How effective is weight reduction?

[Perfect Balance]

We removed all the carpeting in my friends Miata yesterday, and the whole time my dad was basically laughing at us. I told him that it might not be a significant result that you would feel physically, but if you acually somehow tested the car with computers, there would be a difference in the performance. I told him that it would help all parts of the car's performance. Tire wear, braking distances, fuel mileage, acceleration, handling, they all are improved, but he continued to say that we are just stupid and are letting something we saw on videos lead our lives. I argue that they are professionals, and if it made no difference, we wouldn't bother, also, he is putting himself out as better than all the professionals that have tried and experimented with this.

So I want to know, how effective is weight reduction? Does 50 pounds really do anything, or are tuners and race car makers just doing it for the heck of going that 1 millisecond faster on each lap?

 

[Tornado]

Depends where you take the weight from and whether or not you can exploit the weight changes.

 

[Perfect Balance]

Depends where you take the weight from and whether or not you can exploit the weight changes.

I mean just overall making a car lighter.

 

[amp88]

I can certainly feel a difference in my car when it has a full fuel tank compared to near empty. The tank can hold 70 litres of diesel and after a quick Google the density of diesel is supposed to be around 0.84 g/ml, so a full fuel load is close to 60 kilos. The car weighs 1335 kilos so it's not exactly light, meaning that the extra 60 kilos isn't a great percentage change in the car's total weight.

In a car like an MX-5, which is around about the 1000 kilo mark I reckon you should be able to feel the difference of over 20 kilos.

In terms of racing it's often said in F1 that 10 kilos of fuel costs around 4 tenths of a second per lap. 10 kilos in a car that weighs 600 kilos isn't a huge percentage but it does make a large difference.

 

[retsmah]

Dropping 50lbs from a 2700lb car isn't going to have that much of an effect. If it's a race car then yeah strip everything out of it, for a street car I personally don't think it's worth it to take the carpet out.

But yes, taking any amount of weight out will make the car a little bit faster. But if you are only taking out a little bit of weight, it's really only going to make the car a very little bit faster

 

[Dave A]

I can certainly feel a difference in my car when it has a full fuel tank compared to near empty. The tank can hold 70 litres of diesel and after a quick Google the density of diesel is supposed to be around 0.84 g/ml, so a full fuel load is close to 60 kilos. The car weighs 1335 kilos so it's not exactly light, meaning that the extra 60 kilos isn't a great percentage change in the car's total weight.

I can feel the difference between empty and half full in my 306, or half full and full so you can definitely feel small weight changes.

But as retsmah said, is there much point in taking the carpets out in a street car, that .02 seconds quicker to 60 isn't really that relevent.

 

[Tornado]

I mean just overall making a car lighter.

Well, just taking weight away may have adverse effects because you might be destroying the car's natural balance that the car was designed to use.

 

[Keichi Tsuchiya]

Hmm. Try a carbon Fiber trunk or hood, that should give you what you're looking for.

 

[amp88]

Hmm. Try a carbon Fiber trunk or hood, that should give you what you're looking for.

How much does it cost for a carbon fibre bonnet and how much weight do you save? Not exactly cheap weight reduction is it...?

 

[Danoff]

Of course one place to look for weight reduction is the driver. Maybe you could stand to lose 10 lbs. Make sure you void your bladder prior to getting in the car. Actually, better yet, for optimal times, get your little sister to drive the car.

 

[Scaff]

braking distances,

Sorry to break this particular one to you, but weight reduction has little significant effect on your overall stopping distance. How weight is located and its transfer under braking has slightly more effect and the single biggest effect comes from tyres.

So I want to know, how effective is weight reduction? Does 50 pounds really do anything, or are tuners and race car makers just doing it for the heck of going that 1 millisecond faster on each lap?

Done correctly it has a huge effect on a cars performance, but as has already been said it needs to be done very carefully.

Its must always be done with a firm eye on static weight distribution and keeping the centre of gravity as low as possiable, simply striping out weight without thought can ruin a car.

A good road car example of this is the BMW M3 CSL, in which BMW took great care to ensure that weight was not simply just reduced, but that the COG was also lowered. hence the main reason why the carbon fibre roof was fitted.

In purpose built race cars it is common practice to build the car as far under the minimul weight for the class the car is racing in and then use ballast to bring the car up to it required weight. Both so that the minimum weight is achieved and so the weight is kept as low and as close to the centre of the car as possiable, again to ensure the COG is located as low and central as possiable.

The 1 millisecond you are talking about is obviously a bit silly, but they certainly are doing this to gain 1/10ths of a second per lap, because if you are racing over 70 laps, then even a 0.05 second gain per lap is worth 3.5 seconds over 70 laps and thats the difference between winning and losing.

Is it worth it in a street car? Normally no its not, quite simply because you don't have the ability to ensure that the suspension set-up and brake balance can be optimised to use any serious weight reduction you may achieve (unless all you are interested in is straight line acceleration)..

