Gear/tire size question, help me decide!

[yellow1995Cobra]

Well i have 3.90 gears right now.. And im moving to a whole new combo with the s trim and hoping to go atleast 120 in the 1/4.

With the 3.90's and nitto's (275 40) i was just about out of gear trapping what i did n/a this past season.

So what size tire would i need to trap 120+ with 3.90's? Im getting a set of rear welds to match my skinnies and a set of ET streets to go with them.
My other option is to swap my 3.55's back in. I saved them just incase i wanted to swap back. But even with 3.55's could i go 120-125? i kno the ET streets come in 26 and 28 tall.. Let me know what you guys think.

Thanks

 

[cjones]

you could try here:

http://www.corral.net/tech/gearcalc.html

 

[Joes95GT]

I know with a 4.10, a supercharger, and a 26 inch tire, you will run out of RPM's. So, with a 3.90 and the above things, you will barely be running out of RPM's. If you could, I would try to find a 27 inch tire. Does BFG make one? I would go into the Power Adder Forum, and the Supercharger Forum on the Corral, and see what everyone is running. I'm almost positive that a 3.90 and a 28 inch tire would work. I just don't know if a 27 would, and I don't think a 26 would cut it. Does any of that make sense?

Joe

 

[yellow1995Cobra]

Thanks for the input jones and Joe..

I forgot to add this into the mix... When my tranny goes, most likely this spring, i plan on going with the G Force rebuild.. Since i will have the choice of tranny ratio gears, if i went with the lower 2.94, 1.94, 1.34, 1.00 (1st - 4th) would that allow me to see more MPH in 4th? Im kinda confused by all the ratios.. I know that first gear is numerically lower now meaning it should turn more MPH then the stock t5 gear (3.35?) but would that hold true in 4th where they are both 1-1? Am i on the right track here?

Thanks again for the help.

 

[Joes95GT]

Take the 3.35 first gear ratio. Even though the first gear is higher, your 4th gear is still going to be 1:1, which wouldn't allow for a higher MPH in the quarter, because both 4th gears are 1:1. What the higher 1st, 2nd, and 3rd gear ratios WOULD allow is to get you up to your potential maximum speed the fastest. I know this is confusing....

Say the car could do 125 MPH at redline in 4th gear. What the numerically higher trans gears would do is make you accelerate faster and get you up to top speed the quickest, having the same effect as a different ring and pinion. BTW, I thought our cars only had the 2.95 first gear?

I hope I make some type of sense....

Joe

 

[yellow1995Cobra]

Joe, thanks again..

The one thing that i still dont understand is take an LS1 for example. My friend has one, with 4.11's in the rear end and the stock t56. He turns 116-118 MPH no prob. And he is finishing in 4th (1-1).. I always thought it was cause of the different trans gears, but what you say makes sense.

 

[Joes95GT]

I believe the LS1's have the same shift points as us right? About 6200? What size tires does your buddy run on? If they are 26 inch tires, then your answer is right there. He could be running on 27 or 28 inch tires which will allow for a greater MPH because taller tires cut down the rear axle ratio.

Your best bet is to PM Paul (Killercanary), and see what RPM he crosses the traps at. I know he can run his car to 6200 RPM and if I had to guess, I would think he crosses around 5800, which nets him 111 MPH trap speeds on 26 inch tires. He PROBABLY has about 400 more RPM's to use, which would allow for about 5 MPH and that would put him right in the area of your buddy with the LS1 at ~116 MPH. Making sense?

I know what I'm talking about, I'm just not so great at explaining it...

Joe

 

[yellow1995Cobra]

Joe - i believe my friend shifts at 6400, i will have to double check though.. He also runs BFG drag radials on a 17 inch rim.. So i imagine they arent much taller then my nitto's..

What your saying makes perfect sense.. Im still not sure what i want to do though. I will have a set of welds with ET streets and my Cobra R's with Nitto DR's. I would like to be able to go 120 or close to it on the nittos and on the et streets so i may just go with a 26 inch ET street, see how it does at the track.. Then if its not enough tire just put my 3.55's back in.

Thanks joe