39 replies to this topic

[Paul Taylor]

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...

[Bikr7549]

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.

[2F-001]

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.

[Garsted]

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

[Catalina Park]

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.

[Porsche718]

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

 

 

 

[Michael Ferner]

 

. 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.

[Nigel Beresford]

 

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.

[2F-001]

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.

[Nigel Beresford]

... 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.

[Michael Ferner]

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.

[Bikr7549]

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.

[Porsche718]

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.

[Nigel Beresford]

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.

[Nigel Beresford]

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

[Paul Taylor]

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.

[2F-001]

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.

[mariner]

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.

[Bikr7549]

‘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.

[Bikr7549]

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.

[Doug Nye]

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?)...  

 

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

 

(Document image copyright GPL)

 

 

DCN

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

[Nigel Beresford]

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?)...  

 

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.

[mariner]

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.

[Paul Taylor]

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...

[Doug Nye]

They did...

 

DCN

[SteveHood]

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...

 

Hi Paul,

I know this is an old thread, but no-one answered your question... I also wont, because I dont know "which is right", but I do know that iRacing worked with Clark's R2/R11 chassis owned by Chris MacAllister either as or after, it was being converted back from the 49B spec to the original '67 Zandvoort spec by Classic Lotus.

I would hazard that a lot of suff wasn't removed, such as any chassis or tub strengthening additions over the years so there's a decent chance that the weight and balance deviates from the original, whilst still being 'correct' to that particular car.

To the later point about the balance shift in iRacing's 2021 update... the car was 'undriveable' in its original form. Not my claim, but iRacing was seeing a lot of people purchase the car, and not many driving it... so they moved some mass around and now it's... still not driven by very many people...

https://www.iracing....ming-to-iracing
https://www.autoweek...ing-simulators/

 

Edited by SteveHood, 11 August 2023 - 15:42.

[Paul Taylor]

Hi Paul,

I know this is an old thread, but no-one answered your question... I also wont, because I dont know "which is right", but I do know that iRacing worked with Clark's R2/R11 chassis owned by Chris MacAllister either as or after, it was being converted back from the 49B spec to the original '67 Zandvoort spec by Classic Lotus.

I would hazard that a lot of suff wasn't removed, such as any chassis or tub strengthening additions over the years so there's a decent chance that the weight and balance deviates from the original, whilst still being 'correct' to that particular car.

To the later point about the balance shift in iRacing's 2021 update... the car was 'undriveable' in its original form. Not my claim, but iRacing was seeing a lot of people purchase the car, and not many driving it... so they moved some mass around and now it's... still not driven by very many people...

https://www.iracing....ming-to-iracing
https://www.autoweek...ing-simulators/

 

Hi Steve,

 

Thanks for replying after so long. Yes I remember when they released the 49 for iRacing, it had a 61% rear weight bias. Then one day it was magically updated to 56%. That's quite a big shift for a car they supposedly had actual access to and measured in detail.

 

I took a sub out back in January this year for a month, the Lotus 49 was still undriveable. 

[SteveHood]

Hi Steve,

 

Thanks for replying after so long. Yes I remember when they released the 49 for iRacing, it had a 61% rear weight bias. Then one day it was magically updated to 56%. That's quite a big shift for a car they supposedly had actual access to and measured in detail.

 

I took a sub out back in January this year for a month, the Lotus 49 was still undriveable. 

Yeah it's a struggle out of the box.  The setups they built for the car are supposedly for new drivers but certain fundamental parameters are way off and make the car described as "the best car I've ever driven" by people who know what they're talking about, drive either like an oil tanker or an oil slick, with very little space between the two.

I've been looking at those issues for months wondering what was going on, how to fix them... then got a hold of a Haynes book last week, noticed some glaring disparitys between the 2 spec sheets and had a fiddle with some parameters.  If you felt like jumping back in for a test there's a much better, and somewhat period correct, setup here... Lotus_Engineered_-_GP_Legend.sto - and a bit of a discussion about the issues here... https://forums.iraci...eline-car-setup

Edited by SteveHood, 15 August 2023 - 08:33.

[SteveHood]

Thought I'd update the thread as I think I've finally nailed the numbers down.

"Spring Load at Normal Load" in the manual, is actually referring to the Static Load (Sprung Mass / Motion Ratio), in 'Ready to Race' config... i.e with 450 lbs of fkuids/drivers on board..

The sprung mass on the front corners is 210lb. On the rears, 473lb

Fr: 210lb / 0.614 = 342 lbs
Rr: 473 / 0.707 = 669 lb

The unsprung mass is, or appears to be, 64.9lb on the front corners, 28.2lb on the rears.
That gives the car a total weight of 1552 lb, (inc. 450 lbs of fluids / driver, which is 10 lb shy of the claimed weight in the book, possibly due to rounding errors in the calculators I used) and provides for the 35/65 weight balance.

Full breakdown here https://us.v-cdn.net...t-281115-29.png

Edited by SteveHood, 08 December 2024 - 03:04.

[Doug Nye]

And so - how does it now 'drive'....?

 

DCN

[SteveHood]

This doesnt affect our car at all unfortunately.
iRacing's car carries a lot more meat on the front end, with a 44/54 balance.  This latest dive into the numbers is part of an attempt to get them to rework it slightly.

We can approximate the spring frequency deltas Fr/Rr for a more responsive front end, but the rear has relatively less grip than it should and likes to shout about it.

If I can convince the powers that be, there's a small chance of getting something changed in about 3 months.

