Saving Weight

Author
Discussion

Keep it stiff

Original Poster:

1,093 posts

109 months

Sunday 2nd December
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Does anyone have a formula or an estimate methodology that converts weight saving into % of improved track time?

I'm thinking about having custom aluminium bonnet and boot made to replace steel originals and I could go further with other parts. Not cheap of course however I think I could get a 50 kg - 100 kg off a 900 kg car depending on how far I go, how worthwhile could it be?

Kraken

590 posts

136 months

Sunday 2nd December
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The figure that gets bandied around a lot is 3/10ths for every 10kg. Personally I don't see how that can be accurate as it all depends on the type of track. I would have though Silverstone National would have very different acceleration/deceleration demands to Cadwell Park for example. Perhaps as an average it works.

50kg to 100kg will make a huge improvement and is 100% worth doing though. Not so sure when it comes down to 5kg or so in my opinion.


MrJingles705

406 posts

79 months

Sunday 2nd December
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Kraken said:
The figure that gets bandied around a lot is 3/10ths for every 10kg. Personally I don't see how that can be accurate as it all depends on the type of track. I would have though Silverstone National would have very different acceleration/deceleration demands to Cadwell Park for example. Perhaps as an average it works.

50kg to 100kg will make a huge improvement and is 100% worth doing though. Not so sure when it comes down to 5kg or so in my opinion.
Don't know about 3/10th's, but I do know that when the theory has been tested at Castle Combe in the past - 10KG was worth approximately 0.1 sec/lap, on average, when sitting in a Class A FF1600 (minimum car weight 420KG, all up weight with driver minimum 500KG, call it 110 BHP) and running same fuel weight etc.

But... but.... you can lose that easily, and then some, through missed braking points/fluffed change etc.

So chasing weight is not a bad thing, but it's not a magic bullet at the clubman level.


Edited by MrJingles705 on Sunday 2nd December 11:35

roddo

471 posts

131 months

Sunday 2nd December
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I work on 1/10 for every 10kg
This is accurate on our 1050kg car with 170 bhp

Gc285

1,189 posts

129 months

Sunday 2nd December
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Rather than gain the odd 10th concentrating on losing weight, I found I gained much more by testing, testing ,testing and new tyres.
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Drumroll

1,083 posts

56 months

Sunday 2nd December
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I don't know the OP so this is just a statement nothing else.
Frequently see competitors, talking about getting cars down to x kg or losing y kg. Then you look at the driver and think, if you lost z kg you could achieve that. (to make it clear I am not a racing snake more a racing wort hog.)

Kraken

590 posts

136 months

Sunday 2nd December
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Gc285 said:
Rather than gain the odd 10th concentrating on losing weight, I found I gained much more by testing, testing ,testing and new tyres.
Agree but losing 100kg from a car is going to make a big difference regardless and will still make it faster after testing with new tyres on.

Less weight is always a good thing but it's not worth, IMO, spending fortunes to save 5kg as a lot of people do but 100kg with a few relatively cheap panels is a different ball game.

number 46

929 posts

184 months

Sunday 2nd December
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I'm sure that dropping 100 kg would be worth while. That's almost 10% of the car weight. It would be quite a challenge to loose 100 kg in body weight, unless you just cut your body off and just raced with your head!!!?????

Norfolkandchance

1,392 posts

135 months

Monday 3rd December
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In my experience losing weight was exciting because it made the power to weight ratio more responsive to increasing power! So that engine mod that gains 10bhp becomes more worthwhile if the car is 100kg lighter.

I realise this is arguably illogical - the lighter car would be as fast with less power - but I liked it when justifying spend to myself!


andye30m3

3,237 posts

190 months

Monday 3rd December
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Drumroll said:
I don't know the OP so this is just a statement nothing else.
Frequently see competitors, talking about getting cars down to x kg or losing y kg. Then you look at the driver and think, if you lost z kg you could achieve that. (to make it clear I am not a racing snake more a racing wort hog.)
I think I may fit into the category, both me and the car need to go on a diet

MrJingles705

406 posts

79 months

Monday 3rd December
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Norfolkandchance said:
In my experience losing weight was exciting because it made the power to weight ratio more responsive to increasing power! So that engine mod that gains 10bhp becomes more worthwhile if the car is 100kg lighter.

I realise this is arguably illogical - the lighter car would be as fast with less power - but I liked it when justifying spend to myself!

Losing weight (within reason - you don't want to make the car fragile!) is always better than adding power.

As the saying goes, adding power makes you faster on the straights .... but removing weight makes you faster everywhere wink

MrJingles705

406 posts

79 months

Monday 3rd December
quotequote all
andye30m3 said:
Drumroll said:
I don't know the OP so this is just a statement nothing else.
Frequently see competitors, talking about getting cars down to x kg or losing y kg. Then you look at the driver and think, if you lost z kg you could achieve that. (to make it clear I am not a racing snake more a racing wort hog.)
I think I may fit into the category, both me and the car need to go on a diet
I'm in this category myself to be fair wink already lost 2 stone, need to lose a little bit more before the season start.... and then there are the general health benefits etc.

