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Old 10-31-2010, 04:50 PM   #46
Dustdevill
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Quote:
Originally Posted by Rob Farmer
The spacer simply lifts the front end slightly.

I took these measurements off my bike. it's fitted with the original fork springs

Front wheel off floor (Measurement A)= 228mm
Bikes own weight (Measurement B) = 195mm
Me on Bike (Measurement C) = 175 mm

This gives Static Sag (A-B) = 33mm
Dynamic Sag (A-C) = 53mm

Total travel at front = 26.5% which isn't enough according to the Wilbers sheet.
How did you get to 26.5%?
Do you know how much travel these G/S forks allow?
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Old 10-31-2010, 11:16 PM   #47
supershaft
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[quote=Beemerboff]50 mm front rider sag is just about perfect, but only if you have the rear sag within 6/10 mm less.

So set the rear sag to 40/44 and try that.

But for a suspension spring to work best you want it to have between 15 and 20 mm preload on the spring .

And, simply ,if you dont have the correct preload at the sag you want you have the wrong spring and you should change it.

Then when the springs are correct , fine tune the balance, front to rear.

By trial and error, there is no other way.

For whatever reason, Caddy82rats wants less sag in the front. That can be bottom lined big time. Add preload until you get the sag were you want it. Oil has NOTHING to do with it as far as some earlier posts are concerned. Get the sag where you want it. If it is too hard or to soft, try just a tad different preload. Just a SMALL difference in preload can make a big diff in how the ride feels without hardly changing sag at all. I get my preload down to making final adjustments with thin washers. If it still is too soft or too hard, you need a different spring, at least if you do, in fact, want to run that much sag in the front.

Beemerboff, where did you get the idea of a "correct" amount of preload? The correct amount of preload is whatever gets you the right amount of sag and the right ride at the same time as long as you don't have coil binding. How else could you figure it?

After the spring is set up is when I start dialing in my damping via oil or all the other methods available.

That's my $.02.
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Old 11-01-2010, 05:00 PM   #48
Beemerboff
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I got the preload from the instructions which come with Ohlins and Wilbers shocks. Both were ordered specifically to suit my application.

One came with 17 mm preload, the other 18mm. The instruction was , change the preload by a maximum of 2mm either way. So the recommendation was , keep thee preload between 15 / 20 mm.

This gave me the total rider sag i wanted . 40 mm on the VFR,and 45 mm on the GS with a mm or so less preload , 450 lb spring. The springs supplied with the HPN inserts give 50 mm rider sag, 10 % more and exactly what I want, final damping tune is set on the move on the forks, more rebound and less compression. Result is perfect, according to everyone who has ridden it.

Not posted much lately, I got some wierd chest infection , and on the lung scan there there are also - more solid appearing masses which may well need later re - assessment -----.
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Old 11-01-2010, 06:05 PM   #49
supershaft
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[quote=Beemerboff]I got the preload from the instructions which come with Ohlins and Wilbers shocks. Both were ordered specifically to suit my application.

One came with 17 mm preload, the other 18mm. The instruction was , change the preload by a maximum of 2mm either way. So the recommendation was , keep thee preload between 15 / 20 mm.

This gave me the total rider sag i wanted . 40 mm on the VFR,and 45 mm on the GS with a mm or so less preload , 450 lb spring. The springs supplied with the HPN inserts give 50 mm rider sag, 10 % more and exactly what I want, final damping tune is set on the move on the forks, more rebound and less compression. Result is perfect, according to everyone who has ridden it.

Good luck with all that Beemerboff! I hope it is nothing serious!

I thought we were talking forks? I guess I missed something? But even with shocks, that doesn't make any sense. I have read a lot of Ohlins instructions and never came across that. Between having a sloppy loose spring and coil binding for too much preload, any preload that works IS the right preload. With most springs, that's a pretty big spread.
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Old 11-02-2010, 01:13 AM   #50
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I guess I will have to answer my own question
Although most manuals and tech specs about the G/S claims the fork travel to be 200 mm or 210 mm it is in fact only 167mm.

To work out spring travel measure the gap between two coils multiplied by the amount of coils, this will give you the amount of travel the spring will allow before getting coil bound.

