Load rating diff 245 vs 255 Michelin Pilot Sport

[ledslinger]

Considering Michelin Pilot Sport A/S 3 for my 2000 base Mustang on 17 X 9 wheels. The widest tire is 255 40 17 rated for 1477lbs @ 44 psi. The next smaller size is 245 45 17 rated at 1706 lbs at 50 psi.

Why the difference in load and psi between these tires that are nearly the same size? Should this load and psi difference be a factor in deciding which tire?

 

[Quattro Pete]

What is the load rating of the OEM tires for your car? You should just make sure that any replacement tire you get has at least the same load rating or higher.

The reason for the 245/45 having a higher load rating is most likely due to the fact that it has taller sidewalls - more rubber between the road and the rim = more carrying capacity, but maybe an expert such as Capri can expand on this and correct me.

 

[Colt45ws]

The max pressure has no effect on the load. Those will be rated for max load at either 35psi or 36 psi, unless it is an Xtra Load tire in which case max load will be at 41 or 42 psi. Depending on if they are P-metric or Euro-metric.
Like above, what is the load rating of the factory tire?
1477lbs would be a load index of 94 and 1709lbs would be a load index of 99.
Im too lazy to look, but I think the 255/40/17 tires are standard load 94 index and the 245/45/17 are Reinforced (XL) 99 index.
If true, that would be why there is such a large discrepancy.

 

[dparm]

Get the same load index or higher than what's on the car now. It's as easy as that.

 

[bdcardinal]

245/45/17 was the factory 17" size for that year Mustang. Although since you have a 17 x 9 I would be looking more at a 275/40/17 since that is what the Terminators had which came with that size wheel stock.

 

[ledslinger]

Originally Posted By: bdcardinal
245/45/17 was the factory 17" size for that year Mustang. Although since you have a 17 x 9 I would be looking more at a 275/40/17 since that is what the Terminators had which came with that size wheel stock.


The Pilot Sport A/S 3 isn't made any bigger than 255 in 17". Both sizes are above the original tire load rating.

 

[Quattro Pete]

Any reason why you insist on this particular tire model/category?

I mean, they'll be pretty useless in the winter anyway, especially on an RWD car, so you might as well look into proper summer tires instead.

 

[dparm]

Originally Posted By: bdcardinal
245/45/17 was the factory 17" size for that year Mustang. Although since you have a 17 x 9 I would be looking more at a 275/40/17 since that is what the Terminators had which came with that size wheel stock.



275 on a 9" wheel is not a very good fit. On a 10" wheel I'd say yes, but for 9" I would stick with 245 or 255.

 

[Quattro Pete]

Originally Posted By: Colt45ws
and the 245/45/17 are Reinforced (XL) 99 index.
If true, that would be why there is such a large discrepancy.

Good catch. The 245/45/17 is in fact XL-rated, which means reinforced sidewalls, as you noted. That right there explains it.

 

[Colt45ws]

Originally Posted By: Quattro Pete
Originally Posted By: Colt45ws
and the 245/45/17 are Reinforced (XL) 99 index.
If true, that would be why there is such a large discrepancy.

Good catch. The 245/45/17 is in fact XL-rated, which means reinforced sidewalls, as you noted. That right there explains it.

Hah! Yeah, I suspected as much. My bigger 255/45R18 are 99 index SL so when I saw a smaller tire with the same rating my guess was that it was XL.
That would make them a 95 index standard load. Which means the 255/40R17 being a 94 are a lower load index than the stock 17" selection according to bdcardinal.
However! Its likely that the Mustang didn't call for full pressure in those tires.
If for example it wanted 30psi with the factory 245/45R17 then a simple adjustment to 32psi would correct the load rating.
What does your door placard actually say as far as size and pressure?

 

[bdcardinal]

Originally Posted By: dparm
Originally Posted By: bdcardinal
245/45/17 was the factory 17" size for that year Mustang. Although since you have a 17 x 9 I would be looking more at a 275/40/17 since that is what the Terminators had which came with that size wheel stock.



275 on a 9" wheel is not a very good fit. On a 10" wheel I'd say yes, but for 9" I would stick with 245 or 255.


Ford used it with no issues. I have a set of Steeda Ultralites and Konig Villians for my 95 both in 17 x 9 and both have 275/40/17 with no issues whatsoever.

