Sag

[rapido]

When setting the rider sag for my track bike what sort of measurements should I be aiming for. Suspension fiddling is all quite new to me so I did some research on the net and came across conflicting advice. One site suggested that 25mm front and rear was spot on whilst another said anything below 30mm was to hard. What they did seem to agree on was that the front and rear should have the same measurement.

Any suggestions greatfully recieved.

[lorenzo]

It'd depend on what sort of riding you're looking at doing, but certainly, 25mm isn't too hard for the road, it's just a little firm, erring on the sportier side of things. Also, you don't want to be setting your static sag to 25mm at the rear, you're aiming for much less, then getting about 25mm of rider sag at the back.

I'd suggest doing a search on here, you'll find loads of threads all about setting your sag up and pretty much every question you've ever thought of has been answered at some point or other.

[rapido]

It'd depend on what sort of riding you're looking at doing, but certainly, 25mm isn't too hard for the road, it's just a little firm, erring on the sportier side of things. Also, you don't want to be setting your static sag to 25mm at the rear, you're aiming for much less, then getting about 25mm of rider sag at the back.

I'd suggest doing a search on here, you'll find loads of threads all about setting your sag up and pretty much every question you've ever thought of has been answered at some point or other.

25mm rider sag is what im getting on the rear and the front currently. I think ill have to make do with the rear setting as the preload adjuster is bloody impossible to get to. Ive got a Nitron rear shock which you cant get the C spanner on whilst the shock is on the bike. Should of stumped up the cash and got a hydraulic adjuster!

[intra]

http://teknikracing.rtrk.com.au/?scid=28689&kw=4114463

Road Set-Up Suspension Guide

That should help you a bit man.

[2 smokes 4 ever]

millie

coz measuring the laden/rider sag allows you to assess the spring rate without having to ride it

these are the magic figures

Static (Free) Sag = Measured sag of just the bike, no rider, no rider gear

Dynamic (Rider) Sag = The amount the suspension cmpresses with the weight of the bike and the rider

Loaded Sag = the difference between the Rider Sag and the Free sag.

Note - It may help to set all the slow speed damping adjusters to full open when setting sag.

SPRING RATE -

Spring Rate OK - Static, Dynamic and Loaded sag within acceptable range.

Spring Rate too soft - Loaded Sag too much. Static OK but too much Dynamic Sag or Dynamic Sag OK, but too little or no Static Sag

Spring Rate too hard - Loaded Sag not enough, Static sag OK but Dynamic Sag not enough or Dynamic Sag OK, but too much Static Sag.

Road bikes

SAG

Front

Static (Free) Sag (60-70% of Dynamic Sag) 15-20mm

Dynamic (Rider) Sag (25-30% of Full Travel) 30-35mm

Loaded Sag - (Dynamic Sag - Static sag) 10-20mm

Rear

Static (Free) Sag (15-25% of Dynamic Sag) 5 - 10mm Extremely light bikes use less

Dynamic (Rider) Sag (25-30% of Full Travel) 30 - 35mm Street 20 - 30mm Race

Loaded sag (Rider sag - free sag) 20 - 30mm Street 10 - 25mm Race

Actual rear shock spring “pre-load” measured amount, required to achieve proper Sag:

*0-1/8” – Spring rate TOO STIFF for rider/bike combined weight

*1/4”- 3/4” – Spring rate CORRECT for rider/bike combined weight

*>1” – Spring rate TOO SOFT for rider/bike combined weight

Actual front fork spring “pre-load” measured amount, required to achieve proper Sag:

*0-3/8” – Spring rate TOO STIFF for rider/bike combined weight

*1/2”-1” – Spring rate CORRECT for rider/bike combined weight

*>1 ¼” – Spring rate TOO SOFT for rider/bike combined weight

[Agtrak100]

spot on millemille........

It takes time to get used to working out this stuff, but once you have got your head around it you will get your self a far better bike than you thought you had bought... ie adjust the bike you have got correctly, and you will run rings around the latest fad of a showroom floor that has had no qualified adjustment for the new owner of said new bike..... FACT

SteveT

P.S I am constantly amazed watching riders who own a fantastic bike ( show me a current bike that is Crap in the current sports bike market ) and yet they are teetering round beacuse they have no idea what the hell is actually going on and why, and they apperently have no feel from the bike, and there for are very rigid on the bike..... Oh yes they are blindingly fast on the dual carriage way etc, but scared witless on anything less than a straight road.... read understand learn all the time increase your undstanding of what the bike is doing and why.. it will make you faster ..and much more importantly SAFER .....

[David W]

15-20mm Static Sag on the front sounds a bit hard to me.

When my SP2 had a suspension setup, we were aiming for 25-30mm Static. And 5-10mm at the back.

One thing to watch for is some bikes are being fitted with extra long top-out springs in the damper cartridged, which have the effect of pulling the front down and adding 'weight' that isn't there.

[porter_jamie]

For me, spring rate is THE most important thing for your suspension, and everything else comes from that. One way of estimating where your spring rates are is to look at your sags laden v. unladen.

my rule of thumb (which kinda works for me) is you want about 1/3 travel used laden including riding kit, so wind the preload to achieve that, and then get off. if it sags say 10/15 mm unladen then you are probably ok, if the bike tops out the spring is too soft, and if it moves less than say 10mm it is too hard.

this should get you in the ball park. have 2 or 3 rear springs to test, eg 7.5/8.0/8.5 and go testing, you can do this at the track easily between sessions. ideally the rebound adjuster should be somewhere in the middle of it's adjustment, so if a stronger spring has moved the best setting to nearly full on, the shock probably needs a revalve, speak to the shock company and tell them what is happening

Front, use the same rule to get you in the ball park, and tune with oil gap, more oil = harder, dont overdo it. Experimentation is key, and data is king! Go testing to test, not ride round.

ps obviously a (honda) rs125 is going to top out even with a reasonbly stiff spring cos it only weighs about 70odd kg.

one easy way is to find out what the guy that does all the winning uses, and go from there

[David W]

Where has 15-20mm of static sag on the front been mentioned in this thread?

