Weight Reduction vs Cost vs Laptimes

[TTA89]

There was discussion on another forum about how to take weight out of an 03/04 Cobra and the differences that it actually makes. My Recaro seats are supposed to show up today, the main reason for buying them was for a correct sub strap location and harness belt guides but they are also going to save 50lbs over the stock seats. My car is so heavy anyways that I doubt it even makes a difference.

I highly doubt this is anything that I'm going to notice, last weekend at Mosport I had Mick riding with me for a couple sessions and I can't honestly say I noticed a difference with him in the car or when he got out of the car.

I have no doubt less weight is easier on the brakes and suspension but do you think that translates into quicker lap times? I'm sure it comes into play at some point but when the car is already a nose heavy pig, does taking a few hundered pounds out even matter?

I'm guessing with Mick in the car we weighed 4000lbs and then with him getting out somewhere around 3800lbs. I didn't have a lap timer so I don't really know the difference but at least in the way the car felt I couldn't tell.

What about in something lighter like a Miata? Does it brake and handle different with a ~200lb passenger? Any lap times with and without? It makes sense that its easier on the tires, brakes, and suspension as you pull more weight out but does the car really go faster? I have seen cars with headliners and door panels removed, is this even worth it for 15lbs or whatever?

[JackFFR1846]

Mike,

It can make a huge difference but there are things to consider.

My 1600 pound, 90hp Honda CRX turns faster lap times than my old 90 BMW M3 (SSA at the time) with 190hp. When I have a passenger in the car, it adds a significant % to the overall weight and is quite noticably slower.

Be careful to stay within the rules for your class. I run in P, so there are no rules. (hahahaha)

If allowed, you can reduce weight cheaply but it's a painstaking process of looking at every inch of the car and removing or changing everything possible to remove unwanted pounds. Being in P, I'm not limited on the amount of time I can waste in doing this. I feel that removing every single unused wire in the harness is just a starting point.

My car is also a nose heavy pig (after all, I'm a member of Angry Pork Racing) but with the weight reduction, I guess it's a nose heavy piglet.

If you plan to ever resell the car or run it on the street, think carefully about what you're going to remove or just remove stuff that can be later put back in place. When I had my Subaru 2.5RS, I was able to remove about 150 pounds without a lot of trouble and return it to stock when I traded it in. That's reasonable in a street car. More than that and you're cutting things off the car or removing stuff that's not easily replaced later.

I also don't like to spend money on lightening. If you do like to spend money, it gets easier to lighten.

If you significantly reduce the weight, your tires and brakes will last longer as well.

jack

[TTA89]

I'm not planning to turn my car into a track car, I still enjoy driving it work a few days a week and taking it to the beach.

I think a better way to look at it would be the % of weight that you take out of the car to determine if its worth it or not. For instance when a 200lb passenger gets in your CRX you are adding 12.5% more weight to the car. When a 200lb passenger gets into my 3800lb pig its only adding 5.5% more weight to the car.

So basically, in order for me to see the same weight savings as you taking a 200lb passenger out of your car I'd have to take 475lbs (12.5%) out of my car. Yikes...

Its probably a lot more drastic feel in your car than mine, I can slightly feel a difference in acceleration but its very minimal and I wonder if it would make any difference on the track?

I'm just thinking outloud... there isn't much else I can take out of the car and still retain 100% streetability without spending big money and even then the returns (if there really are any) don't justify the cost unless I can pull out 300-400lbs.

Every little bit helps though right?

[timmmy]

The calculation you actually need to do is the power to weight ratio.

The percentage doesnt really matter so much as if your car weighs 3800lbs but makes say 400HP, a 12% reduction in weight would significantly increase the power to weight ratio. (not an accurate example but I am sure you catch my drift) . Its generally easier to reduce weight than to increase HP. My personal preference is to do both

Certainly reducing weight will help corner speed and tire wear so any weight you can lose is going to help.

I used to race motorbikes and the best way to go faster on a bike is to put a smaller rider on it, hence most of the Moto GP guys are 100lbs wet :
so the question is what is your power to weight ratio (use wheel HP as flywheel HP is bogus really)

[TTA89]

3800lbs/500hp = 7.6lbs per HP

3600lbs/500hp = 7.2lbs per HP

I'm more concerned with being able to carry more speed around a corner or slow the car down faster. I think that would be affected more by the weight of the car, but how much would I have to take out for it to make any real effect?

For instance if you can carry 80mph into corner A, with the same suspension, tires and brakes would the car be able to increase its hold and go faster with 1%, 2% 5% less weight in the car or does it start to become more a function of suspension and tires?

I never took Physics.

