Last December I upgraded my trailer tires from Trail America to Maxxis M8008, and also increased one size from 205/75R14 to 215/75R14. At the time I was concerned about wheel well clearance with the larger tire size, which has a radius that is 0.3" larger. Later on, based on my own studies of Dexter tables for torsion axles and communication with the trailer manufacturer, I concluded that there would be at least 1/2" clearance between the new tire at shock load and the wheel well.After each camping trip I inspect the wheel wells for any evidence of scuffing. Until this last trip, no evidence of scuffing. On this last trip, I was heading North out of San Jose on a California freeway and encountered an area of the right lane where there apparently had been some ground slippage. The area suddenly dipped about 6" and continued for perhaps 30 to 50'. I was going between 55 and 60, and I felt the Pilot's suspension solidly bottom out. Well, I thought, this will be a good test of the TT's wheel well clearance.When I later inspected the wheel wells, there was some light scuffing. I am trying to understand how this happened. Perhaps Dexter's tables are wrong and the Torflex spindles moved more than they calculated.I see in a table in Barrystiretech from the Tire and Rim Association that a "grown tire" in the 215/75R14 class will increase its diameter by 0.55". Perhaps that is also a contributor to the problem, but I really don't know what a "grown tire" is. Does it refer to a tire temporarily increasing in diameter due to centrifugal force? Does it refer to an aging tire losing elasticity and just "growing" larger?Just trying to figure this out.Thanks,Bruce

A "grown tire" is exactly what the term implies: a tire that has grown (maybe "stretched" is more apt), usually due to use.It's not a temporary condition.

One other point. Not sure on 14" rims, but rims used for 205/75R15 usually have a 5" or 5.5" width. Minimum rim width for 215/75R15's is 6". Perhaps you might check that also while pondering.

Francesca Knowles wrote:A "grown tire" is exactly what the term implies: a tire that has grown (maybe "stretched" is more apt), usually due to use.It's not a temporary condition.Thanks, Francesca, for the info. The tires are 8 months old and have about 700 miles on them. To my uninformed mind, that doesn't seem like enough to generate tire growth, but maybe it is.Bruce

Chuck&Gail wrote:One other point. Not sure on 14" rims, but rims used for 205/75R15 usually have a 5" or 5.5" width. Minimum rim width for 215/75R15's is 6". Perhaps you might check that also while pondering.The placard on the trailer specifies ST 205/75R14 tires on 5.5" rims, but in fact the original equipment rims are 6". States it right on the back of the rims!Bruce

Bruce H. wrote:........I see in a table in Barrystiretech from the Tire and Rim Association that a "grown tire" in the 215/75R14 class will increase its diameter by 0.55". Perhaps that is also a contributor to the problem, but I really don't know what a "grown tire" is. Does it refer to a tire temporarily increasing in diameter due to centrifugal force? Does it refer to an aging tire losing elasticity and just "growing" larger?Just trying to figure this out.Thanks,BruceIf you were to measure a tire immediately after inflating it, then measure it 24 hours later, you will find the tire has grown. In fact, many tire manufacturers label their tire dimensions as "24 hour measurements".While most of the growth takes place in the first 24 hours, the tire will continue to grow very slightly over time. It is barely measureable, but it does happen.But be careful here. "Maximum Grown" dimensions is just a way of indicating what the tire could potentially become, and NOT what it is actually going to achieve.Further, the "Design New Tire" dimensions listed on that chart are a guideline and not a requirement. Tires can be built smaller or larger than that (BTW, it is the "New Design" dimensions that is measured at the 24 hour mark.)Plus, the "Maximum Grown" is a kind of warning for both the tire manufacturer and the vehicle manufacturer. A tire does not necessarily grow into that dimension.Those dimensions are static, freestanding. Deflected tires (tires under load) do NOT conform to those dimensions. - AND - Tires get distorted in maneuvers. Do a you tube search for tire testing and see how much movement there can be.

