Just got this photo from Curt Winter showing the production kit version of his Big Twin Racers American sportbike. We’ve mentioned Curt’s bike before, it’s powered by a RevTech 100 inch engine and six speed tranny with Ceriani inverted forks and a frame designed and built by Curt. There seem to be a few differences since the last photos so I’m getting some more info from Curt to find out what the current configuation actually is, plus a few details on price.
With the release of the Wakan 1640 last week, Roland Sands building his various sport customs powered by big V-Twins, plus Curt’s efforts and who knows how many more, this is definitely a trend and it’s one I like. Big torque engines with sporty handling, yep, that’s a trend I can live with.
The Kneeslider: Big Twin Racers – American Sport Bikes in a Kit
The Kneeslider: American Sport Bike
The Kneeslider: Wakan 1640 – New French V-Twin Motorcycle
The Kneeslider: Roland Sands Renstar and RSD Grunt
todd says
well torque is no big deal. The average bicyclist pumps out 150 foot-pounds of torque but they aren’t that fast are they? If you want speed you have to have horsepower.
I know these big push rod twins are advertised to have over 100hp but I’m sure that’s only short bursts on a dyno and it’s measured at the crank. It reminds me of those cheap “400 watt” speakers you could buy in JC Witney’s; fine print reads 700 watt peak, 50 watt RMS. Basically if you were to attempt to get your 100hp out of your big twin it would grenade in short order.
Nice looking direction though.
-todd
aaron says
I just realized why yamaha isn’t importing the mt-o1 into the states….
It would kill the grassroots big twin sportbike industry – S&S and buell are probably bribing someone to hold off importing the thing! sure it’s too big and a little ugly, but I’ve had a look at a modified bike and it doesn’t take much to really clean the thing up!
C. J. Luke, III says
Well, I know this is somewhat “off topic”, but I agree with Todd. The “torque” specification on an engine is somewhat meaningless as I see it. The actual torque on a rear wheel is a function of the engine torque that is multiplied by the gear ratio in the transmission and the final ratio that is a function of the ratio of front and rear sprocket…therefore engine torque is a meaningless number and “final” torque is what counts. If you want more torque at the rear wheel, up the tooth count of the rear sprocket or lower the tooth count of the front sprocket or do some combination of both. If you want to compare torque between two different bikes…say a 600cc inline 4 and a 1200cc v2, it seems to me it needs to be a calculated function based on mph/kph vs maximum mph/kph. That would at least allow you to see that with the factory gearing and final ratio, bike A has X rear wheel torque at Y mph and it is capable of Z mph total at U mph.
kneeslider says
Todd and CJ,
Torque IS a big deal and is definitely NOT meaningless, in fact, torque is everything. Torque is what you directly measure, horsepower doesn’t even exist except as an arbitrary calculation based on how much torque can be delivered over a period of time (1 horsepower = 550 foot-pounds/second). Longer explanation of horsepower here and torque here.
When we talk about torque and motorcycles, especially when we’re talking about V-twins, the advantage they have is they deliver a lot of torque at low rpms and continue to deliver a lot of torque for quite a while, the classic “flat curve” but then fall off earlier in the rpm range. Those little 600cc fours can deliver lots of torque, too, but at much higher revs and for a shorter span of revs, therefore the need for a lot more shifting to stay in their high rpm power band which simply means in the higher portion of the torque curve. V-twin street bikes require less shifting to accelerate at normal street speeds, you roll on the power, it’s why it’s so easy to catch a sportbike flat footed because he’s in the wrong gear, unless he’s one of those squids cruising along in first or second gear all the time. You embarass him quick and then by the time he’s all revved up and ready to race, you’re smiling and slowing down. It’s also what makes those slower curvy roads so much fun when you can roll on and easily accelerate instead of shift, shift, downshift, downshift.
Todd, your bicyclist has that torque for a very short rev range, the classic peaky torque curve, a spike then it falls off a cliff. Saying speed requires horsepower is just another way of saying you need your torque delivered differently and the whole point of this torquey V-twin thing isn’t speed anyway, it’s easy, no fuss acceleration at a normal pace, not at the race bike speeds found on the track.
