Wheels, suspension and brown trousers

[Alex Wong1697456877]

Hi everyone - I'm out to pick your brains again!

 

Wheels:

I've been thinking about wheels for some time now. I think a 2.0 Vx Caterham will understeer like mad with SLR wheels as it's so front heavy. I was thinking about 13x7J's all round to try and even it out a bit. Would this be a correct line of thinking? I was also hoping that by using 7J rims at the back, I wouldn't have to do any mods to the rear suspension. Is this correct? Does anybody know what offset I would need for these?

In the mean time, I'm getting some 6x21 ACB's for the front and 7x21ACB's for the rear which goes against my idea above but will be interesting. Best of all, they'll go straight onto my current minotaur wheels.

 

Suspension:

Also, on my last outing at Curborough, I started to feel that the car was a bit soft. It rolls alot around corners and with normal road tyres, it's noticeable that the car rolls into corners then starts to understeer. On powering out of corners, it feels twitchy at the back on the limit. (I span at about 70-80mph around the fast left hander coming up the hill from the start at Curborough - 360 deg, no damage and one very wide-eyed passenger!) It's not as progressive as I thought it was when I used stickier rubber which I think just masked the problem. I wondered what spring rates other people have used on HPC's and what shocks have been tried, or if anyone had any other ideas. My car has 1997 Supersport suspension (widetrack - black front springs ? rating, non adjustable bilsteins, progressive rear springs, rear anti roll bar set one from softest, trailing arms on road setting, and the biggest front anti roll bar (green bushes - not sure about about the actual diameter)

 

Cheers!

 

Alex Wong

alex.wong@lotus7club.co.uk

www.alexwong.net

Home : 44-(0)121-440 6972

Fax : 44-(0)121-440 4601

[flick]

The spring rate's I belive are 150lbs per inch if the spring's have green paint on yhem or 175lbs per inch if they have blue paint on them (ie the spring is painted black but the other colour is on one end

K series should be 150lbs and VX should be 175lbs.

 

Also I belive that the damper travel is restricted by the bump rubers / stops I am going to experiment with my car to see if I can remove part of the rubber, I only have approx 10mm of travel before the rubbers make contact with the damper, When this happens the roll stiffness increases promoting understeer.

 

Regards

Kevin Silcock

kevin.silcock@virgin.net

[Alex Wong1697456877]

My front springs are black with a stripe of yellow on them. What does that make them?

 

 

 

Alex Wong

alex.wong@lotus7club.co.uk

www.alexwong.net

Home : 44-(0)121-440 6972

Fax : 44-(0)121-440 4601

[Barry]

ex-Mike Bees perhaps?

 

Edited by - barry on 24 Apr 2000 23:29:52

[StewartG]

Alex, why are you using the trailing arms on the road setting? Assuming my understanding that the road setting is the upper one is correct then I reckon the race setting gives much better traction out of corners with less oversteer, it seems to let the back end squat down and accept the power.

[SLR No.77]

Alex,

Your rear trailing arm will definately be better in the lower mounting position. This gives a slightly harsher ride on the road but when cornering hard (ie. track)it helps the suspension maintain the correct geometry and stability.

 

The springs you probably need are the Vauxhall race ones (250lb I think, and blue) but if Caterham painted the yellow sripe on yours they should know the rate anyway. Unless it stands for "scared-i-cat!

 

The rear anti roll bar is possibly better forward a hole onto the race setting area to reduce your understeer. It is remarkable how much difference the set up at the rear makes to the handling. Like yours the front of my car non adjustable take it or leave it, so playing with the back is the only choice.

 

Stu.

Novice.

 

[gareth]

Alex

 

I have a race/road HPC and experience the same problems, tighten the rear anti roll bar

move to adj shock for height and buy SLR wheels, in thaqt order, my tuned HPC regularly out handles SLR etc, just balance the understeer with the loud pedal, easy !!!

