I have got some new BMW springs for my R90/6.
They have a white spot of paint at one end. Is this up or down?
Many thanks. Charles
Fork springs. R90/6 which way up
Fork springs. R90/6 which way up
Charles
Replica 1070 R90/S (based on 82 RT)
1975 R90/6
Replica 1070 R90/S (based on 82 RT)
1975 R90/6
-
Duane Ausherman
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Re: Fork springs. R90/6 which way up
We tended to put the paint up, but it really doesn't matter at all. Can you see that the end coils are wound closer together at one end more than the other end?
In my simple way of looking at the physics, there could be a slight difference. The top end of the spring is fixed in place. The bottem end is the one that moves and is part of unsprung weight. Somewhere in the middle of the spring is the average. Were the spring wound with one end far more compressed than the other end, then putting the lighter end at the bottom would reduce the unsprung weight. It is a really minor consideration.
With the uneven winding of the spring, the different parts of the spring have a different resonant frequency. Being that it is a spring in the first place and may have oil on it, it probably doesn't have much of a chance to vibrate. It can squish out to one side and make a noise when it hits the fork tube insides.
Someone may well come up with other aspects that I have forgotten, or never thought about. How long can we obsess over this one? Could it become the next "oil thread" item?
In my simple way of looking at the physics, there could be a slight difference. The top end of the spring is fixed in place. The bottem end is the one that moves and is part of unsprung weight. Somewhere in the middle of the spring is the average. Were the spring wound with one end far more compressed than the other end, then putting the lighter end at the bottom would reduce the unsprung weight. It is a really minor consideration.
With the uneven winding of the spring, the different parts of the spring have a different resonant frequency. Being that it is a spring in the first place and may have oil on it, it probably doesn't have much of a chance to vibrate. It can squish out to one side and make a noise when it hits the fork tube insides.
Someone may well come up with other aspects that I have forgotten, or never thought about. How long can we obsess over this one? Could it become the next "oil thread" item?
Ask the Indians what happens when you don't control immigration.
Re: Fork springs. R90/6 which way up
Thanks Duane,
A good pragmatic answer, simple is good with these bikes, and they can take quite a lot of abuse from owners.
Does anyone have a link torebuilding these forks??
Charles
A good pragmatic answer, simple is good with these bikes, and they can take quite a lot of abuse from owners.
Does anyone have a link torebuilding these forks??
Charles
Charles
Replica 1070 R90/S (based on 82 RT)
1975 R90/6
Replica 1070 R90/S (based on 82 RT)
1975 R90/6
-
Major Softie
- Posts: 8900
- Joined: Tue Aug 03, 2010 1:46 pm
Re: Fork springs. R90/6 which way up
Everything Duane said is true, however, I've always put the tighter coils down, as (I believe) it makes the forks quieter. Since the closer coils do a lot more of the compressing (moving about), having them down in the oil bath gives you a little less noise from the springs (not that I remember ever noticing coil noise on any bike while actually riding).
As far as suspension performance, other than the tiny theoretical unsprung weight difference that Duane brought up, there is none, and you could run one one way and the other the other way.
As far as suspension performance, other than the tiny theoretical unsprung weight difference that Duane brought up, there is none, and you could run one one way and the other the other way.
MS - out