One man rear sag tool

[Fred H.]

I got tired of asking my wife to come out to the garage to help me measure the sag on my bike, and the subsequent "honey do's" I had to promise her everytime she did, so I decided to see if I could make a tool that I could use to do this myself.

Here is what I came up with.  It's (notice correct use of apostrophe here) simply a steel bar with a hole drilled in it so the bolt for the passenger footpeg bracket can stick through it and clamp it to the bike, and then bent to put the caliper where it will hit the top of the rear drive just over the center of the axle. I then used double sided adhesive foam tape to attach my digital caliper to the bar.

All I have to do is centerstand the bike and then put the caliper on the rear drive and zero it. Then take the bike off the centerstand and put it on the sidestand and pull the caliper down so it is touching the drive, and then carefully get on the bike (without bouncing it) and sit on it and balance it. With one finger holding onto a hook attached to my garage wall, I can even put my feet on the pegs and balance the bike. Then I just carefully, and slowly get off and lean it back over on the centerstand (again, being careful not to bounce the suspension) and read the gauge. I'm able to get repeatable and accurate results and it works very well.

The photos were taken with the left bag removed so you could see the way I have it mounted, but I'm able to use it with the saddlebag in place. I also had to temporarily remove the pre-load adjuster because it was in my way when I was trying to fit the bar to the bike.

 

[Fred H.]

Here you can see how I have the bar mounted. The rear bolt for the left passengar footpeg bracket goes though it, and it is pinched between the braket and the frame of the bike.

And here you can see the reading and how much it moved the caliper after I dismount and put the bike on the sidestand to get off and read it.

 

[jimp]

Fred - your two read out pics are confusing. I presume the first one reading 50+mm on the scale, 3.93 on the read out is the "after" or sag reading. Or is the second pic reading 32.42 the sag reading? In other words, when did you zero the gage? On the c-stand? On the side stand?

If you zero'd it on the center stand as you wrote, how did you compensate for the bounce when you took it off the stand?

Good idea, I've been trying to figure out how to do this myself.

Jim

 

[Fred H.]

Don't pay any attention to the scale, only look at the digital readout.  Since I can zero the digital scale at any place I want to, it won't match the scale.  I centerstand the bike, and then zero the digital meter with no weight on the rear wheel. So then, any numbers shown on the digital scale will be the difference between fully unloaded, and loaded.

It's just a whole lot easier for me to use the digital scale, and being able to zero it anywhere I want, means I don't have to do any math to come up with the difference.

Once I take the bike off the centerstand, I then lean it over onto the sidestand and pull the caliper back down till it rests on the rear drive, because it does bounce when it comes off the centerstand and this will mess up your reading if you aren't careful. But I don't re-zero the gauge on the sidestand, so you can see I have about 4.9mm of sag difference between the suspension fully extended, and the bike leaning on the sidestand.

Once I have the caliper pulled down to the rear drive and the bike on the sidestand, I very carefully mount it, straighten it up, and put my full weight on it, and then I get off. I try to do this whole operation without bouncing the suspension, because the caliper will stay in whatever the lowest point of travel the suspension goes to.

I suppose if I wanted to make it even more accurate, I could duct tape the bottom of the caliper to the rear drive so it followed the drive, and then put a digital camera with a remote shutter release pointed at the caliper readout and then remotely trigger the camera to snap a photo of the reading when I had full weight on it. This would eliminate the bounce issue, though it's probably overkill.

 

[jimp]

Got it. I could do the same with my precison analog.

So you're just going for total sag and not worrying about the difference between bike sag and bike+rider sag, or any differences due to stiction. I guess that works just fine for street use and makes it a lot simpler.

 

[zg]

I got tired of asking my wife to come out to the garage to help me measure the sag

:-X  ??? 

 

[Fred H.]

Got it. I could do the same with my precison analog.

So you're just going for total sag and not worrying about the difference between bike sag and bike+rider sag, or any differences due to stiction. I guess that works just fine for street use and makes it a lot simpler.

Correct. I'm not paying any attention to the amount of sag the bike has just sitting on its on weight (static sag).  Though I could measure that if I wanted to, but there really isn't any reason to. The main number you are interested in is total sag with you on the bike, because this is what you'll use to adjust your pre-load to get you in the range you want it to be.

And to answer your earlier question, yes the 32.42 number shown on the digital meter in the photo was my total sag is with me sitting on the bike. You'll also notice my caliper is upside down, so it started out at around 60mm or so when the bike was on the centerstand. Don't let this confuse you. Just look at the digital readout.

 

[jimp]

What confused me was the first 3.93 reading - I couldn't relate it to anything.

 

[Fred H.]

What confused me was the first 3.93 reading - I couldn't relate it to anything.

That is the amount of sag the bike has when it is leaning on it's sidestand, which is the position it was in when I took that photo.

 

[The Pope]

Good work there Fred.  :great:

 

[midlifecrisis]

Excellent idea!  I might even rig up a more permanent sag meter jig, since I've got several of these Harbor Freight digital calipers and won't miss one gone astray.

 

[freebird6]

Excellent idea!  I might even rig up a more permanent sag meter jig, since I've got several of these Harbor Freight digital calipers and won't miss one gone astray.

Boy, If you want to make those up and sell them I would gladly pay for one. Having the ability to adjust it precisely when it is loaded/unloaded and one or 2 up would be invaluable to me.

 

[Fred H.]

FYI, having this tool has allowed me to easily measure and record my sag readings for a variety of loading conditions. Now that I have this data, I no longer have to try to guess where to set the rear adjuster when I'm all packed up and going on a trip. It was well worth the small amount of time it took to make the tool and take the readings.

See attached.

 

[Fred H.]

Here is a link to a 4 inch digital caliper at Harbor Freight that is only $9.

http://www.harborfreight.com/4-inch-digital-caliper-47256.html