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Weight balance of the Lotus 49 (and other race cars)


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#1 Paul Taylor

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Posted 18 October 2021 - 18:00

I was reading the Haynes manual for the Lotus 49 and it said the spring load on the front was 342lbs and on the rear 669lbs. Totalling these together it suggests a sprung weight of 1011lbs or 460kg with a 34/66 rearward weight bias. Add in the unsprung parts and it would be roughly 36/64 and a weight of 508/9kg in total. Does this sound about right?

I also considered data from video games, because in a lot of cases the dev teams get access to real raw specs. In Assetto Corsa the Lotus does indeed have a 36/64 rear weight bias, but in iRacing it has a 44/56 distribution. This seems so radically different. I wonder which is right?

It also got me wondering how it changed over the years from front to rear engines cars, from the 1.5l Grand Prix class to the 3l class, the early aero cars and so on...

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#2 Bikr7549

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Posted 18 October 2021 - 18:20

Spring load does not necessarily equate to vertical load on the tires due to the angle of the springs. And the angle may not (probably is not) the same front/rear, so you may not be able to back out the weight distribution from the Haynes numbers unless you have the angle of the springs, and other suspension layout dimensions.

#3 2F-001

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Posted 18 October 2021 - 18:41

David Hodges' book 'Lotus 49' quotes the following dry weights:

'67 49: 1102lb

'68 49B: 1180lb

'69 49B:1190lb

but I cannot see a reference in to weight distribution.

I guess these can only be estimates due to detail developments during the season.

 

Due to the effects of entropy, my other books and references to the marque are not so easy to locate at the moment... but will look further in due course!


Edited by 2F-001, 18 October 2021 - 23:17.


#4 Garsted

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Posted 18 October 2021 - 21:46

The balance in the Haynes manual is probably for the car alone, but the one in the game with a driver added perhaps?
Steve

#5 Catalina Park

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Posted 19 October 2021 - 06:59

The weight distribution was changed greatly between the 49 and 49B. They moved a lot of weight rearward and changed the front wishbones to move the wheels further forward.



#6 Porsche718

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Posted 22 October 2021 - 07:45

Paul,

 

Bikr7549 is correct in saying ...

 

Spring load does not necessarily equate to vertical load on the tires due to the angle of the springs. And the angle may not (probably is not) the same front/rear, so you may not be able to back out the weight distribution from the Haynes numbers unless you have the angle of the springs, and other suspension layout dimensions.

 

... but there is something to remember even before this. The "342lb" for front and "669lb" for rear is not a static load bearing figure. i.e. - vehicle sitting on a set of scales.

 

342 actually 342 lb/in. In other words - it will take 342 lbs of force to move that spring one inch. So not a lot to with what static load this spring will support.

 

Now you must apply the angle of spring, pickup points etc. The actual term is "motion ratio". This is a leverage factor that is used to determine a spring rate for a given vehicle, and given useage application. Yes, I always use the static corner weight as a starting point in my calculations, but that is only a starting point.

 

It is purely co-incidence that the front/rear "spring numbers" you found for the Lotus 49 - just happen to add up to the  overall weights quoted by Haynes.

 

And this leads to the next factor to apply to any spring rate calculation. The quality of the tyres.

 

If you look at the relatively narrow tyres on a 1967 Lotus 49, and compare them to the 49B or C that ran in 1970, these wider tyres would cause springs rates to be increased to cope with the increased roll factor caused by stickier tyres. This, of course, on a car that has a similar static weight as the 1967 car.

 

You asked about aero. Spring rates will be increased yet again for any given car if wings, skirts, or any other aero design feature in a vehicle. The downward force will be compressing the spring before it even heads into a corner - so spring rates will go up. Again, this for a car that has the same static weight.

 

As far as front engine to rear engine in F1. Really, calculation is always the same. Any top class driver wants a car that is slighly "loose" in the rear. UNDERSTEER - NO GOOD!!!

 

The inherent design of any rear engine race car is so much better as it will natural tend to want to oversteer. The trick is to reign it in. Ask any Porsche driver!!

 

It is just a matter of fine tuning spring rates, shock quality, front to rear rake, ride heights, etc. The list is VERY, VERY long!

