235/80 16's vs 235/85 16's much difference?

[Samandothers]

My equipment trailer is a 12K lb 20'. It has 16" 8 lug single wheels on tandem axles. I do not have a spare but want to purchase one. The tires on my trailer are 235/80's. I have found some single wheels available with 235/85's.
What is the difference?
Is it enough to be concerned if I use the 235/85's as a spare?

Help educate me on the measurements.
Thanks

 

[Diamondpilot]

Here you go:

A tire has 3 measurements. The first is the tread width in mm(235)in your case.

The second is the aspect ratio of the side wall versus the tread width. On your 235/80/16 it is 80% of the 235 mm in the side wall, or 188 mm tall.

Your third is the rim size. In your case the tires are mounted on 16" rims or wheels, whatever you want to call them.

Here is the difference. The width is the same but the side wall height is 1/2" taller form 7.4 to 7.9 inches. This will make the overall height about 1" taller. As you can also see one revolution of the 80 series tire covers 96.8" while the 85 series covers 99.7" and leads to a 3% error in speed or odometer if on a vehicle, which is not the case for you since they will be going on a trailer.


Specification Sidewall Radius Diameter Circumference Revolutions Speedometer Odometer Difference
235/80-16 7.4" 15.4" 30.8" 96.8" 655/mi 60MPH 10000mi N/A
235/85-16 7.9" 15.9" 31.7" 99.7" 636/mi 58MPH 9708mi 3.0%

End result, they will be fine as long as you have plenty of fender clearance.

Chris

 

[Dmace]

This would be a good time to post up my favorite tire size calculator: Tire size calculator

 

[dgl24087]

Or this calculator:Tire Size Calculator - tire & wheel plus sizing

 

[Samandothers]

Thanks for the posts. Chris I appreciate the education on tires. I think for a spare I would be fine with the taller tire. I will verify the clearance on the fenders but I think there is plenty.

Again thanks for the feedback.

 

[Diamondpilot]

No problem. I am sure it will be fine. My buddy has 205-75-15 tires on his utility trailer. He did not have a spare but I had a 215-75-15 on a rim sitting in my barn attic so he took it. Has not had to use it yet but will be better than nothing.

The main thing I warn people is spend $25 at WalMart or Harbor Freight and buy a 6 ton bottle jack and a folding 4 way lug wrench. The first flat I had pulling my boat my trucks jack would not lift it and I ended up breaking the jack. Also the trucks lug wrench was too big so luckily a cop stopped and helped me with a 4 way and a small jack that fit under the trailer.

Chris

 

[davo727]

a cop stopped and helped me

Chris

I dont believe it

 

[Samandothers]

Thanks again Chris.
I have a Jiffy Jack (pull the good tandem up on and raise the bad off the ground) in the truck we carry all the time. I have a regular lug wrench in the truck. The Jiffy Jack has been used a time or two on horse trailers and seems to work well.

 

[JIGBUILDER]

theres a huge difference in those two tire sizes in reliability. The 235/80-16 is a ST (special trailer) tire size. The 235/85-16 is a LT tire size. Do a google on ST tires of any brand or better yet check out RV.net web. With thousands of RVers on the road , many with ST tires are very problematic especially the made in china tires. Their biggest problem is their speed rated to 65 mph max. They build heat quick due to their softride basketball shapped sidewall. That design causes more sidewall flex than a conventional shape like the flater sidewall profile in a semi trailers tire.
Many higher end RV's and equipment trailers come with LT's or are a upgrade option.

When you make a living on the road pulling several size trailers commercially you learn with the help of a well informed truck tire dealer which tires are for the part timers and which tires are there for the long haul. Pun intended


Keep a eye on the ST's for tread/belt seperation and keep them pumped to the max psi.