Still, you can do both I suppose.

dunc_sx

915 posts

133 months

Monday 3rd December
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number 46 said:
I'm sure that dropping 100 kg would be worth while. That's almost 10% of the car weight.
More than 10% surely? smile

Gc285

1,189 posts

129 months

Wednesday
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Kraken said:
Agree but losing 100kg from a car is going to make a big difference regardless and will still make it faster after testing with new tyres on.

Less weight is always a good thing but it's not worth, IMO, spending fortunes to save 5kg as a lot of people do but 100kg with a few relatively cheap panels is a different ball game.
Agreed, I race prototypes and not a lot can be saved without huge expense.

I did however take the wife out at Brands a couple of years ago and managed a time a second quicker with her, than I could manage in qually a month later in the same car.

HustleRussell

15,460 posts

96 months

Wednesday
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Kraken said:
The figure that gets bandied around a lot is 3/10ths for every 10kg.
MrJingles705 said:
Don't know about 3/10th's, but I do know that when the theory has been tested at Castle Combe in the past - 10KG was worth approximately 0.1 sec/lap, on average, when sitting in a Class A FF1600 (minimum car weight 420KG, all up weight with driver minimum 500KG, call it 110 BHP) and running same fuel weight etc.
roddo said:
I work on 1/10 for every 10kg
This is accurate on our 1050kg car with 170 bhp
I am really surprised that it's as little as a tenth per 10kg, especially in the example of the Formula Ford where the 10kg added weight is the biggest disadvantage as a percentage when you consider car weight.

I am simultaneously heartened and worried by this as I have a 34kg car weight disadvantage going into next season and as it turns out that may not be the excuse I thought it was.

Norfolkandchance

1,392 posts

135 months

Wednesday
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MrJingles705 said:
Norfolkandchance said:
In my experience losing weight was exciting because it made the power to weight ratio more responsive to increasing power! So that engine mod that gains 10bhp becomes more worthwhile if the car is 100kg lighter.

I realise this is arguably illogical - the lighter car would be as fast with less power - but I liked it when justifying spend to myself!

Losing weight (within reason - you don't want to make the car fragile!) is always better than adding power.

As the saying goes, adding power makes you faster on the straights .... but removing weight makes you faster everywhere wink
Generally I would be entirely in agreement with this. However, the low powered cars I often compete in it isn't always true. This is because a better power to weight ratio and better braking / cornering that come with lighter weight were not always needed at high speed as wind resistance becomes more of a limit on acceleration than weight. My first competition car was an MG Midget with 75bhp at the wheels and a bit more that 100bhp per tonne. At fast circuits large sections could be taken flat in top. An extra 10 bhp would have increased top speed and therefore reduced lap time. Since I wasn't braking and accelerating very often, 100kg less wouldn't have made as much difference to lap time, even though I would have been able to brake later and accelerate quicker. It would be possible, therefore, for a light car with a better power to weight ratio to be slower than a heavy car with a lot of power. Would have been the opposite on a low speed / highly twisty venue.

CedricN

363 posts

81 months

Thursday
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There is a free simulation software if you want to try out to predict lap time improvements like this, its pretty descent although a bit simple in certain areas.

http://www.optimumg.com/software/optimumlap/

I did several parameter sweeps on my car (1250kg/180hp), removing 10kg was about 0,1s on a 1:20s lap. Try it out for yourself, its a good way to learn how different parameters affects the lap times.

Henry Fiddleton

1,547 posts

113 months

Thursday
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Hi,

I race in series where I am up against much more powerful cars.

Just stating the obvious, its much easier to extract the performance over a lap with an extra 10bhp, as opposed to losing 10kg, on a consistent basis.

My last race this year is a good example:

https://www.youtube.com/watch?v=nlnxlJJqSEs

My car is currently 193bhp and 1035kg with me in it.

Next season aiming for more power, and less weight. And more cost.

HustleRussell

15,460 posts

96 months

Thursday
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Henry Fiddleton said:
Hi,

I race in series where I am up against much more powerful cars.

Just stating the obvious, its much easier to extract the performance over a lap with an extra 10bhp, as opposed to losing 10kg, on a consistent basis.

My last race this year is a good example:

https://www.youtube.com/watch?v=nlnxlJJqSEs

My car is currently 193bhp and 1035kg with me in it.

Next season aiming for more power, and less weight. And more cost.
Well sure, a 5% increase in power is generally going to have a greater effect than a 1% reduction in weight...

Norfolkandchance

1,392 posts

135 months

Thursday
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Also, there is the issue of passing people / being passed. In the 80's or 90's A class was created for the 500 GP bikes that was for 400cc twins. The 400s (basically 250's with an enlarged engine) were allowed to be quite a lot lighter than the 500s. As I remember it, the 400s were solid mid table in qualifying lap times but couldn't use their faster cornering and later braking in the race because the 500s were n the way. So they were easy picking to the powerful 500s on the straights and therefore lost places.