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  #1  
Old 01-13-2013, 06:45 PM
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Default Help with Tire size

I am looking for a knowledgable person who can explain to me how to figure out how changing tire size affects final final gear ratio. I understand the concept but can not figure out exactly how to do the math. I am looking to pick up a set of smaller drag tires for the truck, but I am not sure what size I am after.
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Old 01-15-2013, 09:55 AM
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the sweet spot for drag tires is about 28"...I run 28" Hoosiers or 325/45-17 M&H drag radials..
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Old 01-15-2013, 09:57 AM
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..and I always forget to change tire size at track, dang ..I don't think it affects gear ratio as much as it affects shift points..
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-fast freddie- one quick 05 hemi qc...with over 250k miles on odo... on the 5.7, stoker 6.4 now...Inertia Motorsports 392 stroker
5.7 e.t.'s: 1/8 - 7.85@93.20, 1/4 - 12.10@113.96 juice - 12.96 NA... 6.4 e.t. 12.59@106 NA
2005 Dodge Ram 1500 QC SLT: 12.107 @ 113.960 MPH
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Old 01-15-2013, 10:02 AM
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here is a simple calculator.... plug in stock tire diameter and current gear ratio and new diameter to compute new ratio..

http://www.rocky-road.com/calculator.html
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-fast freddie- one quick 05 hemi qc...with over 250k miles on odo... on the 5.7, stoker 6.4 now...Inertia Motorsports 392 stroker
5.7 e.t.'s: 1/8 - 7.85@93.20, 1/4 - 12.10@113.96 juice - 12.96 NA... 6.4 e.t. 12.59@106 NA
2005 Dodge Ram 1500 QC SLT: 12.107 @ 113.960 MPH
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Old 01-15-2013, 10:06 AM
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but, plug stock tire dia in 'new' tire dia and proposed drag tire dia in 'old' tire dia field ... the guy mislabeled the fields...
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-fast freddie- one quick 05 hemi qc...with over 250k miles on odo... on the 5.7, stoker 6.4 now...Inertia Motorsports 392 stroker
5.7 e.t.'s: 1/8 - 7.85@93.20, 1/4 - 12.10@113.96 juice - 12.96 NA... 6.4 e.t. 12.59@106 NA
2005 Dodge Ram 1500 QC SLT: 12.107 @ 113.960 MPH
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Old 01-15-2013, 07:16 PM
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Thx guys. Are you running 1/4 mile or 1/8th? What rpm and gear are you crossing the traps at?
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Old 01-15-2013, 08:19 PM
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run both the 1/8th (7.8x) and 1/4 (12.1x), I know I'm in 3rd when i cross in the 1/4 and I think I do in the 1/8th as well as i don't think I can be in 2nd at 90+ mph. And I want to stay out of 4th at the 1/4...
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-fast freddie- one quick 05 hemi qc...with over 250k miles on odo... on the 5.7, stoker 6.4 now...Inertia Motorsports 392 stroker
5.7 e.t.'s: 1/8 - 7.85@93.20, 1/4 - 12.10@113.96 juice - 12.96 NA... 6.4 e.t. 12.59@106 NA
2005 Dodge Ram 1500 QC SLT: 12.107 @ 113.960 MPH
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Old 01-15-2013, 10:24 PM
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Fred, I only have a 1/8th mile track near me. I think that I would like to be topping out 2nd prime when I am crossing the finish. What are your thoughts? I know that you have much more experience than I do. Also, I plan on installing a super charger within a year. I am planning aloof my mods around that setup. Thanks again, joe
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  #9  
Old 01-21-2013, 08:47 AM
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Anyone have any knowledge on this matter?
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Old 01-22-2013, 08:08 PM
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I hope 2nd prime is more stable in your 4th gens then it was on our 3rd gens...we would at all cost try to avoid 2nd prime because it eats transmissions (I should know)..we would only be able to access on downshifts anyways, not on upshifts..
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-fast freddie- one quick 05 hemi qc...with over 250k miles on odo... on the 5.7, stoker 6.4 now...Inertia Motorsports 392 stroker
5.7 e.t.'s: 1/8 - 7.85@93.20, 1/4 - 12.10@113.96 juice - 12.96 NA... 6.4 e.t. 12.59@106 NA
2005 Dodge Ram 1500 QC SLT: 12.107 @ 113.960 MPH
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