simonburton

Just had AST coilovers fitted to my Type RA, along with uprated anti roll bars, drop links, anti lift kit, rear lower strut brace - front and rear top strut braces were already fitted. The geometry was also checked.

The car seems to lean more than I expected in fast and tight corners. I know with a Scoob I will not remove all of this due to the size and weight, compared to a caterham etc, but how can I help reduce this further?

BTW - the car is only used for trackdays, so the ride quality isn't really an issue on the road

Adam M

but what is the ride quality like anyway with that set up as I was hoping to go for that.

ozzy

Lowering a car too much can actually induce more body roll. SdB commented on this a while back in that Prodrive handling thread.

Perhaps the AST coilovers just aren't as good as they should be? Are they adjustable in any way?

Stefan

simonburton

On the road the ride is very good; it is even quite difficult to provoke understeer, one thing I was looking to cure, probably along with every other Scoob owner! The ride height has only been lowered by 10mm from standard, although I could reduce a lot more if I wanted to to with the adjustable springs. I think I need to check the spring ratings, as I was wanting a heaveir spring for track use.

If the car was used purely for the road, I would be very happy, as it is, I just need to maybe play around with the settings. I have the dampers on their stiffest setting at the moment, which seemed to be the best solution at Donington, but I will try different settings at the next trackday.

ozzy

Yeah, IIRC Simon mentioned lowering as much as 50mm may upset the body roll.

Keigo

What you want is a set of Tein Type HA from me Fully adjustable, with spring rate 7k front 6k rear. No body roll anymore! E mail me for details if you want keigokato@hotmail.com

Adam M

I had been told that powerstation offered two set ups, one for road bias and one for track bias.

why didn't you go for the alternative.

simonburton

Have spoken with Powerstation, and I do have the track biased set up. I am going to try a 24mm anti roll bar with heavy duty mounts and see how this improves things.
To confirm, the set up does feel good, I just want things a bit firmer, but not rock solid, as I think means that you can loose some feel.

ozzy

What ARB's do you have on it just now?

24mm rear and 22mm front works well, but I guess it depends on your own preferences.

Stefan

simonburton

22mm front and rear at the moment, but I need to double check

DuncanG

What spring rates are you running?

simonburton

285 lb front and 228 lb rear

ScoobySport (SdB)

Hi All

It is true that lowering a MacPherson strut car can increase body roll. The reason is that the roll centre tends to move more than the centre of gravity.

The amount of body roll is a function of lateral force (force acting on the mass of the car (centred at the centre of gravity) during cornering), c/g height, roll centre height and then combined with roll rate (a function of the wheel rates and bar rates, etc).

The roll centre is a theoretical pivot point around which the suspension rolls. So if the roll centre is at ground level, and the c/g is 1m above the ground, there will be more roll (all other things being theoretically equal) that if you raised the roll centre up to 500mm above the ground.

Lowering a MacPherson strut car increases the distance between the c/g and roll centre, so effectively makes the chassis more prone to roll.

This means you need more roll resistance to maintain the same level of roll for a given load.

---

Interestingly, roll is not necessarily a bad thing.

There are two main negative things that roll tends to do :
1) Make the driver nervous
2) Alter the contact patch (by changing the angle that the tyre intersects with the ground)

These are the only really important areas in controlling roll. There are other areas to consider such as transient state response, dynamic camber, etc, etc but you could get lost up your own bum trying to worry about all these things, so best to stick with the big ones.

The problem is that resisting roll has it's negatives.

One of the key factors in mechanical "grip" (mechanical grip meaning grip generated by the suspension, not by downforce - which is all we're really interested in) is sharing the load of the tyres as evenly as possible.

Within it's normal working loads, increasing the load on a tyre increases the grip it can produce in a NON-linear way. To explain this in a theoretical way...

If you add 1kg of load to a tyre, lets say you gain 10 units of "grip". ("units of grip" is a completely made up term for this example, so please don't quote me!! ) If you then add another 1kg to the vertical load, you might only get 9 units of grip back.

So.. with this in mind.. if, during cornering, you transfer load from the inside tyre to the outside tyre (as is impossible to avoid), you lose more grip from the tyre losing load, than you gain from the tyre gaining load, so your overall performance of the tyres is reduced.

Unfortunately, roll resistance increases this load transfer. Whilst it might appear (due to the car remaining more flat on the ground) that load would be more evenly distributed, the facts are that the car is held at it's roll angle by the outside tyre pushing down and the inside tyre pulling up (eg a roll bar) which means more load transfer.

So.. the long and short of, is as with just about every other area of vehicle dynamics, it's a balancing act between the negatives of roll, and the negatives of roll resistance.

Fun isn't it

--

So, the reason for all of this is to say. Are you sure you want to reduce the roll? It is quite possible you do want to, but it's worth being absolutely sure what you're trying to achieve.

It is also true that unless you have confidence in the car, you are not going to be able to make it go fast, regardless of how technically competent the chassis is, so possibly the most important thing is to develop / test until you're the most comfortable.

All the best

Simon

ScoobySport (SdB)

PS.

I meant to mention. It is actually possible (and has been done for testing a number of times) to arrange the suspension so that the roll centre is ABOVE the c/g. In this situation the car actually naturally rolls INTO the corner, rather than away.

Adam M

did you ever see that (I think it was mercedes) triking car which had one wheel at the back, the steering rods caused the wheels to lean into the turn and with the geometry as it was tipped the whoelc ar into doing this.

looked brilliant on track, but I have no idea if it helped at all!

simonburton

Simon - thanks for your post. I think the crux of track driving at the end of the day is driver confidence, and it's been mentioned before many times on SN, that the best mod for any car is to improve the driver. You could have the best handling car in the world, but a bad driver, isn't going to get the best out if it.

I think playing with the current settings, along with continued practice will be sufficient for my humble needs

Adam - that Merc was very wierd!

ScoobySport (SdB)

I think that's sensible Simon

Adam, agreed. That was one of the ones I was thinking of

R.B

Simon nice to see you are going to donno we will see you there mate.

simonburton

Yeah - see you there Rich