RE: Light IS Right: PH Blog

RE: Light IS Right: PH Blog

Author
Discussion

Flibble

6,470 posts

180 months

Monday 2nd May 2016
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V8RX7 said:
I wonder how I've coped for the last 25yrs

I've only had a couple of cars with ABS and I disconnected it in one (a new 406) after it nearly killed me 3 times one winter by refusing to apply the brakes at low speed coming up to junctions and I rolled across them.

I can't remember the last time I locked my brakes, the only time I can remember, was 10+years ago when a dog ran out in front of my car and then just stopped - I stopped from 60 with millimetres to spare, then it wandered off.
Ah, the old "I'm not dead so it's useless" gambit. By which token we might as well still be using cross-ply tyres on cars without airbags and seatbelts.

coppice

8,561 posts

143 months

Monday 2nd May 2016
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V8RX7 said:
I was unaware that the F1 cars used the same system as the 406 - can you give examples ?

I was further unaware that F1 took place with a powdering of snow or wet leaves on the track - when did this happen ?
Don't be disingenous...I was talking about ABS generally as you know. Oddly enough ABS has a use in all conditions. But I have seen an F1 race stopped by snow !

67Dino

3,581 posts

104 months

Monday 2nd May 2016
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Ozzie Osmond said:
Gotta love these "ABS doesn't work" myths.

I've got a special magnet attached to my fuel lines which gives me an extra 5 mpg..... biggrin
Actually, I read somewhere that the magnet thing does work, but just not for the pseudoscientific reason they claim. Works by psychology: apparently, being sub-consciously aware you've put a magnet on the car can make you just a bit lighter on the gas pedal, which in turn can save 5%. Sort of a vehicular placebo. So light IS right in this case...
:-)

robinessex

11,046 posts

180 months

Monday 2nd May 2016
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kambites said:
anonymous said:
[redacted]
It's a significant compromise because it severely limits the caster angle you can run. Especially in a heavyish car. It also tends to necessitate a long rack and a big steering wheel unless the car has a very light nose.

Edited by kambites on Sunday 1st May 17:23
You just described my 1972 Lotus Europa TC. Magic steering.

Guybrush

4,330 posts

205 months

Tuesday 3rd May 2016
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Agreed. The laws of physics can only be defied to some extent by technology and or design - a good handling but heavy car will lose something in the 'seat of the pants' feel.

patmahe

5,744 posts

203 months

Wednesday 4th May 2016
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Like most things in life there is a balance to be struck. Too heavy and a car will handle poorly and wear out consumables faster, too light and comfort/quality will be sacrificed.

It depends too on what you want from a car, even an avid PHer will spend >90% of their time just cruising along with the traffic flow as they have little choice. So comfort is more important during that 90% than lightness, however for a circuit or sports car where the object is to not only be quick but to be able to maintain speed through corners while having nice balanced handling.

So as an overall blanket ideal yes less weight is desirable, but it depends on what is sacrificed to make that happen and the intended usage that decides if its all worthwhile. Its why cars like an S-Class and a Caterham exist, both brilliant cars but in very different ways.

Vive la difference.

james_gt3rs

4,816 posts

190 months

Wednesday 4th May 2016
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kambites said:
Ozzie Osmond said:
Gotta love these "ABS doesn't work" myths.
Ever driven a VX220 hard? Some ABS systems are truly dire. hehe

Any modern mainstream car's system can stop far, far better than me though.
I can confirm the VX220 ABS is awful (some of the time). So the dangerous thing about it is that you never are sure whether it will go into ice mode or not. Genuinely don't know how it was signed off!

Fury1630

393 posts

226 months

Wednesday 4th May 2016
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Fisher Fury
170BHP
600Kg
283bhp / tonne

Guess where I stand?
Some folk have said they've had light cars & they're skittish - either the suspension geometry is wrong or the tyres are too hard or both.
There is an idea that modern cars are heavy "because of all the safety gear". My daughter's Pug 107 has a safety cell (she's tested it) impact crush zones, airbags, ABS, power steering, as well as four proper grown-up size seats & it weighs 800Kg.

Never understood where the "safety is heavy" idea came from. Unless of course you factor in the weight of other stuff, a two tonne car needs to be four times stronger than a one tonne car to achieve the same protection. Think of it like this, the one tonne car will hit a wall & stop - the two tonne car will hit a wall, pass through it & hit the wall behind. Then the rest of the house will fall on it.

100SRV

2,125 posts

241 months

Wednesday 4th May 2016
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Bowler Tomcat 100

3.9 Rover V8
1400kg kerb mass

Safe, light, capable and rapid.

The skeleton (chassis and cage) is lighter - 230kg - (and probably stiffer) than the BIW of many saloon and sports cars (e.g. Aston Martin, Jaguar).
Minimal impact on the surface when green laning and easy to get unstuck if you do get stuck.


