Stupid question of the week

[65 3 times]

OK..... If you release the torsion bars on the trunk lid and let it relax in the catch does it transfer the trunk lid weight to the rear bumper area more than when the torsion springs are engaged and under tension ?????? Dave

 

[Mike Gaines]

Duh....absolutely..I have already done that to mine just to put more weight over the rear of the car...a very simple trick.

 

[khryslerkid]

And just how many pounds of weight are we talking? Just curious.

 

[Mike Gaines]

And just how many pounds of weight are we talking? Just curious.

I do not know....what I do know is that just lifting the deck lid with the springs disabled is really tough. seems like the deck lid weighs about 75lbs when trying to lift it up...probably isn't that much but it sure isn't light...try it and you will see.
If you only use your car for mainly drag racing and you aren't loading groceries and luggage it the trunk, why not do it ?

 

[bobtile]

I did that with mine, so I was curious as well.
This is what I have!
Subtract 3 lbs. For the wood.

 

[65 3 times]

I kind of think it is like putting your feet in two five gallon buckets and trying to pick yourself up. Once the latch catches the weight it matters not if the springs have tension or not. We need a physics professor on this one. Dave

 

[HT413]

We need a physics professor on this one. Dave

Not a college professor, but I do teach high school physics and engineering, so I guess I'll have to do lol.

First, it depends on the car. My 69 belvedere lid turns down at the rear panel so lots more weight is already on the tail of the car. I bet that with the springs installed, something like 75-80% of the deck lid weight is on the hinges and the rest in the latch. it's not like turning the key makes the lid fly into the air, right? (At least with mine anyway).

Now, with no springs, and given that so much of the deck lid weight on my lid is so far back anyway, I bed close to 75% is at the latch.

so we are talking about moving 50% of the deck lid weight rearward maybe 30". I just checked my records, I measured my old steel decklid at 47lbs before I replaced it with fiberglass.

So I'd guess with spring removal, we are talking about moving 20 lbs from the hinges rearward to basically the bumper. I'd say, though it's not as dramatic as battery relocation, every little bit helps!

 

[dla4567]

The weight will shift towards the rear. But due to leverage you will lose a greater amount of weight at the front of the trunk lid. For example; you may gain 5 pounds at the rear of the lid, but lose 30 pounds at the front. (Imagine picking up a 20 pound sack, then imagine picking up a 20 pound sack with a shovel). Make any sense? Would you rather have 2 quarters or 10 nickels? In the end it makes no difference.

 

[Photon440]

The only difference would be less weight in the spring area. Whether the lid is resting on the latch or has spring tension at the front of it will only change the lines of force; the actual weight on the tires will stay constant. For example, imagine you and a friend were lifting two sheets of plywood. In one instance, the top sheet was held up by a spring at one end, in the other instance the top sheet was supported by a vertical edge. In both cases, except for the weight of the spring, the lifting effort by each person would be the same.

 

[Mike Gaines]

You are right....all of you....it is way to complicated for me... I guess the answer to everything here is to sell my steel deck lid and put on a lift off fiberglass deck lid to save about 45 pounds which is almost a half of 10th. Then I will drill out my transmission cross member mount and drill a bunch of holes in my inside door frame, etcetera. What about the front fender inner panels ? Anyone doing anything there and also the radiator support crossmember?

 

[HT413]

The only difference would be less weight in the spring area. Whether the lid is resting on the latch or has spring tension at the front of it will only change the lines of force; the actual weight on the tires will stay constant. For example, imagine you and a friend were lifting two sheets of plywood. In one instance, the top sheet was held up by a spring at one end, in the other instance the top sheet was supported by a vertical edge. In both cases, except for the weight of the spring, the lifting effort by each person would be the same.

View attachment 353984

Not so sure about that. Obviously, the weight of the car doesn't change (other than the small change from taking the springs out). But taking weight from directly over the axle and hanging it over the rear bumper, has the effect of lifting the front end and shifting the car's center of mass a hair toward the rear tire.

It's not much, but as they say, if you want to shave a pound, don't look for one place to cut the pound, look for 16 places to shave an ounce.

 

[HT413]

You are right....all of you....it is way to complicated for me... I guess the answer to everything here is to sell my steel deck lid and put on a lift off fiberglass deck lid to save about 45 pounds which is almost a half of 10th. Then I will drill out my transmission cross member mount and drill a bunch of holes in my inside door frame, etcetera. What about the front fender inner panels ? Anyone doing anything there and also the radiator support crossmember?

This might sound nuts (pun intended), but someone once posted how they once shave a significant amount of weight by trimming all bolts to the minimum necessary length and replacing some in non critical areas with aluminum bolts (who needs bit steel bumper bolts on a fiberglass bumper?)

He put all trimmings and extra / replaced bolts into a bucket so he had an idea of how much he saved.

The idea always appealed to me and I definitely plan to get to it little by little.

