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smcrea's avatar
smcrea
Explorer II
Jan 26, 2015

Wheel Size

Hi Guy's,

I have one more question before I pull the trigger on my New Truck Factory build THIS WEEK!!.. Yes I need to order it this week on my F350 SRW Powerstroke 6 3/4' bed big cab :-)

We're planning a trip to the New England Area from San Diego during the kids summer holidays! :-)

The question is regards to the Wheel size and tires..

Before we begin, My wife and I REALLY like the look of the 20" Wheels.

I looked on the Michelin Website and it looks like here's the two options:

- LT 275/70R x 18E Max load 3640Ib @ 80
- LT 275/65R x 20E Max load 3750Ib @ 80

On paper it says that the 20" can handle more load.

From what I understand is that the 70R and the 65R refers to the ratio of the wheel size vs the height of the tire wall with all other things being equal. Therefore with the 20" wheel being 2" bigger then you would expect the ratio to be smaller IF the wall remains the same height.

So it looks like these are NOT low profile tires..
But what I want to confirm is that the wall is the same height between 18" and 20". Basically I have the same amount of air between the pot hole that I hit and the rim of the wheel.

Any other comments on this are very welcome!.. you guys are always so knowledgable! Seriously a part of all of you is going into this truck! LOL :-).. I'll post a photo when it arrived!

Thanks!

Steve
Tow Vehicles

15 Replies

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  • smcrea's avatar
    smcrea
    Explorer II
    Jan 27, 2015
    So far it seems to me that the only argument FOR 20" wheels is 'Looks' and it is undeniable that the 20" 'look cool'

    However there is a lot more parts to the evasion than looks especially if you use the truck for towing and rough roads.

    It looks like the sensible thing to do is go with the 18's

    Anyone going to scream NO!! ? :-)
  • smcrea's avatar
    smcrea
    Explorer II
    Jan 26, 2015
    Need-A-Vacation wrote:
    Larger wheel generally will give you a rougher ride. See if the dealer has couple trucks (2500 or 3500srw-any motor) with one of each wheel size. Take them for a drive to compare down the same roads, stay in the same lane, etc.

    Personally, I would probably go with the 18's. Better tire selection, little better ride, etc.

    Our truck came w' 20's (bought off lot), and there are a few more tires recently available that will fit our truck (GM's don't like larger tires (much taller) without rubbing). I have been back and forth to switch to 18's for the little better ride and better tire selection. Stock we have 32.5" tall tires, can fit 33" tires, but 34" will rub as I understand.

    BUT.... If the Ford allows you to mount a taller tire without any issues then go with the rim you like the best. If thats something you would consider.


    Good feedback Thanks!.. this seems to concur with what others are saying..although the 20" look 'cool' the ride is a lot rougher on the 20"

    My wife has low profile tires on her little Mazda that she runs around in. We both said 'Never Again'.. :-) It sounds like although the 20" are not Low Pro that they will still have some of the same issues.. rougher ride and easier rim damage and even alignment getting knocked out of waco easier by a pot hole!
  • Need-A-Vacation's avatar
    Need-A-Vacation
    Explorer
    Jan 26, 2015
    Larger wheel generally will give you a rougher ride. See if the dealer has couple trucks (2500 or 3500srw-any motor) with one of each wheel size. Take them for a drive to compare down the same roads, stay in the same lane, etc.

    Personally, I would probably go with the 18's. Better tire selection, little better ride, etc.

    Our truck came w' 20's (bought off lot), and there are a few more tires recently available that will fit our truck (GM's don't like larger tires (much taller) without rubbing). I have been back and forth to switch to 18's for the little better ride and better tire selection. Stock we have 32.5" tall tires, can fit 33" tires, but 34" will rub as I understand.

    BUT.... If the Ford allows you to mount a taller tire without any issues then go with the rim you like the best. If thats something you would consider.
  • smcrea's avatar
    smcrea
    Explorer II
    Jan 26, 2015
    ib516 wrote:
    The 20s are more pricey to replace too. That's why I went with the 18s on my RAM.

    Up to you though.

    As an Example:

    BFG All terrain 275/70/18s 3640# max load - $208 each on tirerack.com
    BFG All terrain 275/65/20s 3750# max load - $298 each on tirerack.com

    That's almost $400 more for a set of 4.

    The 65 and 70 refer to the ratio of the sidewall height to tread width.

    The tread width is 275mm for both, so the 20" tires have a sidewall 65% as high as the tread is wide, so 275 x 0.65 = 178.75mm tall = 7.03 inches.

    275 x 0.7 = 192.5mm tall = 7.57 inches.

    Overall tire diameter/height:
    275/70/18 = 33.2"
    275/65/20 = 34.1"


    THANKS!!! Just after I posted this then found that I had the ratio wrong and came up with the same numbers!! :)

    So I may now change the question and ask what is the impact on having tired with a 1/2" narrower sidewall?

    Thanks!
  • ib516's avatar
    ib516
    Explorer II
    Jan 26, 2015
    The 20s are more pricey to replace too. That's why I went with the 18s on my RAM.

    Up to you though.

    As an Example:

    BFG All terrain 275/70/18s 3640# max load - $208 each on tirerack.com
    BFG All terrain 275/65/20s 3750# max load - $298 each on tirerack.com

    That's almost $400 more for a set of 4.

    The 65 and 70 refer to the ratio of the sidewall height to tread width.

    The tread width is 275mm for both, so the 20" tires have a sidewall 65% as high as the tread is wide, so 275 x 0.65 = 178.75mm tall = 7.03 inches.

    275 x 0.7 = 192.5mm tall = 7.57 inches.

    Overall tire diameter/height:
    275/70/18 = 33.2"
    275/65/20 = 34.1"

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