Fork Spring Rates

I think I have effectively talked myself (with all of your help) out of doing a fork swap.

So instead, I just want to swap the springs for my 100KG fat arse. Think is, I don't know what that equates to in spring rates.

Thanks!

I replaced my youngest son's V50 fork springs with Racetech but they don't list anything on the GRiSO. The new springs really help the V50's dive with his 90 kg weight and brake dive.

I'll be very happy when I finally get down to 100 kg. At my age I need to get to 85 kg.

I had the G11's front forks rebuilt last year and wasn't smart enough to get new springs. I'm not comfortable with rebuilding upside down forks.

I am not sure if this will help but I recently had my suspension set up by a professional here in Sydney. Now I weigh more than 100 kg and I thought the suspension was too soft, he informed me that the springs were fine but that he would re valve the front end and put a new shock on the rear. Best decision I ever made.
Front end is now supple yet controlled and the rear is sublime, so go figure. i asked about a progressive rate spring for my weight and he claimed to be able to make the stock front work, which I am glad to say he appears to have.

I hear you and was thinking the same thing.  A new rear shock because my web-research tells me you can't get a high enough capacity rear spring to fit the stock rear shock.  The Duc specialist I took my GRiSO to said that Italian bikes are typically over damped and under spring for those of us who are 120+ kilos.

Still, I'm on a Quest for the Holy Grail of weight loss.  which is 25 kilos for me

Then I'll revisit the GRiSO's suspension.  For now I just ride it like a horse (off the saddle over bumps) in my daily commutes.

For my longer trips this year I have a Lemans Rosso Corsa with Ohlins to take.  Talk about night and day difference!

Forks rebuilt by K-tech with 9 springs and k-tech valves. Big improvement and now creamy smooth  by comparison. Slight concern on travel seems to almost bottom out under hard braking. K-tech suggested adding 2 turns preload which I have done and now have 4 rings showing - the 4th in line with the top of the fork body. Much better. Travel seems to almost bottom out but not quite so I added one more turn pre-load, now 4.5 rings showing but that seemed to make it harsher on my hands so have gone back one turn and the 4 rings showing. Havent played with the compression damping but k-tech suggest adding a turn or two which should help avoid bottoming and avoid some of the harshness. I am 103kgs ready to ride and the k-tech valving and springs seems a huge improvement. Now fitting the Matris rear![You must be registered and logged in to see this image.]

Let me know how the Matris rear shock goes, are you going standard length or Stelvio length? I see they do a ride height version too, maybe consider that?

Matris 46K is the model I have - described as road and track and I think my competitive track days are behind me so didn't go for the 46R with the high and low speed damping adjustment, thinking 46K should be more than enough for my purposes. Yes its variable length from 319 mm to 329 mm. Comes set at 320 mm but I will fit at 329 mm. Fork Springs are 9 Nmm and K-tech will change for 9.5 Nmm free of charge if that is decided to be best option, but plan to play with compression in the meantime. K-tech suggest trying 2 or 3 more clicks compression and see how that goes. Trying to find the optimum to retain the creamy smooth ride, use all the travel without bottoming out and avoiding any harshness. I am 103kgs in riding kit. Michael in the workshop at k-tech in Derby is very very helpful. And they turned the forks round in 24hrs and parcelforce delivered the next day. Highly recommended. K-tech have done lots of Showa 43mm forks but not for a GRiSO before so have guessed on set up for the weight which so far looks to be pretty much spot on save for the possible risk of bottoming under emergency braking.

Old thread but I had my Tenni GRiSO suspension upgraded a few years ago and at least have some spring rates for you. I was around 100kg and I guess 105-108kg with full tail bag and riding gear. Problem was rebound was slow on front and rear so was compressing on the first bump and then staying compressed through subsequent bumps. Also pot holes were hell.

The stock front fork springs were 1kg/mm stiffness and were fine. He said could go up maybe 5% but not worth it. He replaced the compression valve stack (orifices on the valve were too free flowing so replaced with a more restrictive Racetech valve and a new shim set). Rebound valve was good but new shims. Also changed to 5W Bel-ray fork oil.

