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Discussion Starter #1
Ok, seeing all the nasty snow on the west coast has led me to install the winter tires on the Tribeca, even though there is no snow here yet at all. When it comes I want to be ready. My wife has a long commute thus the reason we like Subaru's for winter driving.

As some of you may remember, I purchased a set of Michelin Latitude X-ice winter tires installed on new ASA alloy wheels from Tirerack. I'm in Canada and I was going to Maine to get my father's tribeca so I had the dealer there get them for me. They had a commercial account with Tirerack and could actually get them a little cheaper than I could. I had no problem getting these tires home and everything went well crossing the border.

I paid $950 in total, including Maine Tax for the 235-65-17 tire/wheel set. Tirerack had OE size 255-55-18 wheel sets but the selection was far less and the cost was significantly more. Narrower tires work better in snow anyway. Besides, I had used 15 inch styled steel wheels from a Forester L on my Forester S (which had 16 inch wheels) for years with no problem. Tirerack said the 17's would fit, I checked the diameter and they were virtually identical 65-17 vs 55-18, so the speedometer should be unaffected.

I thought I might install them myself, but after removing the lug nut caps, and trying to see how tight they were, I realized I was in for a struggle. I'm guessing they had been torqued on super tight. So I opted to go to an independant mechanic friend who always worked on my Forester. I was a little nervous that the bolt pattern wouldn't match on these new wheels. I had asked the dealer to try them out but they hadn't gotten an opportunity.

We got the old wheels off and started with the new ones. They fit on fine which was a relief. The new set of wheels had come with fancy, chrome, acorn style lug nuts since the nuts were visible I presume. Here's where we had a problem. The new lug nuts didn't seem to want to go on properly. The old ones went on really easy but the new ones would start on the studs but would require effort to get them to turn. My mechanic friend said they must be the wrong size and we should not use them. I was inclined to agree. So we used the old lug nuts which worked fine but just didn't look as good.

I came home and after some research, I discovered that the lug nuts were in fact the wrong size. 12mm 1.5 and it turns out this is a popular size but I actually needed 12mm 1.25. The difference has something to do with the thread angle I think.

Called Tirerack and the dealer in maine. Tirerack is sending the new ones to the dealer who is sending them to me. So for now I have the old ones on.

See the pics below. You can see that winter hasn't hit east coast Canada yet.
Pict0025.jpg
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One odd thing, I expected the TPMS warning to go off and it didn't....then I realised that the old tires were in the back of the Tribeca....However, even after I unloaded them, there was still no warning. Tirerack does have the option to install a TPMS sensor but I declined the $400 option....unless they installed it by misstake. It will likely come on soon.

And yes, I will re-check the torque on the tires after a few miles.
 

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Wow they look nice, sounds like you got a good deal too. I'm curious about the TPMS not going off, I wonder why? It seems strange it did not go off, maybe it will eventually who knows? I'm guessing short of high centering you are going to be unstoppable in the snow :)
 

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Discussion Starter #4
Well, I went for another drive today. Still no TPMS warning light. I'm curious now as to if they installed the aftermarket TPMS sensors. Or maybe the lack of a signal doesn't trigger the warning light so much as a signal indicating that the pressure is low in a tire.

I guess if the warning light continues to not come on then I may have to experiment....let out some air on a tire and see if that triggers the light...and thus prove they installed the TPMS sensors. The valve stems have a long fancy chrome covered cap but look like regular valves underneath....not metal looking like the stock TPMS stems. I'm just as happy to not have the warning flashing anyway.

In driving on these tires, I must say I am impressed. They are extremely quiet...just as quiet or quieter than the stock tires. Plus they absorb bumps well. I know our last Michelin Artic Alpins on the Forester were great and lasted well...thus the reason for getting the new Latitude X-ice. It does seem strange to see thicker rubber on the vehicle. If we ever get any snow, I'll let you know how they work.

On another note....does the Tribeca have a limited slip rear differential? Seems I read somewhere that it does.
 

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Discussion Starter #7
SoDealer said:
It does not... it manages left and right torque split through the VDC
So how does that compare to a limited slip rear differential? Will one wheel on the back spin if you get stuck or does the VDC know where to apply power?
 

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Tup said:
So how does that compare to a limited slip rear differential? Will one wheel on the back spin if you get stuck or does the VDC know where to apply power?
There is a really good write up on the system at subaru.com. I would have provided a link, but the silly thing is made up of a bunch of popups that I can't link to. But make the trip over to subaru.com and look for it. It will tell you all you need to know - and then some.
 

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Discussion Starter #10 (Edited)
I'm not sure I understand this differential business. I thought that the limited slip rear differential was a good thing as it would allow both rear wheels to spin instead of just one. So if one rear tire lost grip, the differential would lock and both wheels would spin. For example our 4WD Kubota tractor has a pedal that allows you to do this in case you get stuck....I've used it often.

But the Stability control is supposed to detect a spinning tire and use the brakes on it. This made me think that this is the reason for the Stability control shut off button....so you could allow th elimited slip differential to do it's job.

Also, I've read reviews that say it has a center and rear limited slip differential...follow this link and look near the bottom at standard equipment.
http://www.familycar.com/RoadTests/SubaruB9Tribeca/

Or even Edmunds:
http://www.edmunds.com/new/2007/subaru/b9tribeca/100759732/standard.html

So I'm confused.
 

