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Old 04-22-2015, 07:55 AM   #1
malloy OP
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Straight Rate Springs in F650GS Twin Forks?

What is anyone's experience with aftermarket straight rate springs?

A while ago Indy posted that the F650GS Twin OEM 2009 - 10 fork springs are rated at .49kg/mm. Since the part number for the springs is the same 2006 - 2012 presumably these years share the same rate.

RaceTech offers straight rate springs at .60, .65, .70, .75 and .80 kg/mm. Sonic Springs has just .80 kg/mm. Both of their rate calculators say I should have .80+ springs (165# NoGATT, 195# ATGATT).

If you have used straight rate springs please tell us about them.
Year of bike?
What's your weight?
What rate did you get?
From who?
How long of a preload spacer?
Fork oil weight, amount, measured down?
Other fork mods (Ricor, RaceTech Gold valve)?
How do they perform for your style of riding?
Anything else we should know?

Very much obliged
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Old 04-22-2015, 08:29 AM   #2
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I have a 2010 F650GS that I put in Race Tech .70kg springs with Ricor Intiminators and 5 weight oil with no extra spacer preload. I weigh 200 lbs and ride 80/20 street/dirt with luggage and often 2up and am very pleased. I also put a custom built Yacugar shock & spring in the rear.
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Old 04-22-2015, 01:31 PM   #3
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Btw, the Race Tech calculator said I needed 90kg springs but several suspension pros said that calculator greatly exaggerates. 70kg has been perfect so I'd imagine 90kg would have indeed been excessive.
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Old 04-23-2015, 05:53 AM   #4
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Very useful info, Excite! Especially the part about the RaceTech Calculator being excessive as I couldn't imagine almost doubling the stock spring rate.

Is your weight ATGATT or NoGATT?

When you say "no extra spacer preload" do you mean that you just used the OEM 200mm spacer? RaceTech recommends 20mm preload (different from spacer length). Did you aim for that?

Inquiring minds want to know

Thank you.
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Old 04-23-2015, 08:04 AM   #5
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Quote:
Originally Posted by malloy View Post
Very useful info, Excite! Especially the part about the RaceTech Calculator being excessive as I couldn't imagine almost doubling the stock spring rate.

Is your weight ATGATT or NoGATT?

When you say "no extra spacer preload" do you mean that you just used the OEM 200mm spacer? RaceTech recommends 20mm preload (different from spacer length). Did you aim for that?

Inquiring minds want to know

Thank you.
My situation is unusual because I lengthened the fork tubes by 2" and installed a 2" taller F800GS shock in the rear for better ground clearance. I'm not sure what length spacer they used to make it all work, but I believe they generally went with RaceTech recommendations, with no extra preload added. I weigh 200 lbs without gear.
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Old 04-23-2015, 08:22 AM   #6
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FWIW, I installed the intiminators using the stock springs and the intiminator recommended 5W oil and reinstalled the stock spacers as they were (did not cut them down).

I weigh 185lbs without gear and have found that just the intimantor and extra preload has worked much better than I thought it would .... even with heavy luggage or 2-up riding.
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Old 04-24-2015, 05:46 AM   #7
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Thanks J. R. Like you I have the Ricors + OEM springs. I can't seem to get the rider sag number anywhere near Ricor's recommended 38% (63mm) that I think you posted elsewhere. I've tried a variety of spacer lengths including the OEM 200mm + the Ricor (14mm) like you have. I can get 25 - 33% rider sag but these give a very harsh ride on small pavement imperfections. I think I'm compressing the spring too much with preload to get these numbers, not leaving enough spring to absorb bumps, imperfections. My local roads are very rough!

The OEM untouched set up was very soft.

The Ricors themselves are a great improvement but I think I could do better if I figure out this spring thing. 5 wt oil, 155mm down.

Thanks also Excite for the follow up. You did do some unusual things! Your bike looks cool. Curious who did your installs. Some one in the Bay Area?
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Old 04-25-2015, 03:53 PM   #8
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Malloy:

I might have posted numbers before, but I've been around ADVRider now for so long I forget ....

