Power Thrust Curves
I'm working on a spread sheet for your $64,000.00 question.
If you could answer a few questions it would help me a lot.
You said you started the 1/4 run at engine idle speed.
What is that engine idle speed?
Do you know the overall gear ratio for each gear of your bike?
Thanks for your help.
Half crazy said: "Thought maybe it would spark a conversation about gearing and RPM...."
An extensive rpm range should mean a lower gear is possible, for any given road speed. Maybe translating what appears to be a less torquey machine into a higher effective rear wheel torque.
There's a good chance such a machine would weigh considerably less, further helping to even out the balance when it comes to rates of acceleration.
Meaning? Never underestimate ANYTHING which happens to pull alongside at the lights and you won't go far wrong.
"Do you know the overall gear ratio for each gear of your bike?"
I have them as
That's half crazy's bike and takes into account the primary and secondary ratios also.
Pittsy posted the overall gear ratios from 1st to 6th.
Thanks pittsy for the ratios.
Do they sound right. Did you modify/change the gear ratio on the belt final drive?
One more question,
In your 1/4 mile runs do you shift into second gear sometime in those first 60 feet?
Maybe somewhere at about 44 MPH?
Based on a first gear overall ratio of 10.85, 6200 engine RPM = 44 MPH.
Jag said: Based on a first gear overall ratio of 10.85, 6200 engine RPM = 44 MPH."
That's one very low geared bike.
I got all the ratios from half crazy's post, I think over on the belt drive thread.
What about rpm/mph in top. Suppose I can just extrapolate from the first gear reading.
153 mph? (that right?)
Sounds very near what I'd expect a genuine 125 bhp naked to achieve. It's not an overdrive any longer me thinks.
Idle is between 1000 and 1100 rpm (it hunts a bit because of the cams).
Primary gearing is 1.50:1
1st = 3.20:1
2nd = 2.19:1
3rd = 1.53:1
4th = 1.24:1
5th = 1:1
6th = .92:1
Final drive is 2.26:1 (actual with the present gearing)
Rear tire diameter is 25.8"
I cannot tell you speed at max RPM in top gear. It doubt it would go that fast.
Half crazy said: "Rear tire diameter is 25.8" "
That checks out perfectly with the theory!
(55% of 180mm x 2 / 25.4)+18 = 25.8.
Shift to 2nd comes well after 60', more like 85'. Like I said, it will do 60-ish MPH in 1st gear. You may be correct on the 44 mph in 60' but the top speed in 1st is higher.
Half crazy, based on your tyre dia, I get the circumference to be 2.05m. That's 0.0021km. At 6200rpm and overall ratio in first of 10.85 your rear wheel does 571rpm. That's 1.2 km/min. That's 72.9 km/hr. That's 43.2 mph. (I think!)
That agrees with jag's figure. At max rpm of 6800rpm it'd be 48mph.
If anything, the rolling circle will be a bit less than that.
Maybe my overall ratios are wrong? Something doesn't tally and it could very easily be my head!
I'll spin it to 6200 rpm in 1st tonight and let you know...
Half crazy said: "I'll spin it to 6200 rpm in 1st tonight and let you know..."
While you're out there, may as well whip her up to 6200 rpm in top as well. Should be 153 mph. : D
All in the name of science occifer.
Thanks pittsy and half_crazy for your inputs.
With a wheel diameter of 28.5 inches and a first gear ratio of 10.85 I get 47.4 MPH at 6700 RPM.
Half_crazy indicated he hits about 50 MPH at the end of the first 60 feet. Based on our calculations so far, this seems very reasonable.
So it seems reasonable that half_crazy could stay in first gear in those first 60 feet.
I have tried to factored in variables in the spread sheet so we can see the theoretical effects of weight changes, gearing changes and shift point changes.
It probably seems obvious to half_crazy but the goal of a successful 1/4 mile drag is not attaining the highest possible terminal road speed at the end of the 1/4 mile. It is to do it in the shortest possible time.
