Does anyone have a rational explanation why all tires are smaller than stated? I understand vehicle weight and rim width and tire pressure and all those things will cause variation, but it seems sort of ridiculous. I see folks all the time gaming tire brands just to gain an extra quarter inch closer to the size they ought to be.
The whole thing is stupid. You'd think they would feel an obligation to actually deliver on the size they advertise and put on the side of the tire. But no why would they do that? That costs more money. Can't have that
It all depends on weight. I suppose if I took off my heavy duty front and rear bumper, rock rails and take off the hard top maybe I'll score a half inch lol
The first number on a metric tire is the width. The sidewall height is a percentage of the width of the tire.
The second number is that percent. That number is used to calculate the side wall measurement. The sidewall height or "aspect ratio" of a 315/70/R17 tire is 70% of 315mm.
The third number generally preceded by an "R" is the wheel diameter (in inches - go figure).
The sidewall and aspect ratio are used in metric sized tires to determine the overall height of a tire.
Therefore the height of a 315/70/R17 tire would 34.4" when converted to inches.
But as we all know each tire's actual diameter varies depending on numerous factors.
Just think, if 37's are really 35's then if 35's were really 35 we'd have to do all those things to our jeeps you have to do to run 37's just to run 35's.
315 Duratracs are nowhere near true 35s. They are closer to a large 33" which is why I got rid of mine. Here is a picture of mine with the 315 Duratracs then a pic of mine with the 37" KO2. The KO2 is the easiest way to get a true 35" tire since they measure about 35.5".
315 Duratracs are nowhere near true 35s. They are closer to a large 33" which is why I got rid of mine. Here is a picture of mine with the 315 Duratracs then a pic of mine with the 37" KO2. The KO2 is the easiest way to get a true 35" tire since they measure about 35.5".
Like everyone has said 99% of tire brands are going to measure about an inch less than the size printed on the side. To get a tire that measures right around the 35 mark a 37 inch KO like mentioned. Also the Intercos or Pitbulls but those will probably run you $500+ per tire. Nittos run about 34.5 but are heavy as are the Intercos and Pitbulls. If you look at Interco or Pitbull make sure you get a radial tire. I wouldn't recommend either, however, because they aren't great on the pavement and will wear quickly.
If you are dead set on being right by that 35 inch mark, and mostly on pavement, I'd suggest the KO2s or Nitto Trail Grappler.
Remember that tires have TWO DIFFERENT sizes (radius) depending on how you measure. One is from the ground to the center of the hub when the the tire is under the load of the Jeep. This is the static loaded radius. This dimension determines ground clearance and gear ratios. It is totally affected by vehicle load and air pressure.
The other measurement is from the center of the hub to the top, left or right of the tire. This is the unloaded radius and THIS is the number that correlates with the manufacturer's numbers.
If you are concerned with how much ground clearance you get from the tire then you should be looking at the static loaded radius and comparing how it changes from one tire to another.
If you want to know whether or not the tire will fit without hitting then you are interested in that unloaded radius.
Since the manufactures measure their tires and spec them under no-load conditions the ONLY the unloaded measurement can be used to figure whether a tire is undersized or not. It is totally bogus to measure from the ground to the center of the axle (or top of the tire), compare that to the manufacturer's numbers and declare the tire to be undersized. While that static loaded radius may be interesting and useful, it is not a measure of whether or not a tire is under sized.
Imagine your true 35" tire is at 0 psi. The distance from the ground to the top of your tire (assume 17" rims) comes out to about 26". And nobody would say "hey, my tire is smaller than they said it would be"!
Oh, and let's not forget that the 315/70/17 is not a 35 inch tire. It is not a 35x12.5x17, it is a 315/70/17. Do the math and it computes to 34.36 inches.
Great post. Just wanted to add a little to that last part. Even for the official tire "size" as in 35x12.5x15 or 315/70R17, a lot of manufacturers agree fully that this is not the real life size. For example I've seen more than one tire where the manufacturer stated that both of these 2 sizes were actually BOTH 34.67" when the "size" numbers say they should be 35 and 34.36. So maybe check out manufacturer's specs too, not just the listed "size" which more often seems to be rather arbitrary.
Thanks. I confess this was not the response I was anticipating.
I think the root issue is that we think tire sizes are a statement of tire height rather than diameter. Start with that misconception and it just goes downhill from there.
All true and good info, but misses the point for me. If you are selling a 35x12.50 thats what it ought to be, yet every manufacturrer admits their tire is not that size, mounted or unmounted, weighted or unweighted, pressurized or not. Can you imagine buying a coke in a 12 oz bottle and it only has 11.5 oz in it? Where the heck is the bureau of weights and measures when you need them.
I run my Duratracs at 29psi, new they are 33.75" on the Jeep under load. If you look around online you can price them out lower and with rebates. Discount Tire still gives me the best deal though, I bought mine for $240 each on sale, then there was a Discount Tire rebate available for $50, and a Goodyear rebate for $40 off a set of 4. I submitted all the rebate stuff online after I got them and was mailed two preloaded cards.
Mine are a bit less because I went with a 16" wheel as well..
So if you check now, the 315/70/17 Duratracs still have a $40 rebate from Goodyear, and if you order online there's a $25 discount per tire, and I opened the credit card to get a discount there too, looks like they are doing $30 off wheels this month.
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