Shift Points?

[Nate R]

Here's what someone's school suggests:

 


http://forums.13x.com/showthread.php?s=&postid=400024#post400024


Please read through from my first post as sv650nate to at least my post with the graphs.

What do you think? Have you experimented with this at all?

I'm being shot down, with no real reason given. I gave evidence to support my theory. (The graphs)

I don't KNOW which one is right, but I'd LIKE to.

[duc995@aol.com]

I think you need to know where each shift point puts you AFTER the shift.  In other words...if you shift at redline (after peak HP and torque) but it puts you in a better place on the HP/torque curve in the next gear...then it would be right for you.  For example, with my two-stroke the power band may be 9000 rpm to 12000 rpm, with peak hp at 11,000.  If I shift at 11000rpm I land below 9000rpm in the next higher gear and out of the rpm that the pipe is designed for...BAD!  If I push the rpm past 11000 to say 11500 rpm (same HP as 10500 rpm) I will end up in the powerband of the next higher gear and wa la...I am gone!  Probably not as applicable to diesels (four strokes), but worth thinking about! ;D

[Nate R]

I guess that's what I'm trying to say, in a sense. It's about where the RPMs land when you shift.

[EX#996]

Nate:

My $0.02, but then again I'm not on the track....

Personally at this point in your racing endevor, worry less about the RPM's and shift points and work on the braking and cornering speed.  Once you have that down, I believe your shift points that work for you will follow.  

One nice thing about an SV, if you are a gear too low, the bike will be able to tourque you out of the corner.  If you had an in-line four, that would be a different matter.

Paul doesn't even use the tach (is the Daytona and he can't read the numbers anyways), for him it's just by feel.

Dawn  :)

[Super Dave]

This is road racing.  We have corners.  You have to gear the bike so that it gets through the corners the best.  Yes, shifting in the middle of the corner is wrong under many circumstances.  Some places, a few long corners in a few tracks, yes, you'll do it.  

When going in a straight line, yeah, you're gonna run the bike to a point, probably near the red line and bang the gear.  You're at WOT (wide open throttle) and you want to quickly go through the gears.  But this isn't drag racing where we just bang gears.

In road racing, you've got to slow down the bike and turn in places, then, based on lean angle, the corner's radius, etc. you're going to add some throttle that is related to the amount of traction that you have available.  The fastest way around the track is going to be to try use all of the traction available.  If you're not using it all, then you can go faster.  

Generally, a shift mid corner will distrupt the chassis, and, consequently, the traction that is available.   So, that will slow us down.  If you can whack open the throttle an apply 70HP to the ground leaned over, you're not going in fast enough in the corner.  You'd need to lean it over more and go faster, etc.

Sometimes one would short shift the bike because the engine does effect the chassis.  If you've got more spinning power being applied to the rear, you can effect the height of the swingarm pivot which effects the chassis which can effect weight bias, which can effect traction.

So, back to gearing, one needs traction in the corner.  I know of few bikes that will break traction in a straight line.  You're not at WOT leaned over, unless you're not maximizing your traction force for cornering.  

Nate, I what the shifter right near readline.  So, does Paul Buxton and Sete Gibernau.  Admittedly, I have ridden some slow bikes that we did do some tests on to see where we could maximize straight line speed with shifting.  On the MZ Skorpion that I ran in the restricted Skorpion Cup National Series, it made about 42HP.  Redline was set by the manufacturer at about 7600RPM (imagine what happens on a single when the rev limiter comes in).  We found that it was best, but not by much, if I shifted at 6800RPM's indicated on my tach for best straight line speed.  The extra RPM's were just overrev for me.  

Does this help at all?