So the goal of the first 60 feet is to cover that distance as quickly as possible (shortest time), but just as important, to attain the highest possible road speed at the end of that first 60 feet.
It's not the fastest that wins the drag, but the one with the shortest time.
Finally, I am wondering, and I could be very wrong, but if one has a lot more linear thrust available in first gear than one can possibly use, is this not a waste? Maybe with less potential maximum linear thrust available under 50 MPH in first gear, you could then use first gear to say 60 + MPH.
Alright... 6200-ish rpm in 1st gear is an indicated 52 MPH on the speedo. Being that the gearing was changed and the speedo is approx 7% "happy", so that's an actual 48-ish MPH.
I will add: it is very difficult to watch the tach and the speedo needles at the same time.
It appears I was wrong about the speed/gear thing. I could have sworn it would go faster in 1st gear than that.
Rear tire is actually 25.84" Making the circumference 81.14" if that changes anything.
It's not the fastest that wins the drag, but the one with the shortest time.
Here, you'll love this. I raced my friend in the final. I have him by 10 or more HP so I know I can run him down and win, so I figured I'd take my time, being sure not to red-light, and use the motor to power past him. I was WRONG. I ran 11.68 and he ran 11.97... AND HE BEAT ME to the finish line by 21 thousandths of a second. I was just a bit overconfident.
Yes, but once you shift 2nd, that same thrust is no longer a waste... or in 3rd... etc.
I plugged in your tyre diameter of 25.84 inches.
I used 25.795 inches
At 25.84 inch diameter wheel I get 47.47 MPH at 6700 RPM.
At 6200 RPM I get 44 MPH.
Not big difference but every little bit helps.
It was interesting trying to somehow factor in your clutch during your start.
I estimated about 1/3 of a second to fully engage the clutch. At an idle speed of 1000 RPM it would take an estimated 11 feet and you would reach about 7 MPH.
If you could actually use all the thrust available in that first 2/100 ths of a second you would be at about 3 Gs.
Only 49 more feet to go.
Jag said: " but if one has a lot more linear thrust available in first gear than one can possibly use, is this not a waste? Maybe with less potential maximum linear thrust available under 50 MPH in first gear, you could then use first gear to say 60 + MPH"
You would have to say yes. I can't help thinking that this bike is a bit under geared. Raising the gearing would lower the enormous first gear torque (and therefore thrust) and raise the road speed attainable in first gear. We all seem to agree that what happens in first gear is vital to the final ET. It would make the top gear more of an overdrive again.
Half crazy said: "Rear tire is actually 25.84" Making the circumference 81.14" if that changes anything"
The rolling circle (which is not the tyre outside diameter) is almost impossible to measure. We're near enough already I reckon. With your recent test run and allowing for speedo error, everything is clicking into place, with three of us ending up with the same answer. That's encouraging! Hope you enjoyed your run out.
Half crazy said: "Yes, but once you shift 2nd, that same thrust is no longer a waste... or in 3rd... etc."
That's because it's not the same thrust. With each click of the gear lever less maximum torque is available. You take the max engine torque and multiply it by all the overall ratio to the rear wheel. As higher gear ratios are actually numerically "lower" there is less torque at the rear rear wheel.
Like I commented much higher up this same thread, it is cruel of science to make it that the faster we go the less torque we have, which is when we most need it. And when are going very slow we have too much. It's that damned torque/power thang again.
I hated the OEM gearing. Launching it when it had longer legs was even more difficult. We have to remember that this is a daily ridden bike... with the OEM gearing it was 15 mph or nothing and getting stuck in traffic was a horrible experience, as you would never get the clutch out.
If the goal was best ET, the engine and chassis would have been set up for that. The bike is set up to be my do-it-all bike and that definitely shows at the track. Better that, than having to ride a race bike on a 4 day trip to the mountains.
That's because it's not the same thrust. With each click of the gear lever less maximum torque is available.[/quote]
I realize that, it was a figure of speach.
