timmac wrote:
Who has changed there old 16.5in tires/rims to 16in tires/rims, how much did it drop your rpm's, if so did mpg stay the same, did your HP go down.
Who has changed there old 16.5in tires/rims to 16in tires/rims, how much did it drop your rpm's, if so did mpg stay the same, did your HP go down.
Smaller diameter tires will raise your RPMs, not drop them. (The smaller tires will have to turn more times to go the same distance.)
1970 Explorer Class A on a 1969 Dodge M300 chassis with 318 cu. in. (split year)
1972 Executive Class A on a Dodge M375 chassis with 413 cu. in.
1973 Explorer Class A on a Dodge RM350 (R4) chassis with 318 engine & tranny from 1970 Explorer Class A
![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/tongue.gif "tongue")
There are a couple of tires on 16 inch rims that are actually a larger tire diameter (depending of the profile size) than the 16.5s.
1978 21ft Tioga Dodge 440 Motor,
4.5kw Generac and 80 watts Solar
1984 Goldwing Interstate (Daily driver)
Misc Things I've done to my RV pictures
USAF Retired
To Err is human... To Forgive is not SAC Policy.
My rig had brand new 16.5's on it when I purchased it, but do plan on changing over, if I ever need to buy again.
As much as I use the old Chinook, these ought to out last me though.....LOL.
Man I got to get out more..........
![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/biggrin.gif "biggrin")
Gary Webb
Phoenix, AZ
Kendas wrote:
Hey Griff! You asleep this afternoon/evening? RIM size not tire diameter
Hey Griff! You asleep this afternoon/evening? RIM size not tire diameter
Mea culpa -- you're right. (About rim size vs tire diameter ... I was awake but had other things on my mind.)
I went through the process of changing tire size with MLP, although I stayed with 16 inch rims.
MLP originally had 16 inch split rims and I got a set of used 16 inch one-piece rims. The tires were 7.00-16 6 ply. (And, were probably the same tires that were on the chassis when it left the Dodge factory.) I wanted to go to 235/85R16 but would settle for 216/85R16 if I had clearance problems.
I wrote to several tire manufacturers for advice. Most ignored me completely and a few recommended I contact my local tire dealers. (I had already talked to the local dealers, who were all clueless ... and recommended I contact the manufacturers.) Goodyear responded with a good answer containing lots of useful information.
Once I had the one-piece rims, I bought two used 235/85R16 tires from a local dealer and mounted them on the rims. (No need to balance them ... they're strictly for clearance testing and will be replaced.)
Step one was to make sure the tire sidewalls didn't run against each other when mounted as a pair on the rear axle. With the one-piece rims and larger tires, the gap between the dually mounted tires was slightly bigger than original so the 235/85R16 tires were okay in that department. (Careful switching from bias ply to radial tires ... the sidewalls tend to bulge more in radials.)
Step two was to check clearance between the tires and various chassis parts such as springs, shocks, and steering mechanism. Check both sides of the front axle because the steering mechanism isn't necessarily symmetrical side to side. Again, clearance was ample for me.
Step three was to make sure the tire load capacity is sufficient. The load capacity of modern tires is generally greater than older tires but it doesn't hurt to make sure. MLP's rear axle is rated for 7500 lbs max and the rear springs are rated for 7600 lbs total (3800 lbs max per spring times two springs.) Front axle is rated for 3800 lbs and the front springs are rated for 3400 lbs total (1700 lbs per spring.) The tires I'm looking at (Goodyear Wrangler SilentArmor 235/85R16) are rated at 3042 lbs max at 80 psi so front (3042 x 2 = 6084 lbs) and rear (3042 x 4 = 12168 lbs) exceeds both axle/spring maximums.
Step four -- check tire to body clearance -- wasn't an issue for me because I can adjust the (new) body dimensions to suit the tire instead of adjusting tire size to suit an existing body. However, when you check this part, take into account the springs bottoming out to make sure there's enough clearance between the tires and wheelwell. Also, turn the steering lock to lock to make sure there's enough clearance in front.
