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Discussion Starter · #1 ·
I have a simple question on setting the sag for my '21 950 base model. I have not been able to get the front completely in the air, to measure the unweighted fork length. Can anyone who has done this provide their numbers? I assume this will be the same for a 939 or 950 with the base suspension (all the same parts), and the reference points would be pretty obvious/consistent for those who have done it.

I did not have a problem with measuring the rear unweighted length to some vertical points, nor with the "weighted" values F&R with me on the bike. Yeah, I have been remiss in not doing this over the past 4 months/7k miles, and I am sure given my (ahem, HIGH) weight, that the sag has been off since day #1. :rolleyes:

Thanks for any help, and here is a diagram of what I'm after.
John
44018
 

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I'm not looking at the owners manual but It should be listed in there under inches or mm of travel.
Which is always wrong. :) And even if correct, wouldn't give him what he needs.

The "official" suspension travel numbers that manufacturers list include that bit you get from compressing the top out springs, which really isn't useful travel.

Nobody wants to hear this, but you have to have two people, minimum, to get accurate sag numbers. And even then most people do it wrong.
When I owned Sonic Springs customer generated sag numbers were the bane of my existence. At least 80% of them were not just wrong, but physically impossible.
 
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Thank you for the clarification and shedding some light RD52. I did not know that about the "official" numbers. Definitely important to know.
 

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130mm total front travel, that is what I measured. Go to a suspension clinic and have them do it, it's less than 100 bucks
 

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John, I find the front end of my 939 to be pretty compliant. I'm just a duffer and taken my share of heat here. I'm a believer to have 1/3 sag and the rest to travel. I asked the dealer to set up the bike for 225 rider. I'm thinking they might've set to the factory settings in the Owner's Manual. Whether the did that, I can't confirm. I put another round of preload in the front and played with the adjusters..... that was after I set the the rear.

I found the rear shock to be the the real problem. It's too stiff in harsh bumps and has no compression adjustment. I took a round out of preload and set the (rebound) adjuster to full soft. It's still a little stiff but works great with 25 lb in the saddle bags.

Having said that, I find the bike has a better ride and handles better than any bike I've owned. I might rebuild or replace the shock. I have no issues with the front.

I'd like to take our expert, Rich (RD52), on his offer to help me set it up better. :unsure: He's ridden my bike and I can tell he has some ideas.
 

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Just a though , and I'd appreciate others input but if you are not carrying a pillion , wouldn't the original settings always be too hard. ? I'm 65 kg's 144 lbs and learning how to ride this bike.
Suspension seems so/so but since this is the first bike less than 15 years old that I have ridden , a little unsure of setup.
Will probably take it to an expert once we are out of lockdown in Sydney.
 

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My base model is very off-balance for me (95kg) in factory settings. It would ride nose up, rear low. I think you might be closer to correct. Mind you, sag is just to set the ride height off both ends correct. This will mostly affect steering and cornering ability. Damping settings affect the harshness on uneven surface.
 

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Mind you, sag is just to set the ride height off both ends correct. This will mostly affect steering and cornering ability. Damping settings affect the harshness on uneven surface.
That is a partially false statement. Sag looks a lot like a ride-height adjuster, and it is, but it's more important than that. Sag describes the amount of "extension" range the wheel has when it becomes unloaded - like extending into road irregularities. You could set both ends of the bike up with 0 sag and have a "balanced" bike, but it will still feel really harsh because you will always be topping out the suspension when you roll over any road depressions that require the tire to extend into them, but you wouldn't have any extension capacity in the suspension.

You are correct about steering and cornering ability: Sag can affect the chassis geometry by altering the pitch of the steering tube if you set it up incorrectly. Changing the angle of the steering tube alters how the bike handles because it changes front tire trail. Trail, sometimes called "caster" on a car, is the front wheels straight line stability control- it's called "Caster" because it acts like a caster wheel you find on the front of a shopping cart - where the wheel contact patch trails the wheels point of angular rotation and makes it want to go straight.

Decreasing trail decreases turn in effort and also decreases wheel stability - leading to feeling "nervous" in corners and "wobbly" or "loose" in the straights, a precurser to a tank-slapper. Increasing trail increases turn in effort, makes the bike feel slow or sluggish to turn and can ultimately lead to loss of front tire traction. If your sag is set correctly, it is said to be balanced so that the front and rear wheel sag number, expressed as a percentage of total wheel travel, are the same percentage front and back.

For instance, if a front wheel has 130mm of total travel, 20% of that value is 26mm. If the rear wheel has 150mm of travel, 20% would be 30mm. This would be balanced sag and maintain the manufacturers steering head angle and front wheel trail, even though the actual numbers are different.

On that same bike, if you set both wheels at 26mm of sag, the rear would be lower than the front leading to increased steering head angle and slower turn-in. It also reduces the amount of "extension" the rear tire has which can make the bike feel like it hops over pot-holes.