When we consider the speedometer and tach accuracy (or lack thereof), we're pretty close.
That would probably hurt this old man. JAG, thank you again for your efforts on this. It has been interesting. I learned so much here.
We need to talk Kevin into some 1/4 mile testing of the bikes he reviews. Seeing the ET and 60' numbers would be a nice tool for comparison. Reviewers often list 0-60 mph, 0-100 mph, and 1/4 mile ET, but never 60' time.
"I hated the OEM gearing. Launching it when it had longer legs was even more difficult. We have to remember that this is a daily ridden bike... with the OEM gearing it was 15 mph or nothing and getting stuck in traffic was a horrible experience, as you would never get the clutch out.
If the goal was best ET, the engine and chassis would have been set up for that. The bike is set up to be my do-it-all bike and that definitely shows at the track. Better that, than having to ride a race bike on a 4 day trip to the mountains."
That's a very good point you have made. As I am sure many would agree, there are a lot more important things about biking then who might or could be quicker through an intersection.
We are just playing with numbers on a screen. Maybe with a little luck, learn something.
Yes, a purpose-built drag bike would be a crappy daily driver. Too many compromises for the track at the cost of practicality. Going to the track is maybe a once a year event at most for me. Right now, this is my only motorcycle, so practicality is far more important.
That's what we're here for, right? Interesting discussion with our peers? Many things discussed here and on the belt drive thread were things I had never given any thought to previously.
Half crazy said: "If the goal was best ET, the engine and chassis would have been set up for that. The bike is set up to be my do-it-all bike"
My comment was clumsy. I retract it. I realised afterwards that this is your daily bike. More than that it is pretty special as it is. I can see that from the torque/power curves and gear ratios. To change it would probably ruin that "uniqueness" it has.
Not sure how unique it is, but it works well for me and what I do on a motorcycle. The offspring resulting from Ducati's Diavel raping Harley's Road King. Could be seen as the ultimate compromise between the two, or as an abomination... depends on your perspective.
The Ducati diavel.
An intriguing machine. If my memory serves, it was introduced as kind of a rival to the v max? If not a rival, then at least an alternative. Yet the thing "only" makes 80ft ib's. A BMW GS will pretty much do that. So what is the secret? The GS is described as a slug by some people on this very site. At least the GS gets a mention. Talk about the r1200r and you'll get tumbleweed blowing gently around. Yet in outright max engine torque terms they match the diavel. That one statistic alone must be very misleading.
The R1200R is such a 'standard' bike. I like that too. I test rode all the BMWs and they are really nice bikes, but they don't make me giggle like a schoolgirl. I think the Diavel would make me giggle. The V-Max is too heavy and gawdy like oversized costume jewelry.
One of these days I'll get something along those lines from the used bike market for cheap thrills.
Here's something I can't explain...
In 1st gear it will hold traction and wheelie. Up and over if you're not careful.
In 2nd gear, take it to 2800 rpm, give it the old on-off-on with the throttle and time it perfectly... front wheel lifts a few inches and then the tire spins.
It seems like traction would be more of an issue in 1st, but that's not the case. Doesn't make sense to me at all.
JAG? Any input?
Half_crazy's $64,000.00 answer:
If I got the calculations right these are my preliminary findings.
0 - 60 ft
Theoretical best time 1.60 seconds
Speed reached at the end of the 60 feet works out to about 43 MPH.
Half_crazy's theoretical first 60 feet
Half crazy said: "It seems like traction would be more of an issue in 1st, but that's not the case. Doesn't make sense to me at all."
Doesn't appear to make sense, so let's try to eliminate the easy explanations first.
For the comparison from first gear to second gear to be accurate you would have to be applying full throttle at max torque revs in both gears. Is that the case?
Are you dropping the clutch during the second gear wheelie?
Is body position identical in both cases?
What causes the huge initial spike in the curve?
Max torque comes at 4300 rpm. I'm talking about 2800 rpm.
Same technique in either case. No touching the clutch.
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