$61,915.00 for a 1992 Honda???

Hmmm. I think of acceleration as *being* the transition from slow to fast.
Where's the distinction?

ab

 

yep, that's what I heard. Ride to Skaggs Springs in comfort, then drag
fairings at 120. ST is amazing sport bike

Hell, Ask Larry, he has followed an ST out Pescadero, Larry? Is it
sporty?

 

If you are referring to Andy Burnett's master handling of his ST then yes... he
made the ST looked sporty on Pescadero dragging a knee... but after we traded
bikes it sure didn't feel sporty to me... no sir... it felt more like a
refrigerator full of bowling balls...

Larry L
94 RC45 #2
Have a wheelie NICE day...
Lean & Mean it in every corner of your life...
If it wasn't for us the fast lane would rust...
V4'S are music to the seat of my pants...
1952 De Havilland Chipmunk...
Yank and bank your brains loose...
http://members.ebay.com/aboutme/-xlax-/
http://home.comcast.net/~netters2/
http://www.fox302.com/index.pl?s=vg&user=netters2
http://www.reeky.org/gallery/xlax

 

The human body is almost incapable of sensing speed. That's why you
feel like you're "sitting still" even when you're travelling 500+ MPH
in an airplane.

But, the human body is great at sensing acceleration, which as you
correctly stated, is the change from one speed to another.

Where the problem comes in is that acceleration is purely a function
of torque, whereas horsepower has an element of speed incorporated
into it.

For an engine, the formula for horsepower is:

Horsepower = (torque X RPM)/5252.

So, horsepower is dependent in part on speed (the RPM of the engine).

Even a really "torquey" engine can't make big horsepower numbers until
the RPMs get high. That's why you see diesel trucks with peak
horsepower ratings of only 280HP, but peak torque ratings of 800
ft-lbs. They operate at such low RPMs that even though they're torque
monsters, they never have the chance to make big horsepower numbers.

If you look at the dyno graph for an engine, peak torque always occurs
at a lower RPM than peak horsepower. Since maximum acceleration
coincides with maximum torque, the bike will always "feel" more
powerful at a much lower RPM than where peak horsepower actually
occurs. By the time you reach peak horsepower, the torque (and
acceleration) have already peaked and begun to drop off.

 

Or, do that on an actual sportbike and NOT drag fairings. I liked my ST fine
when I had one, but it would be serious work on a road like Skaggs Springs.

--
Jamin Kortegard
popular sportbike / popular car

"Hokey 600s and trackday usability are no match
for a good literbike at your side, kid."
- Michael

 

i'm sure there are master riders out there who can make anything ride like a
sportbike. for us lesser riders, however, a well tuned suspension, less
frame flex, better tire options, and more ground clearance can help out
quite a bit.


--
-kelly
EuroMotoPoseur Diva
'05 Triumph Speed Triple
'01 Aprilia Falco
'70 Honda CT 70
and some German cars

 

Thanks to a very helpful e-mail from apogee, I realized that I need to
clarify my previous post.

Since the poster I was replying to was talking about rider impressions
versus dyno graphs, and chassis dyno runs are usually done in a single
gear, to simplyfy things, I limited my discussion to the bike's
response within a single gear, not taking into account the effects of
shifting the transmission.

The bike's acceleration is determined by rear-wheel torque, which is
just engine torque multiplied by the gears in the transmission, the
front/rear sprocket combo, and the tire diameter, All of the torque
mulitpliers stay constant for any given gear, so **within any single
gear**, peak acceleration still occurs when the engine is at its peak
torque.

But, if you take into account the fact that torque multiplication
factor changes when you switch gears, in order to achieve maximum
acceleration while shifting gears, you have to decide whether or not
the reduction in torque multiplication when you upshift is offset by
the increased engine torque from the RPMs dropping down closer to the
peak engine torque RPM after the upshift.

The increased engine torque from upshifting is almost never enough to
offset the lower torque multiplication, so if you're going for maximum
acceleration down a 1/4-mile dragstrip while shifting through the
gears, you should choose your shift RPM to keep you near peak engine
horsepower, not peak engine torque. This will keep you in each gear
longer than if you shifted at the engine's peak torque point.

Sorry if there was any confusion.

 

In this case you should ignore both the power and torque peaks. Get a
copy of the thrust curves for your bike, and use the crossover points
to plan your shifts.

http://wahiduddin.net/race/images/thrust1.gif

-- Michael

 

You're certainly correct about the BMW I3 & I4 but they're unique in
at least two aspects:

1) Price is not a concern with BMW's as they're grossly over-priced to
begin with.

2) Both BMW I4 and I3 were/are inferior in terms of volumetric
efficiency when compared to the Japanese and even British I3's.

