530 gearing ?

[CivilRock]

I love those facts. Thanks. I heard those from my co-worker 14 years ago, so I might be twisting the memory a little.

I try and watch drag racing on TV, but they bore the toot out of me. The only thing I like watching is the super slow motion HD of the launch. The other 98% of the show is doodoo. I wish I could find a more technical show about drag racing. I'm sure if they ever made one it would turn into a soap opera and the technical part would get reduced to 3% of the show.

Math quiz: if I'm at 17/47 and my theoretical top speed is 157 mph, and I go to 17/52 what will my theoretical top speed be reduced to? I'm going to try and figure this out before anyone replies (posplayr).

[CivilRock]

142 mph. I think.

[CivilRock]

I do some drag racing and I have a 14, 15, 16, 17T counter shaft sprockets and 45, 46, 47, 48, 50, and 52T rear sprockets for my bikes to get the correct gearing for each bike and motor build.

I'm reading this over again and I have some questions for ya;
1. With all these different combinations, do you have to adjust the chain length? Or do you have enough rear axle adjustment?
2. If you do adjust the chain, do you use spring clip master links? or rivet?
3. Do you run offset counter sprockets to get the chain around the rear tire? If you do, how much offset? And do you use an outer bearing support?
4. In your signature, what is the gearing for those runs?

Thanks,
Kevin

[posplayr]

Another interesting fact about top fuel dragsters is they pull more G's when the Shute is opened than they do on the launch

The chute G's are negative but other that that quite understandable.

unless you can interlock the tires with the track, It is hard to get a traction level greater that 1 and so 1 G is close to the maximum acceleration.

At 32.2 ft^2 (i.e. 1 g) you do the quarter mile in about 4.95 sec at 326 mph.

On the other hand you can easily design a parachute that will pull 3,5,10 g's. Enough that you can rip the mount right off the light weight dragster.

Ever wonder why a rocket car is so much faster? It doesn't rely on tr active effort (it uses thrust) and so it doesn't have a 1 g limit.

[posplayr]

142 mph. I think.

Since you are only comparing rear sprockets then you only need the ratio of those two. If you were changing both then it is the ratio of ratios.

157*(47/52)=141.9

[posplayr]

That I'm not going to hit the rev limiter before I cross the finish. For some reason I thought I was close to redline last time... But now that I replay it in my head, I think I barely got into 5th before the finish. That's right... Hum. Now that I think about it, I was almost able to finish in 4th.


Maybe with a wheelie bar or extended swingarm? But in my case, traction is not an issue. Fighting a wheelie off the line is. That's a 190 road race rear at 20 psi. I was amazed how sticky the track is behind the line. It's like putting your boots down on fly paper.

I had a co-worker that built drag cars in his spare time. He explained to me that the top fuel dragsters accelerated hardest at the end of the strip when the downforce was the greatest. That they are spinning the tires the whole way. They have more power than they can transfer to the ground. I was amazed with that concept. They basically can't apply full power off the start.

I think what I need is a 50t rear and a longer chain both to accommodate the larger sprocket and to move my axle further back in its adjustment range.

Posplayer- you really make me think. Thanks.

-Kevin

Tr active effort is proportional to down force. Down force is weight plus a factor proportional to the square of velocity. My example above is ignoring aero effects which obviously complicate the issue. At low speed however, the aero effects are nil so the analysis still works.

Flying a wheelie forces does put more pressure on the wear wheel (weight transfer) so you are less likely to spin the rear, but if you keep putting in more torque you are likely to flip so that is limited. That is why there are wheelie bars so you can run at maximum weight transfer without flipping thereby maximizing tr active effort.

TE is generally always higher the more weight you have. Also while it might be counter intuitive,. but a certain amount of slip actually increase the tr active effort as well. It is compound dependent but generally always true I believe.

The point is you should be able to increase you gear ratio all you you want until the front wheel popup will cause problems. The traction problem will rear it's head before you lower 5th gear to where you are going through the traps at 9K RPM in 5th. (probably the top of your torque curve)

[CivilRock]

unless you can interlock the tires with the track, It is hard to get a traction level greater that 1 and so 1 G is close to the maximum acceleration.

Interesting. And yes, that's without any downforce, right?

I was looking for more fun facts about top fuel dragsters and I the first thing I found was this Wiki: http://en.wikipedia.org/wiki/Top_Fuel

Interesting points:
They pull and average of 4G going down the track.
The headers alone produce 900-1100 lbs of downforce at full throttle.
At 330 mph the airfoil behind the wheels produces 12,000 lbs of downforce.

[CivilRock]

157*(47/52)=141.9

Ok, I took the long way, but I got the same answer.

What this tells me is that I'm geared way too high. I might need a 16 front and a 52 rear to get 9k RPM at 125-ish MPH. If I'm doing my math right, 16/52 would give me a max speed of 133.6 MPH. That's 3.25:1

Either way, I'm going to need a longer chain and some more sprockets.

-Kevin

[posplayr]

Interesting. And yes, that's without any downforce, right?

