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What are Critical Dimensions required to safely up-size to 16" rim and tires? 220RK

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  • What are Critical Dimensions required to safely up-size to 16" rim and tires? 220RK

    OK folks - after searching I am not finding much engineering data on critical dimensions to up-size tries on my 220RK.

    Currently I am running ST 225/75 R15 on Lionshead 15" Jaguar rims with a 6 on 5.5" bolt pattern. Rims are 15" dia by 6" width with a center pilot hole of 4.25" I have asked GD about the pilot hole separately. Tire dimensions - Section width: 8.8", Outer diameter (when inflated): 28.3".

    Currently I have the following clearances. Distance between tires 6.5". Distance from top of tire to underbelly 4". Distance form tire sidewall to frame 3.5"

    I am thinking the new tires will be the Goodyear Endurance. They have two sizes available ST235/80R16 and ST235/85R16 both load range E and speed rating N

    ST235/80R16

    Max Inflation Pressure (PSI) 80

    Approved Rim Width (in.) 6.0-7.5

    Measured Rim Width (in.) 6.5

    Section Width (in.) 9.3

    Tread Depth (in 32nds) 8

    Outside Diameter (in.) 30.8

    This tire would gain me 1.25" in height, reduce clearance between tires by 2.5" to 4", reduce side clearance by .25", and reduce top clearance by 1.25" to 2.75" clearance

    ST235/85R16

    Max Inflation Pressure (PSI) 80

    Approved Rim Width (in.) 6.0-7.5

    Measured Rim Width (in.) 6.5

    Section Width (in.) 9.3

    Tread Depth (in 32nds) 8

    Outside Diameter (in.) 31.7

    This tire would gain me roughly 1.75" in height, reduce clearance between tires by 3.4" to 3.1", reduce side clearance by .25 and reduce top clearance by 1.75" to 2.25" clearance.

    From what I have read I should try for 4" between tires and 4" above tires - Thoughts????
    Also based on the above, going to 16* tires will probably require 1.5" to 2" lifting blocks on axle saddle to get clearance above tires

    So bottom line what do you folks recommend for clearances needed after up sizing tires?

    Thanks for any thoughts or corrections to my thinking.

    Keith


    2018 Reflection 150 Series 220RK 5th whee, Star White 2022 F350 King Ranch CC Long bed (HAL) (CCC 4062lbs), B&W 25K OEM Companion,. SteadyFast system, Trailer reverse lights, rear receiver spare tire holder, storage tube, sumo springs, Victron MultiPlus 12/120/3000, Solar, Custom 6K axles upgrade, and other modifications.

  • #2
    Yoda -- I'm not qualified to give any sort of input on this topic, Keith. Looks like something our resident engineers will love to "chew" on, though!
    Forum moderators are not GD employees--we are volunteers and owners presumably just like yourself. Unless specifically mentioned otherwise, we have nothing to gain should you choose to purchase a product or engage a service we discuss on this forum.

    2017 Ford F-350 DRW, '19 315RLTSPlus

    Comment


    • #3
      Yoda

      Hi Keith,

      All your numbers, calculations and concerns look correct to me. Running 3" or less of top clearance would be the biggest concern . . . as you have noted.
      Just out of curiosity . . . why are you upsizing the wheels & tires ?

      Rob
      Cate & Rob
      (with Border Collies Molly & Angel + Kitties Hazel & Elsie)
      2015 Reflection 303RLS
      2022 F350 Diesel CC SB SRW Lariat
      Bayham, Ontario, Canada

      Comment


      • #4
        Originally posted by Cate&Rob View Post
        Yoda

        Hi Keith,

        All your numbers, calculations and concerns look correct to me. Running 3" or less of top clearance would be the biggest concern . . . as you have noted.
        Just out of curiosity . . . why are you upsizing the wheels & tires ?

        Rob
        I went and measured new 2020 F350 SRW, 4x4's both loaded and unloaded (several different trucks) and found they sit at least 2" higher loaded than my 04. Depending on the spring package there is about 2" difference unloaded between models too. There appears to be about 3" to 4" of squat when loaded. I am already nose high about 2" to keep 7" bed clearance at tailgate, This is the critical location and dimension base on prior trailer/bed contact with old trailer where I only had 6". I am looking at getting a MAX payload 14000 GVW SRW long bed and finding some information they sit another inch higher when loaded. Dealer has one coming in so I can double check.

        So being an engineer I am doing my thinking and figuring early. I never over think things as you know. Just looking at options - one of which is larger tires and not going to lift blocks, but the numbers don't lie. I wont do anything until I get the new truck later this year or next (were close to having the house paid off so may wait), Upsizing also gives a much larger tire selection too.I don't need the extra capacity.

