Speed Vs. Handling
 

I've been running for the past few years without my spare wheel/tire (15X6 Fuch) in the car in order to reduce weight. Before heading out this am, I thought I'd better quit pressing my luck, and put the spare in the car. The car seems slightly slower now, but it also seems to ride and handle better with the spare on board. Does this make sense, or is it just me?

By the way.....here's a shot of my pride/joy.....'72 T Coupe in Bahia Red.


http://forums.pelicanparts.com/uploa...1261349865.jpg


Thanks,
Frank

It's you. Nice, nice car. Where you at in FLA?

P-cars don't have the preferable 50/50 front to back weight ratio that many sport vehicles have, and tend to be a bit heavier in the rear due to the engine. When you add more weight to the front, it balances out the weight ratio. That's why the cars also handle better with a full tank of gas.

BTW, your car is ***Awesome***. Very, very nice example.

beautiful car! love the '72.

for acceleration, losing the spare would equate to gaining 2 or 3 hp. Even michael schumacher couldn't tell a difference in acceleration in increments that small.

I'm stunned that anybody can tell the difference from such minuscule balance configurations, though car-magazine writers often claim to be able to. Not me. Good lord, there are people who claim to be able to sense differences between tanks of gas...they have my, ah, admiration, I guess. Those are calibrated asses.

Oh, and as for "50/50" being the ideal weight distribution, that's actually a myth. something like 47 front/53 rear is actually ideal for a sporting road car, because then you get a bit more weight aft to help acceleration (assuming rear-wheel drive, of course), and under serious braking you get forward weight transfer to _then_ create a meaningful 50/50 weight balance, when it truly means something. We're talking enthusiastic road driving here, not extreme track situations. In fact you'll find that serious racecars diverge greatly from the supposedly "ideal" 50/50 weight distribution, favoring strong aft weighting. 50/50 is just fine assuming steady-state conditions...like cruising down an Interstate.

I stand corrected. ;)

Well, in regards to the has, consider that each gallon weighs 7+ lbs. Multiply that by, say, 21 because of the size of the tank in my sc, and you are talking about 150+ lbs difference between full and empty. If you can't tell a difference between having someone in the passenger seat vs it being empty, then I'd be surprised. Plus, unlike having a friend in the pass seat, all of the weight of the gas is sitting on top of the front wheels. It completely changes the polar moments for the car.

Michael

Actually, a gallon of gas weighs 6.5 pounds--used to have to calculate that weight every time I flew and did a weight-and-balance--but never mind, I admit to not being able to tell the difference between a full and empty passenger seat. Nor on my 18-pound bike can I tell the difference between having just eaten or just taken a dump. But that's just me. I'm happy there are people like you out there--and I'm sure there are, because certainly Jeff Gordon can discern the effect of an extra half-psi in his right rear at Daytona.

Whether you can tell or not, we have to accept your judgment.

I say a blind test is in order:

Test a driver in his car and in unfamiliar car. While the driver is not looking, you will load up the trunk with weights equivalent of a tank of gas and/or a spare tire. Then load up the cars with 150lb. of weight on the passenger side (covered with a blanket so they cannot see what's on the passenger floor).

Then, have the car drive a designated course. Driver has to tell when the car is loaded and when it isn't.

Categories:

1) Unloaded
2) Spare tire
3) Spare tire + gas
4) Gas - spare tire
5) Spare tire + gas + passenger
6) Passenger only, no spare, no gas

I don't know if I could tell the difference between whether or not the spare was in the trunk and I'm not sensitive enough to tell whether my tank is empty of full either. Perhaps if I drove the car back-to-back empty, then full I could notice? I can however, tell the difference at the track between having an instructor in my car or not.

a 180-200 lb passenger in a 2500 lb car, yeah, I think most could feel that difference on a track.

