/5 frame braces?

[robertklee]

These are for sale on ebay. What is the purpose of frame braces? Thanks.

:usa

[20774]

They're designed to stiffen the frame and minimize the "gummikow" nature of the BMW frame. I think Reg Pridmore ran these on the R90S superbike. Tony Foale likely has used these in his frame designs. I think vanzen on his Ol Cro thread was going to use braces like these.

[lbrackr756]

Unless you're planning on racing your scooter frame braces are not needed. These have to have attachment points welded on, too. Don't bother if you're just doing ordinary riding/touring.

Little Egypt Airheads
'66 R50/2
'80 R100RT
'65 Honda 305 Dream (resto project)

[vanzen]

They're designed to stiffen the frame and minimize the "gummikow" nature of the BMW frame. I think Reg Pridmore ran these on the R90S superbike. Tony Foale likely has used these in his frame designs. I think vanzen on his Ol Cro thread was going to use braces like these.

Udo Gietl designed a modified stock frame to qualify for use on the Butler-Smith R90Ss
to be raced in the AMA Superbike series.
This frame employed welded diagonal "frame bracing" –
as well as mono-shock rear suspension,
altered steering geometry,
a steering head that is plated on all sides with gussets,
and a yoke that connects the rear of the engine case to the frame.
The R90S Superbikes are not fitted with "bolt-on" side braces of any kind.

The success of the Butler Smith racing program,
prompted aftermarket suppliers to introduce facsimiles of this bracing that "bolted-on" to the consumer market.
"Bolt-on" was a necessary feature in order to allow engine removal for servicing,
as well as to simplify installation –
a structural and performance compromise.
Interestingly enough, San Jose once offered a "Superbike Replica Frame" that was quite faithful to the original R90S / Gietl design.

Tony Foale has spoken of the advantages of frame braces on a Type-247 frame
and is certainly a proponent of the handling benefits to be gained
with a frame that does not allow flex / distortion relative to the steering head and the swing-arm pivots.
He has built many gorgeous, functional, state-of-the-art one-up hand built frames for the old BMWs.
Tony is likely the world's premier authority regarding chassis dynamics ...
But he never used "bolt-on" frame braces.

The oLDCRo frame is a one-up design that incorporates diagonal bracing
directly from the top of the headstock to the swing-arm mounting locations
as well as other diagonal frame elements to compose a rigid, almost 'tetrahedron-al' structure.
These elements are a structural and integral part of the frame and certainly not "bolt-on"
(although the right side lower frame rails does, in fact, "bolt-on")

The braces pictured are either original, or a copy of a design marketed by San Jose and later by CC Products.
Actually, they are one of the better offerings of this type,
in that the specifics of the mounting system actually allows them to perform in a functional capacity.
To install them – conical mounting tabs will need to be welded to the frame in 4 places.

Tony Foale speaking of the Type-247 frame:
The main "weakness" of the BMW series /5 /6 /7 frames is in the area of the
SA pivot mounting. Side loads on the rear wheel will tend to make the
upright tubes holding said pivot move fore and aft.
This can largely be prevented by mounting a bracing tube on each side...
These tubes obviously need to be detachable for engine removal etc. and so
the detail of the fixing can be very important to the success of the mod...

[RoboRider]

I rode an R100CS and pushed it hard, scraping pegs on some corners. I was surprised at how much frame flex and wobble I got from this old 1980s machine. It was a great bike, but it could have benefitted from the stiffeners. I agree, if you ride and don't have issues, leave it alone. If you experience flex and wobble, add them.

[robertklee]

Thank you all for your responses. I'm old and slow and don't guess I need frame braces.

:usa

[mymindsok]

If you ride loaded you might need a set of braces.

I first noticed my bikes frame flexing while on my way to a rally with the bags loaded and some stuff strapped across the seat. Going through a clover leaf at speed was a real eye opener! When I tried the same turns on my buddies braced R-100, it was as solid as a rock and I became a believer!

You probably don't "need" any bracing but it sure has made my bikes a lot less nerve wracking and a lot more fun to ride!

[vanzen]

If you ride loaded you might need a set of braces.

I firstnoticed my bikes frame flexing while on my way to a rally with the bags loaded and some stuff strapped across the seat. Going through a clover leaf at speed was a real eye opener! When I trried the same turns on my buddies braced R-100, it was as solid as a rock and I became a believer! Y

ou probably don't "need" any bracing but it sure has made my bikes a lot less nerve wracking and a lot more fun to ride!

and they say braces are just for the speed-demons !
what you say is absolutely true, mymindsok !

I first noticed the gummikuh with the fitting of some sport compound tires & speeds.
Again, only 'worser' when that same set-up was loaded for a touring gig and at road speeds.
Tires just ain't what they used to be – i.e. hard as a rock and slippery as dog snot,
consequently, the frame takes up the slack.