This is how Ducati single-sided swing arms work. The stress on the axle is
actually light--it's all tension instead of some shear because the spacers
(when it's all set up correctly) put the load onto the bearings. If you
leave out the spacer or set the preload incorrectly the axle breaks.
Believe me--I know. I did it wrong once. Didn't die, so it's a lesson, eh?
Right now the Triumph design is a bit goofy, placing all the bending
stress on the axle. It's just like the Ducati without spacers, except the
part is designed to handle the stress of street driving. If all you people
would just slow down you wouldn't have any problems.
Someone would have to do a more complete analysis, but it's not always
true that when you eliminate a problem in one place that it crops up
elsewhere. Replacing a weak link in a strong chain can raise the breaking
point way beyond any likely stress. I suspect we'll find this mod is like
that. I don't see any other weak links except the hub, and we have two
very pretty solutions for that. Which reminds me, I met the folks that do
the other hub that's in Kas' book--they were at the All British Field
Meet/Columbia River Classic with one copy of the book in their booth.
Kas--you should have seen the interest. I bet they could have sold five
hundred copies right there. The Southwick hubs look very nice, but theirs
are frankly nicer. You can kind of tell that in the book. They don't have
a TR3/4/6 version but will make them as soon as they get hold of an axle
and upright. They had a Spitfire in their booth that probably makes 200HP.
Totally outlaw of course--it has Mikuni flat-slide carbs and a bunch of
goodies.
-----Original Message-----
From: Tony Drews [mailto:tony@tonydrews.com]
Sent: Friday, September 05, 2003 1:56 PM
To: FOT@autox.team.net
Cc: fot@autox.team.net
Subject: Re: Fix for TR brakes
Scott, that's a VERY interesting question! Thinking through how this
works, I'm reasoning that it may actually make it less likely to break off
the stub axle. I hope I'm right since I'm running a set of these and I
already rolled one car at Road America... (where I'm going in a couple of
weeks) Please correct me if I'm wrong - here goes my analysis of why this
works...
The inner wheel bearing inner race butts up against the upright that the
stub axle bolts through.
The new part butts up against the inner wheel bearing inner race as well
as
up against the outer wheel bearing inner race.
What this should do is take some of the forces normally applied to the
stub
axle and transfer them to the upright through the very hard inner bearing
inner race.
This will increase the tension forces on the stub axle but decrease the
bending moment that the axle sees. I strongly suspect that the bending
forces are much more likely to break the stub axle than tension forces
are. What I have found is that if I run the bearings with a bit of
preload, all
of the deflection disappears. If I put the couple of thousanths of free
play that I'm more comfortable with there's some deflection but it's
better
than it was.
- Tony Drews
At 09:39 AM 9/5/2003, Barr, Scott wrote:
>Any chance stiffening the stub axle in this way moves the forces around
>in a way which might cause them to start breaking off?
>
>Scott
|