I'm now beginning to overdrive my R55 platform and the front inner wheel / tire is lifting under moderate cornering, causing loss of traction and tire spin.
My previous experience on FWD platforms tell me that a larger rear sway bar installed and adjustable endlinks for the front (to apply preload) would improve this condition.
Does my thinking still hold true for the R55 / R56?

Note: suggestions would be needed for intended light track use; still need daily-driver capability for the vehicle.

- Erik

 

yes yes yes. On the clubman the alta bar on full hard is perfect. its what i run ;-)

 

Definatley a good rsb. A larger rsb such as a 22mm will tend to make the rear unloaded wheel lift during hard cornering. Might want to consider front camber plates instead of the end links if you are not slammed.

 

There are a couple ways to go about this... For the sake of simplifying things(and focusing only on suspension changes which will yield your desired goal), I am assuming you have a good limited slip differential? This car is torquey enough, with a short enough wheelbase, that no suspension changes/tuning is going to help beyond a certain point if you don't have a good LSD.

For a lightly modified production based vehicle, I would take a guess that the most beneficial all around would be a larger rear swaybar. The diagonal load transfer between the outside rear and inside front is the key here. It will help load the inside front during cornering and reduce the lifting a fair amount. The larger rear bar will also bias the roll dist further towards the rear, and the car will rotate easier on corner entry. Getting the car rotated sooner is important, as it will allow you to get back on throttle with the car pointed straighter than before. A straighter car means less of a delta between the radii scribed by the inside and outside front tires... thus, less potential for wheel spin. It also means less front(and overall) body roll at the moment of throttle application... All of this will help to limit inside tire lift and wheel spin.

A smaller front swaybar can also help your situation. I have moved to the base model cooper 21.5mm front bar, for just this reason. This is a little more complicated, though.

All things being equal... ie: front natural freqs and roll dist/rates... a smaller front bar will reduce the upward forces on the inside front wheel, thus reducing lift and consequently wheel spin. However, in practice, this often doesn't play out exactly as planned. By moving to a smaller front bar, you are decreasing the overall front wheel rates during roll... thus, by just changing the front bar to a smaller size, you are decreasing the lift on the inside tire per degree of body roll(Good!)... but you are also increasing the capacity for the front to roll per a given lateral load(Bad!)...

The actual result? Who knows for sure. A definitive answer can be found only through doing all the calculations, modeling the suspension with a program like WinGeo or Solidworks, and analysing the data. However, a little bit of testing can go a long way. If it was my car, I would start with something along the lines of:

*Move from OEM Cooper S 22.5mm front bar to OEM base Cooper 21.5mm front bar
*Increase front spring rate by ~50lbs/in


Next step... Assuming all things are copasetic in the natural frequency/wheel rate world, ie: you have your car setup so that it is balanced the way you like it, you don't really want to change anything other than reducing some wheel spin on corner exit... I would move to the dampers. Increasing the front rebound will slow the rate at which the inside front lifts.

Adjusting shock settings is a quick and easy way to change transient response and car behavior. And good shocks are worth their weight in gold. But, as with all things, changing the rebound or compression will affect behavior in other areas. An increase in front rebound will not only hold the nose down longer during corner exit, but also during corner entry under braking... which will make the car more responsive on turn-in. But it can also make the car more sketchy during braking and corner entry. It is always a compromise.

Having adjustable shocks and adjustable swaybars would be an ideal combination here. Im not sure what you have on your car... but most adjustable swaybars can be adjusted with 2 wrenches in less than 10 minutes if you have a jack and the tools on hand(meaning, it can be done between runs at an autox if you are quick about it). Adjusting the shocks can obviously be done in seconds. Shocks are especially useful as they allow you to alter the transient behavior without changing the steady state balance of the car.

Edit: I would avoid preloading the front bar as a way of tuning out wheel spin/tire lift. I consider bar preload as a tuning option used in stock class racing, such as SCCA Stock(solo II) and Showroom Stock(club racing). While it can certainly work in those situations, it is difficult to get consistent/repeatable results... and Ive seen some really wonky handling traits courtesy of heavily preloaded swaybars. Adjusting the endlink position where it connects to the swaybar arm is a great adjustment to have though.... Being able to adjust swaybar spring rate is a huge help for setting up any production vehicle.

