More psi up front - within limits, and you can search for an in depth explanation by me - will reduce understeer period! This is a universal truth known by all who tune front wheel drive cars. If what I've written seems less than perfect, I invite the reader(s)to go to Tire Rack.com or any authoritative suspension textbook. This tuning technique has been printed perhaps hundreds of times in hundreds of places since 'we' began FWD susupension tuning.

SteveiB, you are correct, at an extreme psi. The truth implies the use of common sense on the part of the reader. Scrub characterisitcs and slip angles do differ from tire to tire, but, the differences are typically minimal. Within a range, more psi up front will; stiffen the sidewall, redcuce slip angles by preserving an optimal contact patch and scrub characterisitcs...the tires essentially ride high on the center...really destroying the action of scrub radius.

I've experienced the condition you describe, but above 45psi cold. Too much psi erodes contact surface area and scrub characteristics.

35psi is the reccommended psi for the Mini. I run 35-36 psi all year long on dedicated Ultra Performance summer tires and my All season Runflats. I've never had any trouble holding a line at slow or triple digit speeds...even at the race track 40-41psi hot remained very stable and predictable...great tire wear at this psi on the track too; all of the tread was being used, no more, no less...well, except for the very edge of the shoulder of the driver's front.

Optimal cold psi depends upon where you are driving; as a daily commuter you can use 34-36psi cold up front and either the same out back or a couple psi lower. If you have a stock set-up, the psi should grow by about 2lbs (hot) with normal to semi aggressive driving. If on a track with a stock set-up, you can begin with 32-34psi. This will grow to about 40-41psi (hot).

If you have dialed in more negative camber up front and have added some degree of suspension tuning - damping -, you may find that starting cold psi should be higher; because the tire is working more efficiently and therefore will not generate as much new heat.

 

On my summer tires I use 33~35 psi. I use 35 psi when I'll be driving a lot at triple digit speeds in the course of a week. I weekly adjust pressures.

 

Perfect

Interesting question for you StevieB; you're driving in Germany? I cannot remember. Do you have access to any info from yourself or other car nuts regarding psi and sustained highspeed driving? The Autobahn is interesting to me because although the speeds can be very high, the % grade and turning radii are extremely gentle. I'm wondering what a cold 35psi tire might work out to be after driving say 120mph???240kph+/- for about a half hour...

 

On the Mini, the steering rack only has on bushing {on the rt. side} The other side is solid mount aluminum steering rack to steel engine cradle. I don't think you would feel much of a difference by replaceing that one bushing.

 

The real question is, does the aluminum bush eliminate any sideways rack movement? If not, the poly bush may help.

BLIZZ, have you had a chance to look at this really closely? Have you had the opportunity to have a look while the car is on an alignment rack, but off the alignment plates...with someone else in the car turning the wheel while you're having a look see? I'll be performing this experiment this week. I'll begin a thread under bushings within a few weeks. I've got a little more work to do...

 

I drove to Frankfurt (about 70 miles) yesterday at between 110 and 115 on cruise, depending on traffic. That's about all I want to push my winter tires. I usually cruise at least 120 on my summer tires. The bends are mostly very easy, although when climbing the mountain near Trier on A62 (Mosel river area), there's a bend that you'll swear you're doing a complete 360. It takes effort to hold the turn at over 100, and the area is wet a lot.

It's common to travel at unlimited speeds and then pass through a "100" kph sign, which are very small in diameter. That's usually where the photo radar is so instintively you stand on the brakes and try and scrub off speed.

 

meb, Have been under my car several times in the last few weekends.
The left side of the steering rack housing flares out to become the mounting bracket itself. The bolts that hold the left side of the rack on go from the bottom up through the engine/suspension cradle directly into the steering rack body. No bushing of any kind on the left side. The bushing on the rt. side is a round rubber bushing.
I suspect there would be more movement in the bushings that seperate the engine/suspension cradle from the unibody itself.
The bushing that I think I will replace next, is the lower engine roll restricter that is forward of the steering rack on the rt. side. Hopefully this will help with some slight wheel hop with take off from stop.