 

[dailydriver]

Originally Posted By: bdcardinal
Originally Posted By: dparm
Originally Posted By: bdcardinal
245/45/17 was the factory 17" size for that year Mustang. Although since you have a 17 x 9 I would be looking more at a 275/40/17 since that is what the Terminators had which came with that size wheel stock.



275 on a 9" wheel is not a very good fit. On a 10" wheel I'd say yes, but for 9" I would stick with 245 or 255.


Ford used it with no issues. I have a set of Steeda Ultralites and Konig Villians for my 95 both in 17 x 9 and both have 275/40/17 with no issues whatsoever.


Many, many, GM f bodies did the same as well, and even beat supposedly superior, and wider wheel to tire width equipped, Teutonmobiles around road courses using that 275/40-17 ona 9" wide wheel setup.

 

[ledslinger]

Originally Posted By: Quattro Pete
Any reason why you insist on this particular tire model/category?

I mean, they'll be pretty useless in the winter anyway, especially on an RWD car, so you might as well look into proper summer tires instead.


QP - What do you recommend?

 

[Quattro Pete]

When it comes to performance summer tires, Michelin Pilot Super Sport has a faithful following here in BITOG. If you have a powerful engine that has trouble holding onto the pavement, this is the tire to get.

 

[SteveSRT8]

Originally Posted By: Quattro Pete
When it comes to performance summer tires, Michelin Pilot Super Sport has a faithful following here in BITOG. If you have a powerful engine that has trouble holding onto the pavement, this is the tire to get.


Practically an understatement.

My car has a bit of a traction issue, and a very large appetite for tires. After seven sets of rubber I finally bit the bullet and ordered my PSS tires.

Truly amazing. Quiet, smooth riding, amazing in the dry, even MORE amazing in the wet. And a 30k mile warranty. I have never gotten more than 19k miles on any brand used yet including Toyo, Goodyear, Hankook, etc...

 

[CapriRacer]

Originally Posted By: ledslinger
Considering Michelin Pilot Sport A/S 3 for my 2000 base Mustang on 17 X 9 wheels. The widest tire is 255 40 17 rated for 1477lbs @ 44 psi. The next smaller size is 245 45 17 rated at 1706 lbs at 50 psi.

Why the difference in load and psi between these tires that are nearly the same size? Should this load and psi difference be a factor in deciding which tire?


First, the 255/40R17 is a Standard Load (SL), and the 245/45R17 is an Extra Load (XL). That is why both the loads and the pressure are different.

If the 245/45R17 was an SL, the load carrying capacity would be 1521# - pretty close to the same.

Oh, and Tire Rack recommends the 245/45R17, and not the 255/40R17. i think that means the 255 would rub.

Discount tire also omits the 255/40R17.

 

[ledslinger]

Originally Posted By: CapriRacer
Originally Posted By: ledslinger
Considering Michelin Pilot Sport A/S 3 for my 2000 base Mustang on 17 X 9 wheels. The widest tire is 255 40 17 rated for 1477lbs @ 44 psi. The next smaller size is 245 45 17 rated at 1706 lbs at 50 psi.

Why the difference in load and psi between these tires that are nearly the same size? Should this load and psi difference be a factor in deciding which tire?


First, the 255/40R17 is a Standard Load (SL), and the 245/45R17 is an Extra Load (XL). That is why both the loads and the pressure are different.

If the 245/45R17 was an SL, the load carrying capacity would be 1521# - pretty close to the same.

Oh, and Tire Rack recommends the 245/45R17, and not the 255/40R17. i think that means the 255 would rub.

Discount tire also omits the 255/40R17.


275 40 fronts and 315 35 rears are commonly installed on Mustangs without rubbing issues.

 

[ledslinger]

Here is a chart of tire sizes for Mustangs that shows up to 275 40 in 17"

http://www.automobile-catalog.com/tire/2000/1511000/ford_mustang_coupe_3_8l_v-6_automatic.html

 

[Quattro Pete]

But why do they show this "WARNING: wide tire!" disclaimer?

 

[gaijinnv]

Originally Posted By: Quattro Pete
But why do they show this "WARNING: wide tire!" disclaimer?


Seems self-explanatory:

(WARNING: any wider tires could not fit the fenders and arches, always check it earlier (!) and in most cases you will need new rims, of course)

HTH