Getting rid of understeer

[Easty-5]

Had a trackday tonight and the car was excellent. My only gripe was the cars tendency to understeer (traction control was off btw). However, the only time it was really noticeable was on 2 corner which were uphill. So obviously the weight transfer will play a major part. The track was also bone dry and it was a warmish night.

I'm running Michelin Pilot Supersports all round and Eibach springs. I also had the Geo setup a few months back to CSL spec. Is there anyway to dial out some understeer without upsetting the current handling characteristics, as I have to admit, it handles pretty epically just now. Very predictable on the limit and not 'edgy' at all.

 

[Bing]

Can't help with your question Easty, but I'm having my geo done at the beginning of October and I'm interested in what is better about the CSL set-up over the standard M set-up ? Or have I missed something and they are actually the same ?

 

[tertius]

Trail brake more, so that you keep more weight over the front wheels.

 

[Z4M-2006]

A Tertius says,trail braking will even out the weight transfer into the corner.

It could be more a characteristic of the track than the car,are you braking heavily into the corner? Missing the inner apex,turning in to late ?

 

[RedUn]

Geometry wise, more camber will help but if you have the CSL geo your more than likely getting to the limits with the stock top mounts.

You can fit camber bolts to increase camber that could help but you will have to get the car re aligned after.

As mentioned it could be your driving style or your tyre pressures, they can make a huge difference.

After that you start going into adjustable suspension and top mounts etc.

Bing, more camber and less toe.

 

[DONDP]

Assuming you had the camber pins pulled when you did the CSL geo? If not that would be the first thing to try.

You can also get more aggressive with the geometry. To get a feel for subtle changes I ran mine with max neg camber on the front ( around 2 degrees ) and 1.8 on the back but completely parallel with regards to toe front and back. From here I could decide how I wanted the geo to affect handling. I have ended up with marginal toe in on the rear 0.4 combined with marginal toe OUT on the front.

Nice lively turn in but might not be to everyones taste on the road.

The other suggestions Redun makes are spot on too.

 

[tertius]

I'm pretty sure from the OP's description (i.e. uphill corners) that it is a weight transfer problem, and trail braking right into the apex will sort it out. Obviously you need to be coming smoothly off the brakes as you approach the apex, you aren't going to be hard on the brakes all the way.

If you try that and it doesn't work then you can obviously look at geo and other changes, but being able to drive around these situations is much more powerful than changing geometry, especially as the OP seems happy with the handling otherwise.

It also means you can carry more speed into the corner, and you should be faster overall.

I had exactly this issue with my 911 and thought it was a geo problem, when really it was a nut behind the wheel problem.

 

[Easty-5]

I think you are bang in the money Tertius. I am pretty aggressive in my driving style. I have been really working on my braking so I am braking later and much harder, then off the brakes before turn in and progressively getting back on the throttle on the initial turn in. I am still really learning the car. I have done 100s of laps over the years at Knockhill but in FWD cars so as you can imagine, the M is a completely different kettle of fish. I have done 5 trackdays now in it and have been getting faster each time. I managed a 63.5s lap on Tuesday, which I was delighted with. Had a passenger and was on EBC Bluestuff pads so was still braking too early as I don't trust them. I reckon a 60s lap is very achievable in the car. 60s round KH in a fully road going car (full trim, road tyres etc etc) is a fast lap. The car is definitely cable of going quicker.

 

[ChawenHalo]

Apart from the above advice getting your brakes sorted will make a big difference too. Oh, and smoothly does it: no point being aggressive and unsettling the car smooth transfers are easier to, manage and the car easier to place. If front is breaking traction that's too much entry speed and too harsh steering inputs, better slow in and fast out.

 

[thepits]

What pressures were you running? Standard or lowered?

Track normally increases stress on tyres, therefore they run hotter so pressure goes up. Too high = less tread on the road so can induce understeer

 

[007MCoupe]

I can confirm most of these suggestions. While it didn't "cure" understeer, this is what I did on mine for the last track day I had (Nurburgring):

"camber shims" aka 3 washers and longer bolts w/pin pulled (got the 'kit' from Turner Motorsports, but any hardware store will do) running -2.3 up front
-2.5 rear camber (adjustable camber arms make life easy!)
trail braking helps immensely

I've got ECS OEM-style rotors with Akebono pads, SS lines, ATE Blue fluid, and Dunlop ZII tires. Much less understeer indeed.

 

[Taz]

oops, I read the title as underwear lol

 

[Paul46]

Believe it or not a set of spacers will help under steer issues, widening the front track can all give a touch more over steer though

 

[mad4slalom]

can someone describe trail braking for me, is this left foot braking whilst still on the throttle aproaching the apex, like i do at the go kart track sometimes ??? :?

 

[tertius]

can someone describe trail braking for me, is this left foot braking whilst still on the throttle aproaching the apex, like i do at the go kart track sometimes ??? :?

Not quite, it isn't necessarily left foot braking but it is keeping a degree of pressure on the brake pedal as you are turning in to the corner. Typically you'd aim to brake hard to scrub off most of your speed, then gently ease off the brakes while you are turning in, but maintaining a small (and reducing) amount of braking as you approach the apex. This keeps the car's weight forward, maintains additional load on the front tyres, so they work better and are less prone to understeer (running wide).

If you just brake hard then come off the brakes totally, the front of the car will unload, and the tyres will (potentially) lose grip and you'll run wide.

 

[abar121]

can someone describe trail braking for me, is this left foot braking whilst still on the throttle aproaching the apex, like i do at the go kart track sometimes ??? :?

Not quite, it isn't necessarily left foot braking but it is keeping a degree of pressure on the brake pedal as you are turning in to the corner. Typically you'd aim to brake hard to scrub off most of your speed, then gently ease off the brakes while you are turning in, but maintaining a small (and reducing) amount of braking as you approach the apex. This keeps the car's weight forward, maintains additional load on the front tyres, so they work better and are less prone to understeer (running wide).

If you just brake hard then come off the brakes totally, the front of the car will unload, and the tyres will (potentially) lose grip and you'll run wide.

Yup. A few years driving 993 and earlier 911s, will help enormously. If you don't transfer the weight forward on turn in with one of those, you'll get bucket loads of understeer. Get it right with that pendulum at the rear though, is a sublime feeling. The Z4M isn't quite the same, but stil, loading the front on turn in is essential if you are pushing on.

 

[thepits]

IMHO the best thing is to brake in a straight-line[ish] into a corner, then on the throttle, but then stay on the throttle - works for me

 

[mad4slalom]

Ah, i see said the blind man! I get it now, thsnks gor that .

 

[exdos]

I find that a quick dab on the brakes on the approach to a corner followed by a sharp(ish) turn on the steering wheel loads the front end and makes the car commence the turn quicker and also encourages a bit of lift-off oversteer: this counteracts any tendency to understeer. Doing this, the sideways movement of the rear tyres without throttle at the start of the turn scrubs speed off and gets the tyres at their slip angle. Once the rear tyres have full grip again and the car is balanced, you can then progressively reapply/feather the throttle to keep the slip angle working. I find that I'm a shade quicker back on the throttle doing this than trail-braking.