Took my new Mini to the track for the first time this weekend. Car was a lot of fun but there are two main weaknesses: lack of power and understeer.

I currently have the JCW suspension and the H-Sport competition rear sway bar (set of stiffest setting). I'd like to make the car a more neutral without changing the struts and sway bars.

I'm thinking front camber plates should help the front tires bite a bit more, thus improving the balance. However, I'm not too eager to suffer the increased ride height from them. Also, perhaps upgraded rear sway bar links to reduce flex back there.

Anyone got any other suggestions?

 

So far, I've only had my Cooper on an autocross course since I had the JCW suspension put in. I'm heading to the track this coming weekend, so I'll see if that changes my mind.

But, for now, I'd say that there is not an annoying amount of understeer in my car. I've got the JCW suspension, the stock sports suspension (not plus) front swaybar, the Helix / RDR rear swaybar on the softest setting, and Goodyear Eagle F1 GS-D3 tires. I had a bit of lift throttle oversteer on the autocross course with this setup. I think that if I had put the swaybar on full stiff, it would have caused me problems. But, the low speed handling may be different than high speed handling, and the autocross course was really slow.

What tires are you using? Perhaps that is a big part of the difference. Other than that, the differences between our cars seems to be the front swaybar (assuming you have the stiffer sports suspension plus swaybar) and the fact that I have a Cooper and you have an S.

I'll try to remember to chime back in after I get som high speed track time with the new setup.

 

Run higher air pressure in the rear tires. About 2-3 psi will make a pretty significant difference. Run like 35 f., 38 rear. Play around with it.

 

I may be misreading your post, but I thought the Cooper did not come stock with a front sway bar. And that the JCW kit for the COOPER includes a front sway, which is why the kit for the Cooper costs more than the kit for the S. S kit uses the stock S front sway, so there isn't one included in the kit. Sorry to sidetrack the thread.:smile:

 

Higher rear tire pressure, relative to the front, will cause more understeer, not less.

Quote:

Originally Posted by ingsoc

Run higher air pressure in the rear tires. About 2-3 psi will make a pretty significant difference. Run like 35 f., 38 rear. Play around with it.

Ask your install folks if they aligned the car after the install. You should expect a little bit more toe in up front with a lowered mini - if the change was not corrected. Even so, if you did not ask for an alignment print out, you will not know what specs they used to align the car. This may be one of the causes for more understeer. The other is a bit more rear negative camber associated with lowering...although your 05 has some slight adjustability. The above two changes combined - assuming these were not returned to near stock, with cause more understeer.

Dunno what the spring rates are??? Closely guarded secret.

 

[QUOTE=meb]Higher rear tire pressure, relative to the front, will cause more understeer, not less.


NEWBY QUESTION: Why, if the rear tire pressure is higher, making the tires presumably stiffer, wouldn't they loose traction sooner than softer fronts ?

I am not saying this is optimal, however, why wouldn't it be similar to a stiffer rear sway bar or stiffer rear springs though ?

 

Meb,
Raising rear pressure gives more oversteer, not understeer. More rear pressure=less rear grip=less understeer .

Plus, you need to remember that it's not all about grip- it's also about corner weighting. The MINI has more weight up front, and [usually] stiffer springs in back. This weight is therefore shifted more towards the front of the vehicle, "planting" the nose in a turn. Now, if you increase rear pressure, you will see even more weight shifted to the front, making the rear even lighter. The rear will therefore come around more easily.

 

It is confusing....

A Cooper comes standard with Sports Suspension, which does include a front and rear swaybar. The Cooper sports package does not include the Sports Suspension Plus (which would give you bigger front and rear swaybars). The Cooper JCW suspension upgrade is supposed to include the Sports Suspension Plus swaybars, if your car does not already have them.