Regards

Scaff

 

[amp88]

In purpose built race cars it is common practice to build the car as far under the minimul weight for the class the car is racing in and then use ballast to bring the car up to it required weight. Both so that the minimum weight is achieved and so the weight is kept as low and as close to the centre of the car as possiable, again to ensure the COG is located as low and central as possiable.

Regards

Scaff

Indeed. Modern F1 cars are built 150 kilos or more under the minimum weight (605 kilos in qualifying trim and 600 in race trim) and then ballasted up.

 

[Scaff]

Indeed. Modern F1 cars are built 150 kilos or more under the minimum weight (605 kilos in qualifying trim and 600 in race trim) and then ballasted up.

They are indeed, its also quite common in the DTM and Super GT series as well, just about any series that requires a purpose built car does it.

Its far more difficult to manage in series that require tight links to the original road car as well, such as the BTCC, but it can still be done, particularly if you acid-dip the body-shell which can save a lot of weight.

I also forgot to mention in my above post about the consideration that must be given to sprung vs. un-sprung weight reduction. As the later has a very significant effect on a car for a much lower reduction in weight, the general rule of thumb being and reduction in unsprung mass is worth the same as a x10 reduction in sprung mass. That however is certainly not something to be playing with on a road car unless you know exactly what you are doing.

Most people however end up increasing unsprung mass on road cars, all those big-brake kits and huge alloys have a down-side.


Regards

Scaff

 

[Dougboy]

How much can the carpets in a 2 seater prossibly weigh? Now its a different story if u strip the whole interior, sound deffening materials, spare tire, AC, etc. But i doubt the carpet will make much difference.

If both driver and passenger took a big poop, the weight reduction would be more significant than removing carpet

Peronally, i wouldnt sacrifice comfort for performance boost you might not notice. On the other hand, higher octane fuel, simple air filter replacement, etc would give it a bigger performance boost than removing the carpet

 

[IMADreamer]

Hmm. Try a carbon Fiber trunk or hood, that should give you what you're looking for.

Your money would be best spent on performance or suspension upgrades. The cost/lb saving of a cf trunk and hood are not going to be as good as a decent engine build or good suspension work.

If you are going to strip the car, strip the whole thing out to really make it worth while. Otherwise you may just be upsetting the balance of the car.

 

[skip0110]

In terms of straight line performace, isn't there a general rule of thumb like XX lbs removed is equivalent to about 1 hp?

(Yes, I realize that the effect of a 1 hp gain is probably not measurable, but it scales up...)

 

[IMADreamer]

In terms of straight line performace, isn't there a general rule of thumb like XX lbs removed is equivalent to about 1 hp?

(Yes, I realize that the effect of a 1 hp gain is probably not measurable, but it scales up...)

In general it was thought that 100lbs of weight equaled .1 of a second in the quartermile.

 

[neanderthal]

only a fanboy wouldnt know the answer for this.

 

[Perfect Balance]

Thanks everyone for the input. I know just stripping the interior on a 2 seater car doesnt do much, but it's just a first step. This carpet removing probably didn't do anything to the car's performance, but it's just the beginning. He is expecting to get light Watanabe wheels, a plastic hood if he cant get carbon fiber. Replace the fenders with fiberglass or plastic ones. Sports seats eventually, a tein suspension for a lower COG. All in good time, but I just want to know how much of a difference it makes. I heard somewhere that if you divide the weight by the power, you get how much lbs of weight each hp has to pull. So if you remove the amount of weight equal to one hp, then it would be like adding another hp to your car. It was something pretty hard to achieve, like 15lb per hp. According to that, to feel any sort of difference it would take like 75lb of weight loss.

EDIT: @Scaff: I figured it would. Almost every car has brakes strong enough to lock the tires, so then its the amount of grip the tires have that would slow the car down. If there is less weight, then there is less momentum to push the car forward, so the car stops faster. It should make sense. I'm sure there is other factors, but I'm can definantly see how it would still make a difference to have a lighter car.

 

[retsmah]

A lighter car will definitley be able to brake harder than a heavier one, everything else being equal.

 

[nismo4life]

You ever see the video of the Ferrari F40 and Lotus Elise on the race track? The ferrari would pull on the straights, the Elise would catch up in every turn, I believe it overtook the ferrari in one of the turns.

 

[Pupik]

Unless you're racing the car in a timed race, there's little to be gained by removing 50 pounds. Like a dentist might say: "You won't feel a thing." You're suffering from a placebo effect if you really think 50 pounds makes much of a difference in ther behavior of a car.

It's like adding 5-10hp to a car. You might hear a difference, but can you feel a difference? Not very likely.

If you go crazy and remove all non-essential components (which could be as much as 500-600 lbs. in some luxury cars, as little as 100-200 in a small car), to turn your car into a racing car, you're not going feel much.

