Rear shocks on a 1979 R100 RT

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Major Softie
Posts: 8900
Joined: Tue Aug 03, 2010 1:46 pm

Re: Rear shocks on a 1979 R100 RT

Post by Major Softie »

khittner1 wrote:Interesting point about the shock travel comparison. I don't remember enough of my geometry and/or trigonometry to compute this myself, but there's at least a little bit involved in converting the shock's compressibility to a "suspension travel" figure at the axle. My Haynes manual agrees with Garnet that the /7 bikes had rear suspension travel of 4.92 inches/125mm, unless they had Nivomats, in which case it had a suspension travel of 3.37 inches/85mm. Ikon's chart does show the "Travel inches to bump stop" of their 7610-1298 shock absorber to be 2.95 inches/75mm. I'll leave it to more recently-practiced geometricians to determine what the "suspension travel" at the wheel axle would be with an Ikon shock that can compress only that much. Given the similarity in appearances of the progressive spring windings of the OE Boge shocks and present-day Ikons, it doesn't seem intuitive to me how the OE non-Nivomat Boge shocks would have had so much more travel before their springs and shock bodies would be fully compressed.
My thoughts as well. 5" of rear shock travel would mean about 8" of rear wheel travel. Your rear suspension bottoming would result in the rear tire trying to make it's way through the rear fender.

I think I know where this misunderstanding comes from. Phil Hawksley lists the specs for the R100 this way:

Spring Travel Front/Rear
200 / 125 mm (7.87 x 4.92 in)


If one did not know better, this could leave one thinking that the spring, or shock absorber assembly, travels 4.92", when it is clearly speaking of what we 'Mericans refer to as "rear wheel travel."

Silly English.
MS - out
Mal S7
Posts: 661
Joined: Thu Aug 05, 2010 5:26 am

Re: Rear shocks on a 1979 R100 RT

Post by Mal S7 »

The oem Boge shock appears to have max 100mm stroke. I measured it the other day. Presumably Ohlins made the bm141 to match that. Id like replacement shocks that match that original travel, but $920 delivered ..
robert
Posts: 471
Joined: Sun Jan 30, 2011 4:03 pm

Re: Rear shocks on a 1979 R100 RT

Post by robert »

barryh
Posts: 739
Joined: Fri Oct 01, 2010 12:30 pm

Re: Rear shocks on a 1979 R100 RT

Post by barryh »

Major Softie wrote:
I think I know where this misunderstanding comes from. Phil Hawksley lists the specs for the R100 this way:

Spring Travel Front/Rear
200 / 125 mm (7.87 x 4.92 in)


If one did not know better, this could leave one thinking that the spring, or shock absorber assembly, travels 4.92", when it is clearly speaking of what we 'Mericans refer to as "rear wheel travel."

Silly English.

That's quite an insight !

Both Haynes and the BMW Repair Manual refer to "suspension travel" but I must admit I've read that wrong for years and assumed for the rear it was spring travel not wheel travel.

In my defence I found a BMW issued spec sheet and a riders handbook which quoted "spring travel" when they meant "suspension travel" Silly Germans (or translators).

barryh
from silly England :D
barry
Cheshire
England
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