If you are going to make broad claims, then document your claims. Give us numbers (from external links preferably).
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Warning: Not a Rave Review of the BMW R1200RT
- Thread starter jamo
- Start date
Arguing about torque and HP is kind of missing the big picture. Speed, acceleration, braking, handling is more of the bottom line, literally where the rubber meets the road. The Michigan State Police test police vehicles every year, including motorcycles. They are kind of like the Consumer Reports for this arena. (See https://www.michigan.gov/documents/msp/2018MYPoliceVehicleEvaluationTestBookFINAL_606385_7.pdf). BMW much lighter (650 vs. 845 pounds), and notably smaller engine too. Look at the data for top speed (no comparison there!), acceleration and braking.
You really should pick a bike that meets your specific needs and wants. No bike is perfect, and what works for one person may be terrible for another. I love my RT, even though my inseam is too short for the bike. I will never ride it like it can be ridden. Not my style, but it is there if I needed it.
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Horsepower is just a calculation, it can't be measured directly. A dyno measures torque at various RPMs and the computer does the math to come up with HP.
HP=RPM x torque/5252. I wonder if some of the argument is the missed constant, 5252.
Either way, Harley build a torque engine, BMW a horsepower engine and as far as the rider is concerned they need to be operated differently.
HP=RPM x torque/5252. I wonder if some of the argument is the missed constant, 5252.
Either way, Harley build a torque engine, BMW a horsepower engine and as far as the rider is concerned they need to be operated differently.
The correct formula: HP = (RPM x TORQUE)/5252. The constant is why I added the mathematical words "proportional to".
stooie
Member
?? Oh yes, it is! The output of an engine is precisely horsepower = torque (in foot pounds) x engine RPM / 5252. And yes, one of the implications of this equation is that at 5252 rpm torque and horsepower are always equal.
If you have another formula relating horsepower and torque, I'd love to see it and discuss it with you.
To add to the discussion, the power to overcome aerodynamic drag is roughly proportional to the velocity cubed.
This is why reducing frontal area and having a low-drag shape are more efficient paths to a high top speed than adding horsepower. It's why my old VFR800 Interceptor with ~ 110 horsepower could reach 155 mph (from other's experience, not mine) while the top speed on our lovely 125 hp RTs with the large protective fairing and windscreen is about 133 mph (per Cycle World review of '15 RT).
Ride long and prosper!
PS: Apologies to 75450 and PoorUB for repeating what they've already posted.
jamo
New member
I'm pretty sure that equation is describing instantaneous horsepower as a function of instantaneous torque at a known rpm, not peak.
What we've been talking about is the peak horsepower, peak torque potential of an engine as a factor - with a gear involved - in its top speed and whether it's limited the vehicle to below 125 mph. The equation doesn't describe maximum horsepower or torque potential of a specific engine. I'd have to conclude Harley's 1800 ccs would be blowing away BMW's 1200 ccs.
You're a funny guy, but this isn't the joke section. (Maybe with Yellow Wolf on the H-D and you on the BMW.
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pglaves
#13338
OK, enough silliness. The BMW RTP is quicker and handles better than even the HD Stage IV. That is its forte. Touring down the road in the Pap Smear leg position is an HD forte. So be it. I have only owned one HD bike - built in Italy in 1972 called the "Shortster"... See: https://californiascooterco.com/blog/?p=12723
pappy35
New member
Clearly you don't understand something. The equation is a simple linear mathematical function that does not account for the mechanical limitations of the machine it's being applied to, it not intended to approximate the performance of any particular engine. Such an equation could of course be derived but it would be, at best, an approximation.
An unobtainium engine with an infinite redline would make infinite HP/torque. Of course, automotive power curves are subject to dozens of factors that limit their output (valve float, con-rod stress, intake/exhaust flow restrictions, cooling, enthalpy of the fuel, drag forces (cube of the velocity!), internal friction, lubrication, heat dissipation, etc., etc.
You can believe whatever you want but I'd bet a week pay that your current RT would blow your old Harley out of the water (if ridden by a third party that's not biased of course).
stooie
Member
Jamo:
You're right, the horsepower equation describes the engine output at any instant. That means that it's accurate for every point on the engine's output vs rpm curve; the point of peak horsepower, peak torque, or any other. While having generous torque makes a bike easy to ride without having to shift a lot, most performance is about having horsepower. By running a low-torque, high-power engine near the peak power and using the transmission to multiply the torque one ends up with superior acceleration and top speed.
