26 vs 28 tire w/4.10

[Why Try]

I searched but the link I found with the spreadsheet is not working.

I have a SRA with 4.10's and 620 HP. I have run 26 10.5 16s and 28 12.5 15 et streets. 26's put me in 5th before the line. 28 12.5 seem to be slugish and I think I had a better 60 with 26's

I'm looking at Hoosiers Quick times now. Thinking of 27 11.5 15. Anyone run the 27's and keep it in 4th? What would the rpm be? Anyone out there OK with making the extra shift?

What size do you all think I should go with?

 

[vrt03cobra]

Just curious, how wide is your rear wheel? When you say you felt the 28's "Slugish" do you mean the car walks more? I've ran 4.10's and in all honesty the 28 would be the best choice for that gear, but you are making more power then I was (Ported Eaton 536rwhp).

 

[Why Try]

15x10. 28s were .1 slower on 60 ft but that may be track or driver related.

 

[Riddick]

Im assuming you have a stock geared transmission for a Cobra, if so here is what I came up with. With a 27" tire you will be at redline in 4th at 127 mph (assuming your revving to 6500). With a 28" tire you will be good for 132 mph in 4th gear.

With that said and your current power level I would stick with the 28 or gear down so you can run 26s or 27s. With 620 at the wheels you should be in the low 130s all day long.

A 3.73 with a 27 in tire will be good for 140 mph in 4th gear. A 3.73 on a 26 will be good for 135 in 4th.

Here is the calculator I was using, just look up the 03-04 transmission gear specs you can fill it all in. Pretty useful calculator...... even if it was designed for a F-Bod .

http://www.f-body.org/gears/

 

[Why Try]

Thanks. That's what I need.