TW, when oh…when will you learn to look at things outside the box?
I've had singles, V- twins, ridden a shit load of Honda VFR's and ST
V4's owned a bunch of I4 and ridden a bunch of boxers but still think
the I3 is the best motorcycle engine, in terms of cost, low vibration
and wide USABLE torque. What's your own perspective beyond your Beemer
and that baby Honda (CB1) I4?

Also for Brutus, a five-valve engine with a large bore as in a single,
twin or triple does indeed have an advantage in terms of volumetric
efficiency at the higher RPMs. Down low though, they breath poorer
due to lower gas velocity. Compromise… being the name of the game.



Bob Nixon, Chandler AZ
01 Sprint ST "RED" 45K miles

 

I think the rear-wheel thrust (pounds) in that chart is just
rear-wheel torque in foot-pounds divided by tire radius in feet. So,
you're still trying to keep rear-wheel torque maximized over time by
deciding when the loss in torque multiplication from the upshift
becomes "worth it".

That thrust chart makes it much easier to "see", though, by
referencing it to bike speed rather than engine RPM. For the
particular chart you posted, a quick glance is all you need to know
that you should shift at about 31 MPH, 55 MPH, 78 MPH, and 103 MPH.

What I'd be interested to know is where those shift points put the
engine RPM relative to the horsepower and torque peaks. I'd venture
to guess that the shifts occur at slightly about peak horsepower in
each case.

 

Kelly, I've ridden at least half dozen VFR's and two ST-1100 V4's and
the only thing I can say is they pull like an I4 or something your new
triple or a twin does not.

Maybe your opinion of the V4 is based on VFR's having 788cc instead of
600cc. To me they fell like a big 600, still having to downshift a lot
to pass and such. I do like V4's as they don't buzz like the I4's and
have a unique sound but I'll take the Triumph triples and recall I had
a GSXR1000K3 for about 6 month until the deer took it and me out. It
was smooth running at or below 7K RPM but buzzed just like any I4 up
at 8-12K RPM.


Bob Nixon, Chandler AZ
01 Sprint ST "RED" 45K miles

 

^^^^^^^^

IMO the SV-650 engine is in a world of it's own, Denise. I've ridden
748,9 Ducs but the SV engine is just better set up all around. The SV
engine will go down in history as one of the finest MC engines
designs, bar none! My point is that it's such a unique case of being
the best of all worlds. Plus those EX500s are 150cc less.

VFR's are just a 750 (7888now) in a world of hot rod 600's; with weak
bottom end torque. So yes they do feel stonger off the bottom but only
when compared to the current 600's. Ride a newer 03-05 GSXR-1000 or
even a 955-1050 triple. Also the big twins (RC-51, Duc's & TL-R) are
stump pullers down low but loose some steam up top.

Bob Nixon, Chandler AZ
01 Sprint ST "RED" 45K miles

 

Minor point: for acceleration, maximal thrust - not rear wheel
torque - is the goal. Yes, they are directly related. But
you are ultimately trying to maximize the force at the contact
patch.

Depends on gearing. Which is why you want to use the thrust curves.
For example, using the chart above, in 1st you would want to
basically run to redline, while in the other gears you would not.

-- Michael

 

Granted, for sure. I just couldn't think of another current production
bike that's an I-2! OK, an EX250, but that compares even less.

I love my SV, even now that it's 5 years old. My fiance rides it to
work all the time and keeps making noise about wanting to put hard bags
on it to make it a "better" commuter bike. I keep retorting that it's
time for him to go buy his own bike!

 

Since the thrust at the rear wheel is directly proportional to the
rear-wheel torque, I tend to think of everything in terms of torque.
The results are the same either way, although you're correct that it's
the thrust that actually moves the bike forward.

I guess it wouldn't be hard to write a spreadsheet to do the same
thing, given an accurate torque curve and the gear ratios for the
transmission. It all boils down to "will I have more torque (and
therefore thrust) at the rear wheel if I stay in the same gear for
another 50 RPM, or if I upshift?" The thrust curves you posted are
the most direct visual representation of the answer to that question.

 

Jesus.

Charlie O'Hanlon sold me a nice '76 750 F for $1500. I think I'll
stick w/ that.

 

On Sat, 23 Jul 2005 17:56:11 GMT, Timberwoof

[...]

Weath is hardly a factor. More like AGE! I'm 60 and have been riding
for over 30 years and have lots of friends who let me ride thier
bikes. Plus I've always had a passion for all engines, Jet's, Rockets,
CI or SI pulsed engines-( that's piston and wankel to you-

How's that for flaunting?

[...]



Bob Nixon, Chandler AZ
01 Sprint ST "RED" 50K miles

 

damn,Holly's right, you ARE getting old and senile.



Me & you & Bad Matt & Holly, some damn T-Shirt ride thing, and I chased
your butt.

 

No, Larry's right--I've seen Andy drag knee on his ST!

 

:

No, Larry has been on a ride with ME where i knee dragged on MY ST

and chased Larry out Pescadero



Andy is merely my inspiration