Tire Load Index Question for the Experts
07-25-2014, 01:37 AM
#1
Rennlist Member
Thread Starter
Tire Load Index Question for the Experts
I need some tire loading education and help please. I have a '90 928 GT with OEM Porsche 19" Carrera Classic wheels off of a Cayman installed. Love the looks and have had them on the car for a while with no issues.
I'm in the process of changing out the rear tires to match the fronts, Michelin Pilot Super Sports. Rear wheels are 9.5"x19" et46. I have 265/30-19's on them right now and want the same size to try and keep the overall diameter close to original size for a 928 (i.e. close to 25"). I ordered the 265/30-19's from Discount Tire, but now they are saying they won't/can't mount them because their "new" computer program says my 928 needs a tire with a load index of 94 (1477 lbs.). The 265/30-19 Michelin Pilot Super Sports have a load index of 93 (1433 lbs.)
Here's where I get lost... The tag on the door jamb of my 928 says rear axle load is 2425 lbs. (2) of the Mich PSS's at 1433 lbs. each would be a load rating of 2866 lbs. which is obviously greater than 2425 lbs. rated for the car. Is there an additional safety factor for the loading that would make the PSS's inadequate in this size for my car?
One last part of the frustration... the tires currently on the rear are Kumho Ecsta SPT's in the exact 265/30-19 size that the PSS's that I want to put on. They have the same load index (93) as the PSS's, and Discount Tire installed them!!! They said they know that, but that was before their computer system update, and they can't install that size now.
Thanks for listening, any help in educating me where I'm not understanding the problem would be greatly appreciated.
I'm in the process of changing out the rear tires to match the fronts, Michelin Pilot Super Sports. Rear wheels are 9.5"x19" et46. I have 265/30-19's on them right now and want the same size to try and keep the overall diameter close to original size for a 928 (i.e. close to 25"). I ordered the 265/30-19's from Discount Tire, but now they are saying they won't/can't mount them because their "new" computer program says my 928 needs a tire with a load index of 94 (1477 lbs.). The 265/30-19 Michelin Pilot Super Sports have a load index of 93 (1433 lbs.)
Here's where I get lost... The tag on the door jamb of my 928 says rear axle load is 2425 lbs. (2) of the Mich PSS's at 1433 lbs. each would be a load rating of 2866 lbs. which is obviously greater than 2425 lbs. rated for the car. Is there an additional safety factor for the loading that would make the PSS's inadequate in this size for my car?
One last part of the frustration... the tires currently on the rear are Kumho Ecsta SPT's in the exact 265/30-19 size that the PSS's that I want to put on. They have the same load index (93) as the PSS's, and Discount Tire installed them!!! They said they know that, but that was before their computer system update, and they can't install that size now.
Thanks for listening, any help in educating me where I'm not understanding the problem would be greatly appreciated.
08-13-2014, 01:32 AM
#2
Rennlist Member
Thread Starter
A little surprised I've gotten no response here... Damon?
But anyway I have Victory!!! Went to another Discount Tire in north Scottsdale and bought the tires, brought in the wheels loose, and had them mount the new tires on the wheels no problem. Just took them back home, cleaned everything up and mounted them on the rear of the GT. Gee, I hope they work OK...
They knew exactly what I was doing and why, and were just as frustrated with their liability minions as I was.
The guys at the store told me they have a lot of "fun" with the tire loading index they are stuck with on their computer system. Apparently basically identical vehicles like a Yukon and Escalade can't have the same larger tires and wheels installed...
Now will be very interested to see how well the Michelin Pilot Super Sports wear, one of the reasons I got them was their reported excellent (relatively) tread life. The Kumhos I replaced gave me 25k miles, not bad for the rears, high performance summer tires, and somewhat of a heavy foot... I will say the right rear was a "little" past the wear bars...
But anyway I have Victory!!! Went to another Discount Tire in north Scottsdale and bought the tires, brought in the wheels loose, and had them mount the new tires on the wheels no problem. Just took them back home, cleaned everything up and mounted them on the rear of the GT. Gee, I hope they work OK...
They knew exactly what I was doing and why, and were just as frustrated with their liability minions as I was.The guys at the store told me they have a lot of "fun" with the tire loading index they are stuck with on their computer system. Apparently basically identical vehicles like a Yukon and Escalade can't have the same larger tires and wheels installed...
Now will be very interested to see how well the Michelin Pilot Super Sports wear, one of the reasons I got them was their reported excellent (relatively) tread life. The Kumhos I replaced gave me 25k miles, not bad for the rears, high performance summer tires, and somewhat of a heavy foot... I will say the right rear was a "little" past the wear bars...