The big issue was the stock rear spring, it was 9.5kg/mm and he upped it to 11.7kg/mm. Changed the shim sets in the stock shot but otherwise left as is.

The difference was that profound that I bought Matris front and back for the new Norge.

Checked via Google conversion and 1kg/MM is 9.81 Nmm so maybe I should go from 9 Nmm to 9.5 Nmm. Will try adding 2 and 3 clicks compression damping to see if that helps avoid the risk of bottoming out, firkscste very close to bottom under hard braking but I haven't yet tried a full emergency stop and don't want to bottom out, lock up at the exact moment I really don't need to! If it looks very marginal or my practice emergency stop does bottom
Out I'll go to the 9.5 Nmm fork springs. Thanks for your input on the spring rates!

Added two turns compression and now forks seem very hard and uncomfortbale so will go back to previous compression setting, and with 4 rings showing for pre-load and then swap for teh K-tech 9.5Nmm (0.97kg) fork springs. Matris 46K rear arrived with 135Nmm spring (13.76kg) and have spoken to the UK importer who is taking it up with Matris. They expect Matris to supply a softer spring - my guess is 115Nmm or possibly 120Nmm (11.7kg or 12.23kg) and then the UK distributor will swap springs - said takes 20 mins. So far so good but its a pain in the @rse having to pull the shock out get it to the distributor, get the spring swapped, get it back and re-install - particularly when I understood I was ordering a bespoke shock built to my weight and riding style! Hopefully it will be worth it. I have purposely not commented on alternative spring rates with the distributor as very interested to hear what he reports back from Matris. I guess the 135Nmm might be fine around a billiard table smooth race track, but not on real world UK roads!

I have a similar issue with the Matris shocks. They supplied 135N/mm rear and I can only get to 55mm sag on the rear 2up. I told them we were 215lb (98kg) and 130lb (59kg) with gear - I am probably 10 lb heavier at the moment since my trip back to Australia. Cadbury chocolate, sausage rolls, pasties and Tim Tams.

This was the answer from Matris:

"The spring rate 135 N/mm in our opinion is correct for this bike and also for the indicated driver/passenger weight.
I confirm you that we have available softer spring rate 115 - 120 - 125 N/mm if needed.
Before to change the spring, please check well preload and rebound adjustment.
The 55/65 mm sag is quite normal on a touring bike lie MG Norge ... 30/35 mm sag usually is for a sport bike."

So a new wrinkle with them saying 55mm is the target? Do I go after 35mm sag or accept the 55/65mm sag. I have 16 of the 17 clicks on preload to get to 55mm.

There is not a 130N/mm so I will try the 125N/mm Is there a rule of thumb to work out what sag would change with a spring that is 93% of the stiffness?

Will have to check my Rebound settings but I thought they were good. No Compression adjustment on this shock.

ecs wrote:

 I have 16 of the 17 clicks on preload to get to 55mm.

Reading your post and i may have read it wrong, the 16 of 17 clicks relates to the rebound damping? If so then that does not set the sag. The 55mm Sag, is set by adjusting the spring tension only. So loosening it up will give you more sag and tightening it will reduce the sag. This is normally achieved by turning the two large rings at the top of the shock, or the knob on the side if you have a preload adjuster. Only when you have done that and set the correct amount of sag do you need to start adjusting compression and rebound damping.

The compression damping is adjusted via the screw on the gas canister on the top of the shock. Rebound by the knurled wheel just below the base of the spring. Preload to achieve the correct sag is set by the two rings on the top of the shock.
Matris have replied to say the same to me about spring rate . I aim to optimise the set up this weekend and to get optimum sag which on the GRiSO I think is 35mm with rider. I have backed off compression and rebound two clicks each. I think I am now 14 out in one and 16 out on the other. Have it written down but not hand. Is a little better and fine on a fresh well surfaced tarmac but still too stiff on what passes for A and B roads here in the U.K. Matris offered me the alternative springs and I am tempted to go 120Nmm. I very rarely go two up and if I do it's my skinny 16 yr old getting a lift not my wife!

That sounds like the same problem with the stock shock, but you also have it oversprung as well!

