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Discussion Starter · #1 ·
I install .85 sonic fork spring with 7.5wt oil as recommended to me but the front dive too much for my taste on hard braking, the reason i update fork.

With the stock spring, the compression was set to the max and compression at 1/4 turn of the max, with .85 spring and 7.5wt oil, the preload was at 4 turn to the max and compression at 1/2 turn to the max, more give me harsh ride but the front still dive too much, my question is at my wheight, 170lbs without gear, if i install .90 spring do i will have harsh ride like if i adjust preload more than 4 turn or crank more compression ajdustment on my .85 spring?

My concern was to reduce front diving but i dont want harsh ride and im not sure if i have the right spring set-up for me, i chose this set-up as recommanded to me (like 7.5wt oil since here in canada, climate was cold and it seem that the 10wt oil was not a good choice in cold climate) and it is definitely better than stock but not perfect for front diving in hard braking.

My olhins rear shock was not installed since my bike was in storage for winter, maybe it will help for front diving, i dont know.

Thank you for your help since i was novice in suspension set-up.
 

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I think your spring rate is OK. You can't always assume that all manufacturers fork oil weights are equivalent. You may need a heavier one. I assume you mean preload rather than compression.
Did you get your sonic springs direct and ship to Canada?
 

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Discussion Starter · #3 ·
Yes, direct from sonic usa and i go with 7.5wt oil for cold climate as recommanded by Nick
 

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There was a post on this forum listing the viscosity of various brands of fork oil. Check out that list to see your brands true viscosity. I was surprised how much they vary.
 

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Discussion Starter · #6 ·
yes sir, i use Silkolene oil 7.5 exactly like you reccomand it to me ;-)

for sure, this set-up is a big upgrade vs stock but hard brake dive is to much for my taste but i dont want harsh ride and i will live with this set-up if it was the best compromise of both world!
 

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yes sir, i use Silkolene oil 7.5 exactly like you reccomand it to me ;-)

for sure, this set-up is a big upgrade vs stock but hard brake dive is to much for my taste but i dont want harsh ride and i will live with this set-up if it was the best compromise of both world!
OK. Try going with a heavier oil to see how you like it. It will increase firmness and reduce initial dive, but not to the level heavier springs will. The 'real' solution requires a revalve with a reworked shim stack.
 

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Hey Nick while we are on the subject. can you give me some guidelines for rider sag front in rear as far as numbers? Also, once rider sag is set, what kind of "free sag"(amount of sag under weight of bike, no rider) numbers should I be looking for?
I come from a dirt bike background where rider sag is 1/3 of total travel and free sag is in the 10%-13% of total travel.
So with that logic:
Front travel is 5.4" (137.2mm) Rider sag is 46 mm and static sag is between 14mm-18mm
Rear travel is 5.1" (129.5mm) Rider sag is 43mm and static sag is between 13mm-17mm
Does that sound right? I read though your Stoltec Project bike post back in October and I think you might have gone over that then, maybe?
Thanks
Trevor
 

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With the stock fork valves you will always be compromising the firmness verses how compliant your ride is. The best solution is to replace the cartridges with any quality upgrade. This also has the advantage of separating rebound and compression valves so that one fork leg is rebound and the other is compression. Also you have adjustable ranges for both.
 

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Hey Nick while we are on the subject. can you give me some guidelines for rider sag front in rear as far as numbers? Also, once rider sag is set, what kind of "free sag"(amount of sag under weight of bike, no rider) numbers should I be looking for?
I come from a dirt bike background where rider sag is 1/3 of total travel and free sag is in the 10%-13% of total travel.
So with that logic:
Front travel is 5.4" (137.2mm) Rider sag is 46 mm and static sag is between 14mm-18mm
Rear travel is 5.1" (129.5mm) Rider sag is 43mm and static sag is between 13mm-17mm
Does that sound right? I read though your Stoltec Project bike post back in October and I think you might have gone over that then, maybe?
Thanks
Trevor
You'll have to see what works for you, but I've had a lot of success (and my customers) with 42 mm front and 38 mm rear rider sag. Try and maintain ~8 mm of static preload on the fork springs (or just buy the Sonic springs I had Rich custom wind...no spacer mods or math on the customer's behalf).

Free sag is commonly used in the dirt world, and nearly always with respect to the shock. Reason being, the two things that matter are rider sag and the amount of travel the rider is using during their intended operation. Most shock shafts are pretty well hidden, so seeing how much travel is being used is often difficult. S,o the combination of free and rider sag measurements provide the rider with information on the spring rate. If you can see the shock shaft (as you can on the forks), I recommend zip tie'ing the shaft and monitoring travel. I prefer to use this because at the end of the day, the amount of travel you're using is really what matters. Given the usage - street or track - the idea is to use the maximum available travel to soak up whatever your terrain throws at it. But, if you're looking to be academic, the accepted industry standard is a shock free sag in the 2-8 mm range (at the tail, not the shock itself). But, I'll warn you, I've found free sag measurements as high as 12 mm to work well on the FZ-09. Between the linkage ratio, road quality, and riding style, the determining factor needs to be how much travel you're left with. Bottoming out is never a good thing.
 
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