Conversely, setting both wheels at 30mm of sag, the front would be lower than the rear, leading to increased steering head angle and over-steer, the sensation that your bike is turning faster than your inputs warrant.

This is one advantage that a motorcycle with a linkage suspension has, by adjusting the linkage you can adjust ride height (and chassis geometry) independently of the spring sag figure. Some bikes without linkages will have a length adjustment on the shock body that does the same thing, but our bikes do not come with this.
 

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@psyopper: To me it seemed that a simplification, rather than a complex answer was needed. It is no rocket science anyways. I don't think anyone would either drop the bike way down or rise it up completely. There are plenty of guides on the net for correct setup anyway. I'd aim for 30% rider sag btw, as 20% is too high in the stroke. Also a balanced bike should be set nose slightly lower (say, 10mm) than the rear, not equal.

I'd go with something like this:

Road_Setup_Guide.pdf (teknikmotorsport.com)
 

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My head is starting to hurt. I am going to jump on my bicycle to think.
Thank god it has non adjustable suspension. 😁
 

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My head is starting to hurt. I am going to jump on my bicycle to think.
Thank god it has non adjustable suspension. 😁
Haha. I feel your pain and felt the same way myself to the point I was afraid to touch the adjustment at all due to not having the manpower to set the SAG myself or the expert personnel nearby to pay to do it for me. That’s a shame because while I agree that setting the SAG according to various instructions found here and elsewhere is probably the best starting point to really dial in your suspension it is not the only way to adjust your suspension for improved performance. I know because after a couple years of riding on the stock settings and finding it the best handling bike I’d ever ridden, curiosity got the better of me.

Reasoning that an individual with years of experience tuning suspensions and access to a lot of data points regarding what works for a broad variety of individuals with different riding styles should be able to help me remotely without first formally setting the SAG, I turned to Dave Moss tuning. I sent him some personal data (I weigh 150 lbs) pictures of my tires and for $40 he sent me some settings to try.

I will say that his experience is more geared to the S model and there was some confusion there at first but more than the value being in the exact numbers he sent, I found value in being guided through the process of trying some different settings and seeing how it affected the handling of the bike. Once I did that, I was able to significantly improve the handling I already felt was really great.

You might give that try while you wait on being able to get to an expert in person. If you’re careful about recording your changes, you can always get back to where you are now.
 

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Appreciate all of your efforts. As I've written, I found the rear shock too stiff. Did Moss make any points about that?

Haha. I feel your pain and felt the same way myself to the point I was afraid to touch the adjustment at all due to not having the manpower to set the SAG myself or the expert personnel nearby to pay to do it for me. That’s a shame because while I agree that setting the SAG according to various instructions found here and elsewhere is probably the best starting point to really dial in your suspension it is not the only way to adjust your suspension for improved performance. I know because after a couple years of riding on the stock settings and finding it the best handling bike I’d ever ridden, curiosity got the better of me.

Reasoning that an individual with years of experience tuning suspensions and access to a lot of data points regarding what works for a broad variety of individuals with different riding styles should be able to help me remotely without first formally setting the SAG, I turned to Dave Moss tuning. I sent him some personal data (I weigh 150 lbs) pictures of my tires and for $40 he sent me some settings to try.

I will say that his experience is more geared to the S model and there was some confusion there at first but more than the value being in the exact numbers he sent, I found value in being guided through the process of trying some different settings and seeing how it affected the handling of the bike. Once I did that, I was able to significantly improve the handling I already felt was really great.

You might give that try while you wait on being able to get to an expert in person. If you’re careful about recording your changes, you can always get back to where you are now.
 

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Appreciate all of your efforts. As I've written, I found the rear shock too stiff. Did Moss make any points about that?
Not directly in terms of it being too stiff but the adjustments he suggested did lead me to overall settings that make for a more comfortable ride. It was previously much harsher, particularly when hitting the frost heaves I encounter here.
 

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@psyopper: To me it seemed that a simplification, rather than a complex answer was needed. It is no rocket science anyways. I don't think anyone would either drop the bike way down or rise it up completely. There are plenty of guides on the net for correct setup anyway. I'd aim for 30% rider sag btw, as 20% is too high in the stroke. Also a balanced bike should be set nose slightly lower (say, 10mm) than the rear, not equal.

I'd go with something like this:

Road_Setup_Guide.pdf (teknikmotorsport.com)
I agree with you, 30% is far better for a road bike.
My head is starting to hurt. I am going to jump on my bicycle to think.
Thank god it has non adjustable suspension. 😁
Ironically, your bicycle geometry works nearly the same as the motorcycle geometry. But yes, without springs and adjust-ability. That bend in your fork? It gives a little bit of flex, but it's functionally the same as the "offset" in your triple clamp in that it sets the trail figure on your front tire.
 
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Did you eventually get the measurement you requested in the first post? I’d be interested in that specific distance at full extension as well. Thanks
 

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Suspension is not a black art.

