Chase the Countryman has a broken runflat on his front passenger side.

We've done about 20,000 miles on the current tires.

Do I just replace the single tire, or get 2 matching ones?

(I have a Subaru buddy who insists I should replace both fronts to make the AWD system happiest)

 

i believe your buddy is correct, driven axel tires should be replaced in pairs

the better question is should AWD vehicle tires be replaced in sets?

tirerack ALEX????????

 

really it should be all 4. You don't want different tires on an awd car. 2 is definitely better than 1, but 4 is best.

 

Here's some advice from TireRack:

I often hear from customers who have damaged one tire on their AWD vehicle that they would like to buy one tire to replace the damaged tire.

Simply installing one new tire runs the risk of drivability problems or expensive drive line damage. I recommend they consider a set of four depending on availability and the tread depth of the three remaining tires. But replacing the other three partially worn tires along with the damaged tire does increase the cost. Another option to consider is shaving the new tire to the current tread depth of the tires that remain on the vehicle.
By matching the tread depth of the replacement tire to the tread depth of the partially worn tires that will remain on the vehicle via the removal of tread rubber from the new tire using a specialized machine that operates as a tire lathe may seem counterintuitive, the value of the mileage sacrificed is considerably less than the cost of rebuilding worn drive line components.
Tire shaving will range from $25 to $35 per tire and is significantly less than the cost of unnecessarily replacing the remaining two or three good tires that still have lots of mileage remaining. But if the tread depth on the remaining tires is 5/32nds or less, shaving may not be the best choice.
Some manufacturers have set parameters for matching the tires used on their four-wheel drive and all-wheel drive vehicles.
Audi: As stated in their owner's manual, "rolling radius of all 4 tires must remain the same" or within 4/32-inch of each other in remaining depth
Porsche Cayenne: Within 30% of the other tire on the same axle
Subaru: Within 1/4-inch of tire circumference or about 2/32-inch of each other
Refer to your owner's manual for additional recommendations from other Original Equipment vehicle manufacturers.

http://blog.tirerack.com/blog/todds-...an-awd-vehicle

 

The problem is that the wheel speed of the tires is monitored to detect slippage that would activate portions of the all-wheel-drive system. This is accomplished by using additional differentials or viscous couplings (sometimes both) to allow for differing wheel speeds experienced when cornering or encountering loose pavement and momentarily spinning a wheel.

 

wow. you guys are good. I guess Chase is getting 4 new sneakers, then.

Time to ditch the runflats, methinks.

 

this is not a runflat vs non-runflat issue, but rather an AWD issue

although replacing runflats with non-runflats is cheaper by up to half depending on brand and specification

scott

 

I agree, I did indeed ask about the AWD issues here. But the bump steer coming from the runflats is something I have never appreciated, and if I'm going to buy 4 new tires, I would rather get something a little less harsh.

 

just curious, what size/brand tire did your CMS come with?

i got the 18" wheels and the tires are pirelli cinturato p7 225/45r18 91v summer and i am quite happy with them once i upped the tire pressure to 38psi

scott

 

Car Talk on NPR says change all four unless you are within a couple of /32nds. Google is your friend and I would trust the car talk guys.

 

Pirelli Cinturato P7. All Seasons. 205/55 R17

 

+1 on the tire pressure. try 'em on 40PSI, even better...


Just sharing...

 

The car isn't all wheel drive guys....it's two, 4 if u lose control. I had a Subaru wrx for 5 years, I replaced them in pairs, not 4! A Subaru is true all wheel drive

Duh tire rack would tell u to replace all four, more coin in their pocket!

 

That was what was originally reported, but its been proven that is not the case.

http://www.motoringfile.com/2011/12/...tem-clarified/

"Originally, MINI’s All4 system was explained to us as being FWD first, then AWD on-demand as a traction control aid. Apparently, this was not entirely accurate. While yes, up to 50% of the engine’s power can be diverted to the rear wheels, the system actually defaults to AWD from the get go, not FWD. Similar to BMW’s Xdrive system, which defaults to a 70/30 split rear to front and is able to divert 100% of power to the rear wheels, All4 starts at 50/50 and is able to re-allocate up to 100% of power back to the front wheels. It’s a subtle difference, but has pretty profound ramifications on our understanding of the system. I clarified this with Heinz two separate times just to make sure we weren’t getting stuck in a language barrier. Each time he was insistent. The system defaults to AWD.

