I am neither tracking, racing, or driving this car to its extreme potential. I would like to equip it with the year round Continental DWS Ultra High Performance tires. However, there is a glitch.

While the Continentals have a 245/35-20 tire for the front, they do not have a 305/30-20 tire for the back. They do however have a 315/35-20 tire that is, for all intents and purposes, the same size as the 305/30-20. Here are some spec.:


305/30-20 315/35-20


There is a speedometer reading difference due to the 315/35-20s being a bit taller. A superimposed picture looks like this.

Side by side Overlay



305/30-20 315/35-20 Difference

Will these rear tires, in combination with the regular size front ones, create a handling problem? These tires have had great reviews at Tire Rack and I have used in a number of other, non sport, cars.

Thank you,

cai

 

Buy a BMW... no all seasons on my 911. Plus the sizing difference will be an issue.

 

I've seen this cause strange warnings with other cars (tire rotation sensors etc), so I wouldn't recommend it - but in the end it's up to you.
You could also pull into your local (performance) tire shop and see what they say.

 

Thank you for your replies. I spoke to the service manager at my local Porsche dealer and he did not recommend the change simply because as both of you have said, this could become an issue due to the AWD nature of the car.

I may opt to drive on winter tires all year round. He said that the only drawback to that is that they will wear out more quickly during the summer. We also agreed that the cost of changing a set of tires twice a year would about even out having to get new tires more often. Less hassle too.

Does anyone here drive on winter tires all year round? What is your experience?

cai

 

I have a second set of wheels with winter tires. Actually, I have a second extra set for track use, also.

 

2013 4S
I run 20's in the summer and 19's in the winter.
The display gives me the option to select 20 summer or 19 winter.
Doesn't ask 305/30 or anything like that.
Jus sayin...

 

And this summer I bought a set of 19's for summer and put them on my winter wheels.
And just selected 19 winter tires on the display.
No problems thru 10k miles...

 

5.4% difference in OD is NOT 'for all intents and purposes' the same size, it's not even close. It's critical on AWD cars that the tires all have the same OD, otherwise the car thinks that the tires that are turning faster are slipping. The car tries to feed more power to the wheels it thinks aren't slipping, creating tremendous wear on the differential.

Plenty of information out on the internet on AWD and mismatched tire sizes. What you are suggesting is a VERY bad idea.

I don't believe there are any UHP all-seasons made in the right sizes for a 991.

 

If you look at the 996 Turbo forums you will find much information about having too big a front/rear tire size difference from normal causing front differential problems. I would think being over 5% out of range on the front could cause problems with the front differential as it does on the 996 Turbo.


As far as winter tires year round why have a 991 or any sports car if you can't drive it the way it was intended which of course means proper summer tires whenever possible. This one reason is why Porsche has the Macan. It gives you almost 911 handling/performance year round.

 

I think that all of you agree on not using the Continental DWSs because of the size difference. I also agree that it would be optimum to have two sets of tires, winter and summer. However, I do not have the space to keep the extra tires and I have to try to explore other solutions. I am not so sure that I would be missing a lot of the car's fun potential by using performance winter tires all year round. What I can say is that these Pirelli Zero summer tires are really, really bad when the temperature dips below 40 degrees F.
Upon looking at the Tire Rack test comparisons of the Michelin Pilot Super Sport and the Pirelli Zero tires, I can see that the Michelin, at least on paper, is a superior tire for encountering the odd rain and water on the road. My short experience with the Pirellis has not been very good. They seem to hydroplane a lot.
Again, I would like to hear from anyone that has experience using winter tires year round.

Thank you.

 

Winter tires, true winter tires, while fine in the winter/cold would likely suffer greatly when driven in higher temperatures in the warmer months. The tires would likely overheat or become so soft they'd wear out in no time.

If all you are facing is 40F temperature or below if you can why not just park the car and drive something else? When I lived in the mid-west I kept my Boxster on summer tires and drove a VW Golf TDi on the really bad days. When the roads were clear and dry I took the Boxster out on its summer tires. 'course, I cooled my jets but did exercise the car.

If you have to drive every day in the winter in all kinds of weather my experience doing this on summer tires -- I spent almost two months in the winter of 2002 with just my Boxster before I bought the VW -- is don't. Get a set of winter tires and wheels. Don't know what to tell you about the storing of these in the off season. You'll just have to find a way/place to store these. But you really should have them on the car in the winter and off during the summer.

 

Stick with OEM Pirelli's. Those are researched and designed for a reason. 4S awd system is very complex and any thing other tha OEM have a chance of over burdening PDK and awd system together. Also don't recommend with sticking with one winter set all year round. Sure they wear out faster but are also heavier, harder with harsher ride. Buy a separate set of winter wheels and tires. You're driving $100K+ car, think about getting another set.

 

Wouldn't that be a third set then

BTW those look pretty sweet !!

 

When it warms up right when I'm about to switch to my summer wheels/tires I find the winter tires are very soft and mushy feeling and that's when it gets into the 50's. I'd hate to see how they feel when it is summer weather.

It is strange because in the cold temps the winter tires feel harder, grip really well and retain that sporty feel.

If I were you I'd look into a place that would allow you to store an extra set of wheels/tires. Maybe you could get a very small storage unit or store them at a friends or relatives ... they really take up very little room.

Maybe your local Porsche dealer can store them for a small fee.

 

Ummm. As far as my wife knows, there are only two sets. I swear, just two, honey.