Weight Distribution For V-8 Conversions

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Weight Distribution For V-8 Conversions

Postby Louisville Lanning » Fri Nov 10, 2017 6:15 pm

Back earlier this year, one of our members asked me about the weight distribution on my conversion. Richard Miller had some time to burn; so he proceeded to compose his thoughts. I was deleting old emails in my 'in basket' and started reading what he wrote before I deleted it. I decided instead to ask Richard if I had his permission to post his email and he agreed. We welcome all comments on this subject. Here's his unedited thoughts on 50/50 weight distribution:


hi John ,,, woke up early this morning ,,,and hey , I'm retired ,, so I type slow ... here goes ..
feel free to edit as you feel necessary ,, and check spelling ..

Why is 50/50 the ideal weight distribution ? answer that and you answer why it isn't ..I know I heard that many (WAY TOO MANY ) years ago.
and back when English sports cars were light , underpowered , and tires had no grip to speak of it may have been true ...but it sounds like it ought to be true ,,, right ?the answer is as I understand it least , that 50/50 has all four of the tires working equally ,,sharing the load so to speak .. and if all four of your tires are the same size and your car is parked on level ground it would be true ..but our cars are dynamic , they are driven and the weight constantly transfers as the car accelerates and brakes and turns ,, and most of us use larger tires on the front ,, did I get that right ? oh ,, they go on the rear ? okay .. important too to know that a tire provides maximum grip when it is lightly loaded ,, this is relative to the weight on it ,,twice as much weight does not produce twice as much grip ,, also they corner at what is known as a slip angle where the direction that the tire is pointed is not where it is actually going ,, not necessary to take my word for it ,, or any of this ,,one book I have in my collection is HOW TO MAKE YOUR CAR HANDLE , AUTHOR IS FRED PUHN ,,, that last bit ,, slip angle ,, also makes Ackermann steering unimportant ,, ( check CHEVROLET POWER ,,,mostly about building chevy race engines but has a good VEHICLE DYNAMICS section ) I will come back to that .. so lets consider three situations ,GO , STOP ,,AND TURN ,, and let me note that I am talking about high power REAR WHEEL DRIVE cars like we have , not fwd or awd or 4wd,..

accelerating I can spin my two rear tires ,, they alone are trying to provide the necessary grip ,,getting weight onto them can help, ever see a drag car launch with its front wheels hanging in the air that's traction ,, but my car is low and weight transfer is not something it does that well , so starting with more weight on the rear helps out there ,,,maybe 60 percent would be good ,, okay that seems obvious .. more weight on the rear helps with GO..

deceleration ,, braking,, now all four tires come into play and it would be good to get the most out of all of them..but weight transfers on braking,,start with half of the weight on the front tires static and dynamically they will end up with more than 50 percent ,, they will be doing most of the work ,, when we would like all four to be working hard,, also different tire sizes should share the load in proportion to their size ,,, unit loading of the tread face ,, so with smaller front tires and larger rear tires you would like to see the tires loaded accordingly ,, only way to get there is to start with more weight on the rear so that all four can work according to their grip potential,, more weight on the rear helps with STOP.. I almost looped a pick up truck without antilock braking and no load when doing a panic stop once ,, graphic lesson in unloading the rear tires on braking..

cornering .. during steady state cornering , no acceleration or deceleration , weight transfer is side to side and with equal size tires 50/50 would be good....but with smaller front tires and larger rear the weight should be distributed accordingly.. braking into a corner deceleration acts like above ,, but just on one side ,, weight transfer onto front you would like to keep the rear tires doing their part and same for acceleration ,, need to get that bite out of the corner,, just need to keep enough on the front to keep them working .

