Where do you measure your sag?


12 replies to this topic
  • Kawirider37

Posted June 08, 2009 - 04:32 PM

#1

A.) Somewhere on the rear fender?

B.) As close as possible to the bolt that bolts the rear fender and the sub frame together?


The reason I ask is because I was measuring at the same place everytime on the rear fender. Turns out that my sag was off, by alot. I knew the manual said to use the bolt but I figure that it wouldn't make a difference if I just used a pin mark 3-4 inches to the right of it on the fender. Especialy if I used the same spot every time. I found that I was off up to 8mm on my bike, and on my buddies bike who has it sprung for a heavier rider, was off almost 12mm.

Just something for you guys to think about and try the next time your having issues dialing in your suspension.

  • grayracer513

Posted June 08, 2009 - 07:57 PM

#2

I'm not sure what you did, but I can measure the sag at 7 different places (or more) and get the same result, as long as it's close to vertically above the axle. :thumbsup:

  • Kawirider37

Posted June 08, 2009 - 08:15 PM

#3

I've tested it several times and sure enough the sag measured straight up from the axle to the fender compared to measuring from the axle to to the rear fender/subframe bolt differ. I'm not the only one that has seen this. I had a few of my friends recheck their sag and sure enough same thing.

This came up while I was having a dscussion w/ a guy at Factory connection about my recently revalved suspension. I was having a hard time dialing it in when I'd run their recommended sag. Well they finaly asked me how and where I was measuring my sag from and after telling him that I measured it between the rear fender and the axle, he told me that was the issue right there. I didn't think that there would be a difference but there was and it made a big difference too. Try it, I ran it by a few guys at my local track that do suspension tests and setups and they didn't beleive me till they tied it.

  • grayracer513

Posted June 08, 2009 - 09:11 PM

#4

The fender mounting bolt at the rear of the sub frame can't even be seen with the number plates on. Measuring from the intersection of the plate and the bottom edge of the fender is easier.

The reason it measures different from vertical is simple trig. The bolt is at an approximate 70 degree angle from horizontal, which means that the difference in measurement will be about 100mm measured at or near the bolt will be about 94mm at a point vertically above the axle. It only matters when you try to use someone else's sag numbers without knowing how they measured it, and only puts you off by 1/4". Staying within 3" of the point where the fender meets the number plate, and using whatever point you decide on over again when you make adjustments is more important than actual numbers.

  • Kawirider37

Posted June 08, 2009 - 09:48 PM

#5

I take the plate off, and measure there. I understand abouyt the degree and measuring at an angle, but the manual confirms the two points to measure between and if you don't measure their then the recommended 90-100mm sag that yamaha recommends in the manual would not be measured out coreectly thus resulting in wasyed time, if you were like me and having an issue dialing in your suspension.

  • grayracer513

Posted June 08, 2009 - 10:07 PM

#6

And, if you look at what suspension professionals do:

(MX Tech) http://www.tootechra...ension_tips.htm

Measure the distance between the rear axle and some convenient point near the fender like a seat bolt.



It doesn't matter what you use, only that you use the same point every time when you make changes. You are never supposed to be able to set to any particular number and have it be right. You have to set, try, adjust, try, adjust the other way, and try that, then decide what works best for you. Consistency is what's important, not specific numbers.

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  • WB450

Posted June 09, 2009 - 08:43 AM

#7

How do you guys set your sag when you don't have any help?

  • grayracer513

Posted June 09, 2009 - 08:52 AM

#8

I'ts hard to do it really correctly, because you should put your entire weight on the pegs when measuring. That's so your measurement is more repeatable and consistent.

It's harder than you think, but I will sometimes sit on the bike backward and take the reading that way. It helps if you tape the tape measure to the swing arm.

  • WB450

Posted June 09, 2009 - 09:21 AM

#9

Thanks, I'll give it a try.

  • grayracer513

Posted June 09, 2009 - 09:23 AM

#10

If you just never seem to have any help around, you can use sand bags, too. Be sure you position them the same way every time. Moving the the weight an inch will change how it reads.

  • Kawirider37

Posted June 09, 2009 - 09:31 AM

#11

I've always used another person, the same person if possible. There is a tool out there, not sure who makes it, but it connects to the swing arm and has an adjustable measuring stick that compresses w/ the bike as weight is applied. It looks like a big upside down air pressure gauge.

  • grayracer513

Posted June 09, 2009 - 09:39 AM

#12

There is a tool out there, not sure who makes it, but it connects to the swing arm and has an adjustable measuring stick that compresses w/ the bike as weight is applied. It looks like a big upside down air pressure gauge.

I think a couple of outfits make those. Motion Pro may be one of them.

But, you may know TT member rickk. He reported having a lot of trouble getting the tool to give back a consistent reading. He would take consecutive measurements without changing anything and each reading would be different. I think this is due to the the suspension over-compressing and then rebounding to its actual sag as the rider applies his weight. If you're going to spend for one of these gizmos, just be aware of that problem.

  • Kawirider37

Posted June 09, 2009 - 04:09 PM

#13

good point, I think I'll stick w/ my trusty tape measure and buddy.





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