| Author | Message | ||
     Bud |
I never got my bike over the 135 mark But I’m the restricting factor ( 200 ponds & build like a brick ) And I really don’t think that the gearing is different on US or Yurop xb9’s Btw, hose getting 7800 rpm out off a 9, I think most off theme cut it short @ 7350-7400 rpm and thanxs for the price Spike, Now I have to consider it as well, if I make up my mind & sell a kidney for my up coming XB12Rss project ( short stoke ) almost the same price as a new engine ?? ( with labor for the bigbore & 49mm throttle & exhaust that is) | ||
| Spike |
I think there are a few communication errors here. It sounds like some are confusing quick revving with high revving. It's clear that the 9 can rev higher with it's 7400rpm redline vs the 12's 6800rpm redline. Quick revving is a different story. When I think of quick revving I imagine the bike being in neutral or with the clutch pulled in. I haven't ridden a 12 yet but I'm willing to bet the 9 will rev quicker when there's no load on the motor due to it's lighter reciprocating mass. If we're talking about quicker revving while in gear under load we're simply talking about quicker acceleration. There's too many factors to guess this one. You'd just have to line the bikes up and see what happens. My money says that the 12's power advantage is enough to overcome any gearing differences. The top speed is a little confusing. It should be a matter of power vs. aerodynamic drag and since they have the same aerodynamics the 12's power advantage should put it on top. It would seem like the 12's taller primary drive ratio would give it longer legs but as stated in the Don Canet quote above, the lower rev limit seems to cut things short at ~140mph indicated. I guess it's possible that a properly geared 9 could have a higher top speed but I haven't heard of anyone indicating any more than 130mph on one. For the record, I like the colors of the 12 models.  Mike L. Ray Price HD/Buell '99 M2 Cyclone (sold) '04 XB12R Firebolt (coming soon) '94 FMII Turbo Miata (daily/track toy) | ||
| Darthane |
Bud, My XB9R will run right up to 7800...if I'm really pounding it and I hit the limiter it bounces upwards of 8100. Not that I normally run it that high, but... Bryan | ||
| Stot |
Hi Bud, Youre absolutely right it was my arse talking about the gearing. Trojan do XB9 gearing sets and I had presumed US/UK had different gearing as with the other Buell models. However, weighing in at a whopping 170lbs in full race gear, I still think I can get 140 on mine  Cheers Stot | ||
| Gonen60 |
2 recent XB12 reviews, both say the 9 will edge out on top speed, due to the 12s Rev Limiter. Does the XB9 have the same sort of rev limiter as the 12? gotta love the "Black and Silver"    | ||
| Misato |
yeah, I'm 6'2" 215lbs. I'm gonna have to start the crack diet to increase my speed | ||
| Aaron |
"I haven't ridden a 12 yet but I'm willing to bet the 9 will rev quicker when there's no load on the motor due to it's lighter reciprocating mass. " I'm not following your logic here ... you're saying that the 12 will out-accelerate the 9, but the motor 12's motor won't out-accelerate the 9's motor? I don't see how that could be. The mass of the heavier 12's flywheel (assuming it actually is heavier) is there regardless of whether the bike is in neutral or in gear. If the 12's motor didn't produce enough more torque to offset it's heavier flywheel, what would be the point in making the 12? | ||
| Jprovo |
I'm willing to bet the 9 will rev quicker when there's no load on the motor due to it's lighter reciprocating mass Spike, How you figure that the 9 has lower recip mass? it has longer rods then the 12, and domed pistons instead of flat top on the 12. James | ||
| Blake |
Same weight, similar gearing, more HP wins every time. Assuming both bikes can hit the rev limiter in high gear, peak speed due to rev limit is governed only by overall drive ratio and rev limit. It has nothing to do with acceleration. An XB12 has significantly more power. It will be quicker in any kind of road or drag race. The question is not even debatable. | ||
| Gonen60 |
Misato...No Future as a Jockey for You Man...  | ||
| Misato |
 I need to get down to 185 | ||
| Tedk |
The XB9 will hit 135mph(approx.) before rev limiter cuts it short. XB12 is faster by about 1 second in the 1/4. 74rwhp vs 92rwhp it's pretty obvious. XB9 has a higher top end... | ||