When I had the suspension upgrade done on my Cooper, I should have gotten the SS+ swaybars. The person who wrote up my service saw that I had the sports package and thought that included SS+, which is doesn't on a Cooper (but does on an S). Rather than argue about it and spend more money to get a bigger front swaybar (which may have been nice) and another rear swaybar (which I don't need), I just let it go... They didn't charge me for the swaybars, so I was okay with things.

[edit]

I almost got it right... All hardtop S's come with SS+ (I'm not sure if that was always true, though).

 

INGSOC and MEB:

You're both right. You need to maximize the grip in the fronts by finding their optimum hot pressures and THEN dial out some grip in the rear by EITHER underinflating or overinflating the rears. Moving away from the optimum rear pressure in either direction will cause a loss of traction in the rear and thus, reduce understeer.

I ran 40 hot all around this weekend and didn't really have a chance to play with tire pressures. Next time I will tweak the rear a bit. I was looking for other hardware recommendations if available.

Thanks!

 

Raising rear tire pressure relative to the front ABSOLUTELY increases understeer and has since the beginning of time. And so, the reverse is also true - with any drivetrain layout. Given that we are all ghosts at some level - we don't know one another or our backgrounds, I will direct the reader(s) to a more outwardly certified information source - The Tire Rack. There you will find what I have written to be true.

If by choice, one has increased rear tire pressure enough to cause the back end to slide around - verb/adjective - then one has simply added too much air pressure - the tire is cornering on its center section - a very dangerous way to induce oversteer in my opinion. Tires grip/work/whatever when the contact patch is allowed to remain in contact with the road thru as much of the suspension travel as is possible. The goal playing with tire pressure - relative to this subject - is to slightly reduce side wall strength by removing a relative amount of pressure so that one set of tires has a larger slip angle than the other. Adding more psi up front relative to the back, AND, within reason will narrow front end slip angles - more grip up front, less in back. This will cause more oversteer.

Can one cause oversteer by adding more psi to the rear tires relative to the front? Sure, very dangerous; loss of grip is sudden and generally without control...no feel either. Here we'll have a tire infalted beyond optimum, way beyond.

When I began playing with tire psi on my stock 05, I tried 35psi up front and 37 psi rear - cold. Very stable back end - understeer. I then reversed the the pressure - crisper turn-in, less understeer. These ar road trials, not track, not autoXing...which might require slightly higher psi. BUT! The psi relationship bias remains the same; smaller slip angles mean more tire grip.

With all due respect to all, we are not both correct. Heat in the tires is relative to many things, tire pressure being one and geometry being another. Lets isolate tire pressure; smaller slip angles produce more grip. So, more psi in the back - relative mind you - will produce smaller slip angles than the front - understeer.

 

It may be easier to understand tire pressures if you measure hot pressures. Most FWD cars will run lower cold pressures in front vs rear for track duty, but that's because the fronts are so overworked that they get a lot hotter than the rear, and the hot pressure actually ends up higher. (Perhaps 40psi cold in front was 50+ when hot, while the rears stayed nearer to 40.)


And alignment settings are everything; eg if you have too much toe-in in the rear it will understeer no matter what.

 

Meb,

Of course, no disrespect felt or meant. But, I have gotta say, it's not all about tire contact patch. If you bias the pressures, you bias weight distribution. Picture a flat front tire. The rear opposite side lifts. The thing is, road tires don't change their shape that drastically to my experience, esp. run flats! Weight does, though, shift. If you increase rear pressure, your front plants better.

I'm not talking a 10 pound differential. A few, rear-biased, makes for a little more oversteer, but nowhere near a snap oversteer. He asked for slight changes... :smile:

 

See below

 

The ride height difference is negligible. Balance is affected due to contact patch and sidewall deflection differentials, front to rear.

 

ireland engineering sells fixed camber plates that only raise the front 3/16's. also consider adjustable lower rear control arms. that way if lowering gave you too much rear camber it can be adjusted out. that means an alingment, as was mentioned already. tire pressure; what MEB said.

