Question for suspension expert

I searched around some but never found the answer. When a manufacturer specs 5" of fork travel, are they accounting for the amount of sag as if the starting point was measured with no weight on the front fork (fully extended)? Or to put it another way. If you apply zip ties to the fork tubes when the bike is sitting on its own weight and after riding the zip ties move 4", does this mean there is 1" of remaining travel available?

Clear as mud, right? Just curious, as I am trying to decide whether to go to a thicker oil. No damping or compression adjustments available on this bike. Just trying to tune the OEM setup a little better. Thanks in advance.

If the manufacture says you have 5" of travel that is the total amount of travel. As a general rule, you want to use about 30% of your travel to sag with rider and gear on the bike.

30% of 5" is 1.5". So if you have 4" of sag, you need to make some adjustments...

Everybody tunes suspension differently, this is just a rough guideline.

Note: If you do make a spring / preload adjustment, you need to consider the effects on rebound and compression dampening if you have those adjustments. If you don't you may need to adjust the weight of the oil you are using to help.

The key is if you increase the spring preload you need to increase the rebound damping otherwise you will have a pogo stick and get booted off when you hit some larger bumps.

hth

Sorry but I do not understand. Total amount of travel is the amount of travel measured with the front wheel off the ground to full compression of fork or is it the total amount of travel with the front wheel on the ground until full compression of fork? I do not know how else to explain.

My question has nothing to do with determining sag, rebound or damping. Thanks for your reply though,

"Total amount of travel is the amount of travel measured with the front wheel off the ground to full compression"

This is a good definition of full travel.

Thank you, I got it.

Just curious, but what bike are you working on?

My new 2017 Yamaha MT-03, pretty much a copy of the Yamaha R3 except no body fairings and no clip ons. Standard handlebar and triple. Suspension is typical Japanese, OK but not great. I don´t want to modify it other than maybe going up to 12 wt from OEM 10 wt oil. Really enjoy the motor and tranny, smooth as butter. She just rips open between 7k and 11k, redlines at 12500.

Forty five years and 22 bikes I have gone full circle and now back on a 321cc 42 hp mini bike. My first bike was a Yammi 60cc two stroke, probably the most fun I ever had when I was 14.

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Sometimes you can get away with slight changes in fork oil weight without any negative impact on the rebound/damping of the forks. I did it in both my KRL 650 and Vstrom 650 and it made a noticeable improvement. Some folks will add something like the RaceTech cartridge emulator stuff, but I never got that fancy. It gives you the ability to adjust settings, but you still have to get inside the forks to make the adjustments.

Setting the sag was a bit of a pain because they offer no adjustment for it. You just have to play with the spacer length for the spacers that sit inside the forks on top of the springs. I used PVC pipe in the KLR and I think metal tubing spacers in the Vstrom.

I will say that if you can get the sag set properly, it makes a big difference in how the bike handles and feels even if the rebound/compression isn't perfect!

That is a good looking ride. A LOT of long time riders here in the states are rediscovering the joys of lighter bikes as well.

For the price and my 71 kg weight the bike handles very well. Thanks for the tips I will change the weight next time I do a service.

At your weight, I would think the forks would be about right from the factory. For a more typical 185-200lb rider, forks on Japanese bikes like that are usually on the soft side. The most common upgrade is a stiffer spring and heavier weight oil to handle riders heavier than the typical Japanese lightweight test riders Before messing with swapping out the oil, I would focus on double checking the sag on the front and rear of the bike. If the front end is diving under braking, you will want stiffer springs. They are an easy swap. I would only change the oil if you experience a pogo effect where hits to the front make it bounce up and down like old cars with blown shocks. Heavier oil would help with that, but it might also make the impact from a bump or hole feel more jarring/jolting. You are trying to find a balance between the two effects.

I plan to ride up to Texas on Wed so when I get back I will check the for sure. I am OCD about suspensions.

Everything Kubo offered is valuable advice (it's rare to see good suspension tips on a forum board). I would only add one bit of insight. With a bike like the FZ-03, strive first and foremost to achieve a behaviorally balanced chassis and then fine-tune from there (if you can). Even if it means the front or back is less than optimal, you'll actually end up with a better ride overall on a streetbike. Stock suspension on small bikes being what it is, perfection will be impossible, but you can still make them behave pretty well.

Yeah I hear you, that is why I am hesitant to change out hard parts since I feel the bike has a very good balanced feel to it now. I have seldom had much success in balancing the front and the rear, it always seemed that I could improve one or the other as with my Versys 08. Once I put on the Yamaha R1 rear shock I realized how bad the forks really were but there was not much I could do with the forks other than a different weight oil. So it was out of sync F to R but still way better than stock. Sharp hits on potholes and topes are tough on any suspension so I may just need to slow down for that crap. Thanks for all of the help.

kiko said:

Sharp hits on potholes and topes are tough on any suspension so I may just need to slow down for that crap. Thanks for all of the help.

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Or get a good dual sport

Haha rub it in. I sold two D/S to get this one MT-03.





