At what speed do we simply "run out of gear"

[DSC]

I was reading that thread most of you probably saw about a civic racing (and beating) a corvette and someone mentioned that the civic would "run out of gear" by the time it hit 150.  I was just wondering, if you had no speed limiter or rev limiter and built your engine up ect ect not talking about any aerodynamics or anything.  At what speed would the Ka tranny "run out of gear"?

[LanceS13]

ok...I just rationalized/derived this formula and it gave me a reasonal number, but if isn't right someone can correct me <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/wink.gif" border="0" valign="absmiddle" alt=';)'>
SPEED=[(RPM)/(GR*FD)]*0.00595*TR
where
GR=gear ratio
FD=final drive ratio
TR=tire radius in inches
RPM=duh!

This gives 159.1mph at 6900RPM, .759 5th gear, 4.08 final, and 12" TR (24" tire)

Find your TR with xxx/yy/zz being the tire size:
TR={[(2*0.yy*xxx)/24.5]+zz}/2

[matic 240sx]

your engine might be going at 159 mph but your acutally not doing it right? &nbsp;resistance (the force pulling car car to the ground) kicks in at 140 right?

[adey]

unless you've got a functional wing/spoiler/whatever, then "the force pulling you to the ground" i believe is known as gravity. <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=':D'> &nbsp; Do you mean wind/air resistance? (i.e. friction w/ the air)

If I'm not mistaken at those speeds we should be experiencing lift, not downforce/pull.

[HippoSleek]

Nice work Lance-engineer boy <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=':D'> &nbsp;That's good stuff!

To the last couple, IIRC, the formula assumes unlimited horsepower (i.e., wind resistance will be overcome). &nbsp;This would allow you to reach the mechanical limits of gearing. &nbsp;Also note that wind resistance ("drag") occurs at virtually every speed, becomes noticeable above about 50 in most cars, and usually limits top speed in cars w/o governors (w/o unlimited hp).

[240meowth]

yah, i've read that the new lamborghini, the mercionoinaofinasdf(sp), is drag limited @ 240mph

also, i've noticed that i am able to hit my speed limit on 4th, which is sad... &nbsp;i'm thinkin 'bout cutting the speed limit, but what are some other device that'll tell me how fast i'm going? &nbsp;i don't want the needle registering a bit off the chart @ 115, while i'm going 150...

[Gismo R]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (adey @ April 04 2002,06:53)</td></tr><tr><td id="QUOTE">unless you've got a functional wing/spoiler/whatever, then "the force pulling you to the ground" i believe is known as gravity. <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=':D'> Do you mean wind/air resistance? (i.e. friction w/ the air)

If I'm not mistaken at those speeds we should be experiencing lift, not downforce/pull.</td></tr></table><span id='postcolor'>
Actually, some of the force due to drag would push our cars to the ground because of the slanted hood and windshield. Most of the force would be pushing down on your car, gravity plus the downward components of the fluid friction.

I'd say that 159 mph is probably a little too high when you take in drag, because the car's power has to overcome air resistance. A more reasonable mph to get to would probaby be around 140ish. But you'd have to have a really loooonng road to get to that speed. Like HippoSleek said, you coundn't push the gears to their limits unless you were in a vacuum.

And Lances13, what's that constant in the formula for?

[drift freaq]

ok guys a little tech here on the drag coefficent the S13 hatch &nbsp;it is .31 . which means its damn slippery add that to a cg of point .29 and you have a car that with a small wing and 200hp could easily hit 140mph . In fact its been done by a friend of mine down in Aliso Viejo and he had another car alongside him to verify the speed. 159 with the right engine on the hatch could be achieved. of course one other thing you guys forgot to &nbsp;take into account is gearing. If you run a J30 VSLD with 3.92 gears your car will have 4% more top end and if you run 3.70 gears you will have 10% more top end thereby putting the 159 mph mark within reach.
mind you know this is the S13 hatch we are talking about
YMMV

[HippoSleek]

hey now... I said nothing about no vacuum <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/tounge.gif" border="0" valign="absmiddle" alt=':p'>

I think you can replicate this just fine in the real world. &nbsp;Take a 300 hp KA+T and run it to redline in 5th. &nbsp;That should be enough hp to overcome drag to that speed. &nbsp;Drag is overcome with enough hp - only the gearing should be your limit.

[LanceS13]

matic: If your engine is spinning at a speed capable of propelling the car 159mph, the car will be traveling 159mph no matter what the air resistance. The only time this would not be the case is in the presence of wheelspin or a slipping clutch.

