Front Fork Sag

[Rick Butler]

Hey Guys,

 

I need some help. You would have thought as many RSV fork springs that I have replaced this past year, that I would have already done this, but I just haven't

 

For anyone that still has stock springs in their RSV and has a motorcycle lift that takes the front wheel completely off the ground, I need your help.

 

I need you to get me the static sag measurement of just the bike as follows:

 

1. Lift the bike completely off the ground to where the forks are extended all the way out.

 

2. Take a 4" length of masking tape place it on the right lower fork leg with one end slipped slightly under the top cover.

 

3. Now use the bottom of the top fork cover as a guide and draw a line on the tape.

 

4. Now let the bike down on the jack to where the bike is resting completely on the ground and slightly off the jack.

 

5. Holding the right handlebar to steady the bike, use the upper fork tube as a guide and draw another line.

 

6. Lift the bike back up and peel the tape off the lower fork leg

 

Now you have a piece of tape with 2 lines on it. Measure that distance and you have the bike's static sag.

 

I need that distance, please.

 

Thanks,

 

Rick

 

I have attached a picture of this tape on the fork lower so you can see what I'm talking about.

[boominup]

Rick, should there be air in the shocks??

Brian

[Rick Butler]

You know Brian,

 

I haven't been running air in my front forks for about 6 years now, so I don't often think of it. However, yes on the air and why don't you pump it up to the maximum psi.

 

Thanks,

 

Rick

[Rick Butler]

Hey Brian,

 

I was just thinking that if you are going to help me out on this, why don't you get me both measurements, with max air and without any air.

 

Whatchathink,

 

Rick

[hig4s]

Just wondering why static sag would be significant on a touring bike?

[boominup]

Hey Brian,

 

I was just thinking that if you are going to help me out on this, why don't you get me both measurements, with max air and without any air.

 

Whatchathink,

 

Rick

 

Hi Rick, I'll attempt to jack my bike up this coming Sat. I have alot of winter "stuff" around it right now but I'll get it done for you. I'm kinda curious myself what the sag might be. I normally run 3 psi in the front forks. It'll also give me a chance to try out my new Craftsman jack.

Brian

[Rick Butler]

Thanks Brian,

 

I really appreciate you doing this.

 

And Al,

 

"Why would static sag be significant on a touring bike"? For the same reason that it's important to a race bike...better handling. So, let me put it this way.

 

Yamaha states that we have 5.5" of total fork travel on our RSV. But it's really more like 5" in reality allowing for the top out spring.

 

Now if the weight of the bike alone takes up 2" and when the rider gets on, it drops another .75". So how much travel is left for bumps from this big heavy touring bike, yeah just over 2". Not really much.

 

The experts say that for a street bike the static sag with a rider should be around 30 - 35mm or about 1.5" max. If it's more than that then you need to increase the preload on the spring to raise the bike up a bit so that it doesn't drop as much when weighted. Now on a sport bike, they have a preload adjustment they can screw down to compress the spring to create more resistance to produce less sag. In our case, we pump 7-15lbs of air into the fork to accomplish this, where the air acts like a progressive spring. And the more air you add, the more it pushes back in the empty space above the oil level in the fork. But if when you max the air in the fork (or compress the spring) and it still drops more than 35mm, then it's time to be thinking about heavier fork springs.

 

The OEM fork spring rate for our RSV is .90kg/mm where I have been using a spring rate of 1.2kg/mm for several years to get my bikes sag within 35mm.

 

It's my contention that for most of us, this bike of ours is undersprung, both front and rear. Now this is not that surprising, knowing that the manufactures build a bike for an average weighted rider, passenger and cargo. But they are able to adjust for this increased weight economically by the use of added air in the forks and shocks.

 

One other issue with increased fork sag over the reccomended level is that it also affects the rake and trail, sometimes with ill effects like premature head shake?

 

It has been my experience that for the best handling, it's better to have springs that are rated for my weight and the way I like to ride. Like they say, the best you have ever ridden, is the best you'll ever know. In other words, your bike could be handling like crap and you would never know it and think that's just the way it's supposed to be. That is unless you have the knowledge and understanding that you could make a simple change and see a significant improvement.

 

Hope this helps,

 

Rick

[hig4s]

I understand what you are talking about, but I still do not see why static sag is important on a touring bike.

 

On a race machine static sag should be approximately 10% of total travel, and loaded sag with rider in full gear should be 30 to 33% of total travel. But on race bikes the rider and his gear has much more effect on the total so I would have to assume that static sag would be much closer to loaded sag on normal street bikes and even more so on a touring bike.

 

It would seem to me the two important indications on a touring bike would be loaded sag around 30 to 33% and when riding on the roughest normal conditions the suspension is using almost all of it's travel.

[Rick Butler]

Al,

 

We are getting into symatics where we are both saying the same thing. I said static sag where maybe I should have said spring sag to make it more clear. Spring sag is the amount the springs compress between fully topped out and fully loaded with the rider on board in riding position. It is also referred to as static ride height or static (sitting still) sag.

