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  #11  
Old Oct 2nd, 2007, 10:05 pm
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JCW JCW is offline
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Quote:
Originally Posted by sandbar
The ideal scenario is that the output shaft from the gearbox should be parallel to the input shaft to the bevel drive, and the paralever system should form a perfect parallelogram. It is clear from the Wikipedia page that the further from this ideal the more fluctuations there are in the angular velocity. That would mean more vibration and increased tyre wear.

Now to the real world.


Yes you are right - and the paralever does not even make a parallelogram. I guess design and production requirements meant a few compromises. But, neverthless, in standard form they are not far away and I guess that BMW find that the effects of the variation from ideal to be acceptable within their parameters for service life and smoothness.

But that does not alter the fact that the best solution is parallel shafts operated by a parallelogram.



Do you think it was a matter of design and production compromises that prevented BMW from making the perfect parallelogram?

It is slightly more difficult than that.

If you go beyond the simple definitions found in WIKIPEDIA and read a real book on suspension design such as Tony Foale's book, you would realized that many more factors contribute to the design of the rear suspension.

The main one in this case is to slightly offset the shift in weight and subsequent suspension changes with acceleration and deceleration. A perfect parallelogram would negating this beneficial action. By bringing the front pivot points on the paralever suspension slightly closer than the rear pivot points, you effectively create a swingarm with an imaginary pivot point near the steering head. This reintroduces a slight shaft jacking effect to counteract the acceleration changes to the suspension.

Quote:
Originally Posted by sandbar
I am afraid that I am always sceptical about comparisons with the PowerCup racers. They only had to last about 150 miles on very smooth surfaces every few weekends and they had attention from mechanics that would be far greater than the majority of road bikes. Tyre wear was not an issue and increased vibrations would probably not be felt or noticed.


No, but failed transmissions would be rather embarrasing. Let me put it this way. Would I rather trust BMW who has the original design goals, specifications and understanding on modifications for their OWN SERIES and OWN MOTORCYCLE?

Or, do I trust someone who makes overpriced cabon fairings (granted your's are somewhat less overpriced than the rest) who comes up with his own design?

HHHHMMMMMMM?

Quote:
Originally Posted by sandbar
That is not necessarily true. In any event surely the BEST solution would be to achieve the required ride height by changes in the length of the shock and THEN change the length of the torque arm to alter the shaft angles so that they are parallel at the midpoint in the normal suspension travel.


Again, too much is being made of PERFECT U-joint alignment. Let me explain...

The monolever suspension of the 1980's had only ONE u-joint. That means that the angular ouput shaft of all these motorcycles suffered this catastrophic vibration you speak of. All those motorcycles, all those rear ends, teetering on the brink of annihalation.

Guess they survived OK for years, huh?
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  #12  
Old Oct 3rd, 2007, 10:21 am
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Captain K12R Captain K12R is offline
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Question from someone that really has no idea what a torque arm does. What is the difference between the evolutionize Arm and Pirate's? Do they both provide a quicker turn in? I want to eliminate the factory arm because it's ugly. If i receive a better ride in the process, that's all the better. I think Pirate's arm looks best, but does it function as efficiently as the evolutionize arm?
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  #13  
Old Oct 3rd, 2007, 12:13 pm
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Pirate's arm is stock in length so doesn't change the ride at all. Purely cosmetic.

Evoluzione's comes stock length but can be shimmed to a longer length to improve turn in.

Sandbar and CC71 has plates that basically accomplish this as well.

As far as which is better, I'd have to say I'd go with getting a longer shock.

But I have evol torque arm, a longer shock AND homemade suspension plates.
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  #14  
Old Oct 3rd, 2007, 1:24 pm
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Captain K12R Captain K12R is offline
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Has anyone tried the Rizoma Paralever? If so, what results have you encountered?

http://www.bmwsantacruz.com/Merchan...roduct_Count=15
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  #15  
Old Oct 3rd, 2007, 5:34 pm
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Resn8 Resn8 is offline
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Hi all

Can i ask another Question how would both work on the same bike, say the modified plates and Evo's torque arm.
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  #16  
Old Oct 3rd, 2007, 9:44 pm
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Quote:
Originally Posted by Resn8
Hi all

Can i ask another Question how would both work on the same bike, say the modified plates and Evo's torque arm.


I found that the more the rear went up, the better the bike transitions. This is more than the plates or the torque arm offered separately. This is offset by a very tall seat AND a sidestand that no longer is functional as the bike tips over too much.

You COULD use both to raise the rear more than each individually and see how it suits your tastes. Or you could use the torque arm at stock length for looks and increased strength and use the plates to make all your ride height adjustment.
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  #17  
Old Oct 4th, 2007, 5:03 pm
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sandbar sandbar is offline
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This looks like it could degenerate into one of those internet/forum discussions where it looks like there is an argument, when what is actually happening is we are talking about different things!!

Quote:
Originally Posted by JCW
Do you think it was a matter of design and production compromises that prevented BMW from making the perfect parallelogram?

Yes I do - absolutely.

However I think that I could have worded that phrase a bit better. You obviously read it differently than I meant it. The word 'compromises' was only meant to apply to 'production'. Maybe the phrase should have read "design criteria and production compromises". My mistake - I am sorry.

