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Old 08-08-2012, 07:54 AM   #15
Bex
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Tim: Who knew the tire rating was as easy as looking at the tag sitting on the end of the door? Not me, thats for sure! In my continuing search for answers, I found this:
Tire size calculator
And also some info from dieselplace forum suggests that a taller tire will be less stable, not that I think that will be noticeable with the two tires I am comparing, especially as one is likely stiffer than the other.
Thought I would post the link as other might find it useful.

Bex
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Old 08-08-2012, 03:47 PM   #16
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Tim, I'm not finished yet!
Looks like we were pretty much all right.
The SL rated tire cannot be put on my truck even though they can take the loading. Because the truck calls for D rated, thats what HAS to go on it, legally. The designation is something called Euro Metric and is making its way across the pond to North America and is in light of many trucks being used more as passenger vehicles and less for load carrying and towing. Euro Metric tires of the same size give a better ride quality at the expense of load carrying capability.
I also just came across why I think the PO put 245/75/16's on the truck. If I read this right: Gearing Up for Taller Tires! Superlift www.superlift.com
Its to give more towing capability by effectively changing the gear ratio by having a larger tire. The expense is fuel economy. So by putting the stock tires back, I should be able to gain in MPG (and every little helps) Funnily enough, I can only get an E rated 225/75/16, no D's so I am back to paying more for the tires, but not as much as the 245/75/16 that are currently on there.
Wow, what a saga.
Now all I have to do is change my order
Thanks everybody for the awesome conversation, I really appreciate it!

Bex
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Old 08-08-2012, 04:22 PM   #17
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Just a quick note; 245/75's are larger in diameter than 225/75's. So, by switching from 245's to 225's, you will be putting smaller diameter tires on your truck. This will effectively increase your numerical gear ratio, with a resultant increase in engine RPM at any given speed. The end result could be slightly lower gas mileage.

For example, if you are currently getting 12 mpg on 245/75x16 tires, switching to 225/75x16 tires will increase your engine RPM'S by around 4% and may result in a decrease in fuel economy by about the same percentage, to around 11.5 mpg. However, the slightly lower gear ratio will improve climbing power on hills and engine braking on long downgrades.
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Old 08-08-2012, 07:04 PM   #18
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Thanks Phoenix. I don't begin to understand that stuff but do check MPG's, so real world test will tell me whats happening. I obviously read the article the opposite to what you have explained
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Old 08-08-2012, 07:08 PM   #19
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You really know how to do your research Bex. As for going to the E rated tires you are really not giving up anything except possibly a few more dollars as long as you inflate properly. Phoenix makes a good point about the 245/75R16 tires being taller in diameter than the 225/75R16 but another consideration is the aspect ratio. the 75 number in the middle of the tire size is known as an aspect ratio and defined as the ratio of height to width when mounted on a rim of known standard size. what this means in the real world is that the tire is 75% as tall rim to tread as it is wide at its widest point-not across the tread. this means that the 245 tire is both taller and wider than the 225 resulting in greater rolling friction. Having sold tires and repaired vehicles for 18 years I can say with some authority that going to a larger tire does not always equate to greater mileage. In fact in many cases owners are greatly surprised to find that they burn more fuel to produce the rpms necessary. Sometimes it works and sometimes not.
sometimes its easier to just go with the flow
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Old 08-09-2012, 07:02 AM   #20
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Taller tires tend to mean greater rolling resistance, so mpg increases are not likely but for those who don't do anything but highway. They also increase the load on the wheel bearings and brakes are less effective.

Stock sizing and load index really is the way to go.

Note, also, that the dual rear wheel loadings are not the same, per tire, as with single wheel. They are downrated, each, somewhat (though the total is obviously higher; the GAWR).

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Old 08-09-2012, 07:30 AM   #21
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Research, sometimes I get the "paralysis from analysis" syndrome and can't make a decision. I spent an hour in the tire shop yesterday explaining what I learned here because the assistants just didn't know what I was talking about (they were supposed to have been trained).
The next closest pricing though was $1700, so I HAVE to stick with these tires from this shop and I know they are good tires, I have had them put on my two cargo vans for the last 5 years. They are made by Cooper Tires, if that means anything to anyone.
The aspect ratio thing comes into play on a duallie of course. I am hesitant to go with a wider tire although I do have spacers. Would there be a benefit on a duallie to having wider tires? I know duallies are not as good as a SRW truck in mud and snow (unless you have some weight on them) is wider better in this case?
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Old 08-09-2012, 07:48 AM   #22
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Research, sometimes I get the "paralysis from analysis" syndrome and can't make a decision. I spent an hour in the tire shop yesterday explaining what I learned here because the assistants just didn't know what I was talking about (they were supposed to have been trained).
The next closest pricing though was $1700, so I HAVE to stick with these tires from this shop and I know they are good tires, I have had them put on my two cargo vans for the last 5 years. They are made by Cooper Tires, if that means anything to anyone.
The aspect ratio thing comes into play on a duallie of course. I am hesitant to go with a wider tire although I do have spacers. Would there be a benefit on a duallie to having wider tires? I know duallies are not as good as a SRW truck in mud and snow (unless you have some weight on them) is wider better in this case?
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Old 08-09-2012, 12:10 PM   #23
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The http://www.tirerack.com/tires/tires....omCompare1=yes price for six Michelin LTX M/S, load range E tires in size 225/75x16, is $1,004, which includes a $70 rebate (for four tires). This doesn't include shipping, or mounting and balancing; but even so, $1,700 for Cooper tires seem pretty high. Just my opinion, but I'd shop around a little. Do you have Discount Tire, Costco, WalMart/Sam's Club, etc. near you? There is enough difference in price to make a day trip worthwhile.

Others may provide better insight, especially since I have never owned a dually pickup, but I would think with four drive wheels in the back, wider tires may be unnecessary. Also, 4WD would even strengthen this argument.

As an aside, if Michelin and Cooper tires were the same price, I'd get the Michelins; but that's just my preference.
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Old 08-09-2012, 05:52 PM   #24
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We have a Costco and Walmarts but the tire bays in WM are run by KalTire locally, I checked Costco, the Michelin LTX are $243.00. I guess thats the result of living in an area that about 60-80 percent of vehicles are trucks.
I agree regarding the Michelin choice. What I am getting is the Canadian Tire "own brand" tires, made by Cooper and they are $134.90 each, so a pretty good price for E rated 85k KM warranty. The set for $1700 was Toyo tires from OK tire.
From what I have read, a duallie gives less traction than a SRW truck, even with 4WD.
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Old 08-09-2012, 06:01 PM   #25
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Actually the aspect ratio can become critical in the case of dual rear wheels. Picture it this way, the bigger and wider the tires are the closer together they become in the space between them. this space is critical for proper cooling of the tires by air flow. Worst case scenario is if they actually touch. When this happens heat builds up very quickly and a blowout is inevitable. Even if there is a gap when installed the sidewalls flex under load and even more due to road conditions so what might seem safe originally can become unsafe very rapidly. Still sounds like you are doing the right thing so this is more in the way of information
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Old 08-22-2012, 08:24 AM   #26
Bex
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I ordered tire. Still not arrived and thats now 3 weeks. One thing I was wondering was about the rims.
Can I get the smaller tire onto the existing rim?
Remember I am going from 245/75/r16 back to the stock 225/75/r16
Thanks!

Bex
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