Is my front suspension okay? - ST1300

[Duporth]

Perhaps I am losing my feel but I find the front suspension on my ST quite touchy when applying the front brake at low speed with the front wheel turned, say when parking or even coming to a stop.
I know care is required on all bikes when doing this, particularly with the heavier bikes. However I can’t recall my ST always feeling this way nor my FJR or Bandit feeling so sensitive.
It is not a critical issue but it would be a sweeter ride on the beloved ST if it were a little more cooperative in this regard.
Any comments will be appreciated.
D

 

[CYYJ]

Hi Duporth:

Front suspension components degrade over time, and your bike is now about 12 years old.

I can tell you that when I overhauled the front suspension on my 2012 ST 1300 a couple of years ago, I noticed a really significant improvement in performance of the front suspension. No doubt at all in my mind that it was worth the time, effort, and expense to do a full overhaul.

Here's a link to the thread where I explained how to do a front suspension overhaul: ST1300 Front Fork Overhaul: An Illustrated Bibliography

Michael

PS: When I made that post, I put too many pictures in a single post. Because of that, they might not all load properly. If you see placeholders rather than pictures, just reload the page (refresh your browser) several times until all the pictures cache locally on your computer.

 

[RaYzerman]

I'm not sure what you mean by touchy, but perhaps you're noticing more dive when applying brakes. This can mean the internals need a good cleaning to ensure the damping passages are open to flow more oil. It can also mean you're finally feeling the stock springs aren't adequate.

I would take the opportunity to upgrade the fork springs, as these bikes are rather undersprung. This too will lessen brake dive, however the proper springs for your weight is the biggest bang for your buck if you're satisfied with the current damping. With stiffer springs, one would likely lower the fork oil level per the spring manufacturer's recommendation to have more air cushion.

 

[RobbieAG]

I upgraded the fork springs on my 1300 to straight rate springs for my weight. It was a big improvement and very economical. I also replace the fork oil whenever I replace the front tire. You probably should check the suspension sag and see what it is. I checked mine and it was definitely too much. Another option to correct that is to keep your existing springs and increase the preload for your weight by cutting longer spacers. That's even more economical.

 

[SMSW]

Before you do any suspension work on your bike you should check and record the sag - how much the bike drops under the weight of the rider complete with all riding gear. If you search for gold valve threads (RaceTech's fork valving) you will find explanations how to do this. Once you know what you have, you can calculate the additional preload needed to put your bike in the middle of the fork travel range (that's done by cutting a new spacer for the top of the fork - lavatory sink tailpiece plastic works well for this.

 

[Duporth]

A wealth of technical guidance there! Thank you very much.
Checking the sag is my first step then.
To be clearer, by ‘touchy’, yes, I mean the suspension seems do dive away so easily even under light front braking. This can upset the ST’s balance, and just at the wrong moment. I have had some near drops lately - not me I hope.
D

 

[Kevcules]

I had a similar problem with my 08 when I got it. I learned about sag and suspension components on here as well. When I see bikes now with their front wheel and fender seemingly tucked down low inside the center section of the front shroud, that tells me their sag is to much like mine was. Since checking mine and adding some more spacer length, my front sits up a lot more, allowing the shock to still have lots of travel left.
Take a picture of your bike's front end if you don't mind before you dismantle.....

Good luck.....

 

[Slydynbye]

Does the ST1300 have an anti-dive valve like the ST1100? Perhaps that needs service as well.

 

[CYYJ]

Checking the sag is my first step then.

Do check the sag, no harm in doing that, but be aware that the amount of concern you need to have about sag and suitability of the original springs is directly related to how much weight you carry on the bike when riding.

I only ride solo, and with all my riding gear on and typical luggage load for a one or two week trip the total payload on my motorcycle (excluding fuel) is about 230 pounds (105 kg). I have found that the OEM springs are just fine, and I have not modified the front suspension in any way.

Michael

 

[Duporth]

Thank you everyone.
D

 

[dduelin]

Do check the sag, no harm in doing that, but be aware that the amount of concern you need to have about sag and suitability of the original springs is directly related to how much weight you carry on the bike when riding.

I only ride solo, and with all my riding gear on and typical luggage load for a one or two week trip the total payload on my motorcycle (excluding fuel) is about 230 pounds (105 kg). I have found that the OEM springs are just fine, and I have not modified the front suspension in any way.

Michael

Respectfully, if you did check the static and rider sag and found it was excessive with a 230 lb payload (it is) did the necessary upgrades to get the suspension right I believe you would think differently about the suitability of the stock ST1300 suspension. Out of the box it's good enough until it's made better. Only then can a quantitative comparison be made.

 

[TMF]

I recently measured sag on my '96 Triumph Trident after forms at 43mm. Home made spacers dropped sag to 34mm. Ride is greatly improved.

 

[RobbieAG]

When I checked my sag it was around 50mm. It should be around 30mm (which it is now with new springs). I may have been able to achieve that with new spacers, but there's a point where too much preload isn't good either.

