what speed is 5k in 4th?

[skeeters_keeper]

I know someone posted the gear ratios around here a while ago... but i haven't been able to find them right now. I'm just tired of not knowing how fast i'm going. I'm also thinking about making a spedo card with the numbers spaced correctly to compensate for my larger tires.

so i have a stock festiva 5spd trany, 175/70/13 tires, and i was turning 5100 rpm in 4th gear (then i ran out of road..). How fast was i going?

[Damkid]

i did this for 5.0zone a while back, hope this helps

http://www.fordfestiva.com/forums/showthread.php?t=7323&page=2

[GenevaDirt]

get a GPS and it tells you how fast you are going ....... worked great when I stuck the 14's on for a bit....I was about 3mph off....

[neanderpaul]

Nate, Dirt is absolutely right. GPS is the answer. I know one of your friends must have one. Or a phone with gps.

[m715]

1st:3.454:1
2nd:1.944:1
3rd:1.275:1
4th:0.861:1 (Overdrive!)
5th:0.692:1 (2nd Overdrive!)
Rev:3.583:1 Just so you know what you are doing in R (Race)
Final Drive Ratio 3.777:1
Speedometer Gear Ratio 0.91:1

[skeeters_keeper]

wow, 4th and 5th are OD? interesting!
thanks m715, thats the info i was looking for. a GPS would be nice, i know a few ppl with them i think, i'll have to see if i can borrow one, i just would like to be able to read my speed from the tach after the spedo is buried. i'm pretty sure at about 5.1k in 4th i'm turning 100-105mph, i'll run the #'s when i get home later.

[JPT]

After running the numbers through a calculator, I get 105.62 MPH.

For a 175/70-13 tire, 3.777:1 final drive and .861:1 4th gear

Section Width = 175mm, 6.9"
Aspect ratio =....70%
70% of 6.9" = 4.83"
4.83" x 2 = 9.66"
9.66" + 13" (rim) = 22.66" tire diameter
Diameter (22.66") x pi (3.141592654) = circumference. 71.18"
71.18" = Distance traveled per revolution
Divided by 12" = 5.932 feet per revolution

Now gears.

3.777:1 final drive x .861:1 4th gear = 3.25:1

5100 RPM / 3.25 = 1569.23 RPM at the wheels

The tire will move 5.932 feet per rev. so 5.932 x 1569.23 = 9294.55 feet per minute

Need to multiply by 60 for hour, so...

9294.55 x 60 = 557672.95 feet per hour

1 mile = 5280 feet

Divided by 5280 feet gives miles per hour, which is...

105.62

Keep in mind that this is "theoretical speed". Tires rarely exactly equal their mathematical size.

[neanderpaul]

100 -105 was EXACTLY my guess but I didn't want to say it for some reason.

[CHills]

^ That's Hilarious, 'bout hurt myself laughing.

[skeeters_keeper]

thanks festivafan! you saved me a little bit of trouble looks like i guessed it right on!

after the exhaust is fixed i'll have to get on a nice piece of hwy and see what skeeter can do, i was just on a little 2 lane rd this am!

[skeeters_keeper]

RPM to MPH calculator!


OK, i just took a few minutes and wrote up a calculator in C++. With it you need to enter the tire size (circumference in inches, you get get that from tirecalc online), gear
(including reverse!), and RPM, and it will tell you your predicted MPH.

it should work for 4 or 5 speed festiva transmissions, but not not anything with different trany's.
its a .exe file in a zip folder, only about 130kb... let me know if you find any glitches:

http://two.xthost.info/skeeterskeeper/RPMtoMPH.zip

its fun to play with... with my tires in 5th if i could hit 6k i would be doing about 154mph... thats scary 0.o ... also should be able to pull 30mph in reverse, though i don't suggest it! lol!

[JPT]

^ Tried downloading the .zip twice. I keep getting "Corrupted Archive" messages. It could be me, but you may want to try uploading it again.

[skeeters_keeper]

don't right-click/download, just click on the link regular and it will take you to a download page. i just downloaded it twice, once from firefox and once from opera, and it seems to be working fine for me... let me know if that works!

[JPT]

Got it. Works just fine.