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Discussion in 'The Perfect Line and Other Riding Myths' started by iamcanjim, Jan 19, 2014.
maybe, fuel consumption is more dependent on throttle opening than rpm
Vibrations can be fun for a short trip, but when doing lots of miles, I prefer a smooth running engine with as less vibrations as possible. That's why HIGH rpms are less "stressful" to me and consequently I use the upper half or better the upper most quarter (depends a bit on cylinder number) of the rpm range.
Manufacturers don't always get it right.
My 2008 Harley Ultra couldn't effectively use 6th gear under about 75 or 80. Mileage suffered and any incline sucked.
My 2010 does much better due to revised gearing and changes I've made to the power.
Oh and mine can scream down the highway bouncing off the limiter at 6100!
Nope. Not particularly true for carbed bikes, and certainly not true for FI bikes. An engine is nothing more than an air pump, and other than when under load (say during acceleration) the sweet spot for air:fuel ratio is approx 12:1 to maybe 14:1 for efficient combustion. Even if you're talking carbs, the fuel is drawn from the bowl by venturi, which is largely dependent on RPM at SS cruising. FI controls fuel flow based on a number of parameters, including throttle position, RPM, engine temp, manifold vacuum and exhaust O2 level.
Engine speed on the highway (65-75 mph) is all over the place, depending on the bike.
Son has an '07 Ducati 800 Supersport that won't get out of its own way in 6th gear at 65- Revs far too low, geared WAY too high, can't accelerate at all. What were they thinking? On back roads, 50 mph or so, he never gets past 3rd gear.
My '92 BMW K100RS revs around 4600 rpms at 70 mph in 5th (5 speed trans), feels ok and will get nearly 50 mpg
It's probably a subset corollary of the Cruiserface phenomenon. Go down the road blatting potato-potato-potato all day.
I always thought that was a major selling point for Harleys, trading top end HP for low end torque making for a more relaxed ride at freeway speeds.
I think you're being intentionally obtuse.
If I'm so off base, why are touring bikes and cruisers tuned for low rpm torque rather than high rpm HP?
You trust the manufacturer too much. Engineers make mistakes. So do R&D departments. So do parts mfrs. So do assembly departments. Why do you think vehicle recalls exist?
You're losing sight of what the OP is talking about. In other words, people ignoring what the engineers designed and taking it upon themselves to "re-engineer" their bikes to run at much lower RPM's then is even remotely necessary, much less advantageous.
most big cc bike will be happy sitting at 70-80mph in top gear.
Reg Pridmore says, "RPMs are your friend."
The bikes are all torque due to the engines, long stroke, long intake runners .....sure combination for a stump puller.
High rpm for a Harley is less than half of most bikes...again long ass stroke, causes piston velocity issues, so you wouldn't tune for that anyway
I agree trying to re engineer a bike to not function as intended is dumb.
But it seemed to me the OP's question is why some folks don't like running at high rpms, guess I was wrong.
Seems some folks see a lot more than I do, I'll leave it to you all to bicker over.
Physically large, low revving, high-capacity engines have associations with "quality" that date back to the early beginnings of the internal combustion engine.
In modern era we have redefined quality as "fitness for purpose". One guy's definition of quality vacation might be a ship-borne cruise and another's an overland trip to the Yukon.
An 1800 Harley and a Goldwing may rev at different rpm's at 80 mph. They are both high-quality designs that have been thoroughly engineered. However riders experience the end result in different ways.
It is great for us as consumers that we have a choice.
I feel left out. I don't notice how fast the engine is running at highway speeds on my Helix. I've done multiple one-day 1000+ mile trips on it comfortably and was incredibly sore on a 750cc cruiser within 50 miles.
In other words, some people find the engine RPMs to be much less of a problem, if at all, than other (dis)comforts. For quite a few people, riding is all about some image that includes low RPM noise. As it was mentioned already, maybe some bikes are more vibration prone than others at certain RPMs due to resonance and damping characteristics?
OP asked about low revs on the Highway - assume he means cruising.
Pretty simple, vibration and engine noise.
Generally speaking the higher the revs the more vibration and engine noise regardless of single, twin, triple or 4 cylinder. All engines have a sweet spot for power and curising (where vibration and noise are not as pronounced) and often the two aren't in the same rpm spot.
If one is crusing at 75-80 mph, you don't need much more roll on power power too initiate a pass since you already running 80, so why not raise a gear to lower rpm as long as there is enough Tq to kep you moving at the same speed without engine lugging.
If I need to quickly pass at 80, or any other speed for that matter, I can drop a gear as quickly as I can wrap the throttle, and that is exactly what I do.
Cruising on the highway I'm going be in low revs, riding the twisties or in heavy traffic where aggressive manuevers are needed, I keep the revs up.
MOST Harley and other Cruiser riders ride at WAY TOO LOW of an RPM while cruising down the highway.
Your 3000 RMP was actually spot on when it comes to V-twin cruisers. The Sweet Spot for a Twin cam is going to be found somewhere between 2900 - 3100 RPM's (best cooling, fuel economy... ) MOST get lugged and are being ridden in 6th gear when they should be in 4th.
In-line twins, triples and four cylinder bikes will of course be MUCH higher.
It isn't based on engine layout, fwiw. 3000 RPM is about the minimum that my V twin really likes to see. The engines end up showing that trend because of the type of vehicle that each typically ends up in, though. The I4 in my GS750 is fine running from 2-4k rpm all the time if I'm riding sedately, but that would be miserable on a sportbike.
This is actually true. Even if you aren't specifically listening for it, your brain processes all the sounds that your ears hear. More RPM typically means more noise, and at a higher frequency. Smaller engines have to rev higher to make power, typically, and usually make a bit of noise doing so. Those things do contribute to fatigue, even if it isn't inherently bad for the bike. That said, if you can't hear the engine over the wind or it's just that quiet, then the RPM won't make any difference to fatigue.