 

[TMF]

If I recall correctly street bikes are generally set to 30 - 35mm sag at the front and track bikes are in the 25 - 30mm range.. My two sport bikes (Triumph TT600 and Suzuki SV1000S) are both in the 30 - 35 range and that's about right for hard street riding without being harsh. If you ride moderately or have lots of bumpy roads maybe aim for 34 - 36mm or thereabouts.

 

[dduelin]

When I checked my sag it was around 50mm. It should be around 30mm (which it is now with new springs). I may have been able to achieve that with new spacers, but there's a point where too much preload isn't good either.

Agreed, the relationship of static sag and rider sag indicates if the spring rate is OK for the bike and rider in normal riding configuration. If excessive preload is required to achieve proper static sag the spring is too soft and when the bike is loaded it blows right through the preload. Under my riding weight of 165 lbs the forks had 47mm of sag. That's 44% sag under bike alone. I set a target sag of 36mm and it only took 16 mm of extra preload to achieve it with the stock progressively wound springs. The stock spacers are 200mm long so I cut several pairs of longer spacers and settle on 216mm ones. If I couldn't achieve target sag with moderate preload I would have had to change springs. Because the stock set up is undersprung and overdamped I next adjusted the fork oil viscosity to reduce damping and speed up compression and rebound. I mixed stock Honda Showa SS-8 fork oil that is nominally 10wt with Honda's SS-7 nominal 5 wt oil in a 1:2 ratio that came out to 6.7 weight and used the stock oil level. I was quite happy with that set up and a revalved stock rear shock.

 

[Igofar]

It shouldn’t shock anyone (see what I did there) but he says it dives under even light braking.
My first thought is his smc or brakes are sticking and or grabbing.
I wouldn’t worry about the forks until the brake systems are 100% first.

 

[Duporth]

Oh… I didn’t even think about brakes. They seem fine, all the wheels spin freely but I realise there may be a nasty effect lurking in the system somewhere.
I am just about to do my 18 monthly flush, which is something I stick to (+ or -). I think it is fair to say my brakes have been ‘well maintained’, but there can always be another prob somewhere I guess, given the complex system on the ST.
Thanks, D

 

[dduelin]

Oh… I didn’t even think about brakes. They seem fine, all the wheels spin freely but I realise there may be a nasty effect lurking in the system somewhere.
I am just about to do my 18 monthly flush, which is something I stick to (+ or -). I think it is fair to say my brakes have been ‘well maintained’, but there can always be another prob somewhere I guess, given the complex system on the ST.
Thanks, D

The brakes should be sorted of course and it's not rocket science to check if they are working correctly. When it comes to suspension tuning it is much the same way - It's not something only a few can understand and deal with. Basic suspension measurements will tell you a great deal of what you need to do if you want to sort it.

 

[STmark1300]

The town I live in has terrible roads. When I hit some the high spots or potholes in the road, it seems to hit hard. Does that in and of itself tell me I need a smoother suspension? I remember trying out a Concours prior to my ST purchase. It had a pretty smooth ride, maybe to smooth. I will do the sag test. But shouldn't the ride be fairly smooth?

 

[dduelin]

The town I live in has terrible roads. When I hit some the high spots or potholes in the road, it seems to hit hard. Does that in and of itself tell me I need a smoother suspension? I remember trying out a Concours prior to my ST purchase. It had a pretty smooth ride, maybe to smooth. I will do the sag test. But shouldn't the ride be fairly smooth?

Suspension can be soft when compressed slowly and harsh when compressed quickly. This is low speed and high speed compression and different factors affect both. Large bumps and holes will require rapid compression and the orifices and/or valves the oil must pass through when the forks compress can be too restricted to allow correct damping so the high speed compression is harsh. The fork can’t compress fast enough to absorb the blow. Oil that is too thick can cause harsh high speed damping as well. If road is smooth and the bumps and holes don’t require fast compression the ride can be very plush and soft until a hard edged bump is encountered. This describes the stock fork valving. A thinner oil and a lower level than the stock 62 mm can help reduce harshness but the fork will extend faster when it rebounds so too thin of an oil isn’t good either. Slightly thinner oil worked well for me in conjunction with getting the ride height correct by reducing sag to about 36 mm. It’s another subject another day on how to compare and choose fork oil.

Aftermarket valving from RaceTech and other suspension tuners alter the size of orifices and action of the shims that bend open under high speed compression to modify how the fork responds to low and high speed compression. This is how the fork can have both good and low speed compression combined with good rebound damping, all tuned to the rider’s weight.

Springs that are too stiff can feel harsh under compression but the stock ST1300 springs are too soft for all but riders under about 160 lbs in riding gear. Stiff springs are not the problem with the ST’s harsh reaction to large fast fork movements. Racetech and others have spring rate calculators to help pick out the correct rate springs for heavier riders.