 

I spend 8 hours a day doing just this.

 

Cheers Steve

 

 

 

#7 Michael Ferner

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Posted 22 October 2021 - 09:47

 

. Any top class driver wants a car that is slighly "loose" in the rear. UNDERSTEER - NO GOOD!!!

 

 

 

 

 

... unless you are braking really DEEP into a corner, then understeer is very much appreciated.



#8 Nigel Beresford

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Posted 22 October 2021 - 09:51

 

Paul,

 

Bikr7549 is correct in saying ...

 

 

... but there is something to remember even before this. The "342lb" for front and "669lb" for rear is not a static load bearing figure. i.e. - vehicle sitting on a set of scales.

 

342 actually 342 lb/in. In other words - it will take 342 lbs of force to move that spring one inch. So not a lot to with what static load this spring will support.

 

 

Maybe, but i have never personally seen an imperial (i.e. lbs/in) calibrated racing car coil spring that was not rated to an increment of 50 or 100 lbs/in, so I would be disinclined to believe the "342" or "669" numbers are spring rates or "spring loads". I would be much more inclined to believe they are axle weights.  My 1968 Autocourse quotes a "Formula Weight" of 1130 lbs for the 49B, so the sum of 342 +669 = 1011 lbs seems a credible weight for a wingless 49 which has not yet undergone all the reinforcement and (inevitable) weight gain needed to cope with the aero loads once they added wings, plus the wider wheels & tyres, heavier brakes etc. 


Edited by Nigel Beresford, 22 October 2021 - 14:22.


#9 2F-001

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Posted 22 October 2021 - 10:16

Indeed, I'm sure most of us know about spring rate (and 'wheel rate' - the effective rate of a spring in a particular installation) - but the document that Paul refers to in the opening post (a scan of a handwritten Lotus 'technical information' sheet now held by Classic Team Lotus) specifies 'Spring Load', not rate.

 

And as Nigel says, spring rates of those specific values don't make much sense.

 

The same document goes on to specify (as a completely separate item) six different combinations of front-rear spring rates, none of which get anywhere the figures under discussion here. (Values quoted for the rear are much higher than the front, presumably due to the inclined installation at the rear reducing the effective rate, whereas the near-upright front coilovers result in a wheel rate closer to the actual spring rate, notwithstanding the mechanical advantage of the upper wishbone operating the inboard mounting).

 

I'm sure Nigel will set me straight if I've messed that up!


Edited by 2F-001, 22 October 2021 - 11:30.


#10 Nigel Beresford

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Posted 22 October 2021 - 10:36

... unless you are braking really DEEP into a corner, then understeer is very much appreciated.

True for mere mortals, but actually a pointy balance is what you really want for a chicane (think Spa Bus Stop) combined with a nice safe neutral-to-understeer balance for high speed corners. This was the real performance secret of the Tyrrell 019 - we had the tools to achieve both. Of course, one of those tools was a driver of the calibre of Jean Alesi, tto be able to exploit and deal with the pointiness. Think Monaco 1990 qualifying...


Edited by Nigel Beresford, 22 October 2021 - 10:50.


#11 Michael Ferner

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Posted 22 October 2021 - 19:33

My point was, it all depends very much on the characteristics of the piece of track you are just negotiating. If you're blasting out of a corner onto a straight, then yes, understeer is not at all what you want. But, braking for a simple change of direction, many TOP CLASS DRIVERS indeed favoured understeer in the braking area, with a touch of oversteer on the exit. And chicanes, well, that's yet another very different animal, altogether.



#12 Bikr7549

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Posted 22 October 2021 - 19:55

Agree that usually springs are rated in even increments, but springs being springs the rates are never exactly that due to manufacturing issues. Is it possible that the referenced springs are nominally 350 and 650 lbs/inch, and the Haynes numbers are measured actuals? Even within a given spring the rate can vary along its length, a small amount.

‘Spring load’ is a pretty well accepted and understood term, the measured load from a spring at a specific length. If the Lotus document (which I have not seen) meant axle weight on each wheel I would think it would say that, as Lotus pretty much lead the way in suspension tuning. Interesting quandry.

Edited by Bikr7549, 22 October 2021 - 19:56.


