Mars needs mid corner grip!

[PranK]

Hi guys,

Had another Wakefield day a few weeks ago, I've done a little bit of suspension work and managed to pick up 2.9s which was great!

But! Although my turn in is now really good my mid corner grip stinks with heavy understeer and really is the weakness in the car. Corner exit speed is much lower than I'd like and I'm struggling to get enough drive out which is important considering my car really is not fast.

I've been told a few theories for this: 

My wheels are staggered. 245 rear and 225 front. 

Next suggestion is because the rear had 15mm spacers and front none, so the track wasn't square.

Is this likely to cause much mid corner upset? Surely I'd be feeling this on corner entry also?

My personal feel is that the Hankook rs4s are at their limit and I may need to start alternating hot and cold laps.

[Duncan]

By far the most likely is simply tyres. Mid corner understeer (generally) is about total front end grip and Hankook RS4 might be better than average but aren't track tyres.

Neither different width track nor different width tyres front to rear would make a noticeable difference. Most cars have different track width from factory anyway. 

Other than tyres, most likely things you can tune are the amount of roll (spring rates and sway bays) or potentially front camber/caster but in modern cars it just comes down to lots of weight over the front.

[GTSBoy]

Yes, as above. If it isn't tyres, I'd suggest softening the front bar. You will give up some of the initial turn in in exchange for some more mod corner grip.

Is it possible to put more rubber on the front? 225 is a skinny skinny tyre for a heavish car at the track.

[bcozican]

2.9 secs is a huge pickup in time!

 

Without knowing specs on car and setup 

Tyres

Suspension tuning, make front softer and or/ rear harder

Diffs

 

Other than that just driving line and style

Edited January 3, 2022 by bcozican

[PranK]

Thanks guys!

It's funny how you can overthink things. I had never considered that my fronts may be too small. The rears are 17x8.5 with 255s and some other e90 owners have seen good results from another pair of rears with 255s on the front. This might be a good option so I'm going to swap fronts and rears for a few days and make sure everything clears.

I do also think I may have hit the limit of the rs4s but the next step up is a lot more pricey. 

The front bar is not adjustable so I'll leave that for now.

Diff is a single spinner unfortunately 🙁

@bcozican car is an 06 330i. M3 front arms (-1.5 camber), Whiteline front and rear bars, Whiteline rear subframe inserts (seem to really only add nvh), Bilstein shocks and eibach Springs. 

 

[Unzipped Composites]

Also driving style as Laine aluded to. If you're too aggressive with the steering input you may be asking too much of the tyres. Are you trail braking at all or just coasting through the corner? Bit of trail brake will put some weight over the front and increase front end grip. Too much will go back to asking too much of the tyres.

 

Could be loads of things, I doubt it's specifically one thing. But driving style is free, so it's a good place to look first. And once you start changing things setup wise it can become very difficult to determine what is driving style and what is setup. Often the best thing you can do is if there is a driving event that facilitates a driving instructor, then get them to do 2 or 3 laps in your car and note their lap times. Don't start changing the setup until you are close to their times.

[PranK]

Yeah I'm absolutely not driving it as well as it could be driven and I was thinking that because I have the turn in so good now, then I need to do something to my own actions through the corner. 

I'm off the brakes as quickly as I can be, I try to get the car to correct speed before I start turning in but that doesn't always happen. I can pull up really well at the end of the Wakefield main straight and be turning in with foot on accelerator but I'm not as clean at the end of the back straight and this final corner is one of the ones I struggle with grip the most.

 

[Unzipped Composites]

On 10/01/2022 at 9:09 AM, PranK said:

Yeah I'm absolutely not driving it as well as it could be driven and I was thinking that because I have the turn in so good now, then I need to do something to my own actions through the corner. 

I'm off the brakes as quickly as I can be, I try to get the car to correct speed before I start turning in but that doesn't always happen. I can pull up really well at the end of the Wakefield main straight and be turning in with foot on accelerator but I'm not as clean at the end of the back straight and this final corner is one of the ones I struggle with grip the most.

 

Yeh so it sounds like you're unintentionally shifting weight to the rear, costing you front end grip. Don't jump off the brakes as quickly as possible, you want to be trail braking up to around the apex. So full brakes on approach, then just before you start turn-in ease off the brakes but not completely, keep a little bit of brake applied to keep some weight over the tyres. How much pressure you apply is directly related to your steering angle - think of it as the reverse of accelerating, you dont jump on the accelerator while you're still at full steer, you ease onto the throttle as you straighten the wheel. Braking is the same, you dont jump off the brakes and turn in, you want to ease off the brakes as you apply steering angle so that as you approach full angle you get to about 10-15% brake pressure to control the pitch of the car.

 

Also no accelerator on turn in, this also shifts weight to the rear. If you're needing accelerator to drive through the corner then it sounds like you are over-slowing the car and need to brake later. Foot on the brakes as you turn the wheel in, hit the apex, unwind the wheel, roll onto the accelerator as you straighten up the wheel.

