Can an XL tire be set to SL psi?

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Hello, I have an 05 Cadillac STS V8. The car came with SL 235/50R17 tires. I just put all new tires on the vehicle in the OEM size except they are XL with a load index of 100. The vehicle weighs 4,000 lbs and with myself, passenger, and some tools etc I am probably driving around at ~4,500 lbs. The factory door sticker says to run the tires at 30 psi front and rear. The XL tires state they have maximum load capacity at a maximum pressure of 50 psi. Obviously the load capacity of these tires far exceeds the weight of my vehicle.

Is it safe to run these XL tires at the factory recommended 30 psi or do the XL tires require a higher psi to be safe? I have been asking around and getting mixed answers. The shop who installed the tires for me said to run them at 40 psi, another post I found online said to stick with the factory 30 psi regardless of load rating, and another source said to never run a tire more than 10% lower than the maximum pressure rating which in this case would be 50-5= 45 psi. I am currently running them at 36 psi and they look and feel fine.

My main concern, and reason behind getting new tires, was traction. The vehicle is RWD with 320 hp and with the amount of rain we get in north FL traction is very important. My old tires, despite looking fine, were simply old (about 4 years), hard, and one size too small (decision of previous owner). On wet roads, anything more than 1/4 throttle and the rear end was all over the place, traction control could not keep up. The new tires seemed to have fixed this issue completely. I bring this up as when choosing the psi to run, traction and safety is my biggest concern. I don't drive much, the tires will probably be replaced due to age not lack of tread. I keep up on maintenance, always check psi, rotate tires, etc. The car mostly sits Monday thru Friday but I do make the occasional trip from Jacksonville to West Palm, about 300 miles each way.

Any input is much appreciated.

Ryan K
Orange Park, FL
 
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Xtra Load (XL) tires are reinforced so they can withstand more weight. And a higher max pressure is allowed when adding more weight. So considering it's a car with not alot of added weight then the factory PSI should be alright.
 

OVERKILL

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Hello, I have an 05 Cadillac STS V8. The car came with SL 235/50R17 tires. I just put all new tires on the vehicle in the OEM size except they are XL with a load index of 100. The vehicle weighs 4,000 lbs and with myself, passenger, and some tools etc I am probably driving around at ~4,500 lbs. The factory door sticker says to run the tires at 30 psi front and rear. The XL tires state they have maximum load capacity at a maximum pressure of 50 psi. Obviously the load capacity of these tires far exceeds the weight of my vehicle.

Is it safe to run these XL tires at the factory recommended 30 psi or do the XL tires require a higher psi to be safe? I have been asking around and getting mixed answers. The shop who installed the tires for me said to run them at 40 psi, another post I found online said to stick with the factory 30 psi regardless of load rating, and another source said to never run a tire more than 10% lower than the maximum pressure rating which in this case would be 50-5= 45 psi. I am currently running them at 36 psi and they look and feel fine.

My main concern, and reason behind getting new tires, was traction. The vehicle is RWD with 320 hp and with the amount of rain we get in north FL traction is very important. My old tires, despite looking fine, were simply old (about 4 years), hard, and one size too small (decision of previous owner). On wet roads, anything more than 1/4 throttle and the rear end was all over the place, traction control could not keep up. The new tires seemed to have fixed this issue completely. I bring this up as when choosing the psi to run, traction and safety is my biggest concern. I don't drive much, the tires will probably be replaced due to age not lack of tread. I keep up on maintenance, always check psi, rotate tires, etc. The car mostly sits Monday thru Friday but I do make the occasional trip from Jacksonville to West Palm, about 300 miles each way.

Any input is much appreciated.

Ryan K
Orange Park, FL
If the tires are the same size as OE, just run the placard pressure (30psi).

As Warstud noted, the XL just means that the tire is appropriate for higher load situations, which your application doesn't fall under. This isn't an LT tire where equivalent weight handling does in fact require higher pressure to match a P-Metric.
 

AZjeff

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Here's a good reply in an old thread from our resident tire expert CapriRacer about this:

Boy do I just love all the opinions being expressed - even the contradictory ones. First: While it may be true that there is a difference in the load table between P metric and Euro-metric (and even Japan-metric if you want to be more encompassing), FOR PRACTICAL PURPOSES, the differences are trivial. The load table is an estimate of the relationship between load carrying capacity and inflation pressure. But tires behave the way they behave and the differences in the load tables are more about the differences in the way each group did their calculations - and much, much less about differences in tires. FOR PRACTICAL PURPOSES, if the tire size is the same as original - and in this case it is - then the pressure listed on the vehicle tire placard is appropriate. Now some folks think adding a few psi (and we're talking 3 to 5 psi) is advantageous, and I used to be in that camp. But there have been changes in the way vehicle manufacturers determine the pressure listed on their placards, so I also think I have to change my recommended practice as well. I now use the placard pressure for any vehicle after about 2006. (yes, it varies) The fact that the tire in question is an XL version doesn't change the load vs inflation pressure relationship. And one last thought, but one that doesn't apply here: Be careful when replacing P type tires with LT type tires. LT type types require 15 psi more (for the same dimensions).
 
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Allow me to add that the load carrying capacity for an SL tire is the same as an XL tire, except the XL can be inflated to a higher pressure. In theory that means replacing an SL tire with and XL tire using the same pressure won't result in a change.

- BUT -

There will be more difference between makes/models of tires than between an SL and an XL. So there will likely be a difference, but the difference is because of the make/model.
 
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The standard load has loadindex 96= maxload 1565lbs AT 36psi.
The XL loadindex 100 = 1765lbs AT 42psi
50 psi is the max allowed cold pressure.
30psi for the SL stands for loadcapacity up to 99mph of 1352 lbs.
1352 lbs on XL needs 30.1 psi, so practically the same 30 psi, because the SL 30 psi is rounded up so most likely calculated for a bit lower load, fi 1325lbs/ axleload 2650lbs.


All calculated with the official european formula for all kind of tires since decades. And since 2006 also in US for P-tires.
Only if determined for higher speed, my calculation can be off.
 
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Allow me to add that the load carrying capacity for an SL tire is the same as an XL tire, except the XL can be inflated to a higher pressure. In theory that means replacing an SL tire with and XL tire using the same pressure won't result in a change.
What is the comparison between a SL tire and a HL tire?
 
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What is the comparison between a SL tire and a HL tire?
I was hoping to avoid this conversation for a couple of years, so I could see what developed. Oh, well!

The best information I have at this time is that HL tires are a separate type of tire, much like P type tires, but carry 10% more load (at the same pressure).

My understanding is that this was a request by European vehicle manufacturers who are converting existing fossil fueled cars to electric. The batteries are quite heavy and would result in the use of larger tires, but there isn't room!

Solution? Overload existing tires? Redesign the vehicle? Nope! Create a line of tires that isn't technically overloaded.

I think this is taking advantage of advances in technology which resulted in greatly more durable tires (less failures). This is the equivalent of running the tires 6 psi underinflated (Remember the Ford Explorer?). Everyone I talked to is very unhappy about this.

The good news is that improvements have been made before and the technology always moves forward. The bad news is that initially, this seems to be a step backwards (at least until the technology catches up!)

Do HL tires come in SL and XL? Unknown.

What about speed ratings? Again, unknown.

I suspect that the initial tire sizes will be unique such that you can NOT get the same size in a P type tire - and that would work in the highly regulated European environment. Not so much in the "cowboy" environment of the US.
 
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