Grab some beers and couple of mates but don’t let them have the beers until you’ve created a besline setup.

Lift the front up against the side stand and measure the front from the wiper. That’s fully extended. Noe sit on the bike (wearing your gear) and measure from the wiper. You’re looking for about 35mm difference. Adjust your preload to get the figure. If you use most of your preload to get 30% of the available travel talk to a race or suspension shop, you might need a ‘stronger’ spring. This just means the spring needs more weight to compress it.

Next, check how much your rear suspension compresses with you on the bike. Adjust preload so you are at 30% of the total travel. Make sure you can pick the rear of the bike up (without you sat on it). You want about 10mm.

The front and rear figures should be similar. Using 30% up with you sat on the bike means you have 70% to absorb bumps and 30% to follow low spots, ideal for the road. For the track its more likely to be 30%/ 70%.

Next, set rebound. Compress the suspension (one end at a time) and allow it to extend. Don’t bounce it. You want it to stop at the top of its travel. Keep turning the adjuster anti clockwise until it overruns the top and starts going down again, then turn it back clockwise so it stops at the top. Do the front, and then the back. Then push down on the middle of †he bike and check it comes bak up (front and rear) and the same rate.

Set your front and rar compression damping in the middle of †he range of adjustment.

Now you can drink the beer.

Next day, go for a test ride. There are lots of websites that give you the symptoms of incorrect damping. Pick one setting to tune (ie front compression) and adjust 1 or 2 clicks at a time untill its right. Work your way through the settings.

It is a good idea to use a zip tie on the forks. If it keeps being pushed to the bottom you need more compression damping. If that doesn’t work you need more front preload. Again, if there is no noticeable effect, talk to a suspension or race shop.

Two things that indicate a problem. If you have no free sag (being able to pick the back of the bike up) on the reat you are going to bounced out he saddle. If you are using all your front suspension travel up (braking) your front wheel is going to lose traction and you run the risk of crashing.

This applies to both Sachs/ Marzocchi and Ohlins uspensions. It doesn’t matter what flavour you have, getting it set for your weight and riding style is vital. A well setup Sachs/ Marzocchi is better than a poorly setup Ohlins. And, setting it right will allow you to get the most out of your bike.
 

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Thank you all. It has been an interesting process so far just gathering info.
To get a Dave Moss report and suggestions for $40 wasn't something I had even considered.
I daresay @theresanothersteve has probably saved me the money! Thks mate 👍
Bloody lockdown. Wife is getting annoyed with holding spanners. Now she has to lift motorbikes..
 

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Thank you all. It has been an interesting process so far just gathering info.
To get a Dave Moss report and suggestions for $40 wasn't something I had even considered.
I daresay @theresanothersteve has probably saved me the money! Thks mate 👍
Bloody lockdown. Wife is getting annoyed with holding spanners. Now she has to lift motorbikes..
Actually, money spent with Dave Moss is money well spent. He did a setup for me when he was in Australia last and has provided advice since.

Failing that, any race shop or suspension shop, or track instructor can help.

While you are learning you will get the settings into increasingly narrow windows. Even the first attempt will be better than no setup, and as you get closer and closer to the ideal you will wonder why you ever hesitated.

Keep a record of the settings as you change them, along with notes about what you changed and why. I use a spreadsheet.

Also, keep in mind you will need to add a little damping to compensate for fork and shock oil aging. It is a good idea to get the suspension serviced. Don't go more than 20,000 ks if you are a keen rider.
 
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Discussion Starter · #20 ·
Ninjabones- No, I never did get an answer to my original question. As noted in the original post, I did not have a problem getting the back wheel unweighted for the full travel measurement and setting that sag. After seeing the large change required for my weight at the rear (must be all the gear that I wear, right? :rolleyes:), I did a very rough approximation for the front: using the delta fully loaded sag from the rear (before and after) as a percentage of full travel, calculated a correction based on the different suspension travel lengths front & rear, then adjusted the front by the same relative amount, assuming the factory was at least consistent. Was that a correct assumption? Probably not. Was it accurate? No way! Was it better than stock, after the significant change that I saw with the rear? Yes!

Fast-forward to last Friday, I took the bike to a shop a few hours away, to have things adjusted properly. Sorry to disappoint some here who stated that "customer generated sag numbers were the bane of my existence", but my rear value was spot-on, and my blatantly guesstimated front value was only off by 1mm- a big improvement from where I started (I initially changed it 5mm). The local shop also looked at some fork stiction issues, and adjusted & discussed all the other fork & shock settings, which was followed by me repeatedly riding some of the best local roads throughout the afternoon, tweaking settings further. I don't consider myself that adept of a rider (have never had a moto on a track, and don't get to ride "good" roads very often), but I had no problem feeling the changes- especially on some of the washerboard chipseal pavement around here, and I am very happy with the results and time taken to do it, even if it cost a day off.

Have fun & good luck! As always, thanks to all the input from the forum!
John
 
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