The Race Tech springs are likely to be the best change you can make to firm up the front end of the G/S. They come in various ratings but the lowest rating is already very hard compared to the stock springs so I'd say go with the 8 N/m or 0.8 kg/mm springs.
The are supplied with spacers as they are 118mm shorter than the stock springs. You don't have to worry about them becoming coil bound as a stiffer spring will have less coils meaning it will be able to compress more than a soft spring.

Spacers allow you to easily make changes to the front suspension, you can add emulators or even a shorter spring on top to soften the front if to hard. You only need to reduce the spacer length by the same length as the spring or emulator added. Nylon bushes makes excellent spacer material. Get your local engineering shop to cut it to the right length on a lathe.

Spring preload in the front should be about 15 mm but can be as much as 25 mm when the bike is fitted with a large tank.
If the sag is still to much you should add a stiffer spring preferably a linear spring like the Race Tech springs.
This will firm up the ride a lot but will reduce nosediving under braking and increase better handling in fast bumpy cornering.

Less change of bottoming the front fork and slightly higher ground clearance.

The downside is that you will loose the plushness and get lots more feedback from the road surface but I'd say feedback is good as you are more aware of what you are driving on and with the suspension being a lot more responsive your ride will be safer and more under control.
These days very few factories fit progressive springs to their bikes for this very reason.

My ideal G/S front end is;
1- Race Tech emulators
2- Race Tech 0.8 kg/mm Spring
3- Teleflex Fork Brace with 2 cm spacer at the bottom instead of 1 cm
4- G/S Workshop handlebar raiser / top yoke stiffener
5- 10 Weight fork oil ( heavier fork oil will make forks respond very harsh)
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Old 11-02-2010, 12:21 PM   #51
supershaft
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Quote:
Originally Posted by Dustdevill
I guess I will have to answer my own question
Although most manuals and tech specs about the G/S claims the fork travel to be 200 mm or 210 mm it is in fact only 167mm.

To work out spring travel measure the gap between two coils multiplied by the amount of coils, this will give you the amount of travel the spring will allow before getting coil bound.

The Race Tech springs are likely to be the best change you can make to firm up the front end of the G/S. They come in various ratings but the lowest rating is already very hard compared to the stock springs so I'd say go with the 8 N/m or 0.8 kg/mm springs.
The are supplied with spacers as they are 118mm shorter than the stock springs. You don't have to worry about them becoming coil bound as a stiffer spring will have less coils meaning it will be able to compress more than a soft spring.

Spacers allow you to easily make changes to the front suspension, you can add emulators or even a shorter spring on top to soften the front if to hard. You only need to reduce the spacer length by the same length as the spring or emulator added. Nylon bushes makes excellent spacer material. Get your local engineering shop to cut it to the right length on a lathe.

Spring preload in the front should be about 15 mm but can be as much as 25 mm when the bike is fitted with a large tank.
If the sag is still to much you should add a stiffer spring preferably a linear spring like the Race Tech springs.
This will firm up the ride a lot but will reduce nosediving under braking and increase better handling in fast bumpy cornering.

Less change of bottoming the front fork and slightly higher ground clearance.

The downside is that you will loose the plushness and get lots more feedback from the road surface but I'd say feedback is good as you are more aware of what you are driving on and with the suspension being a lot more responsive your ride will be safer and more under control.
These days very few factories fit progressive springs to their bikes for this very reason.

My ideal G/S front end is;
1- Race Tech emulators
2- Race Tech 0.8 kg/mm Spring
3- Teleflex Fork Brace with 2 cm spacer at the bottom instead of 1 cm
4- G/S Workshop handlebar raiser / top yoke stiffener
5- 10 Weight fork oil ( heavier fork oil will make forks respond very harsh)
Are you measuring fork travel or suspension travel? The two are different being how the fork is raked.

I agree with about everything you said but suggesting that preload should be between this and that. Why? What ever you wind up with that works for you without coil binding or negative preload at full extension is the correct preload IMO. Is there any reason why it shouldn't be?
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Old 11-07-2010, 10:14 AM   #52
Dustdevill
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Quote:
Originally Posted by supershaft
Are you measuring fork travel or suspension travel? The two are different being how the fork is raked.

