Correct tire size question

[KRAM36]

Originally Posted by Topless

Yes, mount some fresh tires ASAP because 12 yr old tires suck! Ideal sizes for those wheels on a 986 are 235/40/18 and 265/35/18.

Pretty fun discussion on tire diameter differences though. "Twitchiness"??

All 987, 997, 981, 991 run 1" smaller diameter in front than the rear. It adds a little rake to the car so there is more weight on the front tires. This helps to generate excellent car balance in the corners. The idea that all these cars are "twitchy" because of the different diameter has never been discovered until now.

If your car feels twitchy, it needs an alignment.

Well you learned something today again then. On a alignment for street car, the tire rotation makes a big difference when you decide to go for a spirited drive. No my car does not need an alignment as I can fell the twitchyness changing the front tire to a smaller faster rotating speed.

People that race, align their cars much different then street cars. Alignments good for race cars are not good for street cars, if you want to have proper tire wear.

"All 987, 997, 981, 991 run 1" smaller diameter in front than the rear."? You are completely wrong in this statement.

[Topless]

Originally Posted by KRAM36

Well you learned something today again then. On a alignment for street car, the tire rotation makes a big difference when you decide to go for a spirited drive. No my car does not need an alignment as I can fell the twitchyness changing the front tire to a smaller faster rotating speed.

People that race, align their cars much different then street cars. Alignments good for race cars are not good for street cars, if you want to have proper tire wear.

"All 987, 997, 981, 991 run 1" smaller diameter in front than the rear."? You are completely wrong in this statement.

Negative ghostrider, stock 981 Boxsters typically run 26" diameter in front and 27" diameter in rear. I ride right seat in a LOT of 987/997/981/991 cars at the race track as an instructor. No twitch, no unusual tire wear as long as the alignment was set up for the type of driving they do.

I drove my street 986 for 10 years and 100 track days experimenting with a lot of different tire sizes, no twitch unless I had too much rear sway bar.

Here are stock sizes for a 2013 Boxster. Note the difference F/R in diameter and revs per mi. Different sizes, no twitch.
https://www.tirerack.com/tires/tires.jsp?tireMake=Bridgestone&tireModel=Potenza+RE-71R&frontTire=345WR8RE71R&rearTire=645WR8RE71RXL&vehicleSearch=true&fromCompare1=yes&autoMake=Porsche&autoYear=2013&autoModel=Boxster&autoModClar=


My 2009 Cayman runs 25"F, 26"R as stock sizes.
https://www.tirerack.com/tires/tires.jsp?tireMake=Michelin&tireModel=Pilot+Sport+4S&frontTire=34YR8PS4SXL&rearTire=64YR8PS4SXL&vehicleSearch=true&fromCompare1=yes&autoMake=Porsche&autoYear=2009&autoModel=Cayman&autoModClar=

Here are stock sizes for a 987.2 Carrera. 25"F, 26" R
https://www.tirerack.com/tires/tires.jsp?tireMake=Michelin&tireModel=Pilot+Sport+PS2&frontTire=34YR8SPTPS2XLN4&rearTire=64YR8SPORTPS2XLN4&vehicleSearch=true&fromCompare1=yes&autoMake=Porsche&autoYear=2009&autoModel=911%20Carrera%20Coupe&autoModClar=

I think somebody has been yanking your chain a bit KRAM.

[KRAM36]

Originally Posted by Topless

Negative ghostrider, stock 981 Boxsters typically run 26" diameter in front and 27" diameter in rear. I ride right seat in a LOT of 987/997/981/991 cars at the race track as an instructor. No twitch, no unusual tire wear as long as the alignment was set up for the type of driving they do.

I drove my street 986 for 10 years and 100 track days experimenting with a lot of different tire sizes, no twitch unless I had too much rear sway bar.