I agree with Fury1630, Light is definitely the way to go...all you need is clever design and you'll find a virtuous circle.

Edited by 100SRV on Wednesday 4th May 13:23

Tuna

19,930 posts

283 months

Wednesday 4th May 2016
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Up to a point.. after that you're struggling to manage NVH. You might have a very fast driver's car, but you'll only be driving it with a crash helmet, and you won't have any passengers.

It seems to me the 911 and Evora prove the point that if you want a comfortable 'GT' experience, the amount of sound deadening, and solidity of touch points start to dominate the weight. When the chassis is only a few tens of kilos, even if you switch to weightless unobtanium, you're only going to save a few tens of kilos.

My understanding of the aluminium chassis thing is that while Alu is lighter, for a given strength of beam you need a similar weight to an equivalent steel item. The advantage to smaller manufacturers is that an extruded and glued aluminium chassis is cheap to develop and to set up tools for - but the expense is then passed on to customers for each and every model they buy. It's great for niche items, no good for mass production.

robinessex

11,046 posts

180 months

Wednesday 4th May 2016
quotequote all
Tuna said:
Up to a point.. after that you're struggling to manage NVH. You might have a very fast driver's car, but you'll only be driving it with a crash helmet, and you won't have any passengers.

It seems to me the 911 and Evora prove the point that if you want a comfortable 'GT' experience, the amount of sound deadening, and solidity of touch points start to dominate the weight. When the chassis is only a few tens of kilos, even if you switch to weightless unobtanium, you're only going to save a few tens of kilos.

My understanding of the aluminium chassis thing is that while Alu is lighter, for a given strength of beam you need a similar weight to an equivalent steel item. The advantage to smaller manufacturers is that an extruded and glued aluminium chassis is cheap to develop and to set up tools for - but the expense is then passed on to customers for each and every model they buy. It's great for niche items, no good for mass production.
The stiffness to weight ratio for aluminium, steel, and titanium is THE SAME. So to 'gain lightness' but not loose stiffness, in structural terms, have to adjust the section modulus. Carbon has much better stiffness to mass ratio, so in that context, you are onto a winner. But I won't go into buckling, because it starts to get hairy.

kambites

67,461 posts

220 months

Wednesday 4th May 2016
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robinessex said:
The stiffness to weight ratio for aluminium, steel, and titanium is THE SAME.
yes The Young's Modulus to density ratio is within a few percent for all three.

anonymous-user

53 months

Wednesday 4th May 2016
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Fury1630 said:
Never understood where the "safety is heavy" idea came from.
When you drive your 107 head on into an S-class at 50, you'll notice your car is 50 feet back up the road from where you met, with both your and your bank managers engines in your back seat. He'll be late home for his tea.

Tuna

19,930 posts

283 months

Thursday 5th May 2016
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kambites said:
robinessex said:
The stiffness to weight ratio for aluminium, steel, and titanium is THE SAME.
yes The Young's Modulus to density ratio is within a few percent for all three.
That's basically whatI said biggrin

coppice

8,561 posts

143 months

Thursday 5th May 2016
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Ah yes ,the Young's Modulus to density ratio; we speak of little else in my house.

kambites

67,461 posts

220 months

Thursday 5th May 2016
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Pft, surely you can't consider yourself a real car enthusiast without knowing what a Young's modulus is. biggrin

Ozzie Osmond

21,189 posts

245 months

Thursday 5th May 2016
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kambites said:
Pft, surely you can't consider yourself a real car enthusiast without knowing what a Young's modulus is. biggrin
Nooo, you're confusing that with the Renault Modus.

Young's modulus is used to calculate the number of pints of London's finest that you drank before you fell over. It's what the police call "counting back".

bermy boy

42 posts

178 months

Thursday 5th May 2016
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In almost all cases, light weight = more fun. Probably better handling, but almost always more fun. I've got a few cars...the two most fun by miles are the F40 and 1971 Mini 1000. Guess what, both very light. Coincidence?

Huff

3,140 posts

190 months

Thursday 5th May 2016
quotequote all
Truly light and well-resolved cars are a joy at any speed, in a way something of high-power/high-mass equivalency just utterly misses.

Fury1630 said:
Fisher Fury
170BHP
600Kg
283bhp / tonne

Guess where I stand?
Some folk have said they've had light cars & they're skittish - either the suspension geometry is wrong or the tyres are too hard or both.
Fisher Fury R1
170BHP
427kg

Have +1 from me! biggrin

anonymous-user

53 months

Thursday 5th May 2016
quotequote all
Huff said:
Fisher Fury R1
170BHP
427kg

Have +1 from me! biggrin
+1

The more I drive the Atom the more it makes me smile. It's not as dynamically safe as the M3 but, fk me it's fun.