Ballast - how much is too much

[sabat]

Like a freight train, my understanding is that, as long as a vehicle has enough track, traction, and power to overcome drag, it will continue to accelerate, even if it has more ballast than it needs.

If a vehicle on the salt stops accelerating, even though it has more rpm & gear, and isn't spinning, it needs more power or better aero.

So in this example, I should focus on aero, and be comfortable leaving the ballast in place. Am I missing anything?

Thanks,
Dean

[71GSSDemon]

I am less than a rookie here, but I would say aero improvements or more horsepower.  The car has stalled at speed.

Zz

[Stainless1]

Dean, it seems pretty flat from the quarter on, did the tach/speed calculate to 213 as well? I doubt you could have had more than a % or 2 slip since it is quite consistant.  How much ballast do you have now?  What are the front/rear weights on that bike?
But to answer it looks like better tuck or aero is needed... post a picture of the bike.... did any of the picture takers get a down course picture of you? Are you using a stock fairing?
Give us more info on the run... how are you geared?  My plan when we raced the bike was record speed in 5th 500-1000 rpm from rev limiter... That's the plan I use on the car as well.
Sorry I was so busy fixing clutch problems at SpeedWeek I didn't notice what you were riding...
cromag

[tortoise]

An advantage of removing ballast not needed for traction is that less work (power x time) is needed to get to speed, reducing the amount of waste heat generated. Not having to deal with this heat might perhaps allow for a more aggressive tune.

[SPARKY]

Where are you on your HP curve in relation to how much rpm you can turn with out blowing up
If you have rpm left go down in gearing to use it ALL

If no rpm reserve,   give it more gear to see if it can pull it if you really fall off  you have proven to your self that

that all of the ABOVE  are spot on in there responses!

[sabat]

Dean, it seems pretty flat from the quarter on, did the tach/speed calculate to 213 as well? I doubt you could have had more than a % or 2 slip since it is quite consistant.  How much ballast do you have now?  What are the front/rear weights on that bike?
But to answer it looks like better tuck or aero is needed... post a picture of the bike.... did any of the picture takers get a down course picture of you? Are you using a stock fairing?
Give us more info on the run... how are you geared?  My plan when we raced the bike was record speed in 5th 500-1000 rpm from rev limiter... That's the plan I use on the car as well.
Sorry I was so busy fixing clutch problems at SpeedWeek I didn't notice what you were riding...
cromag

Yep, the RPM matched speed with a few % slip. The bike weighs 635lbs with me on it, about 48/52 front-rear. I mounted ~225lbs in lead under the midpoint of the wheelbase, so about 875 ready to run. The engine makes 280hp/165trq in Atlanta, so maybe ~220hp on that hot AF day.

On this pass I left it in 5th and it sat at 9500 rpm for 2 miles, with 20/36 gearing. On the dyno the engine gains ~10hp from 9500 to 10200rpm, which is my comfort redline with this stroke. The fuel mixture was closed-loop correct. The engine checked out fine when I got home.

The aero is not great. The fairing is stock, and 'grudge cut' for the exhaust and ballast box. The rear panels are a wild guess.

[sabat]

An advantage of removing ballast not needed for traction is that less work (power x time) is needed to get to speed, reducing the amount of waste heat generated. Not having to deal with this heat might perhaps allow for a more aggressive tune.

On methanol the engine runs cool, and could go leaner, but other than that it's set on kill. I don't have traction control, so I'm mostly concerned with keeping the tire hooked up.

[sabat]

Where are you on your HP curve in relation to how much rpm you can turn with out blowing up
If you have rpm left go down in gearing to use it ALL

If no rpm reserve,   give it more gear to see if it can pull it if you really fall off  you have proven to your self that

that all of the ABOVE  are spot on in there responses!

I was hoping that leaving it in 5th would have allowed it go 225, the gearing was too tall. Next year I will go to 20/39 and shift to 6th.

[Stainless1]

Dean, you need to work on aero... you hit the aero wall.... I put you in my calculator, 25 inch tire and 1.5% slip hit the numbers... a 20/37 in 5th gave you the record if you pull 10K... and also put you close to the place I shoot for...
But the problem is not gearing, it is aero... the box in particular.  I love the placement, but not the execution...
Here's your winter project... build a box that is 1 inch or so behind the front wheel, the width of the front tire... Oh, forgot to ask, what front tire size.... widening to the width of the rear wheel and about an inch from the tire.  It can be supported in the front from the radiator mount spots on the motor.  If you can integrate a lower fairing into that box that would also aid your quest.
The rear... yep, lots of drag there too... I know there's lots of stuff back there, but it needs a fairing or a tail cover that helps close the hole
You have the power for 225, I think you're probably geared right, and I think you already knew the aero was where you will find the record.

[Seldom Seen Slim]

Hollow swingarm?  Consider filling it with lead shot for some weight.  You won't get 225# in there, but 50-75# is possible.

[sabat]

Dean, you need to work on aero... you hit the aero wall.... I put you in my calculator, 25 inch tire and 1.5% slip hit the numbers... a 20/37 in 5th gave you the record if you pull 10K... and also put you close to the place I shoot for...
But the problem is not gearing, it is aero... the box in particular.  I love the placement, but not the execution...
Here's your winter project... build a box that is 1 inch or so behind the front wheel, the width of the front tire... Oh, forgot to ask, what front tire size.... widening to the width of the rear wheel and about an inch from the tire.  It can be supported in the front from the radiator mount spots on the motor.  If you can integrate a lower fairing into that box that would also aid your quest.
The rear... yep, lots of drag there too... I know there's lots of stuff back there, but it needs a fairing or a tail cover that helps close the hole
You have the power for 225, I think you're probably geared right, and I think you already knew the aero was where you will find the record.

A long narrow box is an excellent idea, thanks. I will work on that first, then the body and the tail. 

[sabat]

Hollow swingarm?  Consider filling it with lead shot for some weight.  You won't get 225# in there, but 50-75# is possible.

I know it's convenient Jon and a lot of folks put weight in / on the arm, but I think it makes bikes feel funky, and if it fishtails it gets hard to reel in. (I think I just made a pun?)  I'd rather have the weight lower, forward, and unsprung.

[stay`tee]

am i correct in how i am reading this Dean ?,, you are slowly feathering the throttle, building speed, while limiting wheel slip, then once at 9500 it hits the wall, dose not make rpm thus no mph , if you twist the throttle to WOT, rpm remains at (or about) 9500,, and regardless of being in 5th or top gear that sucker makes no more rpm

[sabat]

am i correct in how i am reading this Dean ?,, you are slowly feathering the throttle, building speed, while limiting wheel slip, then once at 9500 it hits the wall, dose not make rpm thus no mph , if you twist the throttle to WOT, rpm remains at (or about) 9500,, and regardless of being in 5th or top gear that sucker makes no more rpm

On the pass before, it stopped accelerating at 8750 rpm in 6th gear, for over 30 seconds, at 207mph. On the last pass (above) I left it in 5th and it revved to 9500, still hooked up, but that was all it would do. One more tooth on the rear might have been worth a little more speed, but not enough for me to make another pass, it was so friggin hot.

[Stainless1]

The heat and air density can be a big NA issue.... World Finals would have been a good option for a second race for that bike...