I agree with about everything you said but suggesting that preload should be between this and that. Why? What ever you wind up with that works for you without coil binding or negative preload at full extension is the correct preload IMO. Is there any reason why it shouldn't be?
I am measuring fork travel by assembling the fork components without the fork spring. This will allow you to accurately measure the exact amount of fork travel from a fully extended to fully compressed state.

The preload is relative and can you might be able to adjust it more than 25mm but the rule of thumb is that when you need to preload the springs by more than 25mm the spring is most likely to soft to cope with the weight of rider, machine and luggage.
The relative preload for different types of bikes might vary slightly.

The secret to a well balanced spring setup is one that allows the right amount of sag and still be stiff enough to cope with most situations that cause further compression of the spring. Things like hard braking, jumps and large potholes being hit at speed.
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Old 11-07-2010, 10:27 AM   #53
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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.
What he said.
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Old 11-07-2010, 10:35 AM   #54
supershaft
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Quote:
Originally Posted by Dustdevill
I am measuring fork travel by assembling the fork components without the fork spring. This will allow you to accurately measure the exact amount of fork travel from a fully extended to fully compressed state.

The preload is relative and can you might be able to adjust it more than 25mm but the rule of thumb is that when you need to preload the springs by more than 25mm the spring is most likely to soft to cope with the weight of rider, machine and luggage.
The relative preload for different types of bikes might vary slightly.

The secret to a well balanced spring setup is one that allows the right amount of sag and still be stiff enough to cope with most situations that cause further compression of the spring. Things like hard braking, jumps and large potholes being hit at speed.
You are measuring fork travel not suspension travel. When the forks are on the bike they are at an angle, not straight up and down so there is a difference. It is a lot easier to deal with fork measurements than suspension (chassis) measurements. That is what I do but I know the two are different. It's a good thing we don't have to go through this in the back. I take it no one is measuring the shocks travel versus the suspension travel? Big diff there since the shock is considerably raked.

Sorry but I absolutely disagree with the 25mm preload rule of thumb. Lots of springs come stock with more preload than that. Changing springs on my shock sometimes involves right around 25mm. Some springs are simply longer or shorter for a different rate before the coil diameter or coil per inch changes. This fact throws the 25mm general rule in the trash.

Why would springs that need more than 25mm of preload be too soft to cope? If the spring works nearly perfect with 50mm of preload, it is coping just fine. Why do you need a stiffer spring? Don't get me wrong, I am all for getting down to the correct spring but I can't make any sense of the 25mm general rule.

supershaft screwed with this post 11-07-2010 at 10:52 AM
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Old 11-08-2010, 09:55 AM   #55
Dustdevill
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Quote:
Originally Posted by supershaft
You are measuring fork travel not suspension travel. When the forks are on the bike they are at an angle, not straight up and down so there is a difference. It is a lot easier to deal with fork measurements than suspension (chassis) measurements. That is what I do but I know the two are different. It's a good thing we don't have to go through this in the back. I take it no one is measuring the shocks travel versus the suspension travel? Big diff there since the shock is considerably raked.

Sorry but I absolutely disagree with the 25mm preload rule of thumb. Lots of springs come stock with more preload than that. Changing springs on my shock sometimes involves right around 25mm. Some springs are simply longer or shorter for a different rate before the coil diameter or coil per inch changes. This fact throws the 25mm general rule in the trash.

Why would springs that need more than 25mm of preload be too soft to cope? If the spring works nearly perfect with 50mm of preload, it is coping just fine. Why do you need a stiffer spring? Don't get me wrong, I am all for getting down to the correct spring but I can't make any sense of the 25mm general rule.
Just so that we are on the same page; preload is measured by checking the amount the spacer or spring is protruding out the top of the fork + the dept to which the fork cap will screw into the fork stanchion. It is the actual distance the spring is compreseed from it's full uncompressed length to being assembled in the fork with the fork fully extended.
One can decrease the sag by adding more spacers to the top of the spring thus increasing the preload. This will correct the sag and make the front sit higher but it will not make the spring any stiffer so when you hit a large object with the front wheel the forks is most likely to bottom out.
The right way of correcting the sag is to change the spring for a stiffer or softer spring rate. Adjusting the preload is just a way of fine tuning the sag but not correcting the spring rate.
The 15 mm to 25 mm preload is more specifically pertaining to the G/S fork and not being a suspension specialist and working only on these older BMW models I can't say that the same will apply to all forks.
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Old 11-08-2010, 10:11 AM   #56
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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.