#13 Porsche718

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Posted 22 October 2021 - 19:57

Maybe, but i have never personally seen an imperial (i.e. lbs/in) calibrated racing car coil spring that was not rated to an increment of 50 or 100 lbs/in, so I would be disinclined to believe the "342" or "669" numbers are spring rates or "spring loads". I would be much more inclined to believe they are axle weights.  My 1968 Autocourse quotes a "Formula Weight" of 1130 lbs for the 49B, so the sum of 342 +669 = 1011 lbs seems a credible weight for a wingless 49 which has not yet undergone all the reinforcement and (inevitable) weight gain needed to cope with the aero loads once they added wings, plus the wider wheels & tyres, heavier brakes etc. 

 

I agree. We get springs in 25 ft/lb increments. However, we can now get springs in metric at 0.1 of a kilo increments which may well convert back to "random" ft/lb numbers. Perhaps not in 1967! 

 

So, yes, it is more likely these numbers quotes were axle weights, which is why they so conveniently add up to the vehicle weight.

 

 

a wingless 49 which has not yet undergone all the reinforcement and (inevitable) weight gain needed to cope with the aero loads once they added wings, plus the wider wheels & tyres, heavier brakes etc. 

 

The rear wings on the high wing Lotus 49 were fitted direct to the uprights at the rear, so were in fact "unsprung" - working directly on the tyres, not through the coils. Which is part of the reason the rear wings failed on both cars at Montjuic in 1969, and Hill had two collapse at the undulating Lakeside track in Queensland the same year.

 

The front nose tabs, of course, were working through the fronts springs. Would have made initial set up rather tricky. You would have a variation of spring rate on the front depending on speed (fast or slow corner) with no variation of spring at the back - regardless of speed.

 

Steve


Edited by Porsche718, 22 October 2021 - 20:01.


#14 Nigel Beresford

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Posted 22 October 2021 - 23:03

Hi Steve, yes indeed I am aware the rear wing on the 49 mounted to the uprights, and the infamous Montjuic crashes. I was just banging on about how cars typically just get heavier with as parts are strengthened or added as the development process seeks to enhance performance and reliability.

#15 Nigel Beresford

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Posted 22 October 2021 - 23:11

My point was, it all depends very much on the characteristics of the piece of track you are just negotiating. If you're blasting out of a corner onto a straight, then yes, understeer is not at all what you want. But, braking for a simple change of direction, many TOP CLASS DRIVERS indeed favoured understeer in the braking area, with a touch of oversteer on the exit. And chicanes, well, that's yet another very different animal, altogether.


I can honestly say I have never heard a driver say they didn’t have enough entry understeer, except perhaps on an oval (where they complain about an excessively neutral or loose entry). Usually they complain about an excessively quick turn in or a lazy turn in. Entry understeer is usually undesirable because it produces snap oversteer on exit. And yeah, these were top class drivers

#16 Paul Taylor

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Posted 28 October 2021 - 13:18

The values in my post are listed as "Spring loading at normal load", but it does not specify what springs they were using when they measuring.

 

They also list spring rates and periodicities. It seems that all spring sets are a 30/70 split.

 

97F / 229R
117F / 274R
164F / 370R
 
I'm guessing the actual corner weight figures are not published anywhere. When iRacing first released the Lotus 49, it had a 62% rearward bias. With the current version, it is 56%. That tells me they have not had access to the real car to weigh it.


#17 2F-001

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Posted 28 October 2021 - 15:45

But I'm sure those figures (97F/229R etc) are actual spring rates, not the effective 'wheel rates' , but even if you knew the mechanical advantage of the front wishbones for the inboard mounting, and the angle of inclination of the rear outboard springs, I'm not sure you could infer the weight distribution.  You need either a figure for the weight distribution or the individual corner weights, not the spring rates.

 

That 30/70 split surely says more about the spring installations and angles through which they operate, than about weight distribution?


Edited by 2F-001, 28 October 2021 - 15:56.


#18 mariner

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Posted 30 October 2021 - 10:22

The other thing which confuses spring rates is the widespread use of bump rubbers to give a rising rate on large wheel movements. Originally invented to avoid instant bottoming out loads on brackets etc they became popular the 1960's as suspension tuning devices. 