[tzracer]

This topic is covered in an excellant book by John Bradley called The Racing Motorcycle A technical guide for constructors. One section is devoted to engines and gearboxes. He plots road speed (x- axis) versus driving force for each gear to determine gearbox suitability (such as when a motocross engine is to be used) and shift points. You want to up shift when the curve for one gear falls below that for the next gear. Usually in lower gears there is no overlap - that is the drive force in the lower gear is always higher then that of the next gear - shift at red line. The rpm for shifting can be different for each gear change. Shifting at max power is not the best place to shift. I created a graph using the authors data for a GSXR1100, 112hp at 9750 rpm.

 http://my.execpc.com/~tzracer/rearwheelforce.xls

Gear shifts 1st to 2nd - 10750 rpm
                   2nd to 3rd - 10,500 rpm
                   3rd to 4th - 10,500 rpm
                   4th to 5th - 10,000 rpm

All shifts should be after maximum horsepower if you want maximum acceleration. Interestingly, gear shift points will not change with changes in final gearing, but will change with any changes to internal gearing. After power falls off past peak power, a given gear can still be pushing the bike harder than the next gear can. If you really ant to know the best shift points for your bike, make your own graph for your bike.

Not sure what is meant by "trying to shift at redline loses critical flywheel momentum". The higher the rpm the more flywheel momentum I have. Shifting before redline will have lower flywheel momentum than revving the bike higher and then shifting.

Creating such a graph is not horribly difficult, especially with a spread sheet. You will need a hp graph for your bike, primary drive ratio, internal gear ratios, final drive ratio, radius of rear sprocket, rolling radius of rear tire, and some time. If there is interest I can post the formulas to make life easier.

[Steviebee]

 So, does Paul Buxton and Sete Gibernau.

OMG wheres Paul he's gotta see this !!!
I would just love it one day if im compared to a MOTO GP STAR !!  WTG Paul !!!  hehehehehee

I did some fooling around with this at the drag strip.  and tzracers chart makes a lot of sense.
1 and 2nd gear are so differnt in ratio that u can wind them to the redline.  But 4,5,6th are better left a little less than the redline.  How much depends on your gearing and hp curve.  I've been starting to shift at the  HP peak cause it leaves about 1k rpm for "OOPS" which ocasionally happens.

And Dave's right, theres alot more to be gained on corner speed than acceleration.

[MELK-MAN]

the graph does show the "optimal" shift point just after peak hp. I am no pro but  would agree with that, as others above did as well. Going all the way to redline in every gear will acutally loose time as most (and i mean most) hp graphs i have seen appear very similar to the one you posted. My F4 however is cool... it has no drop off past peak hp..it flattens out at 100hp so if i need to enter a turn without a gear change there is no loss of power, just no gain. Going to redline every time is gonna be kinda hard on motors too i would imagine..

[Dawn]

OMG wheres Paul he's gotta see this !!!
I would just love it one day if im compared to a MOTO GP STAR !!  WTG Paul !!!  hehehehehee

LOL!!!

I already told him.  He got a huge grin on his face.  

Thanks Dave!

Dawn   :)

[tzracer]

Melk-man the graphs I posted were not horsepower, but were drive force at the rear wheel. More force equals more acceleration. Each of the graphs is for a different gear (the black curves), first being the highest and fifth being the lowest. Note that first gear always has more drive force than second gear up to redline. Shifting at redline will give the best acceleration. As long as the gear you are in has more drive force than the next gear, no need to shift until redline or when the curves for 2 gears cross. If you shift too soon, it can put you at quite a low level of drive force.

Note that the large curve on the graph (the reddish curve) is the drive force if the bike produced 112 hp all the time, such as with a continuously variable transmission. Kind of the ideal situation. Notice that as speed increses, drive force decreases.

[MELK-MAN]

Melk-man the graphs I posted were not horsepower, but were drive force at the rear wheel. More force equals more acceleration. Each of the graphs is for a different gear (the black curves), first being the highest and fifth being the lowest. Note that first gear always has more drive force than second gear up to redline. Shifting at redline will give the best acceleration. As long as the gear you are in has more drive force than the next gear, no need to shift until redline or when the curves for 2 gears cross. If you shift too soon, it can put you at quite a low level of drive force.

Note that the large curve on the graph (the reddish curve) is the drive force if the bike produced 112 hp all the time, such as with a continuously variable transmission. Kind of the ideal situation. Notice that as speed increses, drive force decreases.

I only see one graph that says "brake horsepower" with a black line.. it is a typical dyno chart it says, not of a specific bike.. I dont see the chart your talking about..

[MELK-MAN]

ok.. now i see it.. it was a link. WAY to techy for me man.  ;)