 

...so there is no way, in your mind, that the rack can move horizontally?

It's still horribly cold here - I cannot get under the car or get an open bay at a shop occasionally available to me.

Engine mounts...as long as they don't attach to the firewall...if so, not even earplugs will help.

 

I was curious because tire temps are influenced by braking. I assumed there would be very little in a relative short Autobahn run...relative to a track. I guess I'm curious about the effects of braking on tire pressure and Autobahn might be one area to, in some unscientific way, observe tire temps and psi at high speed without brake heat screwing it all up.

I've got to figure a way to determine this one my own ...it's a dirty job you know...

Okay, I've hogged this thread long enough...it's actually off topic too...sorry oneM1KE

 

So the tag on the door tells me. However, that's for 4 people with luggage. In the owners manual, driver only is 30psi.

I was running 35 in the fronts religiously, until I started showing premature wear due to over-inflation, then I statrted doing research. P175/65-15 are best at 32 front, 32-33 rear.

Best wear, best handling, no noise, and best ride quality.

Steve

 

...the MCS may be different; it is heavier and has more power.

 

Maybe I have different road condition and cornering speeds here, my 175/65/15 has about 6/32 outside, 6/32 middle, 7/32 inside on all 4 tires (rotated twice) in about 6500 miles. I run front at 37psi and rear at 41psi, with an 18mm H&R bar.

I suppose if I lower the pressure more, then I'll just get more sidewall roll and more outside wear? From the tire wear pattern I really don't think I'm over inflating, since outside and middle is just about the same. Anyway, the 175/65/15 contis have such huge and soft sidewall, I'd rather lose a bit of grip for better cornering response.

 

Wow, someone actually measures their tread depth....good man!
It looks to me like you could use a little more negative camber, if you have front camber adjusting plates.

 

Abosolutely it is, and different pressures for different tires.

Steve

 

Some good advice here. Get to know your Mini, think of what you want to do with it and change things one at a time. I did several track days and a lot of back road driving before I changed anything on my Mini. Then I though about the primary use I wanted to tune the Mini for. I will do some more track days and maybe some AutoX, but back road driving is the main thing I have the Mini for. I like going places on the really tight roads which often happen to be bumpy. I changed one thing at a time to feel the results before changing anything else. I don't want sudden transfers, I want more predictable transitions, because on the back roads you often have to move suddenly to avoid the unexpected and often you can't just apply power to get out of a situation. The last thing I want is for the back end to start coming around on a one lane road over looking a river canyon with a pickup truck coming the other way. So far I have lighter wheels and more sporty tires, sports shocks and a 19mm rear bar. What a difference all of that makes. The Mini stays flatter, is more predictable and controllable. Maintenance is another big thing. I had an alignment done when the shocks were put on and we found that each wheel was slightly off. The improvement in grip was huge. I also had new brake pads put on and got the metal caliper bushings and bled the brakes. Those improvements were really useful last Sunday when I was on a narrow road with some longer straights ending with tight corners over the crest of a hill. Being able to brake hard with good feel and predictable suspension movement really made a difference.

 

Great advise!

 

I'm interested in knowing how a rear sway bar affects winter driving. Here in Northeast PA we have about 6 months of winter, so encountering snow covered, pot-hole riddled roads is a pretty regular occurance.

Related to this is a DSC question. Today my DSC came on for the first time since I've bought the car 6 months ago. Happened on a left hand turn on an icy road. I have been impressed by how unobtrusive the DSC is in the MINI. On my last car (Mazda RX-8) it came on all the time, even under what I could consider to be normal driving conditions (for a sports car, anyway). My fear is that a rear sway bar would make rear end slide and jump more, possibly activating the DSC more. Turning off the DSC in the winter is not an option for me, since I often rely on the TSC on slippery hills.

Any experience with these issues?

Dave

 

A rear bar will cause the back end to step out when it is slippery. If you purchase an adjustable bar, you can set it to a soft setting for winter. The transfer of weight comes at the expense of rear grip. Tread (no pun) with caution.

