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White, Lean & Very Mean!
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750 Posts
Discussion Starter · #1 ·
I'm a bit obsessed with losing weight from my 5RS. :help:

I put a lot of time into just this for my '16 MLRSS season and managed to shave quite a bit of lard from the car by running lighter seats etc. I'm not talking grams here, I took LOTS of kg's out. :eek: But it was painstaking work at times and did it really make me faster? Really?

Well... I like to think it did, but...

... I can't answer that factually as I have no back-to-back data to give me a conclusive answer (as I was never in a position to obtain it) so I'm keen to learn what others have to say.

We all believe (and it stands to reason) that less weight is not only advantageous from an acceleration point of view, but also less stress on the drivetrain etc and less weight to stop too of course, therefore (in theory) later braking is possible etc too.

For the purpose of my question - consider two identical Evos - one at 1,250kg and one at 1,000kg. Identical specs other than one being 250kg lighter than the other.

While the lighter car SHOULD put in a faster lap than its heavier counterpart on a like for like lap does anyone have any data to prove the science?

Maybe someone has tested this by doing a timed lap with, and then without, a passenger?

Maybe you'd have to remove 500kg before REALLY noticing a marked difference? Maybe not?

Are we talking a tenth faster per 100kg lost? 0.5 secs faster?

Really appreciate input on this. Facts preferred, but happy with well-reasoned opinion otherwise. :smthumbup

Regards, Alex
 

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White, Lean & Very Mean!
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Discussion Starter · #3 ·
Suspension and brakes must surely perform better with say 250kg less overall weight.
You would think so mate, especially brakes. But if suspension is designed to function at its optimum, at a given weight, then maybe not?

Any maybe a car at OE weight needs to lose, say, 500kg before any notable benefits are obvious?

Just playing devil's advocate. Thanks for input :smthumbup
 

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Premium Member
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I can't remember the source but I remember reading something stating that 'on average' a 100kg reduction can improve fuel consumption by around 5%. The weight of an Evo id say is below average so possibly a greater saving again. Science would tell us that as mass decreases, acceleration would increase and as already mentioned would put less stress on the driving components and less energy would be required to give momentum. As far as a lap time would go, there'd be far too many variables to make an accurate comparison imo on such a level.

Aero dynamics is just as important and can be more beneficial when the car on trial probably has the aero dynamics of a jumbo transit.

Not what you were looking for I know but bhp per tonne does count alongside other variables.
 

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The best test is a quarter mile!!!!
250kg = 3 passages in the car extra...
When I drive my everyday car alone or with 4 people in... I can feel the difference at the first corner... The car behaves very differently!!!!
The real debate should be... Do I spend money to add power or spend money to get my car lighter or both!!!!!

:smthumbup
 

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White, Lean & Very Mean!
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750 Posts
Discussion Starter · #6 ·
Not what you were looking for I know but bhp per tonne does count alongside other variables.
Appreciate your thoughts, thanks :)

It all makes perfectly logical sense that less weight = faster.

Not particularly scientific, but the most achievable way of testing it for me would be to do this:

So...
warm up lap alone
hot lap alone
cool down lap alone
pick up passenger
warm up lap w/pas
hot lap w/pas
cool down w/pas

Of course re-runs would be necessary if traffic occurs and the test would need doing several times with an average difference then calculated.

All a bit nerdy lol :lol:
 

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Appreciate your thoughts, thanks :)

It all makes perfectly logical sense that less weight = faster.

Not particularly scientific, but the most achievable way of testing it for me would be to do this:

So...
warm up lap alone
hot lap alone
cool down lap alone
pick up passenger
warm up lap w/pas
hot lap w/pas
cool down w/pas

Of course re-runs would be necessary if traffic occurs and the test would need doing several times with an average difference then calculated.