Mark: Thanks! Like you said, this formula assumes unlimited hp and/or no wind resistance, taking only into account the gearing itself, which is what DSC asked for...not "when do our cars hit an aerodynamic wall?".

Gismo R: [2*pi*(60 min/hr)]/[(12in/ft.)*(5280ft./mi.)]=0.00595 (min.*mi./in.*hr)
It's dimensional analysis to get the units to work out.

drift freaq: I did not forget final gearing. It's in the formula. I've checked the formula and it looks right to me, so 159mph is possible on a 4.08 rear end with the other previously stated variables. Holding the other variables constant, a 3.92 will allow a 165mph top speed and 3.70 will allow 175! Of course, you need the horsepower to make up for the decrease in acceleration capability due to the gearing change and to overcome any conflicting friction forces (air resistance, tire drag) to actually hit that mark.

[DuffMan]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (drift freaq @ April 04 2002,12:23)</td></tr><tr><td id="QUOTE">ok guys a little tech here on the drag coefficent the S13 hatch &nbsp;it is .31 . which means its damn slippery add that to a cg of point .29 and you have a car that with a small wing and 200hp could easily hit 140mph . In fact its been done by a friend of mine down in Aliso Viejo and he had another car alongside him to verify the speed. 159 with the right engine on the hatch could be achieved. of course one other thing you guys forgot to &nbsp;take into account is gearing. If you run a J30 VSLD with 3.92 gears your car will have 4% more top end and if you run 3.70 gears you will have 10% more top end thereby putting the 159 mph mark within reach.
mind you know this is the S13 hatch we are talking about
YMMV</td></tr></table><span id='postcolor'>
Um thats not exactly how it works. If you decrease your gear ratio by 10% you are decreasing the force put to the ground by 10% in top gear.

However you will also run the same speed at a lower rpm, and when you approach redline, lower rpm's have more torque which would increase the force put to the ground.

Whether or not installing a taller rear end would actually help you get a higher top speed or not, is going to depend on what kind of mods the engine has.

[Roly]

Easiest way to figure out what you're geared to do, keeping the stock rev-limiter. Put the car in 5th gear at 1000rpm. Whatever speed it gives you, multipy it by what ever rpm your red-line is at... around 7k rpm.

[Russki]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (Roly @ April 04 2002,5:15)</td></tr><tr><td id="QUOTE">Easiest way to figure out what you're geared to do, keeping the stock rev-limiter. Put the car in 5th gear at 1000rpm. Whatever speed it gives you, multipy it by what ever rpm your red-line is at... around 7k rpm.</td></tr></table><span id='postcolor'>
I've never wondered the EXACT top speed, but that's how I always figured it. &nbsp;Let's say I'm going 82mph at 3,500rpm, so at 7,000rpm (a bit over redline) I would be going 164mph, and I just subtract however much I think the drag and friction would take away, and I come up with a very approximate number of 140mph at 6,900rpm (actual redline). &nbsp;Anything more exact than that I don't really care for unless I would be competing or whatever. &nbsp;You don't get to go that fast too many times, but kinda fun to know what the car can do.

disclamer: just my 2 cents so don't bug me about how off I am.

[LanceS13]

Yeah, I know you said don't bug you, but this is bugging me. &nbsp;If you calculate 164mph at 7000rpm (which is pretty accurate), you're not gonna drop to 140mph at 6900rpm because of wind resistance and other forces of friction. &nbsp;What it seems some of y'all are failing to see is that wind resistance isn't gonna cause a slower speed at a certain rpm, it will limit the maximum rpm that can be reached. &nbsp;If you're motor is spinning at 6900rpm, then your car is going about 160mph. &nbsp;Wind resistance and lack of horsepower will simply not allow the motor to spin to 6900rpm in 5th. &nbsp;If the car is resistance/friction-limited to 140mph, then the engine will only spin to about 6000rpm. &nbsp;After that, it doesn't have the power to overcome the opposing forces of friction and the engine stops accelerating.

[Russki]

I guess I was kinda thinking about that too, it would take way too long for you to reach 6900rpm in 5th with the stock hp. &nbsp;I think I was subcontiously putting that into consideration too, and didn't realize all the factors. &nbsp;I just think of this stuff during rush hour to work, so I know it will be inacurate.