 

The GLTL mechanics have told a story of Graham Hill insisting on them cutting off part of the bump rubbers on his 49 in 1968 - I think at Oulton Park practice  and Colin Chapman on his late arrival at the circuit going ballistic at them for doing it. " Its my car, I decide " was the gist of his anger at them and Hill. Probably fair comment as cutting them down too much would risk a suspension failure.



#19 Bikr7549

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Posted 31 October 2021 - 00:43

‘but even if you knew the mechanical advantage of the front wishbones for the inboard mounting, and the angle of inclination of the rear outboard springs, I'm not sure you could infer the weight distribution.’

I don’t agree with this as the entire weight of the car reacts thru the springs to the ground, so given the actual load on the springs (or rate and installed height) and the linkage geometry you could get the weight distribution. At least when the car is sitting still-once in motion the lift (+ or -) will affect those numbers, as will the effect of bump stops when they come into play.


Edited by Bikr7549, 31 October 2021 - 01:32.


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#20 Bikr7549

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Posted 31 October 2021 - 03:51

Edit-the springs support the entire sprung weight of the car, not the total weight. So wheels, tires, part of the springs and shocks and links would not show up here.

#21 Doug Nye

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Posted 31 October 2021 - 09:15

Wandering back into ancient history - this from the Brentford Public Weighbridge, 1956...  

 

For the boringly logical modern metricians our sneeringly Imperial 'cwt' (hundredweight) measurement indicates 112lbs and the 'qtr' (quarter) measurement 28lbs (remember?)...   :cool:

 

I do wonder who the 162lb driver might have been...

 

(Document image copyright GPL)

 

GPL-VANWALL-WEIGHTS-1956-SMALL.jpg

 

DCN


Edited by Doug Nye, 31 October 2021 - 09:20.


#22 Nigel Beresford

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Posted 31 October 2021 - 13:29

Wandering back into ancient history - this from the Brentford Public Weighbridge, 1956...  

 

For the boringly logical modern metricians our sneeringly Imperial 'cwt' (hundredweight) measurement indicates 112lbs and the 'qtr' (quarter) measurement 28lbs (remember?)...   :cool:

 

I do wonder who the 162lb driver might have been...

 

 

DCN

 

Doug, 162 lbs / 73 kg fully kitted is a pretty typical weight even for a top line driver these days. Often for convenience one finds out which mechanic weighs roughly the same as the current pedaller and gets them to sit in the car on the setup pad. I expect it was the same "back in the day". Still, it would be nice to think someone more glamorous made the trip to Brentford especailly!


Edited by Nigel Beresford, 31 October 2021 - 13:35.


#23 mariner

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Posted 31 October 2021 - 13:40

Thanks for that image Doug, i assume it is a Vanwall?

Using metrics to compare to later cars 14cwt 1 qtr etc is about 735kg or 1,600lb. Less the 162lb driver that's about 660kg - a lot more than many contemporary claims , and more than the similar 4 cylinder BRM. was supposed to weigh.

The 1.5 litre formula was the first with minimum weight limit of 450kg. So despite having 50% less engine size and 200 bhp vs 280 ?) for a Vanwall the power to weight ratio would be the same - but bit less with a driver onboard..

Actual acceleration would be affected by drag as well but the 1.5 litre cars had a lot less frontal area too.

#24 Paul Taylor

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Posted 01 November 2021 - 01:33

Very interesting Doug! I noticed that item #9 was calculated wrong, shouldn't the total weight by 18cwt 2qr 0lbs?

 

In any case, I gleamed the following figures from that:

 

Weight balance "dry" + driver = 51.5% rear

Weight balance + 35.5G fuel in rear tank only = 61.4% rear

Weight balance + 55G fuel in rear/side tanks = 59.7% rear

 

Fuel density = 7.8 - 8.08lbs per gallon

 

Having such huge swings in weight balance over a race distance must have been somewhat difficult to contend with, particularly when it comes to deciding spring rates, suspension setups etc. That's presuming they bothered with all of that back in the 1950s...



#25 Doug Nye

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Posted 01 November 2021 - 22:10

They did...

 

DCN