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Author Topic: Bike question: Head stock angle-rake  (Read 3687 times)

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Offline rgn

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Bike question: Head stock angle-rake
« on: June 29, 2012, 08:50:24 PM »
I'm thinking about running a closed circuit road race machine (modified production?) next year here in Australia, but think the head angle on this bike will not be conducive to good stability on a loose surface at speed. 

What is the minimum angle some of you run.  I'm just wondering how the current crop of super-sport bikes handle-perform at around 24 degrees at which many of them are set oem.  This 87 FZR1000 is set at just under 24 degrees, it's wheel base, weight and general geometry is similar to a modern R6, but with 150rwhp. 

Would I be better off building something specific for the salt flats?  How much damage does the salt in general do to a motorcycle over a meeting?  I ask this because I have a bike that I would like to run in production, but don't want it ruined.  Cheers!
Ralph.




Offline maj

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Re: Bike question: Head stock angle-rake
« Reply #1 on: June 30, 2012, 04:29:12 AM »
I'm probably going to add some controversy to this thread
my LSR busa has a 5 deg rake
my 99 gix750 is std ,
guess which handles better on the salt esp in the wet or loose which seems more common than firm salt lately









Its the 750 , esp in the wet or loose salt or dirt
2010 at bubs it was about the only 200+ mph bike handling well and i'm pretty sure it was the steepest rake
Don't ask me why
just finished changing the busa frame back to a stock angle frame ,which is now biting me as the fairing is based around the rake   :-(

Salt will get into your wiring, ign, steering bearings, swingarm pivots, shock and forks ,and more , all can be reduced with prep and after salt care , silicone grease all non sealed connectors,pre grease everything that moves, and anytime you remove a bolt for any reason grease the thread before reassembly
Aussie salt is much more harsh on things than Bonneville , don't know if its due to the mine or just a different balance of salts , Aussie stuff is more crystalline whereas the Utah stuff is sort of softer
« Last Edit: June 30, 2012, 04:39:46 AM by maj »

Offline rgn

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Re: Bike question: Head stock angle-rake
« Reply #2 on: June 30, 2012, 10:35:42 AM »
Hey Maj, thanks for the insights.  I can probably increase the angle slightly by dropping the rear a couple of inches.  I hear you regarding the corrosive nature of salt, and will probably strip the bike completely afterwards, to clean and inspect.  The bike above is still waiting on finalisation of moulds for side fairings and belly pan, so will be a little more aerodynamic.

I saw a photo last night of guy called Greg Watters bike on the aussie site, both his rear tyre was trashed and the bike was caked with salt, what a mess!  it sounds like the aussies are planning a grass meet soon so may look into running in that later this year.

I'm guessing you pretty much through every thing you think you know out the window in this LSR caper, so will be interesting!

Any other input will be appreciated.  Thanks.

http://img.photobucket.com/albums/v378/maj750/P1000387.jpg

Offline maj

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Re: Bike question: Head stock angle-rake
« Reply #3 on: June 30, 2012, 05:15:16 PM »
Yep thats my tire
Omeo will not realy be grass, whats there is sparse and when mown short and removed then rolled its going to be more hardpacked clay with the root mass undistrubed , hopefully holding it together better
we may completely change this strategy once the first meet has been held and we see how it lasts and if the traction level can be inproved
With it currently underwater i'm pretty sure there will be little to mow anyway once dry

Offline Jon

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Re: Bike question: Head stock angle-rake
« Reply #4 on: June 30, 2012, 05:41:44 PM »
Tony Foale did some interesting tests on the effects of rake and trail.
His book has some explanations of why a steeper rake is less effected by surface irregularities.
I can scan and email the relevant pages if you want.

Thanks
jon
Underhouse Engineering
Luck = Opportunity + Preparation^3

Offline maj

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Re: Bike question: Head stock angle-rake
« Reply #5 on: June 30, 2012, 06:35:52 PM »
Yes please  :-D


Offline wobblywalrus

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Re: Bike question: Head stock angle-rake
« Reply #6 on: July 01, 2012, 11:33:49 PM »
Ralph, it can be easier to keep the rake the same and to change the steering stem offset to increase or decrease trail.   

Offline 1212FBGS

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Re: Bike question: Head stock angle-rake
« Reply #7 on: July 02, 2012, 08:41:57 PM »
leave it stock unless the tire contacts the exhaust or radiator when you slam it... if so, your better off raking the frame just enough for clearances... when you rake the frame you are effectively moving the cg rearwards... only change the offset in the clamps if you want busy or twitchy handlebars.... do not go beyond 30deg unless you want the front end to wander without steering input feel.... yes you can change the effective neck numbers by altering the front and rear ride heights but then you can throw the rest of the bikes geometry off.... if your worried about corrosion, dont take it
kent