        There is one other possible option and that is to replace the spring packs with a higher arched/rated set, but that is another search for later assuming I can determine what axles and springs I have. I'll haft to send an email to Dexter sometime. Part number on tag 7763221 does not match anything on their web site.

        There is not much information out there on this subject. Mostly folks just doing it with no mention of clearances. E-trailer recommends 4" between tires and several aftermarket suspension folks have the 4" implied based on the spring compression charts, etc. and as howson has indicated I am hoping some experts might be able to help. Hopefully information learned may help someone else.

        Well enough said. Need to start more seeds for the garden.

        Back to my corner
        Thanks
        Keith
        2018 Reflection 150 Series 220RK 5th whee, Star White 2022 F350 King Ranch CC Long bed (HAL) (CCC 4062lbs), B&W 25K OEM Companion,. SteadyFast system, Trailer reverse lights, rear receiver spare tire holder, storage tube, sumo springs, Victron MultiPlus 12/120/3000, Solar, Custom 6K axles upgrade, and other modifications.

        Comment


        • #5
          Hi Keith I upgraded to a 2019 F350 long bed and had similar clearance concerns. Before I explain what I did I’ll caution you that this might not apply to the 2020.

          I frequent a few Ford forums as well as RV forums and the trend of pickup truck bed height increasing is frequently mentioned and discussed. In the F350, they use a larger spacer between the spring and the axle in the read end than they do on the F250. Many people have replaced their spacer with a F250 space to lower the bed, and this is what I did. I also replaced my ubolts and nuts at the same time, some argue this is not needed but I figured better safe than sorry. This coupled with switching to the endurance tires (kept my stock wheels) gave me enough of a drop that I could raise the ball on my Andersen and give me more clearance to the bed rails.
          Forum moderators are not GD employees--we are volunteers and owners presumably just like yourself. Unless specifically mentioned otherwise, we have nothing to gain should you choose to purchase a product or engage a service we discuss on this forum.​

          Neil Citro
          2018 Reflection 28BH Pepwave
          2019 F350 6.7L Long Bed Crew Cab

          Comment


          • #6
            Originally posted by ncitro View Post
            Hi Keith I upgraded to a 2019 F350 long bed and had similar clearance concerns. Before I explain what I did I’ll caution you that this might not apply to the 2020.

            I frequent a few Ford forums as well as RV forums and the trend of pickup truck bed height increasing is frequently mentioned and discussed. In the F350, they use a larger spacer between the spring and the axle in the read end than they do on the F250. Many people have replaced their spacer with a F250 space to lower the bed, and this is what I did. I also replaced my ubolts and nuts at the same time, some argue this is not needed but I figured better safe than sorry. This coupled with switching to the endurance tires (kept my stock wheels) gave me enough of a drop that I could raise the ball on my Andersen and give me more clearance to the bed rails.
            Thanks ncitro - Ill keep that in mind for when the time comes. Did you lower the front too to keep from going nose high on the truck when loaded? Just wondering.
            2018 Reflection 150 Series 220RK 5th whee, Star White 2022 F350 King Ranch CC Long bed (HAL) (CCC 4062lbs), B&W 25K OEM Companion,. SteadyFast system, Trailer reverse lights, rear receiver spare tire holder, storage tube, sumo springs, Victron MultiPlus 12/120/3000, Solar, Custom 6K axles upgrade, and other modifications.

            Comment


            • #7
              No, it was naturally raked from the factory with the rear and sitting higher than the front, now when loaded with the trailer it sits about level. I think the old blocks were four inches and the new were two. There was also an aftermarket company that made 1” blocks as well that some went with.

              I think this was the main forum post I worked off of (it’sa long read)

              https://www.ford-trucks.com/forums/1...-rear-end.html

              Forum moderators are not GD employees--we are volunteers and owners presumably just like yourself. Unless specifically mentioned otherwise, we have nothing to gain should you choose to purchase a product or engage a service we discuss on this forum.​

              Neil Citro
              2018 Reflection 28BH Pepwave
              2019 F350 6.7L Long Bed Crew Cab

