Balance vs. weight reduction

[Sicklyscott]

Some of the modifications to add lightness take the weight off of the front (i.e. lighter battery) which got me thinking about balance vs. overall weight. Is it better to keep the front end heavy while just doing weight reduction in the rear? You may leave 100-150 lbs on the table between the spare, tools, jack, battery, some AC components, bumper (short hood car), etc. which isn't a small amount of weight.

Or is it better to strip out as much as possible to get the car as light as possible and learn how to manage balance through driving methods?

Curious to hear your thoughts.

[DRACO A5OG]

Strip, DIY height adjust to close to where you want it and then have it professionally corner balanced at a known trusted shop or borrow the scales and DIY. In a pinch you can try the tripod method???

[BK911]

Street or track?
Are you driving at 99%?
At the limit around every turn?
If not, I would guess your weight distribution doesn't really matter.
Even in the twisties going "fast" most of us couldn't tell if a car was corner balanced.

[Flieger]

My opinion is that a bad corner balance is really obvious once you get a good one.

In terms of front/rear balance I'd say go for light because you can always add back ballast right where you want it. That would be an interesting test to conduct- let the stopwatch be the judge.

[Cajundaddy]

Weight affects cornering, braking, and acceleration. Balance primarily affects cornering only. Drop the weight and adjust balance after she is light and fast.

[Maxhouse97]

I've wondered the same thing, but you can make other adjustments for what a light front end would result in - presumably understeer. That would include more negative camber up front, wider track, wider tires, etc.

But as mentioned it would be neat to see what the trade factor would be between weight and balance vs. speed.

This is why I have limited weight reduction in the front because I value predictable handling over outright speed.

[Elombard]

I have also wondered about moving the battery to the smugglers box. It moves the weight to between the axles but really lightens the front. Is it to the detriment of handling? I think this has come up before and some of the experienced car prep pros agreed with the above statements. Also, Porsche probably did some study on this when they were racing these cars. I think the lightening we are all doing is based on stuff the race teams did?

[shaunmbenson]

Everything effects everything else -- it just may not be a big effect. 10lbs here, 10lbs there -- but it still all changes things. But so does amount of gas and tire psi etc etc.
In other words - if you aren't tracking tire temps and pressures and adjusting camber, castor, and toe based on that - or even if you do but then don't change tires for weather - or drive new roads with more left turns all of a sudden - then you are already not at that top percentile limit of handling vs car prep.
So pull out all the weight you want and then see how it feels for awhile. You can always put the spare back in -- or get a new set up to match the new distribution.
My mechanic/race instructor used to make me run laps with bald tires -- like metal showing.
Now everyone can cry foul but he was old school and I was impressionable -- and I also dropped 3 seconds at Streets of Willow when I put back on proper tires cause of what I learned with no grip on the rear of a rear-engine car.

Can't wait to hear how it goes!

[911pcars]

Balance is something you can't readily change unless you physically move things around, like the battery. However, you an always add fuel to the tank for added front end weight. Should be plenty of ballast there. Instead, strive for lightness. Pick what lightness path to pursue; body panels, delete extraneous components or lightweight substitution.

Sherwood

[Bill Douglas]

Add lightness. Whether it's the placebo effect or not, I don't know, but the SC feels snapper, more alive with weight gone. I'm not fiberglass doors or anything dramatic, I've just got rid of things the car doesn't need.

[afterburn 549]

Imo the batt in the smugglers box is wrong . You want the batt as far ahead of you as possible .
If you center all your weight you get a spinner!

[javadog]

Originally Posted by afterburn 549

Imo the batt in the smugglers box is wrong . You want the batt as far ahead of you as possible .
If you center all your weight you get a spinner!

I disagree. Moving the battery to the smugglers box moves weight from the left side of the car to the right, which reduces the imbalance left-to-right caused by the driver's weight.

Porsche ran weight distributions that approached 70:30 in some of their race cars and did just fine. Given the engine location in a 911, you'll never get a polar moment of inertia as low as a 914, which is still quite driveable.

JR

[Driven97]

Originally Posted by afterburn 549

Imo the batt in the smugglers box is wrong . You want the batt as far ahead of you as possible .
If you center all your weight you get a spinner!