All a bit nerdy lol :lol:
I'd use at least 2 passengers. Id try and throw in 150kgs additional to yourself (unless you're massive) :)
 

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acting daft since 1969
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19,575 Posts
i know from going from my skinny 1225 kg ,e6 rally car to my full weight e7 rally car now,which is likly to be around 1400 kg ,i can tell you youd notice 250kg ,the new car feels heavy it does everything harder it stops slower it goes slower ,i cant say it corners slower because ive not pushed it hard enough
but whenlooking at weight saving youve to lok at EVERYTHING ,you dont lose KGs here and there ,i wss getting down to 40 grams ,lightened bonnet hinges ,stuff liek the magnesium cam cover on a later engien was 1/3rd th eweigth of the alloy one ,it all starts to add up
 

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Phil
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11,023 Posts
It's perhaps interesting that over the years the lightest cars in UK Time Attack have not necessarily been the quickest. In fact, a few of the quickest are surprisingly heavy.

I don't have any objective data on the matter, but I suspect that in some cases pure weight shedding can be to the detriment of things like balance and chassis rigidity and therefore that it's not simply a matter of weight saving alone that will facilitate faster lap times.
 

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Premium Member
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I've always put my fastest laps down with a passenger !! Don't know if it evens the weight out more or I was just trying to show off :lol:
 

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Not a scientific answer, but I will only take one adult passenger on fun rides in my Evo because I know from experience of other fast cars I've owned that fully loaded 0-60 feels like a lifetime, cornering definitely changes and stopping times are noticeably longer.
Over the Christmas period my wife volunteered me to pick up some of our friends in the Evo, I didn't see the fun in driving a fully loaded Evo so I took my silver bullet 1.6 Ford Focus instead.
If you've taken 250 kg's out, it will have made a huge difference :smthumbup
 

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acting daft since 1969
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19,575 Posts
but all things being equal a car 100 kg lighter will always go faster in an evo thats 7% to 8% which is allot

TA is difficult to compare as cars are vastly differant as as the drivers

what wuld be intresting would be to se some fo these TA cars loss some of the wings and fins because whilel th ecar may be light adding so much wing elements can cancel out that in no short measure
 

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White, Lean & Very Mean!
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750 Posts
Discussion Starter · #14 ·
It's perhaps interesting that over the years the lightest cars in UK Time Attack have not necessarily been the quickest. In fact, a few of the quickest are surprisingly heavy.

I don't have any objective data on the matter, but I suspect that in some cases pure weight shedding can be to the detriment of things like balance and chassis rigidity and therefore that it's not simply a matter of weight saving alone that will facilitate faster lap times.
Thanks for your input Phil. :smthumbup

I am of course trying to simplify matters by pitting a 1250kg car against a 1000kg one for the purpose of this.

Underneath it is all is a minefield of variables and theories and you yourself know what lengths and time can be involved with weight shedding to the extreme. It's a topic I'm very interested in but one that seems particularly tough to ascertain any specific or factual answers on :)

I felt my car was more competitive as a result of being lighter, and I guess results don't lie. Interesting re your point on some of the TA car weights. :thumbup:

I can well understand that from a standing start a lighter car has a fair advantage as there's the initial acceleration period, but maybe for TA or circuit-type racing when there may be no standing start maybe other factors become more important than losing 100kg for faster lap times.

Massive topic.

Alex
 

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White, Lean & Very Mean!
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Discussion Starter · #15 ·
I've always put my fastest laps down with a passenger !! Don't know if it evens the weight out more or I was just trying to show off :lol:
Crowd pleaser ;) :smthumbup

Interesting though - you're not the first that had said that to me re being faster with a passenger. The other chap thought the car felt better balanced with both front seats filled.
 

