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Girdraulic vs girder - "B" vs "C" RFM - Handing issues

Spqreddie

Well Known and Active Forum Website User
VOC Member
Dear All, probably this has already been discussed in the past, therefore fell free to delete this post and address me to an older one,

but I would like to ask you if you think there is any sensible difference in handling between the B and C Rfm,
I', rebuilding my "B" Rapide with a C RFM and Girdraulic forks.

For the bike to be period correct, I would need a "B" RFM. If I eventually find one, could I still use it with the girdraulic at the font? I understand the difference being only 1/2 inch in length (a part from the seat stays and brake cable abutment) so it should be imperceptible to the average rider, right? Being shorter might even help cornering, while only slightly worsening high speed stability.
Any counter indication then for mixing B RFM and Girdraulic at the front? How different is the girder geometry from the girdraulic? In Know Thy Beast, I’ve found figures for the RFM but no
reference or drawing for girder vs girdraulic dimensions. In Richardson book, there are some figures for the Girder, but nothing on girdraulic. Somebody knows which the differences are (if there are) in terms of steering angle degrees and dimensions? There are any drawings with figures for B and C series cycle dimensions and geometry?

I've also understood that many still prefer the girder as lighter and it remains a bit lower than the girdraulic, right?
Any problem in mixing B and C cycle component?

Thanks!
Eddie
 
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vibrac

Well Known and Active Forum Website User
VOC Member
I have the best of all worlds on the alphabet twin
B forks C frame D engine
Girdralics are hard, they dont bend
Bramptons are hard to beat, on bends
 

davidd

Well Known and Active Forum Website User
VOC Member
Edmondo,

Yes, you can mix and match without creating a monster. I use a B RFM on the racer to get the shorter wheelbase.

In the post on Comet Suspension, which I am sure you remember, the was quite a discussion on why the stock Bramptons appear to work better than the stock Girdraulic. I think that with the use of the 14" spring or Rob Staley's springs, that the Girdraulic can be far superior. This is mostly due to ecellent damping being easily available for the Girdraulic while there is no hydraulic damping that is easily available for the Brampton.

Tim is correct, but for the Brampton I think you have to say "smooth bends." I have two friends that ride their B's several times a week and they have both complained to me separately in the las two weeks that they are really taking a beating due to rough roads. So, it depends a little on the conditions you are driving in.

I also think that it has been stated here that the Girdraulic is lighter in weight than the girder, but if the Grirdraulic is not sprung correctly it can feel quite wooden, so it is probably fair to say the handling of the Brampton is lighter.

Finally, many Brampton forks are corroding from the inside. I have crushed tubes on two forks with just my fingers. I do not think the fork as a unit will fail, but it is something to keep in mind when weighing the "pros" and "cons."

David
 

Albervin

Well Known and Active Forum Website User
VOC Member
David has summed it up quite well. I know of many mix and match combinations and I think Vincent was smart enough to make every "improvement" able to be retrofitted. I had a C RFM on my B Rapide with girders for ages and no problem. Fitting a B RFM was NOT a simple case of swapping over the two. There is a B RFM on UK e-bay at the moment but it is not cheap!! With a modified coil over damper front end and a 21" front wheel I prefer my B over my A and C on any road. The only real advantage of a B rear end on a B bike is the look (for the average rider) as I still have a modern tyre that fits without rubbing anything. As I said swapping over is not simple; new mudguards and chain guard is just the beginning unless you weld the old holes in the mudguard and do some cutting and welding on the chainguard. Make sure you start with a good handful of shims too.
 

Diogenes

Well Known and Active Forum Website User
Non-VOC Member
"How different is the girder geometry from the girdraulic? In Know Thy Beast, I’ve found figures for the RFM but no
reference or drawing for girder vs girdraulic dimensions. In Richardson book, there are some figures for the Girder, but nothing on girdraulic. Somebody knows which the differences are (if there are) in terms of steering angle degrees and dimensions? There are any drawings with figures for B and C series cycle dimensions and geometry?"

A fairly comprehensive set of graphs and dimension tables for A/B/C/D front suspension movements, solo and sidecar, is given in

http://groups.yahoo.com/neo/groups/frontforks/files

That YAHOO Group is primarily a source of data, rather than a discussion forum.
 
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