              Comment


              • #8
                I have a 2016 Reflection 303 RLS. It came with the 15" tires and rims as described above too. However, the newer 303 RLS comes with 16" tires and wheels. My neighbor has one so i can easily measure dimensions. It does not appear that GD changed anything on the axles between 2016 and the newer models. It appears that they just put on larger tires. Can anyone at GD confirm this. If I move to 16" tires, I can get a higher load range. I also bought a new 2020 Chevy 3500, and it sits higher. So now I have a slight nose up issue. The larger tires would equalize this I think. All of the measurements I have taken on my trailer with 15" vs my neighbors with 16" look essentially the same. I can match what my neighbor has, but would like to confirm with GD folks before I do this.
                Tony G
                2020 Chevy Silverado 3500 Highcountry
                2016 Grand Designs Reflection 303RLS
                KTM 250XC

                Comment


                • #9
                  Originally posted by Tony Godrich View Post
                  I have a 2016 Reflection 303 RLS. It came with the 15" tires and rims as described above too. However, the newer 303 RLS comes with 16" tires and wheels. My neighbor has one so i can easily measure dimensions. It does not appear that GD changed anything on the axles between 2016 and the newer models. It appears that they just put on larger tires. Can anyone at GD confirm this. If I move to 16" tires, I can get a higher load range. I also bought a new 2020 Chevy 3500, and it sits higher. So now I have a slight nose up issue. The larger tires would equalize this I think. All of the measurements I have taken on my trailer with 15" vs my neighbors with 16" look essentially the same. I can match what my neighbor has, but would like to confirm with GD folks before I do this.
                  Tony,
                  Welcome to Grand Design's Technical Forum. One of the moderators can address your question and I'm sure he'll respond soon.

                  Howard

                  Cate&Rob
                  Forum moderators are not GD employees--we are volunteers and owners presumably just like yourself. Unless specifically mentioned otherwise, we have nothing to gain should you choose to purchase a product or engage a service we discuss on this forum.

                  2017 Ford F-350 DRW, '19 315RLTSPlus

                  Comment


                  • #10
                    Originally posted by Tony Godrich View Post
                    I have a 2016 Reflection 303 RLS. It came with the 15" tires and rims as described above too. However, the newer 303 RLS comes with 16" tires and wheels. My neighbor has one so i can easily measure dimensions. It does not appear that GD changed anything on the axles between 2016 and the newer models. It appears that they just put on larger tires. Can anyone at GD confirm this. If I move to 16" tires, I can get a higher load range. I also bought a new 2020 Chevy 3500, and it sits higher. So now I have a slight nose up issue. The larger tires would equalize this I think. All of the measurements I have taken on my trailer with 15" vs my neighbors with 16" look essentially the same. I can match what my neighbor has, but would like to confirm with GD folks before I do this.
                    Hi Tony,

                    I have a 2015 303RLS (still on its 15" wheels and tires). I have worked with a few other owners who have upsized to 16" and I believe that everything you say in your post is correct. I am going to tag one of the Grand Design repsGDRV-Megan and ask Megan to confirm that there are no suspension changes when a 303RLS is ordered with 16" vs the base 15" wheels and tires.

                    In interim 2016, a 2" square tube spacer was added between the bottom of the frame rails and the suspension hangers. You must have this spacer, to consider upsizing to 16" wheels and tires.

                    A couple of thoughts . . . if I may . . . Don't over estimate the ride height change that you will get with larger wheels and tires. The radius difference is between 1" and 1 1/2". Be cautious on "upgrading" (over strengthening) the tires. The suspension and tires are designed to "share the load" and are sized to the weight of the trailer. If the sidewalls of the tires get a lot stiffer, they won't absorb their share and the suspension and trailer body will take more of a beating.

                    I have 5 seasons and 25,000 miles on my 303 with its original 15" wheels and I am on my second set of tires. This combination works well for the weight it is designed too carry.

                    Rob
                    Cate & Rob
                    (with Border Collies Molly & Angel + Kitties Hazel & Elsie)
                    2015 Reflection 303RLS
                    2022 F350 Diesel CC SB SRW Lariat
                    Bayham, Ontario, Canada

                    Comment


                    • #11
                      Perfect input. I will wait to see what GD may post. In the meantime, I will go out and look to see if it has the 2" tube added. My secondary thought is to move my kingpin box down (I think there are one or two hole positions lower). to bring the nose back down. I drag my tail in some of the areas I go camping in due to my bike rack on the back. That did not happen until the new truck My old 2003 Chevy 2500 sat a bit lower and had no problem with tail drag. Interesting that the bed height from the bottom of the bed to the top of the rails stayed about the same. It is a 3500 4WD with 20" wheels which makes it overall taller than older models.

