W4MBG
Williamsburg, VA
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i wonder how much that kiss spacing will shrink when you load the tires. could you measure the spacing both before and after you take the 225s off? i would like to see how they compare to mine.
1999 Winnebago Minnie, 29', Triton V10, mostly stock. So far...
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McZippie
USA
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Joined: 10/21/2009
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W4MBG wrote:i wonder how much that kiss spacing will shrink when you load the tires. could you measure the spacing both before and after you take the 225s off? i would like to see how they compare to mine.
Yep... Good idea, I'll take that measurement for both sizes.
Unless anyone has a better/different idea, I'll measure the kiss spacing for both new (235)and old (225) wheels when on MH at 60lbs.
* This post was
edited 06/19/12 08:49pm by McZippie *
2009 Ford E350 Diesel Cutaway Limo Bus
2010 Jeep JKU Rubicon (Toad)
1942 Bantam T3 Trailer
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pnichols
Santa Cruz Mountains
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Quote:... i wonder how much that kiss spacing will shrink when you load the tires
That's one reason for keeping the duals' sidewall spacings as large as possible.
Another reason is the "other" much heavier loads: These are the momentry loads when hitting sudden bumps in the road and the normal bouncing the RV does all the time. These very heavy instantaneous loads will of course push out the sidewalls (a lot?) further in addition to the continual loading from raw RV weight.
A third reason for good sidewall spacing is for heat dissipation off the sidewalls that are facing each other. Have you ever felt the hot sidewalls of your tires from highway travel ... which is even worse in the summer? This heat needs to get removed as fast as possible to keep tire reliability and longevity high. It stands to reason that as large as possible kissing distance will do this heat removal best. (I have an unproved theory that it's this sidewall heating in all six of a Class C RV's tires that contributes to early sidewall cracking.)
You can get spacers to put between the dual rims if your wheel lugs are long enough. I know nothing about using these, but if they're not too thick they should help. Of course they do increase a bit the bearing torque from each outer tire of the dual sets.
Phil, 2005 E450 Itasca 324V Spirit
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McZippie
USA
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Mounted the new 235/85/16 on the MH. Kiss spacing was the same as the old the 225/75/16. I knew that wasn't right, I expected 235s to be about 1/4" to 3/8" less... Remembered that the Alcoa outer rims with 225s have about 1/4" inch less offset than the Ford inner steel rims.
So for my new 235 set-up with new Alloy outer rims that have the same offset as the Ford steel inner rims, the Kiss spacing stay the same at 1-3/8"
If using two later model Ford steel dually rims, the kiss-spacing would decease about 5/16" when changing from 225/75/16 to 235/85/16.
The next two picture confirm the 5/16" decease of kiss-spacing.
1. picture of two Ford steel rims with 225 tires 19-3/8"
2. picture of two Ford steel rims with 235 tires 20"
Difference between the two (20" - 19-3/8" = 5/8")
Kiss spacing is half of the 5/8" or 5/16"
This picture compares the width of one 235 tire (right-side) and one 225 tire (left-side). Both are mounted on later model Ford steel rims.
Comparing the height of 225/75/26 and 235/85/16 tires.
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McZippie
USA
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pnichols wrote:
You can get spacers to put between the dual rims if your wheel lugs are long enough. I know nothing about using these, but if they're not too thick they should help. Of course they do increase a bit the bearing torque from each outer tire of the dual sets.
The whole reason for this thread is to document how much kiss spacing would decease on a Ford E350/450 using stock steel rims, when changing from 225 to taller 235 tires... AND NOT USE SPACERS BETWEEN THE DUAL RIMS!!!
The E350/450 rims are hub centric. Using spacers between the rims moves the outer rim off the hub centric lip.
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McZippie
USA
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FWIW department... Here's the math from one of my old posts that computes the 5/16" kissing space decrease when changing to taller 235/85/16 tires from 225/75/16 tires.
Clicky to old past:
When my current Michelin LTX MS LT225/75R16/E Tires wear out, I plan on replacing them with Michelin LTX MS2 LT235/85R16/E
Section Width for the 225/75 is 8.8" on a 6" Rim
Section Width for the 235/85 is 9.3" on a 6.5" Rim
I don't foresee any problem with dual kissing or rubing issues since the space between the dual tires will only decrease by .30" or slightly less than 5/16"
Here's the dual spacing math:
A 235/85 mounted on a 6" rim instead of the measured 6.5" rim reduces the section width by .20" to 9.1"
Adjusted section width 235/85.... 9.1"
Less Section Width 225/75.... 8.8"
Total .3"
Each of the two larger tires has a section width that is .3" wider than the small tires. So for two tires mounted as duals the total combined section width for the two tires would increase to .6" or approximately 5/8".
Half of the two larger tires combined .6" section width is on each side of the rim. So the dual spacing between the two tires would be .3" or approximately 5/16"
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McZippie
USA
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Did a long test ride with the 235 tires over all types of roads and different speeds. The taller 2 1/2" tires are noticeable softer with less bounce over uneven pavement. Best improvement was the greatly reduced rear axle hammering over pavement breaks. Everything else was pretty much the same.
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pnichols
Santa Cruz Mountains
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Brent,
Excellent work ... a very thorough batch of homework and analysis!
My main reasons for not changing over to seven LTX M&S2 235/85R16E tires on our E450 were not wanting to spent the $$ to do it right by changing rims, and not wanting that much additional vehicle lift so as to keep cab and coach access reasonable for the DW.
The LTX M&S2 215/85R16E tires I had installed give me about 0.6 inch higher vehicle height (about 1.2 inches larger tire diameter than the stock 225/75R16E tire size) ... which is better for us than no lift at all for offroad travel. The slightly narrower tread width of the 215 tire is of no concern to me - it probably even increases wet/slushy road traction a bit as well as reducing wet road hydroplane chances.
I just hope that Michelin used a better material formulation for their sidewalls so as to maybe slow up their sidewall cracking.
If you haven't already, you might want to read on the M&S2 tire that all of the tread belts are no longer steel. Some of the belting is now some other exotic (?) material.
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crawford
Dandridge Tenn.
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I been using 235/85-16 on stock wheels for 4 years I think most people who talk about it, talk out there butts. But then I been thee and doe it...
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McZippie
USA
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crawford wrote:I been using 235/85-16 on stock wheels for 4 years I think most people who talk about it, talk out there butts. But then I been thee and doe it...
Yep... I remember you got some pretty rough treatment from a few and they had me convinced that you were running an unsafe tire size.
Kind of strange that I too had the same 'unsafe' kiss spacing for three years and wasn't aware of it. My Alcoa outer rims with less offset with stock 225/75/16 tires have the same kiss spacing as Ford stock rims with 235/85/16 tires.
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