Tackling Understeer - Aero mods and Tyre Widths?

[MikeE]

 

 

For the 3 years I've had my R400 Duratec it's always suffered from understeer in high speed corners to a lesser or greater extent despite having changed the springs, fitted Nitrons and having the suspension setup by Gary May. I've tried the usual things like playing with tyre pressures, adjustable roll bars, damper rates etc but still haven't managed to dial it out completely.

 

Having now gone from a 230bhp to 280bhp engine I'm expecting that the understeer maybe now be worse (I know it's called throttle control ) so was interested in peoples experiences of Aero and tyre width (I run ACB10s and CR500s but will probably go the slick route too) solutions which have made a difference.

 

1 - So do the CSR front wings and nose winglets make a difference? (think someone like Adam Hay might be able to answer this) - are there any other aero tweeks which would help?

 

2 - I'm thinking I probably need wider rear tyres anyway (running R500 widths at the moment) so while I do that I'll need to tackle the fronts too - what are the options and what effect are they likely to have?

 

I think a combination of CSR front wings, new wingstays and wider rims all round might do the trick but that's obviously going to be a significant outlay so want to know if anyone can confirm that the Aero part is actually worth the investment?

 

cheer

 

R400 Duratec Build and Modification Pictures

here

 

Edited by - MikeE on 28 Dec 2007 14:29:22

[Jason Plato]

let some one else try your car on track befoe you throw money at the problem 🤔

 

odds are its driver style and carrying too much speed in to the corner or turning in too sharply and hence getting poor weight transfer.

 

Dave

 

 

 

here is C7 TOP

Taffia rear gunner

[Irrelevant]

think someone like Adam Hay might be able to answer this

Hmmmm . .. all I know is that CSR wings running very close to the tyre will give less lift that a standard wing running miles away from the wheel. Whether this will help you, who knows; it can't do any harm though.

What sort of understeer do you get? Turn in, mid bend, or exit?

Do you have 2 way dampers? I do and find that being able to change bump and rebound independently has been very useful in the past.

[ELV15]

Mike,

 

I too suspect driver style. However since my car (or driver ) behaves in the same way I'm quite interested in the answers you get. 😬

 

Regarding the aero modifications, see this thread: here

 

I would think that you would have to be carrying quite a bit of speed for the aero mods to make a noticeable difference in cornering. From the above article it seems that the biggest gains would be inboard shocks ($$$) and a splitter under the nose

 

 

 

ELV15 - Tom in California -

200hp duratec powered 2003 Clubsport Build pics here: here

[Alaskossie]

Has anyone tried the carbon-fiber airfoil sections that Mog and Fluke offer for the front upper and lower wishbones?

 

Do these offer a measurable increase in downforce? In theory at least, the look as if they might. Any opinions?

 

Alaskossie

[Slipper man]

The first thing I would change is the CR500's. Mine understeered like a pig on them. 048R's transformed my car, and Dave J reckons Toyo's are even better. Either are half the cost too. I wouldn't change the rears to start with: I ran my R500 on 7" tyres all round for a while and never had any problems so I would be amazed if with 280 BHP you couldn't get by with the sizes you have.

 

 

[Gambo]

Stick the standard size large number plate down where it is supposed to be and fit a low as you can. Greatly reduces the air that goes under the car.

It won't 'transform' the car, but it will help in the higher speed stuff.

 

RED 2.0 HPC 230BHP here

[MikeE]

Nah can't be driver style I have the smoothness of Alan Prost 😬

 

It may well be I try taking too much speed into the corner but frustrating none the less.

 

It tends to be in high speed corners, typically something like the last corner at bedford autdrome, a 90mph right hander. It turns in just fine (so not a weight transfer issue?) but then starts to understeer mid corner and can be horrendous if you try and get on the throttle all the way to the exit.

 

At the end of the day I can of course take less speed into the corner but the car isn't displaying the characteristics I'd like - i want it to be more 'pointy' so if it's going to start sliding then it'll be at the back first. So how do I achieve that other than slower in, 1 gear lower and then use the throttle to adjust the attitude from the apex out?

 

Adam, I thought you had the CSR front wings (and custom wingstays) and before I went to all the effort and expense I wanted to know if it made a appreciable difference?