What he said.
Quote:
Originally Posted by PolloAsado
What he said.
Sag and spring rate are directly connected; higher spring rate will reduce the sag and visa verse.

If the spring does not bottom out it does not necessary suggest the spring rate is correct. The rider can take it very slow and only stick to good road surfaces so his bike just never bottom out.

The fork travel on the G/S is only about 6 inches so 2 inches of sag is way to much.

The recommended fork oil for these forks is 10W and increasing the oil weight will increase the damping for both compression and rebound making the fork response very slow.
Never compensate for a soft spring with heavier fork oil or increasing the preload excessively.
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Old 11-08-2010, 10:38 AM   #57
supershaft
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Quote:
Originally Posted by Dustdevill
Just so that we are on the same page; preload is measured by checking the amount the spacer or spring is protruding out the top of the fork + the dept to which the fork cap will screw into the fork stanchion. It is the actual distance the spring is compreseed from it's full uncompressed length to being assembled in the fork with the fork fully extended.
One can decrease the sag by adding more spacers to the top of the spring thus increasing the preload. This will correct the sag and make the front sit higher but it will not make the spring any stiffer so when you hit a large object with the front wheel the forks is most likely to bottom out.
The right way of correcting the sag is to change the spring for a stiffer or softer spring rate. Adjusting the preload is just a way of fine tuning the sag but not correcting the spring rate.
The 15 mm to 25 mm preload is more specifically pertaining to the G/S fork and not being a suspension specialist and working only on these older BMW models I can't say that the same will apply to all forks.
I am following you on what preload is. Nevertheless, a lot of springs do not stick out of forks and are down in there quite a bit.

You are correct in that preload doesn't change the spring but you are very wrong about the SHOCK/FORK'S spring rate. This seems to be a popular misconception. The spring rate itself doesn't go up but preload increases the spring rate of the shock/fork. From start to finish and at every increment in between, preload increases the force necessary to move the shock/fork. No, it doesn't change spring rate. It changes shock/fork rate. That is why increasing preload makes your shock/fork feel stiffer. That isn't magic. Adjusting preload is much more than just adjusting sag. It doesn't change the spring BUT the spring is in the shock/fork and the shock/fork has limited travel.

That is great advise but specifics are not general. That preload might work for you with those springs at the sag you choose to run. There is nothing general about that scenario. I am just trying to help!
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Old 11-08-2010, 10:46 AM   #58
supershaft
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Quote:
Originally Posted by Dustdevill
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.

What he said.

Sag and spring rate are directly connected; higher spring rate will reduce the sag and visa verse.

If the spring does not bottom out it does not necessary suggest the spring rate is correct. The rider can take it very slow and only stick to good road surfaces so his bike just never bottom out.

The fork travel on the G/S is only about 6 inches so 2 inches of sag is way to much.

The recommended fork oil for these forks is 10W and increasing the oil weight will increase the damping for both compression and rebound making the fork response very slow.
Never compensate for a soft spring with heavier fork oil or increasing the preload excessively.
Spring rate AND preload are directly related to sag.

I totally agree to never compensate a too soft spring with more damping but what is excessive preload? The only answer to that question is coil binding! If it works other than that, it works!
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Old 06-15-2012, 09:00 AM   #59
zenben
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Quote:
Originally Posted by zenben View Post
Of the three G/S that I've owned, all had the right side damper rod assembly come apart during use.
The damper rod unscrews from the top retaining portion, so that retention of the fork slider and damping are both handled only by the left side of the fork.
This is probably a tad dangerous, but easy to both check and fix.
I've put both the current damper assemblies back together with a helping of loctite to prevent this situation in the future.
I just dismantled another set of G/S forks to discover the right side damper had come apart in use.
The left side was also loose, and would have come apart eventually.
This is a trend, and Loctite advice given above is worth observing.

The top portion of item #9 on the fiche will unscrew during normal use:

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