brainstorming ... - Wrist Twisters
 
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post #1 of 14 Old 06-24-2011, 11:08 AM Thread Starter
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brainstorming ...

The well known weak link on a 919 is the frame, swing arm, and suspension. The suspension is easily fixed with a rc51 fork swap and ohlins bits. Then the only short fall with the suspension is the lack of progressive linkage.

My questions are :
Has anyone swapped swingarms with a cbr and retained the linkage?
how would someone beef up the frame?

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post #2 of 14 Old 06-24-2011, 11:14 AM
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When you start delving into modifying the frame, etc structural components, you might as well buy a better base bike But, if you have the money and patience, the sky's the limit man!

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post #3 of 14 Old 06-24-2011, 11:24 AM
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Quote:
Originally Posted by Ferris Bueller View Post
The well known weak link on a 919 is the frame, swing arm, and suspension. The suspension is easily fixed with a rc51 fork swap and ohlins bits. Then the only short fall with the suspension is the lack of progressive linkage.

My questions are :
Has anyone swapped swingarms with a cbr and retained the linkage?
how would someone beef up the frame?
The nonsense about the 919 frame is that and nothing else but.
I have 2000 km of track time on my 919.
The frame is more than adequate for street tires on the track, case closed.
What needs improvement is the suspension components if the bike is going to be pushed and the rider wants some predictable chassis margin.
Even the swing arm is OK, the pogoing is squat and shock related.
The swing arm angle is too flat.
So with an aftermarket shock you can lengthen it , which does two things.
You reduce the net squat force and reduce the force needed to get the bike leaned over. (raise the front too)
There's a Brit on the site that grafted a linked swingarm on, can't remember the details but it can be done - but you lose being able to use the Y tube so must go to a side mount 4:1.
A prepped 919 front end or prepped F4i front end will be better than a stock RC51 front end.
A prepped RC51 front end will be better yet.
The 919 front end is adequately stiff.

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post #4 of 14 Old 06-24-2011, 11:27 AM
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Stupid question of the day...
What exactly is a linked swingarm. If I am looking at a bike with/without a progressive linkage, what am I looking for? (Tried searching on google, but I just kept finding forums with people selling ATVs.)



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post #5 of 14 Old 06-24-2011, 11:35 AM
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found a pic. hope it helps.

hard for me to describe
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post #6 of 14 Old 06-24-2011, 11:36 AM
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Quote:
Originally Posted by crakerjac View Post
Stupid question of the day...
What exactly is a linked swingarm. If I am looking at a bike with/without a progressive linkage, what am I looking for? (Tried searching on google, but I just kept finding forums with people selling ATVs.)
It's a good question so don't feel badly asking about it.
A linked swing is one that has a multi pivot linkage arrangement between the end of the shock and the attachment point to the swingarm.
Past that it gets complicated but let it suffice to say that the chassis input energy can be more desireably "shaped" to allow better suspension system control.
A side effect of this, is that in ball park terms, the required spring rate is halved in comparison to a linked swing arm.

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post #7 of 14 Old 06-24-2011, 11:38 AM Thread Starter
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A linked suspension is one were the shock does not mount directly to the swing arm and frame like the 919 but rather uses linkage to connect the shock to the swing arm.

Mcromo - i have plans to do a gilles triple and ohlins rc51 forks, marcesini forged mag wheels and brembo cnc monoblocks. I already have an ohlins shock. Im short so raising the rear is not an option. With that stuff done, your saying i should be good?

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post #8 of 14 Old 06-24-2011, 12:02 PM
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Quote:
Originally Posted by Ferris Bueller View Post

Mcromo - i have plans to do a gilles triple and ohlins rc51 forks, marcesini forged mag wheels and brembo cnc monoblocks. I already have an ohlins shock. Im short so raising the rear is not an option. With that stuff done, your saying i should be good?
You've sketched out a real nice build. I also see you are prepared to spend some $, so I'm assuming the RC51 front end will be fully prepped and not just a simple graft. LDH/DK can take care of that, and ask them point blank if there is tangible benefit in retrofitting different low speed compression adjustment needles.

