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PostPosted: October 10, 2017, 7:15 am 
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JackMcCornack wrote:
wrightcomputing wrote:
...57% on the rear at 1760lbs with driver. Since going on a diet I...am down to 1640lbs with driver.
Whoa! That's some diet, dude! Seriously, 120 pounds?

Car diet not driver diet. I'd already dropped a lot of weight off the car and was adding around 70lbs of ballast. The ballast was under the diff which is why I lost the rear weight %.

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PostPosted: October 15, 2017, 4:05 pm 
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40/60 is pretty rear-heavy. I wouldn't have picked that as the ideal, though maybe it depends on the application.

I would have guessed the ideal was closer to 45/55. That's about what an F1 car is, though I know it is regulated there.

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PostPosted: October 18, 2017, 7:56 am 
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Omaha Vette Graveyard wrote:
40/60 is pretty rear-heavy. I wouldn't have picked that as the ideal, though maybe it depends on the application.

I would have guessed the ideal was closer to 45/55. That's about what an F1 car is, though I know it is regulated there.



You are right it depends on the application. When Ferry Porsche designed the rear engine sportscar, a good deal of post war popular racing in Europe was what was done in hill climbing. There the 40-60 weight distribution was working very well (ie: acceleration, braking and rapid succession of stiff cornering). :cheers:


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PostPosted: October 20, 2017, 9:29 am 
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Typically as the power to weight goes up you want higher rear weight distribution. Each car will vary but I think 55-60% on the rear is ideal.

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PostPosted: October 22, 2017, 11:19 pm 
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I would have thought the ideal would depend more on the level of available traction.

Maybe it's another way of saying the same thing though; heavier usually means less traction per pound.

When traction is high, weight transfer is high and the front tires get pretty light under acceleration. Also, rear-heavy cars tend to have narrower front tires to avoid oversteer issues, and that can create problems with braking in a high-traction environment when a higher percentage of the stopping power is in the front.

If one were on a low traction surface, I figure they'd want 70+% on the rear during acceleration and 70+% on the front during braking.

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PostPosted: October 23, 2017, 1:37 am 
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Hmm, over thirty years ago I used to have a modified '65 Corvair that beat up on the current Porsches.
Also had a Fiat 850 Spider that did VERY well in the twisty bits, to the point of annoying the sport bike riders of the day.
My 67 XKE went like hell each outing, until the disc brakes faded.
But my Noble P4 was the one that really spoiled me so that I now try to make almost everything some sore of "Mid-Engine", IRS equipped, or both.
My Trick-6 and Alfa/Dio are both being built "Forward mid-engine" with the drivetrains well behind the front axle centerline.
For the TRIumph/buiCK V6 putting the engine further forward would certainly simplify the build but would also tend to retain the tail happy handling. I've spun a stock GT-6+ on the dry road at moderate speed with no excess or sudden moves.

I would say that engine placement is much more important for an all-out race car than anything driven normally.
Rear engine can be compensated for, as can every other possible engine placement to a large degree.

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PostPosted: October 23, 2017, 2:23 pm 
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Omaha Vette Graveyard wrote:
Also, rear-heavy cars tend to have narrower front tires to avoid oversteer issues, and that can create problems with braking in a high-traction environment when a higher percentage of the stopping power is in the front.

If one were on a low traction surface, I figure they'd want 70+% on the rear during acceleration and 70+% on the front during braking.
This is an example of why I called the rear-engine layout "largely misunderstood" in my original post. The car with the tire width distribution more closely matching its weight distribution starts of with the advantage when all four tires are being worked. Especially in higher powered cars, where even neutral and front-heavy cars also generally have wider rear (narrower front) tires in opposition to their weight distribution, this results in braking typically favoring the rear-heavy cars. Similarly, 70% on the front during braking would be closest to 'ideal' for a reverse-trike.

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