neutral handling

[sdio]

Hi all,

What is the pistonheads wisdom with regards to setting a caterham up for neutral handling?
My understanding is the fundamentals are: the antiroll bars selection then spring rates then geo in order to maintain neutral behavior at the widest range of driving conditions.
Which combination offers the most neutral handling?

[DCL]

The geometry of the suspension is such that the biggest (strongest) influence is the ride height at the front. Springs, dampers, camber and rake all play their part too, but generally the spring rates and dampers are near enough that they do not need changing before the ride height, camber, and rake are set properly. In more detail, toe and bump-steer, and tyre pressure, are worth getting right too. Anti roll bars are really secondary and are best left standard (ish) until you have a good reason to change them.

Edited by DCL on Sunday 1st January 22:28

[sdio]

DCL said:

The geometry of the suspension is such that the biggest (strongest) influence is the ride height at the front. Springs, dampers, camber and rake all play their part too, but generally the spring rates and dampers are near enough that they do not need changing before the ride height, camber, and rake are set properly. In more detail, toe and bump-steer, and tyre pressure, are worth getting right too. Anti roll bars are really secondary and are best left standard (ish) until you have a good reason to change them.

Hi,

ride height is 80mm under the sump 145mm at the front where the tubes change from round to square and 170mm in front of the rear wheel arch.
The antirollbar is the green one and with LSD the car understeers like nothing else driven before.
When you drive close to the limit the car is neutral though..
The problem is on very tight corners and when turning in violently where the car just understeers.(see goes straight)
There is no antiroll bar at the rear the springs are standard bilstein adjustables. Front is wide track.

I am of the opinion the this is caused by wrong stiffness front and rear thus a need for a rear anti roll bar and may be a softer (?) front one??

Edited by DCL on Sunday 1st January 22:28[/footnote]

[footnote]Edited by sdio on Monday 2nd January 12:59

Edited by sdio on Monday 2nd January 13:00

[DCL]

There's no easy figures to dial in and get good handling as each car, and driver, tend to be different. But from what you've said, I think you are running far too high (particularly for track) 120-130mm at your reference point is a good start. Then adjust the rear for 10-15mm rake (at the square tube at the front of the rear arch). Camber 1.5-2.5 degrees, and toe 0, or slightly toe out, tyres 18 PSI. Take it from there, but each car and driver will like variations on those basic setting.

If you are new to the car then you will learn (or more kindly, adapt) to the different driving style the RWD Caterham needs to get it to work. Trail braking in particular helps enormously with the slow speed turn in you are describing.

Edit to add: A rear anti roll bar may help, but start on the softest settings

Edited by DCL on Monday 2nd January 13:34

[AndrewGP]

sdio said:

I am of the opinion the this is caused by wrong stiffness front and rear thus a need for a rear anti roll bar and may be a softer (?) front one??

I think you are on the right lines. When I first bought my Superlight it had the green one on the front ARB and the middle hole for the rear ARB (which you don't have) and it understeered like mad. I changed the front ARB to 1/2" orange (99% sure it was that but I sold the car two years ago) and kept the rear ARB on the middle. I then had the geo done by Solutions Racing near Witney and again from memory, there was 10-15mm rake and about -2 degrees camber up front with a touch of toe out. The result was amazing, it was on the oversteery side of neutral but not excessively so and really confidence inspiring to drive.

[BertBert]

It's also hard to tell the effect of the LSD. They certainly can have the effect of causing understeer.

Have you got a watts linkage at the back or just training arms? If you have the former then changing the rake has less effect on under/oversteer.

Bert

[sdio]

BertBert said:

It's also hard to tell the effect of the LSD. They certainly can have the effect of causing understeer.

Have you got a watts linkage at the back or just training arms? If you have the former then changing the rake has less effect on under/oversteer.

Bert

Hi Bert,

Yes i have the watts linkage at the rear.
Does that mean the rake is not as important in my case?
I have about 20mm or rake now.

[sdio]

AndrewGP said:

I think you are on the right lines. When I first bought my Superlight it had the green one on the front ARB and the middle hole for the rear ARB (which you don't have) and it understeered like mad. I changed the front ARB to 1/2" orange (99% sure it was that but I sold the car two years ago) and kept the rear ARB on the middle. I then had the geo done by Solutions Racing near Witney and again from memory, there was 10-15mm rake and about -2 degrees camber up front with a touch of toe out. The result was amazing, it was on the oversteery side of neutral but not excessively so and really confidence inspiring to drive.

So what is it with the green antiroll bars.
Is it an old setting of the "sport suspension" which has now been superseeded with the softer orange + a rear antirollbar or is it just a track focus set up as my car began it life as a roadsport race car back in 99?

[sdio]

DCL said:

There's no easy figures to dial in and get good handling as each car, and driver, tend to be different. But from what you've said, I think you are running far too high (particularly for track) 120-130mm at your reference point is a good start. Then adjust the rear for 10-15mm rake (at the square tube at the front of the rear arch). Camber 1.5-2.5 degrees, and toe 0, or slightly toe out, tyres 18 PSI. Take it from there, but each car and driver will like variations on those basic setting.