Having said all that, I have a question for you. How much Track Days/Nights do you plan on doing ?
IF you say "lots" and you expect to be at Intermediate or faster group pace, then I very strongly urge you to consider using a rear shock with length adjustment. Yes, one can get by without it, but the 919 responds very well to the chassis being raised overall, so if you can get lift capability, go for it. To be honest, with the rest of your build sheet in front of me, I can not fathom why you would not want an adjustable length 3 way shock for the rear. If you can't swing it now $ wise, perhaps down the road ?

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post #9 of 14 Old 06-24-2011, 12:50 PM Thread Starter
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Thanks for the info on the rear shock. Ill keep that in mind for when im "done" win my build and get bored. My track experience is limited but there are some sweet hidden roads here and i kill any ss rider that wants to ride along. So my ability to push the limits of the 919 is pretty good.

Btw, when i say ohlins rc51 fork i mean made by ohlins and not honda forks prepped by ohlins. I say, if your gonna go, go all out.

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post #10 of 14 Old 06-24-2011, 01:14 PM
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All that makes sense. Thanks for the input guys.

Basically, what I gather is that a linked swingarm takes less force to compress the spring (since there is more leverage) which allows the rear shock to be tuned better. Or something like that.



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post #11 of 14 Old 06-24-2011, 01:16 PM
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Quote:
Originally Posted by Ferris Bueller View Post
Thanks for the info on the rear shock. Ill keep that in mind for when im "done" win my build and get bored. My track experience is limited but there are some sweet hidden roads here and i kill any ss rider that wants to ride along. So my ability to push the limits of the 919 is pretty good.

Btw, when i say ohlins rc51 fork i mean made by ohlins and not honda forks prepped by ohlins. I say, if your gonna go, go all out.
A bondafide Ohlins front end and a, ah, fixed length 2 way rear ????

Do you already been riding on Ohlins rear ?

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post #12 of 14 Old 06-24-2011, 01:41 PM
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Quote:
Originally Posted by Ferris Bueller View Post
A linked suspension is one were the shock does not mount directly to the swing arm and frame like the 919 but rather uses linkage to connect the shock to the swing arm.

Mcromo - i have plans to do a gilles triple and ohlins rc51 forks, marcesini forged mag wheels and brembo cnc monoblocks. I already have an ohlins shock. Im short so raising the rear is not an option. With that stuff done, your saying i should be good?
ahhh...so my XR600R has a better rear suspension than my 919? lol

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post #13 of 14 Old 06-24-2011, 01:57 PM Thread Starter
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Quote:
Originally Posted by mcromo44 View Post
A bondafide Ohlins front end and a, ah, fixed length 2 way rear ????

Do you already been riding on Ohlins rear ?
Already have one ... even had room to mount the preload adjuster at the exhaust hanger point since i have a low mount system
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post #14 of 14 Old 06-24-2011, 03:00 PM
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Quote:
Originally Posted by Ferris Bueller View Post
Already have one ... even had room to mount the preload adjuster at the exhaust hanger point since i have a low mount system
OK, you scratch hard on the road.
I'm assuming you get on the gas hard after exits or from time to time on the straights.
You have the 1028 # per inch spring, but I don't know how much preload you have on it.
What is your Free Sag dimension ?
What gearing do you have ? What do you weigh before riding gear ?
How much shock stroke are you getting ? ( I have a zip tie on my shock shaft)

With an 1100 # spring on my Penske with 6 mm Free Sag, 17/45 gearing, standard shock length, and the Penske in its original 2 way configuration, I was consistently able to hit the bottom out snubber under extreme transitions and throttle. Closing down the hi speed adjuster helped, but not enough. (I have since remedied things). I'm 170 # before riding gear.

I have been wondering for some time now, whether the HO201 has got significantly more low speed compression damping force than the "standard" Penske one typically gets when buying for a 919.
Hence my question above to you.

I'm really looking forward to your comments, and arctic954 should be too.

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