Winter Tire Size difference for 2011 CTT
12-20-2016, 02:30 AM
#1
Intermediate
Thread Starter
Winter Tire Size difference for 2011 CTT
When I purchased my 2011 CTT, the PO was nice enough to throw in a set of unused Nokian Hakkapeliitta Winter Tires for me.
Pretty exciting - thought i would pick up a set of 20" wheels, and install winter wheels for the Chicago winter.
Found a really good local deal on 20" x 9.5" Porsche wheels, and was about to pull the trigger, but decided to check the Nokian tires again, and it turns out they're 275/40R20 tires, *not* 275/45R20.
My current shoes are a 275/45R20 Conti DWS.
Per my calculations, this is a 3.4% diameter difference, which seems fairly significant for speedo calcs. Having never changed tires on the 958 CTT before, i thought i would ask if this is a cause for concern.
So, any thoughts on my options?
1) Buy 20" wheels, mount current 275/40R20 tires, and deal with the speedo differences
2) Sell 275/40R20 tires, buy 20" wheels and new 275/45R20 tires and mount
3) Sell 275/40R20 tires, and stick with current Conti DWS tires.
From driving in current conditions - we've had 2 large snow storms over last couple weeks, and there's a fair bit of snow and ice in alleyways and unplowed roads - the car seems fairly surefooted on dry pavement when the snow has been plowed, and also, we don't really have inclines here. Having said that, on unplowed roads, and during heavy snows, i've definitely felt the car want to go sideways a couple times, thought it always corrects back just fine.
This is my first time with Conti tires. My 2004 CTT had Michelin Latitude all seasons, and it seemed waaaay more sure footed than the 958 CTT in the snow and on ice. I'd like to think this is purely a function of the Conti's vs the Michelin, but would love to be educated further if this is not the case.
Pretty exciting - thought i would pick up a set of 20" wheels, and install winter wheels for the Chicago winter.
Found a really good local deal on 20" x 9.5" Porsche wheels, and was about to pull the trigger, but decided to check the Nokian tires again, and it turns out they're 275/40R20 tires, *not* 275/45R20.
My current shoes are a 275/45R20 Conti DWS.
Per my calculations, this is a 3.4% diameter difference, which seems fairly significant for speedo calcs. Having never changed tires on the 958 CTT before, i thought i would ask if this is a cause for concern.
So, any thoughts on my options?
1) Buy 20" wheels, mount current 275/40R20 tires, and deal with the speedo differences
2) Sell 275/40R20 tires, buy 20" wheels and new 275/45R20 tires and mount
3) Sell 275/40R20 tires, and stick with current Conti DWS tires.
From driving in current conditions - we've had 2 large snow storms over last couple weeks, and there's a fair bit of snow and ice in alleyways and unplowed roads - the car seems fairly surefooted on dry pavement when the snow has been plowed, and also, we don't really have inclines here. Having said that, on unplowed roads, and during heavy snows, i've definitely felt the car want to go sideways a couple times, thought it always corrects back just fine.
This is my first time with Conti tires. My 2004 CTT had Michelin Latitude all seasons, and it seemed waaaay more sure footed than the 958 CTT in the snow and on ice. I'd like to think this is purely a function of the Conti's vs the Michelin, but would love to be educated further if this is not the case.
12-20-2016, 02:19 PM
#2
If you change tire sizes for winter, the only dimension that you should consider changing is width. Diameter should not be changed (engine will spin faster at any given speed with 40s on the car vs 45s).
With Cayennes you need to make sure the maximum load rating of each tire is at least as high as the maximum gross vehicle weight (fully loaded with fuel and 5 passengers plus some extra weight for "cargo") divided by 4. These are pretty heavy vehicles and tires made for sedans may not have enough load capacity for a loaded Cayenne so check that spec on the tires you have also. Tire Rack has some good tools for seeing what tire options you have if you change wheel diameter... or keep stock wheel diameter and change the width/profile numbers to get tires that are still for 20" whieels but are narrower with same outside diameter. When you use a narrower winter tire, you raise the pounds per square inch at the contact patch and that helps the tires "bite" in snow and rain. An inch narrower than stock tires produces a useful improvement in winter traction (snow and rain/wet roads). Also, winter tires made for highest traction on ice, like Biizzak tires and similar types from other manufacturers, only have the first half of the tread compound in the "ice loving" compound. After you wear the tire half-way down, the rest of the tire has "conventional" rubber so those 'great on ice' winter tires won't be any better than any other winter tire once they are half worm.
With Cayennes you need to make sure the maximum load rating of each tire is at least as high as the maximum gross vehicle weight (fully loaded with fuel and 5 passengers plus some extra weight for "cargo") divided by 4. These are pretty heavy vehicles and tires made for sedans may not have enough load capacity for a loaded Cayenne so check that spec on the tires you have also. Tire Rack has some good tools for seeing what tire options you have if you change wheel diameter... or keep stock wheel diameter and change the width/profile numbers to get tires that are still for 20" whieels but are narrower with same outside diameter. When you use a narrower winter tire, you raise the pounds per square inch at the contact patch and that helps the tires "bite" in snow and rain. An inch narrower than stock tires produces a useful improvement in winter traction (snow and rain/wet roads). Also, winter tires made for highest traction on ice, like Biizzak tires and similar types from other manufacturers, only have the first half of the tread compound in the "ice loving" compound. After you wear the tire half-way down, the rest of the tire has "conventional" rubber so those 'great on ice' winter tires won't be any better than any other winter tire once they are half worm.