The higher the final gear number, the faster you accelerate, and the lower the top speed, correct??

I thought ATS made a final gear also? What about the Jets and Spoon final gear??

Do you think it would be overkill to lower the ratios and have forced induction??

Thanks

Chris

 

[QUOTE]Originally posted by cjb80
[B]The higher the final gear number,

 

I dont understand.. when I say "top speed" I dont mean acceleration, I mean the top speed that the car can go..

I dont see what that has to do with the power curve..

 

I didn't say power curve. I said torque curve! .. and, if you guys forgive me the lack of modesty, I'll be arrogant enough to assert that I understand that "top speed" means "top speed" and not acceleration. Sounds pretty basic to me.

The reason why top speed relates to torque is that torque relates to force in the way explained above and that a car top speed is basically dependent on its aerodynamic drag.

If this is confusing to you, remember that aerodynamic drag is nothing else but a force that operates in the opposite direction the car is moving.

When the amount of force generated by drag equals the amount of force wheel torque generates as it's applied thru the tyres, the car stops accelerating and you've got your top speed.

If after regearing you've got more wheel torque than before at the previous maximum speed, the new max speed will be higher. If you got less, it will be lower.

It's not possible to predict whether you'll get more or less without looking at the torque curve. It's true that you know that overall wheel torque, will be increased proportionally to the rate of gearing change on constant rpm, but that is not enough, because the ratio of speed to rpm will also be changed when you change gearing!

So, if your max speed was attained at 8.3krpm, and you increase gearing by 5%, you will get more 5% wheel torque at 8.3krpm. But you will be going 5% slower, so you need to compare the original torque at 8.3kprm with the new torque value at 8.7krpm (8.3 + 5%). This may be less or more depending on the torque curve.

I'll give you a real life example: There are many cars where top speed is not attained in top gear. These are usually geared for fuel economy. But they are a living example where a shorter gearing can provide a greater maximum speed.

Anyway, I'm sure Sev will make a much better job at explaining this to you .

 

[QUOTE]Originally posted by Luis
[B]That's it.

 

I was thinking of the same thing myself, goint to 205 50 in the front and 225 45 in the back would be a nice difference, however it will look goofy and if i lower it, i get moved to superstock and rendered less competitive in autoX...

 

No Luis, i am afraid you have covered it all.

However i just want to show him an example. Here are the stats for each gearing change from last page.

4.1 Gear (stock)

0-60 5.0
0-100 12.4
0-140 34.03
1/4 mile 13.70
Top speed 150 MPH

4.3 GEAR

0-60 4.9
0-100 12.2
0-140 35.13
1/4 mile 13.69
Top speed 148 MPH

4.44 GEAR

0-60 4.8
0-100 12.1
0-140 33.38
1/4 mile 13.57
Top speed 149 MPH

4.77 GEAR

0-60 5.0
0-100 11.9
0-140 32.71
1/4 mile 13.54
Top speed 144 MPH


Notice that the top speed on the 4.44 gear is higher then the 4.3. There is a good example for you.
I would also like to add one thing, the only time that a shorter final drive will without a question 100% lower your top speed is if your car is geared in a way that it hits the rev limiter in the highest gear, so basically, the car is limited by gearing and not drag. Therefore if you gear it 2% shorter, your top speed will be 2% slower in every other case, it is like Luis explained.

 

I understand what you guys are saying, I was not considering drag because it seems to me that you can get over the drag problem with a slight increase in power (this is based off of watching the video of an s2k doing 175 or something like that..)

Thanks for the gearing information, very interesting! Who makes a 4.7 gear??

 

Sev,

So how much more torque/horse power are you getting with the 4.44 Gear Change? How would you launch a car like this? Is the torque curve higher? Or is it just shifter from right to left? I would love to see a dyno of this mod.


Thanks,
Bobby

 

Allright, back with some numbers. I worked out the 'torque at the wheel' numbers for the S2000 as well as the HSV R8 (not WRX) ... reason being as I have all the information here as well as the 2 cars parked in front. HSV R8 is a good 'contrast' to the S2000 as it is a 5.7L V8 pumping out 260kW (350hp) and 485Nm (compared to the S2000's 180kW/208Nm). The R8 is a fair bit heavier at 1705kg comapred to the S2000's 1260kg. The R8 also is geared at 75, 130, 210, 330kph. Last of all the R8 has 235/40/18" wheels/tyres. These two cars are very comparable (in the straughline) but they do the job very differenlty so the 'numbers' should show it. The R8 totally whoopes the floor with the S2000 when the S2000 is at low revs (bellow 5k) ... it's like the S2000 is going backwards, Though, in VTEC the two cars are very close and the S2000 is actually a fraction quicker in the 2nd and 4th gear.

So, what I did is find out exaclty what revs both did at all speed increments (ie. 10, 20, 30kph etc..). This allowed me to tell exaclty what torque is available to the cars at that speed from the power/torque curves. Then I multiplied it by the gearing (gear ratio, final drive and gear reducer (when applicable)) that is optimal for that speed. Then I worked out the circumference or the tyres and divided the "numbers" by that. Last of all, I multiplied the R8's numbers by .74 (to account for thr weight difference). These are the numbers I got:

S2000 R8 (%difference reletive to the R8)
----------------------------------------------------------------------
10kph - - 1434
20kph - 1571 1679 -7%
30kph - 1689 1778 -5%
40kph - 1671 1838 -9%
50kph - 1892 1911 -1%
60kph - 1916 1871 +2%
70kph - 1119 1697 -34%
80kph - 1249 1000 +24%
90kph - 1249 1011 +23%
100kph - 1273 1011 +26%
110kph - 907 1002 -10%
120kph - 916 981 -7%
130kph - 907 903 0%
140kph - 864 828 +4%
150kph - 598 627 -8%
160kph - 598 624 -7%


These numbers do not look correct :-( Bellow 50kph I'm expecting good 50% advantage to the R8 (read my post about when I lined them up). Rest of it looks about right, but at low speeds (bellow 50kph) the R8 has a serious advantage .... any idea why these numbers don't show it?

ps. The % difference is very similar to my "Speed vs Power" table and varies only by a few %. The "Speed vs Power" graph is telling me more or less the same thing as the "Speed vs Torque at the wheel" graph .... though, side by side testing of the two cars tells me differenlty. Wonder what is missing from these calcs ... I really thought, I took everything into account :-(