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Old 11-01-2013, 07:31 PM   #1
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Tire Size Change ??

Hello All

I have to replace all the tires on our 2000 25' Springdale TT as part of the path back to the road,one of the many things since we bought it. It's has 14" tires on it now and am thinking of Putting 15" on it for a little extra road clearence and a higher load rating. My question is, how much travel does a TT wheel need under tow ?? So i have a better idea if i have enough clearence in the wheel well for the added inch.

I think i have decided on Kenda Tow Star tires,i know from past experience they make a good mortorcycle tire and one of the few who gives a warrentee on there ST Trailer tires, although the Hi Runs from Walmart are the best price.

Many thanks Again Jim

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Old 11-01-2013, 09:31 PM   #2
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Every ST tire I know of has a mfgrs. warranty. How well they honor their warranty is another subject.
Tandem axle tires must have a minimum of 2" between tires or they may rub when hot. Measure the distance between the top of the spring and frame, the tires must have that amount between the tire and bottom of trailer to prevent contact.
Your movement to 15" tires gives you much more safety and reliability, they are even available in load ranges F and G if the requirement is there; you will not need them. Of course appropriate rims must be purchased at that time too.

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Old 11-03-2013, 07:50 AM   #3
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When you say 14" to 15", you are talking about the diameter of the wheel, not the height of the tire overall.
You can go to a 15" wheel with a smaller aspect ratio (side wall height) and keep the same overall diameter of the tire, but why? Or a 15" wheel and taller/wider tire, but not sure what you want that for.

If you stay with your 14" wheel and get a taller sidewall, you will increase the overall height of the tire. That means slightly less RPM (revolutions per mile), but also more rotating mass. Your trailer will also sit higher, so think about the trailer's pitch toward the tongue as well as the stabilizer jacks being an inch or so higher off the ground.
Any time you get a taller sidewall on the same size wheel, you get more sidewall to flex and that creates heat, which is bad.
You will also have a reduced effect on your trailer brakes from the increase in rotating mass and the effective increase of the lever acting against the brake.
Personally, I want to keep the whole center of gravity as low as possible. It's more stable and more aerodynamic. If the load rating of your current size matches the load rating of your axels and max trailer weight, there's no reason to change.
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Old 11-03-2013, 03:05 PM   #4
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A couple of things to worry about if you go up an inch in wheel diameter. Of course you must have new wheels, so just be sure the new wheels meet the width and weight-carrying capacity specs for the new tires.

I'm a big fan of increasing the weight capacity of most stock RV trailer tires. Many have barely enough weight capacity to meet the combined GAWR of your trailer. Keystone is one of the culprits that shrimped on tire weight capacity. My 2000 Keystone Sprinter blew out two stock tires on the first long trip. They were ST205/75R15C. I replaced them with ST225/75R15D, and that was the end of my trailer tire problems. The ST225s required 6" wide rims, so even though the old tires were also 15", the old rims were only 5.5" wide.

The bigger tires reduced the clearance in my wheel wells to just barely. So I had rubbing between the top of the tire and the underside of the wheel well when I hit a bigger than normal bump. So I tried to avoid chug holes and big bumps. I drug that trailer about 100,000 miles over 10 years, without any more tire problems and without any real damage to the wheel wells.

My newer TT has ST205/75R14C tires with 1820 pounds weight capacity per tire. The TT's GAWR is 1,400 pounds per tire, so I have over 20% excess tire weight capacity. I like 20%or more excess tire weight capacity, so I'll probably not go to the available ST205/75R14D when it's time for trailer tire replacement. However, those tires have 2150 pounds weight capacity per tire @65 PSI, and they are the same width and height as the stock tires. So if your trailer has ST205/75R14C tires, consider upgrading to load range D instead of to a bigger tire.

I'm a Maxxis trailer tire fan, and they make ST205/75R14D tires. So consider those when you upgrade your tires.
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Old 11-03-2013, 05:14 PM   #5
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Well Thanks Guys
Decided to stay with the original size F78-14ST/ ST20575D14 and ordered them today, Road Star's by Kenda. I fiquired since the original tires ( the same ) are still on the TT and although in horrible shape, they lasted 13 years. The price fits our pocket book better and we are going thru a bit of jingle getting it roadworthy again and being able to use the same wheels helps a lot. At 1760 load , i think we a fairly comfortable as the dry weight of th TT is under 5,000 #s and it's just me and the wife and i don't see ever going near the GVWR.

Also have new electric brake assemblies , bearings and a load dist. hitch on the way . Maybe soon we will be able to take a shakedown trip .

Many thanks for the input and any more will be appreciated.

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