calculate speed of tires
- Thread starter rcox
- Start date
Sniper
Well-known member
The speed of both vehicles, and everything attached to them would be the travel speed at which the tow vehicle is traveling I believe. Are you meaning rotations per mile perhaps? If so that information can be obtained from the specific tire manufacture, or maybe someone with math skills far better than mine will chime in with a formula.
Ted_Dee
Well-known member
I will attempt to make this simple. Multiply the diameter of the tire by 3.14 (Pi) this is the circumference.
divide 1056 by the circumference to get the distance.
Multiply the result by MPH to get RPM.
20" tire X 3.14 = 62.8
1056 / 62.8 = 16.8 X 50 MPR = 840 RPM
15" tire X 3.14 = 47.1
1056 / 47.1 = 22.2 X 50 MPR = 1120 RPM
I hope this is correct
divide 1056 by the circumference to get the distance.
Multiply the result by MPH to get RPM.
20" tire X 3.14 = 62.8
1056 / 62.8 = 16.8 X 50 MPR = 840 RPM
15" tire X 3.14 = 47.1
1056 / 47.1 = 22.2 X 50 MPR = 1120 RPM
I hope this is correct
danemayer
Well-known member
Why are you trying to figure out the speed?
Most trailer tires are rated for a maximum of 65mph, above which you will cause damage to the internal structure, eventually contributing to a tire failure.
If you don't trust your speedometer for some reason, many GPS devices calculate and display your actual speed.
Most trailer tires are rated for a maximum of 65mph, above which you will cause damage to the internal structure, eventually contributing to a tire failure.
If you don't trust your speedometer for some reason, many GPS devices calculate and display your actual speed.
I think you might have the right process but need an extension to bring both of them to mph. the camper tire having 5 inches less diameter would have to be going at greater speed to keep up. the problem is camper tires are not supposed to exceed sixty five for safety reasons but what speed would the truck have to go to not exceed the sixty five for the camper? my son in law is gong to get a camper with these stats and I don't want him having blow outs on his first trip.
Sniper
Well-known member
I totally understand what your trying to get at, however the calculation I do not believe can be made off of wheel diameter(s), but rather the outside tire diameters(s) using tire roll out distance. Again someone with math skills far better than mine would have to verify this, but I believe that roll out would have to be part of the calculation. Thanks rcox. Now you've got me attempting to engage my mind in some useful manner for a change. LOL
Shortest Straw
Caught In A Mosh
Add to this quandary that the NHTSA, last I read, does not even test trailer tires to the same specifications of vehicle tires. So, the 65 mph rating for trailer tires is pure speculation, a guess if you will.
danemayer
Well-known member
Speed = distance / time.
60 mph = 60 miles / 1 hour
60 mph = 60 miles / 60 minutes
60 mph = 1 mile / 1 minute
If the trailer is moving a distance of one mile in 1 minute, it's traveling at 60 mph. Notice that the calculation works equally well for trucks, trailers, cars, boats, planes, things skidding on the ground. It also doesn't matter what size tires you have. It's based on distance traveled, and time spent traveling that distance.
But maybe it's not speed that you're trying to determine.
And by the way, tire engineers rate the tires based on mph, not rpm. And I've never heard of NHTSA testing tires to determine speed ratings. As I understand it, the tire companies use an ST standard that defines max speed at 65 mph. How closely the manufacturer adheres to that is unknown.
60 mph = 60 miles / 1 hour
60 mph = 60 miles / 60 minutes
60 mph = 1 mile / 1 minute
If the trailer is moving a distance of one mile in 1 minute, it's traveling at 60 mph. Notice that the calculation works equally well for trucks, trailers, cars, boats, planes, things skidding on the ground. It also doesn't matter what size tires you have. It's based on distance traveled, and time spent traveling that distance.
But maybe it's not speed that you're trying to determine.
And by the way, tire engineers rate the tires based on mph, not rpm. And I've never heard of NHTSA testing tires to determine speed ratings. As I understand it, the tire companies use an ST standard that defines max speed at 65 mph. How closely the manufacturer adheres to that is unknown.
giving the problem further thought the parameters have changed. the 15 and 20 are rim sizes so the tire circumference is a whole new addition to the outcome but I do thank those who gave input and am sure that someone out there has delved into this before and can shed more light on the answer. it might cause someone else to think when they have the same combination of tire sizes as to what their camper tires are going thru. thanks again
Shortest Straw
Caught In A Mosh
Well, maybe I have my jargon incorrect, but they come to the 65 mph for trailer tires by a different means and do not test them to full capacity. So yes it is unknown and yet folks spew this 65 mph number out, from a government source, like it is gospel.
I think the OP is trying to see if revolutions per minute put the smaller diameter tire at a higher speed that a larger diameter tire.
I put the tire size from my NT I had in Discount tires calculator and compared it with the tire size from my pickup. The tires on my pickup do 106.8 fewer revolutions per mile than the trailer tires do. They are 4.5 inches larger in diameter than the trailer tire. If I understand the speed calculations correctly, you would need to maintain around 55 mph to keep the speed of the smaller tire at around 65. Smaller tire needs to travel faster to keep up with the larger one, higher rpm.
Bob&Patty
Founders of SoCal Chapter
Simple, a 15" tire/wheel is spinning faster than a 20" tire/wheel traveling at any given speed. I guess I am not following a reason to know this. JMHO, someone is over thinking this for some reason. A semi truck with a "low boy" trailer behind it has little wheels and tires on it. The semi tractor more than likely has 11.24.5 wheels on it. They don't have a problem with the small tires on the trailer spinning at least 2 X's as fast as the tractor tires and they are hauling heavy loads.
travelin2
Pennsylvania Chapter Leaders-retired
JanAndBill
Well-known member
As speed is a measurement of the object in question moving across a given distance, the only time the circumference of the tire is relevant is in programming the truck ECM, so it can properly calculate your speedometer to reflect your current forward/reverse movement. If a truck were traveling 65 mph then it stands to reason, any trailer that truck is pulling would also be traveling 65 mph. Since manufacturers rate their tires as to SPEED and not REVOLUTIONS then a truck traveling at 65 mph would not be exceeding the trailer tire rating of 65.
I had a driver one time that always grumbled when he hooked to one particular trailer that had smaller than normal tires on it. I asked him why one time and his response was "It's so much lower in the back then at the tractor, that means I'm constantly pulling it uphill".
I had a driver one time that always grumbled when he hooked to one particular trailer that had smaller than normal tires on it. I asked him why one time and his response was "It's so much lower in the back then at the tractor, that means I'm constantly pulling it uphill".
