suspension improvement and adjustment

[Gary in NJ]

Oil weight is tricky and is an adjustment of last resort. First, there no real standard between manufacturers for fork oil weight (look it up - it’s all over the place). Even staying with the same manufacturer you may find that you are between weights - and now you have a concoction that you may not be able to replicate.

It’s far easier to add or remove a 1/4 ounce at a time. Remove the fork cap (one at a time) and with a syringe with some tubing you can add or remove an exact amount. Add oil to slow the rebound, and remove to make it faster.

It’s real easy to add/remove oil. It’s a pain in the ass to drain the oil and replace it, only to learn that you don’t like the result.

 

[Sdaniels]

Yeah, I've seen the writeups about suspension fluid weights. Seems the only standard to get consistency is using the same brand...but like you said, that would mean a complete draining of fluid to prevent mixing the two weights. Hopefully my son will be happy with the setup as it stands now. He's still very new to motorcycling. I'm betting he'll be happy with any improvement over the stock setup, which is practically guaranteed with this setup. Fine tuning can occur later.

 

[John Smith]

What do you recommend for someone 295lbs?

I use Maxima 15w fork oil.

The preload is just a starting point. Final preload will be determined through sag measurements, both static and loaded. For that reason I always install adjustable fork caps. It makes setting sag and any future adjustments much easier.

What do you recommend for someone that’s 295lbs?

 

[Gary in NJ]

Welcome to the Forum John.

You could benefit from some suspension changes. My primary concern is that the shock is probably fairly compressed, which removes weight from the front wheel. With the OEM suspension the steering feel is already vague, and this nose up attitude makes it worse. So at a minimum I would re-spring the shock and forks.

The OEM spring rate for the shock is 12.5 kg/mm and it is a 7 x 2.25" coil (RaceTech). The RaceTech calculator suggests a spring rate of 17.18. That rate falls between available rates of 17.0 kg/mm and 17.8 kg/mm. I would choose the 17.0 spring.

The OEM spring rate for the forks is 0.77 kg/mm and the RaceTech calculator suggests 1.04 kg/mm. Once again, this suggested rate falls between available rates of 1.00 and 1.10 kg/mm. In my experience the RT calculator leans towards the too high a rate side, so I would suggest a rate of 1.00 kg/mm. If you choose a dual-rate spring, I would choose one with a starting rate no less than 1.00 kg/mm.

These two changes will help produce the correct free and race sag (putting the bike in balance), but will not improve the dynamics of the suspension. The forks on the FZ6 are under dampened, producing pronounced brake dive. However, they also tend to hydrolock during fast movements, resulting in a punishing ride. You can try a heavier weight fork oil, say 10w or 15w, which will improve fork dive, however the ride over harsh bumps will be worse. Damping rod type forks inherently have this worse-of-both-worlds characteristics. Gold Valve Emulators cure these problems by bypassing the damping rod for a rate-based valve.

There are no easy solutions for the shock. The OEM shock is an emulsion-type shock, and like the damping rod fork, it was chosen because it was inexpensive. Since the shock isn't rebuildable, the only solution is to replace it (the 17.0 kg/mm rate noted above would be correct for any replacement shock). The shock determines the ride comfort of the bike, and it's importance can not be over emphasized. There are some threads in the forums where members have modified shocks from other bikes to work on the FZ. I have done this in the past on other bikes and I was never happy with the result. The only plug and play solution that I'm aware of (that is currently in production) is a Ohlins shock. That is a $600 investment - but Ohlins will send it to you with the correct rate spring - and if you think about it that way, it's only a $450 investment.

So at the very least (and for your safety), respring the forks and shock. Depending on your budget and your commitment to the FZ as a bike you will keep, there are options to improve ride and handling.

 

[John Smith]

Welcome to the Forum John.

You could benefit from some suspension changes. My primary concern is that the shock is probably fairly compressed, which removes weight from the front wheel. With the OEM suspension the steering feel is already vague, and this nose up attitude makes it worse. So at a minimum I would re-spring the shock and forks.

The OEM spring rate for the shock is 12.5 kg/mm and it is a 7 x 2.25" coil (RaceTech). The RaceTech calculator suggests a spring rate of 17.18. That rate falls between available rates of 17.0 kg/mm and 17.8 kg/mm. I would choose the 17.0 spring.

The OEM spring rate for the forks is 0.77 kg/mm and the RaceTech calculator suggests 1.04 kg/mm. Once again, this suggested rate falls between available rates of 1.00 and 1.10 kg/mm. In my experience the RT calculator leans towards the too high a rate side, so I would suggest a rate of 1.00 kg/mm. If you choose a dual-rate spring, I would choose one with a starting rate no less than 1.00 kg/mm.

