Oversteer: Just want this straight in my head

gorrie · Post by **gorrie** » Tue May 29, 2007 8:14 pm

OK.. I've got a bit more oversteer than I would ideally like, which makes for lairy driving in the wet (1 frustrating tracknight, 1 track spin, 1 broadside on roundabout all within the last month). Some of the antics in the wet are going to be down to the A048 tyre, but it always seems to be snappy oversteer as opposed to a general lack of grip.

I know the 135R uses the 195 tyre at the front which will likely promote a more positive turn in and perhaps a more oversteery car as opposed to understeery.

I want to dial out a little bit of oversteer (without making it understeery).

According to the history/paperwork, it looks like the geo was possibly done when the previous owner got MMC to reduce the ride height to 120/120. So, I would rather not touch the geo set-up unless I have to.

The 2 options I can think of then are to play with the tyre pressures, or to adjust the front ARB (do you need to get geo re-done if you change this?).

Assuming the pressures are all spot on (they were the other week), am I correct in thinking that reducing the rear pressure by a couple of PSI, and increasing the front pressure by a couple of PSI would have a net effect of dialling out some oversteer... or have I got that the wrong way round? If that is correct... I could then find a road setting and then reduce from that pressure evenly all round when going on track.

With regards to the front ARB.. would softening this up a bit reduce the oversteer effect or is that the wrong way round? If adjusting that, does it affect the current geo meaning I would need it re-checked?

I don't want a drastic change here... so maybe playing with pressures is the way to go.

Maybe I'll go and play some GT4 on the PS2 and work it out !!

Andy.

mac · Post by **mac** » Tue May 29, 2007 8:24 pm

Softening off the front ARB should give more understeer and doesn't require
the geo to be redone.

I'd have a look at the flat set up 120/120 as most cars have some form of rake. The 135R handbook had the factory geo settings - perhaps try and go back to them if they are different from what you have.

Mac

gorrie · Post by **gorrie** » Tue May 29, 2007 8:37 pm

The handbook says the 135R came as 130/130, but could be reduced to 120/120 for track work. There is a receipt to suggest the lowering was done by MMC so would assume they checked the geo as per the handbook.

I've checked the height as it sits in my garage and it's 120/120.

I'll dig out the handbook and see if it shows how to adjust the ARB.

So, is playing with the pressures a waste of time then?

Post by **Shug** » Tue May 29, 2007 9:01 pm

No - just tends to be a fine-tuning thing. If you're suffering major gobs of oversteer, start with the big things and work down.

Also, a bit more toe-in at the rear is one way to try and calm the back of the car down.

gorrie · Post by **gorrie** » Tue May 29, 2007 9:11 pm

Cheers guys... might have a play at the weekend... either that or wait until TT trackday and see how it goes in the (hopefully) dry.

Andy G · Post by **Andy G** » Tue May 29, 2007 9:36 pm

i'd get the geo done at CLCM. Tell Willie how you want it to handle and leave him to it. Can be very confidence inspiring and only £50

robin · Post by **robin** » Tue May 29, 2007 9:40 pm

I didn't realise the 135R had an adjustable roll bar.

There is no reason for the car to be really oversteery unless the rear tyres are just so far past best/so old, that they don't grip anymore. If it were me, I wouldn't trust the current geo is right - I would take the car to CLCM or Falkland or similar where they have good measurement kit and find out what the current geo is, then work from there.

Cheers,
Robin

gorrie · Post by **gorrie** » Wed May 30, 2007 7:55 am

Yeah robin... according to the marketing blurp I read it's adjustable. Although, 135R handbook supplement doesn't seem to tell you how to adjust it.

OK... I might just wait to see how TT goes before playing with the settings. The wet probably exaggerates any oversteer. If it behaves on a dry track, then it may be down to the tyres.

robin · Post by **robin** » Wed May 30, 2007 8:10 am

I'm not sure doing nothing is best approach - the geo can be hideously out despite it having been set in the past - either because it wasn't set right - it does happen - or because something has broken in the meanwhile. When I got my 135R, it had +ve camber on the front left. When we measured the RLC at CLCM finally, we had +ve toe on the rear right wheel because the toe link had worked itself loose and so the rear wheel was folding out under load. If you are finding that the car snap oversteers you really should do something to find out why before you end up in the hedges or worse.

The ARB is adjusted by moving the position of the drop link in the ARB tails. If you look at the bottom of the front uprights you'll see the drop link (more-or-less vertical bar, a few inches long) bolting through the end of a round bar that has been flattened and has at least one hole drilled through it. The adjustable ARBs have more than one hole and you unbolt the drop link and move it back and forth to make the ARB softer or harder.

Cheers,
Robin

tuscan_thunder · Post by **tuscan_thunder** » Wed May 30, 2007 11:00 am

mac wrote:Softening off the front ARB should give more understeer

not so sure about that myself - at high speed it'll control body roll and, in theory, allow the suspension to remain closer to where it wants to be, but it'll add understeer at lower speeds.

It's an undamped spring which will always have a reverse action at one end to t'other.

Get it geo'd - they're so sensitive it makes sense. Run more rear toe in to help kill some oversteer. That way you are not altering the way the front acts, only the back and your are changing the handling balance slightly.

Changing something at the front to have an effect at the rear is something I would only do after performing work at the rear.

A decent tyre gauge is always going to be a boost (none of this petrol station forecourt crap) and setting the pressures, and maintaining them at a stable level, makes sense.

Remember to only change one thing at a time: don't geo it AND alter pressures - you won't know which has had the effect

mac · Post by **mac** » Wed May 30, 2007 11:25 am

Fair point. I know where the rear of my (now Mandy's) car is - so I adjust the front ARB depening on the driving conditions (softer for road/stiffer for track)

Mac

tuscan_thunder · Post by **tuscan_thunder** » Wed May 30, 2007 11:55 am

aye, that makes sense - you're adjusting the f/r balance.

Post by **simon** » Wed May 30, 2007 1:30 pm

What pressures are you using?

gorrie · Post by **gorrie** » Wed May 30, 2007 2:38 pm

As per the book Simon (26F/28R when cold). I then dropped them 2psi all round when the were just slightly warm before going on track... so probably 3psi.

Didn't need to drop them again after that because it was too cold/wet that I didn't manage to get any temp in them anyway !!

Was thinking on bring the F/R pressures to be the same as an experiment... but sounds like the consensus is to go get a geo done.

Post by **simon** » Wed May 30, 2007 11:15 pm

I'm running 23f 25r cold then drop to the same on track once fully warmed up. 28 cold is pretty high for A048s and when warm mine rise by around 6/7psi.