RV Tires; One of a different size?? Help!

[RickorJudy]

Help! We are currently travelling in Mexico and are unable to purchase an RV tire (ST).  Today we purchased one truck tire LT, to become our spare, which is of slightly different size than our trailer's 4 running tires.  Any opinions -- or better yet, good knowledge  --- about driveability? control? danger? safety? damage? if or when we ever have to use the new "spare" as one of our running tires with 3 of the 'other' size??  Here's the data.  Current tires (4): Load range D, ST235/ 80R16.  Spare: Load Range E, LT235 / 85/R16.  Thanks for any and all help. 

 

[John From Detroit]

Trailers are a special case but the rule on cars and trucks (And this should apply to trailers as well) is all axles get same size tire

IE: both steering tires should be identical,  both rear tires (or all 4 if it's a dual wheel on the rear) identical,

Each axle needs matching tires.. Else there WILL be handling and control issues

Having used space saver spares... I fully agree with the above wisdom

 

[Gary RV_Wizard]

There's nothing wrong with using LT tires on a trailer or any other RV. Mismatched tires is a different question, though. It is best if all tires match, or at least the tires on the same axle. You said the new tire is "close", but without specifics we can't guess how close it is. Sometimes a slight difference in the numbers can make a large difference in the circumference and sometimes tires with widely varying numbers are actually all but identical in their critical size, e.g. rolling diameter and circumference. Fortunately, trailers aren't too sensitive to that sort of thing.

Last, sidewall stiffness can vary a lot, even among different brands with the same spec numbers.

Bottom line: be cautious if you have to use that tire, but don't worry yourself to a frazzle.

 

[Carl L]

Trailer axles are dead axles and they do not steer in turns.    Simpliicity here is a virtue.  As long as the tires are not grossly mismatched, as if you used a passenger service P tire with trailer service ST tires or lilght truck LT tires, you should be ok.    ST with LT tires are a better mix and should be ok.  Best is all the same service type and size.

 

[Karl]

Current tires (4): Load range D, ST235/ 80R16.  Spare: Load Range E, LT235 / 85/R16.

The "235" number is the tread width in millimeters, the "80" or "85" is the ratio of the tread width to the sidewall height, the "16" is the wheel (rim) diameter. In your case, barring a huge difference in circumference (and there shouldn't be much), either size should work for you. The load range "E" is designed and built to handle a heavier load than the "D" tire, so you should be fine.

 

[Karl]

the "80" or "85" is the ratio of the tread width to the sidewall height

I should have explained this a little further. Using the 235/80 R16 tire as an example,  you would multiply the 235mm by .8 (80%) to get the sidewall height - 235 X .8= 188mm.  If you want, you can convert millimeters to inches by dividing millimeters by 25.4.

 

[RickorJudy]

Thanks so much for all the information.  We will continue on our journey, not worry ourselves to a 'frazzle'  (I liked that), and, if it happens that we need to use the slightly larger spare for a reallly long distance will purchase a match for it so that the 2 on one axle match each other.  The roads are not always the best here (understatement) so we definitely want everything working on our side.  Other than that -- I think we will now have a carefree trip further south -- LT tires are readily available in Mexico, so we will find the match at a later date if necessary.  Thanks Amigos!  ;D

 

[Gary RV_Wizard]

Enjoy your Mexican adventure and Vaya con Dios.

 

[Just Lou]

If you do the math as Karl suggested, there is one inch difference in total diameter between the two tires properly inflated.

31.7" v/s 30.7".  As the guys also mentioned, sidewall stiffness and inflation pressure variances will make it hard to notice if you need to use it in an emergency.  If it were me, I would probably migrate to all LT load range "E" tires.

jmho, lou

 

[Karl]

Lou,

Good suggestion. The difference in revolutions/mile is 656 for the ST tire and 636 for the LT, or about 3% - not enough to even notice on the speedometer or affect overall performance, and you get a higher carrying capacity in the process. Prices shouldn't be much different either.