Forum whore
Sure you can. Here are some racewinning dimensions.Originally Posted by Muciek
wheelbase 1200 mm
fork yokes offset 0 (yes, zero) mm
rake angle 16°
trail 90 mm
Concentrate all masses so that the center of gravity will be directly in front of your knees.
No8 Wire Extraordinaire
Whimper. 16. . , degrees?!?!
Please say its for Shopping trolley racing?
Don't you look at my accountant.
He's the only one I've got.
Forum whore
The decisive factor is the trail, not the rake angle. You can even have the same 90 mm trail with zero degrees of rake, but that would necessitate 90 mm offset in the fork yokes, which would place the total center of gravity of forks and front wheel 90 mm behind the steering axis.
I proposed 16° rake because that minimizes the offset, and with zero offset the steering inertia is also minimized, which is good for both swift steering and rider feedback.
Low personal B.M.E.P.
All good and correct, Frits but really only suitable for lightweight bikes - and riders...As the OP wanted.
But try that on anything heavier and you run into fork stiffness problems quite quickly.
Which leads us on to the land of funny front ends......
Highway Biker
Thanks Frits for all the info.I'm not so lightweight, with protective gear it's bit over 90kg. Any tips on rear shocks ? Bike should have around 30hp (125cc rotary valve).
Forum whore
Grumph, would you care to define lightweight? Below there's a picture of a friend of mine, next to a normal human being (me).
He tips the scales at well over 100 kg and he is a multiple 50 cc champion in the German SimsonGP series. The frame dimensions I quoted above went into this bike.
PS: I love funny front ends.
Wenever I feel the need to take my mind off two-stroke development for a moment, I start sketching hub-centre front ends, lateral suspension, etc.
Anorak
People are more aware of very small differences in Trail than even notice rather large differences in rake.
(Paraphrased Foale)
There is some good oil in his book even your example is castor based
Kinky is using a feather. Perverted is using the whole chicken
Hardcore Biker
Chris Cosentino started off with near zero rake with offset for trail with a Hossack/Fior FFE on his first Rotacular single (600+ Rotax) and later went to around 16 degrees with zero offset. He's using something around the latter for his Moto2 project.
http://moto2-usa.blogspot.com/
Unfortunately the daily grind doesn't seem to be providing enough extra cash and time to do anything on the V4 recently.
cheers,
Michael
Low personal B.M.E.P.
Define lightweight ? Well Frits, my daily bread is earned working on engines for big Post Classics which alone weigh more than that bike pictured...
Given also the limitations of correct period forks stuck on the front of said big mutha motors, fork stiffness is a subject of which I have considerable empirical knowledge...Oh, and the forks on that bike are lovely - much better than I'm used to working with.
I'm well aware that those dimensions given will work, but feel no driving need to transfer them to the big lounge chairs I work with.
I worked with John Britten (briefly...) and have no desire to go anywhere near a funny front end for the rest of my life thanks....
No8 Wire Extraordinaire
I have to admit to being stuck in the mud, my experiments from early age really amount to dropping the front through the clamps until it started to self steer when leant over & then back a tad. I didn't have different offset clamps so found 23 deg was good. but I was also messing around with too long a wheel base but it was real short on the dyno so figured it must be ok. but was aware that I was really having to spang it far over when other bikes seemed to steer much shorter turning circle. too stupid to do anything about it, but I'm done now. I've won multiple NZ 50cc titles but clearly we're backwater compared to Europe. At 80kg I was always too big for a 50 racer. . . . but now I feel kind of inadequate.
Don't you look at my accountant.
He's the only one I've got.
Forum whore
I wish I had. We met in Italy in 1992 and I liked many of his views. But although the Hossack front end that he used does have some advantages over telescopics,
I would prefer a different solution: hub-centre or four-bar steering.
Muddler/Dabbler.
Trouble is, the good old telefork works (bit like poppet valves) they don't tick all the boxes but they work day in, day out, without a murmur! The hub centre jobs and the Hossack style are probably fine but susceptible to damage (small bent tubes etc.) which if damaged would knock the machine's ability to steer properly and are not really suitable for enconomic mass production.
And,......Let's face it, whatever they say, carbon fibre can shatter!
Or something like that! - I think.
Strokers Galore!
Low personal B.M.E.P.
Talk to Wob when you meet up. His experiences were much later on than mine - I was in there very early but the rot was visible then.
There's supposed to be a Britten "public teardown" at the ChCh art gallery today or tomorrow. Don't know who's doing it - but I probably know them.
Almost tempted to go and sit in the front row and ask awkward questions.....
Low personal B.M.E.P.
It was well known in the race crowd here that JB had repaired at least one Carbon fiber wheel...And,......Let's face it, whatever they say, carbon fibre can shatter!
Or something like that! - I think.
It came up in discussion with Hans VonDer Marwitz (spelling sorry ) when a bunch of us sat for the FIM Tech Steward tickets under him.
As an active scrutineer who saw the bikes on a regular basis I was forthright when the IOM came up also.
I reckoned I'd have asked for all the Britten wheels - bare - inspected and marked them.
I'd have asked the team to log which rims were used each session - and asked marshals to observe any curb climbing incidents and report them.
As it turned out rims were the least of their troubles.
Forum whore
I need all the help I can get so as me and Mr.JS were building up another FXR we have decided to go with these numbers J has cut and re-welded the steering head to steepen up the rake and we are just working out how much to chop out of the swinging arm. We measured J's bike and it is 1230 with work having been done to shorten the swinging arm so I reckon we can get close
There are currently 2 users browsing this thread. (0 members and 2 guests)
Posting Permissions
Reply With Quote
Bookmarks