 

[Scaff]

EDIT: @Scaff: I figured it would. Almost every car has brakes strong enough to lock the tires, so then its the amount of grip the tires have that would slow the car down. If there is less weight, then there is less momentum to push the car forward, so the car stops faster. It should make sense. I'm sure there is other factors, but I'm can definantly see how it would still make a difference to have a lighter car.

A lighter car will definitley be able to brake harder than a heavier one, everything else being equal.

OK this discussion has been had before, and in a lot of very technical detail.

i can assure you that the single biggest factor in stopping distances is the tyre compound, weight distribution and transfer are a second order effect and the actual weight behind that.

As I said above weight reduction is not a significant factor in stopping distances.

Please have a read of the full discussion that was had on this subject in the GT4 and brakes thread, which can be found here...

https://www.gtplanet.net/forum/showthread.php?t=58993

..., please also be aware that this is a subject I have trained people on in the motor industry. Do not dismiss it out of had because its a GT4 thread, a lot of the discussion in the thread relates to the real world and looking at how GT4 relates to it.

That weight plays a significant factor in reducing stopping distances is a misconception in the same way that bigger discs and uprated pads will always stop a car in a shorter distance (which unless the original brakes are not up to the job is not true).

The single best real world example of this is the Lotus Elise and Range Rover, and the fact that from 100mph a Range Rover will stop quicker, despite being significantly heavier than an Elise.

Regards

Scaff

 

[Holdenhsvgtsr]

removing carpets wont do much,what kind of seats are in the car? if they are heavy eletric ones,taking them out and fitting buckets seats might take .3 of 0-60 time.
A friend of mines did this to her arosa,she took out the whole interior including front and rear seats and just fitted 2 bucket seats and and harnesses.that reduced the weight of the car to around 900kg,maybe even a little under.the only problem then was the car was sitting higher than standard(was already on lupo gti suspension) so she then had to get a set of coilovers to lower it back down.she also complained it was too slow when i was in it
Also the star performance fabia took out its interior for a knockhill trackday and he said he noticed a huge difference in how the felt and responded.

That weight plays a significant factor in reducing stopping distances is a misconception in the same way that bigger discs and uprated pads will always stop a car in a shorter distance

bigger disks wont really do anything,it all depends on how much contact the pad has with the disk,uprated pads is the way to go.

 

[Scaff]

bigger disks wont really do anything,it all depends on how much contact the pad has with the disk,uprated pads is the way to go.

In regard to improving brake feel, modulation and reducing brake fade, etc. I would agree, but once again the do very little , if anything to reduce the overall stopping distance of the car (until you start to experience brake fade - but thats a totally different matter).

This is one of the clearest and most straightforward articles I have seen that explains it.

http://www.teamscr.com/grmbrakes.html

It was originally published in Grassroots Motorsports (Dec 2000) and was written by James Walker, Jr. of scR motorsports.

Whiel I strongly recomend that anyone with an interest read the full article it can be summerised in the following excert

You can take this one to the bank. Regardless of your huge rotor diameter, brake pedal ratio, magic brake pad material, or number of pistons in your calipers, your maximum deceleration is limited every time by the tire to road interface. That is the point of this whole article. Your brakes do not stop your car. Your tires do stop the car. So while changes to different parts of the brake system may affect certain characteristics or traits of the system behavior, using stickier tires is ultimately the only sure-fire method of decreasing stopping distances.

Regards

Scaff

 

[skip0110]

In regard to improving brake feel, modulation and reducing brake fade, etc. I would agree, but once again the do very little , if anything to reduce the overall stopping distance of the car (until you start to experience brake fade - but thats a totally different matter).

Braided steel/hard lines will result in the single biggest improvement braking feel.

Pads will improve cold stops/modulation.

Incresing the numebr of pistons will increase pad life by more evenly distributing braking force over the pad area. Thus allowing the use of a quicker-wear, more effective pad.

I agree that if your brakes can trigger the ABS, you are braking as quickly as you can in a panic situation. However, brake modifications can improve braking in other situations by allowing you to better modulate and stay out of the ABS. Braking right before the ABS threshold yields the quickest stops (if you can manage it accurately).

 

[Dave A]

Braking upto the point right before your tyre's will lose grip if the quickest way to stop, no increase in disk size, number of pistons or pad's will increase that grip limit of your tyre's.

 

[Perfect Balance]

Ok people, try to stay on the original topic. I'm not really interested in the brakes. I already know basically everything you guys have said so far about them, I was just saying that they at least pay a very minor role in braking distances. If you brake in a car by yourself, then stick another person in it, unless it really messes with the weight distribution and transer, it will take longer to stop, I've experienced this a lot while driving.

Try to stay on topic, I really need this.

 

[Metar]

I guess minor weight-reductions don't really matter, for everyday uses. But when it becomes drastic, well, you start gaining on circuits. I reckon that since you told us your friend is going to further reduce weight, he also means to take it out to trackdays (the upgraded clutch, too).. In there, it could make a difference, I think

 

[Slick Rick]

If you want a cheap weight reduction solution, just remove your spare tyre, jack etc... That will save you about 15kg