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Headshake at 170mph

Posted: Wed Mar 28, 2018 7:29 pm
by harky
On my first run over the Long Course I had intended to have a run to see what speed the bike could do as it was set up/geared.

But after this I decided to pack up and have a rethink:

Some will find this pretty funny and I do too NOW after a couple of days off the bike.

Still working to identify and resolve the problem.

Also I did EXACTLY the same speed - to the third decimal place - as the day before on the short course and all without any indications of a problem.

Re: Headshake at 170mph

Posted: Wed Mar 28, 2018 10:28 pm
by Stayt`ie
Steve, that made me giddy :shock: ,, you say you did the same speed on the short course, no problem,, were you off the throttle quicker and on the brakes harder and earlier, not as slow of a backoff as the long course ???

Re: Headshake at 170mph

Posted: Thu Mar 29, 2018 7:42 am
by harky
the bike shook last year when Dave B had a ride , ( 150mph ) i re set / checked head stem bearings , made laser front to rear wheel aligner , ( and now have a “ trammel “ that l use to rear wheel align to the swing arm shaft
Dave and i discussed the way we shut down , and seems i shut slower than him , we also think we sit differently, i tend to lay flat on the airbox and further forward ( we are similar weights )
My thinking at the moment is
remove the front wing tabs
remove the 40 kgs of lead from the front of the swingarm ( it is ridgid on the back )
steering damper is a busa ( with 15 w fork oil ——- so has more drag than normal —- oil is normally very light ,like sewing machine viscosity )
I have weighted the bike with me on it , and had 60 kgs bias to the rear —- not ideal
The bike has a std gen1 engine , and because i sit below the rear wheel ( plus other stuff ) is A
if i go back to rear suspension it will be have to be M
didn’t realise i hit the orange witch hat , dented my yoshi pipes —- bummer
oh and to answer your question
I always roll off the throttle , and use little or no rear braking ( it has hand rear brakes )

Re: Headshake at 170mph

Posted: Thu Mar 29, 2018 8:41 am
by Stayt`ie
yup, I think when we were talking on the lake I mentioned that it would have been interesting to see if you got back into the throttle and applied more rear brake would have made it behave,,

I don't think aero (at that speed) is the problem, could be if you were faired, but not naked, and its happening on decell,,

to me, it looks as thou the thing is "hunting" ,, what is the wheel bias(%) with you, then with Dave ?

Re: Headshake at 170mph

Posted: Thu Mar 29, 2018 9:21 am
by harky
my data shows i did give a surve of throttle during the event
i do remember letting the bars go “ light “ ie not fighting it and didn’t apply any rear brake ( something i might bo next time )
though i would be really pleased if i don’t experience that again
funny i remember there was a lot of noise in side the helmet
as previous stated i have a 60 kgs rear bias , Dave hasn’t sat on it when it’s on the scales
i did move forward and rear and the weight shift was very little , only a few kgs
Dave and i are within 2-3 kgs of each other , I am just a little taller,
So for the sake of argument, we are really not a lot different
We do sit differently
I am prepared to scrap this thing ,( and go on with my FF project ) but feel that it’s unfinished business
i will run it again next year
it was an ex Allan MORRISSION stunt bike ( look at utube ) so it’s history is dubious, and to see the front to rear wheel alignment
( with the lazer i made ) be very parallel was reassuring
i think that an A bike with steering limit if 30deg saved us from being SPAT off , i will never know , but recon i went from steering stop to stop

Re: Headshake at 170mph

Posted: Thu Mar 29, 2018 11:21 am
by Stayt`ie
in this game, especially with the 300+k bikes, any small weight difference makes a noticable difference, not so much on the naked, moreso faired :)

Re: Headshake at 170mph

Posted: Thu Mar 29, 2018 12:04 pm
by coffeesnobs
Damn that was a spooky ride. Did well to collect the cheap cone and not the expensive Tag Heuer timing beam beside it though!

That part of the 4 mile was pretty loose and cut-up by Wednesday, I know I had trouble finding a nice path through it and lost a couple of mph there every run. That would be the biggest difference between the long course and the short course speeds.

My 2 cents...
deceleration weight shift to the front caused it, some more throttle would have settled it down faster by moving the centre of gravity back and transferring weight off the front. More rear brake might have helped transfer some weight back too although on a rigid frame it won't do as much as a sprung rear "squat".

With so much extra weight in the back of the bike you are pretty much throwing a dart feathers first.

Stiffer front end will transfer more weight through the tyre, more rake will help it point straight and a stronger steering damper (not lighter) might help too.

Re: Headshake at 170mph

Posted: Sun Apr 01, 2018 11:44 am
by coffeesnobs
Thinking more... what about bar-end weights? You didn't mention if you had any.

Kawasaki released "ergo bars" for my street bike that were just 20mm higher at the ends (same inside mounting point so just a small angle change and they tripled the weight of the bar-ends to suit. Might be something else to consider?

Re: Headshake at 170mph

Posted: Sun Apr 01, 2018 3:30 pm
by harky
we get such a short time to test / adjust things it is hard to do changes

@ this stage
i will remove the swing arm weight
remove the “ tabs” on the front guard
remove the ram air intakes
re consider my front fork travel ( i have limited the travel to about 35mm bump from ride height )
steering dampering is confusing , some have little to non
others have a lot ?
mine is ( @ a guess 15/20% more than a std busa )
so that is undecided
there is more
my cooling @ the rear is not effective @ low speed ( the return run ) i had a water spray system setup but the pump failed
ho hum ! sometimes despite the best effort and prep ——- stuff doesn’t like the trip to the lake
so 11 months to get ready —— oh an an engine upgrade
as a man i once worked for said
there are 12 hours in the day and 12 hours in the night ——- @. 5.0clock just think you stated a new day , that worked for a while but i got really tired after a few new shifts

Re: Headshake at 170mph

Posted: Sun Apr 01, 2018 5:24 pm
by Stayt`ie
More rear brake might have helped transfer some weight back too although on a rigid frame it won't do as much as a sprung rear "squat".

beg to differ here,, on a rigid it will throw weight to the rear, similar to towing a rope behind a boat, pulls 'em straight,, however with sprung rear suspenshion, weight will be transferred to the front, :)

Re: Headshake at 170mph

Posted: Mon Apr 02, 2018 1:04 pm
by harky
the bar ends are something i hadn’t heard of , interesting, !

and your early comment about not hitting the other timing pod
I was a passenge .
I used to wonder how timing equipment was hit / damaged in the past and now i have a better idea !

in “ John Mc Guinness “ book. Built for Speed
he refers to the noise coming out of his helmet ( when he had a tank slipper )
I remember there being A LOT of noise in my helmet
and that’s were any comparison between he and I end !