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01-27-2008, 10:53 AM
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#11
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Senior Member
Join Date: Apr 2007
Location: Parker, CO
Posts: 7,643
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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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it was good to be back
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01-27-2008, 11:05 AM
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#12
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Member
Join Date: Apr 2007
Location: S.F. Bay Area, CA
Posts: 50
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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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John
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01-27-2008, 01:25 PM
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#13
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Senior Member
Join Date: Apr 2007
Location: Pasadena, CA
Posts: 785
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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.
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Very helpful, thanks
R
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2006 SMB 4x4, EB-51, 6.0psd
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01-27-2008, 11:27 PM
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#14
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Senior Member
Join Date: May 2007
Posts: 477
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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?
__________________
96 RB E-350 460v8 4x4 Custom RestoMod
Warn12kWinch,FFloater,LSlip,Pwtrx Locker 4.10 305x70x16 ToyoMTs,Eagle Alloys,Stove,4CF Ppane Fridge, Air CompTank,Supersprings, Bilstein Shocks,Deavers,CastIron Diff Case, Bullet Proof ReBuilt Transmission, Tubulator DeRale Trans Pan Cover, SSExhaust, KyoceraSolar, Tripplite UPS, 8D AGM, TivoHD, 24in HDLED
95 FJ80 ARB/Kaymar/Emu
2005 AMG CL65 691hp 875tq
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01-27-2008, 11:35 PM
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#15
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Senior Member
Join Date: Apr 2007
Location: Parker, CO
Posts: 7,643
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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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it was good to be back
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01-28-2008, 09:32 AM
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#16
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Senior Member
Join Date: May 2007
Location: San Diego, CA
Posts: 989
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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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2007 Ford RB Diesel SMB 4x4 Pueblo Gold; Custom configuration (aisle layout); PIAA 580 driving lights; Picked up on Oct 19, 2007.
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01-28-2008, 10:45 AM
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#17
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Senior Member
Join Date: May 2007
Posts: 477
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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...
__________________
96 RB E-350 460v8 4x4 Custom RestoMod
Warn12kWinch,FFloater,LSlip,Pwtrx Locker 4.10 305x70x16 ToyoMTs,Eagle Alloys,Stove,4CF Ppane Fridge, Air CompTank,Supersprings, Bilstein Shocks,Deavers,CastIron Diff Case, Bullet Proof ReBuilt Transmission, Tubulator DeRale Trans Pan Cover, SSExhaust, KyoceraSolar, Tripplite UPS, 8D AGM, TivoHD, 24in HDLED
95 FJ80 ARB/Kaymar/Emu
2005 AMG CL65 691hp 875tq
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02-01-2008, 08:02 AM
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#18
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Senior Member
Join Date: Dec 2007
Location: Lake Tahoe, NV
Posts: 296
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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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02-07-2008, 10:36 AM
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#19
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Senior Member
Join Date: Dec 2007
Location: Lake Tahoe, NV
Posts: 296
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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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02-07-2008, 11:05 AM
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#20
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Senior Member
Join Date: Apr 2007
Location: Parker, CO
Posts: 7,643
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Yeah don't tell your wife she'll get used to it.
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