[drift freaq]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Duffman.....
Um thats not exactly how it works. If you decrease your gear ratio by 10% you are decreasing the force put to the ground by 10% in top gear.
However you will also run the same speed at a lower rpm, and when you approach redline, lower rpm's have more torque which would increase the force put to the ground.
Whether or not installing a taller rear end would actually help you get a higher top speed or not, is going to depend on what kind of mods the engine has.
</td></tr></table><span id='postcolor'>

no, actually Duffman I am not wrong. It is true that you can increase top speed by putting in taller gears. I already knew about the less or more Torque statement you are trying to correct me with but you are the one that has it off sligtly not me.
A classic example of what I am talking about is to compare a 1971 Datsun pickup to a 1971 Datsun 510. The pickup used the same engine as the 510 and was comparable in weight .
The truck used a 4.21 final drive and the car used a 3.90 both engines put out 96hp . Oh yeah just to let you know the 510 weighed in at 2000lbs . Now the truck would top out at 85-90 miles an hour due to the gearing and the car would top out at 110.
Now having owned a 510 2 door and having a friend who owned the truck this was an actual proven example. <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/tounge.gif" border="0" valign="absmiddle" alt=':p'> &nbsp;<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=':D'> &nbsp;<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/hehe.gif" border="0" valign="absmiddle" alt=':hehe:'>

[Gismo R]

drift freaq, I don't know much about the cars in the 70s, but are you saying that the slower one was a truck and the faster one was a car? Trucks are waaay less aerodynamic than cars. There's more surface area on the front view of a truck (well, most trucks), plus that tail gate acts like a damn parachute. I don't know much about gearing so I'm not going to say you're wrong, you could be right. I'm just saying that the reason the truck topped out at a lower speed could have been due to drag.


On another note, friction takes away energy, and transfers that into heat and/or sound, it doesn't take away velocity. Air resistance is affected by speed, meaning the faster you go the more resistance there is. So, if your engine is spinning at an rpm that would put the car at 160mph then you car is going to be going 160mph, unless there was some major slipping through the drivetrain. Air resistance doesn't slow your velocity it only slows the rate at which velocity is changing, which is called acceleration. <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'>

[sykikchimp]

drift that was a real world example but not a very good one b/c of interpretations like those taken by Gismo.

What he is saying (and has already been said) is that the taller the gear, the less times the tires will spin faster at the same given rpm. &nbsp;(given unlimited horsepower as Hippo was so kind to re-iterate.)

so at 6900 engine RPMS.. &nbsp;the tires are rotating at a given rpm themselves with the 4.08 gear.

reduce it to a 3.70 gear
so at 6900 engine RPMS the tires are rotating the before mentioned speed PLUS the percentage rate ( i think 24.5%?) of change b/w the gears.

Once again I will also re-iterate. &nbsp;UNLIMITED HORSEPOWER

[DSC]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (Gismo R @ April 04 2002,12:41)</td></tr><tr><td id="QUOTE">drift freaq, I don't know much about the cars in the 70s, but are you saying that the slower one was a truck and the faster one was a car? Trucks are waaay less aerodynamic than cars. There's more surface area on the front view of a truck (well, most trucks), plus that tail gate acts like a damn parachute. I don't know much about gearing so I'm not going to say you're wrong, you could be right. I'm just saying that the reason the truck topped out at a lower speed could have been due to drag.


On another note, friction takes away energy, and transfers that into heat and/or sound, it doesn't take away velocity. Air resistance is affected by speed, meaning the faster you go the more resistance there is. So, if your engine is spinning at an rpm that would put the car at 160mph then you car is going to be going 160mph, unless there was some major slipping through the drivetrain. Air resistance doesn't slow your velocity it only slows the rate at which velocity is changing, which is called acceleration. :)</td></tr></table><span id='postcolor'>
I don't think thats entirely accurate gizmo. Often, wings may be added for downforce but will add drag (and more friction with the road but thats another issue) and limit top speed. So given the same ammount of HP, weight, and gearing and two different cars the less aerodynamic of the two cars will hit a speed where it simply cannot go any faster without added horsepower to combat the ammount of wind resistance at that speed.

Edit: oh and the more aerodynamic car will ofcourse hit that "wall" at a higher speed...forgot where I was goin with the post.

[LanceS13]

Gismo is entirely right...he pretty much restated what I've been saying.
drift freaq seems to be on the right track but is forgetting some variables. It is true, the bigger the final drive number, the lower the top speed (due to gears, not opposing forces). But you have to take into account tranny gear ratio and tire diameter as well...and were the speeds you recording taking at redline in 5th?

[Gismo R]

I don't understand what you're saying is inaccurate.