Time for a change. I think the MT is the only bike I have owned since 1967 that I can flat foot. LOL

Nice Yamaha! I have used 20 weight fork oil when the manufacturer calls for 10 weight many times with great results. For $10 in fork oil you could really make the forks feel better.

Thanks I think I will move up to 15 for starters and see how that goes. The suspension is ok for most of my riding, it is just the sharp hits like topes and potholes at speed that launches me airborne. Without any adjustments like rebound or damping, I may have to just live with it. A change of oil weight is my only cheap option.

kiko said:

Thanks I think I will move up to 15 for starters and see how that goes. The suspension is ok for most of my riding, it is just the sharp hits like topes and potholes at speed that launches me airborne. Without any adjustments like rebound or damping, I may have to just live with it. A change of oil weight is my only cheap option.

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Just to be clear, a heavier weight or thicker oil will make bumps feel more harsh because the thicker oil will flow through the damping/rebound valves slower. This reduces the ability of the forks to absorb hard fast hits. Lower weight or thinner oil will flow through the valves faster. This will allow the forks to compress more quickly upon impact to absorb a hit. Having adjustable suspension usually means that you can control the fork's ability to flow the oil more easily or to resist the flow for a given oil. It might also include the ability to adjust the preload on the spring for setting your sag without having to get into the internals of the fork.

The really nice suspension will not only include that level of adjustment, but it will also include separate adjustments for high speed and slow speed movement of the suspension, one for those sudden hard hits and the other for the slower more rhythmic flowing of an undulating road surface. On the rear, it may also include a ride height adjustment. Then there is the high end stuff that allows all this to be adjusted on the fly at the dash with the flick of a button to change settings among various presets!

Anyway, getting back to your comment about topes, it sounds like you are experiencing a harsh jolting ride. That tells me that the combination of oil and compression/rebound valves you have now is restricting the flow of the oil. This means that when you have a sharp sudden input, the oil causes the fork to essentially act like a solid because the oil unable to get through the valves is incompressible and will stop the form from compressing at the rate it needs too in order to effectively absorb the hit. Thinner oil would solve this problem, not heavier. Fork oil is relatively cheap and easy to replace. I would start by going from 10 to maybe 7.5 and see if that helps. Keep in mind that this is only a solution for those hard hits. If things are fine for the normal riding without the hard hits, then you might make things worse for that range of operation. In which case, if the 10 weight is fine for everything but those hard hits, you may want to stay where you are and just slow down for the hard stuff. Sadly, inexpensive suspension involves a LOT of compromises, which is why it is inexpensive.

When I first started riding, everyone made me think that the first thing I needed to do to a new bike was get a full exhaust and a power commander to max out the power. I had a VFR, so the sound aspect was definitely sweet with the aftermarket exhaust!! I thought it was money well spent and that the bike handled fantastic until I spent the money to install high quality suspension. I was blown away in the difference between the before and after!! At that point, I decided that the most important upgrade to any bike I ever bought would be the suspension. Good suspension will make the bike handle better and thus go faster more easily than just adding power. It makes the bike easier to ride in a controlled manner. It CAN get expensive if you go all out, but you can also make significant improvements without spending a small fortune. Springs and oil are cheap. Even revalving is not super expensive. Changes to the rear are generally more expensive, but they also pay with big rewards in handling, especially if you carry a passenger or luggage very often.

Thanks I agree I will need to do some research and see what internals the forks have. I may just have to live with it. New fork internals with good adj rear shock will run about 1500 and up. Heck the bike only cost me 4700 OTD. LOL this happens to me everytime I get a new bike.

kiko said:

Thanks I agree I will need to do some research and see what internals the forks have. I may just have to live with it. New fork internals with good adj rear shock will ron abiut 1500 and up. Heck the bike only cost me 4700 OTD. LOL this happens to me everytime I get a new bike.

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I went through this with my KLR 650. It is a great budget bike. However, one does not have to push it very hard to start exposing its weaknesses, the suspension being one of the more glaring short comings! So I put in new progressive springs and oil. That was better in general, but horrible on wash boarded roads and for those sharp fast hits. So then I switched to Race Tech straight rate springs. That made a world of difference. The rear was too soft, but I did not want to spring for a totally new rear shock as that was a lot of money. I bought an aftermarket stiffer 410 series spring and had that installed on the stock shock. It made a big difference because it got the sag closer to where it should have been, but the lack of any real damping control stayed an issue. It needed heavier oil which I was unable to do.

All those changes helped, but in the end, I was still left with a heavy bike that only performed adequately at best. On rough trails, the inability to absorb hard hits meant that trying to roll over a big rock bounced the front end and usually sent me flying off the trail instead... I tended to fall down a lot, which hurts... I teasingly justified buying my KTM to my wife by explaining that the better suspension and handling meant I would crash less and not get hurt as often. There was more truth to that than I realized!

So that dilemma always remains. Do you get a less expensive bike and then try to address its inadequacies with after market parts and money, or do you pay more upfront for the whole package with the better bits included from the start? I've gone both routes and there are benefits to each depending on your situation. But if I had the choice, I think I would opt for the better upfront package when I could. But like I mentioned earlier, it is all about compromises...