Trailer Modifications and 8 inch to 12 or 13 inch Tire and Wheel Upgrade Recommendations

Question:

I am re-factoring a PWC trailer to haul 6 kayaks. It previously had 8inch tires and I want to upgrade them to either 12inch or 13inch tires. I have the clearance under the fender and payload wieght wont be an issue. I plan to do a lot of highway driving. So the question is: what size tires are appropriate: 4.80-12, 5.30-12 or ST175/80D-13? Thanks.

asked by: Pat

Expert Reply:

To upgrade to a larger tire you will have to upgrade to a larger wheel as well, and with that in mind you will want to make sure that the bolt pattern of your new wheel and tires match the existing bolt pattern on your current trailer. I have included a helpful article explaining how to determine the bolt pattern of your existing wheels.

Depending on the existing bolt pattern on that your trailer is currently set up for I recommend the following:
4.80-12 - 4 on 4 bolt pattern # AM30620; 5 on 4-1/2 bolt pattern # AM30660
5.30-12 - 4 on 4 bolt pattern # AM30780; 5 on 4-1/2 bolt pattern # AM30820
ST175/80D-13 - 4 on 4 bolt pattern # AM3S030; 5 on 4-1/2 bolt pattern # AM3S050

These recommendations are based on an assumption that your current 8 inch wheels have a 1/2-20 wheel bolt size, and are based on the product that you referenced to ask your question. The recommendations provided are all wheel and tire combinations that require a 1/2 inch diameter wheel stud. If your lug nuts are a different size let me know and I can make updated recommendations.

For the wheel and tire recommendations above the wheel pilot hole are as follows: for the 4 on 4 bolt patterns the pilot hole is 2.84 inches, for the 5 on 4-1/2 wheels the pilot hole is 3.19 inches, the ST175/80D13 5 on 4-1/2 is also 3.19 inches, finally, the ST175/80D13 4 on 4 has a pilot hole of 2.65 inches. These are especially crucial measurements if you have a hub centric wheel, in which the hub of the axle centers the wheel on the axle. For this case the pilot hole needs to be slightly larger than the axle hub. To determine if you have hub centric wheels you check to see if your current wheels use lug bolts or lug nuts. Hub centric wheels are used in conjunction with lug bolts. If your trailer uses lug nuts, then the wheel is lug centric and the conical shape of the lug nuts when threaded to the studs of the hub assembly center the wheel.

If you determine that you do have a hub centric wheel, then additional modifications will have to be made to upgrade the hub of your existing trailer as well and in that case I would need the bearing numbers on your axles to make the appropriate recommendations.

Considering that your trailer is a personal water craft trailer (PWC) it is likely that you have a 2,000 pound axle associated with your trailer. Please verify this the axle weight capacity is usually stamped on the axle itself or on a specifications tag located on the trailer. I have taken this into consideration for the recommendations provided above for the specific tire sizes that you mentioned, and have recommended an appropriately load rated tire and wheel combinations.

For highway driving a narrower wheel and tire would provide a smoother ride for your modified trailer. Depending on the configuration of your existing 8 inch wheel and tire as compared to the above recommendations it is likely that the new tire and wheels will be narrower than your existing 8 inch wheel and tire. You have inspected the vertical clearance under the fender but also keep in mind that the depending on your final choice of the replacement tires, it may be of a different width or diameter of your current 8 inch tires. I advise taking a width and total diameter measurement of your existing 8 inch tires, and compare this number to both the overall diameter and the section width on the product pages for the recommended tires to make sure that you do not have any interference with the existing fenders or attachments/brackets, trailer frame, or suspension. I have included a link to a couple of helpful articles explaining measuring a tire including width, and total overall diameter of wheel and tire.

Please be aware that with the modifications that you have done to your trailer in addition to the larger tires it will affect the handling of the trailer. Keep this in mind when towing and make adjustments as necessary. For example if you upgrade to a significantly larger tire you might need to adjust the rise of your trailer hitch connection to the towing vehicle. I have also included a helpful article for your reference regarding measuring and choosing an appropriate ball mount.

I have included links to parts listed above as well as some helpful articles for your reference.