alright like the title says im trying to calculate my max speed in each gear since i have a cx and no tach. first off let me just say that im not really going to be redlining it that much, if at all, before i get a tach but i was just curious about what my top speeds are in each gear.
Heres my setup:
Car:95 Cx hatch
Engine:h23a1 (6500rpm redline i believe)
Tranny Ratios:
1-3.307
2-1.857
3-1.320
4-1.034
5-0.812

Tires:165/70/13


Im not 100% sure about any of my calculations so please correct me about anything thats wrong.

From the tire size i got that the overall diameter of the tire was 1.84ft which has a circumfrence of 5.78ft. This is where im not sure if im right or not but i think i am because my answers made sense. if the rpm of the engine the rpm of all cylinders? meaning at 6500 does that mean that the crank is spinning at 6500/4? thats what i used and it gave me realistic numbers.

heres my calculations:
6500/4=1625

1st gear- 1625/3.307=491.38 rev/min for the wheels => 491.38 * 5.78=2840ft/min => 32.27mph

i did the same thing for each gear and got the following results:

2-57.48mph
3-80.86mph
4-103.22mph
5-131.44mph

like i said i could have very easily done something wrong especially when dividing the engine rpm by 4 because i dont know if thats right or not. answers didnt make sense unless i did that. anyway, any corrections are welcome and no i dont plan on using these speeds as the exact speeds for redline, just more of a curiosity thing.

 

You're close, but that's because you made two errors that compensated each other.

6500 RPM means just that, your crank is spinnen 6500 times a minute. SO you shouldn't divide by 4.

However, you forgot the end reduction (or whatever it's called in english, I'm dutch). It's the fixed gear that reduces rpm from your gearbox to your wheels. It's somewhere between 3.8 and 4.2 I guess (look it up in your manual), so your calculation produced plausible outcomes. Scratch the 4 and use the proper end reduction, and you'll be fine.

 

thanks. i guess thats the final drive ratio youre talking about? thats 4.266. recalculating my numbers i got the following:
1-30.26mph
2-53.89mph
3-75.81mph
4-96.78mph
5-123.24mph

the numbers for 3rd and 4th seem a little low. Im wondering if i calculated the circumference of the wheel incorrectly. Im at college now and im cars at home in the shop so i cant go out and measure it.

 

Gear ShiftRPM Speed @ 6500 RPM
1st N/A 31.1
2nd 3650 55.4
3rd 4620 77.9
4th 5092 99.5
5th 5104 126.7
RPM in top gear at 70mph: 3591


I got this from this:
http://autocrossing.com/cgi-bin/gearcalc.cgi

I didnt know your final drive though.

 

these were my results when i used my final drive:

Gear ShiftRPM Speed @ 6500 RPM
1st N/A 31.3
2nd 3685 55.1
3rd 4576 78.3
4th 5092 99.9
5th 5104 127.3
RPM in top gear at 70mph: 3575

so i really wasnt too far off with my calculations when i did it the second time. thanks a lot for the help