Unsprung weight

Stolen from MC-Chassis-design email list - practical example of
reducing unsprung mass - 4 seconds a lap !!

"This is lifted from the Burge racing website - the brothers who have
been
running Norman Hossack's original Yamaha chassis (number 3?) for the
last
few seasons

http://www.members.aol.com/arcticla/index.html
"I rebuilt my Harris Rotax for the 2004 ACU Supermono Series, fitting
new
exhausts and generally tidying and rationalising a few bits and pieces.

I had some problems at the first rounds at Pembrey, where I crashed out
of
the second race. Otherwise I've finished every race and had a great
season.

I've been pondering the whole Supermono v Minimono question for a long
time
and considering whether, because the current minimum weight limit of
95kg,
there's a middle way? So, by way of experiment I decided to run GP125
sized
wheels on my Harris to see what would happen.

Big investment? Not really. I was able to take the 3.5" rim off my
front
Astralite and mate it to the existing rear hub. Then I dusted off the
complete TZR front end from my 250 single racer, together with it's
lighter
forks and single 300mm disk.


The result? An instant 4s reduction in lap times at Castle Combe and
Cadwell!! Who says performance costs money?! The bike was very light
steering and nimble and I could run and turn into corners sooo much
later.
The reduction in weight and reciprocating mass made a big difference to

acceleration and braking too. I moved up from 8th to 4th in the
air-cooled
series in those two meetings and now seem to be running with a whole
different group of people. I'd say that was a successful experiment and
a
great way of making a 14 year old bike competitive. "

 

The last line sums it up.

 

If you're implying it was because he put new tech on an old bike, not
true. The 125 kit in question was of the same vintage as the original
rims and front end (I think the "dusted off the complete TZR front end"
sums it up well).

In short, lighter sprung components made it quicker - not just power to
weight (although taking 5Kg off a 100Kg bike isn't trivial) but it also
gave him better cornering

JL

 

The great thing about Hammo's almost indecipherable vagueness is that it
almost certainly never means what you think it means, unless that's what you
think it means. Win-win situation every time.

Nev..
'03 ZX12R

 

<chuckle> Yeah, OK. True, it could mean anything.

JL

 

not a racetrack.. was IoM

Nev..
'03 ZX12R

 

Ahh, OK then, apology accepted.

<wanders off whistling in blithe ignorance of any sarcasm>

JL

 

Geez they're clever buggers these pommies, moving a whole island to the
midlands - impressive.

JL
(caldwell and mallory park actually)

 

No Clem, click the link, not IOM.

There are people far better qualified to comment than me, but 4secs a
lap on the average track generally means you're going a lot faster,
doesn't it ? The funny thing is this is on a bike at an equivalent level
to the ones you say are all you need because it's max capability isn't
particularly high...so this is something you could do in the real world
and get more capability on a bike where you'd notice it.

Err nothing, he pulled the spare bits out of the back shed and dusted
them off...

JL
(and even if he'd bought them, the answer would still be not very much -
how much do you reckon a pair of 15 yr old TZR125 rims go for ?)

 

If you really need them, I'd say $800 each?

If you don't, you could probably get them for nothing......

Moike

 

X-No-archive: yes

Yeah they're under that pile of TRX850 brake callipers!

 

Never owned one myself, don't imagine they sold many here - but I'll
bet there'll be shitloads in the UK where learners have to have 125s
and the OP is located

;-P

JL