| Author | Message | ||
     Davegess |
150 mph with 100 hp is good. Where did it do that? Bonneville take 5 to 10% more power to reach these speeds because of altitude and tire slip. What was the HP on that first Team Elves bike? It did 161 mph on gas and I don't think it was very much over 100 hp. | ||
| Buellnick |
That photo angle of the K1 reaffirms that the K1 is kind of ugly and good-looking at the same time...in a German kind of way... Not sure where the Germans ran the K1 for tests...but in those days, most autobahn stretches had no speed limits. Where do they run the K bikes these days? Of course, any comparison would have to be apples to apples. The Cd is published for BMW K1. The general math exercise above put the K1 figure in the ballpark. Would be interesting for EB or somebody in the Buell brain trust to weigh-in on this and shed some light on drag coefficients of Buell bikes... Maybe this is one of those mystery numbers that HD corporate doesn't want to publish... | ||
| Anonymous |
The K1 did not have a CD of 0.34, it had a CdA of 0.34 square meters. Good numbers back then, but not as good as a Buell RR-1000. Cd and CdA make a big difference. If the BMW actually had a Cd of 0.34 it would have gone about 220 MPH because the A is so small on motorcycles. BTW, the 1125R went almost 170 mph at Daytona with 116 RWHP, so that should give you an idea on the CdA. It's no XBRR, but it's really good for a partially faired bike. | ||
| Steve_a |
I googled the K1, and there are plenty of claims in road tests that it had a CD of 0.34 -- just as there are claims in road tests that a recent Aprilia had a CD of 0.31. In the case of the Aprilia, it was easy to find a reference that made it clear Aprilia was talking about a CDA in meters squared, not a CD. Most motorcycle journalists don't really understand the difference, and reported the number as a CD. As anon said, if the K1 actually had a CD of 0.34, it would have gone a lot faster. It's interesting to go look back on the well documented study of the Can-Am 125 Bonneville bikes from 1973-74, which involved extensive wind tunnel testing. Once you see what they had to do to achieve a .3 CD, you'll be a little more suspicious of the road test claims for the K1. As for aerodynamics, Buell generally doesn't give out specific data on its bikes, and the number that gets our attention is CDA, because both the frontal area and drag coeffient are equally important in determining aerodynamic performance. One data point however: the CDA for the XBRR was under 0.27 meters squared. (Message edited by steve_a on December 21, 2007) | ||
| Buellnick |
So, any idea what the numbers are for the old RR, XBRR, and the 1125r? 170MPH is outstanding for an unfaired bike. I wonder what a better tail section would do while keeping the bike half-faired up front... Hmmm Since this thread started as FULL FAIRING discussion... I'm curious, were there any FULL FAIRING tests done with the 1125r - lets say an 1125r with XBRR bodywork?? related question... RWHP on XBRR? Top Speed on XBRR? | ||
| Gregtonn |
When approaching peak speed, limited by aerodynamic drag, weight (mass) is not a factor. Not sure why you added the last part but it makes this statement incorrect. Had you said "maintaining peak speed" you might get by with it in an ideal world. Approaching implies acceleration (a change in "speed") which would definitely make mass a factor (see Newtons second law of motion). | ||
| Imonabuss |
No, Gregtonn, I think he is essentially right. Assuming a long straightaway, as is usually required for top speed runs in this range, I'll bet the mass becomes negligeable in the equation. And that is the point. | ||
| Buellnick |
I wonder if the "under .27 Cda" of the XBRR could be approached using the 1125r with an XBRR body work transplant? I guess we'll wait and see what the racing version of the 1125r looks like...some day. BTW: Why is it that Buell doesn't give out specific numbers? Lack of transparency regarding a product is usually not a good thing unless you are protecting proprietary secrets or hiding something. ...reminds of HD not publishing HP figures for their bikes. | ||
| Old_man |
Although the old "dustbin" style fairings are not allowed in racing. I wonder why someone doesn't put them on a road bike? It could really cheat the wind. | ||
| Buellnick |
I think we're in for a big awakening. The next big deal in racing will be aero... I wonder what Buell is doing in that area. An 1125r is already good...with good aero characteristics it will be super... Anybody with photoshop and time... put an XBRR or RR1000 fairing on an 1125r. Lets see the pic... | ||
| Gregtonn |
Imonabuss, Does F=MA mean anything to you? | ||
| Toona |
Would be interesting for EB or somebody in the Buell brain trust to weigh-in on this and shed some light on drag coefficients of Buell bikes... Buellnick, You are "talking" to one of the "Buell brain trust" when posting/responding to Steve_a, maybe you should look at his BadWeB profile and do a little research. | ||
| Jaimec |
Toona, Steve_a's profile is rather sparse... | ||
| Elvis |
F=MA tells you how quickly the bike will get to its terminal velocity (keeping force constant, a more massive bike will have a lower acceleration). But once it reaches its terminal velocity, the force of the engine = the force of wind resistance (and any other friction ). That's why you have a fixed velocity as opposed to any acceleration (either positive or negative) at your top speed, because the two force vectors are matched. At that terminal velocity, the mass isn't a factor. | ||
| Rocketman |
Does this mean fat blokes are as fast as thin blokes? Could have sworn I implied that the other day  Rocket | ||
| Elvis |
Land Speed Racing - Fat bloke will have slightly larger surface area so more friction. Also, fat bloke has higher normal force pushing down and increasing friction on bearings. Subtle, but everything else being equal, I'd say the fat guy might lose one or two miles per hour in LSR. Road Racing - Fat guy takes longer to accelerate, more brakes and distance to slow down, will have to take turns slower because more force will be required to change direction (and force is limited by tires). Weight's a HUGE disadvantage in road-racing (everything else being equal). | ||
| Gregtonn |
Thanks Elvis your first post proved my point (again). | ||
| Elvis |
