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What is the purpose of a tire, generally speaking?

The wheel has gone through numerous changes since it was first invented. I don't know if early man ever used solid stone wheels on a cart or not but if so, those would have been a huge problem. If you hit a bad rut hard enough, the wheel might have split in two and that would have been the very first truly "flat tire". :sidelaugh: Jumping ahead to the 1900's when pneumatic tires competed against solid rubber tires, the companies such as Goodyear and Firestone were struggling with developing more suitable tire carcasses. Canvas was one of the early choices but it did not work all that well. Flat tires were so common that many cars came with two spare tires. So, here we are today and technological advancements have produced tires that are absolutely light years ahead of anything found on cars 100 years ago.

A tire is supposed to do several things. First of all, it is supposed to support the vehicle it is mounted on. It should be resistant to the elements such as water, sunlight, gas, oil and other chemicals that it might encounter. It should try to provide a decent ride for the passenger/s while giving excellent tractive capabilities to start and stop the vehicle. It should not lose contact with the rim at the bead when subjected to high speed turning or heavy side loading. It should have wear characteristics that will justify its cost.

Tires come in all types of "ratings". Some car tires are "speed rated" to show that they can withstand constant vehicle rates up to 200 MPH, as an example. Almost all tires are "Load Rated" to show how many pounds they can safely support when inflated to a certain pressure. Other tires are rated for environmental conditions such as "Mud & Snow" or "All Season Radial". Truck tires are rated for location on the vehicle such as "Steering Service" or "Trailer Service".

One of the things that often comes up when owners of LT's and GT's talk about tires, is ply rating. In truth, it is AIR that supports the vehicle, not the tire. The tire is simply a vessel that contains the air so it can support the vehicle. We pressurize air inside this vessel and we measure that pressure by a unit known as Pounds per square inch. On the heavy trucks I own, the tires are inflated to 90 PSI minimum and as much as 110 PSI. We do that to minimize the flexing of the sidewall of the tire. Flexing causes heat. Heat causes deterioration to the tire carcass and so does the flexing. The two combined will cause tire failure in short order. High pressures in tires call for a strong tire carcass to contain the air. Therefore, it is common for such tires to have a PLY RATING of 10, 12 or 14.

Another tire problem comes from a brutal environment, such as the one found in mining and quarrying operations. The tires used on those huge machines can have ply ratings in the 40's to protect against sharp rocks impacting the sidewall and tread areas.

So what does all of this mean to those who own a 1000 LB garden tractor? Our top speed is less than 15 MPH. We are driving on grass or in dirt. Carcass temperature is not an issue as it is for a Ferrari owner. With only 1000 LBS to support by four tires, we are talking about an average loading of 250 LBS. You can put that much weight into a construction wheelbarrow that has a single tire on it. The manufacturer of the tractor states in the Operator's Manual that it is OK to run as little as 8 PSI and as much as 15 PSI in the tires. Your automobile probably calls for 28 to 32 PSI by comparison.

On all garden tractors and lawn tractors produced by Colt, Case and Ingersoll, 2 ply tires were spec'd. Only the front tires on the 600 series had a 4 ply rating due to the front end loader being present. When it comes to low speed vehicles such as these tractors, sidewall flex is important when it comes to "ride quality" because the tractor is unsprung. The only "suspension" you have is the flexing of the sidewall. You should want to retain that flexing for another reason besides the comfort factor for your fat ass. Flexing often aids in finding traction because it will allow the carcass to conform to the ground and increase the size of the "contact patch". The contact patch is the total area the vehicle is riding on. This contact patch is what keeps your car from sliding off the road while negotiating a curve at 60 MPH. In relation to the size of the tire, the contact patch is small. If you over-inflate a tire, the contact patch is often reduced in size. If you under-inflate a tire, that too can sometimes reduce the size of the contact patch. But, it is a well-known fact that letting air out of tires when you are off-road in sand or other similar conditions can increase the size of the contact patch and get you out of trouble.

So..... what's the point to all of this, you ask? Well......to me it's simple. Stick with 2 ply tires front and rear on your tractor UNLESS there is an overwhelming reason to do otherwise. What might that overwhelming reason be?