 

The bottom issue is that we don't want a spring that is undersprung (or wore out) enough that we are constantly bottoming out the forks on larger bumps.

 

But when you say 33% of total travel, that comes out to about 1 5/8" or 40mm which I would probably be ok with.

 

But, we don't have near the issue with our fork springs that the GL1800 has. I just measured the spring sag on a brand new Gold Wing and without the rider it dropped 55mm or 2 1/4". And when the 250lb rider got on it with his feet on the pegs, it dropped to 70mm or almost 3". The reason for this is the spring rate of the OEM springs which is .70kg/mm.

 

To me it's more of a handling issue but I'm also running Race-Tech cartridge emulators to make it even better.

 

Rick

[hig4s]

Al,

 

We are getting into symatics where we are both saying the same thing. I said static sag where maybe I should have said spring sag to make it more clear. Spring sag is the amount the springs compress between fully topped out and fully loaded with the rider on board in riding position. It is also referred to as static ride height or static (sitting still) sag.

 

The bottom issue is that we don't want a spring that is undersprung (or wore out) enough that we are constantly bottoming out the forks on larger bumps.

 

But when you say 33% of total travel, that comes out to about 1 5/8" or 40mm which I would probably be ok with.

 

But, we don't have near the issue with our fork springs that the GL1800 has. I just measured the spring sag on a brand new Gold Wing and without the rider it dropped 55mm or 2 1/4". And when the 250lb rider got on it with his feet on the pegs, it dropped to 70mm or almost 3". The reason for this is the spring rate of the OEM springs which is .70kg/mm.

 

To me it's more of a handling issue but I'm also running Race-Tech cartridge emulators to make it even better.

 

Rick

 

Sorry about the semantic confusion.. I'm use to saying static sag and race sag myself, from years racing and playing with dirt bikes.

 

I'm surprised about the Wing, 3" does seem like way too much on a bike that only has 5.5" of total travel. Does that Honda have air adjustments on the fork?

[Guest KitCarson]

Wellllll........don't know much about what all of you are talking about......but my new wing with its feet on the ground has maybe 3/4 of an inch of fork travel two up at the most.......and it has an anti-dive mechanism on the front forks.......when you hit the front brakes there is not one tiny bit of fork dive.....straight and true......SureFoot can stop in a heartbeat.......that was the main important factor in my choice of the Wing.......those brakes.....and the way the suspension holds so true on the road. Do not myself act like a flat track rider anymore.......in fact have gotten quite lazy and spoiled .....like those videos you all have been posting about the enjoyment of the ride....that just about explains me perfectly. Just get out and go....really does not make a difference where.....just somewhere!! The suspension on the Wing is in conjunction with the linked braking system as far as I can tell......and having ridden most of the new bikes except the Victory.......is just about as perfect as humans have invented so far. Nope no suspension gripes from this rider.

[Rick Butler]

Welllll Kit,

 

I'm not sure how or why Honda chose their design on the GL1800 suspension, but you only have one anti-dive unit in your left fork. And you have a cartridge fork in the right leg and a dampening fork in the left leg. But, it seems to work for alot for those folks that shell out that kinda money for this bike. But like I have quoated previously, "The best you have ever ridden is the best you will ever know". It would probably surprise you how this bike would handle with a proper suspension.

 

I have attached an interesting article produced by MCN on what one of the leading suspension experts thinks of the GL1800 suspension. I have a friend who just got his forks back from Traxxion Dynamics and is putting them back on as we speak. Should be interesting in hearing what he thinks of the change?

 

Well heck, Don won't let me attach my pdf pages because they are too large? So if you would like to read them, I'll e-mail them to you.

 

Brain, do you have those measurments?

 

Rick

[boominup]

I wasn't able to touch my RSV this weekend. We got nailed by another snowstorm up here in New England and I've been going around plowing out driveways. I'm still committed to do this so please be patient with me. I've got cabin fever so bad this year I'm practically going nuts!! Global Warming??? If you believe in that, I'll sell you the Golden Gate Bridge!!

Brian

[Carbon_One]

Rick I just changed out my stock springs for a set of the Sonic I didn't take any measurements of the sag with the stock set up but did after remembering this post. My findings with the Sonic springs are as follows.

My measurements are from the bottom of the fork tube to bottom of the upper cover.

Front wheel off the ground, forks fully extended = 15 1/2"

Biked lowered with full weight on the forks but not depressed in anyway = 14 3/4". Results indicate that the amount of drop is then 3/4" .

Note here that Sonic gives a thick walled plastic tube for a spacer to be cut to length. Now I don't know if they gave me the right length of tube or not but when I cut their tube in half the spacers come about 1" below the top of the forks. When the caps are installed there was only slight pressure on the springs. Lowering the bike to the ground resulted in static sag to be 2". Not acceptable there at all. Adding 1" to the spacers then brought them even to the top of the fork tubes. This game me the results above. Haven't ridden the bike yet as we're still in winter mode here.

