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Old 09-28-2011, 05:32 PM   #1 (permalink)
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Purchased new tires

I purchased new tires today. They're Goodyear Wrangler SR-A's.

The Continental CrossContact LX (LRR) was on my list, but the dealer said my size was out of stock with no est. return date. To boot, TireRack no longer lists it in 225/75R15, so I suspect that something is up with that.

Anyway, I think the SR-A is stock on some vehicles, and Consumer Reports ranked its rolling resistance to be excellent (although I don't know their methods). I suspect that it's the kind of tire that has low rr, but isn't technically considered "LRR."

My initial impression is that they are a lot stickier than my General Ameri GS60's, which had 35,500 on them when I prematurely changed them out. (One was pretty much near the wear bars, winter is coming and I just barely bought them in time for a GM rebate). I can definitely feel the resistance when accelerating. Maybe some of this is just new tire feel, since the tread is 11/32, but better traction in bad weather was what I wanted.

I also went down to 36psi from close to 40.

In a few weeks I'll have some data to look at for FE. I'm just hoping to stay above 23. Currently getting a little over 23.5 on my commute.

If FE drops I think it'll be that extra incentive to build the air dam and fog light covers, although I hope it doesn't.

Thanks for reading.

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Old 09-29-2011, 09:30 PM   #2 (permalink)
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When I put the new tires on my truck, I did a coastdown test at 32 PSI, then repeated the test at 47 PSI (sidewall maximum). The difference was dramatic.

I get excellent traction on snow and ice at the higher pressure. The only negative is rumbling and banging over tar strips.

Tires are Nokian WR size 235/75R15. This is 2% larger than stock.
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Old 09-29-2011, 09:55 PM   #3 (permalink)
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Try get your hands on a GPS for a couple days, use it to see your actual distance vs. your odometer readings. New tires = bigger overall diameter, generally.
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Old 09-29-2011, 10:01 PM   #4 (permalink)
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why low psi???

the difference between 36 and 40 is nothing,so why not 32?

I'd be at 44-47
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Old 09-29-2011, 10:31 PM   #5 (permalink)
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Good idea Bruce. I've got a Garmin, but never thought of using it for this application. I realize that tires of the same listed size can vary a little bit among brands. Plus, there's the tread depth factor. Surprisingly, engine rpm is very close at speed - too close to compare with a tach.

I changed pressure, because I want to get the best possible tread wear out of these. I know that many on here would say that max sidewall (or close to it) will not wear out the center of modern tires, but I need to quantify that for my own eyes before deciding. Plus, I can't seem to get myself a good tire pressure gauge. The local auto stores all have these Slime gauges that read bar and psi...but the psi measurement is barely legible!

I'm not sure if I can trust the chalk test for tire wear. Maybe I'll try it.

Mcrews, what may have jaded me is this: As of late, I had been experiencing some wheel hop in the rain. Maybe it was due to an empty bed or my tread level at the time. But in my mind I blamed it partially on the higher pressure, even if there may have been other factors. For this reason, I wanted to start out cautiously.

You're right though, JR, the difference is definitely there. I just don't know how much rr to attribute to the deeper tread versus the lower pressure.
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Old 09-29-2011, 11:30 PM   #6 (permalink)
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tire hop in the rain is caused by the rain not getting pushed thru the treads.....ie worn uot tires.
Despite what 'might seem' logical, a tire does not "blow up like a balloon'.
Yes, a 10psi tire is flat.
but a tire at 40 psi IS NOT bigger around than a tire at 36psi.
A tire at 40 psi is not curved or bulging in the middle.
First, it just cant happen. there are several steel belts.
second, by design, a tire's flexability is in the sidewall. not the tread.

What I trying to say is that your thought process is a little flawed.
Tires 'wear uot' by wearing against the road. by 'rubbing'. 36 or 40 will make no decernable difference in the life of the tire. BUT it will cost you mpg.

you really ought to review the vast number of posts on this topic.
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Old 09-30-2011, 01:58 PM   #7 (permalink)
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Alright, I think I'll look through some topics and see what I find. Don't get me wrong - I'd rather be at a higher pressure for longer coasts.

Since I only ran higher pressure on my generals for about 2,000 miles, I couldn't make any visual judgements on wear rate.

I should note that my alignment was off some. That got fixed when the tires were mounted.
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Old 09-30-2011, 09:49 PM   #8 (permalink)
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Going from 35 PSI to 40 PSI in my tires made NO noticeable difference in fuel economy. It DID make the ride more harsh. The rougher ride wasn't worth the unnoticeable difference in FE
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Old 10-01-2011, 11:59 PM   #9 (permalink)
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You may need to inflate closer to 44psi which is right around max Psi for most 15" tires. I generally run 50psi on my 15s (max rating of 44psi). This has dramatically increased the rolling distance on coast downs.

Comfort is ultimately more important so go with works for you. I quickly grew accustomed to the extra harshn.
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Old 10-10-2011, 10:56 PM   #10 (permalink)
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Well, first fill today with the new tires.

I got 24.4, which is well above my typical commute tank of high 23's.

Despite the rr observation above, I made one important driving change. There are two or three hills that I had been downshifting from 4th to 3rd to tackle (DWL style). Now I use a more open throttle position - although well above WOT - and climb them in 4th. No lugging at all.

I've also used 5th a bit more liberally, down to about 45 mph on flat ground.

It's just one fill, so I can't get overly excited, but it was nice to know that the tires did not adversely affect mpg. In fact, maybe I'm entirely wrong and they have lower rr.

Anyway, there's my update.

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