Jump to content
SAU Community

Recommended Posts

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.

Link to comment
https://www.sau.com.au/forums/topic/483159-mars-needs-mid-corner-grip/
Share on other sites

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.

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. 

 

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.

  • Like 2

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.

 

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.

  • Like 2
  • 3 weeks later...
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.

  • Like 1
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.

  • Like 1

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 :)

 

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).

  • Like 1

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.

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.

  • Like 1

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • I have engineer in my job title One of or motto's though is "we make and we break"
    • This is actually 2 whole different trains of thought that need to be addressed separately. No, as Matt says above, "Engineer" is not a directly protected title. A lot of guys who just do mechanical design via CAD, with or without even some sort of associate diploma in engineering, often have the job title of "Design Engineer". A train driver can probably still describe themselves as an engineer. But, to usefully get employment with anyone as a proper engineer, you're going to have to have at least the necessary and relevant degree qualification. You're not going to get a job as an electrical engineer if you have a chem eng degree, unless you can demonstrate x number of years of working in that capacity, sufficient knowledge, etc. Having the degree is at least in indication that you've seen the relevant text books, even if you haven't read them (like pretty much the last 10 years of graduates!). To be a self employed engineer.....you could get away with quite a lot pretending that you're suitably qualified, without actually being a proper engineer. But, you will find yourself unable to work for a large section of the client space because a lot demand CVs and capability statements when considering contracting for any engineering work these days. Insurances too. If you're not a proper engineer, it will be much harder to obtain proper PI insurance. Insurance companies have gotten hip to that. The "Professional Engineer" thing is a thing in Australia. If you have the right qualifications and experience you can apply to the relevant engineering top level body (mostly Engineers Australia, the less said about whom, the better), to be assessed and approved as a Chartered Professional Engineer, CPE. There are high bars to get over and a requirement for CPD to maintain it. The RPEQ thing is similar-ish, in that you have to demonstrate and maintain, but the bars are a little lower. It is required to be RPEQ in order to sign off as an engineer on any engineering design in Queensland. The other states haven't fully followed suit yet. There's "engineering" and there's "engineering". Being an engineer that signs off on timber (or even steel) frames for housing projects, council creek crossing bridges, etc, is a flavour of civil engineering that barely warrants the name, description and degree. That would be soul crushing work anyway. Being an automotive engineer working in the space where you have to sign off on modifications to cars and trucks would also be similarly soul crushing. At least partly because of the level of clientelle, their expecations, depths of bank balance, etc. And that brings us to your second question. No, we do not have professional engineers "do vehicle inspections". Well, not the regular roadworthies, etc etc. That's done by mechanics. There might be some vehicle standards engineers at the various state govco inspection stations where cars go to get defects cleared and so on, but that's because they (the cars) are there specifically for defect inspection and clearance and so the stakes are a little higher than on an annual lights and brakes working check. But, if you modify a vehicle in Australia, you have to get it engineered. A suitably qualified (and effectively licensed, which I will get back to) automotive engineer will have to go over the application, advise on what would be required to make the mods legal, supervise some parts of the work, inspect and test the results, and sign off. The "licensed" aspect comes from there being a list of approved engineers to do these things in each state. They have to jump through hoops set up by the govco vehicle standards divisions that mean only the suitably qualified can offer to and approve such mods.
    • It's got a problem Prank... It looks like both washer spray caps have fallen off this car... 😛
    • Meh, it's only got to last another 10 years or so until you'll be forbidden to drive it. Keep it dry and forget about it.
    • The title of Engineer is not protected. However different states have different rules about what an Engineer requires to operate. Engineering for a motor vehicle modification is very different to engineering for a bridge, electronics, etc, including what that engineer needs as certifications.   In Canberra, "Engineer" is the loosest category with basically nothing stopping you calling yourself and engineer and designing a bridge or building. From what I've reviewed, QLD has the strictest requirements through RPEIQ.
×
×
  • Create New...