Shortening front forks.

I saw Stroud race the Britten at Daytona and Laguna Seca in 1994.

It was an awesome piece of machinery that gobbled up other motorcycles
like Pac-Man gobbling yellow dots...

 

You'd have to adapt a smaller diameter scooter wheel (maybe a 12~14
incher) to any motorcycle fork that you might find.

The typical small motorcycle front wheel just wouldn't fit under the
front "fender" of an NZeta...

http://en.wikipedia.org/wiki/Čezeta

 

Nothing on the NZ market that I can afford suits - anyway, I have fond
memories
of the scooter ...

I live rurally beside State Highway 1 so _anything_ I buy has to do 60mph
inside 30 seconds or I'm toast. Sure, I can ride a 2 wheel bicycle or a
scooter.

 

The original wheel is sufficient - 12" and there's just room for
two yokes below the head. Machining up yokes is not a problem
and gives me the chance to increase the trail. (curreently 75mm/3")
Modifying other forks would make fitting a disk brake easy.

Didn't think of Wikipaedia, must have a look!

 

I worked with John on the follow-up motor. Sadly he went and died of
cancer before it was built. Seems to have reappeared on the Chch
"jetpack" flying thingy, but I wasn't part of that.
Did put a bit of thought into the V twin but there wasn't much more bhp to
be had.

Greg.P.

 

"fender"? is that like "mudguard" or "front bumper"?
The dividing line is the chrome strip - petrol tank above, metal below
is frame. (well, upright sheet metal, rolled bottom edge, "L" top edge)
There's 6"/150mm of wheel travel and still several inches of extra space.

 

(Thanks for the marque name, interesting photos here and there on the
web. I've never seen a Cezeta/Nzeta in person but it reminds of a number
of Euro scoots from that era.) I was wondering if you'd have to change
rake and therefore trail, maybe better high-speed stability is what you
have in mind but personally I wouldn't want to change the low-speed
behaviour. If the main goal is stronger braking, an alternative might
be to consider beefing up the stock forks to mount a disc and caliper,
maybe similar to the way the leading-link Ural models do it, plus
possibly heavier shock and spring since they probably need replacement
anyway.

 

It's not a good idea to try going faster than about 50 mph on a
scooter with moderate sized wheels, because the diameter of the tire
not only affects handling, it affects ride quality and traction as the
tire rolls over tiny bumps in the pavement.

Some of the larger scooters have gone to 18-inch wheels to manage the
bump problem.

 

More nonsense. Ever ridden any of the new generation of super-scoots?
No, thought not. I rode a 400 Burgman a couple of years ago. Opened my
mind. Damn thing did over 90 and handled really well.

And if you think about it (which you don't) your complaint would apply
to every single bike with (say) wheels of 16" or less, not just
scooters.

And some go just fine on smaller ones. And in any case, the real problem
with smaller wheels is the twitchiness of them.

You know nothing.

 

You prove that you know less every time you challenge an obvious fact.

 

Nope, sweetie-pie. Wrong again.

 

It doesn't matter how much you beg, I'm not going to explain the
effects of
vibrational frequency on traction as regards rubber tires beyond
saying that, when the vibration stops, you're about to crash.

 

Right. So all small-wheeled bikes are dangerous.

Do you have a minimum size that you consider to be safe? If so, what? We
need to know.

 

Who's this "we" you're referring to? Are you in bed with Spacker
again?

 

I think changing the rake would be more than I'm prepared to attempt,
given that it's set by and within the body structure. It shouldn't be
hard to increase the trail a fraction. (it's 75mm/3") Either making new
and extended leading links or triple plates if I go with alternative
front forks.

The "Y" fork structure might be rigid enough, but I'm only going to find
out at the worst possible moments! The standard spring/damper units are
simply CZ long travel rear spring/damper units and presumably will
be long past their prime.

Greg.P.

 

My NZeta in the 1960s was quite stable at up to around 70mph.
(down-hill, tailwind and prayer ;-)
That's really (one of) the reasons I'm interested in rebuilding one.
PS handbook claimed 59mph top speed (95km/hr) and I regularly achieved
65mph on the speedo. (eventually)
The upside down bathtub structure is/was extremely rigid and the
long-travel suspension handled local conditions very well.

 

I've ridden may bikes with much worse handling than the NZeta scooter,
eg Harleys, worn Nortons, Triumphs ...

Greg.P.

 

27" rims are generally safe!
;-)


- Bigger wheels don't fall into big pot-holes as badly as small ones.
- Smaller wheels give better acceleration. ;-)
- Smaller wheels have less gyroscopic effect. (rider/bike stability)
most other effects relate more to suspension than size.

Greg.P.

 

Modern sportbikes have tires with an outer diameter of 22 to 25
inches, anything smaller will lose traction on all but billiard-smooth
pavement and anything larger than 25 inch diameter will out-track
badly when the rider tries to turn into a corner.

I got heavy into this business several years ago and was the OP that
started this thread.

http://groups.google.com/group/alt....&lnk=gst&q="good+vibrations"#6476145991efd6f5

I got into the vibration problem in the first message and went on to a
study of spring preload and how to adjust sag to avoid hobby-horsing
over bumps at the desired cruising speed.

 

That would be a matter of suspension rather than tyre diameter. (down to a
point where the radius is greater than about 1/3rd the depth of ruts,
holes and corrugations)
A lighter wheel can obviously follow irregularities quicker than a heavier
wheel. (sprung vs unsprung weight)


and anything larger than 25 inch diameter will out-track
badly when the rider tries to turn into a corner.

Is there something magic about 25"?

"Hobby-horsing"? (rebound(?))
(Sorry, possible language problem there)

Have you considered damping rates???

Regards,
Greg.P.