Thanks Elvis your first post proved my point (again). I guess I'm not sure what your point is. We're talking about terminal velocity here, and therefore mass and acceleration are only factors in terms of how much space and time you have to start and stop. Since Land Speed Records do not record those startng and stopping times and distances and since you are effectively allowed infinite time and distance to start and stop then mass and accelerations are not factors in the value (terminal velocty) being measured and discussed. Do you disagree with that statement (because I think the other posts I've read to which you seem to be taking exception mirror that statement), or are we getting hung up on semantics regarding 9th grade physics that we all understand and agree upon? | ||
| Elvis |
Okay, I just re-read everything, and I think I can straighten all this out. Gregtonn, I think you're getting hung up on the word "approaching". If you look at "approaching" implying the bike at 100 going to 200 then yes, mass is a factor, but when the original post said "When approaching peak speed, limited by aerodynamic drag, weight (mass) is not a factor.", I don't think the intent was to discuss going from 100 to 200, but rather to discuss going that little bit from 199 to 200. At that point, yes, mass is a factor, but a NEGLIGABLE factor, because you're talking about a tiny, tiny acceleration and, therefore, mass is a factor, but much, much, MUCH less of a factor than wind resistance. At that point. When you are approaching (nearly at) terminal velocity 99% of the force of the engine is battling wind resistance and 1% is accelerating. At the true, terminal velocity, (very difficult to reach in the real world) 100% of the engine force is battling friction, because as you approach terminal velocity, you approach zero acceleration. Would we all agree on that? (Message edited by elvis on December 23, 2007) | ||
| Old_man |
You have explained it very clearly. Well done. | ||
| Rocketman |
I just know that a porky fella named Dave Jeffries took the road racing world by storm, until his death. He remains a TT great of all time, and at 6'2" and 200lbs, I know he spent more time accelerating his mass around The Island than he did lording it along at full throttle. Such makes me wonder where the scientist gets beaten by the seemingly not possible. Rocket | ||
| Elvis |
I think that is a true testament to Mr. Jeffries skill. He is overcoming an inherent handicap and therefore must be an exceptional rider. . . . not impossible, but it would make things harder. Note also that the TT is a very diverse race with all kinds of riders and bikes and big swings in times. It hasn't become refined to the point that odd riders and bikes can't compete. The rough edges haven't yet been filed down. Now consider MOTO-GP. How many fatties do you see running there? I doubt Jeremy McWilliams keeps his trim figure just because his wife likes him that way. (Message edited by elvis on December 23, 2007) | ||
| Gregtonn |
Elvis We are in agreement. | ||
| Buellnick |
Full fairings might help bigger riders... | ||
| Blake |
Dave G., "150 mph with 100 hp is good. Where did it do that? Bonneville take 5 to 10% more power to reach these speeds because of altitude and tire slip." The amount of power lost at altitude is offset by the reduced aerodynamic drag, both of course due to reduced air density at altitude. The tire spin does rob additional power. Not sure how much of a factor it is though at 150 mph. Tire spin definitely becomes much more of a factor as speeds climb. Since aerodynamic drag increases proportionally with speed squared, at 200 mph you'd have 78% more drag than at 150 mph. The math is (200/150)2 = 1.78 = 178% Yikes! | ||
| Blake |
Greg, Yes, by "approaching" I meant near to terminal speed. Like Imonabuss stated, it isn't that mass isn't a factor at all, it's that it is negligible. For instance, you could double the mass of a motorcycle and still reach peak speed; it would just take a bit longer is all. Thus in that respect, mass has no effect on what the peak speed capability of a motorcycle is, given that you have adequate tarmac and time to get there. Motorcycle land speed racers who are running near to and over 200 mph have learned that added mass is a major benefit for helping to keep the rear wheel from excessive spinning (more weight on the rear contact patch). | ||
| Court |
>>>>For instance, you could double the mass of a motorcycle and still reach peak speed; it would just take a bit longer is all. Which is why last year . . . while playing in the 210+ MPH range . . . that Aaron had to place considerable parasite weight on the swingarm. There is a point where it becomes easier for additional power to spin the rear wheel rather than provide locomotion. This may or may not have been a factor in the two spectacular crashes (no injuries) at Bonneville last year. | ||
| Rocketman |
I take it you meant 'parasitic', unless of course you're referring to Aaron?  sorry, couldn't let that one pass us by, lol Rocket | ||
| Rocketman |
Yes Elvis, one would have to agree with that, but it still remains rather odd that DJ managed such for his bulk when we take into account the so few seconds ahead that separate DJ's times from others in his races, and the times set in the races that followed when his time was beaten. That is to say, all those riding the TT at the sort of lap times around DJ's fastest lap, are so very close, which suggests there's a parity in skill between each rider, the limiting factor of bike and course must share also a parity, yet DJ was a porker in comparison to all the others. If he were 30lbs lighter I wonder if your explanation, which I'm in agreement with, would have proven DJ even greater than he was. Then again, it might not have done. As they say, "stranger things have happened at sea". Rocket | ||
| Elvis |
It would be interesting to see a real analysis of how a larger and smaller rider actually do things differently. A taller, heavier rider may be able to compensate for the larger mass he has to haul around by gaining some leverage. His larger, more highly place mass may allow him to transition more quickly with an aggressive enough riding style. Back on the subject of the full fairing, I was just playing around in photoshop. Something like this should be possible by cutting up some existing XBRR bodywork:  It's interesting also to note the color scheme of the original XBRR was very close to this (with black upper fairing). Since the 1125R was in development prior to the unveiling of the XBRR, could something like this be close to a bike we may actually see in the future? |
