Can ST235/80R16 Tire Be Used as a Spare on 5th Wheel That Has ST235/85R16 Tires

Question:

Can I use an ST235/80R16 as a spare tire for my 5th wheel trailer that has ST235/85R16 tires? Any problems? Any advantages? This is only for a spare tire. Thanks.

asked by: Chuck

Expert Reply:

Both of the trailer tire sizes you referenced, ST235/80R16 and ST235/85R16, fit the same wheel sizes. Both will fit 16-inch wheels with widths of 6-, 6-1/2-, 7- and 7-1/2-inches. The dimension that differs between these two tires is their overall diameter when they are inflated to their rated pressures.

ST235/80R16 tires will have an overall diameter of approximately 30.9-inches while a fully-inflated ST235/85R16 tire's overall diameter will be approximately 31.6-inches.

The other difference between the two sizes is their load capacity. An E-rated ST235/80R16 tire has a maximum load capacity of 3500-lbs at 90-psi pressure, while an E-rated ST235/85R16 tire has a maximum load rating of 3640-lbs at its 95-psi inflation.

This size difference is acceptable for a short time/distance until you can reach a safe place to have your standard tire repaired (provided that the load rating is adequate) but I do not recommend driving any longer than absolutely necessary with the smaller diameter tire.

You may care to have a look at the linked article on tire sizes.

expert reply by: Adam R