Added Tire Size Calculator
 

Okay, folks...

It took some doing and had to rip off a lot of code from a lot of places, but I got a working HTML Tire Size Calculator together. :happy-dancing:

I plan to expand it when I have time, but this should be enough to get people through the tough stuff.

Check it out here:

Power Hungry Performance Forum - FAQ: Utilities

I have changed squish to 7 as it actually seems to be closer to many of the tire size rev/mile ratings I checked. If anyone has suggestions, I'm happy to hear 'em.

Enjoy. ;)

Feel free to use this spreadsheet (all or parts of it).

Squish of 7?
Mine was closer to 3.6%

I found when looking through my math that I was calculating squish on both sides of the tires, although I still don't include the rim. The new calculations only squish one side of the tire.

Ah - we're probably just playing with words here, but really, the effective diameter or radius is what is reduced by squish. It really does not matter what the rest of the tire looks like, the only thing that's important is the distance from the spindle to the ground. That governs how many revolutions the PCM will see in a mile (or the effective circumference).

I think the "squish" effect SHOULD be applied to both sides, because as far as circumference goes, it's 2 x pi x radius, and the radius is reduced the same way on all sides of the tire (as it touches the ground).

If you calculate the "squished" part of the radius, it would be: (unloaded tire radius - rim radius) x squish, which is then added back to the rim radius to get the squished radius. This is multiplied by 2 to get the diameter and then by pi to get the circumference.

You get the same result with this calculation: (unloaded tire diameter - rim diameter) x squish + rim diameter, which gives the diameter (adjusted for squish) directly.

If you DON'T separate the non-deforming rim from the rubber, then a 3% reduction gives about the same result.

- Jack

???? I click on the link and I can see the heading (tire size calculator) at the bottom of the screen... and that's all I can get. What am I missing?

It's a setting in your browser, or your browser itself. I think this application does not like IE (and I don't either). :hehe: Firefox renders the page just fine.

But, I think Bill's idea about not applying squish to both sides of the tire is a bit "off". You can also download and use a perfectly good calculator as part of Pegasus. It's called the "Gear Ratio Calculator", and is one of the tools in Pegasus. Just change the default "squish" value to 7% and enter your Tire Size as 275/65-18 (my tires) - notice the "dash" between 65 and 18.

- Jack