Three simple questions - pls point me

[lsrengineer]

lsrengineer,
If, instead of plotting tractive effort versus speed, you plotted horsepower in the upper gears along with the drag (expressed as HP) optimum shift points would virtually leap off the page, and the effect of changing gear ratios would be much more apparent and easily matched to each other and to the drag curve.

@ Interested Observer, I've plotted hp in each gear vs. speed and you are correct the best shift points show up nicely.  I checked against a plot of rear wheel torque vs. speed and the engine rpm for best shift shows the same points.   I'm cleaning up the graphs/etc. for posting.  This round was using stock motorcycle info. e.g. final drive and tire size.  Good tip thanks.

[Interested Observer]

Yes, they should agree since it is all the same information.  It is just that with the Hp approach the curves aren't all scrunched together.

[lsrengineer]

Yes, they should agree since it is all the same information.  It is just that with the Hp approach the curves aren't all scrunched together.

yes, it's the same info, exactly what happened using the torque approach, hard to read - I'm going to put the drag HP on there but I need to figure the drag as a function of speed.  The motorcycle is listed at 173 mph max.  Should I find the constant that makes the 1/2 A Cd rho v squared line cross the 6th gear line at 173 mph?  That's what I was planning.  Thanks.

[Interested Observer]

If you have real-world data that sounds like a good approach.  Choose appropriate air properties, frontal area, and then fiddle the Cd to get it to fit.  (Assuming that was a WOT terminal speed, and not just the max governed rpm.)

[Interested Observer]

Also, are drive train power losses accounted for, or at least approximated?

[SPARKY]

Are those PROVEN RPMs or they off factory charts  we found out the hardway the factory red line was based on Tach swing!!

LSR is all about minimizing drag of any kind and maximising TE for the speed you need to run 

HAVE fun, enjoy the learning curve---it will be steep  oh btw  welcome to our sick addiction !!!

[lsrengineer]

Also, are drive train power losses accounted for, or at least approximated?

The input is from a dyno run, so I think the energy loss for the drive train and tire should be in the values to at least some degree. 
I'm not sure of the gear the dyno run was made with so could have some error there, I've read where 4th gear has been used; 6th will have higher tire (but on a roller?) and chain speeds.  So... good question, I may need to re-visit.  I think for the first pass and seeing trends this should be OK.   Along the same lines - as the tire grows the contact patch changes I assume, I wonder how this changes the rolling resistance, maybe the tire becomes harder and flexes less, this may or may not reduce rolling resistance it could indent the salt more causing the tire to run on an uphill slope.

[Old Scrambler]

Good Read..............I would add that as the tire may grow, the air deflection will decrease..............the unknown is pressure to the salt..........it seems to me that more speed would reduce downward pressure.........unless properly countered by downward air at the tail.

I am running a 20-hp 4-speed motor at an average of 82.5 mph..........shifting from 3rd to 4th is very critical............I changed my rear sprocket by 2-teeth and went about 2 mph faster without wind but slower with a 3 mph head wind.  Our goal was to build the best torque curve possible and let the hp fall where it will.

[Interested Observer]

Old Scrambler:
Your gearing change moved the power curve peak nearer to the drag curve, resulting in more power available, and hence more speed.  Then, the head wind raised the drag curve, resulting in it intersecting the power curve earlier, resulting in less speed.  As will be obvious when lsrengineer publishes his curves.

What exactly is a “best torque curve”?  You’re spittin’ in the wind worrying about torque instead of power.

[SPARKY]

RPM X TQ
_________  = HP
5252

[lsrengineer]

If you have real-world data that sounds like a good approach.  Choose appropriate air properties, frontal area, and then fiddle the Cd to get it to fit.  (Assuming that was a WOT terminal speed, and not just the max governed rpm.)

For me this exercise turned out very informative.  This result compares with hearing gearing doesn't matter.   I modeled a stock GSXR 750.  Used dyno data smoothed with Excel trend lines.  A graph type per what I.O. recommended earlier/above tells the story very clearly.  Taller gears shift all lines to the right, shorter to the left.  The top speed can be obtained by selecting the gear with the highest line.  You see that they don't dip much.  If you stay in 6th gear and put in much too tall a gear you will slow down if you don't shift down.  If you have a transmission with not close enough ratios, you might get stuck in one of the dips.  Of course this is a simple model and many other things are in play but still it might be of some interest to see it plotted.  Many here know all this apparently.

Now I need to get back to the project of predicting where on the track this happens.

[Old Scrambler]

Thanks Sparky..............Yes, I was spitin in the wind............until I got out on the salt to test our bench-racing theory.  Now I am reading and listening to learn how to go faster.........but I think another important factor is my small motor versus my 200 pound body!

[SPARKY]

OS   I was agreeing with you  ----I work with torque also 

I will take more tq at a higher rpm I only have to give up a little HP    I say you about had it perfectly geared --all about maximizing TE for the total drag at a given speed. you picked up more drag you went slower

[Old Scrambler]

I am also agreeing with you, Sparky. So far what I get from all of this technical stuff is very good for basic information and interesting for discussion.......but going beyond what we know (already have) and building something for the next text-book is the goal. I can feel a good amount of acceleration when in top gear, but my 201.44cc motor seems to have a built-in rev limiter at 7,200 rpm. 

[SPARKY]

I think that is why the after mkt has black boxes  Also maybe you need to get you a turbo BUSA---they love FAT BOYS  lol