Depending upon the bolt pattern for the 16.5 rims, changeover may be a hassle. If I recall correctly, most 16 inch rims have 8 on 6.5 pattern. You may have to change the drums (or rotors) and brakes to get that bolt pattern. Alternatively, you can swap rear axle if change is necessary. (Yours is probably a Dana 70 so I'd stick with that or go to a Dana 80 axle, such as found in newer Dodge trucks.)
I think we discussed how to read metric tire sizes previously ... if not (or if you don't want to wade through all 190+ pages in this thread), I can put up a description.
![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/awink.gif "awink")
Go ahead and post the description please (You know someone is going to ask).
Ken
Kendas wrote:
Go ahead and post the description please (You know someone is going to ask).
Go ahead and post the description please (You know someone is going to ask).
Okay, here's draft text and images for a page I'm working on for my site. (Standard dilemna -- work on motorhome or work on website?)
The images and text are copyrighted so please limit yourself to fair use rules ... do not republish without express written permission from me.
So, the first figure you need for your calculations is the tire diameter. You can ask the tire dealer or manufacturer or look it up online, at places like www.tirerack.com or www.1010tires.com. Or, you can figure it out yourself using the information listed in the tire size. The first number (235 in my case) is the tire width, in millimeters, the second number (85) is the profile, which is the sidewall height represented as a percentage of the tire width, and the third number (16) is rim diameter, in inches.
First, convert the tire width (235 millimeters) into inches by dividing it by the number of millimeters per inch (25.4). (235 / 25.4 = 9.25 inches)
Second, calculate the sidewall height by multiplying the tire width (9.25 inches) by the profile (85% or .85). (9.25 * .85 = 7.86 inches)
Third, find the tire diameter by adding the sidewall height times two (7.86 * 2 = 15.72 inches) to the rim diameter (16 inches). (15.72 + 16 = 31.72 inches)
-- I like to check the figures against other sources to make sure there's no mistake. I double checked the results above against the figures on 1010 Tires' website and they match.
![[image]](http://www.riffgan.com/misc/rv_net_stuff/Tire1.jpg)
![[image]](http://www.riffgan.com/misc/rv_net_stuff/Tire2.jpg)
![[image]](http://www.riffgan.com/misc/rv_net_stuff/Tire3.jpg)
Note: Tire circumference is the starting point for calculating engine RPMs and speedometer gear ratio. (Different tire size will change your speedometer reading ... which, on older Dodge trucks, can be corrected with one part, a wrench, an o-ring, and thirty minutes work.)
Most all tire people these days are "measuring" these tire specs as "revolutions per mile".
A much MORE accurate way of doing this.
MasterBoondocker wrote:
Circumference ? .. tire height ? ? ? ..... NOT.
Most all tire people these days are "measuring" these tire specs as "revolutions per mile".
A much MORE accurate way of doing this.
Circumference ? .. tire height ? ? ? ..... NOT.
Most all tire people these days are "measuring" these tire specs as "revolutions per mile".
A much MORE accurate way of doing this.
Circumference is necessary to calculate the "revolutions per mile" and diameter (i.e., tire height) is necessary to calculate circumference.
In fact, calculating (or looking up) revolutions per mile is the next step in determining engine RPMs and speedometer ratio ... but, I wanted to limit my post to tire size calculations.
Yes, you can look the necessary information up -- I listed two online sources for that kind of information -- and hope they didn't miscalculate and didn't mistype the information.
I mentioned crosschecking the information to ensure it's accuracy ... saves headaches in the end. (I recall a set of ruined new brake shoes because I didn't doublecheck the crossreferenced rear axle seal.) You can't necessarily trust the web (or books and magazines) because I seen numerous cases where a single miscalculation is regurgitated -- ad nauseam -- across multiple pages and multiple sites.