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Discussion Starter #11
OK, While driving today, the TPMS finally figured out that there were no more sensors present sending it info(since we now have our winter tires on). The TPMS warning light started to flash. There is a long interval between flashes....around 5-7 seconds. It's not too annoying so I don't think I'll have to cover that part of the instrument panel.
 

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Tup said:
I'm not sure I understand this differential business. I thought that the limited slip rear differential was a good thing as it would allow both rear wheels to spin instead of just one. So if one rear tire lost grip, the differential would lock and both wheels would spin. For example our 4WD Kubota tractor has a pedal that allows you to do this in case you get stuck....I've used it often.

But the Stability control is supposed to detect a spinning tire and use the brakes on it. This made me think that this is the reason for the Stability control shut off button....so you could allow th elimited slip differential to do it's job.

Also, I've read reviews that say it has a center and rear limited slip differential...follow this link and look near the bottom at standard equipment.
http://www.familycar.com/RoadTests/SubaruB9Tribeca/

Or even Edmunds:
http://www.edmunds.com/new/2007/subaru/b9tribeca/100759732/standard.html

So I'm confused.
The Tribeca has no rear LSD.

How a rear LSD works:

power in the vehicle flows evenly through the rear differential and is split to the wheels. In an open diff, power flows to the side with the least resistance... if a wheel is slipping... say on ice... the power automatically flows to that side, thus robbing the side with traction of power. A rear LSD... either electronically senses... or uses a viscous fluid. An electronic/mechanical system senses the wheel spin and clamps down on the free spinning side so that the power flows to the side with traction. A viscous system uses a fluid that thickens the more it's churned... the free spinning side churns the fluid faster so that the fluid thickens... thus slowing that side down... forcing power to flow to the side with traction. The Tribeca uses its VDC to electronically sense when a wheel is slipping. It then applies the brakes on that individual wheel in varying degrees to force the power to the other side, thus foregoing an LSD.

clear as mud?
 

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SoDealer said:
The Tribeca has no rear LSD.

How a rear LSD works:

power in the vehicle flows evenly through the rear differential and is split to the wheels..... The Tribeca uses its VDC to electronically sense when a wheel is slipping. It then applies the brakes on that individual wheel in varying degrees to force the power to the other side, thus foregoing an LSD.

clear as mud?
Yes- actually quite clear. The 'beca kinda' simulates a LSD by monitoring wheel spin and using the brakes to limit slip. So far, in my limited dirt experience- it works quite well.
 

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Tup said:
...One odd thing, I expected the TPMS warning to go off and it didn't....then I realised that the old tires were in the back of the Tribeca....However, even after I unloaded them, there was still no warning. Tirerack does have the option to install a TPMS sensor but I declined the $400 option....unless they installed it by misstake. It will likely come on soon.

And yes, I will re-check the torque on the tires after a few miles.
I don't understand why the original TPM sensors aren't just retained and put into the new tires. It appears to be part of the valve stem, which typically gets replaced every time you replace a tire. right?
http://www.cars101.com/subaru/tiremonitor.html
 

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Discussion Starter #15
morey000 said:
I don't understand why the original TPM sensors aren't just retained and put into the new tires. It appears to be part of the valve stem, which typically gets replaced every time you replace a tire. right?
http://www.cars101.com/subaru/tiremonitor.html
Yes, the TPM sensors are part of the valve stem. The reason I don't have them in the winter tires is that they are on separate rims. Next spring I will re-mount the all season stock tires with the TPMS sensors and hopefully the system will remember them.

Just got some snow last night and I went out to play with the Tribeca and the winter tires. I was very happy with the grip the Latitude X-ice gave. Even with ABS in slick wet snow I was able to stop pretty well. I was also happy with the stability from the stability control. You can really feel it working. I went to a parking lot and tried the system with the stability control on and off. It does seem strange to hit the gas and turn the wheel only to have the engine quiet down as the stability control kicks in...and then the engine races again when you get grip.
 

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I checked out the wheels at Tirerack after reading your post. They had an 18 inch set on clearance for $109 per wheel in the silver paint finish. The sensors were about $40 each. I got Pirelli Scorpion Ice and Snow tires. What a deal compared to here in Canada. Less than 1/2 the price overall. Imagine getting snow tires in June. Wish that Tirerack had an oulook in Buffalo so I could have saved shipping and broker costs.
 

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I installed the new tires and Rims last week and everything was perfect. The Pirelli Scorpion Ice and Snows are terrific. However the sensors did not hand shake with the TPMS- after driving for 20 minutes or so the tire pressure warning started flashing meaning a problem (low pressure it stays on solid). The valve stem sensors are the same as OEM, they are Schrader 333 mHtz. I guess because each sensor has a unique identifier number you must hand shake they to the car. This makes sense as how else would the car differentiate your readings from other nearby cars. It would have been brilliant to be able to have a built in function wheel sensor syronization function to allow you to do this yourself

My dealership didn't charge me this time but will in future which will be whenever I do a the semi annual change.

You can purchase a TPMS scanner on E-bay for 3$00-400, however I don't know what else is needed to complete the task. If anybody knows if a do it yourselfer could do this please let me know.
 
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