All the mods done on my bike have been done by an amateur ... me!

My rough calculations go like this:

Published suspension travel F650GS: Rear 170mm / Front 180mm

Recommended sag for dual sport bikes:-
Rear 30% of suspension travel,

Front 20 to 25% of suspension travel.

So for the F658GS that would be:
Rear: 51mm Front: 36mm - 45mm


I can get the rear sag OK for myself, ATGATT, and good load of gear.
I can not get quite enough preload for all of the above and 2nd rider.
self & passanger and light gear OK


On front right now I have about 60mm sag which is (like your setup), too soft per recommendations.
On the other hand it is MUCH better than stock, and I have chosen to ignore it for now.
Next time I disassemble the forks I will likley bump the preload a bit or go up a bit on spring rate or maybe replace the spacer tube with a short spring of higher rate ...

one of my old dirt bikes had that set up - 2 linear rate springs of different rates with a washer inbetween to square things up ...
I am surprised at the length of the spacer tube in our forks ... perhaps that saves weight and $$$ without any sacrifice for performance, or perhaps it just allows BMW to use the same spring that is used for some other application


Anyway ... let me not babble on ... things seem "OK" for me at this point.


I have dropped the front forks in the triple-tree by 10mm as otherwise when fully loaded I had the faint beginnings of head-shake/tank slapper. Stiffening up the front suspension would exacerbate that so ... if you go in that direction be careful!








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Old 04-26-2015, 06:41 AM   #9
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Thanks for the detailed reply, J.R.

The greatest sag I've gotten is 57mm, 32%. This was with 190mm spacer + a 2.5mm washer between the spacer and springs + the Ricor @ 14mm (total preload package of 206.5mm). The least is 49mm, 27%, with the OEM 200mm spacer and the Ricor (214mm package; forgot the washer). There have been others in between. Interesting is that a 1mm reduction in spacer almost always yields a 1mm (1 for 1) increase in sag. I hadn't expected that close of an affect. But always the ride seems harsh.

The OEM box stock was 73mm, 40%! I too was also surprised to see such a long spacer (200mm) and short springs (377mm).

All work done by an amateur
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Old 04-26-2015, 01:47 PM   #10
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Quote:
Originally Posted by malloy View Post
Thanks also Excite for the follow up. You did do some unusual things! Your bike looks cool. Curious who did your installs. Some one in the Bay Area?
Thanks.

https://superplushsuspension.com
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Old 04-27-2015, 05:42 AM   #11
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Interesting looking place, Excite.
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Old 04-29-2015, 06:00 AM   #12
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bump
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Old 04-29-2015, 10:30 AM   #13
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Quote:
Originally Posted by malloy View Post
Thanks for the detailed reply, J.R.

The greatest sag I've gotten is 57mm, 32%. This was with 190mm spacer + a 2.5mm washer between the spacer and springs + the Ricor @ 14mm (total preload package of 206.5mm). The least is 49mm, 27%, with the OEM 200mm spacer and the Ricor (214mm package; forgot the washer). There have been others in between. Interesting is that a 1mm reduction in spacer almost always yields a 1mm (1 for 1) increase in sag. I hadn't expected that close of an affect. But always the ride seems harsh.

The OEM box stock was 73mm, 40%! I too was also surprised to see such a long spacer (200mm) and short springs (377mm).

All work done by an amateur
Interesting....
Where did you get the washers?

I don't have much to compare to, so harshness, or lack of it, is perhaps I've just got used to .....
Or it could be that the Intiminators just made thing so much better for me that I was elated and moved on to other farkles ;-)

I might try adding 2.5 - 5mm of shim action before next big trip (loaded down) just to see what happens....

Thanks,
Jim

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Old 04-30-2015, 05:53 AM   #14
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Jim - The shims are hardware store items: washers for 1/2" bolts!
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Old 04-30-2015, 09:22 PM   #15
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Jim - The shims are hardware store items: washers for 1/2" bolts!
Excellent ... Thank you
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