Here are stock sizes for a 2013 Boxster. Note the difference F/R in diameter and revs per mi. Different sizes, no twitch.
https://www.tirerack.com/tires/tires.jsp?tireMake=Bridgestone&tireModel=Potenza+RE-71R&frontTire=345WR8RE71R&rearTire=645WR8RE71RXL&vehicleSearch=true&fromCompare1=yes&autoMake=Porsche&autoYear=2013&autoModel=Boxster&autoModClar=


My 2009 Cayman runs 25"F, 26"R as stock sizes.
https://www.tirerack.com/tires/tires.jsp?tireMake=Michelin&tireModel=Pilot+Sport+4S&frontTire=34YR8PS4SXL&rearTire=64YR8PS4SXL&vehicleSearch=true&fromCompare1=yes&autoMake=Porsche&autoYear=2009&autoModel=Cayman&autoModClar=

Here are stock sizes for a 987.2 Carrera. 25"F, 26" R
https://www.tirerack.com/tires/tires.jsp?tireMake=Michelin&tireModel=Pilot+Sport+PS2&frontTire=34YR8SPTPS2XLN4&rearTire=64YR8SPORTPS2XLN4&vehicleSearch=true&fromCompare1=yes&autoMake=Porsche&autoYear=2009&autoModel=911%20Carrera%20Coupe&autoModClar=

I think somebody has been yanking your chain a bit KRAM.

Not negative. Just because a number goes from 26 to 27 does not make it a full 1", nor does your statement that ALL 987, 997, 981, 991 run 1" smaller diameter in front than the rear hold true.

I can tell the difference, you can't, no big deal.

Only person yanking chains is you. My Boxster is my DD and it's my only vehicle, it's been that way since 2014. I notice everything on my car when something changes. I personally do not like faster rotating front tires, it throws off the balance to me.

I'll will always recommend getting your tires to rotate as close as possible to the same speed. Nothing wrong or illogical in my recommendation and you're not going to change that.

[wrs986]

This car was so well cared for but the previous owner was not a “car guy” and I figured the tires would need to be replaced ASAP.
How far off will my speedometer be if I go from 265/40/18 to 265/35/18?
Right now it’s within 1 mph of my GPS. Is the speedometer reading taken from the rear or front tires? I’ll run down to tire rack next week and replace the Potenzas. What was oem for this car?

[PaulE]

Originally Posted by wrs986

This car was so well cared for but the previous owner was not a “car guy” and I figured the tires would need to be replaced ASAP.
How far off will my speedometer be if I go from 265/40/18 to 265/35/18?
Right now it’s within 1 mph of my GPS. Is the speedometer reading taken from the rear or front tires? I’ll run down to tire rack next week and replace the Potenzas. What was oem for this car?

The speedometer reading comes from averaging the abs speed sensors from all 4 wheels I believe. I read it on the internet so it must be true! If you use the stock 18 inch tire sizes your speedometer will read about 2-3 mph higher than what a mobile phone GPS speedometer app is showing. There is an EU regulation or German law that fines auto manufacturers for all cars they sell whose speedometers read lower than actual speed. We've owned 1 Audi, 3 BMW's and 1 Porsche and that's always been our speedometer experience with German cars. And then there is a US law that requires all auto manufacturers to have accurate odometers so the warranties don't run out sooner than they should. So with the right sized tires your speedometer is going to read a little higher than actual speed and your odometer is going to be accurate.

[KRAM36]

You and Topless both got owned and now you're just posting crap.

wrs986 go with the 235/40/18 front and 265/35/18 rear and you will be very happy.

[maytag]

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Just deleted my reply..... go ahead; own away. I'm out.

Sent from my SM-G970U using Tapatalk

[JayG]

All I can say is Topless knows what the F he is talking about and has the experience very few here will ever have.
Come out and drive with him and see who owns who

If you don't believe me talk to a few hundred PCA Zone 8 members that know him as well as his knowledge and skill and they will also confirm he knows his stuff.

Drop mike

[TeamOxford]

Bueller (KRAM)? Bueller (KRAM)?

Just waiting.........

TO

[KRAM36]

Originally Posted by Burg Boxster

[cough] horsesh_i-t [cough]

And I don't mean switching from summer to winter as you tried to squirrelgoat with earlier... )

Kiss my ass. I can tell the difference ,,I,,

Originally Posted by JayG

All I can say is Topless knows what the F he is talking about and has the experience very few here will ever have.
Come out and drive with him and see who owns who

If you don't believe me talk to a few hundred PCA Zone 8 members that know him as well as his knowledge and skill and they will also confirm he knows his stuff.

Drop mike

Topless know what he is talking about. Mike drop? I know what I'm talking about also .FO Mike drop ,,I,,

[Geof3]

Popcorn anyone?