Sometimes going really soft on the spring does not work. I know when i raced the TT, we spent lots of time trying to soften the rear end after using the bike on track, but to no avail and it was simply the shock was not capable of high speed damping in those conditions. We change the shock and ended up with he same spring rate. Riding on the road is always a compromise between comfort and handling especially as you ride at different speeds on many different surfaces.

Like all things it is a matter of taste how your bike rides. The trick with suspension changes is to set the sag and then keep notes as to what you adjust and when and make sure you ride the same route when you test, and only adjust one thing at a time!

Agreed. Lots of fiddling ahead. I would like to think the Matris damping is up to the job and I can optimise it. I've asked Matris to confirm what they expect full shock travel to be in normal use and I'll put a tie wrap on the shock to see what I've got. Feels like very little at the moment!

Is there some ride height adjustment available? I have just pressed the button on a second hand Stelvio shock as i want more ride height and a stronger spring rate, and more suspension travel so i am interested to see how it will work out. I know Paul Brice is having similar issues, but there are lots of folk on here who have had success with them, so maybe they will chime in with some settings.

Yes the Matris is adjustable length from 319mm to 329mm. I have it set at 329mm. I think Damping will be good as I do notice the difference with just 2 clicks off on compression and rebound and I am from memory roughly half way in adjustment - 14/28 clicks or 16/32 clicks. I think it came set at 12 and 14 clicks out. When I ordered I gave them my riding weight at 103kgs and that I aim to avoid motorways whenever possible and ride A and B roads in the UK which do not have the best surface, so i had hoped they would supply a shock specced to suit, but I think 135Nmm (13.76kg) spring is too hard. Others here have commented that 100kgs rider tends to result in an 115Nmm (11.72kg) spring, so my thinking is that Matris promote a stiffer spring so I will go for 120Nmm which I hope is the optimum. Ill get fiddling with the settings this weekend and see what I can do before I ask for the 120Nmm spring.

One thing you need to consider, the more you increase rear ride height, the more you shift the centre of gravity forward, meaning increase weight bias to the front.

I did my bike in stages and had to go softer rear spring, harder front after altering geometry.
I'm at +60mm rear, -30mm front and -50mm wheelbase, -40kg weight.

Always remember, with a single adjustment you alter five aspects of geometry.

Good point. I am thinking initially of raising the front of the bike back up initially as i want to increase ride height overall. Then the playing begins :-)

I'm hoping Matris will drop the spring rate on mine. Despite your experiences with 'softer spring not always the answer'; there is no combo of settings on my Matris that makes it feel like it is doing any suspension at all; I can only get to around 24mm rear sag with me and bike (and that's with pre-load completely loose)......if a softer spring doesn't work, it'll be time for a sprung saddle

Matris will supply an alternative spring - have offered me 115Nmm, 120Nmm. Not quite clear if this is an exchange, an 'extra' or just a free spare. Pain the @rse having to take the shock off and change the spring etc. I aim to 'fiddle' with the settings this weekend and see what I can do to optimise it.

Matris have responded to say they recommend between 40mm and 45mm of static sag on the rear shock with rider. So that is what I will aim to achieve. If I cant achieve it then it confirms the spring is too hard......

That is interesting, for race setup i always set it at an inch 25mm, for the road 30 to 35mm, that amount of sag seems a lot to me, especially given the short amount of travel at the backend

Its a heavy bike so maybe their set up science is to allow more travel. I'll try to get to their recommended settings and see. Strange as when I ordered it the UK distributor confirmed that the shock was completely bespoke and didn't need any specialist set up, just fitting and was pre-set for my weight/riding style/use by Matris. I'll measure the sag as it is on the supplied Matris set up first and then see if I can get to 40mm.

That doesn't sound right to me (and is the opposite direction I'm currently going with their shock fitted). I can get to 42mm rear for me at 75 kg plus bike if I wind the pre-load to none at all. I think (I know jack shit about suspension setting up) based on riding it that it doesn't work; and strangely for me at least winding pre-load on and cutting the sag down to mid-late 20'smm is actually better. No idea why BTW; think it's something to do with dynamics of both bumps and dips but see disclaimer.

Let us know how you get on because I think 40 mm will require no pre-load ie spring at top of max max point it can go!