These two changes will help produce the correct free and race sag (putting the bike in balance), but will not improve the dynamics of the suspension. The forks on the FZ6 are under dampened, producing pronounced brake dive. However, they also tend to hydrolock during fast movements, resulting in a punishing ride. You can try a heavier weight fork oil, say 10w or 15w, which will improve fork dive, however the ride over harsh bumps will be worse. Damping rod type forks inherently have this worse-of-both-worlds characteristics. Gold Valve Emulators cure these problems by bypassing the damping rod for a rate-based valve.

There are no easy solutions for the shock. The OEM shock is an emulsion-type shock, and like the damping rod fork, it was chosen because it was inexpensive. Since the shock isn't rebuildable, the only solution is to replace it (the 17.0 kg/mm rate noted above would be correct for any replacement shock). The shock determines the ride comfort of the bike, and it's importance can not be over emphasized. There are some threads in the forums where members have modified shocks from other bikes to work on the FZ. I have done this in the past on other bikes and I was never happy with the result. The only plug and play solution that I'm aware of (that is currently in production) is a Ohlins shock. That is a $600 investment - but Ohlins will send it to you with the correct rate spring - and if you think about it that way, it's only a $450 investment.

So at the very least (and for your safety), respring the forks and shock. Depending on your budget and your commitment to the FZ as a bike you will keep, there are options to improve ride and handling.

So essentially upgrade the rear shock to the Ohlins S46ER1 shock and the front fork springs to 1.0KG/MM W/ 15wt fork oil as well as the GVE from race tech?

 

[John Smith]

Welcome to the Forum John.

You could benefit from some suspension changes. My primary concern is that the shock is probably fairly compressed, which removes weight from the front wheel. With the OEM suspension the steering feel is already vague, and this nose up attitude makes it worse. So at a minimum I would re-spring the shock and forks.

The OEM spring rate for the shock is 12.5 kg/mm and it is a 7 x 2.25" coil (RaceTech). The RaceTech calculator suggests a spring rate of 17.18. That rate falls between available rates of 17.0 kg/mm and 17.8 kg/mm. I would choose the 17.0 spring.

The OEM spring rate for the forks is 0.77 kg/mm and the RaceTech calculator suggests 1.04 kg/mm. Once again, this suggested rate falls between available rates of 1.00 and 1.10 kg/mm. In my experience the RT calculator leans towards the too high a rate side, so I would suggest a rate of 1.00 kg/mm. If you choose a dual-rate spring, I would choose one with a starting rate no less than 1.00 kg/mm.

These two changes will help produce the correct free and race sag (putting the bike in balance), but will not improve the dynamics of the suspension. The forks on the FZ6 are under dampened, producing pronounced brake dive. However, they also tend to hydrolock during fast movements, resulting in a punishing ride. You can try a heavier weight fork oil, say 10w or 15w, which will improve fork dive, however the ride over harsh bumps will be worse. Damping rod type forks inherently have this worse-of-both-worlds characteristics. Gold Valve Emulators cure these problems by bypassing the damping rod for a rate-based valve.

There are no easy solutions for the shock. The OEM shock is an emulsion-type shock, and like the damping rod fork, it was chosen because it was inexpensive. Since the shock isn't rebuildable, the only solution is to replace it (the 17.0 kg/mm rate noted above would be correct for any replacement shock). The shock determines the ride comfort of the bike, and it's importance can not be over emphasized. There are some threads in the forums where members have modified shocks from other bikes to work on the FZ. I have done this in the past on other bikes and I was never happy with the result. The only plug and play solution that I'm aware of (that is currently in production) is a Ohlins shock. That is a $600 investment - but Ohlins will send it to you with the correct rate spring - and if you think about it that way, it's only a $450 investment.

So at the very least (and for your safety), respring the forks and shock. Depending on your budget and your commitment to the FZ as a bike you will keep, there are options to improve ride and handling.

Thank you so much

 

[Gary in NJ]

John,

I'm not saying you have to go full-in on an upgrade. I'm just letting you know what is available. If you upgrade the shock, and rebuild the forks with RT components, it will transform the bike. You'll also be investing $1,000 into the bike, so make sure it's a keeper because you'll never get that money out on resale.

The shock model type you noted is correct. The Ohlins description is "STX46 Street Shock for FZ6 04-07 (YA403)". This is a gas filled shock with screw-type pre-load adjustment, and adjustable rebound damping - no fluid/air remote. See the link below. Oh, also confirm that your FZ6 is a 2004 to 2009 (S1 or S2). You can find these at a discount from online dealers - they all built to order and then shipped. But I think the fastest way to get one is to order direct.

Street S46 Shock (YA 403) | Öhlins USA

A well-proven monotube design, the Öhlins STX 46 shock absorber sets the standard for performance, quality, and durability. A major suspension upgrade for your Adventure, Street, or Naked Sport Bike. It features a large 46mm main piston and an internal gas reservoir within the main body of the

www.ohlinsusa.com

 

[Sdaniels]

If you choose a dual-rate spring, I would choose one with a starting rate no less than 1.00 kg/mm.

...but go with the straight rate spring