Boxerworks.com

Can you replace the /5 long wheel base frame with a /7 frame? Can I bring with it the top and bottom yokes and keep the /5 headlight forks and drum brakes? I don't care about having the numbers match.

The short answer is yes. There may be differences in the brackets for mounting relays and such, under the tank. Why do you want to do this swap?

Tim has summed it up well.
Any telescopic R or K forks will fit onto any air-head frame.
Bearings are all the same, it's a "bolt-on" affair,
but trail #s may be affected (if marginally) depending upon the specific choices.

Tim Shepherd wrote:The short answer is yes. There may be differences in the brackets for mounting relays and such, under the tank. Why do you want to do this swap?

Isn't the /7 frame less prone to flex than the earlier frames? Double backbone, and additional lateral tube beneath the headstock?
I don't know for sure - just remembering stuff.

R65 Rob wrote:

Tim Shepherd wrote:The short answer is yes. There may be differences in the brackets for mounting relays and such, under the tank. Why do you want to do this swap?

Isn't the /7 frame less prone to flex than the earlier frames? Double backbone, and additional lateral tube beneath the headstock?
I don't know for sure - just remembering stuff.

You are correct, Rob. Add to that: the brackets for the front brake hose grommets.

I believe the newer frames are stiffer and all. That said, I can't feel the difference. I'm no great shakes as a rider but wish I was. In other words, I ride as sportingly as my ability allows me to do safely but I can't feel the difference in the frame.

Much more difference is felt by me in the riding position. On my Cafe Racer, there is a noticeable difference in the frame stiffness due to pretty extensive modifications. Still, I can't say if it's really made me faster. I can say that the position is more fun for me.

As an example of what I'm saying, right now, the newer, fatter, swing arm/drive shaft is off the Cafe Racer and in its place is an older skinny one with a solid shaft instead of the cush drive. What I feel is the solid shaft's more positive drive. I can't feel anything that I can honestly say is the difference between the beefier newer swing arm and the older model. I'm not saying there isn't a difference. I'm saying that at my level, I can't feel it. In the end, the large swing arm will have the solid shaft so I'll have the best of both worlds.

Chuey

The double back bone came out on the R90S and shortly after on all models. Don't feel bad Chuey, very few can feel the difference. Many make claims, but ....................

X-Helen Twowheels always said: "If it ain't stiff, it ain't worth a f#¢k"
She was not a motorcycle chassis designer, however ..

BMW's frame stiffening was a necessary response to the higher power output of the R90s & 100s.
Keep in mind that "what is felt" will be an entirely subjective response
that speaks as much or more to the sensitivity and skills of the rider
than to chassis performance and ability.
Without pushing some limits, differences "felt" by a rider may be quite subtle –
Turn up the power & / or speed a few notches,
and even the insensitive rider should "feel" ... something.

Or, try the Quick Lesson:
Ride a favorite and familiar wandering road briskly on an MC with a contemporary chassis,
and then return to ride that same road at the same speeds on an old airhead –
The positive evolution of chassis design will become quite obvious.
Try this with a 2007 R12S and then a 1978 R100 –
and you will be nothing less than AMAZED
at how much "work" it is to get that old bike 'round a corner !

vanzen@rockerboxer.com wrote:
Or, try the Quick Lesson:
Ride a favorite and familiar wandering road briskly on an MC with a contemporary chassis,
and then return to ride that same road at the same speeds on an old airhead –
The positive evolution of chassis design will become quite obvious.
Try this with a 2007 R12S and then a 1978 R100 –
and you will be nothing less than AMAZED
at how much "work" it is to get that old bike 'round a corner !

I did that about 10 years ago on a BMW test ride day. Then got on my favorite old R60/5 and rode home. I could not help feeling "What a POS." As a result I have not ridden anything "modern" since.

I love life in my wobbolly old underpowered world.

Even the difference between my '76 bike and my '83 and '84 bikes is surprising. Mostly, that is down to the clutch and transmission.

It is the rider that is the limiter on my bikes.

Did R90Ss come with the strengthened top tube? That would mean their frames were different than their contemporaries in the R90/6, etc., no?

Chuey