This might be really boring to some out there so be warned. Ok so im trying to figure out the Rpm of my wheels from the rpm on the tach. Im driving and set up the example in my head of the engine running at exactly 6000 rpm which is easily converted 100 rps. Then my guess was to divide by the gear ratio, which of course depends on the gear you're in, lets just say first gear. And according to the site i read the ratio is 3.23:1. Then i get an answer of 30.95 rps. Well im pretty sure that is not right because i get a final speed of 99 mph in first gear!!! so help me out with this one, i think im missing an idea behind the gear ratio, or is there some other system that is reducing spin?

thanks

oh yeah the reason i was thinking this was that on the bay bridge the average speed of cars is about 60 mph which causes wheels to appear to go backwards. This i know is due to the lights on the bridge which if i remember are 60hz strobelights really. So i was wondering if i could match the rpm exactly so that the wheels were spinning at 60hz, or a fraction of 60hz that would allow the wheel to stand still in the strobe effect.

 

I hate to say it, but you think too much.

 

i like your style... but at the same time, i cannot answer your question. if you figure this **** out and can get a nice photo, post it up, id like to see.. on a side note however....

have you ever put a stobe light to a real low setting and blinked during the time the light flashed.. to open your eyes in complete darkness?? its dope

lsd

a closed mind, is a lost mind

 

Thanks, yeah i actually have done that with a stroblight, its pretty sweet. I like how its somewhat light with your eyes closed, then when they open its total darkness.

So any engineers around here want to help me?

 

pm SLAIN here on h-t he may be able to help you, just link him your thread

 

I'm guessing you have to divide by the final drive too (4.4) and get ~7 rev/s. That works out to ~28 mph.

*edit* If you go here and put in 6000 as the redline, you get 28.6.

http://www.autocrossing.com/cgi-bin/gearcalc.cgi

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by acurciv &raquo;</TD></TR><TR><TD CLASS="quote">Ok so im trying to figure out the Rpm of my wheels from the rpm on the tach. </TD></TR></TABLE>

these 2 aren't quite related or easiest way to go about it.. you need to know how much of a distance your tire covers to make a full revolution, then.. lets say 60mph, you'd have to divide 60 by that number, then you'll know how many revolutoins are covered in 1 hour, then divide that by 60 and you got rpm for your wheels.

 

That works too:

22.8 in diameter wheel = 71.7 in circumference

60 m/h = 316,000 ft/h = 5,280 ft/m = 63,360 in/m

63,360/71.7 = 883.6 rpm or 14.73 rps

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by vtec.dc2 &raquo;</TD></TR><TR><TD CLASS="quote">

these 2 aren't quite related or easiest way to go about it.. you need to know how much of a distance your tire covers to make a full revolution, then.. lets say 60mph, you'd have to divide 60 by that number, then you'll know how many revolutoins are covered in 1 hour, then divide that by 60 and you got rpm for your wheels.</TD></TR></TABLE>

sure they are related. i just dont want physics to haunt me again.

 

This also depends on how many spokes the wheel has. If it had one spoke, it would have to rotate at 100 rps (from what I read most lights are 50hz which means it flashes 100 times per second.) If there were two spokes, it could rotate at 50 and still look frozen. 4 spokes and 25 rps..etc... (unless I'm really screwing this up because it's late)

 

Hey im glad some of you guys out there care about this crazy stuff. Ok so using the final drive of 4.4 and the wheel diameter that you guys gave me i get at 6000 rpm in first gear a wheel frequency of 7.036 rps which is the same as 7.036hz right? Ok then i calculated the speed of the car to be exactly 22.665 mph, only after a few conversion errors. So it looks good to me.

Now im interested in gettting the wheels spinning at 60hz. This might just be a problem considering my current lack of funding on builing the worlds first 242.72 mph type r. Also getting up to that speed on the bay bridge just seems a little, well insane!! So i'll be back with a fraction of that number that will allow a wheel to stand still. Also i dont think the number of spokes will matter in this since all spokes will have the same frequency as the entire wheel.

thanks all.

 

1 Hz is one cycle. AC is a sine wave, 1 up one down per cycle. Like I said, a 50 Hz light flashes 100 times a second. What you're talking about with multiples of the frequency would only work for the wheel spinning fast than the light is flashing. Ok, if a wheel has one spoke, and it's spinning at 100 rps, every time the light flashed, it would be at say the 12 o'clock position. If the wheel was going 200 rps, it would go around twice for every light flash, so it would still be in the 12 position. But anything less than 100 rps, the spoke is going to look like it's going backwards, because it's not making it all the way around before the light flashes again.

If you have 4 spokes, you can get away with 25 rps because each spoke only has to move 1/4 of a revolution before the light flashes again to make it look like it's still. This is very hard to explain.

That speed at 6000rpm should be closer to 28 mph, by doing the calculation and also the link I gave.

 

Apparently there are a lot of people who think too much.

 

7.0363 rev/s * 71.7 in circumference = 504.48 in/s

504.48/12 = 42.04 ft/s

42.04/5280 = .0079621 miles/s

.0079621 * 3600 sec/hr = 28.663 mph

 

So here it is, the final answer.

X = F(264)(gear ratio)

Where X is Tach's RPM
F is your desired frequency (in Hz)

So if i want to have the wheel spin at half the lights frequency, 60Hz/2 = 30Hz then the closest i could get would be redlining in 5th, id need an engine rpm of 8791.2, which is just out of range for my R. But i think i could get the same effect if i were going a quarter of the lights frequency, 15hz which is easily obtained at 5781.6 rpm in 3rd at a speed of 60.68 mph. Or even better it would work at 3366 rpm in 5th.

Wow so basically i just wasted a whole lot of time calculating this equation that given the constaints of the car will only give me a ok stand still effect at a quarter of the street lights frequency. But on a side note i aced my mechanics of solids test today, so this couldnt have been that big of a waste.

and maybe one day i'll take little video clip of my wheels at exacly 15hz standing appearing to stand still while i drive along at 60.68 mph. Now all i need from you guys out there is a method that will allow me to get the car at exacly 3366 rpms!! Any electrical devices you know of or can make?? lol

 

Dam you GeeReg!!! Adding more complexity to the spoke issue and then the cosine wave action or what they tell me is 60hz in the US but may actually be 50 like you say. So now im gonna have to change that whole equation!!!! Still not totally convinced on the spoke issue though. My thoughts are that if its an even number of spokes and evenly spaced then either one or the other spoke will be in the same position when the light came one. Ok well im getting to tired to actually think or write this out in anyway that makes since. But yeah dam you!!! hahahahah

 

*edit* Didn't see you replied.

I don't know how else to really explain it.

 

Oh i follow and drew out a diagram to assure myself this, you are right. Im just to tired to actually write and make sense. Thanks for keeping this idea straight and truthful too