- you need new rubber but you absolutely cannot find 2 ply tires anywhere in the size you need.

- you own a property that has nasty things growing on it that routinely cause flat tires and a higher ply rating will resist puncturing.

- you have modified the tractor in some way that has upped the loading on the tires to the point where going to a 4 ply or even 6 ply carcass is essential.


When it comes to ease in mounting, dismounting and inflating tubeless tires, the 2 ply is the hands-down winner. Try slipping a pair of 6 ply tires onto 8" rims and you are in for a struggle. Try removing those 6 ply tires later on and thoughts of cutting them off will spring to mind. If you put 6 ply tires on the rear of a 400 Series, they will support the tractor with almost no air pressure due to sidewall stiffness. The main reason to put air into them is to keep the bead seated on both sides. Yes...... there are some advantages to a higher ply rating but there are also disadvantages because that stiff tire carcass won't conform to the ground like a 2 ply carcass will. You need to add a huge amount of weight to the tractor to make that happen. Choose your tires well. Do not assume that a 4 ply or 6 ply tire is automatically superior to your 2 ply OEM tire. Case engineers could have spec'd any tire. They chose the best overall tire for the application and that's what you should focus on. :thumbsup:
 

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How's about the pro/con of adding a tube to the two ply tire? Are there any advantages to adding a tube to the LGT or to the trailer that it may pull or to a small 4 x 8 trailer. I'm restoring and old trailer (4 x 8) for my son who takes his lawnmower and tiller to grandma's house. It has rotten tires that need to be replaced ...(480/400-8). For my Case 448 I've used slime products on the front and rear along with plugs on the rear OE tires. The thorny hedge and locust trees have caused some headaches until I got the place policed up better. Hope this fits into the discussion. Mike
 

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Discussion Starter · #3 ·
Inner tubes are nothing more than an airtight vessel to maintain tire pressure. They do little to increase the structural integrity of the tire casing itself. If a tubeless tire has deteriorated badly due to age and UV exposure to the point where air is seeping through the carcass, then the installation of a tube will extend the life of the tire. But this decision must be made carefully. On a lawn or garden tractor, it's rarely a life threatening situation if the carcass suddenly opens up and allows the inner tube to rupture. The tire goes flat.... end of story. You just go out and purchase a new pair of tires.

Running badly deteriorated tires on cars, trucks, trailers etc that can reach highway speeds is a completely different story. If the carcass fails while travelling at more than 45 mph or so..... you run the risk of involving other motorists in this mishap and that could lead to personal injury or worse. To me, it isn't worth the risk.

In my original post, I mentioned the fact that certain areas of the country have vegetation problems such as thorny hedge and locust trees which can often cause tire punctures. I would not blame anyone for moving to a 4 or even a 6 ply rated tire to put an end that problem if all other avenues had been exhausted. But as you say, diligent property maintenance can solve the problem.

And yes, your post certainly fits into the discussion.

Thanks for joining in.
 

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That's a mouth full Tom. :think:
For me I prefer 2 ply on my tractors for the reasons you stated, but I have not found 2 ply available for the type of tire I had been looking to use. Case in point my modified 226. I had to settle on 4 ply's.

FYI: I put my tires (4ply & up) on top of the stove to heat them up before mounting, used along with dish soap, this makes them more pliable for mounting. Not too hot, of coarse! :wink:
 

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:wtf: As my deceased wife might have said....WTF. But now that she's gone, I might try that when I wrestle with the new trailer tires. Nah, she wouldn't have said that but her words would have been just as pungent. :smile:
 

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The other important thing to think about is traction. The 2 ply's will produce greater rim pull force due to increased 'adhesive patch'. That assumes the correct air pressure is used. Hard tires have significantly smaller adhesive/contact patches and you'll notice a difference when you leave burn marks all over your yard if you launch with a lot of jerk. Another bonus is lower compaction due to the increased patch. That is significant in areas in which you must run the same path all the time (along fences, around trees, landscaping, etc.).
 
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