Transmission ,
Postmaster
Joined: Mar 2008
Posts: 3,255
Likes: 0
From: Sweet Home, OR
I'n not questioning anyboy's math or formulas here so don't take offense!
I'll bet you dollars to doughnuts that your tires are not 33". Most tires advertised as 33" are actually closer to 32, some even less.
More importantly though is what I call the "rolling radius."
What I mean by that is the distance from the road to the center of the hub.
I'll bet you on the average 33" tire that measurement is 15.5-16".
If so then you need to plug in 31 or 32" respectively into your formula(s).
It won't make a huge difference but it will be different.
Just a thought.
I'll bet you dollars to doughnuts that your tires are not 33". Most tires advertised as 33" are actually closer to 32, some even less.
More importantly though is what I call the "rolling radius."
What I mean by that is the distance from the road to the center of the hub.
I'll bet you on the average 33" tire that measurement is 15.5-16".
If so then you need to plug in 31 or 32" respectively into your formula(s).
It won't make a huge difference but it will be different.
Just a thought.
Posting Guru
Joined: Dec 2008
Posts: 2,347
Likes: 1
From: Maysville, Kentucky
I hate math with alot of numbers sometimes. Hit the wrong button.
Ok at 2000 in overdrive the math shows 67.45 mph my speedo show 62 so its of 5 mph. Ok so i did do the math right the first time.
Ok at 2000 in overdrive the math shows 67.45 mph my speedo show 62 so its of 5 mph. Ok so i did do the math right the first time.
Lead Driver
Joined: Nov 2003
Posts: 6,900
Likes: 3
From: Campbell River, B.C.
Yup, I got 67.45 as well.
Dodge, if you read my earlier post you'll see that I mention that none of these calculations assume any slip at the torque converter or tires. I also make mention of he variaton of tire size from one tire to the next.
I had some Baja wide tracks on my truck for a while and when they were almost bald they measured about 32" unloaded. My new tires (still the same 235/85/16) with full tread are closer to 31.5.
GPS or radar are probably the only reliable way to ge accurate speed but I find gearing calculations fun. What can I say, I fell down the stairs one too many times as a kid.
Dodge, if you read my earlier post you'll see that I mention that none of these calculations assume any slip at the torque converter or tires. I also make mention of he variaton of tire size from one tire to the next.
I had some Baja wide tracks on my truck for a while and when they were almost bald they measured about 32" unloaded. My new tires (still the same 235/85/16) with full tread are closer to 31.5.
GPS or radar are probably the only reliable way to ge accurate speed but I find gearing calculations fun. What can I say, I fell down the stairs one too many times as a kid.
Postmaster
Joined: Jun 2007
Posts: 2,621
Likes: 1
From: Sweetwater Texas
The only other way to accuretly get speed is to get to a steady speed on the interstate with a stopwatch and as soon as you pass a milemarker start the stopwatch then at the next one stop it. Then you can do more math to tell you your true speed. To make this more precise time yourself for about 5 miles worth.
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Freshman User
Joined: Sep 2006
Posts: 46
Likes: 0
Hey Guys ,
I made the calculation with my current tire sie Lt215 85 16 measure to be 29 in , with 3.55 rear end
this put me at 2500 RPM at 59 MPH
if I change the tire to 235 at the RPM it will put me 67 MPH.
This is a big diffrence , will plan on changing that to bigger tires size
I made the calculation with my current tire sie Lt215 85 16 measure to be 29 in , with 3.55 rear end
this put me at 2500 RPM at 59 MPH
if I change the tire to 235 at the RPM it will put me 67 MPH.
This is a big diffrence , will plan on changing that to bigger tires size
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 15
From: Nutter Fort, WV
Be very carefull running 235 tires on a dually.
If they rub between the tires, heat builds fast and a blow out soon follows.
Any load on the truck will probably have 235 tires together at the bottom.
Which is the reason for the 215 tire width.
Also most manufacturers have revolutions per mile on their web site for all of the different sizes, tire models and tread patterns as well as a static load diameter.
If they rub between the tires, heat builds fast and a blow out soon follows.
Any load on the truck will probably have 235 tires together at the bottom.
Which is the reason for the 215 tire width.
Also most manufacturers have revolutions per mile on their web site for all of the different sizes, tire models and tread patterns as well as a static load diameter.
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 15
From: Nutter Fort, WV
I have actually seen 325/75-16 tires on a dually.
But two sets of 2" spacers were need to clear both the springs and between the tires.
Everytime I ever saw 235 tires on a dually either they had spacers between the wheels, or the tires were so close they didn't dare put anything in the bed or they would rub.
A truck that can't haul anything, even more so a dually that can't haul anything is a very large waste of money.
But two sets of 2" spacers were need to clear both the springs and between the tires.
Everytime I ever saw 235 tires on a dually either they had spacers between the wheels, or the tires were so close they didn't dare put anything in the bed or they would rub.
A truck that can't haul anything, even more so a dually that can't haul anything is a very large waste of money.
Thread Starter
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Freshman User
Joined: Sep 2006
Posts: 46
Likes: 0
Dave ,
That is great
what you are saying is that I can use any tire size as long as I put enough spacer to have clearance between the tires.
That makes good sense, for me it is more common to have 245, 265 75 R availabe than the 85 R tires. 1" spacer will do me
Good News we finished the springs today , probably put 4" of lift which is plenty all with the current load on the truck. The Utility bed is loaded with Tools , specialty tools and a miller trailblazer and set acetlyne bottles .
That is great
what you are saying is that I can use any tire size as long as I put enough spacer to have clearance between the tires.
That makes good sense, for me it is more common to have 245, 265 75 R availabe than the 85 R tires. 1" spacer will do me
Good News we finished the springs today , probably put 4" of lift which is plenty all with the current load on the truck. The Utility bed is loaded with Tools , specialty tools and a miller trailblazer and set acetlyne bottles .