[timmmy]

certainly your initial bang for your buck will come from A) Tires, B) Shocks, C) Springs, D) Suspension Geometry, E) Weight Distribuiton., and not specifically in that order.

You may find some moving of weight may help, mount your battery in the trunk, use a fuel cell etc. Tires and good suspension is definatley the first place to start.

Although simple weight reduction at the track like removing the carpets, spare, jack etc also helps - like you said - every little bit.

As I am sure someone here is going to say soon, so Ill beat them to it. The real key to carrying more corner speed / reducing your lap time is MORE SEAT TIME! the best way to learn (in my opinion) is to do 2 seasons in a bone stock miata on snow tires

H

[enjoythemusic]

Removing weight is good, but it is not linear. The P to W ratio is the way to think about it initially. There are also other factors such as WHERE the loss is done. Losing 50 lbs of unsprung weight (wheels, brakes, etc) make more of a difference than 50 lbs of sprung weight (the engine, seats, body, etc.). other here have made excellent suggestions/comments.

PS: hello everyone from me @ Lime Rock Park

[LDP82]

at Watkins Glen i really noticed when i went out with out my instructor. i was a bit faster down the straight but the biggest thing was breaking, it took me a lap or two to adjust my braking zones i was finding with the ~200lbs lighter car i could brake a good deal deeper (this was in a modded boxster)

I now plan on getting 20 lbs off me and as much as I can off the miata.

[DanB]

Power/weight is generally a pretty good predictor of straight-line performance. Actually, heavier/more powerful can beat lighter-weight with the same power/weight in the 1/4 mile.

But at the road course, weight is far more important. Lighter weight can beat heavier, even if the lighter car has a slightly inferior power/weight.

Speaking in broad generalisations, of course!

Problem is, it can be VERY difficult to get weight out of a car.

Keep the 03/04 as a road car, get an old 3200 lb. late 80s/early 90s Mustang, gut it down to below 3000 lb., and put a built 347 stroker in it

[ctkag]

Why do you think that Raj is so fast?? The fact that he weighs half of anyone else has to help!!

I'm at the point where it's probably easier to remove 20 lbs from the driver than to find another 20lbs to take off the car.

[DanDarcy]

Mike-- if you want to keep your Mustang streetable, its almost impossible to lose weight. My 1997 Mustang weights 3600#s and has 57% of that on the front wheels. I still have the AC working and the Mach 460 AM-FM-CD plus a full back seat even though I have an eight point roll cage. I don't know what class you run but in ST1, which I run, I could remove the ac compressor, back seat, rear carpet, stereo, and not much else. The weight reduction would not be much and it is nice , on those hot days, to sit in pit lane ,waiting to go out , with the ac on. I do like my comfort. So unless you want to build a pure race car --- I'd say " forgetta bout it"

[TTA89]

My car is classed in SPA due to coilovers and smaller blower pulley, so I can basically do anything in this class but I modified the car so its fun to drive on the street and yet still fun to drag race, auto x, and open track.

Although its fun to compete for the top spot, I'm not willing to destroy the streetablity to make it competitive against track only cars. I was just curious what everyones opinion was on the actual effects of weight.

I did buy a set of seats so my harnesses will work correctly, those seats saved ~50lbs over the stock ones. I was originally going to sell the stock seats but they really look nice in the car and make it easier to get in and out so I'll probably swap the stock seats back in between events. Although the Recaros aren't bad at all, I wouldn't hesitate to drive to NHIS or drive it back and forth to work.



We had an Auto X this weekend and my car has some front end issues so I co-drove a couple other peoples cars. I drove a couple different 03 Cobras that are setup simiar to mine and then I drove a 96 Cobra with a Blower on it thats probably 300lbs lighter, solid axle vs my IRS and the block in that car is Alum vs Iron in my car. He also has a Tubular K-member and Arms with a lot more neg camber than I can get with the stock K. The turn in on the car was a lot better than the 03s, I'm wondering if its the weight or the extra neg camber? Probably a bit of both...

[JackFFR1846]

He's probably got some toe out dialed in.

I found a seat at the Factory Five open house to replace my passenger seat. 16 pounds lighter than the one that was in there (I weighed them both). 1%...... Another 85 pounds to reach my goal

jack

[rajito]

Another 85 pounds to reach my goal

You can reach that goal by giving your car to me

Raj

[gread]

Corner weigh the car on a set of scales, then do whatever it takes to move you weight backwards. You can accomplish this without spending a ton of money. Losing the weight anywhere is not always the best solution. It hurts your car to lose 100lbs from the rear. It might not look cool, but pick-up the front end, add some camber with a little toe-out and see what happens.