GS650GT Front forks sag after rebuild

[Antonius]

GS650GT - I've had the forks re-chromed, replaced seals and both DU rings, and refilling with 15w oil. With the forks fully extended, distance between bottom fork brace and dust seal is around 183mm, from this I've worked out the fork sag to be around 85-90mm.
I could be wrong, but this to me seems a bit too much. With my gear on I'm around 95kg (15st, 210lb), so not that heavy.
What do you think could be causing this sag, tired springs? Tried pumping air into it, but pressure is not holding, this is with new air valves and o-ring seals too, could this cause the excessive sag?

 

[Big T]

Old, worn out fork springs

 

[Antonius]

Old, worn out fork springs

Do you think by putting a few washers between the two springs could create a bit of preload and overcome some of the fork sag?

 

[Big T]

Yes, but new fork springs would be much better

 

[RichDesmond]

It's a lot too much. 35mm of total sag is about right on most street bike.
The stock springs were too soft when new, and haven't gotten better with age.
Adding preload does make the sag a bit less, but the spring rate is still exactly the same. New springs from a good aftermarket company are the fix.

 

[Antonius]

New springs it is then. I can only find progressive springs for these fork, and their length is around 80mm shorter than the combined length of the two original springs, would I have to make this length up with a spacer to get the right preload?

 

[Rob S.]

I went with Race Tech straight rate springs. Many recommend Sonic springs, because a member here owns the company. In any case, I've never heard anyone here recommend progressive rate springs.

You've got to buy the correct rate depending on your fully geared up riding weight, plus your style of riding.

 

[RichDesmond]

...Many recommend Sonic springs, because a member here owns the company...

Used to own the company.

 

[Rich82GS750TZ]

Antonius,
If you ask RichDesmond real nice, He might tell you exactly what you need from Sonic straight rate springs. He'll probably need some info like your weight, etc. I know's he's gotten a lot of folks here set up and happy with fixing their front suspension woes. I haven't done it yet, but may in the future.

 

[RichDesmond]

Yep, I'd need the riders weight and a description of how you ride. Be happy to help.

 

[salty_monk]

I weigh 11 stone and the stock springs are even too soft for me.... You can cut the closely wound springs off and replace with solid spacer to make the forks stiffer but there is only so far you can go before the spring gets coil bound (not enough gaps between the coils left to equal the fork travel).

With stock springs you can get to about a 43lb spring weight before that happens, I would say you want more like a 55lb spring.. FYI progressives springs are 50lb once the close coils bind & you get the full rate of the straight wound part.

 

[Antonius]

Just received email back from Race Tech with details of their spring set which contain bits for preload. Still thinking about going with progressive springs, simply because I can source them here in the UK, and they would cost half as much as importing any from US.
No rush to get this sorted, need to get a few things for my Ducati first.
Thanks for your advice.

 

[salty_monk]

You could always cut the "progressive" end off the progressive springs (the closely wound ones) & add the same amount of height back in solid spacer. Put a washer at each end (between the spring and new spacer & at the other end between the Progressive spacer and the new spacer or make the new spacer the height you cut off plus height of progressive spacer). For spacer plastic pipe works well. They call it schedule 40 pipe here, not sure what the equivalent plumbing pipe is in the UK but it's an ABS pipe.

That would give you a 50lb start point (similar to racetech 1.0 from memory) to add additional preload too. I've done that on a couple of bikes in the past.

 

[Antonius]

I've just ordered a pair of Hagon progressive springs (quite cheap at ?89). I going to compare their length against the two factory springs (long and short), and work out what length of spacer to get enough preload. Not keen on the idea of cutting off any bit of the new progressives, problem around this area the roads a bit bumpy, having the springs too firm I fear would spoil the ride. Got a pair of new Hagon shocks on the back, just need to balance the front with the rear.

 

[RichDesmond]

I've just ordered a pair of Hagon progressive springs (quite cheap at ?89). I going to compare their length against the two factory springs (long and short), and work out what length of spacer to get enough preload. Not keen on the idea of cutting off any bit of the new progressives, problem around this area the roads a bit bumpy, having the springs too firm I fear would spoil the ride. Got a pair of new Hagon shocks on the back, just need to balance the front with the rear.

Cut the spacer so that the total stack length is a little shorter than stock. If you make it the same length you’ll have too much preload with the better springs. Ideally you’ll want the springs compressed about 20mm with the fork cap screwed in.