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Old 01-21-2012, 02:26 PM   #11 (permalink)
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Originally Posted by got2run5 View Post
Okay, but what about the rim still being .5 in wider. I was hoping that by keeping the same size tire that the .5 wouldn't matter. What are your opinions on that?
The wider rim shouldn't aggravate the projected frontal area of the car,so the 'air' shouldn't be able to tell the difference since the tires are the same.

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Old 01-21-2012, 03:14 PM   #12 (permalink)
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Originally Posted by hat_man View Post
What about going the other way. I have 225's and would love to go narrower. Any idea on how much narrower I could go. Even a ballpark figure is OK. I would like to keep my current rims only because they are alloys and fairly light, not because they are "aero" in any way. I'd love to fab some "moons" for them though.
Narrower tires on your wheels? How wide are your wheels?
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Old 01-22-2012, 07:45 AM   #13 (permalink)
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Originally Posted by hat_man View Post
What about going the other way. I have 225's and would love to go narrower........
Why would want to go narrower? Narrower tires have higher rolling resistances.

But if you are considering going both narrower AND taller at the same time, that MIGHT be the right direction. The way to know is if the load carrying capacity goes up.

So chieck the tire specs. Not only will they tell you what the allowable rim width range is, but they will also tell you about load carrying capacity.
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Old 01-22-2012, 01:03 PM   #14 (permalink)
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Why would want to go narrower? Narrower tires have higher rolling resistances.
I'm curious. How does that work?
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Old 01-22-2012, 02:38 PM   #15 (permalink)
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Quote:
Originally Posted by hat_man View Post
What about going the other way. I have 225's and would love to go narrower. Any idea on how much narrower I could go. Even a ballpark figure is OK. I would like to keep my current rims only because they are alloys and fairly light, not because they are "aero" in any way. I'd love to fab some "moons" for them though.
Go as narrow as you want. I frequent cars "scenes" where stretching tires is very popular, and never seen anyone "break the bead". Look on here and you'll get an idea of how far it can go without problems.

Tyrestretch.com - Image Library



Stretch as much as you want. As long as your sidewalls aren't at a 45 degree angle you should be fine.
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Old 01-22-2012, 10:45 PM   #16 (permalink)
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Yup, its true. For the 225, I might blindly suggest 205, depending on what the rest of the size is.
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Old 01-23-2012, 06:24 AM   #17 (permalink)
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I'm curious. How does that work?
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Old 01-23-2012, 09:10 AM   #18 (permalink)
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Quote:
Originally Posted by CapriRacer View Post
Thanks for that. I have a question to pose:
I am building a 5th wheel trailer with (2) 2000 pound rated axles, and the common tire size in that situation is ST175/80R-13, with a 24.1" dia. 23.2" loaded height, 1360 LB capacity. I have planned around the ~23.2" loaded height. Other design factors require that I keep the diameter around this value.
I can't find any resistance data on these tires.
The super low crr bridgestone b381's are available in a 185/70R14 with a similar diameter and a 1200 pound capacity.
The trailer's planned load values are closer to 900 pounds per tire, about a 10% cushion below axle rating.
So this tire is slightly wider, but has a lower aspect ratio. Any thoughts? Are trailer tires low crr to begin with?
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Old 01-23-2012, 02:12 PM   #19 (permalink)
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Quote:
Originally Posted by skyking View Post
Thanks for that. I have a question to pose:
I am building a 5th wheel trailer with (2) 2000 pound rated axles, and the common tire size in that situation is ST175/80R-13, with a 24.1" dia. 23.2" loaded height, 1360 LB capacity. I have planned around the ~23.2" loaded height. Other design factors require that I keep the diameter around this value.
I can't find any resistance data on these tires.
The super low crr bridgestone b381's are available in a 185/70R14 with a similar diameter and a 1200 pound capacity.
The trailer's planned load values are closer to 900 pounds per tire, about a 10% cushion below axle rating.
So this tire is slightly wider, but has a lower aspect ratio. Any thoughts? Are trailer tires low crr to begin with?
You beat me to it. Let's start a thread on TT tires starting with your post. Sidewall stiffness, alone, makes it worthy of such (not just rolling resistance) in trying to determine best choices.

LT tires are the likely choice I'll make (not ST, appear to be junk tires) with a per wheel weight range of 1,800 - 2,200-lbs depending on the eventual tandem-axle travel trailer bought and outfitted. (A possible tridem would be below 1,700-lbs per wheel at GVWR.)

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Last edited by slowmover; 01-23-2012 at 02:18 PM..
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Old 01-23-2012, 02:55 PM   #20 (permalink)
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Quote:
Originally Posted by CapriRacer View Post
Thanks for that! I'll admit that I'm still trying to wrap my head around some of the conclusions regarding the lower rolling resistance of wider tires because I still find the subject to be somewhat abstract. What can I say? I'm a visual/kinesthetic kind of guy.

Regardless, I always try to look for other contributing factors, so I still want to look more closely at how the RR results were arrived at. Just a shot in the dark here, but could one of the major contributing factors to increased RR on wider tires have something to do with weight to surface/frontal area ratio?

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