[Nick]

The first 7 I drove was a pre-96 1.4 ss and it handled beautifully. My 98 1.6 ss seems to handle faster but doesn't 'feel' as nice. Initially it understeered horribly (bought new so all settings were standard). I had a long chat with Derek Moore at Classic Carriage and we started off by changing the radius arm settings away from the road setting which made some difference. Next step was a geometry setup; I haven't got the settings to hand but this made a bigger difference, though the tendency was still to understeer. This was most noticeable at corners like the first right-hander at the end of the back-straight at Cadwell Park. I then played with tyre settings (again on Derek's advice - he runs all the Graduate (?) Sevens) and ended up with 18 psi front and 16 psi rear. This gives a neutral feel. Putting just one more psi in the front induces oversteer. I was surprised at the difference changing the tyre pressures can make - and it doesn't cost a thing! Incidentally, an accurate gauge is handy.

 

http://www.sound-dist.co.uk/ do one guaranteed to within 1 psi for about 20 or 30 pounds I think. Even the expensive Racetech ones, etc are not guaranteed.

 

I almost went for a stiffer front anti-roll bar to kill the dreaded understeer but ended up sticking with the original; I like the reasonably compliant ride and thought a stiffer bar would upset this. The original also looks a bit purist. wink.gif

 

There are so many variables, I have found it helps to chat with someone who really does know what they are talking about, and then change things singly, noting the changes and any differences they make on a familiar bit of road.

 

I'm not sure if any of that is any help to you but there you go!

 

Nick

[Andrew Russell]

Just as well that you did stick with the original front anti roll bar, I think if you had gone for a stiffer one, the understeer would have been worse! My understanding is that you should have stiffened up at the rear to dial out the understeer.

[Alex Wong1697456877]

I have thought about using the race setting on the trailing arm but I think this will stiffen up the back and cause more oversteer on powering out of corners. I asked Juno Sportscars, Caterham and have asked Derek Moore in the past and they all say that stiffening the back will make it very loose at the rear. Juno and Caterham both favoured using heavier springs - about 300 at the front and 200 at the back as a rough guide. The Bilstein Race dampers were also suggested to go with the springs.

 

In the mean time, I've ordered the de-dion ends for the ACB's (.25 degree) and was wondering what cambers people use at the front? I gather that Arylium have used up to 4 degrees -ve camber but most people use alot less I think.

 

[Nick]

Andrew

 

Now you've got me confused! Ho well, it seems OK at the moment so I'll stick with it as is! I was told a stiffer front anti-roll bar would induce oversteer but I shan't argue with you as I haven't a clue what I'm on about really. Second hand knowledge and all that!

 

Nick

[Tim Seipel]

Try 1 to 1.5 dergrees negative camber at the front but NO more. It will still tramline like a B!?£$!&d though. Put the rear trailing arm to the race position for stability. Try disconnecting the rear bar and use a smaller front one Green is 19mm by the way try orange or red.

 

Tim Seipel

[Alex Wong1697456877]

What exactly does the race setting do compared to the road one?

 

[Andrew Russell]

Nick, sorry for confusing the situation...I have read that it was actually Colin Chapman's theory that to counter understeer it is best to stiffen up the rear, either by increasing spring rates, tightening up anti roll bar, or a combination of both. Another overlooked method of reducing understeer is to raise the ride height at the rear. All work as I've tried 'em.

[Nick]

Andrew

 

Don't apologise, as it prompted me to look into it a bit more and discover I'd been misinformed! I've since read a few articles on the net, as well as calling in today at Hyperion Motorsport, and you're quite right! Hyperion also mentioned ride height, as well as playing with the back end.

 

That said, one of the comments they made was 'just drive the thing and don't mess around with it!' which is pretty good advice really!

 

It's just that my 7 doesn't 'feel' quite as good as one I drove a few years ago; there again, that one wondered all over the road at 100 mph (did I say road, I meant race track...) whereas mine doesn't. All compromise I guess, even with a 7.

 

I'm off to Anglesey at the weekend for my first track day of the year, and it's bound to be a case of cheesey grins whatever setup I have!