That written, spring rates and bar rates together will determine what will really happen; there is an appropriate ratio of bar to spring rate used to achieve total wheel rate. If you get a bar that is far outside the ratio window, you will have a car that snap-oversteers...in any condition.

 

A swaybar might make winter driving a bit more challenging (ie. tail happy). The same thing happens when you drive in water, just not as much.

Remember, the MINI has a good deal of understeer built in. If you get a swaybar, the softer settings will dial out understeer without necessarily causing oversteer (unless you hit the brakes hard when going around corners). In the winter, your grip levels are just lower but the physics are the same. That's why most people set their swaybar to full soft for winter driving.

As for DSC, let it do it's job. Swaybar or not, it's usually going to keep you on the road. Unless you really get a beefy bar, you should be fine.

 

Like people said, what happens in Winter is similar to what happens in the wet only at a lower threshold. It is also what happens in the dry, at a higher threshold, since the physics are the same, as was pointed out. I like to get out on a rainy day and push it a bit to see what the car does as things happen at much lower speeds. I used to get out at the first snow and practice sliding in a big parking lot when I lived in a colder place.

At the track you can figure out what is happening in the dry in a more controled way, which is better than finding out on the street all of a sudden. I like to drive the track first with street tires so that I reach the limits at lower speeds and feel what the car is doing. I think that getting sticky tires upfront can lead to some real wake up experiences when you suddenly reach the limit, possibly after a not so smooth input, after thinking that you are sticking so well.

The other day when I was taking my first drive on a narrow canyon road with my new sway bar and shocks I realized that a corner I had just entered was shaded and still wet from rain the day before due to runoff that I hadn't seen. I had the car set up for mild understeer and it simply pushed about a foot while staying stable and hooked right back up with out me doing anything. So I just kept motoring as if nothing happened but was pleased that it did what I had wanted it to do. If I had an aggressive rear bar it would have snapped right and required correction while it headed for the cliff wall. That was not the moment to discover the effects of an aggressive bar.

 

Winter with a rear sway bar:

Well I can answer that question. With my 18mm H&R sway bar (SS suspension) set to stiff, the car is extremely neutral. Give it throttle, the car will understeer, but lift even slightly, the rear will begin to slide. Even just turning a 90 degree corner on snow, and tap the brakes a little, the rear will want to slide.

That said, the car is still VERY neutral, so it slides real slow, a little bit of counter steer or throttle will bring it back to understeer again, right away.

The above is for packed snow, not fresh fluffy snow (usually just understeer there). Personally I found the car a bit too tail happy after the first month or so driving like that, so I set my sway bar to soft until summer time

 

My take on winter driving and a rear swaybar is this:

I'm going so slowly around corners that there isn't much suspension loading (side to side) going on, so the bigger rear swaybar isn't really do much at all.

Of course, everyone else is right... if you do hit a corner hard the swaybar will cause problems. But, if it's snowy, why would you be taking corners fast anyway?

 

I thought that was true as well, but even at very low load (about 0.2g cornering force on my G meter) there is a notcible difference between the stiff and soft setting on my 18mm bar on snow.

I think the reason is because the stock Minis are already tuned to very close to neutral to begin with, so even a little change like that is noticible.

 

I don't think that's correct. There's no way the stock MINI is tuned to be neutral. It understeers like crazy. Even my H-Sport comp on the softest setting still allows understeer.

One thing to remember is that you will experience different over/understeer situations depending on how hard you turn the wheel. The snow has so little traction that if you just whip your wheel around quickly, you still might understeer with a huge rear bar. On the other hand, if you go into a constant radius turn and just accelerate to the point where you lose traction, then the rear will come loose.

 

...lift and you'll spin. Keep your foot in it - within reason - and you'll drive thru the turn. You can use a little of both to find a line that works...but it's those off-camber closing radius turns that seem to help a slide go on for almost ever. And typically, with unbelievable uncanny consistency, there is always a telephone pole right there at the apex waiting to collect your front end. :impatient

The term 'mechanical keying' is used to generally define the grip mechanism. It doesn't take a lot of force in the snow to remove mechanical keying entirely. And, as we all know, all snow is different; some is gripy, some is not...salt and sand laden snow is...well, not