R26 rear suspension sidecar springs

[bwprice100]

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Hi All

I have just taken delivery of uprated rear suspensions springs for 'Albert' my R26 I am restoring. These are the springs that are fitted when the bike has a side car but I won't be fitting one; i wanted to fit the stronger springs because I am big boned

What I have now found is that although they are beefier they are 11.5 mm shorter than the standard solo ones and this is confirmed in the BMW manual.

The question is why are they shorter?
I thought that maybe the bike needs to sit lower when the sidecar is fitted.

I also thought that I could fit a 11.5mm spacer to bring the ride height back to solo specification.

Any thoughts.

Brian

[bwprice100]

[rolf]

Hallo,
shorter springs...if you rest your big-bones/or the side-car on the 26 it sinks more than without these weights....with side-car springs it sinks (nearly) exact the same way if you have with solo springs and no side-car

[bwprice100]

Thanks for the reply rolf but I don't properly understand it.

Brian

[rolf]

Perhaps my pidgin-english?

When you sit on the bike.....it sinks in the springs because of your weight (it's getting lower)
If you adapt (?) a sidecar....it sinks also (because of the weight of the SC)....with side-car and one person it sinks more than normal (because the of weight of the person plus Side-car)
SC springs are stronger....they don't let the bike sinking so much....so, if they has the length of the solo-springs....the bike was too high (higher than solo springs and one person) with SC and one person. that ist the reason why they make them shorter.
Better?

[27-steib]

 Hi Brian,

Maybe Rolf can confirm that the Springs from the R69s are stronger and have the same length, as the 1 cylinder bikes. Maybe thats an option for ypu

I fitted a sidecar tp my R 27 and changed the springs from the R 69 S, but i did not measure the difference, when I got them, and thats 20 years ago....

Best regards Jan

[bwprice100]

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Hi All

Sorry for the slow response but I had a lot of fettling to do to assemble the rear shocks on my R26.

I have fitted the shorter sidecar springs and I will see how they go.

I think there has been a bit of a misunderstanding about my question; I know that a shorter spring can fit the calculations for what is required but the same can be done with changing other parameters such as wire diameter so it can be made to fit the calculations even if the springs are the same length.

If you look at this site you can see it is the number of coils and the thickness of the wire that affect the spring rating and not the length. that is to say that you can have a spring with all the same parameters and make it shorter and it has no effect but change the number of coils or the wire diameter and it does have an effect. that is if we ignore the spring bound condition. this means that the rating and the loaded position can be achieved regardless.
http://www.acxesspring.com/spring-calculator.html

Having now assemble and fitted the suspension units to the bike I have found that if a stiffer spring of the same length was used it would then need a special tool to compress the stiffer spring but the fact that it is shorter make it possible without a spring compressor. With the original spring it is soft enough to fit to the bike. The part of the assembly that would prove difficult is feeding the thread end of the damper through the frame tube and then fitting and screwing on the parts that hold it captive.

Brian