Another interesting clarification about All4 has to do with speed. As an All4 equipped MINI reaches highway speeds, the multi-plate wet clutch that sends power to the rear wheels starts to disengage progressively, sending less and less power to the rear wheels as you go faster. At approximately 80 mph, the rear wheels are disengaged entirely for the sake of efficiency. We knew that there was a point at which the system reverted to FWD, but it’s new and interesting to find that it’s a progressive process. So at say 60 mph, the power split might be 60/40 front to rear. Then at 70 mph, it could be more like 80/20."

 

Well thank you for that!

Tell me this, when I hit the button beside the sports button, TRACTION shows up, then if I hit it again, traction is off, then if I hit it again, nothing shows up...what's the difference in nothing showing up and when it says TRACTION?

 

I was chatting with the guys at the dealer the other day, and the topic of the ALL4 system came up. I mentioned this article, and they still insist that it is an "on demand" system! One of the mechanics was in on the conversation, and he said the same thing. . ."on demand"!

I really wish we could get the real story some time!!

 

https://www.northamericanmotoring.co...ml#post3419611

 

The All4 system can be both "on-demand" and proactive. Tell the dealer guys to read the MINI Countryman brochure in their own showroom:
"Torque split is instantaneous and varies seamlessly based on multiple factors, including speed, steering angle, and acceleration".

 

my dad's countryman s all4 has the same tires and standard suspension

compared to my cms all4 with sport suspension and pirelli cinturato p7 summer 225/45r18 tires, dad's rides like a cadillac

scott

 

Spitballing here, but this is my theory...

On simple AWD systems, it probably doesn't matter if the tires are replaced in 4s. Since the majority of the time, they default to just one axle. Example of this type (guessing here...) would be a Honda CR-V. You'll generally note that rotating tires is recommended because one axle primarily does the work.

More complex AWD systems such as (guessing again...) BMW's X-drive, or Acura's SH-AWD require tires to be replaced in 4s because both axles do a lot of the work. Both axles probably vary the torque all over the place depending on just about every driving condition.

We the consumer are generally told to replace them 4 at a time because, frankly, most of us have no clue if the AWD system is of the simple/cheaper variety or the complex/expensive variety that has computer monitors at all 4 wheels checking on the different rotational rates at each wheel.

The problem we have at the moment, is that we're not 100% positive how complex the Countryman's system is due to conflicting reports of how the system works.

Basically, replacing 4 is Always the safe bet to cover your bases. Just not always the cheaper route...

 

http://m.youtube.com/watch?v=ooQRxlChvMw

This should help explain things....it's not all wheel drive

 

Eh, I've seen that video before...

My take away was that it was an overly long sales pitch for 'symmetrical awd'.

Not that I'm saying it's a bad system or anything, I realize it's good. Just that so much stock is taken in to it being symmetrical that I think it devalues a superior system. Subaru's system is simply better/more efficient at diverting a larger percentage of power to the wheels that need it whereas the competition diverts little to less of their total power to the wheels that need it. Just because the axle is unequal lengths doesn't mean an awd system can't redirect power. It just needs more trickery in the transfer case and differentials is all.

None of this helps explain whether or not the Countryman is of the simpler variety that can get away with only two tires changed or if it requires four though...

 

between the extra stress on the clutch, the fact you can't light up the rear wheels, and the way it drives in comparison to my subaru, IMHO the motoring file document is correct.

 

not sure what a video from 08 has to do with a new AWD system developed 2 years later. This is a newer, and from most reports, better system than xDrive.

 

Maybe my understanding of it is off...

For example, I could never light up my tires on either my front wheel drive biased 98 Audi A4 Quattro nor the rear wheel drive biased 05 X-drive BMW X3 nor the X-drive 335. Doesn't mean any of those aren't true awd vehicles, just means your Subaru had a strong rear drive bias (was probably tuned for that effect) A true awd shouldn't let you light up a tire at all.

Edit:
I'm sorry, I read your reply wrong... so my above comments probably don't make sense.

Regardless, I think we can only speculate at this point whether Mini's system lets you get away with replacing tires in pairs...