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Discussion Starter #1
Today Frday Nov 12
went to Tucson 5 FFR's had a weigh in party at Micheal Treece's place with NASCAR scales:

Old 3850 weights w/out driver:
LF 512 lb RF 532 lb Front Total 1044 -->46%
LR 645 lb RR 589 lb Rear Total 1234 -->54%
Lft Total 1156 Rt Total 1121

Grand total 2277 lbs

With driver 44%/56%

Interesting, huh?
 

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extremely interesting. I always wondered what the exact weight distribution was on the FFR. This is of course dependant on what engine, rear -end, etc you are using, but a very good example of how well they are proportioned. I never did think it was 50/50 but fairly close. It is no wonder why they handle so well. Great stuff!! If I could squeeze in q question Larry without starting a new topic, what are your thoughts on the vintage wheel systems as opposed to trigo?? I hope this will not derail your thread. Thanks, Mert
 

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Discussion Starter #3
what are your thoughts on the Vintage wheel systems as opposed to Trigo??
Trigo and Vintage exactly the same sizes, backspace, and look. Vintage maybe a more exact copy; valve stem closer to spokes for example. Vintage adapter and pin system may be superior to Trigo because of centering issues with Trigo adapters (at least 2 yr old ones with chrome pins)

During the weigh in, Old 3850 had about 1/2 tank of gas when weighed.
 

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Larry,

Can you measure the exposed threads on each of your coilovers? You're cross weights are off a bit.

You are going to want to tighten your left front and right rear springs some. Your want your diagonals to add up to the same weight or be really close. Right now, they are off by about 76lbs, and it will get worse with you in the car.

Dont worry to much about it, but the car will handle better if you get it closer


David
 

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Discussion Starter #5
David,
Yes I can measure the threads.

You are saying by adjusting ride height one can equalize the weight readings?

Very interesting.
 

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Discussion Starter #6
BTW

With driver and trunkempty the weights are:
LF 571 lb RF 521 lb Front Total 1092 -->44.5%
LR 725 lb RR 639 lb Rear Total 1364 -->55.5%
Left Total 1296 Rt Total 1160

Grand total 2456 lbs

Diagonals are
LF-RR 571+639=1210
RF-LR 521+725=1246

Maybe all right?

[ November 13, 2004, 01:44 PM: Message edited by: Larry N. Johnson ]
 

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Snake Charmer
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I'd say that's pretty close.

There shouldn't be too much of a shift in the diagonal weights as you burn the gas in the tank.

What's the change in the longitudional weight distribution between a full and empty tank ?
 

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I thought I read that the cross-weights (which Larry's was ~48% without driver) is more significant. That should keep a "balanced fell for left and right turns.
 

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Discussion Starter #9
Gasoline weighs about 7.5 lb per gallon
Mustang tank is about 16 gallons
Pretty much all the weight on the rear, equally divided left and right

So if we change level by a third of a tank, say about about 5 gallons, that's only about 38 lbs less on the rear.

On this car the rear would go from 1364 to 1326, so if the front stayed at 1092 lb, the total would drop from 2456 to 2418, and the front/rear distribution would be 45.2%/54.8%...not much of a change. Still very incredible, assuming the scales are right.

The diagonals would not chgange as the tank is centered and the weight would come off both left and right at the same rate.

So, maybe Old 3850 has close to neutral balance... is that what is being said??

[ November 13, 2004, 01:48 PM: Message edited by: Larry N. Johnson ]
 

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I an not trying to change the subject or hijach the thread, but the corner weights got me thinking about the spring ratings.

The fronts average a bit over 500 and the rears a bit over 600. How does this correspond to spring ratings? Should a car have springs rated similar to the weight of the car's corners?

Tanner
 

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Larry, yes you can adjust balance by adjusting cross weights.

Thats a bit closer with the driver. If you add about and 1/8 inch more preload on the left front and right rear, you should be pretty good.

Tanner, It does correspond to spring rates. If you do some searches, you will find a number of people putting 550-600's in the rear of IRS cars, but not upgrading the fronts. The reason for it as you noticed was weight.

