Stiffer standard front forks

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Kev Rev
Posts: 27
Joined: Thu Nov 24, 2016 6:10 am

Stiffer standard front forks

#1 Post by Kev Rev » Thu May 24, 2018 9:13 am

Anyone successfully stiffened up their standard front fork set up.?
I rode mine for the first time since a full resto to have it MOT'd and the front felt way too soft and felt like it would bottom out if pushed hard.
I rebuilt them with 5w fork oil, was wondering if a new modern set of progressive springs and 10w oil may give me the type of feeling I am after?
Thoughts and recommendations welcome please

AHAMAYfrank
Posts: 92
Joined: Thu Jul 21, 2011 9:02 pm
Location: Outside Carrollton, Georgia

Re: Stiffer standard front forks

#2 Post by AHAMAYfrank » Thu May 24, 2018 11:20 am

The short story is: Race Tech lists the STD fork spring rate as .39 kg/mm and recommends .88 for a 200 pound Rider on the street, so yes your springs are a good bit too soft. Yamaha commonly used soft springs with a bunch of preload back then.

In a damper rod fork the oil viscocity mostly controls the rebound damping so changing oil weight will have minimal effect on the compression side. If you are interested in a progressive spring rate you can add to the oil height or volume which will increase effective spring rate by reducing air space in your fork.

RT also has a cartridge emulator that will allow you improve and adjust compression and rebound damping. I have this setup on a number of my bikes and I am very happy with the results.

Frank S.
1973 Yamaha AT3 e-start, 1977 Yamaha TY250D, 1985 RZ500, 1987 Suzuki RG500CH, 1991/2014 TZR450F Yamaha, 1991TZ250B Yamaha, 1991 Yamaha TZR250R, 2005 Scorpa SY250R, 2017 Ducati SuperSport939S (for the runners)

Linx
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Location: Stratford Upon Avon UK

Re: Stiffer standard front forks

#3 Post by Linx » Sat Jun 09, 2018 4:39 am

I bought some Hagon progressive springs but found them too hard. I'm going to try just adding pre-load to the standard springs and 10wt oil.

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phildu31
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Location: Toulouse France

Re: Stiffer standard front forks

#4 Post by phildu31 » Mon Sep 10, 2018 11:07 am

Hi.
Do you know what are the spring rates of your Hagon progressive fork springs ?
Generally, there are two different rates depending on the compression level.
I can't find this information on Hagon web site ( Ref : 400-123-04 ? ).
Thanks.

Linx
Posts: 169
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Location: Stratford Upon Avon UK

Re: Stiffer standard front forks

#5 Post by Linx » Mon Sep 10, 2018 11:22 am

Sorry I don't know but I have an update in my issue. I had air in my forks. I've now gone back to the Hagon progressive springs with 10wt fork oil and I've cut 2cm off each spring. I'm happy with it now.

Sent from my HTC Desire 530 using Tapatalk
:smt006 Current Bikes
1984 47X RD500LC, 2018 Triumph Speed Triple RS, 1999 Honda CB600F Hornet
Past Bikes Include
RD250LC, RD350YPVS LC2 Race Bike, RD350F2, 1976 CB400F

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phildu31
Posts: 430
Joined: Tue Jul 19, 2011 7:49 pm
Location: Toulouse France

Re: Stiffer standard front forks

#6 Post by phildu31 » Mon Sep 10, 2018 12:04 pm

I also use 10W with stock springs and disabled anti-dive.
10W seems the best option for stock fork.
At first, I was little bit surprised with the stock spring rate stated on the Race Tech site : 0,39 kg/mm, that's way too low !
But then I compared the free length of the Race Tech replacement springs : 377 mm, with the original fork springs ( RD/RZ version ) free length : 498 mm.
And all that makes sense : original springs are so awfully soft that 120 mm are needed on free length !!
The funniest is that only 55 kgs of pression are needed to use the 140 mm full extent of the fork.
Stiffer springs are definitely the way to go.

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