I'm going to be replacing my worn BF Goodrich A/T tires today at Discount Tire. They offer siping (small razor cuts in the tires to improve traction/longevity, supposedly) if I choose to have that done.

I'm thinking, though, that it will decrease the longevity of the tires, not increase it. Had it done on the original tires I'm replacing and now they're worn unevenly (mildly) in the middle of the tires, even though I've been real careful about keeping them at 35 psi. And I'm thinking they got worn that way because the centers of the tires were more spongy (weak).

So...I think I'll do one of two things: Either not get them siped or if I do get them siped, I'll decrease psi in them to 30 to get more even wear/longevity.

Right now, I'm leaning towards not getting them siped. I do live in snow country/Colorado, but I'm not at all convinced siping helps with much.

 

I wouldn't get them siped. The tire maker designed the tread to be as efficent as possible. If they thought extra little cuts would improce traction then I'm sure they would be doing it from the factory.

 

If they cut through the tread like a knife then the siping will help on roads, rocks etc because there will be enough traction to OPEN the cuts. On ice however there is minimal traction to do this. Factory siping as you probably noticed is actually small slots in the tread. That does help with on ice traction because of more biting edges.

As for increasing/decreasing PSI for longevity I call BS. The best way IMO to see what the optimal pressure for any vehicle is to chaulk the tires across the tread. Drive forward a bit on a totally flat cement etc surface. Take a look at the chaulk marks & see where they've rubbed off.
If they rub off on the middle of the tread you're over inflated, outside of the tread they're under inflated. What you're going for is the chaulk marks across the tread to wear off evenly = optimal tire pressure for those tires on that vehicle with that weight etc.

The easiest/most efficient way is to pump the tires up to factory recommended maximum PSI & work down. That way you're not constantly inflating the tires in a parking lot etc.

 

Thanks for the comments. I like the chalk suggestion. I'll try it.

I didn't get the siping done because in the end I think it's a gimmick used to jack up profits. And I agree: There's already some siping on the manufactured tires. And these tire manufacturers have put millions into research/testing. Why would they not do extra siping on their tires if it bettered tire performance.

Don't think I'll be using Discount Tire again. When I made the appointment to have the tires put on and showed up, they had already written me up for siping and for a "road hazard warranty" (for about $60). Told them no on both but I had to tell them specifically to remove those items, when in fact, they should have asked me first if I wanted them. It's pretty obvious they're just in the business of taking advantage of brain-dead/unsuspecting customers (probably a good forty percent of their customers, if not more).

 

Yeah that's sad companies resort to crap like that... ASK 1ST! Anyway, siping like the cut through process is ok for pavement, rocks etc. On ice it doesn't help & I have that siping on mine, same process.
The company screwed up on the tires I ordered (take-offs from another customer) I wanted the 32 x 11.5 BFG KM2's, they siped 32 x 11.5 BFG KM's for $30/tire. When I got to the company my company deals with (cheaper installation) I noticed they were different. They took off the $120 for siping so I kept the tires. So I know they don't help on ice & true siping (look at a winter radial) has hundreds of siping/material removed - not cut through. Plus a winter radial has a much different compound.
I'm glad you like the chaulk idea, it shows exactly what I spoke about & is different for every tire on every vehicle. It's truly the best way to see exactly what that tires PSI for that vehicle is best - a flat/even footprint!
Just make sure you chaulk each tire because the front & rear tires have different loads on them.
Post the results if you don't mind... It's interesting the difference you should see in PSI & what you figured was right.

 

Okay. Sure, I'll post a reply. Gotta find some chalk first, though. I'm gonna guess the PSI will be somewhere in the mid-twenties. So much for the car manufacturer's recommendations (35 PSI). Hmmm...actually, I do have chalk--a chalk line. So maybe I'll just snap a chalk line on each tire.

Interesting actually about PSI and gas mileage too. You'll get a ton of different opinions on the internet as to what the optimal PSI for gas mileage is, but I did a pretty extensive gas-mileage check one time on an old Olds Cutlass and was really surprised to find that there was no difference in gas mileage between 35 PSI and 25 PSI. None.

 

OK best gas mileage will be as hard as you can pump up the tire too = less rolling resistance.
Doing that you'll sacrifice ride comfort, handling, tire wear/longevity, safety & take the chance of popping a tire because you hit a speed bump too fast lol.
A flat footprint across the tire tread is the best of all the worlds, the "happy medium" if you will. Going beyond or below that means you'll sacrifice something by doing so.

I just wanted to see/hear what your chaulk line turned up for results.
Mid 20's for a PSI? That just sounds odd for a SUV tire, 235/70 etc, but we'll see.

 

Still haven't done the chalk thing. Too busy with other stuff at the moment, but I'll probably be getting to it soon (the Blazer's our second car, so it's still sitting idle).

On MPG/tire pressure: Yeah--I know what the theory is--less friction with higher pressures, and all that. But when i did the actual test (many years ago), the gas mileage was the same at 35 PSI and 25 PSI. I know it doesn't make any scientific sense, but that's how it came out. I was really surprised.

I have no idea where the pressure on these BFG A/Ts will be after I do the chalk adjustment. Was just wild-guessing at mid-twenties. We'll see.

I'll let you know.

 

Okay, I tried chalk today to find the highest PSI that would erase the chalk mark/line across the tread. I snapped a chalk line actually, though, instead of using a stick of chalk. Didn't work all that well; hard to read, etc., but I had to go down to about 25 PSI before it was all erased.

So anyway, I tested it another way: I used a putty knife to see if I could slip under the outer edges of the tires at the center/contact point with the cement. And even at 35 PSI, there was contact on both sides of the tires.

The bottom line is that it doesn't make sense that my previous set of the same tires (BFG A/Ts) were worn in the middle with the tires consistently inflated at 35 PSI, although i still think the siping I had done on those tires caused increased wear in the middle, where most of the weight was born, because of the sponginess (weakness) caused by the siping. Don't know, though.

Anyway, I have decided to run these new ones at 30 PSI this time instead of 35 PSI. Maybe that'll help some. We'll see what happens over the next couple of years.

 

Hey Hermit,
good to see a fellow mountain goat here on the forum. I worked part time for sears years ago in the tire shop. We used to get customers come in with siped tires complaining of premature tire wear and no noticeable improvement in traction. I think it is a sales gimmick, like the other guys said.

Tire pressures using the chalk marking is a pretty good idea. I'm gonna try it myself.