C.J. Luke says
Hmmm…I re-read my post and I see that I didn’t get my meaning across well. I don’t agree that torque is meaningless…but I do think that the published torque numbers are meaningless. You can easily modify the performance of a bike by adjusting the final ratio. The transmission and final drive ratio serve as torque multipliers. The perfect example of this is droping a tooth or two from the front sprocket and adding two or three teeth to the rear sprocket. HP is work done over time and torque is force applied at any instant in time…the other variable is inertia. How fast can the engine accelerate from the minimum torque range to the maximum torque range for any given load? An inherent weakness in the big V twins is inertia, it limits the maximum rpm and the “speed” at which it can accelerate.
hoyt says
Well done, Curt. It is very cool to have someone build these bikes as a one-off or as a kit. From the info. on Curt’s site, it looks like he can build many types of bikes.
Hopefully Baker Drivetrain or Jim’s H-D Products are working on a compact transmission for this new custom bike direction.
street riding is all about torque, unless you ride in a straight line.
aaron says
I’ve gotta throw my $.02 in on the acceleration of a twin…
CJ luke – surely the MOI of a big twin crank has little effect compared to the MOI of the rest of the drivetrain and rear wheel/tire
and there are some twins out there pulling off some seriously fast et’s when they run nitro….
C.J. Luke says
Hi Aaron,
There are two moments of inertia (MOI) that are of major concern. The first is the valve train, and the second is the crank shaft+pistons. Take two similar builds of a V twin and make one a “push rod” type valve train and the other an “over head cam” type. The overhead cam will be capable of turning higher rpm than the push rod type if the MOI of the crank+pistons will allow it. Replace the connecting rods and pistons with titanium rods and pistons and the engine is now capable of higher rpm but is also capable of attaining those rpm faster.
But this isn’t the point of my original post. I maintain that the “numbers” that we look at don’t tell the “story”. If I told you that I had two bikes of equal weight and fundamental design specs (wheelbase, rake, trail), and one had 100 hp and 100 ft lbs of torque, while the other had 100 hp and 50 ft lbs of torque, you could not predict which bike would perform the best in a given venue.
In other words, hp and torque don’t tell us what we need to know.
Earl says
Well, say what you will about torque and so forth… but why do these people keep cramming low-rev cruiser engines into sportsbike frames? I love V-twins, but surely the Ducati approach is preferable to the HD in this application.
todd says
as in the bicycle scenario, the fact that the bicyclist can put out 150ft-lb of torque (a very flat tourque curve over the entire rpm range, tapering off at high revs due to inertia) is of little value to both speed OR acceleration. Why? When you convert all that torque to HP considering the speed he can crank his pedals at peak torque (150 RPM) he’s only putting out 0.6HP, hence the 30 mph peak.
The argument that torque is everything would suggest that a bicyclist could out accelerate a 100ci V-twin. Why can’t he? Because he can’t apply that torque to the pedals at high RPMs. Big push-rod twins have a very narrow power band, much more narrow than sophisticated overhead cam, 4-valve motors. You could say a big twin has a “peaky” power out put. If a bike makes power from 2000 – 6000 RPM it only has a 4000 RPM power band likewise if a bike can only manage to begin making power a 4000 but can continue building power through 15000 RPM it has a much broader power band.
Now if a 600 can manage 50ft-lbs to a big twin’s (supposed) 100ft-lbs consider that the 600 can be geared substantially lower, to C.J.Luke’s point, allowed by the broad power band. This raises the rear wheel torque to or beyond that of the big twin which cannot lower its gearing because of its low, narrow power band without then giving it many close ratio gears. I think H-D has a 6 speed now right? Can a H-D top 100 mph even with all those gears?
OK, now add the fact that most big twins weigh substantially more…
-todd
todd says
further comparison: I have a ’77 peugeot 103 moped, as in motorized bicycle with pedals. its little 50cc is severely restricted putting out 2 HP and approximately zero torque. On that bike I can accelerate to 30 mph much much more rapidly than I can on my bicycle. The moped also weighs 3 and 1/2 times as much as the bicycle. On the bicycle, to reach top speed as soon as possible despite the tremendous torque advantage I have to shift at least 5 times. The moped doesn’t have to shift at all since it has 2 HP and a much wider power band.
