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Old 10-30-2013, 09:01 AM
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Safe Tire Selection

I am needing to replace all four tires on my rig. I have an OEM rim for my 2005 F350 PSD SRW, which is 18x8. I've had (2) previous tires upgrades, with this one being my third, since I've moved on from stock (275/65 18). The first upgrade I went to was the Mickey Thompson ATZ sized in 305/70 18", with no issue. Then followed this with the Dick Cepeck FC ll, in the same size (305/70 18"). I've experienced a bit of rub on the control arm but nothing to worry about as I also have had a Donahoe Racing 4.5 lift. Both the Mickey Thompson and Dick Cepeck tires I've owned have specs stating rims size ranges between 8"-10" are adquate. However, on a visit to America Tires, they want to install their Falken Rocky Mountain sized in 325/65R 18" and from what I read on the spec sheet, it asks for rim sizes between 9"-12". I then looked at another size offering in the same brand with 35x12.50 18" stating rim size ranges from 8.5"-11". My question is am I safe with being a little over the OEM spec I currently have in the 18x8? Rim upgrade is not an option for me at this time due to $ constraints; however, I do tow and this includes long miles of summer trips. Need some advice.
Thank you.
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Old 10-30-2013, 09:37 PM
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Stay within the size limits, the side to side will be like a knife on a hot air balloon.
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Old 10-31-2013, 03:33 AM
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There's no way you can clear 325s on a stock truck
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Old 10-31-2013, 05:30 AM
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Each truck is a little bit different, my 05 cleared 325 65 toyo AT's and then 35's with a level kit. The went to 37's a icon 4.5 all cleared.
It totally depends on the wheel offset, some have stated they run 36's on stock.

The mfg's know their sidewall construction and how each will flex under GVWR which is what they have to plan you will tow, because Ford says you can.

Why upgrade when you liked the MT's go back with them, they now have a ATZ P3 version that is even better than the original ATZs.

Or Toyo AT II's would be my next choice.

Denny
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Old 10-31-2013, 06:25 AM
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agreed, its all on the wheel width and offset along with the side wall flex.

a narrow wheel and a -24 offset can net a taller tire.

I call em pizza cutters.
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Old 10-31-2013, 07:28 AM
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Thanks guys for the input. I went ahead and upgraded to an aftermarket rim sized 18x9, with -12mm offset. I'm running 305/70 right now and I had them running on the stock 18x8 rim on both MT and DC tires, whose specs are identical listing compatibility with 8"-10" rims. I'm happy with 35's for now, but with this offset and increase in rim diameter, are there any tires out there in a 36" for this rim and fit properly with this offset? I would like to hear from some of you guys out there with the same or approximately close offset numbers with a 18x9 and 36" tires with pics, if possible. The reason why I went to a wider rim was to give me more options for tires should I need them, especially in load "E" tires.
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Old 10-31-2013, 09:21 AM
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I am running 35x12.5x18 Toyo M/T's on 18x9 0 offset wheels with 5" backspace on a 4.5" RC lift. The only place they are close to rubbing is the back edge of the fender and fender liner when turning. The biggest thing that will make you not clear is offset. I would be able to clear more if I didn't have a 5" backspace. I was thinking of doing 37's but they won't fit with a 5" backspace.
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Old 10-31-2013, 04:24 PM
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You need a + 18 Offset with 9" wheels to keep the stock back spacing and tire inside the fender.


+ Offset is actually pulled in not pushed out.

- Offset 12mm and 35's might and for sure 36's will rub on the inner fender which you can trim or zip tie back to the fender weld point.

Denny
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Old 11-01-2013, 08:53 AM
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I was wrong on the -12mm offset. I'm not exactly sure on what the offset is but I did tell the Discount Tire (DC) guy what size tire I was currently running 305/70 18, which fit on my 18x8 rim. The OEM rim did well with riding sized tires with these measurements even though there was some rubbing on the control arm which I never felt but could see the wear marks the tire was leaving. Another guy there at DC as I mentioned wanted to install the 325/65 18 tire on there but those tires needed at least a 9" rim. My next question: currently I'm going to continue running the 305/70 18 tire for a bit; however, if I wanted to go to a taller tire say a 36" or close to it, what kind of offset would I be needing to fit a taller and perhaps wider tire with the 18x9 rim? I already have a 4.5 DR lift so I can clear the tires as the current 35"s clear with room to spare. Thank you.
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Old 11-09-2013, 08:29 AM
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I was wrong yet again (obviously not the first or last). The offset on the new rims are -12mm; 18x9, and they do not rub! I'm running 35x12.50 with no clearance issues. Rims sit very nice and do not stick out very much. I even repainted the inside of the control arms to see if the tires rubbed and "nope." They clear. I was somewhat disappointed that Dick Cepeck has discontinued the FC ll tire. I had to get the "new" Fun Country tire which appears to have a more aggressive tread and stands pretty tall and a lot tread on a meaty tire. We'll see how they perform. I kept two original FC ll tires on the truck since they have a lot tread left. No reason to buy all four tires if the originals still have plenty of meat left over. Thanks for all of your input and help. Much appreciated. Now my issue is to see if I might be eligible for a tire adjustment with the DC FC ll that had the tire separation. The tire has only approximately 20k miles on them and a little over two years old.
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