You are right about the design's attempt to diminish the rise and fall of the rear of the bike due to the shaft drive - the so called 'jacking' effect.

However it does not alter the fact that if you want to eliminate any vibration (or the effects of it) from a shaft that has two universal joints, then the input and output shafts should be parallel. The further the shafts are away from parallel the greater the variations in angular velocity and therefore the increase in vibration and tyre wear.

I think we agree!!

Quote:
Originally Posted by JCW
The monolever suspension of the 1980's had only ONE u-joint. That means that the angular ouput shaft of all these motorcycles suffered this catastrophic vibration you speak of. All those motorcycles, all those rear ends, teetering on the brink of annihalation.
Guess they survived OK for years, huh?

I do disagree with you about this. From the moment that BMW started to produce bikes with bigger engines and noticeably more power (compared to modern bikes that is a relative term) in the mid 70s with the R90S and then the 1000cc R100RS, the misalignment of the shaft became more and more of a problem. There was a continuous program of development on the drive train to reduce the vibrations and associated problems. There were vibration/shock dampers in the shaft ( late 70s) and a similar change to the gearbox in the early 80s. Alignments were changed, mountings were moved - all trying to address this issue.

There were no bevel drive pivots to wear and the shaft had its own seperate oil bath. The problems were not 'catastrophic' because the shafts and joints etc were over engineered. I don't think that they differ much in size from the parts used today, but even the most powerful BMW road bike of the 70s (R100RS)only developed about 70 hp IIRC.

In those days BMWs were also renowned for high tyre wear - again compared to modern times, that is a relative term.

Even before those days, this kind of realignment was necessary.

Crankshaft, gearbox output shaft and drive shaft as near as possible a straight line.

If anybody wants to find out if the vibration can be a problem, then just remove the bevel drive and re-connect the shaft so that the universal joints are out of phase.

Just think - the whole problem could be solved with the use of constant velocity joints

sandbar
www.sandbarcomposites.co.uk
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  #18  
Old Oct 4th, 2007, 6:18 pm
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Agreed with what you said.

However, BMW who has access to both types of joints chose the U joint based on the fact that by design, the paralever suspension can control the angle of misalignment to acceptable levels. It's not a problem in my and BMW's view.

Problems with CV joints are recognized...

By their design, the ball bearings in the cv joint slide and shear. They do not roll as other "bearings." They develop significant heat and waste a bit of energy at anything other than 0 deg. All this is "minimized" by the use of high tech lubes (our friend MOLY) but in high torque applications they are insufficient. They also very sensitive to dirt and other contamination.

Nice discussion...

Sorry, I thought you were picking on me by quoting only me in your first response.

(But I stand by my statement that producers of carbon fiber products WAY OVERCHARGE for essentially the same setup and production that is required for a quality fiberglass peice. That I'm learning quickly making my own solo seat.)
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  #19  
Old Dec 20th, 2007, 10:27 pm
battleborn battleborn is offline
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Sandbar "Dog bones"

Being a fan and invested in Evoluzione components (thank you for being in business Ken) I opted to try the Sandbar Composites "dog bones" if I get the chance to ride my bike soon I will follow up on the turn-in performance... On the short ride home it seemed responsive but that could have been my 50+ year old brain just enjoying the ride. Once I am out of the casino that I'm evaluating here in sunny Aruba we will see if I make any bets on the dog bones.

Wonder what adding the torque arm now would achieve along with the "dog bones" Ken any thoughts or is it just over kill?

keeping the rubber side down...
Douglas in Las Vegas

Check my bike out on www.2wtmag.com READER'S RIDES search using make...BMW of course, it was ride of the month for October 2007 and the only BMW amongst the other speed machines.


Quote:
Originally Posted by evoluzione
i know you emailed us this question but i thought i should answer it here. when i first read it something didn't make sense. then i clicked on the link and understood. in the future, if you plan on asking questions and quoting a source, i would recommend that you include the actual quote, not just try and paraphrase. the actual statement sandbar makes is:


"Changing the rear ride height by changing the length of the paralever torque arm is not the correct way, because it also changes the angles between the various shafts in the drive train. The driveshaft uses normal universal joints (and not C/V joints) and the more that the input and output shafts deviate from being parallel, the greater will be the vibration and tyre wear. There will also be excess strain on the paralever bearings and probably the gearbox as well."


now to answer your questions. during normal riding, the angularity between all of the shafts is constantly changing (every bump you hit changes the suspension angles). i do agree that more angularity is not good but how much is too much? i can only go by the fact that the factory powercup race teams used much longer torque arms and after ten's of thousands of miles on hundreds of bikes we've not had any issues. i realize that sandbar is offering a different solution to the same issue (better turn-in) and i'm not sure i agree with everything they say but basically their statements are true. but i also feel that our design is well within the design parameters of the original suspension design.

bottom line, if you feel uncomfortable using our torque arm, please just send it back for a refund.
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  #20  
Old Dec 20th, 2007, 10:50 pm
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JCW JCW is offline
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That site's retarded.
Sorry.
The chicks have way too much clothes on and are ugly. The bikes more so.

Your bike's cool, though. I assume the Power Commander was a custom job. Your A/F ratio is far too smooth to be stock.

This gives me some hope as no one wants to sell me a rapidbike. :wtf :wtf :wtf
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