Another comparison: I have a 1970 yamaha 90cc 2-stroke twin. It revs to 12000 rpm and puts out 7 or 8 HP. I also have a ’69 Honda trail 90, king of torque but also 7 or 8 HP (I have 7 motorcycles…). The yamaha (with a 5-speed) will leave the honda in the dust running all the way up to 70+ mph. The honda (with a 4-speed, well actually 8) struggles to get over 50 mph and won’t pull hills in top gear. Why the difference? Because of the Yamaha’s much wider and higher power band it can be kept in each gear longer and its overall ratio can be lower. Each bike has to be shifted just as rapidly and just as often, in fact I have to shift the yamaha less often despite the fact that it’s a “peaky” two-stroke with a “narrow power band”.
-todd
hoyt says
todd – your power band comparisons don’t seem to account for the whole story.
The stroker motors make power with a limited rpm range. This doesn’t mean their power band is narrow. Looking at the rpm DIGITS as an indication of a power band doesn’t explain the power available.
True, an inline 4 continues to make power over a wider rpm range when you look at the rpm as digits. But, consider the power created between any given 2000 rpm differential for each type of engine.
Also, a big twin power band is wider than an inline 4 when you talk about street riding….especially since the power from an inline 4 is really only tapped into at race track engine speeds.
todd says
Hoyt, please explain how a 4000 RPM spread is wider than a 11000 RPM spread? What are “race track engine speeds”? If a motor is designed to run efficiently at 10,000 it is best to run it at 10,000. If I was used to diesel tractors your line of thinking would suggest that 4,000 is a “race track engine speed”.
I think if a person tends to lug an engine around the street at 4000 rpm then yes, a motor that was designed to run at 4000 rpm will achieve better results than one that was designed to be run a 10,000. For some motors, 10-15,000 RPM is not a “race track engine speed”, it is merely the speed at which it was designed to be the most effiecient.
None of this detracts from the truth that a bike that can apply more HP to the ground is faster and can accelerate harder than one that can apply less, regardless of the torque output or characteristics.
-todd
hoyt says
todd – You are saying a big twin has a narrow power band based solely on the numbers on the tachometer. Although the max rpm range is around 6000 rpms, there is a lot of usable power available throughout. Many people will rightfully argue this spread of power is wider than an in-line 4 engine in terms of street riding.
Earlier you stated, “well torque is no big deal.” Have you ridden a big twin bike ? (H-D, Guzzi, or any of the twins from Japan)
Does a Triumph Rocket III have a wide power band? Or, does it not because it can’t rev to 14000 rpm?
todd says
Sorry to be taking up all the bandwidth…
Yes, I have ridden all the above, though sadly, I’ve yet to have ridden a twin cylindered Ducati. The most powerful push-rod bike I’ve ridden is my father-in-law’s severely massaged sportster. No doubt it accelerates hard, a dramatic improvement over the stocker, but in short busrts no less. That said, I’ve owned 300cc dirt bikes that will seriously walk away from it – up to 60 or so – in short bursts.
Do yourself a favor, go out riding with a diverse group of friends. One that has spent tens of thousands of dollars on his big Hog and another that added a slip-on to his GSXR1000. Convince them to ride your (in my case that day) 33 HP honda single as you explore the hype of each bike. You will no longer doubt which puts on the speed faster between the two. Oh yeah, I still say the big push-rod twin has a short power band. As soon as I felt the power was coming on strong I was supposed to shift. On the Gixxer I had to shift often too but that was because I was climbing well into tripple digits before my senses caught up with me. I can’t even imagine what a Hyabusa is like.
Sorry, I don’t have the specs of a Rocket III nor have I wished to test ride one, especially when the Scrambler was begging to be tried.
Fun topic, and I’m glad the kneeslider allows us to ramble on back and forth. Excellent site.
-todd
Curt Winter says
Todd.
