What's the saying - HP sells bikes, TRQ wins races.. Its difficult to understand how a lesser hp engine can easily win a race with a larger hp engine, but when you do understand how that can happen, you've gained knowledge that few have.

P.S. it's all in the TRQ curves..

 

What matters is where the rubber meets the road. The amount of thrust force generated at the tire contact patch, which depends on engine torque and overall gear ratio, determines the acceleration of bike and rider. If I was bored and motivated an interesting exercise would be to build a spreadsheet where I enter transmission gear ratios, sprockets, tire radius, etc. to get the overall ratio. Combined with a torque curve expressed as a piecewise equation and picking some other variables such as shift rpm and rider weight I could estimate thrust, acceleration, time to speed, etc. Could be useful to understand the effect of changes in those input variables. Like, what will be the change in my 0-60mph time if I drop one tooth on my CS sprocket. Or compare a bike's performance with different torque curves leaving all other variables constant. My feeling is that the greater integral/avg. torque over the useful rpm range is superior to one with a higher peak but less integral/avg. assuming the same rpm range is considered. What most folks probably get hung up on is peak HP but TQ-gearing is really where it is at and that is more difficult to understand or quantify without doing a little math or testing. To me using HP as an energy method of analysis is more suited for top speed with air resistance or elevation change. Guess I am done thinking out loud. Off to the garage. I have a new mosfet R/R for my KLX and troubles on my Magna to sort out.



Merry Christmas to all!

 

I've already built a spreadsheet in Excel to calculate speed at given rpm with given sprocket size and tire diameter. I used it to see what would happen with different tire sizes when contemplating doing both supermoto and dual sport wheel sets for my 650. All the variables are there, plus it was done for a six speed as well. I have it with the 2009 KLX250S ratios.

Not a problem to send it out as an attachment to an email if you want a copy.

Fairly easy to work with in that the variable cells are labeled and the calculation cells are right.

I had done a number of spreadsheets in similar style for inspection processes to measure countersinks to allow for the several different sizes of blades we used in a machine tool inspection process using gauge ball bearings.

It's kind of fun to develop spreadsheets with the math, kind of why I did it for the bike stuff. Used it on the 650 for the tires, on the 250 to figure some sprocket combinations to use larger sprockets rather than drop to small CS sprockets all the time, and used it for an XR650L for one rider.

Feel free to PM me or, if possible, simply email me. Not a problem to share it.

 

This sounds very similar to gearing commander's page. I am less interested in speed vs. RPM than I am interested in acceleration/velocity estimations based on torque vs RPM tabulated data. I could play with a graphical torque curve but what I would prefer is the table of data logged by the dynamometer. Now if anyone could get me one of those in excel format(MS access unskilled) I might have some geeky engineer fun.

 

With a dyno run just make a list of the torque/rpms and then use that to reference from the rpm/gearing data, use the mass of the bike & you and you have the instantaneous acceloration data. It is just so simple!

 

I offer the sheet because it already has the gearing rpm relationship formulas present. From there you would need to do the work to set up formulas to perform various power to rpm and gear relationships. Just saves time dealing with the preliminaries was all.

Thing you would need to add are the specific values for torque at given rpm, which would require dyno work to attain said values.

The thing is my calculator is actually an editable Excel file that, provided one has the skills and the formulas needed for the calculating cells, can be added to for whatever purpose one wants. That on-line convertor does not give you that capability since you do not have a spreadsheet in hand.

 

Wow, Snappster's got it to go.. I can send you a "ton" of my and Houstons4's dyno run data files. They are ".DRF"s and open with the DynoJet WinPeP 7 software - and it is free to download and use...

I haven't tried to look at these files with wordpad, etc etc, so I don't know what's in them... Has to be RPM's with matching TRQ numbers doesn't it?

 

If the data is formatted in a suitable fashion it may be able to be cut and pasted into Excel maintaining the column/row format, otherwise it would be hand enter time.

 

Put the files in drop-box or google docs and send me a link. I managed to graphically lift the rpm vs TQ data from one of klxster's dyno chart images using autocad. It was slightly tedious but the data was usable, except I only used data at each 100rpm to make the whole process tolerable. I have managed to analyze rear wheel thrust with the data for each gear and approximate coefficients of aero drag, wheel rolling resistance, and frontal area such that the calculated top speed was reasonably close to the speed I get on my bike: 83 mph on flat road zero wind. While the numbers may be "right" or "wrong", the effort will give insight as to the effect that changing one of the variables will have on bike performance. Now that I have gotten down to a table of mph vs. net external forces I should be able to calculate acceleration for each gear. If I integrate the regression fit of the acceleration curve calculated from the net force data I should be able to get a velocity curve. Then if we set the shift point around to RPM acceleration drops off we should get the approximate best acceleration of the bike/rider combo rowing through the gear box. One problem may be in switching from a rpm domain function to a time domain function. I have yet to think on it. Too much fun.

 

Holy Crap, seems you can quantify the rider experience - given a set of performance mods and the attending data !!!!

I'll get some "Dyno data files" setup for your perusal at my earliest convenience..