just wondering, my car seems to accelerate better with my 185/60-13s than with 195/50-15s.... does going with smaller tires raise your final drive ratio or something? if so, than with an ls tranny im running at a fd of around 4.47 with the smaller tires?

educate me please.... thanks.

 

A smaller tire does increase the final drive ratio.
It has to do with the overall circumference(Spelling, sorry!)

The 13" will take let's say 3ft to roll one complete rotation
The 15" will take 3ft 3in.

This will mess with your speedo to. Your car will be going faster with the 15" at 65mph on the speedo Your actual speed will be 68 - 70 mph. But with the 13's your speedo would be right on.

Hope this helps!

 

so how would you know how i could figure out what my fd would be then with the smaller tires?

 

Final drive is a gear set in your transmission. It is expressed as a ratio (4.733:1) and is not affected by tire size.
A good may to figure out how much yer speedo will be out is here:
http://www.1010tires.com/TireSizeCalculator.asp

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Raw B &raquo;</TD></TR><TR><TD CLASS="quote">Final drive is a gear set in your transmission. It is expressed as a ratio (4.733:1) and is not affected by tire size.</TD></TR></TABLE>

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by thesmogman &raquo;</TD></TR><TR><TD CLASS="quote">A smaller tire does increase the final drive ratio.
It has to do with the overall circumference(Spelling, sorry!)</TD></TR></TABLE>

so which is it? anyone else?

 

Tires with different circumferences will throw off the speedo. They do not affect the transmission's final drive, but they do affect your effective gear ratio.

A tire with a larger circumference will go further during one axle rotation than one with a smaller circumference. Calculate the circumference of the stock tires and then the different-sized ones and compare them and you'll get the percentage difference/correction factor.

 

Smaller diameter tires <U>do</U>, in effect, give you a higher final drive ratio. I used a gear calculator to compare 92-95 Civic EX transmissions. The one in green has 23" tires with a raised final drive, and the one in red has 20" tires with a stock final drive - everything else is the same. I messed with the final drive down to the ten-thousandth decimal in order to make the gearing identical. Check it out here...and you are right about the LS being at 4.47 with those smaller tires, so your acceleration should be better like you said.