 

We are among friends, so apologies necessary at all - vigorous conversation is a great thing!

As MarkBradford wrote, contact patch and sidewall deflection are very easy to control with tire pressure. Ultimately, we are changing the shape of the contact patch, and therefore, slip angles. By reducing tire pressure, the contact patch will grow front to back - more than side to side - increasing the size of the slip angle. Sidewall strength is also reduced.

All things equal, a wider tire does not put 'more rubber' on the road. (by equal, I mean to compare similar tire species as there are differences among manufacturers within the same tire size) A wider tire will have a wider contact patch left to right - inside to outside of tire. This same tire will also have a shorter contact patch - front to back. I would expect the total contact patch area between a 205/45/17 and a 215/40/17 to be very very close. The shape determines the mechanical advantage and the slip angles.

I included the above because it relates to tire pressure; reducing relative tire pressure changes the shape of the contact patch, increases the slip angle, and ultimately, reduces mechanical advantage created by a wider, but shorter foot print.

Ingsoc, I understand your comments. But I believe that the above have far greater affect, at this level, than weight transfer. If I were working with F1 cars the weight transfer might actually show up on radar. And yes, if you fool with tire pressure while corner balancing your car, the results will be altered...

BFG9000 - right on!

Back on topic...MarkBradford, try a little toe out, or try to get as little toe-in as possible. I cannot remember exactly, but my front toe is set at something like 5/64" toe-in - I drive a lot of highway miles so a little toe-in is better for me. A larger rear bar sounds like a very logical next step. I beleive that there are a couple of camber plates on the market that do not change ride height per se. However, at least one of these places all the load on 3 or 4 bolts and not the uni-body...interesting trade-off...

 

Are there rear bars out there that are more aggressive than the H-Sport Competition Bar set on stiff? (380% stiffer than stock)

Re: redistributing the load to the bolts instead of the unibody - I presume the camber plate goes on TOP of the shock tower and the strut mounts to it, above the shock tower then, thereby effecting a vertical pulling force on the body rather than a push from underneath?

Thanks,
Mark

 

Don't know. This is a hollow bar whos rate is very close to a 22mm solid bar but much lighter. I personally can't use more than 22mm on the street. I think Onasled has more actual experience with different bar weights on and off the track.

Yes. However, Ireland Engineering makes an interesting option; a fixed 1.25 neg degree strut bearing. This mounts just like stock. This appears to be a great option if you cannot adjust height. Set your toe after the install and you're on your way. I believe Morefun installed these and is happy?

Michael

PS - I'm still waiting for the warranty to run out before mods...this is a company car not technically owned by me. Accountants and lawyers frown upon mods to non-personal cars before warranties expire - the reason I do not yet posses actual experience. Another 6-7k miles and that will change.

 

I'm not too familar with the JCW kit. I have a question about it. What exactly does the kit include? I couldn't really find anything that I trusted online about it besides a stiffer linear (looked like) spring and a matched shock.

Also, where in the corner is the car pushing? (going in center, coming out...)

 

JCW suspension on an MCS = springs and shocks.

The car pushes in all circumstances with the JCW setup and the rear H-Sport bar. Trail braking into a high speed sweeper at, say 70 mph, requires a more aggressive application than I'd like. This car is so light and purposeful in all it's other motions that the one thing that really stands out to me is the understeer.

 

pulley and intake should fix the power part.

 

So it's pushing going in, through the center, and coming out? Or is it just goin g in?

 

They're certainly on the menu (in fact I've had a pulley sitting here for weeks) but I certainly wouldn't call the issue "fixed" once they're installed. I guess it's all relative though...

 

It feels like it turns in well (the steering is lively and direct) but it pushes throughout the whole damn turn. There is no oversteer to speak of unless violently provoked, and even then it seems like electronic fvckery tries to bring things back to zero yaw, even with DSC turned off.

 

I'm assuming you don't know what you'r shock travels are. How much is the car rolling over when it's pushing?