Like you I also ride with friends that have a wide variety of equipment. Iv’e raced and ridden lots of defferent bikes, everything from 80s 125s 250s and 500s. I won a national on the 500, even though it was a heavier bike and not nearly as nimble as the smaller ones it had power that was unmached. I know what your talking about when you describe the sensation you got while riding the gsxr. Those bikes are insanely fast, I used to own one. All this talk about hp and torqe could go on for ever, when trying to explain the advantage of torque you must keep in mind why it is that torque is so attractive, engines that produce large torqe numbers typically don’t rev high. The engine in the BIG TWIN RACER makes usable power and torque between 1000 and 6000 rpm. A modern 4 cylinder engine makes its usable power and torqe between 10,000 and 13,000 rpm. The twin has a wider power band. I have ridden this bike on tight roads were the speed never exceeds 60 mph, Iv’e also ridden with friends that have been on gsxr 1000s and zx 1100. On roads that are tight, and speeds that are kept below 80mph, Iv’e yet to be passed due to outright excelleration, this bike pulls harder out of the corners than either of the two previously mentioned machines. Thats not to say that this thing will walk all over them on a track because it won’t, it won’t even come close. But thats not the intent, the intent is to have a bike with a broad usable power band. The wider the power band the less shifting you have to do. I know these bikes aren’t for everyone, but I do know thay are a thrill to ride, Iv’e had more fun on this thing than Iv’e ever had on my qsxr.
hoyt says
Todd – I ride with diverse bikes on roads that matter to me most (20 – 30 mph turns of varying diameters over different grades).
R1, R6, Buells, GSXR 750, Triumph Speed Triple & my V11 Guzzi. The Guzzi was right at home thumping through the curves perfectly at about 4500 – 5000 rpm.
This is not to say I don’t appreciate or admire modern, compact high tech bikes. But, the experience of a bike made with modern frame geometry, frame materials, suspension, and a big old torquey motor is hard to forget long after you park the bike.
todd says
I agree these bikes have more soul – I’ve never owned a bike with more than two cylinders – I’m just being realistic. From my experiences and understanding of torque and its relation to horsepower (a measure of work done) I’ve concluded that a bike with more horsepower is more powerful than one with less even if it has more torque.
I agree with Hoyt’s assesment of the Guzzi. i’ve ridden a friend’s 850 LeMans and it’s a hoot but it wasn’t any quicker than my brother’s SV650. Does that make the LeMans an entry level bike now?
I think the main point that is being explored in these type of bikes and these posts is that a person does not need all the power that is available from bikes now-a-days. That Gixxer I rode was amazing blasting down a straight road but kind of boring through the mountains it had no soul. I think I never made it beyond 3rd gear and that was that long straight. I’m consistantly able to keep up with these guys despite me regularly bringing sub 50 horse bikes to these rides.
People like these big twins because they don’t look mass produced, they remind us of american hot-rodding, and if they’re over 40, don’t make them feel like a ricky-racer/squid. The bikes are simple and easy to fix (just ask my father-in-law, he’s always working on his harley), and they have soul. Who cares if you can’t keep up with an R6 when the light turns green, at least you’ll look and souond cooler and less anonymous, you’ll probably have better luck with more mature women as well…
-todd
Curt Winter says
Todd.
If the 50 hp bike that you take on these rides is able to keep up with your friends on sport bikes, then would it be safe to assume that high reving high horse power multy cylinder sport bikes are overkill and less affective on the backroads that most of our riding is done on. A smooth power delivery and a wide controlable powerband is much more user friendly and doesn’t require constent shifting to keep the motor happy. Keep in mind that most all sport bikes are designed to turn quick track times, that doesn’t mean their the best backroad bike or the best sport touring bike. In order to have the best backroad bike you would typicly want a broad smooth reving torquey power band, thats why you see so many people stuffing big v-twin motors in good handling sport bike chassis, it just makes sence.
Gordy says
Good luck Curt, I wish you well.
(If you have not done so already, take a look at Ecosse, Confederate and American Cafe Racers for ideas on how to solve the short gearbox challenge).
Curt says
Thanks Gordy.
The main reason I used the standard primary and gear box was because it was available and something that people could relate to. Something that could be serviced by any dealer. At some point I would like to offer a shorter powerplant, maybe my own transmission and primary assembly.
Gordy says
I understand your reasoning.
While large volume manufacturing is dominated by piece-cost concerns the smaller scale operations such as your own are usually, and understandably, ham-strung by the lack of investment capital (for specific tooling, etc.). I guess that will be a problem for you when seeking to develop your own gearbox. But with what you have achieved so far I think that you will get there one way or another.
I’ll follow your progress with interest !
hoyt says
imagine the possibilities when the compact transmissions are available on the aftermarket from Baker Drivetrain and others!
Would the V-Rod tranmission internals in a custom machined trans. box work with the big twin?