RPM/Gear Ratio/ MPH, Claculator

WZ JUNK · March 25, 2004, 06:38:28 AM

I need to verify some numbers before I buy some tires. I found a calculator on the net but the numbers do not sound right to me. Do any of you know of a site on the net that will figure top speed for me on 5500 RPM, 4.10 rear gear, 1 to 1 final ratio on transmission, 26" tall tire?

purplepickup · March 25, 2004, 07:48:41 AM

According to this one the speed is 104 mph with that set up. That sounds like a drag racing combo.

PeterR · March 25, 2004, 08:51:53 AM

Quote from: "WZ JUNK"I need to verify some numbers before I buy some tires. I found a calculator on the net but the numbers do not sound right to me. Do any of you know of a site on the net that will figure top speed for me on 5500 RPM, 4.10 rear gear, 1 to 1 final ratio on transmission, 26" tall tire?

A reasonable guide for MPH is,

(RPM)X(Tire height in inches)
336X(Diff ratio)X(Gear ratio)

This assumes the effective rolling radius is half the tire height which is not quite correct. You can make a closer estimate by measuring the distance from ground to wheel center, then using double this figure as the tire height in the equation.

in your case

5500X26
336X4.10

=104mph

WZ JUNK · March 25, 2004, 09:28:42 AM

Those are about the same figures that I came up with. It is hard to figure the tire size right and I hate to buy a pair of slicks and then not have what I need but I think I am going for it. I have a big race in two weeks.

exsedan · March 25, 2004, 11:12:07 AM

You might be able to use the info at this site. I use it quite often....jb EXSEDAN

http://www.bgsoflex.com/auto.html

SKR8PN · March 25, 2004, 12:03:59 PM

Quote from: "WZ JUNK"Those are about the same figures that I came up with. It is hard to figure the tire size right and I hate to buy a pair of slicks and then not have what I need but I think I am going for it. I have a big race in two weeks.

You gonna be using NOS? If you do,your calculations just went out the window...........You will need a LOT more tire or a LOT less gear.
Just something to think about

purplepickup · March 25, 2004, 12:32:36 PM

I don't know what type slicks you're planning on running, but non radial slicks can grow in diameter up to 3" at the top end depending on speed and width. I don't think radials grow much at speed.

WZ JUNK · March 25, 2004, 12:53:50 PM

I found some used M/T 8 inch slicks that are 26" tall. I know that I want to turn the engine around 5500 if it will stay together. It is hard to figure because I do not know my top end speed. I guess I will buy them and see how they do.

The Mopar at MOKAN meet is the weekend after NSRA at OKC. The problem that causes is that my torque converter is being made and shipped this week and it will be next week before I get it in the car. Then I go to OKC for the weekend. That means that I will not have a chance to try it all out before the day of the race. I will give the car a try on the streets here by the house but it is hard to tell much. Besides that there is a lot of traffic now where in the good old days the road were pretty empty most of the time.

Fat Cat · March 25, 2004, 01:57:49 PM

Quote from: "WZ JUNK"I need to verify some numbers before I buy some tires. I found a calculator on the net but the numbers do not sound right to me. Do any of you know of a site on the net that will figure top speed for me on 5500 RPM, 4.10 rear gear, 1 to 1 final ratio on transmission, 26" tall tire?

Yes I do. There are about 6 different calculators in the tech section of this very site. Located here