Perfick

[StewartG]

I'm searching my sole and bank account for the reasons. Should I have my car flat floor set up or not? Surely this only optimises the thing for perfectly flat straight roads. I've heard some racers deliberately miss tweak the corner weights to help with the predominant right hand corners on most circuits and all roads have a camber. I'm wondering if it might be better to set things empirically. For example if one front wheel repeatedly locks first under braking then maybe the platforms can be adjusted to compensate.

[captain chaos]

I'm new. So please explain what is checked/adjusted during a flat floor set-up and what are the benefits if any for a mainly road user.

thanks

[Peter Carmichael]

If you don't mind getting your hands dirty, you can get a very decent flat floor setup at home without special tools. Have a look at:

 

Flat floor setup without the flat floor.

 

The purpose of a flat floor setup is to make sure that when loaded, the car runs straight and level, allowing the suspension geometry to work as designed. There are other advantages associated with minimising the stored energy in the chassis so that it doesn't spring back on you unexpectedly.

 

One important consequence of a properly flat floored chassis is that you will not get one wheel locking up prematurely under braking. Here is a bit of theory:

 

The car weighs a fixed amount and the sum of all the weights supported by each wheel will equal this weight. The centre of gravity is at a fixed position so you cannot *move more weight to the front* which Arrowstar tried very hard to convince me they were achieving. The proportion of the weight supported by the front compared to the rear tells you where the CofG is in the fore/aft axis. The proportion of weight supported by the LHS compared to the RHS wheels tells you where the CofG is in the left/right axis. What you can achieve is the equivalent of sticking a knife underneath the table-leg of the rocking restaurant table. Yup, that's right. The uneven loading you are trying to correct is based on diagonally opposite pairs of wheels. You are trying to avoid having one diagonal lightly loaded and the other heavily loaded.

 

The CofG is bound to be off-centre. You should be aiming for a setup optimised for the way you use your car most often. i.e. for race use, optimise for the weight distribution when carrying just a driver; for road use optimise for average weight of driver and half the weight of your heaviest regular passenger.

 

Some practitioners aim to get the front wheels with exactly even wheel weights believing this will give the best braking, however this oversimplifies matters because dynamic weight shifts alter the weight distribution, especially with progressive rear springs. I prefer to aim to get the diagonals evenly weighted.

The car can run straight and level with widely varying corner weights. i.e. a light diagonal and a heavy diagonal.

 

My method gives you a very accurate 'even front wheel weights' setup; you can then see what difference at the rear RHS platform is required to account for the off-axis driver loading and juggle things so that half of the correction is made at the front and half at the back such that the car remains level. By the time you have done this you are near enough flat-floored to within a kilo or two.

 

To do it properly you ought to subtract the mass of the wheels and other unsprung components at each end.

 

Edited by - Peter Carmichael on 13 Sep 2000 16:29:58

[big daddy]

Oh

[Peter Carmichael]

Is that all I get for an informative and pertinent post on a technical topicquestion.gif An 'Oh'question.gif

 

Grrrrrrrr...mad.gifsmile.gif

 

 

[big daddy]

Uh-huh

[captain chaos]

Thanks for the reply Peter, as i wrote the posting I had a feeling deep in the recesses of my soul that it would be yourself who would reply. I always say "actions speak louder than words" You don't live in Shrops by any chance?

[dogvet]

Peter,

Is in paragraph 3 of your link correct? or am I being thick!

sentence starts" Raise the rear a small amount...and adjust the "front" platforms. surly this would be difficult if the front of the car is lowered to the ground, as indicated before hand? Is this not difficult as the springs are tensioned or is it that the are upside down shock platforms making this easier?

Thanks in advance.

[Anna Rexia]

Dear Peter - never uses a sentence where a paragraph will do !

[Rory McLeod]

Peter C. At least by attempting to reply you know someone is trying to understand what you say. CofG makes sense but the major varible weight disurbance takes place in the passenger seat, therefore, set the fronts in balance and vary the rears, the diagonal system works for a standard 4 square race car but a Caterham has a rear set cockpit.

(promise i dont work for Arrowstar!)

[Peter Carmichael]

dogvet, you are not being thick, but I didn't write that I jack up the front to take the load of the springs to adjust them. The gist of what I wrote is correct but the practicality is different, as you spotted.

[Peter Carmichael]

If you had a four-square racing car, then even diagonals would also guarantee even front wheel weight and even rear wheel weight. I have never seen or derived the maths that explains it but I thought the fact that even diagonals ever get mentioned means there must be something in it for non-symmetric loadings. (gosh, how naive).

 

When you are braking you get a very large weight shift onto the front wheels, dependent on the height of the CofG. The force required to keep an unevenly loaded car in a straight line under braking is uneven also, but the clamping forces on the disks are constant, side to side. What this means is that, however infinitessimally, you are having to steer the car to keep it on line while braking. How the balance of this correcting force is meted out between the tyres is indeterminate without a lot more careful analysis and a heap of assumptions.

