4.8 Rear Spring for 155lbs rider too much???

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4/28/2021 12:42 PM

Ok, so I need come guidance... I have a 2017 FC 450, and I had had my shock serviced and the bladder and spring were replaced, and they also changed the valving.

My question is, I weigh 150-155lbs (without gear) and that seems a bit much for what I've read. Could they have changed the valving or run different oil to make that much of difference in spring rate? I called and they said with gear I am right on the edge of 45 or 48. Race Techs site said I should be a 45 so I am totally confused.

I have set my race sag at 102 and my static sag is 52mm

It does feels a bit rough coming out of corners and does seem to kick/deflect a bit more than with the stock 45 spring.

Any guidance would be greatly appreciated!

BTW - My front forks are WP spring conversions with 46 springs.

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4/28/2021 12:56 PM

What spring manufacturer?

If you have 105mm sag, the spring should have 7mm preload. So if it's a 260mm spring, it should measure 253mm (with bike on stand).

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4/28/2021 3:24 PM

OK, to be clear, we are talking spring rates in N/mm here like KTM and WP use in the manual and on their markings?

Do not confuse 48N/mm with 4.8Kg/mm.

If we are talking 48N/mm that is almost guaranteed to be way too stiff for a 150lb rider.

For reference, the stock spring in the FC450 is 42 or 45 N/mm (depending on year) and the manual states this is targeted for a rider up to 187 lbs. I am 180 lbs and I swapped the 42N/mm spring from my FC350 for the stock 45 N/mm spring from an FC450.

I can't imagine there's any amount of valving you could change to make a 48N/mm spring work for a 150 lb rider. And your sag numbers suggest the spring is way too stiff for you.

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Powerband in every gear !

4/29/2021 6:19 AM

Stock is 45N/mm which is good for about 188lbs.
48n/mm is way too stiff for your weight you really should try the 42N/mm.
For what it’s worth I happen to have a 42 I can send it to you for 60 shipped but I’m not trying to sell you anything it’s just sitting in my garage.

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4/29/2021 5:00 PM

I’m 160, so about 185 with gear and get around the track ok. I was thinking about trying the same on my 19 350. The stock seems to blow through the bottom of the stroke easy. And my rear fender shows it. I’ll probably try some more clicker settings first. The real fix is different linkage though. Ride engineering, FC, and Luzon/N2D and others all make linkages for the bikes with a different rising rate to beef up the end of the stroke from what I understand. It’s a bit above me honestly. Some require a stiffer spring as well so the spring you have may be correct for a different linkage.

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4/29/2021 7:06 PM

soggy wrote:

I’m 160, so about 185 with gear and get around the track ok. I was thinking about trying the same on my 19 350. The stock ...more

I'm 180 without gear, so like 195-200 with gear and get around the track pretty good. With the stock 42 spring on my 350 I was touching the fender too much. It doesn't help that I like to run the sag a little on the too much side. So, I put the 45 spring on and initially felt like it was too big of an increase. Was wishing I could find a 43 or 44 but such a thing does not appear to exist. After opening the HC 1/4 turn and going in 2 clicks on the rebound it now feels pretty good and I am used to it. In order to get my sag, I have almost no preload on the 45 spring.. like 1-2mm. I suspect you'll be even worse off in this respect at only 160 lbs.

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Powerband in every gear !

4/29/2021 8:07 PM

soggy wrote:

I’m 160, so about 185 with gear and get around the track ok. I was thinking about trying the same on my 19 350. The stock ...more

FGR01 wrote:

I'm 180 without gear, so like 195-200 with gear and get around the track pretty good. With the stock 42 spring on my 350 I was ...more

Thanks for the feedback, ironically it is what race tech specs for me (or closest too anyway)). What are you running your sag at? More then 105?

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4/29/2021 8:18 PM

soggy wrote:

Thanks for the feedback, ironically it is what race tech specs for me (or closest too anyway)). What are you running your sag ...more

The Race Tech recommendations seem on the stiff side. It tells me I need a 4.76kg (46.7N). Like I said, I can barely get my sag with the 45N. I couldn't imagine putting a 47 or 48N on. I have my sag set 106-109 range. Even if I go to 105mm, it's barely any more preload.

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Powerband in every gear !

4/29/2021 11:12 PM

soggy wrote:

I’m 160, so about 185 with gear and get around the track ok. I was thinking about trying the same on my 19 350. The stock ...more

FGR01 wrote:

I'm 180 without gear, so like 195-200 with gear and get around the track pretty good. With the stock 42 spring on my 350 I was ...more

Cannon Racecraft and Race Tech both have 43n(4.4kg) springs available and Q-Spring has a 44n(4.5kg).

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4/30/2021 7:40 AM

slipdog wrote:

Cannon Racecraft and Race Tech both have 43n(4.4kg) springs available and Q-Spring has a 44n(4.5kg).

The Race Tech ones I believe say they are shorter and require an extra spacer. I was like, to just go from 42-43 ain't worth all that.

Isn't Cannon the company used to or still does produce one of the more well known brands?

I never heard of Q-spring. Their 44 sounds like a good option.

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Powerband in every gear !

4/30/2021 8:07 AM

FGR01 wrote:

The Race Tech ones I believe say they are shorter and require an extra spacer. I was like, to just go from 42-43 ain't worth ...more

Cannon is out of Oklahoma and tend to have the largest range of rates available per application as well as make custom springs wound to your specs.

Q is out of Holland and imported through Innteck USA who also are the US importers for SKF

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4/30/2021 12:00 PM

Your dag tells you all you need to know, you are way off.

155=42nm
175=45nm
190-200=50nm

Makes a difference if you are tall, go stiffer side. Not more than 7mm preload in my opinion.

36-40 static 102-105.

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5/1/2021 6:27 AM

Thanks everyone for your thoughts! I have spoken with another well-known shop, and I have decided to use a progressive link to help remedy the issue.

Thanks again!

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5/1/2021 10:57 AM

soggy wrote:

I’m 160, so about 185 with gear and get around the track ok. I was thinking about trying the same on my 19 350. The stock ...more

I had N2Dirt do my valving, and I'm using there knuckle. They increased my rear spring by 3 rates stiffer. Surprisingly it works.

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5/2/2021 9:57 AM

soggy wrote:

I’m 160, so about 185 with gear and get around the track ok. I was thinking about trying the same on my 19 350. The stock ...more

NeedMoto wrote:

I had N2Dirt do my valving, and I'm using there knuckle. They increased my rear spring by 3 rates stiffer. Surprisingly it ...more

Thanks for the info, I was wrong about the spring I have. It’s a 4.6 kg so 45(n/mm). Which should be in the ball park for me at 180-185 with gear on

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