 

YES start with an Hsport rear sway bar, then you can think about other things. Camber plates will be the biggest help since you intend on tracking the car cause a MINI is a tire eating machine without them.

 

Curious, how will camber help producing a off-weighted contact patch?

Well, thanks to MINI USA, the damn 2009 JCW didn't come with the available option...
So, I'm currently ultilizing the electronic differential lock (EDL, which pulsates brakes) and anti-slip regulation through dynamic traction control (DTC, drive-by-wire throttle lift).
Am I for putting one in? Sure; but the downtime, tear-apart and related cost for such is slightly overbearing at this current time.
No doubt I would not be complaining about such if a true mechanical limited-slip (preferably a Torsen) differential was in from the get-go.

Tackling both very soon.

What's happen in your specific cases? Curious as the inconsistances you received.

Great info; appreciate the personal feedback!

- Erik

 

Better steering geometry during turns helps the contact patch.

 

Ahhh... Bummer.

A good LSD makes all the difference in the world. I just finished installing the Ford SVT Torsen in my R56 and it makes an enormous difference when powering out of corners. I'll have a true chance to try it out at an autox next weekend...

I am not really familiar with how well the ELSD works, but based on your wheel spin issues, I am guessing not that well. The suspension can certainly be tweaked to help wheel spin, but without a good diff, it is hard to eliminate the problem entirely.

It is not a cheap endeavor, certainly... but it is well worth it IMO, if you are serious about getting the car to handle its best.


I heavily preloaded the rear bar on my track car(Honda) one time, when having the rear suspension apart before a track day. The car was awful the next day... It felt as if the swaybar was binding up at corner entry, and the bar rate went from typical semi-stiff to enormously stiff. I couldn't trailbrake at all without the rear-end trying to swap ends.

I suspect preloading the front bar would cause a substantial amount of understeer under heaving lateral G loading.

Of course, my example came from preloading the bar equally on the left and right sides. If you were to preload one side more than the other, the bar could bind up turning one direction but not the other. Not really what you want...

Adjustable endlinks are great for insuring that the swaybar isnt preloaded when you lower the car and/or corner-weight it.

 

IMO better shocks and a better alignment (front plates and rear control arms) are the best first steps for a Mini that's going to see the track or auto-x. Actually any Mini really since the standard shocks suck so bad.

Rear adjustable 19mm bar is a good addition to that. Springs or coilovers (if done right) also can improve things but I think the 2 most glaring problems are the pansy OEM alignment and the crappy OEM shocks.

Both will improve front end grip, with the shocks really helping the inside front stay on the ground over tarmac that isn't perfectly smooth.

A rear bar will also improve front end grip, but its sort of covering up the problem instead of solving it correctly in my opinion. An improvement for sure, but there is more to gain with the better alignment and better shocks. But the bar is dirt cheap. For my car, I'm still on the stock rear bar and I'm perfectly happy with my set-up. I would add one if I autocrossed, but I don't feel a strong need for one now.

Agreed on using adjustable endlinks to remove preload from the bar.

- Andrew

 

I do agree that a good alignment and good shocks are requisite pieces to the handling puzzle.

However, Im not sure I would call a larger/stiffer rear bar "covering up the problem"... If the problem is not being able to put power down and lifting the inside front wheel, the diagonal load transfer between the outside rear and inside front at corner exit is one of the most important tools we have to tune around this issue.

 

I think Andy is saying that the stock front suspension geometry is not very good. Changing out the rear bar does not do anything to the poor front geometry.

 

Right, "covering up the problem" is probably the wrong use of words as the rear bar will directly help that issue. I just see the better front end alignment as more of a priority in general. Maybe not the solution for this particular problem, but something that should be fixed first IMO. So maybe I was getting sidetracked.

-Andrew

 

Gotcha. And agreed.



We may all be putting the cart before the horse here, though.... Im not sure this problem will ever go away without a good mechanical LSD.

At least not in a S or JCW... just too much torque.