larger sway bars front and rear. This lowered the center of gravity and reduced body roll. While it may sound cliche', the car handled like it was on rails, and felt every bit as nimble as the TR6 I also had at the time.

 

73pony

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As mentioned above, a battery relocation to the rear passenger side makes a difference. I also lowered the car 1" all around, aluminum intake, removed AC, larger front sway bar (1 1/8"), all new stock style suspension components (I boxed in the LCA's to stiffen them), 12.7:1 steering conversion, 17x8 in front 17x9 in rear, KYB Gas-A-Just shocks all around (kind of stiff). These mods made a complete night and day difference in how the car handles in the corners. So I reduced weight in front by removing or lightening items and relocated some of that to the rear to help weight distribution (getting closer to that 50/50 mark), this along with the lowered center of gravity and stiffening of the LCA's and larger sway bar all work together to improve handling. While just doing a weight distribution change will help some it is a combination of several things to really see and notice a difference. Hope this helps. 

 
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As far as front weight bias, you can replace the Mach 1 urethane bumper with a chrome, or even fiberglass, version and save at least 100 lbs. What worked for me way back when, was lowering the car 1" in front, 1/2" in back, using stiffer springs and shocks and larger sway bars front and rear. This lowered the center of gravity and reduced body roll. While it may sound cliche', the car handled like it was on rails, and felt every bit as nimble as the TR6 I also had at the time.
Wow. I never though that the urethane bumper was that heavy. Good to know.

 

vintageman

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Yea, the 73 front bumper I have is heavy as hell, especially when it has the mounting brackets on it. I will be going with a chrome front bumper, already have the 71-72 front bumper mounts installed.

Tom

 

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Wow. I really can't see myself running so close to the edge to really notice a difference in front bumper weight.

 

Fabrice

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I can only say that I did not regret removing the heavy 73 bumper on my grandé and relocate the battery in trunk above rear axle. The heavy Intake, waterpump, fan etc.. replaced by aluminium ones, these without GC in mind, but combined all together it gave a massive difference in handling, especially on the highway exits we have here, where the car would plunge on the front under hard braking and loose grip on the rear while in the curve. Unless you go for originality, these easy changes do really make a difference. Reminds me I should be enjoying all this very soon again! Yeah!

 
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I can only say that I did not regret removing the heavy 73 bumper on my grandé and relocate the battery in trunk above rear axle. The heavy Intake, waterpump, fan etc.. replaced by aluminium ones, these without GC in mind, but combined all together it gave a massive difference in handling, especially on the highway exits we have here, where the car would plunge on the front under hard braking and loose grip on the rear while in the curve. Unless you go for originality, these easy changes do really make a difference. Reminds me I should be enjoying all this very soon again! Yeah!
Did you replace the urethane bumber for the chrome?

Sent from my SAMSUNG-SM-G930A using Tapatalk

 

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Ounces add up to pounds.

Aluminum Intake manifold.

Headers instead of cast exhaust manifolds.

Aluminum heads.

Fiberglass hood (with or without hinges).

Remove AC.

Aluminum accessory drive kit for alternator etc.

Fiberglass front bumper.

Aluminum water pump.

Fiberglass fenders.

Battery relocate.

All that adds up to quite a bit.  

Have you exhausted all of the "tuning" options to make your car handle?  What is it doing?  Oversteer?  Understeer?  What are your alignment numbers?

 

c9zx

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This old post may be helpful. 




 
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Have you exhausted all of the "tuning" options to make your car handle?  What is it doing?  Oversteer?  Understeer?  What are your alignment numbers?
I don't have an specific issue with the car handling at this time, but there is always part of me looking for more performance if there is. I am brain storming at this time.

 

Don C

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Don't forget the driver, wonder how much a remote control system would weigh?  :classic_biggrin:

 
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Doing some math based on Chuck's car weight results.

Total: 3,583 lb (58.25/41.75 F/R%)

Front: 2,087 lb; Rear: 1,497 lb

Let's make a couple approximations (simplified not taking into account the weight distance from the CG)

Assuming a battery weight of 40 lbs, but adding 20 lbs of wiring equally rear/front:

Weight: 2,047/1,537 (57.18/42.89 F/R%)

Assuming the front bumper is 100 lbs, and adding a 20 lb bumper (??) - these may be amplified in real life due to how far is forward.

Weight: 1,967/1,537 (56.14/43.86 F/R%)

EDIT PS: in summary, approximating:

-by shifting ~35 lbs from front to rear will shift the weight by 1%.

-by removing ~70 lbs of front weight will shift the weight by 1%.

 
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Bentworker

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I dig you breaking out the math!

With 3500 pound car if you moved 35 pounds from the front to the back you would reduce your front by one full percent and raise the rear one full percent.  A 57/43% car would become a 56/44% car for example.  I follow that math, seems like a good reason to move the battery, or at least go with one of the lightweight lithium ones up front.  

 

detritusmaximus

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Don't forget that controlling the weight transfer (fore and aft, side to side) is a big piece of the puzzle. Even if you get 50/50 distribution, weight transfer can still cause you problems. Especially if your weight balance requires moving things further from the cg...the longer the pendulum, the more it takes to control it.

 
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