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Old 09-01-2020, 02:33 PM   #1
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Changing tire size?

Sorry if this has been covered before (Iíve tried searching and didnít find threads) - my TT came with Westlake 235/75r15 tires and I want to get better tires. But, Westlake is the only tire in 235 size, yet many other brands come in 225. Will there be any problem if I change to a 225 tire on my single axle TT?
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Old 09-01-2020, 03:33 PM   #2
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225/75R15's are only a little more than Ĺ" smaller diameter so changing to them won't be a problem. You probably won't even notice the difference.
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Old 09-02-2020, 08:42 PM   #3
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Thanks Bama.
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Old 09-02-2020, 08:58 PM   #4
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The Westies are pretty good tires, IMHO. Unless you need to swap due to age or failure, no need to preemptively do so.
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Old 09-02-2020, 09:00 PM   #5
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Whether you can downsize the tires would depend on the maximum load rating of the tires and the gross vehicle weight rating of the trailer. It’s not just the tire size, but the load range/ply rating of the tire also affects the load rating. All those number are published and/or molded into the tire sidewall.

So, to answer the question, you need to gather some information. The absolute yes or no answer is all there in the numbers.
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Old 09-02-2020, 10:26 PM   #6
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The 235/75/15 is likely an LT tire. An ST 225/75/15 will have more load rating than the tires you have.

Look at the sidewall spec for your tire and compare to the 225s
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Old 09-02-2020, 10:29 PM   #7
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Originally Posted by VR51 View Post
Sorry if this has been covered before (Iíve tried searching and didnít find threads) - my TT came with Westlake 235/75r15 tires and I want to get better tires. But, Westlake is the only tire in 235 size, yet many other brands come in 225. Will there be any problem if I change to a 225 tire on my single axle TT?

Yes there can be major problems by going from St235/75R15 to ST225/75R15 unless you go up in Load Range (and inflation) as the 225 has lower load capacity so you could end up overloading your new tires and suffer a tire failure.


Are the 235's the OE size as shown on your certification label? What Load Range (D or E?) are the 235's? What is the load capacity molded on the tire? Inflation?
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Old 09-02-2020, 11:02 PM   #8
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Quote:
Originally Posted by VR51 View Post
Sorry if this has been covered before (I’ve tried searching and didn’t find threads) - my TT came with Westlake 235/75r15 tires and I want to get better tires. But, Westlake is the only tire in 235 size, yet many other brands come in 225. Will there be any problem if I change to a 225 tire on my single axle TT?
I don't see it.

Westlake Radial Tire

Note: A lot of smaller trailers now have OE all terrain tires. Some even with passenger/euro metric tires. The Euro metric 235/75R15 with a load index of 108 at 36 PI will actually qualify with more than 10% in load capacity reserves for your 3500# axle. The passenger (P235/75R15 108) will not qualify.
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Old 09-03-2020, 12:30 AM   #9
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I don't see it.

Westlake Radial Tire

Note: A lot of smaller trailers now have OE all terrain tires. Some even with passenger/euro metric tires. The Euro metric 235/75R15 with a load index of 108 at 36 PI will actually qualify with more than 10% in load capacity reserves for your 3500# axle. The passenger (P235/75R15 108) will not qualify.
Might be one of these which is why I said it might be an LT tire.

https://westlaketireusa.com/tire-sea...ze=235%2F75R15
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Old 09-03-2020, 01:20 AM   #10
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Might be one of these which is why I said it might be an LT tire.

https://westlaketireusa.com/tire-sea...ze=235%2F75R15
Because you described your tires with a Euro-Metric designated size (235/75R15) I could only spectate in my last post that you probably have A/T tires. Euro-Metric tires use a different load inflation chart which is not the same as any of the other charts. The Euro-metric will have more load capacity than a "P" passenger tire but follows the rules for passenger tires installed on RV trailers. That rule is to de-rate their load capacity (found on the tire sidewall) by about 10% for use no RV trailers.

Westlake does make this tire as an A/T tire: Fits: 15" x 6" rims
Tire size: ST235/75R15
Section width: 9.3"
Outer diameter: 28.9"
Load range: D
Ply rating: 8
Maximum load: 2,910# at 65 psi
Maximum speed: 75 mph (speed rating L)

Westlake part # WST54FR

Westlake has always been behind on updating their tire info. Designated tire sizes have been exclusively used since 2010.