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White, Lean & Very Mean!
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Discussion Starter · #16 ·
but all things being equal a car 100 kg lighter will always go faster in an evo thats 7% to 8% which is allot

TA is difficult to compare as cars are vastly differant as as the drivers

what wuld be intresting would be to se some fo these TA cars loss some of the wings and fins because whilel th ecar may be light adding so much wing elements can cancel out that in no short measure
Yes, so many variables mate - that's the main problem. And yes if aero is creating more drag than efficient downforce then I could well understand it'd be a negative. Thanks for adding your thoughts :smthumbup
 

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Super Moderator
Jesus built my car
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does anyone have any data to prove the science?
As has been said, loads of factors in this but sticking to weight alone the speed you can corner is something like

(coefficient of friction * (car mass + downforce) * gravity * corner radius) / car mass

then you take the square root of that figure to get maximum cornering velocity. If nothing changes but the mass then as the mass goes up the divisor goes up so the velocity goes down. Vice versa as mass goes down the divisor goes down so the velocity goes up. What's interesting is that on the top of the equation you have mass and downforce but only mass on the bottom so increasing downforce also increases cornering velocity as it appears only in the divider and not the divisor.

So for a 1200kg car with 100kg downforce (I read somewhere an evo spoiler generates about 80kg) on good tyres (ones that will hold 1 lateral G in a corner) driving on Earth (where gravity is about 9.81) going around a 200m radius curve.

Sqrt(1 * ((1200 + 80) * 9.81) * 200) / 1200) = 45 m/s (100 mph)

And one that weighs 1000

Sqrt(1 * ((1000 + 80) * 9.81) * 200) / 1000) = 46 (103 mph)

So dropping 200kg gains you 3mph on that radius bend. Let's say instead we fit better tyres that can hold 1.1g

Sqrt(1.1 * ((1200 + 80) * 9.81) * 200) / 1200) = 48 (107mph)

As you can see weight is not as important as raw grip which is why simply buying better tyres is far quicker and easier than ripping out your aircon, and why the later evos are still faster than the earlier ones despite additional weight.

Obviously there are many other factors at play here especially when considering the entirety of the corner, the weight transfer of the car etc, and this only covers a constant corner not acceleration down straights etc but the above is the basics so I'll now let someone who didn't even bother trying to answer the question pick holes in my maths\phrasing or introduce "moments" etc to explain why all of this is rubbish :D However if anyone can expand on the above in a constructive manner I too would be more than interested to learn more.
 

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also another thing to think about is weight bias. if a car has say 65% of its weight over the front axle and you start removing the interia etc you could be making the handling worse.
I read in some racing book around 20 years ago that some ameaters would lose weight in the car then put bags of sand in the boot to try and get 50/50 over the axles.
 

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Premium Member
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less weight on a like for like basis is allways a good thing. but you will only really get the full benefit from appropiatly rated springs and better still corner weighted. so for example a car that is completly as per it left the factory from say the front seats forward, but completely stripped rear, tiny fuel cell, as much weight gone as possible (say you somehow save 40kg and completly untouched suspension will never handle as good as the car that is perhaps standard weight, but on the suspension setup that was designed for the original weight distribution. in a nut shell i think its worth considering the suspension and as a result the change in geomatry is the main thing to consider. im in no way a setup guru but its one of the things ive allways thought about if i were to go on an obsessive weight shedding plan. having said that, the lighter car with the weight bias/suspension setup accordingly is going to be an improvement id have thought
 

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It's perhaps interesting that over the years the lightest cars in UK Time Attack have not necessarily been the quickest. In fact, a few of the quickest are surprisingly heavy.

I don't have any objective data on the matter, but I suspect that in some cases pure weight shedding can be to the detriment of things like balance and chassis rigidity and therefore that it's not simply a matter of weight saving alone that will facilitate faster lap times.
Your car was silly fast because it had Gav driving.

Had your car been 200kgs lighter in the right places when Gav was driving it would have gone even faster.

Pure weight shedding from an evo will only be detrimental if you are a complete numpty. For example, if you took the front under dash cross bar out along with the rear cross brace section behind the back seats and didn't replace those two parts with anything else...like a cage, you'd have a pretty floppy car.

Building a light Evo is not all or even mainly about removing metal from the chassis either. You don't have to take much from the chassis to get your car light. It's more about the things you choose not to bolt back onto the car....for example a dash board, and it's also about the things you do choose to bolt onto the car. For example titanium exhaust, FG doors, carbon roof, carbon prop, lightweight wheels. You can still have a lightweight car without it being floppy.

Here's some proof:


 
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