| Steve_a |
Same weight, similar gearing, more HP wins every time. Assuming both bikes can hit the rev limiter in high gear, peak speed due to rev limit is governed only by overall drive ratio and rev limit. It has nothing to do with acceleration. An XB12 has significantly more power. It will be quicker in any kind of road or drag race. We're talking about several mutually independent performance items here. First, there's top speed. In the case of either XB9 or XB12, under ideal conditions with a well tucked in rider, it's determined by the rev limit and stock gearing. In other words, both XBs are gearing, not power, limited. The only difference in gearing between the two is the primary ratio, 1.5:1 on the 12 and 1.66 to one on the 9. Assuming the rev limiter kicks in at 6800 on the 12 and 7800 on the 9, that means the combination of gearing ratios and redline ratios will mean the 12 will have about a 3 percent lower top speed than the 9 -- but it will get to that speed more quickly. If the rev limiters kick in at 6800 and 7500, they'll have just about the same top speed. (I'm not sure of those numbers, particularly for the 9; my notes indicate the 9 has a 7500 rpm redline, but don't say where the ECU logic kills the fun, and they say that the 12 has a soft skip starting anywhere from 6400 to 6800 after 3 seconds, and a hard skip after 5 seconds; I assume a hard skip or a complete shutdown occurs above 6800, but it may be 6900.) Second, there's acceleration. As Blake indicates, the 12 has a greater power and torque difference than the gearing difference, so it will out accelerate the 9. I have computer simulations that show that using Quarter-Pro, a dragstrip simulation program that I model many motorcycles on, and that is amazingly accurate if fed the right data. We'll be seeing real world numbers very shortly, but it will shock me if the 12 isn't at least 1/2 a second quicker in the quarter, particularly considering CW's original, seemingly slow number for the 9. Finally, there's how quickly the engine revs with the clutch in, the rider blipping the throttle. It's quite possible that the 12 revs more slowly here. If the flywheel inertia increased by a greater percentage than the torque increased at any given rpm, the force to crank inertia ratio is worse for the 12, and it would rev more slowly out of gear. I'm not saying that is the case, as I haven't ridden the two back-to-back, but it's at least possible. The 12 would still be quicker in overall acceleration, because there the engine has to accelerate both the flywheel and the vehicle and rider mass, and the last two dominate, even when you get flywheel up to Evo Big Twin levels. Engine revviness is a mixed blessing; it's easier to blip the throttle on a quick revver for a downshift, and shifting in general is usually easier. But quick revvers also break traction more abruptly at the limit. That said, I'd love to see Aaron try chopping a bunch of weight off a 12 flywheel and see how the bike responds afterward. | ||
| Aaron |
I don't see it, Steve. You have two motors, both with minimal load on them. Motor A can rev up quicker in this situation than motor B. Now you're trying to tell me that you add equal load to both motors (bike and rider) and all of a sudden motor B can rev up more quickly? Huh? F=ma ... it's a linear relationship. Increase the mass that has to be accelerated and keep the force the same and the acceleration rate goes down proportionally. Why would the acceleration rate go down more quickly for the 9 than the 12 when equal load is added to each? edited by aaron on September 02, 2003 | ||
| Bud |
There’s one way off cutting this discussion short !! Lady’s and gentleman….. let’s race ( dragstrip or track ? ) 10 bucks on the 12 to win’s gr,m | ||
| Elvis |
Aaron, the key is you don't have minimal load. The different gearing allows the larger engine to push harder while spinning slower. Given the same gearing, you are absolutely correct. The more powerful engine will spin faster and the rear wheel will spin faster. With different gearing, the bigger engine can push harder while spinning slower (but the rear wheel will be spinning quicker). I haven't worked the numbers, so I can't say for sure, but in theory Steve can certainly be correct. | ||
| Glitch |