A long time ago there was a funny thread on a car board. This guy with his BMW, would go on and on about his tire pressures, and how he swore he could tell a 2 lb difference in the handling of his precision built machine.

he could feel the difference if he put a few extra pounds in the front, or the rear, he could feel the handling difference, more oversteer, understeer, etc.

until one day he lost all the air in one of his tires. and destroyed the tire by doing his entire 15 mile commute on a flat - without even knowing it was flat! When it came to a "blind" test, this fellow could not tell the difference between 32 lbs of pressure, and ZERO lbs of pressure.

That's funny! Did he admit it or did someone call him on it? Gotta admit, doofus that I am, I can sense a flat in 50 feet. Did just a couple of weeks ago. (Volvo, fortunately, since I don't have a spare in the 911...trying to save all that weight, dontcha know...)

Addding the spare does 2 things
1) the car is heavier and will accelerate, stop and change direction more slowly
2) you have increased the cars polar moment which slows the speed of pitch and yaw motion.

Yes, of course, but what interests me is who can sense those lateral and longitudinal changes. Certainly a skilled and experienced professional competition driver can, just as a skilled and experienced wine connoisseur can detect a vintage and a bottling. Me, I like just about any wine in the $12-$15 bracket and I can tell the difference when I very occasionally drink from a $500 bottle, and my hat is off to anybody who can sense when a spare tire has been replaced or removed, but when there are no quantifiable standards, I have to wonder who talks the talk and who walks the walk.

I'm surprised you can't tell. I can tell between a 1/2, and 1/4 tank of gas. I can tell when the spare is out. I can tell when the tire pressure changes front-to-rear. And I can really tell the difference when I'm lugging a passenger around. And that sense is not unique to driving a 911. (But I must admit the difference is only truly noticeable on the track, where you're pushing the car to it's limit.)

The trick is learning to modify your driving to capitalize on what the car is doing well.

he hadn't talked about his super-perceptive automotive skills for a while, and when the flat happened, he posted it right away without really thinking about it.

he got called out about it, and made it funnier by fighting it (it's always funny watching someone fighting the unwinnable fight).

that was a while ago, in the infancy of automotive internet, around the late 90s. how time flies.

anyways, I swear my 911 drives better and smoother when the windshield is super clean. true story.

someone once told me that the spare is actually there for safety reasons. It acts as a barrier for front impacts. I dont have my spare. I would be interested to know if you guys run the track full of gas or low on gas?
At my last DE, I bought the 109 octane racing fuel and felt no difference at all.

any octane above the bare minimum that the engine needs just makes it harder/slower to ignite the mixture. You can(I didn't say will) actually lose power w/ too high an octane rating.

The spare as crash protection thing has been debated on this board for years, and it's either an urban myth or a serious part of an engineering study that nobody seems able to find.

Formerly Steve, I can't believe you can't feel the difference between a full tank and an empty tank! The car settles down noticeably. I can feel it just pulling out of the gas station. A spare tire on the other hand would be barely noticeable.

Hey, I give up, I've put myself up as a target and I'm not going to continue apologizing.

It's like what I say to my wife, and she too is baffled: "Ya know, I _really_ like Hershey's chocolate. I think it's terrific and I actually can't tell the difference between it and all these fancy foreign chocolates." There will always be people who are baffled that I don't prefer Godiva or Ghiradelli's, and good for them.

There are people who claim to tell the difference between a warm vacuum tube and a cold transistor in a hi-fi system, who claim to tell the difference between a 1998 and 2001 Stag's Leap bottling, between a platinum print and a high-quality black-and-white, between superb sushi and outstanding sushi...

But it's all fish to me, and I'm happy eating whatever I get.

No question (for me) discerning tube vs. solid state......that's a fact (for me),..still measureable,.....you gotta' love that even-order harmonic structure...it's "warm".,..especially , compression.

No question as to discerning the the difference between the two noted Stag's Leap's vintages,....we sucked on the grapeskins of a '86 Petrus this weekend!!

Back to P-cars,....I can feel the difference after loading the gas tank, especially to FULL...settles the car, for sure.