Different strokes - typically the highest performing cars use a mid engine format to get the mass as centralized as possible. This lowers the polar moment of inertia, and lets a car change yaw angles quicker.

Not to say it's the only answer - C5 and later Corvettes have a 944-like setup of an engine up front (but pushed as rearward as possible) and a transaxle in the back, yet still are brutally effective cars.

The 944 itself of course is the opposite of centralized mass with the heavy stuff on each end, and it was known as a very sweet handler throughout it's run. Note that's not listed as fastest.

Our old 911s have a comically short wheelbase and and engine hanging way off the back that makes our cars plenty unstable as is. On the other hand, moving around 40lb a bit isn't going to change the world either. 40lb is about 6.5 gallons of gas. Can you tell the handling difference in your car between a full tank and 3/4 of a tank?

[RichardNew]

The difficult is finding a local shop with a set of scales. Then hoping they know how to use them.
Once you drive a balanced 911 you'll never want to go back. Ride height measurements can only get you close.



Here's an article on all of this

Richard Newton

[panzerfaust]

Originally Posted by javadog

I disagree. Moving the battery to the smugglers box moves weight from the left side of the car to the right, which reduces the imbalance left-to-right caused by the driver's weight.

Porsche ran weight distributions that approached 70:30 in some of their race cars and did just fine. Given the engine location in a 911, you'll never get a polar moment of inertia as low as a 914, which is still quite driveable.

JR

disagree, i prefer the weight far froward and low as possible. you can still keep it up front and move it to the right.

funny, nobody here notice how much better the front end bites going into a corner hot with a full tank verses a empty tank?

early rallye cars where developed under the minimal weight than they ballistic the cars with weights back up the front corners.

ive read 3 or 4 road impressions (pretty rare period mag test) on the lighten homologated special SCRS which i recall had much more unfavorable F/R weight balance when compared to a SC or 3.2. the testers have complained it handled oddly compared to the much heavier standard road cars. Frere was one of the reknown tester/author whos personal car was a standard 911.

perhaps the factory intent was just to build them and let the teams sort them out knowing that they will be swapping out most everything on the suspension? prodrive had extensively developed there SCRS's. they threw a lot a weight back up front like the oil tank.

i suppose its all a compromise since its much easier to remove weight from the front to make the car a little quicker but at the expense of the handling balance.

[javadog]

Originally Posted by panzerfaust

funny, nobody here notice how much better the front end bites going into a corner hot with a full tank verses a empty tank?

Given that no changes are made to the car to adapt it to the wight distribution when it changes... it's not a surprising conclusion.

This all assumes that the car is set up to take full advantage of whatever weight distribution you end up with.

Obviously, there's a limit to how far you can go, but moving a battery around isn't going to change things enough to make the weight distribution a problem.

JR

[Driven97]

Originally Posted by RichardNew

The difficult is finding a local shop with a set of scales. Then hoping they know how to use them.
Once you drive a balanced 911 you'll never want to go back. Ride height measurements can only get you close.

Richard Newton

Richard, we're not talking about corner balancing in this thread. We're talking about total L to R and F to R distribution, which cannot be changed with a corner balance.

[bkreigsr]

Originally Posted by panzerfaust

funny, nobody here notice how much better the front end bites going into a corner hot with a full tank verses a empty tank?
.

not funny - my car was set up (balanced) with a half tank of gas and if I run a full tank it will push me off track quicker than you can say the understeer.
As far as the OP's question, when I replaced the front lid with carbon fiber (less by 56 lbs.) I had to downsize the front anti-sway bar from a 22 to a 19.3 (Tarett) to get the car back to where it was before the reduction.
Bill K

[bkreigsr]

Originally Posted by Driven97

Richard, we're not talking about corner balancing in this thread. We're talking about total L to R and F to R distribution, which cannot be changed with a corner balance.

Say what?
You've just defined a successful corner balance.

[Driven97]

Originally Posted by bkreigsr

Say what?
You've just defined a successful corner balance.

You can only do cross car percentages LF+RR vs RF+LR with a corner balance.

Moving mass of the car around is very different than changing the height of a corner of the suspension.