If you are new to the car then you will learn (or more kindly, adapt) to the different driving style the RWD Caterham needs to get it to work. Trail braking in particular helps enormously with the slow speed turn in you are describing.

Edit to add: A rear anti roll bar may help, but start on the softest settings

Edited by DCL on Monday 2nd January 13:34

You are for sure right in most of the points made above:
1.I certainly have too little camber in the front, you can tell by eye.
2. I dont know the geo settings on the car and will adjust these with the string method once i will learn what setting to try out, thus my general questions on setting the handling to neutral.
3. Does indeed the watts linkage make the effect of the rake less apparent?
4. The car is 100% for fast mountain driving, there is no in town/motorway or track use.
5. Yes i am very new to caterham ownership (less than a month) but very well familiar with the elises and have adjusted my driving style accordingly and also use trail braking to avoid understeer but this is just a temporary remedy to get rid of the understeer which should not be present in a car as such.

My experience with the elises has teach me that first i need to have the right stiffness front and rear, then i adjust the roll centers (for adjustability of handling), then use a geo setting as little agressive as possible to get the required behaviour.
In caterham world this might not be case this is why i reached out to you all to get your view and experiences.

[DCL]

The Caterham is not a fully independent suspension car and the de dion tube makes the rear roll centre fairly static. It isn't really adjustable, so most of the balance is achieved with the front, which has a very dynamic roll centre. Ideally the bottom front wishbone should be level, but if you are using it for mountain roads then you may need more clearance. More rake may help under-steer, but it's really the angle of the rear A frame that's important - and that's a balance between forward weight transfer and anti-squat. The 13 inch tyres you've got will set the rear roll centre a little lower so the front will be happiest at a lower height.

Using anti-roll bars, or stiffer springs, to over-ride the the inherent set-up may give you the handling you want, but it's not the best way as it will compromise grip, particularly in the wet.

Edit just correct myself - the wheel size does not change the rear but makes the front lower for similar balane (I think!)

Edited by DCL on Monday 2nd January 18:48

[AndrewGP]

sdio said:

AndrewGP said:

I think you are on the right lines. When I first bought my Superlight it had the green one on the front ARB and the middle hole for the rear ARB (which you don't have) and it understeered like mad. I changed the front ARB to 1/2" orange (99% sure it was that but I sold the car two years ago) and kept the rear ARB on the middle. I then had the geo done by Solutions Racing near Witney and again from memory, there was 10-15mm rake and about -2 degrees camber up front with a touch of toe out. The result was amazing, it was on the oversteery side of neutral but not excessively so and really confidence inspiring to drive.

So what is it with the green antiroll bars.
Is it an old setting of the "sport suspension" which has now been superseeded with the softer orange + a rear antirollbar or is it just a track focus set up as my car began it life as a roadsport race car back in 99?

No idea. My car was a late 2001 superlight and they all came with a rear ARB, but other than that I don't know. Best not to over think it and just change what you need to get the result you want

[Dave J]

the green bar is a legacy of the thinking at the time of soft springs supported on stiff bars.

drop the front 5mm
raise the rear 10mm
fit an orange front bar
have rear bar on softest
dial in 1.5 deg neg front camber
16psi rear / 18psi front
crack on 👍

[Dave J]

and how old are the tyres ?

makes a difference

[sdio]

Dave J said:

the green bar is a legacy of the thinking at the time of soft springs supported on stiff bars.

drop the front 5mm
raise the rear 10mm
fit an orange front bar
have rear bar on softest
dial in 1.5 deg neg front camber
16psi rear / 18psi front
crack on ??

Hi Dave,

No idea on the age of the tires these are 048 and do get very much better after they worm up and reach abt 40C.
this seems to be in line with my thinking at the moment but did wanted to hear others with experience telling me the same...
Cheers

Edited by sdio on Monday 2nd January 20:14

[Dave J]

the year will be on the sidewalll

[sdio]

Dave J said:

the year will be on the sidewalll

Hahaha,

DOT 230508

[Aeroscreens]

Tyre dates normally take the form of 4 numbers in a 'rounded rectangle' i.e 2416 meaning the tyres were made in the 24th week of 2016.

[sdio]

Aeroscreens said:

Tyre dates normally take the form of 4 numbers in a 'rounded rectangle' i.e 2416 meaning the tyres were made in the 24th week of 2016.

Hi

I was expecting to find 4 digits code as well rather than 6.
I translate the 230508 as 23week 5th month 2008

[sjmmarsh]

It could be week 50 in 1998 as they just used 3 digits prior to 2000. The car would need to low mileage for the tyres to be that old though. Do you have a photo of the DOT code?

Steve

[damdy-cash]

Hi Guys, good discussion. What castor setting would be a good starting point and what would change if moved to the one or other direction? Cheers Volker