I've been riding around with a case of oil , tranny fluid, and parts for an upcoming repair visit....I do carry a VERY HEAVY tool bag, as well...(still) other stuff under the bonnet. Funny to see this thread, as (just) today, I removed the toolbag, parts extras, case of oil, spare tire, jack,,..pretty much everything. Not sure how much weight it totalled (easily 150 pounds?)....drove her all day like this at 4 different times,..with and without a passenger.......un-frikin-believable........I'm speechless...talk about "darty"......

Yes, I understand that the weight reduction will yield relative gains,..it's just that I don't track her, nor have any huge concerns with what I want to carry....I've kinda' gotten' used to it.......however,....

My eyes were really opened with today's experiment.

...I'm usually happy with what I get to eat, too.

Best,

Lets play with some numbers.

On my car jack, tools, & spar was 50 lbs.

A 2600# 911 (w driver) has about 40% weight in the front or about 1040# on the front wheels.

The front spring rate is about 122 on each side or 244 combined.

It should ride about 3/16" lower in the front.

That is about a 5% increase in weight on the front.

This might make feel like one has about 5% softer front shocks.

It might make your front tires feel like the air pressure is 5% lower.

That is about 2% of the total driver car weight.

If making 150hp or about 128rwhp. That is equal to about 2.5rwhp or not quite about equal to adding a sport muffler.

Of course, a sport muffler also makes a car sound faster so it seem like more.

Or something like that.

Really
 

I imagine this would be problematic...

It's not just the weight.
 

http://forums.pelicanparts.com/uploa...1261368584.jpg

At our Gingerman DE, I suggested that the owner of this car replace his spare tire.
Not only would it help to better balance the car, but also offer some crash protection as well. I usually don't take pictures of cars after track mishaps, but he wanted to thank me and show me that it worked.

lmao!!!!!!!!!!!!!

Do you ever notice a difference in a light plane when taking off with a passenger or without one ?

BTW, my 78 targa handles better with a passenger. My 80 with the track setup was less sensitive, but it really did not want to turn in to a tight corner without a dab of brakes.

As in, ''I will not turn in.''. But then it had pretty tight LSD, and was already a very light car.

I drove a '64 VW Van for years when I was (much) younger. As everyone already knows, these vehicles are probably in the top 10 as being slow and cumbersome.

What I found amazing at the time, was when I loaded it down to the max with people, band equipment, drywall, lumber etc., the van was able to completely maintain it's power and speed...the considerable extra weight did not seem to affect the driveline's characteristics.

I attributed it to the transaxle's reduction gear boxes. Those wacky Germans...

When I was a kid and I road raced 400 pound motorcycles, I could feel the difference on the race track when I refueled with 4 gallons of gas, only because the fuel tank was mounted high and it very, very slightly slowed the ability to flick from side to side, and very slightly increased the tendancy to wheelie out of tight turns.

I could not feel the difference on the road.

With my 911 and my Cobra, I've autocrassed with and without a passenger, and quite frankly, I can't feel the difference in handling or accelleration.

I find it quite funny when I re-read the old road tests in Car & Driver where they extoll the handling virtues of one 911 over another because the 2nd coupe had a sunroof. The editors claimed to be able to tell the difference in handling because of the extra weight of the sunroof motor.

Regards,

Jerry

I've worked in fields dealing with characteristics of the human senses & perception. Years ago I noted that humans have a fantastic (& typically untapped) capacity to discern fine distinctions among similar stimula. The realization of this capability is based upon their need, interest or education, combined with personal idiosyncracies (& their environment, natch). An example might be a concert violinist selecting their instrument. There is a great deal of "natural" variation in this trait, but I have been most impressed with the underlying capability for anyone's improving their discernment (distinct from belief in their own potential or self-confidence). I am not implying anything about one's capability to perform a task. And of course, there are always outliers.

i'd guess this varies according to how much hp and suspension/tire each of us has. in my 2.4 i can definitely feel a difference with a passenger. never put more than 10 gallons in the car so can't really say on the gas thing.