I was looking for more fun facts about top fuel dragsters and I the first thing I found was this Wiki: http://en.wikipedia.org/wiki/Top_Fuel

Interesting points:
They pull and average of 4G going down the track.
The headers alone produce 900-1100 lbs of downforce at full throttle.
At 330 mph the airfoil behind the wheels produces 12,000 lbs of downforce.

Homework assignment, if the vehicle is experiencing an average of 4 g's of linear acceleration down the track, how fast (ET and top speed) will it do the quarter mile?

4.5 sec at 4.0 g's is 562 mph in the quarter mile. I had the right formula just screwed up the units making it the wrong result.


Hit they don't pull 4 g's down the track. If there is 4 g's it is down force. 1 g is weight and three g's are thrust and aero effects.

[posplayr]

Ok, I took the long way, but I got the same answer.

What this tells me is that I'm geared way too high. I might need a 16 front and a 52 rear to get 9k RPM at 125-ish MPH. If I'm doing my math right, 16/52 would give me a max speed of 133.6 MPH. That's 3.25:1

Either way, I'm going to need a longer chain and some more sprockets.

-Kevin

Next time you are out going down the freeway at 80 mph. Drop down into 4th gear. See if that is comfortable. That might be as much gearing as you want.

For the 1100 the gears are 1.125 in 4th and 0.961 in 5th

1.125/0.961 = 1.17

If you stick with the 17T gear in front you would need a 56 tooth rear
If you drop to 16T front then you would need a 53T rear to get the same effect as dropping from 5th to 4th gear.
(I used a simple spreadsheet ratio calculation to get this)

Since you probably never got out of 4th gear in your quarter mine this would be a good place to gauges the drive ability of that type of gearing.

[stetracer]

Homework assignment, if the vehicle is experiencing an average of 4 g's of linear acceleration down the track, how fast (ET and top speed) will it do the quarter mile?



Hit they don't pull 4 g's down the track. If there is 4 g's it is down force. 1 g is weight and three g's are thrust and aero effects.

Yes the do pull 4 G's down the track 0 to 100 mph in .8 seconds

[posplayr]

Yes the do pull 4 G's down the track 0 to 100 mph in .8 seconds

OK I corrected my math error.

[stetracer]

I'm reading this over again and I have some questions for ya;
1. With all these different combinations, do you have to adjust the chain length? Or do you have enough rear axle adjustment?
2. If you do adjust the chain, do you use spring clip master links? or rivet?
3. Do you run offset counter sprockets to get the chain around the rear tire? If you do, how much offset? And do you use an outer bearing support?
4. In your signature, what is the gearing for those runs?

Thanks,
Kevin

Yes I have to adjust the chain length. I have several different size pieces of chain so I can use any size sprocket and any wheel base my 4" adjustment will alow me to go. I use 2 clip type master link and I use the 1/4" offset countershaft sprocket with no bearing support.
The gearing on my 85 1150 on the 9.72 pass was a 17/47 but that is a nitrous bike and it only uses 4 gears in the 1/4 mile unless I use the No2 then it will use all 5 gears at close to 158 mph.
The 84 GSX mostly stock motor was using a 15/48 gearing. I am using 16/48 now and I can run the 1/4mile in 4 gears or 5 gears it did not make much difference in et or mph. I am going to try 17/50 next and just use 4 gears

[jimb12]

I was out on a ride yesterday and realized there's a much easier way to figure this out. I noted that in top gear at 60 mph I was at almost exactly 4,000 RPM.

So if my redline is 10,500 RPM, then my theoretical* top speed is 157 MPH.
Oh, and I'm 17/47 (not 48).**

I want to be in the high 10 second range and I'm guessing 125mph. End of story: I don't think I'll run out of gearing. If anything, I should think about going to a 49 or 50 rear sprocket.***

-Kevin

* - I don't know if my bike has enough power to get there.
*2 - I remember reading about MotoGP bikes in 2005 or so having a wheel speed difference of about 30 mph on the straights. So in order to go 200 mph their theoretical gearing has to be in the 230 mph range.
** - 1150 motor, 530 chain, 17t front, 47t rear, 190/70-17 Dunlop rear tire.
*** - I would do this today, but my axle is adjusted all the way forward. I'd have to buy a new longer chain. (or extend the one I have)

Don't use the speedometer for your calculations, they are full of crap. Use the timing lights on the track.

You can get a pretty good calculation by sitting on your bike, have a buddy mark on the ground where the rear wheel is and wheel reference point, move straight forward ONE revolution and mark it, then measure the distance in feet. Then use formula as follows:

(engine rpm times distance in feet) divided by (gear ratio times primary ratio times sprocket ratio times 88)

Result is speed in mph. Won't be as precise as gathering data with a datalogger but certainly much closer than using the speedometer.

[CivilRock]

(engine rpm times distance in feet) divided by (gear ratio times primary ratio times sprocket ratio times 88) Result is speed in mph.

Love it. I'll get all those variables and report back.

I hope you guys aren't tired of seeing my dorky and endless posts and questions.

Another variable I just looked up was the max power RPM, and it's lower than I thought at 8,000 RPM. When I was road racing, I knew the max power RPM and I would try and straddle it with the needle for each gear. I don't even know if that's the best method, I think I just made up the rule for myself.

What RPM should I set my shift light at?

-Kevin