 

Slipperman - don't understand your comment, you think I'll be ok with 7" rears when my Duratec should have 50bhp and 30lb/ft more grunt than your R500 Surely I need more grip at the rear! I did run with 7" slicks all round with the 230bhp 2.0l last summer and destroyed the rears in a morning 😳

 

 

 

R400 Duratec Build and Modification Pictures

here

[Irrelevant]

Mike: I do have CSR wings and DIY wingstays but I do not definately know if they make a difference. I did perceive a difference when I went from high stays to cut down wheel hugging stays on my Crossflow though. So with this in mind, and having heard about the unofficial windtunnel tests done at MIRA, as well as Caterham's own tests, I thought I'd do all I could and fit tyre hugging CSR stays on my Gigabusa. They certainly seem to work - it handles like it's on rails, miles better than a Crossflow. Though, come to think of it, this may not be entirely down to the CSR wings 😬.

 

As far as your belief that it's not weight thansfer . . .. according to my Allan Staniforth suspension bible, for mid-corner understeer, as long as your car isn't bottoming out....

 

If the front does not roll excessively try:

1. Softer front spring rate

2. Increased front rebound

3. Reduce front ride height

4. Soften front ARB

5. Reduce front compression

6. Increase front camber on loaded wheel

 

If the front does roll excessively try:

1. Stiffer front ARB

2. Increase front compression

3. Increase front spring rate

4. Ensure no excessive droop in front suspension

 

Have you tried all these? If not, I would, as making CSR stays is not fun

[sopris]

What diff are you running? A strong LSD will tend to induce understeer.

[Irrelevant]

sopris: Yep . . . . remembered this the other day but then forgot about it 😳. Dannyboy has just had his ramp angles/pre-load modified by R&R and says it improved understeer.

[Slipper man]

Good point - it makes a big difference. The standard settings are for a big heavy car like a Sierra XR4 and make a Seven understeer, though mainly in tighter (i.e. slower) corners

[MikeE]

I have the standard issue R400 diff from a year 2004 Caterham kit, whatever that is Anyone know if this would benefit from being modified and if so is it a diff out job (i.e. a pain in the 4rse 😳)

 

 

 

R400 Duratec Build and Modification Pictures

here

[Slipper man]

It would benefit, but it is a diff out job. If you don't do much track work, don't bother

[Irrelevant]

MikeE: Apparently, or so I'm told, Caterham never used to modify the ramp angles. Now they do. When they changed, I don't know. Maybe call Caterham if nobody knows.

[david nelson]

What sz tyres are you running front and back? Diffrent tyres will also give you diffrent handling. This year I swopped from ACB10's to Khomo's. After a season of sprints and hill climbs i still can not find the right settings. The Khomos are very stiff and i have had to increase the damping loads compared with the ACB's.

 

I recently posted a question about % front to back with weight. If 2 cars are set up with the same camber/toe, the same rake, but one driver is 60kg and the other is 85kg then there must be a diffrence in front and back weight. This will then affect the handling due to weight transfer. It appers that the lighter drive had more problems with overstear while the heavyer on had understear.

 

I think Adam and Dave have said the main things. either driving style and or set up.

 

get yourself a data logger and play with the settings. also use a vidio recorder to help with analasis.

[Stuart Faulds]

I can't believe that no-one has mentioned spring rates

[Irrelevant]

I did......

[david nelson]

He did

 

 

[Richard Price]

Apparently, or so I'm told, Caterham never used to modify the ramp angles. Now they do. When they changed, I don't know. Maybe call Caterham if nobody knows.

I too suffered with more understeer than I liked. My early 2002 supplied ZF diff had the modified 30° ramps fitted, but the preload was too high, at around 65ft/lbs.

When I swapped final drive ratios, Phil (at road and race) pointer this out and swapped the bits to reduce the preload. The car is now much easier to drive around the limit, with progressive power oversteer, to replace the understeer followed by snap oversteer that I had previously.

To check the preload, remove one wheel, but lower the car so that the other is on the ground, then try to turn the other drive shaft with a torque wrench. the pre load is the torque at which the drive shaft starts to turn.

The recommended figure is some where around 35-45ft/lbs.

 

 

[IanJ]

Have you thought about trying softer compound front tyres? When I switched from A021Rs to A048Rs I went for Soft compound on the fronts and Medium compounds on the rears. This has transformed the car and I am a lot happier with the handling which feels a whole lot more "pointy" than it used to.

 

Ian 😬 1.6K SS Superlight #006

Penn Sevens Here

[Stuart Faulds]

Ah, sorry - my mistake. That should sort him out.