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Help selecting rear spring rate
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TOPIC: Help selecting rear spring rate

Help selecting rear spring rate 2 months, 2 weeks ago #557965

  • bowber
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A few questions for those experienced with messing with trail/enduro suspension.

My DR350s is fitted with a 5.7 kg/mm rear spring but I'm wanting a heavier rate spring and I've been recommended 8.1 kg/mm, this seems like a huge change to me but plenty of people have said they use it.
However I have a different damper fitted and the heaviest spring I can find is 6.3 kg/mm.

The 5.7kg/mm is definitely too soft when I ride and if I do the sag measurements it is to soft.

So what I'd like to know is how much difference going from 5.7 to 6.3 and 8.1 kg/mm springs will make.

If the spring was only £40 or so I'd just get it and try but they are £87 each so not a cheap mistake.

I'm also getting 0.45 kg/mm front springs, up from 0.41 kg/mm.

Thanks
Steve

Re: Help selecting rear spring rate 2 months, 2 weeks ago #557974

have a look on here bowber

www.racetech.com/

theres a spring calculator on the site which may be of help
whats the wether forcast ..wheres me map

Re: Help selecting rear spring rate 2 months, 2 weeks ago #557979

  • bowber
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Hi Steve

Yeh I've tried that but a lot of people have commented that it's not very good. It tells me I need 0.46kg/mm fork springs and a 5.6kg/mm rear spring. The fork springs seem about right but the rear spring is definitely to soft, by quite a way as well.
Most of the spring suppliers seem to offer DR350 rear springs in the range of 7.2 - 8.1 kg/mm so I think that's telling me something

The spring size I need is 63 60 270 free length, very common on 90's Japanese MX bikes. My rear unit is off an RM250 (1989)

Steve

Re: Help selecting rear spring rate 2 months, 2 weeks ago #557993

Just a thought but have you set the compression and rebound clickers back to standard?
Yamaha FZS1000 Fazer...the KTM 450 EXC-R has gone

Re: Help selecting rear spring rate 2 months, 2 weeks ago #557999

  • bowber
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Scott_rider wrote:
Just a thought but have you set the compression and rebound clickers back to standard?


There is no standard for this bike, the suspension is not the original hence buying new springs.
I do have the original suspension but the rear damper is buggered and the forks are not far behind, in fact to forks are DR fork I have are not the originals they were very battered and even had a dent big enough to stop the travel part way down!
Even if the original suspension was fitted it's very sort and I tend to push on a bit so I like firm suspension.
Original DR fork springs were 0.39kg/mm and 0.44-0.48kg/mm seems to be a regular upgrade
Original DR rear spring is around 5.7kg/mm and I've seen from 7.2-8.1kg/mm mentioned as an upgrade, quite a jump I was thinking.
However using KTM's EXC owner manual as a guide they go from a 70kg rider using a 69n/mm spring to a 90kg rider using a 76n/mm spring.
n/mm are slightly different than kg/mm because of the force of gravity (9.8) so 76n/mm = 7.76kg/mm

This is why I'm wanting some real world experience of how much difference each step up in spring rate makes.
I have a friend who used to do a lot of suspension work on WP for his KTM team but getting hold of him is rather difficult these days!

Steve

Help selecting rear spring rate 2 months, 2 weeks ago #558006

bowber wrote:
A few questions for those experienced with messing with trail/enduro suspension.

My DR350s is fitted with a 5.7 kg/mm rear spring but I'm wanting a heavier rate spring and I've been recommended 8.1 kg/mm, this seems like a huge change to me but plenty of people have said they use it.
However I have a different damper fitted and the heaviest spring I can find is 6.3 kg/mm.

The 5.7kg/mm is definitely too soft when I ride and if I do the sag measurements it is to soft.

So what I'd like to know is how much difference going from 5.7 to 6.3 and 8.1 kg/mm springs will make.

If the spring was only £40 or so I'd just get it and try but they are £87 each so not a cheap mistake.

I'm also getting 0.45 kg/mm front springs, up from 0.41 kg/mm.

Thanks
Steve


Where are you getting them from
I need some better fork springs too
We buy things we don't need

With money we don't have

To impress people we don't even like

Re: Help selecting rear spring rate 2 months, 2 weeks ago #558032

  • bowber
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  • 1200cc
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Ebay Johnny.
Just do a search and they come up.

Steve
The following user(s) said Thank You: johnnyboxer

Re: Help selecting rear spring rate 2 months, 2 weeks ago #558042

it seems to vary quit a bit depending on the shock .

me big tenere ohlins ended up with a 90nm on it me ccm which is 70kgms lighter has a 100nm on it ?which can suggest the intenal workings /oil flow of the shock .rebound rate have a part to play on the spring required



ive just run the crf 250 through ractechs calculator its around 8kgms heavier than the dr but not that far away
...
standard spring is 9.5kgm ?

100kgm rider 20kg luggage ..120kgm comes out at 12.927kgms spring which is well over double what you have at the moment ..

if i run it solo at 80kgms its 11.1

the rm is only a very light stroker as well thus the weak spring ??

confused ...so am i

i ran the rm250 through thesame calculator and it spat out 5.42 kgm



anyway if its any good to you the crf was undersprung at 9.5gkm .. for me ...
so if thats anything to go by a 9kgm spring wouldnt be out of the way on a bike of similar weight and travel ..

id go by the dr forums and work off that

just trying to help but ive confused meself ..theres a wild differnece between the crf calculations and the dr ??in fairness the crfs calculations make sense the drs dont .. oh well
whats the wether forcast ..wheres me map
Last Edit: 2 months, 2 weeks ago by minkyhead.

Re: Help selecting rear spring rate 2 months, 2 weeks ago #558047

  • micksea
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bikes with linkage suspension will vary from bikes without linkage as the linkage changes the ratio of force going through the spring. (probably explained badly but I'm sure you get the drift)

Re: Help selecting rear spring rate 2 months, 2 weeks ago #558049

micksea wrote:
bikes with linkage suspension will vary from bikes without linkage as the linkage changes the ratio of force going through the spring. (probably explained badly but I'm sure you get the drift)


trangulation / leverage / mounting angle ..different shock ....youve really fucked it up now mick

good answer and probably the correct one
whats the wether forcast ..wheres me map
Last Edit: 2 months, 2 weeks ago by minkyhead.
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