[drift freaq]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">drift that was a real world example but not a very good one b/c of interpretations like those taken by Gismo.
</td></tr></table><span id='postcolor'>

true sykik, Ok my bad for using a example that could be poked holes in.
Lance, I know about the variables but I was just trying to prove my point which you stated and I know is correct. I know I was on the right track . I used a poor example, my bad.
I was merely responding to Duffmans overlooking the whole gearing issue which does have effect.
Now with that I think we have thoroughly beaten this thread into the ground hahaha its been fun . I am done
have a good day guys.

[gh6o6]

<!--QuoteBegin--Gismo R+April 03 2002,2<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/wow.gif" border="0" valign="absmiddle" alt=':0'></span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (Gismo R @ April 03 2002,2<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/wow.gif" border="0" valign="absmiddle" alt=':0'>1)</td></tr><tr><td id="QUOTE"></span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (adey @ April 04 2002,06:53)</td></tr><tr><td id="QUOTE">unless you've got a functional wing/spoiler/whatever, then "the force pulling you to the ground" i believe is known as gravity. <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=':D'> Do you mean wind/air resistance? (i.e. friction w/ the air)

If I'm not mistaken at those speeds we should be experiencing lift, not downforce/pull.</td></tr></table><span id='postcolor'>
Actually, some of the force due to drag would push our cars to the ground because of the slanted hood and windshield. Most of the force would be pushing down on your car, gravity plus the downward components of the fluid friction.</td></tr></table><span id='postcolor'>

i suppose you think plane wings have downforce because they are slanted on the top and flat on the bottom
http://www.howstuffworks.com/airplane2.htm

[Ballistic-Mobile.com]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (DSC @ April 04 2002,11:00)</td></tr><tr><td id="QUOTE"></span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (Gismo R @ April 04 2002,12:41)</td></tr><tr><td id="QUOTE">drift freaq, I don't know much about the cars in the 70s, but are you saying that the slower one was a truck and the faster one was a car? Trucks are waaay less aerodynamic than cars. There's more surface area on the front view of a truck (well, most trucks), plus that tail gate acts like a damn parachute. I don't know much about gearing so I'm not going to say you're wrong, you could be right. I'm just saying that the reason the truck topped out at a lower speed could have been due to drag.


On another note, friction takes away energy, and transfers that into heat and/or sound, it doesn't take away velocity. Air resistance is affected by speed, meaning the faster you go the more resistance there is. So, if your engine is spinning at an rpm that would put the car at 160mph then you car is going to be going 160mph, unless there was some major slipping through the drivetrain. Air resistance doesn't slow your velocity it only slows the rate at which velocity is changing, which is called acceleration. <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'></td></tr></table><span id='postcolor'>
I don't think thats entirely accurate gizmo. Often, wings may be added for downforce but will add drag (and more friction with the road but thats another issue) and limit top speed. So given the same ammount of HP, weight, and gearing and two different cars the less aerodynamic of the two cars will hit a speed where it simply cannot go any faster without added horsepower to combat the ammount of wind resistance at that speed.

Edit: oh and the more aerodynamic car will ofcourse hit that "wall" at a higher speed...forgot where I was goin with the post.</td></tr></table><span id='postcolor'>
Okay guys...
Both of you are correct <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=':D'>

Lets rework the example. &nbsp;Take the body off of the truck and leave the drivetrain alone. &nbsp;Drive both vehicles to redline in 5th gear and the truck chassis will have a slower final speed because of the higher gearing of the final gear. &nbsp;See equal hp/equal wind resistance/higher gearing= slower final speed.

[wherezmytofu]

http://www.geocities.com/z_design_studio/
heres a gearing calculator..makes it much easier <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'>

u can get 1-3mph more then gear wise from momentum..but it will go down after a while <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/tounge.gif" border="0" valign="absmiddle" alt=':p'>

[Jeff240sx]

I was gonna post the mathematical way to find out the speed at redline in a 240sx, but apparently Lance got me to it, by a couple days <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'>

Next thing. &nbsp;There are 3 main parts to why a car will hit a wall at speeds.
1) &nbsp;Aerodynamics. &nbsp;This is the largest, by far, factor in the limit a car can go.
2) &nbsp;Tires (Drag mainly, but it is all sitting on the tires, so they become the culprits). &nbsp;Friction, drag, the weight of them. &nbsp;This is much less that aerodynamics.
3) Driveline losses. &nbsp;The loss of horsepower thru the driveline will give you less hp to push the car, thereby limiting the engines ability to rev faster, and make the car go faster.
-Jeff