BFG Mud Terrain actual sizing?
- Thread starter kiwi
- Start date
If I do, will you believe my results? Or will you say I did it wrong or lied? I'll do it, and not only that, I'll do it at two vastly different tire pressures. However, if you are going to just poo poo my results, I'm not going to expend the effort.
you're gonna have to explain that one. Pretty sure my hub gets closer to the ground when I let air out of the tire.
EDIT: It might have just clicked. If you cut the treat off a tire and flattened it out, it's a length. It doesn't shrink or expand based on pressure. One revolution of the hub is going to be the length of that tread, or the circumference of the tire. Lowering pressure causes more deformation at the contact patch but it doesn't change that length.
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Starrs
TJ Guru
According to your profile you have 2.5"OME. YOu don't want to run a true 33" or a fake 33" at that lift height. You want a fake 32".
CaptainBanana
New Member
Even with both spares side by side the metric 31.5 towers over the BFG 32. I've been buying 4WD tyres for over 20 years now but I've never thought to actually measure the tyres until I got this TJ with these bfgs and thought gee they look really small.
Whether it is true that bfgs run small or whether metric size tyres run bigger for the same calculated size I'm not sure but I'm now leaning towards going to metric sizing because where we live legally speaking you can only have a tire two inches bigger than stock according to the tyre placard so it makes more sense to get a tyre that's bigger with the same indicated size on the side wall.
No one is going to feel or have any statistically significant performance differences with the tires they choose due to some very small size differences. The discussion is really just a waste of time. Getting tires that are better rated for your environment will be far more impactful.
Well, let's think through that a bit, using some critical thinking skills. When the guy measures the marks, its 2,155mm apart, or 84.84". Divide that by pi (3.14159), and you get a rolling diameter of 27.01". Now divide that by 2 to get the rolling radius - 13.51". After he deflates the tire and repeats it, there may be a slight difference. It's very hard to tell exactly how close it is from that video, but I think most people would say that difference is fractions of an inch at most. Let's be conservative and say it's 1/2" shorter, so 84.34". Divide that again by pi and you get a rolling diameter of 26.85". Now divide that by 2 to get the rolling radius - 13.42". So, on the radius, that's a difference of 0.09". If the tire on the left has a rolling radius of 13.51", does the tire on the right look like it's got a rolling radius of 13.42"?
Scaling those photos, if the tire on the right has a rolling radius of 13.51", the one on the right has a rolling radius of about 12.20". Now, let's go backwards. Take that rolling radius and multiply by 2 and then by pi to get the rolling circumference - 76.65", which is 8.19" shorter than the first measurement, and there's no way that the "error" you point out is even of that order of magnitude.
So, what is the conclusion from the video? Rolling radius (as shown in the picture above) isn't really related to the rolling circumference (the distance between the marks), and the reason for this is that the tire's circumference is fixed and doesn't appreciably change with inflation pressure.
I'm still going to do Mr. Bills' experiment this weekend, and I am confident I'll get similar results.
Oh, and I don't run drag tires on my TJ. Do you? DOT radials are designed not to expand, unlike drag tires. If tire rpm mattered, you wouldn't be able to calibrate a TJ speedometer by changing a gear in the speedometer drive. The speedometer would only be accurate at one particular speed.
You are correct, and i wouldn’t have created this discussion had i been buying brand new tires, since i would have a large selection and could get any size or brand i wanted
But the tires i’m asking about are on marketplace, so i was just curious about the actual size of a BFG Mud terrain
I personally like my BFG KM3's. Do I think they are smaller than other 35's? Some, but not enough to be noticeable. They are bigger than every 33 on the market and it is noticeable. I suppose the same would be true of every 33 on the market being bigger than 32's and 31's.
No issues with your math. Kinda gotta take issue with the claim that "rolling radius isn't really related to the rolling circumference." Seems like by definition they're related by
(2 pies).And I wasn't claiming that rolling circumference is 2pi(hub height). Pointing out that is itsn't is a very interesting observation and I had to chew on that for a while. I got to thinking about the tire tread like a tank track. But the distance/rev does change, just not as dramatically hub height. And this implies some amount of slippage or compression/expansion at the tread blocks.
re: rolling circumference vs speed and pressure, see below. But they're talking about car tyres so maybe it doesn't apply to tires?
https://www.researchgate.net/public...ement_of_dynamic_radii_for_passenger_car_tyre