Sonic vs Progressive springs

[GSJim]

Now that I'm totally confused about shocks (see other thread), I might as well work on fork springs too.

The front end of my bike is bouncing like a pogo stick, so I'm doing a lot of reading on springs. At the moment I'm leaning toward straight rate springs (Sonic) instead of Progressives.

Mr. bwringer provided a great review of Sonic for his GS850 and recommends them for above average sized guys who ride real fast. I'm around 195 lbs geared up, carry a tank bag and ride sort of normally, but hope to step it up a bit as I get familiar with the bike again.

I emailed Sonic regarding the GS650G and had a response within 20 minutes telling me that they would make springs for my bike and had just added them to the catalog. This is the fastest response received since I started my suspension search, so I'm really impressed with Sonic's customer service.

Has anyone here used Sonic springs in a mid-sized bike like mine? I would be interested in any comparison between Sonic and Progressive. I think we all agree that the OEM springs are junk.

Thanks.

Jim

 

[salty_monk]

Use Sonic springs & Racetech Emulators... or if those are 35mm forks on the 650 these will probably work: http://www.mikesxs.net/products-19.html#products $54

You could also do some calculation & cut down your springs then add more spacers to suit.
You could spend what you save on the springs on the emulators...

Just an idea. I did this recently & posted some links for the spring calculation resources I used. It's tough to get stock springs up to 50lb as you run out of spring travel but mine are now at 43lb/inch with Emulators. Stock I calculated there are something like 22/28 lb/inch (Not tried them yet but I have never got near full travel on my 1000 with Progressive springs in it so these might work fine, plus it allows me to keep the bike on the road & play with springs later as that's the easy bit).

Progressives are 35/50lb an inch (0.9kg/mm). For your weight Sonic might recommend something a little higher 1.0kg/mm. You can see on Sonic's website.

Dan

 

[GSJim]

I exchanged emails with Rich at Sonic about my bike. The spring rate calculator on his web site gave various answers between 0.9 and 1.0 kg/mm depending on my estimates of bike weight and riding style. Rich recommends 0.9 kg/mm and 15wt fork oil for my setup, which is as good a starting point as any I can think of.

I checked Salty_monk's posts and found that 0.9 kg/mm is 50 lb/in, which is the same as the high range on the Progressives. If I already had Progressives or anything with a known rate, I would try cutting them but I only have the original springs of unknown rate and age-related sagging. I have no idea what the rate is for the stock springs, but the bike is under-sprung even with extra air in the forks. I would like to eventually try emulators, probably the next time I do fork seals. Fortunately I can play with springs now without damaging the seals.

Again, I am really impressed with how fast Rich at Sonic answers emails.

Jim

 

[salty_monk]

You can calculate your stock rate easily enough.....

 

[speedyandypandy]

Progressives rated springs are ok if your riding style changes alot, like one day packed up, one day with a pillion, one day without load. And might be the best solution for old bikes, when there isn't many settings you can play around with. Atleast for road bikes.
Cutting a spring to get a more correct spring rate isn't that ok, since fork travel will be shortend it could end up shorter than the forks full travel lenght, and is very bad.
The way you cut the spring could effect the steel, wrong heat treatment could mess up your spring in all kind off ways. Use a hacksaw and a handfile and go slow.
Someone said springs gets old and tired, in a interview with one of UK leading suspension companies said they measured all springs that come in, they found that old springs haven't lost much of the original rate.
What I read into this is that it's the rest of the fork/damper that needs a overhaul, not the spring that needs changing out.
Linear springs are predictable, and are easy to dail in, wouldn't consider anything else.
Just my 50-cents...

 

[GSJim]

salty_monk, I guess I could calculate the rate of the old spring, but I think I will do something un-GSR-like and spend some money. I plan to order the Sonics to have a good starting point for experiments.

speedyandypandy, the forks were rebuilt last year with new seals and fresh oil. I asked the guy who did the work to install new springs but he said they weren't needed. I regretted the decision the first time I rode the bike. Adding more air isn't enough to compensate for the undersprung forks.

Thanks for the replies.

Jim

 

[GSJim]

The Sonic springs arrived a few days ago and I picked up some 15wt Belray fork oil. Further details and some pictures will be added to my project thread in a week or two when I install the springs.

Jim

 

[tkent02]

Did you get the emulators?
I have the Mike's XS emulators in my 650G, they kick ass.
Wish the rear rode as smoothly as the front.

 

[FullThrottle82]

I have talked and rode with Rich at Sonic and he is a great, knowledgeable guy. I have his springs in my GSXR forks on my GS1100E and they are great. I think I paired them with 15w oil. You will be happy with them.

 

[GSJim]

Did you get the emulators?
I have the Mike's XS emulators in my 650G, they kick ass.
Wish the rear rode as smoothly as the front.

I'm just doing the springs this time so I don't have to completely disassemble the forks and drill the rods. I will add emulators the next time I do the seals. The seals were done last year and I should have changed the springs at the same time.

Jim