I'm so confused. I thought ya made engines bigger to go faster more quickly. Why would Buell (or anyone else) make a bigger engine that's slower? More power = less speed? Could someone please spell this out for me, I'm just not getting it. But, from what I think I understand so far, I have to side with Aaron.  I do know that I'm happy with my bike though... | ||
| Elvis |
Imagine two guys on 10 speed bikes. Both about the same weight, but one a lot stronger. The stronger one puts it in the highest gear (largest sprocket on front, smallest sprocket on rear). The other guy puts it in the lowest gear (smallest sprocket on front, largest on rear). When they go, the stronger guy will have more power, he'll push harder, but his feet will be going around slower. He'll go faster than the other guy even though his feet are spinning slower. | ||
| Steve_a |
Aaron, the revviness comparison is for the no-load condition only, clutch lever pulled in. A classic example would be an early eighties KTM enduro and MX bike -- the main difference between the two being the heavy flywheel on the enduro model. Engine tune used to be identical. The enduro would rev far slower when you were zinging it, and the bike would feel much heavier to ride because it was harder to break traction and kick the back end around. But acceleration, with the bikes in gear under load, wouldn't be much different. Flywheel mass changes how a bike feels, and how quickly it revs when the tire breaks away, but has only a marginal effect on acceleration. Going from a Japanese Four level of flywheel -- very, very little -- to an Evo Big Twin level (so much flywheel the engine doesn't really blip when you give the throttle a click snap in neutral) costs only about 0.25 second in the quarter. That's a lot on a racetrack, but not much subjectively. (BTW, my simulations show that going from the Buell level of flywheel to Suzuki TL-R level might be good for 0.05 to 0.10 seconds in a quarter -- but it would be harder to launch.) I'm not disagreeing with you; I'm saying something different -- that "revviness" in terms of subjective feel is something you generally get when the clutch is pulled in, not when the bike is in gear and the clutch engaged. And that's entirely proportional to the ratio between engine torque and rotary inertia (flywheel), as in, Torque = Rotary Acceleration * Iz, the exact analogue to F=ma for a rotary system. One more thought experiment. Imagine chopping an XB9 flywheel down to nothing. The motor would pick up revs almost instantly when you blipped the throttle with the clutch in. But it would still not out accelerate a stock XB12 in a straight line. | ||
| Gonen60 |
Bud, Your Right. I don't think either bike has a massive advantage, so I think it's anyones race. especially on a road course. Look at the AMA "SuperStock" class...Some of those Pesky 600s whipping up on the bigger 750s. | ||
| Glitch |
Thanks Elvis! Sometimes I just need over simplification... | ||
| Aaron |
"Aaron, the key is you don't have minimal load." You're telling me that in neutral (or with the clutch pulled in), that's not a minimal load situation for the motor? "The different gearing allows the larger engine to push harder while spinning slower. " The torque output of the motor doesn't change with gearing. Unless you have a turbo diesel or something, that varies it's boost with load. But anyway, that's not what I was questioning. This was about acceleration rates of the two motors, loaded versus unloaded. "Given the same gearing, you are absolutely correct. The more powerful engine will spin faster and the rear wheel will spin faster." Well, I never said that, and what's more, it's not true. Assuming it's got the power to overcome it's load, the motor with the higher rev limit will spin faster and the faster rear wheel will be a function of the motor rpm and the gearing that sits between them. But again, I was questioning Steve's assertions about loaded versus unloaded acceleration rates and how the winner changes between them, not speeds. "With different gearing, the bigger engine can push harder while spinning slower (but the rear wheel will be spinning quicker)." Again, the bigger motor pushes harder regardless of the gearing that sits downstream from it. Gearing just transforms the torque/rpm makeup of the motor into some other torque/rpm makeup. Which is why the product of the torque & rpm (aka power) is the relevant metric for performance. Back on subject ... Steve's assertion