                      The other problem I already dealt with on my new truck was that Chevy changed the puck positions on the 2020 from the earlier trucks and nobody had yet made adapters to fit the new puck positions. I bought the truck last November just after they came out. Had to wait several weeks to even be able to put in my hitch from my old truck.
                      Tony G
                      2020 Chevy Silverado 3500 Highcountry
                      2016 Grand Designs Reflection 303RLS
                      KTM 250XC

                      Comment


                      • #12
                        Originally posted by Tony Godrich View Post
                        Perfect input. I will wait to see what GD may post. In the meantime, I will go out and look to see if it has the 2" tube added. My secondary thought is to move my kingpin box down (I think there are one or two hole positions lower). to bring the nose back down. I drag my tail in some of the areas I go camping in due to my bike rack on the back. That did not happen until the new truck My old 2003 Chevy 2500 sat a bit lower and had no problem with tail drag. Interesting that the bed height from the bottom of the bed to the top of the rails stayed about the same. It is a 3500 4WD with 20" wheels which makes it overall taller than older models.

                        The other problem I already dealt with on my new truck was that Chevy changed the puck positions on the 2020 from the earlier trucks and nobody had yet made adapters to fit the new puck positions. I bought the truck last November just after they came out. Had to wait several weeks to even be able to put in my hitch from my old truck.
                        Tony--forum hint: use "Quote" when replying or tag the member you're conversing with in a conversation. To tag, use the @ symbol followed by their name, like this: Cate&Rob
                        Forum moderators are not GD employees--we are volunteers and owners presumably just like yourself. Unless specifically mentioned otherwise, we have nothing to gain should you choose to purchase a product or engage a service we discuss on this forum.

                        2017 Ford F-350 DRW, '19 315RLTSPlus

                        Comment


                        • #13
                          Originally posted by Cate&Rob View Post

                          Hi Tony,

                          I have a 2015 303RLS (still on its 15" wheels and tires). I have worked with a few other owners who have upsized to 16" and I believe that everything you say in your post is correct. I am going to tag one of the Grand Design repsGDRV-Megan and ask Megan to confirm that there are no suspension changes when a 303RLS is ordered with 16" vs the base 15" wheels and tires.

                          In interim 2016, a 2" square tube spacer was added between the bottom of the frame rails and the suspension hangers. You must have this spacer, to consider upsizing to 16" wheels and tires.

                          A couple of thoughts . . . if I may . . . Don't over estimate the ride height change that you will get with larger wheels and tires. The radius difference is between 1" and 1 1/2". Be cautious on "upgrading" (over strengthening) the tires. The suspension and tires are designed to "share the load" and are sized to the weight of the trailer. If the sidewalls of the tires get a lot stiffer, they won't absorb their share and the suspension and trailer body will take more of a beating.

                          I have 5 seasons and 25,000 miles on my 303 with its original 15" wheels and I am on my second set of tires. This combination works well for the weight it is designed too carry.

                          Rob
                          I do have the 2" square tube spacers that appear to be welded to my frame for mounting the suspension to the frame. I also have two additional holes I can move the kingpin box up, which would lower the nose about 2" (looks like the holes are about 1" on center. I have to watch my nose to truck bed rail clearance, though. Any idea what torque these kingpin box bolts should be tightened to?

                          I have a sliding hitch, but my neighbor does not and has the same truck bed (6.5'). Not sure how much I would have to jack knife my trailer to actually hit the cab. Maybe I don't need the slider? Bought it at the recommendation of the RV dealer.

                          Anyway, thanks for the input. i am enjoying this forum.
                          Tony G
                          2020 Chevy Silverado 3500 Highcountry
                          2016 Grand Designs Reflection 303RLS
                          KTM 250XC

                          Comment


                          • #14
                            tgodrich

                            I use a manual slider hitch . . . for a bunch of reasons (in addition to cab clearance) that we can get into at a later date. Be careful of reducing the bed rail to verhang clearance. Less than about 6" and you risk contact if you get into uneven ground. The manual slider hitch in the rearward position can help with this.

                            I expect that you are going to fit in very well on this forum. Try the search tool in the upper right corner to find past discussions on whatever comes to mind.

                            Rob
                            Cate & Rob
                            (with Border Collies Molly & Angel + Kitties Hazel & Elsie)
                            2015 Reflection 303RLS
                            2022 F350 Diesel CC SB SRW Lariat
                            Bayham, Ontario, Canada

                            Comment


                            • #15
                              Any idea what torque these kingpin box bolts should be tightened to?
                              Buried in the Lippert Manual, down loaded mine from their website, are the torque requirements for the hitch.
                              John
                              2018 Momentum 395M
                              2018 Ram 3500 Dually
                              Every day is a Saturday, but with no lawn to mow.

                              Comment

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