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Old 06-15-2009, 02:32 AM   #1
Caddy82rats OP
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BMW R80 G/S Fork setings ?

Hello

my G/S fork seems to had something like a too soft spring ?
When I put my weight on the bike, the fork go down of 5 centimeters (2 inches), I've set the rear Olhins for 2 centimeters (a litel more than 1 inche)
Oil is 10w the previous owner had changed fork springs for new BMW.
Any draw back about some progressive springs ? I want to stay with this fork, his dual disc and BMW fork brace





The entire bike



Thanks in advance for all reply
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Old 06-15-2009, 04:03 AM   #2
Rob Farmer
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I keep trying progressive springs in various bikes but cannot get on with them. Most folks seem to like them though.

I've got similar issues to yours with my G/s since fittng a Wilbers rear shock a few months ago. I'm going to try fitting preload spacers to see if it helps.
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Old 06-15-2009, 04:12 AM   #3
PaulRS
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Give these guys a call;

http://www.hobbyist.nl/

They make their own set of springs, 46,50 with 6 months return garanty.

I've fitted them on several older airheads with good results.

Paul.
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Old 06-15-2009, 04:14 AM   #4
Caddy82rats OP
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Quote:
Originally Posted by Rob Farmer
I keep trying progressive springs in various bikes but cannot get on with them. Most folks seem to like them though.

I've got similar issues to yours with my G/s since fittng a Wilbers rear shock a few months ago. I'm going to try fitting preload spacers to see if it helps.
I think spacer's do the job for your shock, a good aloy "washer", this is OK if the spring isen't too soft, the spacer only place at an other point the time where the bike go down with your weight, if the spring is too soft, the chock stay too smouth.
Apologizes for my poor english
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Old 06-15-2009, 04:50 AM   #5
PaulRS
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Shortening the spring will make it stiffer.

Just cut-off, say 2-3 cm and add a spacer of similar lenght, testride.
Repeat if neccessary.

Paul.
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Old 06-15-2009, 07:34 AM   #6
Wirespokes
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Springs too soft and too much sag are two entirely different things.

If the forks don't bottom out, then I'd think they're stiff enough.

Sag is handled with pre-load spacers. The travel on these forks is supposed to be close to 8 inches, so 2" of sag should be about right.

Why are you using 10wt oil? Spec is something like 5 or 7.5 - if you are using stiffer springs, stiffer oil would be necessary, but otherwise it would make for a harsher ride.
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Old 06-15-2009, 08:30 AM   #7
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Quote:
Originally Posted by Wirespokes
Springs too soft and too much sag are two entirely different things.

If the forks don't bottom out, then I'd think they're stiff enough.

Sag is handled with pre-load spacers. The travel on these forks is supposed to be close to 8 inches, so 2" of sag should be about right.

Why are you using 10wt oil? Spec is something like 5 or 7.5 - if you are using stiffer springs, stiffer oil would be necessary, but otherwise it would make for a harsher ride.
Springs are BMW ones changed 2 years ago
Oil, I've put 10W because it was stiffer and in my storage , but the result is not better.
The fork doesn't botom out but act lik if I was having 2.5W oil and weak springs
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Old 06-15-2009, 08:47 AM   #8
StephenB
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So, it is bouncy (bouncing)?
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Old 06-15-2009, 08:55 AM   #9
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Not really bouncy but for me terribly not enough "brake" on botoming (or going down) the fork never botom on normal use.
Afrer reading reply and wrinting my feeling I suspect a bad oil, it was in closed botle in my storage but I suspect it to be out of order
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Old 06-15-2009, 09:54 AM   #10
StephenB
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This is a linear not progressive spring, so the "braking" when getting closer to the bottom doesn't happen. Before you open it up, try 15W or even 20W oil to see what happens. I had the same problem with my G/S and made a very successful experiment. Read here:

http://www.stephenbottcher.net/BMW/springrates.htm

Maybe that helps. I still got a couple of pieces of springs left over. You are welcome to it. I still owe you for the KTM tacho (which I never got to work right).

A bientot.
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StephenB screwed with this post 06-15-2009 at 10:07 AM
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Old 06-15-2009, 10:42 AM   #11
Caddy82rats OP
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Thanks Stephen
In first I'm going to drain the fork oil and to put some Bel Ray in it and see whats hapends. After that progressive springs could be an interesting try
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Old 06-15-2009, 10:43 AM   #12
ChromeSux
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some say a good rule of thumb is that the springs are correct if when in the real rough stuff you bottom out every now and then but not often.
i like my suspension to have sort of a plush ride, i have noticed that when on a real rough jeep road or single track with steep areas with ruts etc that it does bottom out sometimes.
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Old 06-15-2009, 03:29 PM   #13
One Less Harley
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Caddy-looks like you've been spraying some paint on the old girl. Looks good.
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Old 06-15-2009, 03:57 PM   #14
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Volume

Try increrasing the volume to 225ml or even slightly more but not past 250ml as this is where hydraulic lock willl start to happen.

Spacers and spring amputation work well but this is a no cost reversible modification.

The effect of more oil is to increase the compression damping mainly at the compressed end of the stroke without effecting the rebound. ATF (auto tans fluid) about 7.5 wt depending on brand and type works well for me and is cheap.
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Old 06-15-2009, 04:12 PM   #15
PaulRS
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Quote:
Originally Posted by Rucksta

The effect of more oil is to increase the compression damping mainly at the compressed end of the stroke without effecting the rebound.
Nope. (sorry )

By adding more oil, you reduce the volume of air above the oil and by doing so the trapped air will act like a spring.

Adding too much oil will eventually push that airpressure op to a level the forks will not compress anymore and feel rockhard. (like your hydraulic lock)

Paul.
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