 

[Photon440]

taking weight from directly over the axle and hanging it over the rear bumper

But it isn't doing that. The lines of force may take a different route but the balance of weight stays the same. The weight is where it is and is being pulled down, how it is attached won't affect it. If there are two similar balances such as this, both weights will drop down the same even though they have different attachment points.

 

[65 3 times]

I agree. With the latch closed it is like winding up a spring and attaching both ends to the same surface.. This kind of stuff keeps me crazy cause my brain goes back and forth depending on how good the argument is.....Dave

 

[bobtile]

Science wars!!!!!
Im taking this to the discovery channel.

 

[HT413]

But it isn't doing that. The lines of force may take a different route but the balance of weight stays the same. The weight is where it is and is being pulled down, how it is attached won't affect it. If there are two similar balances such as this, both weights will drop down the same even though they have different attachment points.
View attachment 354055

Call me a geek, but I'm loving this conversation. Now let me just say, I'm not sure if my typed words are coming across how I intend, so I'll just say that im having fun with this and am in no way 'arguing'.

That said, I'm thinking of this from purely a point of view of lifting up the deck lid. With no springs, I have lots of weight to lift, and with the decklid closed, the weight that i am lifting rests on the latch.

Now with decent springs, my effort is significantly reduced. This, in my mind, means that since we are lifting basically at the latch point, the latch must see less weight as well. The thing is that the decklid weighs the same, so where is that weight going? Im thinking that the springs are lifting that weight for me, but the weight isnt going away. (Like someone said above, that would be like standing with your two feet in buckets and lifting yourself off the ground.) No, the weight has to go somewhere, so the springs are removing some weight from the latch and transfering it to the hinges.

 

[65 3 times]

OK HT413 you are a geek !! Isn't it great. I feel sorry for PC correct non geeks. Who else would relish in going over 100 mph in a 51 year old car !! Anyway I called an engineering buddy of mine last night and he promptly yawned and said all we were doing is loading a spring against a fixed point. (latch) Said when lid is closed it makes no difference. About an hour later he called me back and said he wanted to think about it more. I'm borrowing a digital scale and building a model of Photon440's plywood and spring drawing. Film to follow. Geeks United.....Dave
(Call Animal Planet instead)

 

[dla4567]

Call me a geek, but I'm loving this conversation. Now let me just say, I'm not sure if my typed words are coming across how I intend, so I'll just say that im having fun with this and am in no way 'arguing'.

That said, I'm thinking of this from purely a point of view of lifting up the deck lid. With no springs, I have lots of weight to lift, and with the decklid closed, the weight that i am lifting rests on the latch.

Now with decent springs, my effort is significantly reduced. This, in my mind, means that since we are lifting basically at the latch point, the latch must see less weight as well. The thing is that the decklid weighs the same, so where is that weight going? Im thinking that the springs are lifting that weight for me, but the weight isnt going away. (Like someone said above, that would be like standing with your two feet in buckets and lifting yourself off the ground.) No, the weight has to go somewhere, so the springs are removing some weight from the latch and transfering it to the hinges.

You are focusing on the weight of the lid to the car instead of the weight of the car to the suspension. You are not factoring in the rotating force. As the mounting point is moved further from center the greater the rotational force, thus keeping the downward force centered according the the weight of an object, (not the size). To shift the weight or the lid to the car, you move its mounting point. The shift the weight of the car to the suspension, you move its center according to weight.

 

[HT413]

Haha, this sure hurts the brain! Dla, photon and the rest, I hear what you're saying and heck, I may turn tail and agree with you, just not yet!

Let's imagine that we have 2 scales on the car. One measuring weight on the latch, one measuring weight on the hinges (ok, maybe one per hinge).

Let's then increase the spring force so it won't quite let the deck lid close. Where is the weight then? Can't be on the latch, has to be on the hinges, right? Even if you force the lid to latch, the spring will be pulling upward on the latch and pushing downward with the same force on the hinges (equal and opposite direction, but split between the 2 hinges).

So this over-strong spring will remove all weight from the latch and transfer it forward to the hinges.

Then with rotational force (what we call Moment), it's true that the center of mass creates a rotational moment that forces the decklid to close, but the spring is effectively cancelling this rotational force (moment) out.

I think. Haha.

 

[dla4567]

The spring is causing the rotational force and transferring it to the car. Example: with no spring it takes 20 pounds of force to lift lid above the latch. With spring it takes only 1 pound of force to lift the lid. That means the spring is putting 19 pounds of upward force on the lid. Equally, it is putting 19 pounds of downward force on the latch. When you remove the spring you feel the extra weight of the lid but are forgetting to subtract the loss of down force on the latch that the spring was creating. You can feel the force of the lid against gravity but can not feel the down force so it gets forgotten. But it is still there. "For every action there is an opposite and equal reaction". You are weighing the lid. We are not concerned with the weight of the lid, but the transfer of the weight of the lid. The transfer of the weight is at its center regardless of its mounting point.