Question about teadrop wheels

Hello everyone.
Wondering if you can offer a first time builder some advice? I am building a woody on a Northern Tool 8 X 5' kit. The kit came with 12" tires and I just realized that the max speed for these tires is 55 MPH. Since I will be doing all highway miles on this, I would like an option to be able to go upwards of 70 MPH. Hoping you can give advice on my 2 options below:
1) Upgrade to a larger 15" wheel. This is the preference. But all the wheels I have come across so far will not fit... the inner wall of a 15" tire will hit the teardrop side wall. Please see the picture below of the clearance I currently have for a 12" wheel. So the question is. Would you know of a 15" wheel that is designed for scenarios like this? Or do you know of an extension spacer... one that has worked well for teardrops? I was told by a friend to search for a spacer that has its own set of studs if I go this route.
2) Search for a 12" replacement tire that has a thicker ply... one that can withstand the higher speeds. This is my second option (a different friend told me about this one). Anyone have any references for tire dealers that would sell such a tire?
Any overall words of wisdom? I guess I would like a larger tire for the aesthetics and for a smoother ride. But I will go with the 12" option if you guys think I should.
OH, BTW, this trailer has a 5 stud orientation. I am guessing the stud spacing is a universal 5 stud layout... I measured the distance between holes in the wheel and came up with approx. 2 11/16". NOTE, I originally purchased a 15" wheel, replacement set at Menards and it fit the stud layout perfect (but had to return because of the side wall issue). I then purchased a 13" wheel, replacement set at Menards and the same thing... fit the studs perfect but side wall issue.
Thanks much!
scott

Wondering if you can offer a first time builder some advice? I am building a woody on a Northern Tool 8 X 5' kit. The kit came with 12" tires and I just realized that the max speed for these tires is 55 MPH. Since I will be doing all highway miles on this, I would like an option to be able to go upwards of 70 MPH. Hoping you can give advice on my 2 options below:
1) Upgrade to a larger 15" wheel. This is the preference. But all the wheels I have come across so far will not fit... the inner wall of a 15" tire will hit the teardrop side wall. Please see the picture below of the clearance I currently have for a 12" wheel. So the question is. Would you know of a 15" wheel that is designed for scenarios like this? Or do you know of an extension spacer... one that has worked well for teardrops? I was told by a friend to search for a spacer that has its own set of studs if I go this route.
2) Search for a 12" replacement tire that has a thicker ply... one that can withstand the higher speeds. This is my second option (a different friend told me about this one). Anyone have any references for tire dealers that would sell such a tire?
Any overall words of wisdom? I guess I would like a larger tire for the aesthetics and for a smoother ride. But I will go with the 12" option if you guys think I should.
OH, BTW, this trailer has a 5 stud orientation. I am guessing the stud spacing is a universal 5 stud layout... I measured the distance between holes in the wheel and came up with approx. 2 11/16". NOTE, I originally purchased a 15" wheel, replacement set at Menards and it fit the stud layout perfect (but had to return because of the side wall issue). I then purchased a 13" wheel, replacement set at Menards and the same thing... fit the studs perfect but side wall issue.
Thanks much!
scott