Gear/tire calculator

[Grant R.]

Threw this excel spreadsheet together today. It calculates tire size from P-metric dimensions and uses that with tranny gears and final gear to calculate speed and it graphs it. I made it to compare different gears and tires sizes and visually be able to see it to find the best combination.
Enjoy!

www.ludicrouslouis.com/wp-content/uploads/2007/03/gearcalculator.xls (http://www.ludicrouslouis.com/wp-content/uploads/2007/03/gearcalculator.xls)

let me know if you see anything wrong or anywhere it could be improved.

Grant Rogers
www.ludicrouslouis.com

[XcYZ]

Thanks Grant. I have a spreadsheet that I should upload that has all the popular transmissions gear ratios. You can put in tire size, gear ratio, RPM, transmission, and it will give you all your shift points, RPM, mph, etc.

[Grant R.]

Scott, could you email me your spreadsheet. I'll combine them and upload a more complete one for everyone to have.
Thanks!

Grant Rogers
www.ludicrouslouis.com

[californiacuda]

Another fun calculation that can be done is the total tractive effort at the tires, where Total tractive effort at tires= ( tractive effort at engine(torque) X transmission ratio X final drive ratio / tire radius in ft) X drive line efficiency.

So if an engine makes a max of 400 ft/lbs of tq than in 1st gear (2.87) with a final drive ratio of 2.73 divided by tire radius 11.93/12 in ft X drive line efficiency say .85

The total ft/lbs at the tire = (400 X 2.87 X 2.73 /11.93/12) X .85 = 2,691ft/lbs at the wheels, if the final drive is changed to 3.11 than (400 X 2.87 X 3.11 / 11.93/12) .85 = 3,066.

So, when the final drive was changed to 2.73 allowing more top speed the tire tq in 1st gear went from 3,066 to 2,691 ft/lbs. The max tire tq effort can be calculated for each gear.

[Grant R.]

Cool. I think I'll add that as well. I'm not sure how useful it actually is to know, but pretty interesting. thanks

Grant Rogers
www.ludicrouslouis.com

[californiacuda]

It is possible to calculate the static and weight transfer on the rear drive wheels during acceleration so as to know when the tires will blow off.

Hot Rod magazine did a big write up a while back with calculations.

[Grant R.]

I posted a new version. You can select P-metric, Diameter or revs/mile for the calculations.

www.ludicrouslouis.com/wp-content/uploads/2007/03/gearcalculator.xls

Grant Rogers
www.ludicrouslouis.com