919 Frame Flex - Wrist Twisters
 
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post #1 of 11 Old 06-04-2006, 09:55 PM
roktbox
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919 Frame Flex

Took the Niner up into some of my favorite mountain roads (Hwy 47 - NW Oregon) on Saturday morning, got to the "GO BABY!" point, commenced to the thrashing and immediately thought something was out of sorts. I felt like a kid at the dance that can't, so he just throws himself all over and hopes he doesn't poke his date's eye out. WTF?!!

Oh, yea. I'd just done a trackday Tuesday on the Gix (heresy I know, but ..) and it took a few turns to remember, "Don't be alarmed, folks. Just sit down, relax, and enjoy the ride." Felt like a dadgum waterbed, man. All the posts LDH has made re: frame flex .... now I know, now I know! I think I'll rename her The Goose.

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post #2 of 11 Old 06-05-2006, 06:39 AM
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Now that I've had several thousand miles to get to know the 9er, I have started pushing her a little harder with the Pilot Powers. While riding yesterday I noticed that it sometimes feels "squirrely" coming out of turns when on the gas. Didn't really notice it before. Running rear tire at 38lbs.

Is this the notorious frame flex I've read so much about?

It's a fool who looks for logic in the chambers of the human heart.
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post #3 of 11 Old 06-05-2006, 07:18 AM
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I havent heard about frame flex on these bikes.. I have however heard a lot about the suspension getting a bit wallowy in riden very hard thru the twisties..

Mitch
'83 Suzuki GS750E
'02 Honda 919
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post #4 of 11 Old 06-05-2006, 09:46 AM
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The suspension is crap on the 919 & the flexi-frame plus the lack of braced swingarm all add up to the problem, but if you are riding around with 38psi in your rear tire then you aren't anywhere even remotely close to a pace that will tax the inherent weaknesses of the 919 anyway...

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post #5 of 11 Old 06-05-2006, 10:07 AM
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Quote:
Originally Posted by Lord Duckhunter
The suspension is crap on the 919 & the flexi-frame plus the lack of braced swingarm all add up to the problem, but if you are riding around with 38psi in your rear tire then you aren't anywhere even remotely close to a pace that will tax the inherent weaknesses of the 919 anyway...
What would you recommend as tire pressure for finding the flex? Of course translate that into a streetable range. I read one of your posts talking about 30 psi and by the time they warm up you would be fine. Is this good on the street?

post #6 of 11 Old 06-05-2006, 12:10 PM
 
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what would be recommended tire pressure for a track day?

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post #7 of 11 Old 06-05-2006, 12:19 PM
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I think it depends slightly on the brand of tire, but I set the cold pressure on Dunlop 208GP's around 28 front / 29 rear and then check them immediately after exiting the track. Depending on the ambient temps, I would expect to see about 3 psi gain or maybe a bit more if it's hot out. If you do do a trackday there will most likely be a tire vendor on site and you might ask them or one of the instructors. Walk the pits and see who's running your tire and ask those guys as well. Anyone else?

post #8 of 11 Old 06-05-2006, 12:21 PM
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First off tire pressure alone is not going to find the limits of your bikes chassis. You've got to be able to ride the bike semi-proficiently to do that.

& if you are riding around at 38psi in your rear tire then you are sliding more because of the tire than the chassis or suspension I guarantee it & you are limiting how hard you can push the bike due to that slippage.

There is no magic one size fits all tire pressure setting, but most tires except Diablo's & Power Race's are pretty good around 30-35psi Rear & 32 Front street or track for most riders. There are some that need to be custom tailored more or less to the individual tire, but that is less important for street riding. As a street tire you want a tire that is running a reasonably lower pressure say 34-36psi in thee rear & about 32 in the front this will give you a more complaint ride & more grip.

Track needs are different as a couple psi too high or too low can drastically alter the tires wear rates and/or handling especially since many times the tires are not given sufficient time to get up to proper operating temp when the rider first gets on the track because nobody wants to waste 5-10 minutes of the 20 minute session getting the tires up to temp. Track pressures are typically a couple pounds lower than I have described above for street tires.

Street tires as a whole are less susceptible to problems from too little or too much air pressure while DOT race tires are very sensitive to pressures.

http://www.919.org/tires.htm

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post #9 of 11 Old 06-05-2006, 07:57 PM
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Aha..
Thanks for that pressure info LDH.
I've seen other posts you've made commenting on pressure choices and had poured over your 919.org site for just this info.
(by the way, been meaning to offer a huge thanks for the info you've made available on your site plus in this forum and others, been very helpful, cheers)

I've been aware for some time that the pressures stated on the bike and in the owners manual were for max load etc, but wasn't sure just how low was more appropriate. Cheers for that.

Now I'm off to get me a decent tyre guage.

Sorry for the slightly off topic reply.

post #10 of 11 Old 06-06-2006, 07:38 PM
 
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The 919 is a fun "street" bike but it has its limits....

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post #11 of 11 Old 06-06-2006, 07:44 PM
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Quote:
Originally Posted by DrSardonicus
The 919 is a fun "street" bike but it has its limits....
And you certainly know them Dr. Sard.

It's a fool who looks for logic in the chambers of the human heart.
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