old school 700-15s to newer metric

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Mar 29, 2025
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upgrading my 6000# dexters.

had some 7,00-15's 6 ply load C's

decided on some smaller 205/75-15 10ply load E's

Also decided to grab 4 new backing plates in total, then 2 more hubs for the front idler.

I hope my decision was a good one on the size gamble. Ol' WallWorld had a deal, $42 each So i jumped, and jumped fast.. Hauling cars and iron, and i wanted to lower the ride height, add more braking, and get a better sidewall just for peace of mind and stability.

They used 16ga 6 wire for everything, so I pulled a fresh 30ft lead of 10/2-12/1-14/4 7way to back center for a newer junctions, both front and back, without ants, added a breakaway, ripped out the old 16ga (!!!!) for the electric brakes/lights and decided to go with 4 wire LED's 4" lights for a reverse as well.

the old 16ga wire with incandescent @ almost 30ft from the truck bumper, when i tried to run blinkers, i ended up with 4 way flashers. No wonder i kept getting horns and the bird when using my blinker and waiting for a moment to merge.....I'm not sure if this was a previous DIY or just how things were wired back in the mid 80's? This is the first time i've gotten quiet involved with the trailer, and i know my father never did anything wire related on it.


I've had this trailer for 30 years, i knew the tires were roached, but i got to looking at the 6 conductor, and the UV rays melted the coating off everything. Then when i took apart the junction box, i spit up my beer and just walked away only to return with new hardware.....

look at the wires!!! all i did was remove the cover. It's amazing of the rainbow switch-a-roo.....
The black to red, red to black, white to yellow, taped off lead. Just crimp an eyelet and set it on the post! It won't hurt anything and gives options later!, then the add-a-THHN only to go back up the front for corner markers? why not junction box up there first? I couldn't believe what i uncovered. I kinda understand what they had going on, but good god, just keep the colors the same function from plug -> junction -> light. There's no reason to flip and flop..

After this weekend Everything on this trailer should be a step forward. Especially for diagnostics with a meter. I hope anyways.

For cross-eyed reference, bottom center comes from plug, left and right goes to lights, and "i think i'll add brakes, and tail markers, back 30ft up front" comes out the center top. ***!?!? And i didn't just hang the new wire on the frame, i spot welded 3/4" pipe and pulled all the wire through there. It exposed in the corners, but that was just so i can an easy way to jump to the next straight, and made it easier to pull, and reduced the chances of snagging it by 99.99%. I was going to use conduit and hangers, but that stuff is flimsy, bends easy, and welding was easier and stronger then drilling holes in the frame just to use some bend-easy bracket. I hate drilling. I'm lazy.

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I'm not sure what the wire size has to do with tires and/or wheels.

- BUT -

A 7.00-15 Load Range C doesn't have an exact replacement in modern tire sizing. The closest in a trailer tire is an ST205/75R15 LR C. Here's the specs:

7.00-15 LR C: OD is 29.62" with a 7.95" width a a 5.50" rim with an allowable rim width range of 5.00" to 6.50" with a load carrying capacity of 1710# at 50 psi

ST205/75R15 LR C: OD is 28.31" with a 7.99" width a a 5.50" rim with an allowable rim width range of 5.00" to 7.00" with a load carrying capacity of 1820# at 50 psi

Net: The ST205/75R15 is smaller in diameter by about 3/4".

And you can use the lower 50 psi rather than the LR E's max of 80 psi.
 
I'm not sure what the wire size has to do with tires and/or wheels.

- BUT -

A 7.00-15 Load Range C doesn't have an exact replacement in modern tire sizing. The closest in a trailer tire is an ST205/75R15 LR C. Here's the specs:

7.00-15 LR C: OD is 29.62" with a 7.95" width a a 5.50" rim with an allowable rim width range of 5.00" to 6.50" with a load carrying capacity of 1710# at 50 psi

ST205/75R15 LR C: OD is 28.31" with a 7.99" width a a 5.50" rim with an allowable rim width range of 5.00" to 7.00" with a load carrying capacity of 1820# at 50 psi

Net: The ST205/75R15 is smaller in diameter by about 3/4".

And you can use the lower 50 psi rather than the LR E's max of 80 psi.
I got side tracked.

I'll get a moderator to lock or delete the thread.

And i eyeballed and guessed a metric replacement. 205 75 15 seemed like a good guess, I guess

Nice copy and paste.

Tires spooned on nice this morning. I didn't have any new valve stems laying around unfortunately, and tire shop is closed.

And they're getting 80psi. I'm stacking two cars at once. I need reasons to replace axle bearings.
 
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