[Andrew Russell]

Nick, thank the Lord that I was right, you had me questioning myself for a while. I would agree with Hyperion generally, but when my car first came to me it was set up all wrong, being far too low at the rear and with 200+ bhp of XE Vauxhall engine the handling was not all that it should have been. Understeer? You'd better believe it! Raising the back to a more sensible level improved matters no end and now I just use the rear anti roll bar for fine tuning when I feel the urge... I should pass my thanks on to Ken Campbell, the Scottish Sevener or at least, one of them, for first commenting upon my ride height.

 

Talking of Ken, I do not recall seeing any mention of him since the adoption of the new format of Blat Chat, unless he is under a pseudonym. Used to be good for the odd controversial topic......

[Site Manager]

He's here wink.gif

[Andrew Russell]

Yes, but where.....I hate all this subterfuge!!

[Alex Wong1697456877]

You'll recognise him.....

smile.gif

[V7 SLR]

Alex,

 

I understand the reasons for the lower setting, but not the upper. I can explain the effects relative to rear-wheel steering thus...

 

The wheel-end of a trailing arm describes a circle around the chassis-end of the arm. As the wheel-end moves up and down, it will also move forwards and backwards. This is more exaggerated the further away from horizontal the trailing arm is allowed to get. If you set the chassis-end at the upper position, the arm is always off-horizontal meaning the amount of fore/aft movement is significantly greater than when the chassis-end is in the lower position. This is rear-wheel steering which is an undesirable effect.

 

I'm not sure why the upper setting is termed as a "comfort" setting.

 

I don't know whether the following is pertinent or not but....

 

In the upper position, as the de Dion tube moves upwards, the clearance from the diff is increased until past-horizontal is reached. When building a de Dion car you have to cut off a lug off the back of the diff to enable the de Dion tube to clear the diff during extreme upwards travel. In the "handling" position your trailing arms are horizontal so as the axle moves upwards, the de Dion is always moving towards the diff, so you make sure you have cut enough off the lug to clear the de Dion in this configuration. If your car was set up in the upper position, it might have only have had enough of the lug cut off to clear the de Dion in the "upper" configuration.

[Andrew Russell]

Alex and Site Admin,

What am I missing here, I've been looking for clues but haven't picked up any. I spend too long on this infernal PC during work time and at home, as it is...please don't make me go through every posting since the beginning of this system....blush.gif

[Mike Biddle]

Alex, I fitted 13 x 7.5J rims with the standard 19mm offset to the rear of my HPC and had to mod as follows. Grind a little off the corners of the De-Dion tube end plate, Turn the trailing arm mounting bolts around so that the roll bar links fit on the inside, and fit dished trailing arms from the superlight. The rear tyres are 8 x 22 ACB 10. I think you should be OK with 7J rims, but to be safe I would reccomend an offset of 10mm.

 

Re suspension I think your biggest problem is the front anti roll bar, which is probably too stiff. You don't mention which roll bar you have on the rear, but try stiffening it up a few notches before you do anything else. Trailing arms on track setting is also much better. I have 350Lb front springs, adjustable front anti roll bar, 200Lb rear springs, and 3/8" rear roll bar on one from hardest setting. This seems to work very well, but I was interested in some of the other comments about ride heights, does anybody have any figures for settings?

[Marius]

Alex, I fitted the Superlight R wheels inc. AVON ACB 10 onto my HPC without changing any geometries at first and believe it or not it did not (!) understeer anymore which was main-problem at first. I´m still trying different set-ups but don´t worry about the R-type wheels, they´re fine ! (exept the price, but that´s what Image is for).

[Pierre Gillet]

What are the SLR wheels? How do they look like? With which tyres ,etc.

Pierre

 

 

[Marius]

Superlight R wheels are split-rim wheels (two pieces), 6.5" front and 8.5" back, normally fitted with AVON ACB10 tires, very sticky but you have to get used to them. Oh, and they don´t last very long. See some Superlight R´s on the Caterham website. Cheers !