 

I reckon that with a smidgen of toe out at the front and with even diagonals you could get the last bit out of your threshold braking. Toe in at the rear will also help to keep things stable.

 

As for the major weight disturbance being in the passenger seat, flat flooring a car optimises it for a single loading condition only. My advice for a race car is to get it set up perfectly for race conditions, with a race fuel load and the driver's weight only. For the road, I suggest making sure that the most extreme, commonly encountered load conditions (1. Heaviest driver only; 2. Lightest driver, heaviest passenger) are evenly spaced on either side of optimum.

 

The even diagonals setup minimises the spring energy stored in the chassis. Chassis springing is undamped and residual energy means you are likely to get an asymmetric response with that spring energy appearing unexpectedly. (This observation requires the chassis springing to show a rising rate characteristic.)

out on a limb mode>

 

Edited by - Peter Carmichael on 14 Sep 2000 10:27:21

[Nick]

Peter - very interesting, thanks, though (as you will see) my own understanding is somewhat limited! I guess it's like asking 'how long is a piece of string' but what do you make of the following settings on my 1998 1.6K ss, running on 'standard' Bilsteins, red bushed front arb, rear arb (on firmest setting) 13" AO32Rs, narrow track, LSD?

 

Front toe out 2.5 mm

Rear toe 2.5 mm - I don't know if that's in or out - I said I was ignorant! Hopefully you can surmise?

 

Front ride height 132 mm

Rear ride height 140 mm

 

Front camber 2.1 both wheels

Rear camber 1.8 (left) and 1.9 (right)

 

Corner weights (with 70 kg driver)

Front left 140.5 kg

Front right 139.5 kg

 

Rear left 174.5 kg

Rear right 188 kg

 

Weight of car (half a tank of fuel, 7 litres oil, water, tools, etc) 572.5 kg

 

At a recent flat floor setup, Hyperion raised the ride height as the car was pretty well resting on the front bump stops as, apparently, Caterham switched to longer shocks at the front which only really suit wide track.

 

Maybe it's me but I feel the car is a bit understeery.

 

If you have any comments, I shall try to understand them!

 

Thanks very much

Nick

 

Edited by - Nick on 14 Sep 2000 10:50:01

[Nick]

DOH! Double posting, sorry!

 

Barry, I keep getting this error message when I post:

 

Response object error 'ASP 0158 : 80004005'

Missing URL

/blatchat/post_info.asp, line 292

A URL is required.

 

Maybe that means something to you!

 

 

Edited by - Nick on 14 Sep 2000 10:49:04

[Peter Carmichael]

Hmmm. Stiffest rear anti-roll bar setting. Toe-out by the book. Cambers pretty much spot on. Softer than my front anti-roll bar. You have about 10kg more on each of your front wheels compared to me. I have forgotten what the red bushed front ARB means. Is it 1/2in or 5/8in?

 

I think the rear ARB is too stiff - it looks wrong. Even though the car is understeering this isn't the answer and it wrecks the ride quality and compromises traction out of corners.

 

I'd look at stiffening up the roll stiffness at the front with ~300-350lb/in springs (Juno) (you didn't mention springs so I assume they are standard). The standard dampers won't be ideal, but will cope with this change. With that in place I would slacken the rear anti-roll bar to its second softest setting on each side. To cure the understeer I would look at rear ride heights. (assuming radius arms)

 

If you have adjustable platforms, wind them up two turns at the back - this won't affect the flat floor settings. If you go too far the car will feel horribly twitchy and will constantly feel like it is trying to swap ends. I like to leave it with a bit of understeer that you have to overcome at turn-in.

[pie_boy69]

This adjustment that peter is talking about, Raising the rear by 2 full turns will make a dramatic difference.

Whilst at the recent Brooklands day Peter helped me make this cahnge after complaining that the front felt a little bit understeery, once this change had been done the car felt som much beter a t the rear I couldnt believe that such a little change would have such an affect on the car.

All i need now is more power!!!

 

Keith Pickering

superlight T7 KCP

[Peter Carmichael]

Or then again, maybe the understeer is because you have managed to get your k-series as heavy as a Vauxhall. How did you manage that? cool.gif

 

Superlight - 488 kg with FIA rollbar and half tank of fuel.

 

Coo, I'm an Archangel...

[Steve W]

Keith you only just spent all that money to get more power ? Getting used to at already ? Car in for new springs and dampers next week. Not sure about getting a rear anti roll bar fitted. Then Peter can get his Di Dion tube back. Peter are you OK to pick it up at the 7 workshop open day on the 23rd ? THanks again and see you then.

 

 

[Nick]

Thanks for your comments Peter.

 

When I said standard Bilsteins, I meant the whole caboodle - sprinds, dampers, and all those other bits that I just call 'shocks'!