In general, the larger the engine displacement, the more peak torque it should potentially have. Harley's have big engines and thus generate impressive torque. Most Harleys are tuned (design of cams, intake manifold, valve size, exhaust design, etc) to not breath very well at higher revs. Thus they run out of torque at higher revs sooner than the RT and can't generate the peak horsepower that the RT can.
Note that top speed is all about power, not peak torque. An engine with relatively modest torque (say PoorUB's R1) but lots of power can out run the HD (and the RT) at the top end. Using the winning combination of high power and lighter weight the R1 can run away and hide from all of the other bikes in this discussion in both acceleration and top speed.
Note the performance data in PKPilot's posting #122 above. The Harleys were quickest in 0 - 20 mph runs, pretty close to the RT and FJR in 0 - 60 runs, but then ran out of breath and were slower 0 - 80 and much, much slower 0 - 100.
Also, you make interesting use of the word "potential". Could an 1800 cc V-Twin be designed to blast away an RT? ABSOLUTELY! Ducati's 1300 cc V-twin, 209 hp (and 400 lb!) Panigale will walk away from any of the bikes we're comparing here. It's not about potential; it's about the engine and bike as it's designed. The Harley's relatively low power and higher weight happen to give it lower top speed and limit its acceleration.
If this sounds like I'm throwing stones at Harleys, it's not meant to. Lots of people have them and love them. The bike suits them. Lots of people also have Harleys and BMWs and like both of them. Good for them. The great thing about a free market is folks can choose the bike that fits their particular set of desires.
Ride long and prosper!
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It makes no difference whether it is peak or instantaneous. The equation is the equation. If you have a certain RPM and torque to go along with it you can calculate HP. Doesn't make any difference peak, instantaneous or constant.
stooie
Member
Somehow, this thread has begun to smell like a troll came out from under the bridge, cast a line, and hooked a fair number of fish...
DG
I bet you're just saying that 'cause you're shocked to see me flopping around in the sand on the river bank trying to get the hook out!
Riding is about how it feels
Thanks to all for the technical info, but maybe just for me it kind of overlooks the point: what makes us happy, as riders. Back in 1985, I was riding my second airhead, an R100t, when my dealer said I had to try the new K100RT. So I did and was awestruck at the high-end acceleration. Then, I was so happy to be back on my twin and feel the motor work. In more than 50 years on motorcycles, most of my bikes have been Beemers (currently aR1200RT, the “best” ever. But the most relaxing of all was my new ‘92 HD Electra Glide Classic. After returning to BMWs, the Harley seemed to have been held together by paper clips. But I’ve always missed the easy low-end torque ever since. It’s a different ride, and it’s all in what you want, and can afford. IMHO.
Thanks to all for the technical info, but maybe just for me it kind of overlooks the point: what makes us happy, as riders. Back in 1985, I was riding my second airhead, an R100t, when my dealer said I had to try the new K100RT. So I did and was awestruck at the high-end acceleration. Then, I was so happy to be back on my twin and feel the motor work. In more than 50 years on motorcycles, most of my bikes have been Beemers (currently aR1200RT, the “best” ever. But the most relaxing of all was my new ‘92 HD Electra Glide Classic. After returning to BMWs, the Harley seemed to have been held together by paper clips. But I’ve always missed the easy low-end torque ever since. It’s a different ride, and it’s all in what you want, and can afford. IMHO.
taran1900
Member
Somehow, this thread has begun to smell like a troll came out from under the bridge, cast a line, and hooked a fair number of fish...
DG
Yep.
Somehow, this thread has begun to smell like a troll came out from under the bridge, cast a line, and hooked a fair number of fish...
DG
I kinda felt that way from the start!
I didn't think that the OP was a troll. Except for his closing remark, "I'd have to conclude Harley's 1800 ccs would be blowing away BMW's 1200 ccs.", I thought he was just a disgruntled BMW owner, not happy with his dealership, not happy with the performance and the amount he paid for his 2015 R1200RT. Maybe he will come back and defend himself.
gsinnc
Well-known member
Just frustrating that he is comparing 2 VERY different motorcycles each with their own strong points. Both nice bike just different.
Funny when I bought my first BMW I owned a Yamaha Royal Star which was very much like the Road King. And I was buying a BMW (R1100RT) because it WAS different. Better handling and better in the mountains! I loved them both but there was no comparison because they have very different personalities. One can never replace the other.
