I know discount tire and other have this information at hand, however what happened to pie x diameter…?
Saying this it is worth noting that accurate diameter is also on the tire websites so you may as well do what you say!
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Saying this it is worth noting that accurate diameter is also on the tire websites so you may as well do what you say!
Pi x 2 x Distance from hub to ground. The tire will compress some and it’s driven diameter could be a bit smaller than the published diameter
You are saying 2 x radius = diameter?
Or pointing out there is a slightly more accurate way of calculating the miles per revolution? I can see that.
No way. The circumference is the same even if it's not a perfect circle or deforms during rotation.
Dealer dinner but apparently you can mostly
Follow the FSM. Oil filter housing comes out, unbolt the rack, there’s a tilt required to get it out. Reverse procedure.
Correct but the actual tire circumference will change based on pressure and tread wear.
UPR LC
GOLD Star
I think what skrypj is saying is the tire when mounted and under the weight of the vehicle will have an "effective" diameter equal to the hub-to-ground radius times 2, not the published tire diameter. Same phenomenon as changing tire size itself. Can be tested by airing the tire way down and recording speed via GPS then do the same for a fully aired up tire, if you wish to test the theory.
To determine change in speed (due to new tires) in relationship to speedometer, my recommendation is to use a phone app that has GPS to determine vehicle speed at low speed and high speed (30mph and 70mph) and compare both speeds to your vehicle speedometer. Take note and adjust your driving speed accordingly. To conduct the test, I find open flat road and repeat the test multiple times to confirm accurate results from the GPS.
On my F150, which I could actually adjust the tire size in the BCM on, my published 34.4” OD KO2’s ran as something like a 33.5” tire at 38 psi. Very similar weight truck to a Land Cruiser too at around 6400 lbs empty.
If you assumed your tire is the published diameter, your correction factor will be almost as incorrect as just using the uncorrected speedometer.
This.
I corrected with GPS for my KO2’s I mentioned in my last post. I did a trip from UT up to Glacier NP in MT and during a 200 mile stretch I tracked on GPS my odometer in the truck was only of by 0.2 miles
And that was a 34.4” tire set as a ~33.5” in the BCM.
My current 315/70’s on my LX are only showing ~16.5” hub to ground at 40psi
Oh and just FYI, Ford puts the "driven circumference" for the Raptor's factory 315/70R17 into the BCM as 2651mm or a 33.2" diameter.
Ill check my LX tune in VFTuner to see what that shows the tire size as.
EDIT: My LX Tune shows 15.22" as the radius of the tires. That would give us a 30.44" tire diameter on a 31.9" tire.
Ill check my LX tune in VFTuner to see what that shows the tire size as.
EDIT: My LX Tune shows 15.22" as the radius of the tires. That would give us a 30.44" tire diameter on a 31.9" tire.
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I hope @gaijin is enjoying the 
My 2 cents is the circumference does not change if the tire is deformed by the weight of the vehicle on it. The diameter is slightly less at the hub to road distance, but the deformation causes the diameter to be slightly more either side of that, keeping the overall diameter the same as published (or actually measured off the vehicle at correct psi).
Does the tire get larger the faster you go from centrifugal force?
My 2 cents is the circumference does not change if the tire is deformed by the weight of the vehicle on it. The diameter is slightly less at the hub to road distance, but the deformation causes the diameter to be slightly more either side of that, keeping the overall diameter the same as published (or actually measured off the vehicle at correct psi).Does the tire get larger the faster you go from centrifugal force?
You're right that the tire is still going to be the same total distance around but that doesn't have any factor in how fast or slow your hub is rotating. Only the distance from the hub to ground matters.I hope @gaijin is enjoying the
Keeping on the same tire I was talking about, BFG publishes the diameter as 34.4" but has a rev/mile of 604. 5280/604 = 8.74' = 104.9" circumference. The diameter for a 104.9" circumference is 33.39"
Yup, this is why I recommend for others to do their calculations based on the manufacture provided revs/mile. This uses consistent methodologies that also consider load and resulting radius. Which cannot be just simplified as diameter and circumference. Then again, none of this requires this level of accuracy so diameter differences should be good enough as a first order approximation for speed and MPG deltas.
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I guess I’ll give up understanding this. BFG is claiming the effective tire diameter is an inch less when running down the road, calculated from numbers showing they think the tire is not the same total distance around when deformed. The circumference for a 34.4” tire is 108.1 and for a weight-deformed 33.4” tire is 104.9. Do they calculate revs per mile based on maximum load and pressure?
hoser
SILVER Star
Yes, the tire diameter increases with rotational speed. Best seen on drag racing vehicles when doing burnouts. As mentioned, pressure also changes the diameter. Manufactures measure tire diameter at maximum rated pressure. Inflate your spare tire to maximum and you'll notice the tread is more convex than it is flat.I hope @gaijin is enjoying the
Does the tire get larger the faster you go from centrifugal force?
Early TPMS didn't use tire pressure sensors but rather used the ABS sensors to detect rotational speed. The tire low on air will rotate faster than the rest.
As for revolutions per mile, I would ignore it because it will based on either no load, maximum PSI OR maximum rated load (and max psi).... which none of us do.
hoser
SILVER Star
For your enjoyment...
Or find your percentage, and (in my case) do 35 x 1.07 = 37.45
EDIT: also, next time you do a longer run, keep a GPS app up and delta ODO to GPS. That's the percentage I use (7%), which is reflective of exactly what my truck is doing at my inflation/setup. (inflation: see also @gaijin related works)
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Just compare GPS speed reported in most any app against the speedo and so the math. On 35s I’m off by about 8%, based on my tests at 60 and 80 mph. Ymmv
Going back to changing my own oil. The Toyota filter housing has its own special tool. But I am swapping over to the Jowett. Being a cheap arse I really do not want to buy the Mr T tool. So what are my options for removing the original housing besides going to a local dealer and having them do the swap? I have the Jowett socket so install is not a problem.
Also I am replacing the drain plug with a Stahlbus Valve I already have one which is M20 x 1.5 for the Jowett Double checking that the oil pan is plug is M12 x 1.25. I ask because I thought they were the same. As that is what I recall from a message from Brian Jowett. But it has been a while.
Also I am replacing the drain plug with a Stahlbus Valve I already have one which is M20 x 1.5 for the Jowett Double checking that the oil pan is plug is M12 x 1.25. I ask because I thought they were the same. As that is what I recall from a message from Brian Jowett. But it has been a while.
