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Old 01-27-2008, 10:53 AM   #11
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I believe I've read that the speedo is calibrated by computer to match the gear and tire size, not through changing a speedo gear (like Jeeps) nor to match the stock configuration. Sure there are other reasons to match or approximate the stock configuration but I think you can then set you speedo to match.

One of my issues with only 20K left on my warranty is that the SMB config has my speedo off by ~7% and the low range puts approximately 4x the actual distance on the odometer. I suppose it won't matter as long as I don't have a warranty failure before 81000 or so but I kind of got robbed of that last 6K of coverage, not to mention bits and pieces that stack up from being in low range (driving 60 miles down a twisty dirt mountain road for example puts about 240 miles on the van).

As far as 33s/35s go I really like the height of the van (climb in climb out height) with side steps and 33s. I'm worried that with 35s it will just be that inch too much. I also considered 34s but I haven't found them in an E range tire I like.

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Old 01-27-2008, 11:05 AM   #12
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To calculate the tire diameter in inches, you need the full tire size from the side of your tire. Say you are running a 285/75 R16. That’s a 16" wheel, with a tire that’s 285mm wide and whose sidewall is 75% of the width.

To make the calculation, first you calculate the sidewall height in millimeters, which is 285 x .75, or 214mm. To convert to inches, divide 214 by 25.38, for a result of 8.42 inches. That’s the height of the sidewall. Double that, add the 16" inches for the wheel itself, and you have a total tire diameter of 32.84 inches, or what everyone would call a 33" tire.

Obviously, a different height ration (the 75 in the code) or a different wheel size will change the result.
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Old 01-27-2008, 01:25 PM   #13
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Quote:
Originally Posted by Roubo
To calculate the tire diameter in inches, you need the full tire size from the side of your tire. Say you are running a 285/75 R16. That’s a 16" wheel, with a tire that’s 285mm wide and whose sidewall is 75% of the width.

To make the calculation, first you calculate the sidewall height in millimeters, which is 285 x .75, or 214mm. To convert to inches, divide 214 by 25.38, for a result of 8.42 inches. That’s the height of the sidewall. Double that, add the 16" inches for the wheel itself, and you have a total tire diameter of 32.84 inches, or what everyone would call a 33" tire.

Obviously, a different height ration (the 75 in the code) or a different wheel size will change the result.
Very helpful, thanks
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Old 01-27-2008, 11:27 PM   #14
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Ok, I'll do it.

A 315 75 16 Tire in Inches

315*.75=236.25
236.25/25.38=9.31
9.31*2=18.62
18.62+16=34.62

35's


Toyo has a 305 70 16 Open Country M/T
305*70=213.5
213.5/25.38=8.41
16.82*2=16.82
16.82+16= 32.8

33's like the 285 75 16's.. Almost the same size but Wider Tires?
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Old 01-27-2008, 11:35 PM   #15
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Just another reason to go to 37s. They don't come in 335/80 R16 so no need for math!
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Old 01-28-2008, 09:32 AM   #16
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I actually saved this link that Jage gave me several months ago. It is great for tire size comparisons and conversions.

http://www.miata.net/garage/tirecalc.html
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Old 01-28-2008, 10:45 AM   #17
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That was a useful site!

I didn't know the 305 70 16 was close to the same size as 285 75 16 size tire, and it's wider! (END selection)

I have the 285's now but always wished it was wider...
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Old 02-01-2008, 08:02 AM   #18
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Met with Craig at Salem Kroger yesterday. Looked at several vans with 4X4 conversions. After looking at one in particular, my wife said, and I quote, "Ours won't be as high as this one, will it?". The one we were looking at had their basic 3 1/2" lift with 245/75 R17s on it. I said it will be a little higher, but not much. In light of this, I changed from my original preference of 285/75 R17s with a 4" lift to 285/70 R17's with a
3 1/2" lift. It will still be fine for our needs, which is part main road travel, fire roads, and some legitamte 4 wheel roads. No Rubicon or rock crawling. By the way, I had a test ride in a finished unit and it was remarkable. oclv
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Old 02-07-2008, 10:36 AM   #19
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After looking at all the photos in the album here, I called Craig at SK and am changing back to 285/75 R17's (34") with a 4" lift instead of
285/70 R17's (33") with the 3 1/2" lift. The photos here are very helpful. Thanks. oclv
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Old 02-07-2008, 11:05 AM   #20
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Yeah don't tell your wife she'll get used to it.
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