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Post by jdbrees on Jul 4, 2008 8:48:08 GMT -5
This is interesting. I would not have thought rebound/compression parameters of the rear wheel would contribute to violent lock-to-lock oscillations of the front wheel (tank slap). I will confess nearly complete ignorance about motorcycle chassis geometry and how it affects handling. I suspect I'm not the only one on the forum that would appreciate an education on this subject from those here in a position to know  . While the shorter clip-on or clubman handle bars aren't the cause of tank slappers, their lack of mechanical leverage (as compaired to standard width handle bars) must certainly make it more difficult to regain control of the front end. |
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Post by StewRoss on Jul 4, 2008 19:42:06 GMT -5
I've had clip-ons torn from my hands several times on several different types of bikes including the SR500, but I always grab them very quickly again while they're moving around. Doesn't do much for the thumbs though...  It often occurs through bumpy corners under power or in one case on an unexpectedly bumpy straight...sure gets your attention!  The ZXR750 used be prone to it at times and we were able to fix it up by a judicious tightening of the head stem bearings...but a damper would certainly have assisted... There's a good video clip of a guy on a black Fireblade at the IOM. It started off as he crested a rise and rapidly got worse. It ended up with him being visciously spat off. I have come pretty close to that myself over the years! Main thing about suspension in my opinion is to have it balanced front to rear...we used to test the suspension on our MX bikes by pushing down on the place where you sat and the front and rear should go down pretty well together, not the easiest thing to do on a road bike I agree...suspension that favours either end or badly set damping can cause handling difficulties...hard rear will make the bike kick up at the back...opposite at the front. Balanced and it rides over the bumps evenly. Damping changes control the speed either way depending on the complexity of your suspension. The SR as standard has fairly soft suspension which is fine for normal type riding...but if you start to push it you'll notice that it has it's limitations. The front is very basic and can need some re-work if you want to get the best out of it. Better quality shocks at the rear matched to stiffer springs and possibly damping or oil weight changes at the front will improve the SR no end. Something like Ikon shocks with their 3 position rebound damping adjustment or more expensive options depending on your purse are a good investment. Ask Rick (Wizz954) about his modifications. He's done his for racing but the general idea applies. Other modifcations such as frame and swing arm modifcations are also possible but are not often required on the road bikes...depends a lot on your outlook and how much playing around you wish to do. I am still fitting a steering damper to one or two of my SRs eventually for quick riding regardless. Call it insurance. Just a few ideas for you. SR  |
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Post by manxman on Jul 4, 2008 22:32:21 GMT -5
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Post by jdbrees on Jul 5, 2008 9:40:26 GMT -5
Some of these side mounted linear dampers look like they could really cause serious leg damage in the case of a spill  . |
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Post by manxman on Jul 5, 2008 10:52:30 GMT -5
Some of these side mounted linear dampers look like they could really cause serious leg damage in the case of a spill . Rubber side down, shiney side up |
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pcnsd
Full Member
Posts: 113
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Post by pcnsd on Jul 5, 2008 11:51:03 GMT -5
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Post by jdbrees on Jul 6, 2008 0:08:17 GMT -5
Thanks for the great links PC, although when I read "The effect that the design characteristics of a bike have on these instabilities can be investigated by examining the eigenvalues of the linearized equations of motion" I was reminded of the saying "be careful what you ask for" ;D. Seriously though, there was a lot of good information there. When I think about it I can't decide whether I'm more amazed that through trial and error, average Joe racers have found solutions to handling problems, or that the engineers have found the mathematics to describe the complex relationships and interactions of two wheeled dynamics. Either way, they both deserve a tip of the hat! While the Wickpedia entry suggests a few general ways chassis design and setup can influence "instability" it seems to me the gist of it is that on any particular modern motorcycle, given the right circumstances (chassis, speed, road irregularities, etc) a harmonic feedback loop (tank slapper) will occur with a mathematical certainty........ . |
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Post by joneill4 on Jul 7, 2008 11:26:47 GMT -5
I have always been fighting head shake on my SR. Not tank slapping mind you. I recently got a pair of springs from ebay. When I went to install the I realized that I did not have stock shocks. They are from FML made in USA with 2 piece springs. The previous owner had the preload jacked up to the max. When I put the new springs on, I left the preload at the lowest setting. The head shake is gone. I do bottom from time to time, and I could probably find an adjustment with no shake and no bottoming.
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Post by jdbrees on Jul 7, 2008 13:14:04 GMT -5
The previous owner of my SR had progressive rate fork springs installed. I am not bottoming, but I feel there is too much dive when braking. I suspect heavier oil would improve the diving, but I need to learn more about suspension tuning and diagnosis before I start changing things. Glad to hear you got yours sorted out.
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Post by joneill4 on Jul 10, 2008 18:42:01 GMT -5
Hey Jerry, I recently changed the fork oil also. The manual calls for 182ccs of oil. I got about 160ccs out and I put 190ccs back in. I had huge dive problems that seemed to get a lot better. Its an easy job, so don't be afraid of it. The biggest problem is that fork oil costs $13/ quart.
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Post by blacksmithjk on Jul 18, 2008 17:43:26 GMT -5
Manxman I have a question on measurement on the fine mount you show for the frame end of the steering damper. Can you give me a distance out from the frame on the main pillar? It looks to me like two to three inches but something more on target could be a lot of help as I am looking at fabricating a similar mount out of a solid block as I do not have Al welding resources.
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The ZXR750 used be prone to it at times and we were able to fix it up by a judicious tightening of the head stem bearings...but a damper would certainly have assisted...
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