Preload = Ride Height?

For what its worth I'll throw my hat in the ring.

It's a bit pedantic but free sag and static sag are the same thing. Once the suspension is fully extended its fully extended and so there is no sag. Just had a quick shufty at Keith codes video and he refers to fully extended suspension not free sag.

Measuring sag on the front forks can get a little complicated especially if there is a long top out spring, because the top out spring and stiction can have a big effect on your sag measurement.

To try to eliminate the effect of these on your calculation I would do the following. To reduce the effect of the top out spring fully wind in the pre load so maximum pre load is set before measuring the fully extended suspension. Once measured return the pre load to original setting.

To take stiction out of it when the rider is sat on apply weight to the bars to settle and measure. Then with rider still on lift the bar's and let the forks settle and have rider gently put his hands on the bar's, take a second measurement. The difference between the two is stiction and the average of the two will give you rider sag.

It is true that pre load will affect ride height. But ideally adjust pre load to give the suspension action you like and afterwards adjust ride height with forks thru yokes or shock ride height adjustment to give the geometry that you want.

Hope that helps.

TB

 

This reply is just an arrow to the above.

TB

 

Nice post TB, but lets not over complicate it. The front static sag (which is the same as free sag, and cant say I’ve ever seen that term used before the last few days or so!) is just 30mm as a starter. Ignore bumpstops or anything else, most have never taken them out and it just adds questions IMHO. It’s simply 1/3rd or travel (ish) with rider (some like softer, some like a bit firmer).

For track, its less than road.

 

Just to say that you shouldn't really use preload to adjust ride height. I know mx is different to road bikes but same theory.
Linkage should be used on rear and forks up and down in triples on front.
We used to always change my settings on my race bikes in practice and leave them for the day as otherwise it gets confusing. As @bradders says don't make big changes or lots in one go.

 

Agreed. Getting the suspension how you like it is the important thing, how you get there is less important.

Being aware of the variables and guidelines should be useful tho.

TB

Not sure why bump stops have been introduced.

 

I took that as the mention of top out spring.

 

@comfysofa did you read @bradders link in the pinned post?

http://www.gostar-racing.com/club/motorcycle_suspension_set-up.htm

It's v. informative and easy to follow. Thanks Bradders

 

@PGP
https://www.pgperformance.co.uk/

Highly recommended

 

As you can see this is Dildo Baggins quote so I'll let him get involved in this as its got nothing to do with me.

OK none of what you have said has anything to do with what I have said or referred to. Referring to top out springs in the forks when measuring SAG has got nothing at all to do with bump stops. BUT, has quite a lot to do with measuring SAG.

If a set of forks has a long top out springs and you measure the suspension with no pre load (ie fully backed off) and then measure the suspension with all the pre load applied then you will get two different measurements. That is why it is important to apply full pre load to get the most accurate measurement of fully extended suspension (when the top out springs are long).

This has got sweet FA to do with bump stops but is essential for accurate SAG measurement.

Now, you obviously feel very strongly about this but I suggest you go over this thread again. I, Topbox, did not mention bump stops or dicking about with linkages. However, I do understand the implications of long top out springs (and why they can be found in sports bike forks), I'm not convinced you or Bradders do.

TB

 

I misunderstood what phrase you were using, like I said. I know the basics, and have a reasonable understanding, but what’s inside is voodoo...but equally is using ‘standard, shipped kit’ the 1/3rd travel applies to everything as a starting point. Although I do know that a progressive spring will behave very differently to a linear one, if that helps, and how to make a progressive one a linear one with some plastic tubing and a hacksaw

 

Just had a quick look, essentially a top out spring stops metal-to-metal, opposite of a bump stop I’d guess. So with no load, if for example forks had 130mm travel, the springs may reduce that to 125 or 120. So, when you measure it, it won’t ever show 130mm as it can’t. So 1/3rd of travel still works per se, as its 120 not 130, then adapt from there

Dave Moss has a video on this.

But Comfy - i’d Just still measure Meade as 30mm static/gee sage, 40mm with you on it, and see how that goes