Slightly offtopic - Crazy Girder on an R1

[sebatron]

http://thekneeslider.com/archives/2008/06/05/r1-with-girder-front-end-update/

just picked up my next (bobber) project , less forks (and it's an uncommon bike).
who's up for some homemade girders?

On a more serious note - Isn't it logical that the axle is in line with the steering head? The more I look at different bikes, the less I see where this is the case.

 

[VonYinzer]

Yes and no. Its all about rake and trail. If the math is right, itll be fine.
Check out the info here: http://dotheton.com/index.php?topic=12664.0

 

[sebatron]

Not to digress into one of my future problems, but... how the hell do i work out anything without being able to track down the original forks?
finding original trail, fork length and offset will be worse than finding a needle in a haystack so i won't be able to replicate the original setup.
is there any "magic numbers" for rake and trail as far as handling goes?

 

[VonYinzer]

What kind of bike is it? Any manual will have those numbers in the spec sheets, and if ya dont have a manual Im sure you can find the numbers online somewhere. Read through some of the info on that page. It explains a lot of the issues your talking about.

 

[sebatron]

doing a bit of field research at this point
the bike in question is a honda nv400 custom. if you anyone sees a manual, tell me.
i'm resorting to changing the front end over. either building up a girder, or getting one off another bike. i'll read this page thoroughly to see what i can come up with...
cheers von!

 

[crazypj]

Not to digress into one of my future problems, but... how the hell do i work out anything without being able to track down the original forks?
finding original trail, fork length and offset will be worse than finding a needle in a haystack so i won't be able to replicate the original setup.
is there any "magic numbers" for rake and trail as far as handling goes?

You have no need of original forks or even original 'numbers'
Of course there are 'standard' numbers for rake and trail, streetbikes are in the 3.5"~5" trail area with around 60degree head angle (+/- ~3deg)
Choppers with extended forks are shallow and trial bikes are steeper with trail in the 0~6" region
There is frequently more trail on choppers of poor/bad design (often 'show bikes)
Look 'cool (PHAT :) but often unrideable

PJ

 

[sebatron]

hey, didn't spot your reply PJ.
if anything i'll want it to handle better than original, and i'm not a fan of the ridiculously long fork look.
mental note taken (3.5-5" trail, ~60deg head angle)
turns out the chassis is pretty damn close to some vt's so i might be able to adapt some existing forks... but there's a vf1100 front end on ebay im watching keenly. the fatter front tyre, bigger tubes and twin 4-piston brakes look mighty appealing.

 

[Staffy]

There is a school of thought that says a properly set up dampened girder or springer design is superior to that of a telescopic, due to its ablity to operate without altering the wheelbase of the bike, especially on a rigid frame. That said, if it's not properly done it'll suck balls.

 

[crazypj]

hey, didn't spot your reply PJ.
if anything i'll want it to handle better than original, and i'm not a fan of the ridiculously long fork look.
mental note taken (3.5-5" trail, ~60deg head angle)
turns out the chassis is pretty damn close to some vt's so i might be able to adapt some existing forks... but there's a vf1100 front end on ebay im watching keenly. the fatter front tyre, bigger tubes and twin 4-piston brakes look mighty appealing.

Better is entirely subjective.
whats better for you may suck for me.
It depends on intended purpose.
With fatter tyre you will probably want less trail and slightly steeper head angle, makes steering lighter' but less stable at 'higher' speeds (over 40mph)
The extra wide girders look pretty ridiculous to me, probably based on Brittan's carbon fiber fork.
Machined from alloy, looks 'heavy' even if it isn't

PJ


went back and looked at pics then read information.
24degree angle will give 66 degrees from horizontal which is pretty steep.
Looks to have about 50~60mm trail which is going to make it pretty twitchy with that head angle.
They didn't do enough research into girder forks, different length links would give the trail they wanted and could be set up to make it more stable as they compress