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flex in aluminum frame is a different story compared to steel frames.



What's twin shock has to do with HD anyway...

all bikes with disc brake are copy of Honda CB750? who's coping who? who cares...
 

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Re: What they didn't mention

1961? You realize they don't make the panhead anymore right Bob? '61 was long before I was born so it wasn't me giving you the ride.

I have the H-D catalog in front of me and just ordered some goodies for the Geezer Glide. She'll be breathing a bit better once I'm done.

Just remember if you do get a Dyna Sport, hire someone to follow you to pick up all the parts that fall off and a hazmat team to clean up the oil slick.
 

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I won't recheck your calculations,but they intuitively seem about right. However, I would clarify that the lean angles you cite refer to the angle between the center of the contact patch and the center of gravity of the bike/rider unit. With very wide tires, the contact patch moves well to the inside as the bike leans, requiring the bike itself to lean further, partially offset by the amount by which the rider leans off.



If you examine pictures of GP bikes, or even AMA Superbikes, the apparent lean angle of the bike looks to be well past 45 degrees.



Even if the maximum vertical component relative to the track is as high as 50%, this is still a significant problem. Assuming that the bike encounters a vertical bump of 1". If the suspension fully absorbs that bump, there will also be a horizonal suspension deflection of 1" so either the bike or the tire's contact patch deviates from its intended course. Given the realtive inertia of the bike and rider, it is likely that the tire does most of the deviation. In either case, traction is seriously compromised.



It is always a pleasure discussing technical issues with you, and I always come away with a better understanding of the subject as a result.



Best Regards

Bob
 

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So Ducati is dealing with totally different issues than, say, Honda in developing their GP bikes? Certainly, the specific ways they design and construct their frames to achieve the desired flex will be different, but the objectives are exactly the same. Laws of physics don't give a $hit about frame material.



Not sure (maybe some Harley historians here can confirm or deny) but I believe that Harley had the first disk brakes on a production bike -- before the CB750, and sportscars had em before Harley, and airplanes had em first. You are right, who cares?



In case you missed it, this reference is a good-natured dig at some of the Harley guys who are always accusing the Japanese of copying Harley, as well as some of the sportsbike guys who are always putting down Harley (as well as anything other than a race replica sportsbike) for supposedly employing obsolete technology.
 

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Assuming that the bike encounters a vertical bump of 1". If the suspension fully absorbs that bump, there will also be a horizonal suspension deflection of 1" so either the bike or the tire's contact patch deviates from its intended course.

Actually, the front suspension can pretty fully absorb the front bump except for friction losses from sidewise deflection of the downtubes. If frame flex or some other rear-lateral suspension scheme is properly calibrated, the front and rear could in principle be synchronized to minimize steering problems. I think that's the thrust of all the development we're seeing. Damping is probably the hardest part.

Always a pleasure

Jule
 

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Re: What they didn't mention

No no, i read all of it, and have actually been keeping up with this site for the better part of several years. This article took me for a turn though, i will admit.

I caught the jest in the article, it was in responses where i started believing you were halfass serious.

No harm, no foul, its an off day.

And, actually i have a very keen interest in harleys. i have only owned 2 suzukis but i learned to ride on a dyna sport.

One day i will weld up my own (sporting) frame with a big ole Merch in it with some dirt track high level pipes, the whole thing will be polished stainless and aluminum. Top spec brakes and suspension. imagine a homebuilt confederate, with ground clearance. And for 30 grand less.

Hehe, bikes are all good by me, id ride a friggin Ural everyday if i had the chance
 

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Re: What they didn't mention

>>One day i will weld up my own (sporting) frame with a big ole Merch in it with some dirt track high level pipes, the whole thing will be polished stainless and aluminum. Top spec brakes and suspension. imagine a homebuilt confederate, with ground clearance. And for 30 grand less. <<

Bring it on!!

My own fantasy Harley would be a Dyna Sport with 17" (or "18, if it looks better) wire spoke wheels (I am a Luddite at heart) with sport-touring rubber, longer high-end shocks (Ohlins, if they have anthing that will work) to get more clearance and quicker steering, moderate rearsets (still leaving room for passenger pegs) and moderately lower bars, upgraded brakes, a moderatly breathed-on engine and a Corbin seat. Basically, a naked, 2-up sport-touring rig that is a little different from the typical BMW roadster, etc.

Cheers

Bob
 

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The 35mm forks on my SR500 certainly have no difficulty deflecting sideways enough to absorb any bumps encountered while leaned over -- of course they also bend around every other direction as well -- fore and aft (you can actually see it bend back under hard braking) and torsionally (counter-steer hard and the wheel catches up a fraction of a second later). The USW forks on my Ducati are a lot stiffer and those on superbikes and GP bikes are much stiffer yet. My guess is that Honda started the flexible steering head thing for just this reason.



Actually, it seems that maybe fork tubes should be oval instead of round, so they could be very rigid fore/aft and more flexible laterally.



 

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I'm pretty sure that was tried, and discarded because of manufacturing/sealing problems. I'll try a search. Has anyone else heard about oval forks?



Seems like a flexible steering head puts the flex in the wrong part of the chassis.
 

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Girder forks can be tuned for stiffness in twist and fore-and-aft bend, with more flexibility in side-to-side bend. It's the back wheel that's the problem.



Seems like what's needed is a sprung frame pivot raked the same as the fork pivot that meets the ground at the middle of the wheelbase. Looks to me like the axis would pass pretty near to the swing arm pivot center. Hmm...
 

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Nope. Pushrods

This from an article by Steve Anderson -- For more info CLICK HERE

"The valve gear is as simple as it can be for a four-valve boxer: A single camshaft mounted high in each head opens each pair of valves via a very short pushrod and a single rocker arm with an extension for each valve. Valve lash can easily be set through screw adjusters. The camshafts are chain driven from a jackshaft under the crank; the jackshaft also carries the oil pump."

OHC would likely have made the engine wider, compromising cornering clearance. Also would make valve adjustments more difficult. My best friend's wife does her own valve adjustments on her R1150C.

Bob
 

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Actually, i have a book that goes through harleys history. i found it very interesting to find a picture in there of a harley that looked very nearly like a CB750. It was in inline 4. harley made it as a prototype but ditched it. this was a year before the CB750 came out.



Could you just imagine if harley had actually produced that bike? especially if it outperformed the hondas......the motorcycle industry could be worlds different then it is right now.
 
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