The middle of the 2smokes post you quoted a bit further up.

[porter_jamie]

Ok..but where in your process do you actually look at how much travel you are using when riding the bike?

Race bikes with data logging have suspension pots fitted to allow the suspension's dynamic behaviour to be assessed. You want the suspension to be as compliant as possible without consistently bottoming out..

"estimating where your spring rates are" gets you in the parrish. i agree to a point (edit to add) 'about the compliant', but an unnecessarily soft spring will(might) make the bike have a low ride frequency, ie a bit wallowy which the rider might want to mask with too much damping. The best measure is the lap timer. i am looking at race technology suspension travel pots, do you have any experiance of them or similar, and do you think the immediate benefits are worth it? have DL1 already

[porter_jamie]

My fundamental problem with relying on static sag measurements to indicate anything to do with spring rates is that it does not take into account what is happening dynamically. True - but it gets you in the ballpark, you then go testing with a box of springs

Take two riders, identical bikes, identical rider weight - using the static sag 'magic numbers' method they both need the same springs with the same amount of preload. Well, yes

But one is a slow group novice type and the other is a fast group warrior type...Should they really be using the same springs and same preload? you've got to start somewhere

A component of the force that compresses the spring is the speed of the bike - common sense; hit a bump at walking pace and it will compress the spring less than hitting it at 100mph.

So you've got your two identical riders and bikes and you want them to be using the same amount of suspension travel when they are riding as fast as they can. So you need to measure how much suspension travel each is using and fit softer or harder springs so that they are just on the verge of bottoming the suspension out. The slower rider is going to need softer springs than the faster rider…not necessarily, slower riders tend to have less finesse on the brakes and throttle and can 'spike' the brakes for want of a better expression, and bottom the forks, but what you say follows.

If the slower rider starts getting faster then the springs will need to be changed for stiffer ones. Agree to this comment, but why do you think a slower rider on otherwise identical bikes and weights would want lower spring rates, when his team mate is seconds a lap quicker on a harder spring? Do you think it is because a softer bike feels easier to ride, has a 'wider' limit? (dunlop v. michelin kinda thing?) What is the benefit for novice group man for the softer setup?

All suspension setup is compromise but if wallowing is occuring how do you know it is because the spring is too soft? If you try a harder one and you go faster than upping the damping on the softer one, then it is too soft. If the suspension is bottoming out all over the circuit then the springs are too soft..but if the suspension is only just on the verge of bottoming out at the highest loading location on the circuit (think the bottom of Paddock Hill at Brands) then the wallowing shouldn't be viewed as a result of the wrong spring rate but more the prelaod or damping..IMO

I'm not clever enough to prove or disprove this with science, but I have a theory that for a particular tyre there is an ideal wheel rate. One way of comparing like with like is converting it into ride frequency. I would be interested to know what the ride frequecies of a proper gp125 is v. 250, wsb, bsb and motogp. I have a feeling they might be similar, maybe 1.5hz? I could be talking cobblers though

If you can log front wheel speed, Throttle position, lambda, coolant temp, front and rear brake pressure, front and rear suspension travel then you've got enough data to go out and win national championships.

RPM?

[porter_jamie]

Why does he want - need - softer springs? Because with harder springs the suspension isn't moving enough...The longer the suspension travel the more accurate and controllable the damping is, the more compliant the suspension is the better the tyre tracks the road surface . Fundamentally, what is the point of having 100mm of suspension travel if you are only using 50mm of it?

I'm not sure if I'm with you 100% here. I might infer from that that long travel is better than short(er), which probably isnt what you are saying - for example if you used motorcross forks on a road racer I'm sure using the whole 6 odd inches of travel would not work. Again, stopwatch is the measure - if only using 80% of travel is faster, then so be it. However I am willing to be proved wrong, with data! Off to buy some pots then..

[porter_jamie]

You've taken the analogy a step too far...

My SM has about 200mm of usable suspension travel, if I went out on the SM track at mallory with the FM racers I would be hugely slower than them. Are you therefore saying that I shouldn't be using all of my 200mm of suspension travel becasue I am not as fast as the guys who are using all of the suspension travel?

Unless there is a very good reason (such as lap times improving due to quirk in dynamic forces as a result of track/rider/suspension set up) you want to be using all of the available suspension travel at whatever your maximim rate of progress is. Both on the road and track.

Your example of fitting stiffer springs to stop a wallowing issue is heresay (in terms of what you were actually 'curing') because you have no idea how much of your suspension travel you were using on that circuit - it might well be that you should have had stiffer springs in the first place because you were bottoming out in normal use.

i'm not saying anything - i dont actually know, but i want to. you maintain that you should use as much travel as you can. This might be true, i have no reason to believe it, or disbelieve it, but i can't get my head around the reason why this is. isnt it a bit like saying your front sag should be 15mm?

you want to be using whatever travel gives you the best lap time - i can understand this.

am i missing something?