Gear Ratio Tire Size Chart?

[chargergirl]

Is there such a thing and where can it be found. Tweaking the Belvedere and need to find the ratios. Help! Thanks!

[greenpigs]

Do you mean how the tire diameter effects the ratio? Moparts has a chart that might be what your asking about. http://www.moparts.org/Tech/tech/index.html

[chargergirl]

Well that would be good if we actually had a 1/4 mile track in Bugtussle...it's only 1/8 of a mile. Only game in town so we're stuck with it. Are there any ones out there that can be changed?

[71superbee]

Will this help?

http://vexer.com/automotive-tools/speed-rpm-calculator

[firefighter3931]

Will this help?

http://vexer.com/automotive-tools/speed-rpm-calculator

This calculator works good for determining rpm at specific speeds. If using an auto trans don't forget to factor in converter slip. 

For simply figuring out axle ratios the basic math will do. I use 26in for the tire diameter because most cars came with that size tire. 

So to calculate, you divide the new tire size into 26 and multiply by the axle ratio.

For example ; you plan to run a 28in tire with a 4.10 axle ratio so :

(26/28) x 4.10
.928 x 4.10 = 3.80

**The 4.10 axle is basicly a 3.80 with a 28in tall rear tire.



Ron

[Ghoste]

No wonder I'm getting so much better mileage than I thought I should!

[c00nhunterjoe]

I like using that 69 charger dashboard calculator thing. There was a link to it on this site somewhere. You plug in your tire size gear ratios and trans data and can view speed and rpm in each gear via the charger gauge cluster

[68X426]

MyMopar has a gear ratio calculator that's quick and easy.

http://www.mymopar.com/gearratio.htm

[BSB67]

I guess in today's age where everything is on line, I should not be surprised.  But we are gear heads, right, we figure stuff out, right?

Take 3 minutes and figure it out.  Inches to ft. to miles, minutes to hours, and pi (3.14). 

(tire dia. x rpm)/(336 x rear axle gear ratio) = mph  (manual transmission with 1:1 final gear ratio)  Substitute 355 for the 336 for 5% slip with an automatic.

You can now figure for any of the variables, tire size, mph, rpm or gear ratio.  You can figure " how fast am I going in first gear at 3000 rpm",  or "what mph am I going in second gear when I shift at 6000 rpm."

You can do all this faster than you can ask the question of " where can I find ...."

[Ghoste]

You big meanie.   

[68X426]

I guess in today's age where everything is on line, I should not be surprised.  But we are gear heads, right, we figure stuff out, right?

Take 3 minutes and figure it out.  Inches to ft. to miles, minutes to hours, and pi (3.14). 

(tire dia. x rpm)/(336 x rear axle gear ratio) = mph  (manual transmission with 1:1 final gear ratio)  Substitute 355 for the 336 for 5% slip with an automatic.

You can now figure for any of the variables, tire size, mph, rpm or gear ratio.  You can figure " how fast am I going in first gear at 3000 rpm",  or "what mph am I going in second gear when I shift at 6000 rpm."

You can do all this faster than you can ask the question of " where can I find ...."

Yeah but on-line works when drinking. 

[chargergirl]

Doing all these things and thanking everyone for their comments and help! Like I tell every newbie...you've found the right place great assistance. We found our answers through all the calculations and then fell over this.

www.wallaceracing.com/Calculators.htm

Love the Vexer calculator! Figured out our 4.30 gear was dropped to 4.01 when the 30" tall tires were put on. So need to change this or we have a nice street racer instead of race car.

Thanks again guys!

[andrew8]

Have you seen this calculator on cargister site?

Gear Ratio Calculator

[BSB67]

Is there such a thing and where can it be found. Tweaking the Belvedere and need to find the ratios. Help! Thanks!

There is a simple equation:

(tire dia.)x(RPM)/(355 x axle ratio) = MPH

The 355 accounts for an automatic tranny w/ about 5% slip.  Use 336 in place of the 355 for a manual tranny.

[Mebsuta]

Will this help?

http://vexer.com/automotive-tools/speed-rpm-calculator

This calculator works good for determining rpm at specific speeds. If using an auto trans don't forget to factor in converter slip. 

For simply figuring out axle ratios the basic math will do. I use 26in for the tire diameter because most cars came with that size tire. 

So to calculate, you divide the new tire size into 26 and multiply by the axle ratio.

For example ; you plan to run a 28in tire with a 4.10 axle ratio so :

(26/28) x 4.10
.928 x 4.10 = 3.80

**The 4.10 axle is basicly a 3.80 with a 28in tall rear tire.



Ron

Awesome.  QFT.   Thanks.

[John_Kunkel]

The problem is how one determines the actual tire diameter. A simple tape measure across the wheel or around the circumference is iffy. I like to paint a small dot of enamel paint on the center of the rear tire tread and roll the car forward...measure between the dots on the floor to determine the actual rollout of the tire then divide by 3.1416. 

[Ghoste]

How far out would the diameter be though?  Can it be far enough that you couldn't determine the ratio, for example, would the actual diameter versus the reported diameter be off enough that you couldn't figure the difference between 3:23 and 3:55?

[John_Kunkel]

I admit to being anal when it comes to correct speedo pinion selection, that's why I use the paint dot method....and I never use charts, I do the math.

Look in a Coker Tire catalog and see the various diameters listed for the same size tire from different manufacturers.

[Ghoste]

Nothing wrong with that, the willingness to sweat the details are what separate the winners and as for the math, thats what "blueprinting" is all about. 

[polywideblock]

so is there a "list " of various factory tyres and their respective diameters      

       i'v got a set of radial T/A's, a set of cooper cobras and am looking at micky Thompson s/t 's   now ,are they all the same diameter 

[Mebsuta]

BFG and Cooper have things like diameter, tread width, section width, etc on their sites.  

If people bought Firestone Wide Ovals or Goodyear Polyglas etc  in 1970, where they all exactly the same diameter to 2 decimal places? 

[Troy]

But even if you know the exact diameter when you install the tire and it's sitting in your garage the tire expands and contracts with heat and RPM. Not to mention the tread wears off over time so it's continually getting smaller. Your measurements are only good for the exact time that you took them.

Troy

[John_Kunkel]

That's true but, with known beginning component dimensions, you can make decisions based on math i.e. if the computed math result isn't dead on the number of teeth available on the pinion you can choose a tooth up or down to compensate for wear/growth.

The point is moot because few speedometers are that accurate anyhow but it's gratifying to see the odometer match the paddle markers mile-after-mile.  

[Troy]

Yes, I prefer to be exact. These days I just track speed with the GPS.

Troy