Keep in mind, other factors come into play. Roll center, center of gravity, shocks and swaybars etc. With that said, you cant necessarily pick spring rates because of the corner weights, but it is a valuable data point.

David
 

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Scalded Cat
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I did a 4 corner weigh in as well a couple of months ago and my totao weight was 2285 without the driver. I have all 4 corners written down somewhere. I'll have to go find it to see how we compare. I never did get in the car though to see what that ended up though. Although I'm a bigger guy than Larry is. Last I checked I weigh in at about 235.
Todd
 

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Discussion Starter #15
Bob
Excellent technical article! Thank you for the link.

So what is being said here and in the article:

1. To get good handling the sum of the
1.1 Left and right should be the same

1.2 The diagonals want to be close to the same.

1.3 Front/rear loads are a function of car use, i.e., traction favors rear heavier.

2. One can adjust the weight on any one corner by adjusting the ride height using spring preload.

3. The spring rate is one factor in the corner weights, but really the ride right determines how much weight is on that corner.

Question: How much "weight" can be adjusted by the spring preload? 50 lbs or less? more?

Snakes Skin Yes, that original engineered dsidepipe hanger is proprietary. Not available for copying. I will check you car next time to see if you owe any royalty. ;)

Todd, your car, with the 351 and Alum heads and solid axle, weighs about the same as Old 3850. Somewhere, someone said a solid axle car is 50 lighter than an IRS car. So I guess a 351 w/ Alum heads is 50 lb more that 5.0 EFI.

Regarding battery location, I saw an FFR yesterday with the battery located on the driver's side in the trunk. Seems better for balance to located it on the passenger's side. We don't have that many items to move around for static balance, but the battery is one.

[ November 14, 2004, 03:58 PM: Message edited by: Larry N. Johnson ]
 

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Larry,

Easily 50 lbs can be adjusted with spring preload.

Theoretically you could balance almost the entire weight of the car on one diagonal, with the other diagonal barely touching, like training wheels on a bike. In practice, though, chassis stiffness, spring rates, and adjustment range limits will limit this.

My personal opinion is that corner-weight problems lie behind those few FFR's that seem to have squirrely handling (or braking) despite good wheel alignment.

Forrest
 

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Discussion Starter #18
Pink
Never thought about that trailer trophy as a ballast. Good idea. Wonder if I should ask the Bat to add 50 lb paint to the right rear?

Forrest,
Excellent points. I am starting so see that one could change the corner loads by adjusting ride height. Hard to imagine at first.

Regarding squirley behavior in those few FFR's, I wonder if the left-right balance might be behind the few that are squirrley on accelleration? Old 3850 takes off straight as an arrow.

BTW, the scales were the nice ones:
Scaling a car involves checking and optimizing a car's static weight and crossweight. Four wheel scales are required, one under each tire. The floor must be level; use shims under the scale pads if needed. "Zero" the scale before placing the vehicle on the pads. Bounce the car at each corner to unbind the suspension, then roll the car onto the scales.



Sophisticated electronic wheel scales like this Intercomp unit cost $900-$2,000, depending on features, accuracy, and options.
This would be a cool investment for our local FFR clubs.

Another cross-weight adjustment tool might be a 25 lb bottle of NOS! :D
 

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Larry,

Theoretically, the L/R weights should be the same. Practically, they are not, and without adding weight, its tough to do on a street car because the only total weight that counts, is the one with the driver in the passenger seat.

Besides moving stuff around like the battery etc, the only thing you can do, is get the diagonals near perfect, and this is fairly easy to do with the spring preloads as we have discused.

Forest, you could be right with your assumption on screwed up corner weights.

I have found that getting the right and left preload exactly the same(the same amount of exposed thread on the coilovers) and adding about 1/8 to 3/16" preload the the front left will get the diagonals pretty close. Granted, this is only a starting point, but its been close on a few FFR's I have done.

When your corner weights are off, you have a condition known as wedge. What wedge does, is make the car oversteer in one direction and push in the other direct. Basically, the car will handle differently from right to left.

David
 
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