Duramax Diesels Forum Truck of the Week
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Old 02-15-2017, 08:54 AM
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Default 33x12.50x20 with 4.56 gears 6 speed?

Is anyone running 33s with 4.56 gearing and the 6 speed alli? How does it do on the interstate? RPM @ 70? 80? Im wanting to go smaller with my tires. Im currently on 37s. I dont want to regear unless i have to. Or does anyone know a good site i can use as a calculator that will take into consideration the internal gearing of the allison? Thanks
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2003 LBZ Powered. 8" fabtech, 37" Toyo, Built tranny by Trey Fox, Bt lockup box, 5" magnaflow w muff. , egr delete, pcv reroute, 3" diamond eye downpipe. Efi by Rob, 4.56 gears, afe metal intake, afe mouthpiece, bestop power steps, Lmm front and rear seats. 13.88 ET
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Old 02-15-2017, 08:56 AM
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I have a funny feeling the truck will be screaming at 80
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Roderiques ATV Built Motor, HSP Twins, NLX88/Danville72R,
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Old 02-15-2017, 09:09 AM
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Thats what i was thinking. I may regear to 4.10s and call it a day.
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2003 LBZ Powered. 8" fabtech, 37" Toyo, Built tranny by Trey Fox, Bt lockup box, 5" magnaflow w muff. , egr delete, pcv reroute, 3" diamond eye downpipe. Efi by Rob, 4.56 gears, afe metal intake, afe mouthpiece, bestop power steps, Lmm front and rear seats. 13.88 ET
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Old 02-15-2017, 09:11 AM
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For a 33" tall tire I'd go back to a stock 3.73 personally.
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Old 02-15-2017, 09:15 AM
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Quote:
Originally Posted by carter_44 View Post
For a 33" tall tire I'd go back to a stock 3.73 personally.
^this. 4.10s might makes sense with 35s but I am a big fan of the way my buddy's lmm drives with 35s and stock 3.73s
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05 LLY CC/SB
Roderiques ATV Built Motor, HSP Twins, NLX88/Danville72R,
S&S 200s, S&S 10mm & LBZ, Tuned by Danville Performance
Suncoast Competition trans and Goerend Converter
1125hp/1628lbft 10.52@132

Thanks to
Chris @ Roderiques ATV in Westport MA
Mark Broviak @ Danville
Joe and Dave @ HSPdiesel
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Old 02-15-2017, 10:28 AM
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33" I'd use stock 3.73 gears. 35" I'd use 4.10s. 37" 4.56 is perfect. All in those I said is because the driveability would be better in towing and daily driving. I had 33 on 3.73 and it was perfect. 35 on the 3.73 was a bit lugging for towing. Now I have 37's and they suck on 3.73. I'm still running 3.73, soon will be upgrading to 4.56 to help with towing. Those are better for 6 speed transmission.
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Old 02-15-2017, 11:08 AM
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Thanks everyone for the input. Looks like ill put the factories back in.
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2003 LBZ Powered. 8" fabtech, 37" Toyo, Built tranny by Trey Fox, Bt lockup box, 5" magnaflow w muff. , egr delete, pcv reroute, 3" diamond eye downpipe. Efi by Rob, 4.56 gears, afe metal intake, afe mouthpiece, bestop power steps, Lmm front and rear seats. 13.88 ET
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Old 02-15-2017, 11:41 AM
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I just regeared 3.73 to 4.30 I made my own calculator and it was very close.

33" Tires with 4.56 gears @80 you would be at 2366 RPMS
33" Tires with 4.10 gears @80 you would be at 2127 RPMS
33" Tires with 3.73 gears @80 you would be at 1935 RPMS

Stock with 265-70r17 (31.6") @80 would be around 2005 RPMS
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