[Doug Nye]

I guess it would help if I had any idea whatsoever what 'IRacing' might be.  I guess it's some kind of online activity then?  

 

DCN

[PeterElleray]

Thought I'd update the thread as I think I've finally nailed the numbers down.

"Spring Load at Normal Load" in the manual, is actually referring to the Static Load (Sprung Mass / Motion Ratio), in 'Ready to Race' config... i.e with 450 lbs of fkuids/drivers on board..

The sprung mass on the front corners is 210lb. On the rears, 473lb

Fr: 210lb / 0.614 = 342 lbs
Rr: 473 / 0.707 = 669 lb

The unsprung mass is, or appears to be, 64.9lb on the front corners, 28.2lb on the rears.
That gives the car a total weight of 1552 lb, (inc. 450 lbs of fluids / driver, which is 10 lb shy of the claimed weight in the book, possibly due to rounding errors in the calculators I used) and provides for the 35/65 weight balance.

Full breakdown here https://us.v-cdn.net...t-281115-29.png

if we're still quoting '49' numbers here i would question the rear unsprung weight, as the car had both outboard brakes and outboard coil over dampers. ?

[SteveHood]

I guess it would help if I had any idea whatsoever what 'IRacing' might be.  I guess it's some kind of online activity then?  

 

DCN

I'm afraid nether my pockets or contact book is sufficient to get in the cockpit of one of these for real.
 

 

if we're still quoting '49' numbers here i would question the rear unsprung weight, as the car had both outboard brakes and outboard coil over dampers. ?

I would agree the rear seems unreasonably low, however, there is very little room for manoeuvre working directly from the book quoted figures this is based on.

The book cites:

Suspension geometry (Motion Ratios): 0.614 / 0.707
Static Loads: 342 / 669
Total Weights: 1562 / 1102
Spring Rates: 67 / 229, etc...
Spring Frequencies: 1.67 / 1.84. etc...

If there's an alternate way to calculate this which brings the unsprung mass of the rear corners to a seemingly sensible level, I dont know how to find it.

However, I think most of the rear suspension, except perhaps the lower half of each coil over unit, is being counted as sprung mass, leaving just the upright, wheel, trye and brake unit technically outboard of the spring.  That does still seem an awful lot to fit into 28 lbs though.

Edited by SteveHood, 08 December 2024 - 21:27.

[PeterElleray]

I'm afraid nether my pockets or contact book is sufficient to get in the cockpit of one of these for real.
 

 

I would agree the rear seems unreasonably low, however, there is very little room for manoeuvre working directly from the book quoted figures this is based on.

The book cites:

Suspension geometry (Motion Ratios): 0.614 / 0.707
Static Loads: 342 / 669
Total Weights: 1562 / 1102
Spring Rates: 67 / 229, etc...
Spring Frequencies: 1.67 / 1.84. etc...

If there's an alternate way to calculate this which brings the unsprung mass of the rear corners to a seemingly sensible level, I dont know how to find it.

However, I think most of the rear suspension, except perhaps the lower half of each coil over unit, is being counted as sprung mass, leaving just the upright, wheel, trye and brake unit technically outboard of the spring.  That does still seem an awful lot to fit into 28 lbs though.

yes, even taking half of those items out of the equation i think the wheel, tyre and brake disc would account for that on their own.  i have some cad models of components from that era and adding inertia properies gets me to just under 20lb for the wheel, disc and hat, without the tyre. Then you have the caliper, upright, hub, bearings, universal to add in. On the other hand the front seems high if you are taking out the same elments, so i would question the basic split front to rear if thats where the unsprungs are coming from.

[SteveHood]

Turns out to be a decent amount of room for manoeuvre.

Have got the unsprung to 53 Fr, 40 Rr, without doing too much damage to the balance.

[PeterElleray]

Turns out to be a decent amount of room for manoeuvre.

Have got the unsprung to 53 Fr, 40 Rr, without doing too much damage to the balance.

ok, but the rear should be heavier than the front. The cars had same size brakes (at least at first) front and rear, rear had wider wheels and tyres and larger heavier upright assembley, and half a driveshaft. Countering that the front rocker would be a little heavier than the rear top link and top radius arm.

[SteveHood]

The numbers that fit iRacing's car are 33 Fr, 60 Rr.
There's even less wiggle room over there, with fixed corner & total weights. And they had access to the real chassis during restoration.

Transplanting those unsprung numbers to the real car gives a 31/69 balance in the 'Normal Load' config.

[VWV]

https://www.motor1.c...-f1-gaming-rig/

 

Looks like in this rig the whole rear end is "unsprung" but it would look good in a man cave.

[PeterElleray]

The numbers that fit iRacing's car are 33 Fr, 60 Rr.
There's even less wiggle room over there, with fixed corner & total weights. And they had access to the real chassis during restoration.

Transplanting those unsprung numbers to the real car gives a 31/69 balance in the 'Normal Load' config.

i wonder if they had the opportunity to do a definative weight check on scales for the complete car. Very difficult to organise in my experience.  I think the bottom line is you need to look at what each corner consists of and do some simple calcs. The rear just can't be as light as the original figure and the front almost certainly not as heavy. Work forward from that and from the overall weight - if you trust it - rather than what you read in a magazine or a book, unless you are very confident of their source. Even a corner weight sheet from Classic should be questioned closely to determine what was on the car. Don't accept 'everything' as the answer. Everything seems to mean different things to guys working on the car !