driving style and tire construction , and power to weight all play a part in IDEAL weight distribution ,, so there really is no one set of numbers right for every car and driver,,at least that is my opinion and the reasons behind it

ever hear of polar moment of inertia ? try this experiment ,, get a carton of eggs ,, remove all but four eggs,, put two eggs at one end and two at opposite end , grasp the carton in the middle and twist it back and forth ,, rotate it ,,, feel the inertia? the initial resistance to movement followed by resistance to stopping ? now move all four eggs into the center and repeat ,, feel how much easier it is to turn the carton back and forth ??
that's why we like MID-ENGINE !!!,,,, late model Corvettes and old Porsche 928 have engine at one end and transaxle at other ,, they are like eggs at end of carton ,, high polar moment ,, good because it makes a car stable ,, doesn't want to change direction suddenly ,, easier to drive .. mid engine is like eggs in middle of carton ,, low polar moment allows it to change direction quickly ,, also makes it less stable ,, better be on your toes driving one.

consider how a car actually turns ,, when you steer the front tires into a corner the front end is yawed into the corner and the car turns around the inside rear tire ,, a lot of weight up front ,, a typical front engine car ,, has a lot of inertia up front and takes a lot to yaw the front end to the side ,,but move the engine to the rear and the front end is easier to deflect ,,yaw ,, to the side and start the cornering..
get the carton of eggs .. put four eggs at one end ,, that's the front of the car ,, grasp the rear end ,, the end without the eggs and move the front side to side,,
that's the resistance to starting to turning that a front engine car has ,, turn the carton around ,, put the engine at the rear ,, grasp the rear where the eggs are and move the front end without the eggs side to side,, feel how much easier it is to turn the front into the corner ?

but you don't want weight outside of the wheel base ,,keep it all between the wheels if possible .. outside of the wheelbase weight has an effect out of proportion to the actual weight...if you have a 50 pound battery up front in a car directly over the front wheels its weight is directly on the front wheels ..
start moving it to the rear and when it is half of the wheel base its weight will be 50/50 front to rear ,,, move it directly over the rear wheels and its weight will be 100 % on the rear wheels ,,,, but keep moving it to the rear and what happens is like a teeter totter . as the battery moves rearward more weight will move to the rear ,, it will transfer off of the front and onto the rear ,, the battery still weighs 50 lbs but its effect on the cars balance becomes out of proportion ,, best to keep weight inside the wheelbase ,, outside the wheelbase it acts like a pendulum and has a greater effect than it should..

so move the mass close to but in front of the rear axle,,

Ackermann steering ,, tires are elastic and deform under steering /cornering loads ,, the more weight /load on a tire the higher this deformation can be and the tire still grip ,, slip angle ,, Ackermann says that the outside tire is running on a larger diameter circle than the inside tire is .,,the diagram shows the car turning around some imaginary point to the inside of the rear axle,,therefore the outside tire should turn less and the inside tire more to match the relative circles they are following ,, great stuff if you are GM and building cars for granny to go to the mall in and she doesn't want to hear her tires going EEEEEEEEEEEEEEEEE while driving at 5 mph and turning on concrete into a parking spot ,,, but because of this tire slip angle thing and the fact that weight transfers from side to side while cornering the outside tire has more weight on it and can run at a higher slip angle ,, the inside tire has less weight on it and runs at a lower slip angle ,,, don't you just love pictures of Porsches with a front tire in the air ? makes me think of a dog at a fire hydrant,,, so the outside tire can actually be turned more and the inside should be turned less ,, the reverse of Ackermann steering .. but your tires will go EEEEEEEEE when parking ...don't blame me .. I learned that from CHEVROLET POWER book vehicle dynamics section ,,, they basically say Ackermann doesn't matter...

well John ,, that's all that occurs to me right now ,, form a line for differing opinions ,, I am willing to learn ,, and you are right ,, browsing thru the members cars section I am flat out amazed at the skill and craftsmanship shown out there ,,every time I go to the garage now I look at my car and think "I gotta up my game "
John Lanning
President - V8 Registry
President - Derby City Corvair Club
'65 Corvair / Mid Engine Cadillac Conversion
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Louisville Lanning
 
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Location: Louisville, Ky

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