 

You will gather, therefore, that although I have achieved Deity status here, I am a complete novice at getting my hands dirty - how do I adjust the rear platforms? Would it be OK to do this with current springs? You're right, I have rear radius arm, adjusted to the sportier position (I can't remember which that is and it's pouring with rain so don't want to find out!)

 

The red bushed front arb I have has a 52 mm circumference - 16.55 mm diameter, which is something like 0.65" which is about 5/8".

 

What dampers would you recommend to go with Juno springs?

 

Can I book you to help me set things up at a track day?! Actually, I'm half serious...! I had wondered about hiring Hyperion for a day.

 

Keith, thanks too for your comments.

 

Nick

 

[Nick]

Peter, mine's a 1.6K Supersport, not a Superlight. FIA roll bar plus all those extras like a windscreen and a heater and a spare wheel! There were some tools on the boot but that was about it I think. 18 psi all round at the moment, just to bung that into the equation - not much weight there though!

[Peter Carmichael]

erm... in no particular order.

 

The standard Bilsteins are fine with the uprated springs. Not ideal, but neither you nor I have a damper dynamometer so I am not recommending anything else. Juno have been toying with the idea of getting one...

 

The front ARB is perfect at 5/8in. That is smaller than my 18mm one, but I am advising you to go for stiffer springs than I am running. The roll stiffness needs to be balanced, front to back. The softer back end will give a more settled feel in high speed corners.

 

The extension pieces on the widetrack dampers can be removed. You may have to do this to get a minimum of 10mm damper travel clear of the bumpstops for a sensible ride height.

 

Keith, how have you found the car behaves on the road since Brooklands? I had done the same to mine earlier in the morning and following a run down to Sussex last weekend I had it up on an improvised jack made of oak timbers to trim the ride height down again. The setup that I had driven to Brooklands with dated back to a wet trackday I did at Goodwood on April 5th (I believe it snowed on the way down) and was set to understeer on purpose. I have only lowered it by one turn, which has made it very amenable on the road.... Keep playing...

 

Yes, I wouldn't mind helping set you up for a track day. Just make sure it is a trackday with good pit facilities, er, like the up and coming club Cadwell Park day. If it is feasible I will consider anything. It's all just mucking about with cars to me.

 

Steve, I'm fine to pick up the de Dion tube at the open day. I might even be collecting an engine!

[Nick]

Peter, hmm, I'll get back to you re Cadwell, if that's OK. It clashes with something else so I hadn't given it much thought. However, if you will definitely be there and could make some headway with my suspension....!

 

I have just looked at the rear shocks. At the base of the spring there are two threaded 'collars'; it looks to me like one controls the length of the spring whilst the other tightens onto the first to lock it in place. Is that what you mean by adjustable platforms?

 

The collars have slots around their perimeters, so a C spanner with an inverted 'bobble' on the end would be needed to adjust them - which trees do these grow on?!

 

You say that the standard dampers won't be ideal - can you recommend any? You subsequently said you are not recommending replacements but I'm unsure whether you meant you do not think replacements are strictly necessary, or whether you would rather not get into that area.

 

Clear as mud!

 

Thanks,

Nick

[Peter Carmichael]

When I wrote "not ideal", I was inferring that the diference between the theoretically ideal and the close approximation of the standard dampers was small. I really think the Bilstein units do a great job and wouldn't use anything else without a lot of research and a stack of dynamometer data. The risk of getting something woefully wrong is just too great.

 

The "collars" are the "adjustable platforms". If they are unlocked, you can usually move them by hand and don't need a c-spanner. Left loose I have never seen them move of their own accord, so I don't bother locking mine any more than just spinning up the lock ring by hand (very gently). The threaded sleeve that they sit on is not positively restrained but does not usually turn of its own accord - just watch out for it. A squirt of WD40 might be an idea before you start back there.

 

The mention of Cadwell was a gentle tease. I love Cadwell but haven't been up there this year.

[Nick]

I did wonder about your reference to Cadwell's good pit facilities...! It's my favourite track. Have you been to Anglesey? It's similar but smaller - Easytrack have a day there on 7th October - can I tempt you to either?!

 

Cheers

Nick

[Nick]

Peter, I haven't got round to new springs yet but adjusted the rear ride height today - very easy when you know how!

Rear platforms up by 2 complete turns as you suggested. Drove round some roundabouts, etc to evaluate; speed is somewhat limited of course, so not as informative as a circuit but the best I could do. Slight improvement.

Rear platforms up another 2 turns - noticeably less understeer, even oversteer.

Changed rear arb from 4 (stiffest) to 2; in so doing, had to adjust the arb 'arms' to the correct length so as not to tension the arb at rest.

Definite difference from before I started playing. Car felt more rear biased - not sure if this is because it is a new feel, or because I have gone too far. A trackday will tell I guess!

 

Thanks very much Peter for your help. I hope to meet up with you at a trackday as I would be very interested in your opinions of my setup, and to buy you a bevvy - at day's end of course!

 

All the best, Nick