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Old 01-10-2009, 04:41 AM
  #3  
TopspeedLowet
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Join Date: Apr 2008
Posts: 504
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The final RPM that you are willing to turn at the finish line will be the deciding factor on the diameter. The 4.11 gear is going to need a short tire to give your mouse much leverage off the start line. a 100" roll out tire. For instance if you think you are capable of say 137 MPH in the Q. with your 4.11 gear and an auto trans with a good converter and a 100 roll out tire your RPM in the traps should be near 6240. If that sounds low RPM for your motor then you might look at a shorter roll tire. I use this rule for guessing RPM differences, for every inch change in tire roll out the final rpm will change about 75 RPM +or- a few. If you think that your hot rod is going to eclipse 137 MPH say, 145 then your RPM with the 100" tire might be 6600RPM in the traps. I am sure that you are seeing a trend here on the tire question now. The tire roll out is the paramount variable, this issue usually leaves you with a narrowing tire choice for widths and compounds. I run a 3 speed trans in my 7 second door car and of course the more tire patch you can get under the car the more forgiving the traction. When you end up with a little tire in roll out the only way to recapture the foot print is by width. If your car is not restrictive in the wheel tub area and you are a bracket racer. Most folks go for the width so you don't have to have a perfect start line every time to get out of the box. Don't run tubes in your slicks to keep the mass down and to be safe. Get what is available for roll out and get the wide one would be the best advice one could give you until you know exactly how fast your car will run the Q. your tire roll out the second purchase will be more clear once you run something of a known roll and get a result. Borrow a buddy's to see what your car likes then you will have more info to get that expieremental purchase behind you. Your 4.11 gear may be the next issue you might look at if you had say 4.56 you could look at larger diameter tires or be able to RPM with out buying shorter tires yet if the RPM's I stated are low for you.
Sorry about the bad spelling.
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