These are designated sizes:

235/75R15
P235/75R15
LT235/75R15
ST235/75R15
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Old 09-03-2020, 11:30 AM   #11
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Because you described your tires with a Euro-Metric designated size (235/75R15) I could only spectate in my last post that you probably have A/T tires.
I am not the OP...I was speculating what the OP actually had as well.
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Old 09-03-2020, 01:47 PM   #12
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I doubt that Westlake uses Euro-Metric sizing. More likely that the Op just gave what he thought were the numbers. This is not uncommon as few people seem to realize the letters in fromt and behind the dimensional numbers are important.
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Old 09-03-2020, 03:52 PM   #13
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Thank you for the fine comments and questions. I’ve checked the tires and gotten the following information that I hope is of help for this thread…

Westlake CR857+
ST235/75r15 110/105L
Load range C - 6 PR (2 Poly, 2 steel, 2 nylon)
Max load single 2340 pounds at 50 psi ( my trailer is a single axle )
Speed rating ‘L’ 75 MPH
DOT JUMT 1FL 2517

My trailer’s dry weight is 2547#; Sticker says weight of cargo should never exceed 678 pounds. I have put ~650 miles on these tires. We camp mostly in forest service CGs with some dispersed camping mixed in. A lot of the roads used have steep grades of 6-8% commonly and go over 8K-10K elev. passes.
My big concerns are that these tires are C rated, and are possibly China bombs.
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Old 09-04-2020, 12:46 AM   #14
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Thank you for the fine comments and questions. Iíve checked the tires and gotten the following information that I hope is of help for this threadÖ

Westlake CR857+
ST235/75r15 110/105L
Load range C - 6 PR (2 Poly, 2 steel, 2 nylon)
Max load single 2340 pounds at 50 psi ( my trailer is a single axle )
Speed rating ĎLí 75 MPH
DOT JUMT 1FL 2517

My trailerís dry weight is 2547#; Sticker says weight of cargo should never exceed 678 pounds. I have put ~650 miles on these tires. We camp mostly in forest service CGs with some dispersed camping mixed in. A lot of the roads used have steep grades of 6-8% commonly and go over 8K-10K elev. passes.
My big concerns are that these tires are C rated, and are possibly China bombs.
I don't see the problem. You have a maximum of 4680# of tire load capacity supporting a maximum axle load capacity of 3500#.

The AT tires are new in the ST market. Not very many brands build them. Did you not know you had AT tires on your trailer?
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Old 09-04-2020, 08:09 AM   #15
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Thank you for the fine comments and questions. Iíve checked the tires and gotten the following information that I hope is of help for this threadÖ

Westlake CR857+
ST235/75r15 110/105L
Load range C - 6 PR (2 Poly, 2 steel, 2 nylon)
Max load single 2340 pounds at 50 psi ( my trailer is a single axle )
Speed rating ĎLí 75 MPH
DOT JUMT 1FL 2517

My trailerís dry weight is 2547#; Sticker says weight of cargo should never exceed 678 pounds. I have put ~650 miles on these tires. We camp mostly in forest service CGs with some dispersed camping mixed in. A lot of the roads used have steep grades of 6-8% commonly and go over 8K-10K elev. passes.
My big concerns are that these tires are C rated, and are possibly China bombs.



Thanks for details. Dry weight and cargo weight are interesting but meaningless unless you know your actual loaded weight. As a minimum you need to get on a truck scale and learn the axle weight for each axle. - Just spot the trailer so each axle is on it's own pad.
Assume 53% of the axle load is on one end of the axle.
Use that number to consult tire Load & Inflation tables to learn tire inflation needs and what your Reserve Load is.
I recommend at least 15% Reserve Load.
You may find that smaller tires i.e. St225's migh give the load capacity you need IF you go up to LR-D or LR-E.
Be sure to confirm your wheels are rated for your measured load and for 80 psi before you switch to LR-E if you decide to go that route.
If you have to change wheels going to 16" might give you greater tire oprions but you need to confirm clearances on all sides and between the tires.
Some may not like my suggestion to change tires but as long as the load capacity is increased and clearances are OK I would see no reason to not consider that option.


Side note. I don't understand the use of AT tires on a trailer unless you are seeing the trailer slide around a lot.
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Old 09-04-2020, 08:31 AM   #16
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A CAT scale wonít do this for you, but at the 2019 rally, we had each tire weighed (loaded as normal for a trip). From that, you can still calculate the weight on each axle, plus you will know if your weight is well-distributed left to right.

Until you can get that done, definitely weigh each axle.
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Old 09-04-2020, 08:40 AM   #17
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A CAT scale wonít do this for you, but at the 2019 rally, we had each tire weighed (loaded as normal for a trip). From that, you can still calculate the weight on each axle, plus you will know if your weight is well-distributed left to right.

Until you can get that done, definitely weigh each axle.



Yes I know that CAT scales and similar do not give individual tire position weight. That's why I suggest people use a 53% figure of the axle scale reading. I cover this in detail in my blog on RV Tire Safety
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Old 09-04-2020, 08:45 AM   #18
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I was just relating our good fortune at getting each tire weighed. That opportunity does not present itself often.

Not having that opportunity this year, we did the CAT scale while heading out for our (belated) first trip.

Your posts on tire safety are greatly appreciated. I pay much more attention to my tires now than when I first got my TT. Thank you.
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Old 09-04-2020, 09:24 AM   #19
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The tires are OE on my TT that I bought 7 months ago. I greatly appreciate all the info so far.

Iím hoping that the issue of the quality level of Westlake tires will be addressed - are they worth keeping if the loaded weight is acceptable, or are they a blowout waiting to happen? The research Iíve done on the brand is all over the map = from ďtheyíre junkĒ all the way to ďtheyíve gone 5000 miles with no problemsĒ
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Old 09-06-2020, 10:54 AM   #20
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ttt
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