[PranK]

On 12/01/2022 at 10:59 AM, Unzipped Composites said:

Yeh so it sounds like you're unintentionally shifting weight to the rear, costing you front end grip. Don't jump off the brakes as quickly as possible, you want to be trail braking up to around the apex. So full brakes on approach, then just before you start turn-in ease off the brakes but not completely, keep a little bit of brake applied to keep some weight over the tyres. How much pressure you apply is directly related to your steering angle - think of it as the reverse of accelerating, you dont jump on the accelerator while you're still at full steer, you ease onto the throttle as you straighten the wheel. Braking is the same, you dont jump off the brakes and turn in, you want to ease off the brakes as you apply steering angle so that as you approach full angle you get to about 10-15% brake pressure to control the pitch of the car.

 

Also no accelerator on turn in, this also shifts weight to the rear. If you're needing accelerator to drive through the corner then it sounds like you are over-slowing the car and need to brake later. Foot on the brakes as you turn the wheel in, hit the apex, unwind the wheel, roll onto the accelerator as you straighten up the wheel.

Damn, thats great advice, thanks! 

I definitely think that I'm jumping off the brakes suddenly. I think everything I do with the brakes is sudden movements. I brake late and as hard as I can but then I'm too committed to have time to get off them slowly, I quickly release brakes and steer. I don't think I'm applying any acceleration until I'm mid corner. Do I need to be able to heel-toe here or is the easy brake release and slight trail braking over before I start to accelerate?

BTW, I swapped front and rear track wheels to see if the wider 255 rears would fit the front and they do. I drove around the block and did some big lock turns and no scrubbing at all. Car felt really stable. So, I might try to get a second set of my wheels and mount the new rears to the front to use a square 255 set up.

[Unzipped Composites]

On 01/02/2022 at 9:03 AM, PranK said:

Damn, thats great advice, thanks! 

I definitely think that I'm jumping off the brakes suddenly. I think everything I do with the brakes is sudden movements. I brake late and as hard as I can but then I'm too committed to have time to get off them slowly, I quickly release brakes and steer. I don't think I'm applying any acceleration until I'm mid corner. Do I need to be able to heel-toe here or is the easy brake release and slight trail braking over before I start to accelerate?

BTW, I swapped front and rear track wheels to see if the wider 255 rears would fit the front and they do. I drove around the block and did some big lock turns and no scrubbing at all. Car felt really stable. So, I might try to get a second set of my wheels and mount the new rears to the front to use a square 255 set up.

 

Trail braking really comes afterwards, you should be heel-toeing if you're clutching in on downshift and that should be happening before you start turn-in.

 

Once you've started turn in, you want to keep the weight of the car steady so that the front tyres are using all available grip to bring the front around. When you clutch in, you shift the weight again, so you don't want to be doing it once you've got too much steering angle. 

 

You want to be hard on the brakes on approach, downshifting as you do. In a manual h-pattern with a cable driven throttle body, your revs drop off when you clutch in, so then your tyres are rotating faster than your engine and that upsets the balance of the car when the clutch re-engages. You heel-toe to bring the revs back up to road speed and keep the tyres happy. If you've got a sequential/automatic, or drive-by-wire throttle body with auto-blip, you dont need to heel-toe.

 

As you start turn-in, you should be just about in the correct gear for the corner, trail-braking by easing off the brake but not completely off it until you apex. It's not really happening 'slowly', it's happening smoothly. As you turn the wheel in, you ease your foot off. As you turn the wheel out, you ease your foot onto the accelerator. All of that can happen quite fast, but it needs to be smooth to keep the weight of the car steady and not ask too much of the tyres.

[PranK]

Thanks so much for that Martin, got some new things to try out now.

The car is an auto but with really good paddles. Its had a transmission flash and the revs blip with downshifts so no real drop in revs. Its surprisingly good.

Good to know I dont need to heel-toe because i'm rubbish at it

 

[GTSBoy]

On 2/2/2022 at 8:04 AM, PranK said:

Good to know I dont need to heel-toe because i'm rubbish at it

Heel & toe is strictly a 3 pedal technique anyway. What you'd be considering, if anything at all, is left foot braking. That way your concerns about the time required to move foot from brake pedal to throttle as you transition from trail braking to power on go away. I mean, that's something that you'd do an a 3 pedal car anyway, at that stage in the corner. This because at that stage in the corner you'd only need to be using the left foot for the clutch (and hence need to consider heel & toe) to change gears because something had just gone totally wrong (like the clown in front of you spinning across your path, etc).

[soviet_merlin]

Possibly obvious, but if you are not used to it please try left foot braking at slow speeds first. As in something like walking speed.

I still remember teenage me driving my grandpa's Merc ~15 years ago. Only fancy old people cars had automatic transmissions. Tried braking with the left foot because the right was itchy or some stupid reason like that. It felt like I would have launched myself through the windshield if it wasn't for the seatbelt.

[Unzipped Composites]

Haha yeh, left foot definitely needs a bit of training to get the muscle memory to know how much pressure to apply. Weirdly it's a little bit easier on the race track than on the street though, probably because you tend to be going from full pressure and easing off, rather than on the street where you tend to ease into the brakes as you slow to a stop. Takes less muscle memory to do it in that order.

[niZmO_Man]

You gotta dance like a rally driver