is that perhaps the 9's motor accelerates faster in a minimal load situation. Basically what he's saying is that yes, the motor's torque is lower, but it's possible that the flywheel mass is so much lower that the acceleration ends up being greater anyway. What I'm having a hard time conceptualizing is how that could be true, and yet when roughly equal loads are applied to each motor (actually less is applied to the 9 due to it's gearing advantage), all of a sudden the 12 has the higher acceleration rate. It seems to me like if the additional torque of the 12 isn't enough to overcome it's presumed heavier flywheels (and we don't know if they really are) and result in a greater unloaded acceleration rate, what would be the point in doing the 12? And, it seems like the additional load should affect the two acceleration rates equally. But maybe not as a percentage, which is what his "dominates" statement is all about. I'm still chewing on all this. I took a lot of Physics but it's been a few years, my abilities to conceptualize aren't what they used to be. | ||
| Aaron |
Steve, you just hit the key to conceptualizing this, thank you. A zero-mass flywheel would result in infinite acceleration in the unloaded situation, even with .1 ft-lbs of torque. But with load applied, the acceleration rate would plummet. Makes sense. It's a percentage thing. | ||
| Elvis |
The torque output of the motor doesn't change with gearing. Did I say it did? I said a larger engine would produce more torque at a lower RPM. "Given the same gearing, you are absolutely correct. The more powerful engine will spin faster and the rear wheel will spin faster." Despite your convolution, this statement is absolutely true. Everything else being the same, a more powerful engine will spin faster and the rear wheel will spin faster other wise it wouldn't be more powerful, would it? Again, the bigger motor pushes harder regardless of the gearing that sits downstream from it. Gearing just transforms the torque/rpm makeup of the motor into some other torque/rpm makeup. Which is why the product of the torque & rpm (aka power) is the relevant metric for performance. I never claimed otherwise. I simply stated that it was, in fact, pushing harder. I'm sorry if I misinterpreted your statements, but nothing I said wasn't true. | ||
| Mikej |
"A zero-mass flywheel would result in infinite acceleration in the unloaded situation" Connecting rods, pistons, rings, all have mass and affect acceleration rates. Cylinder fill and mix ratio and ignition aspects also affects acceleration rates. If you put a piston in a cylinder/head assembly on a bench with compressed combustable gas and ignite it then how fast will the piston be traveling when it exits the cylinder without connecting rods or a flywheel to contend with? | ||
| Shazam |
edited by shazam on September 03, 2003 | ||
| Mikej |
 edited by mikej on September 03, 2003 | ||
| Aaron |
Mike, it was a extreme example to illustrate a concept, don't take it literally. "Everything else being the same, a more powerful engine will spin faster and the rear wheel will spin faster other wise it wouldn't be more powerful, would it?" Well, the 12 doesn't spin as fast as the 9, and yet it has more power, right? Power is the combination of rpm and torque. How fast it's spinning is only half the equation. | ||
| Turnagain |
9_ 12_ | ||
| Buckinfubba |
Wow all this technical speak has me feeling like sophomore algebra class and physics and study hall rolled into one. My head hurts but I ain't that smart anyway. But I know something from a little birdie....yes on a dragstrip the 12 is faster than the nine. By how much I am not aloud to speak. Big question here is on the street ....does the difference matter much. I don't know it comes down to the rider in the seat. But second....who gives a big wailin yahoo. Very few of us here are professional riders and very few are racers. Those that are ...get the 12 its a no brainer. I've ridden both and I like the 9 better for where I ride. Maybe I suck the 12 gets away from me on a tight twistie road. The 9 is planted to the road I like that myself. To help this discussion along....just a lil more...on the difference....Ted what you said earlier about it being a second faster...your off...which way I just can not tell... on with the discussion please Brian tilley hd/buell buckinfubba@hotmail.com 704-872-3883 |