 

Oh one other thing I just checked. The 14 3/4" measurement is with 5 lbs of air in both forks. Removing the air resulted in the bike lowering an addition 1/4" to 14 1/2"

Hope this of some help for you.

Larry

[Rick Butler]

Larry,

 

The plastic tubing that Sonic supplied was grey shedule 50 PVC and is what just about everyone uses for preload spacers. If they only supplied one piece, it probably wasn't enough for both forks. You can go to Lowes or Home Depot and get some more, where it you really need longer spacers. Or I'm sure Rich will send you a couple of pieces if you need him to.

 

Once you have set your fluid level (120-130mm from top) with the springs out and forks completely collapsed, you can extend the forks to where they stop and put the springs back in to measure the preload spacers. Measure the distance from the top of the springs to the top of the forks. Before you do this go ahead and drop 2 washers on top of the springs. This will allow for this thickness where you can take one out which will go on top of the spacer before you screw the cap in. At a minimum the spacer should come to the top of the fork tube. That way it will compress the springs by the thickness of the fork cap which is about 26mm. Sometimes I go a couple of mm more to get some extra preload for a heavy rider.

 

Regardless if I read you right, you need longer preload spacers.

 

Hope this helps,

 

Rick

 

 

I still need someone to get me the spring sag from just the weight of the bike with stock springs.

[Carbon_One]

Ok Rick got ya there. I did do as you said but rather than getting another piece of pcv piping I just cut some thick walled steel tubing I had here on hand. Then added them to the spacer I got with the kit. Apparently someone forgot to add enough of the sparcer material in my order.

Boy talk about a pain getting those caps on and started.!!!!!!! At the least Yamaha could of done was center that protuding nipple for the air valve so you could get even pressure on the cap while staring it in the threads.

Can't see where what I did will make any difference opposed to getting a new pcv piping of the proper length so will leave well enough alone for now. Don't want to take the fairing away/apart again. Too much hassle.

Larry

[Guest tx2sturgis]

Rick, I will try to get that measurement for you on my bike, either today or more likely, tomorrow, if you dont have it by then.

 

 

[Guest tx2sturgis]

Got it.

 

1-7/16 inches from unladen to resting on center, level concrete, no rider.

 

Since I couldnt mark the tape while sitting on the bike, I didnt get that one. My 07 Venture is more or less stock, no aftermarket springs or anything else that would throw off the readings. I had taken it for a short ride, so the fork oil was still cool, but not cold. I dont run any air in the front forks at all, although I may add some air later.

 

I also got to try out my lift, it has the frame extensions needed by this type of bike.

 

Hope this helps.

[Squeeze]

...

Since I couldnt mark the tape while sitting on the bike, ...

 

A Wire Strap comes in quite handy for such Things. I got one permantly of the left Forkleg. It can move without harming anything and stays where it is when moving stops.

[Guest tx2sturgis]

A Wire Strap comes in quite handy for such Things. I got one permantly of the left Forkleg. It can move without harming anything and stays where it is when moving stops.

 

Yeah, if Rick needs that reading, I can probably figure out a way to do it. A wire strap, thats a 'zip tie' I assume, or thats what we call em here. Im assuming that might slip under the fork tin, or maybe give a false reading if it doesnt move just right. I'd prefer to have someone sight it for me, but I hate to bug the neighbors for that...they already think I'm...uh...different...and actually, I AM!

 

I'll figure something out if need be. I'll be in the company of riders in a few days, and I can do it then.

 

 

[Squeeze]

Sorry, Zip Tie didn't come to my Mind, so i used a Translator which gave me Wire Strap...

 

And another Sorry for suggesting a Zip Tie, i should have known better about the Tin.

[boominup]

Rick, I finally got to measure the sag on my 03. With no air in the fronts, it measures 1 13/16". With 7 psi in the shocks, it measures 1 1/2". It was kind of a B*%#h measuring it by myself but I think I am pretty close. I just changed my shock oil before putting it into hibernation so I don't know if this will change after putting a few miles on it. Brian

[Rick Butler]

Brian,

 

That was pretty much what I suspected. Like I said earlier, the spring rate for stock RSV springs is .90 kg/mm. With 1.20kg/mm springs it drops about 1" with just the weight of the bike and just another 3/8" when I get on it and this is right on the money for the reccomended 30-35mm of loaded spring sag. But, what you did showed that by adding air in the forks, it will change the ride height and not allow the bike drop as far as it did with just the standard preload on the spring. Regardless it also shows that the stock springs (even when new) are undersprung just for the weight of the bike and even worse when the rider gets in it. I'd now be interested in what a 99 with stock springs would measure to show how much sag is lost over time?

 

Thanks Brian and Brian,

 

Rick

[boominup]

You are very welcomed, Rick. BTW, my 03 has 15K miles on the clock. Hardly broke-in!

Brian

[Guest tx2sturgis]

Hey no problem...and who IS this imposter? Another Brian?

 

lol

 

Ooops...he joined before me...ok...maybe I'm the imposter!! Thats it!

 

Lesseee...who can I impersonate next?