What is a "Grown Tire"? | Good Sam Community

21 Replies

Airstreamer67
Explorer
Dec 09, 2013
The last time I had a "grown" tire it was due to belt separation. The middle of the tire had expanded, thus creating an oval shape rather than a flat surface. The lining of the wheel housing began showing signs of rubbing, and I had difficulty placing the expandable wheel chocks between the tires. Beware of these conditions if they occur.
facory
Explorer
Dec 05, 2013
Bigger is not always better. The trailer is fitted with specific wheels and tires that are optimal for the performance of the trailer. Shouldn't mess with it.
hehbr
Explorer
Dec 03, 2013
I have a Windjammer trailer that had a tire clearance problem causing the tires to rub the wheel wells. The trailer manufacturer replaced the axles with mounting brackets providing more clearance. In my calls to Dexter their engineer told me they recommend a minimum of 3 inch clearance to allow for the axle flexing.
Yardvarkers
Explorer
Nov 30, 2013
A tire that, with use, has slightly increased in size.
:h
Bruce_H_
Explorer
Nov 30, 2013
DavidP wrote:
Dexter requires 3 inches of travel between the top of the tire and the wheel well on torsion axles. I have about 3.5 unloaded and 3.25 loaded. What is your measurement?

With the larger (ST 215/75R14) tires and before the axle upgrade, it was about 1.2". After the axle upgrade, about 1.9". This is with the trailer loaded to nearly GVWR, but about 350 lbs. under GAWR.

Bruce
DavidP
Explorer
Nov 30, 2013
Dexter requires 3 inches of travel between the top of the tire and the wheel well on torsion axles. I have about 3.5 unloaded and 3.25 loaded. What is your measurement?
Bruce_H_
Explorer
Nov 29, 2013
camperforlife wrote:
Please post what you learn. I don't have torsion axles but was planning on going from 205 75R 14 to 215 75R 14 tires when the originals blow or need replacing........whichever occurs first. ;)

Well, I painted the tops of the wheel wells and encountered two more instances of light scuffing. Both were associated with encountering transitions from "road under construction" to good pavement.

I couldn't live with the tires occasionally hitting the tops of the wheel wells. The OEM Dexter #10 Torflex axles on my trailer had a start angle of 22.5* down. Dexter sometime this year came out with a new variation, a 32* down start angle. According to the Dexter tables, this would provide an additional 0.99" clearance between the top of the tire and the wheel well at full load.

I ordered a new axle with the 32* down start angle directly from Dexter and had it shipped to my Lance dealer, who installed it. The whole thing set me back $779.

When I measured the new distance between the top of the tire and the wheel well, it had increased by 0.7", not the 1" from the Dexter table. Don't know what to make of that. Nonetheless, I now have peace of mind about the running gear.

Bruce
coolbreeze01
Explorer
Jul 22, 2013
I had a boat trailer with torsion axles. It prematurely wore a tire and I had it aligned. Then I up-sized replacement tires and never had another problem.
Slownsy
Explorer
Jul 22, 2013
Maybe you calculations wasn't correct, I wood think it coud be extremely hard to calculate how mutch it can travel unles it has a solid stop, and .5" is not a lot.
thomasmnile
Explorer
Jul 22, 2013
Bruce H. wrote:
camperforlife wrote:
I would simply spray paint over the scuff and keep an eye on it to see if it scuffs again. It could just be a case of an extreme road condition that created a one time problem. A 6" drop is not common, I don't think in my 40 years of driving I've ever encountered that large of a drop. At this point, it is either keep an eye on it or go back to stock.

Biggest dip on a freeway that I can recall as well. Good advice about the spray paint--think I will do that. Thanks.

Bruce

Please post what you learn. I don't have torsion axles but was planning on going from 205 75R 14 to 215 75R 14 tires when the originals blow or need replacing........whichever occurs first. ;)