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Old November 27th, 2020, 03:25 PM   #1
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Front suspension travel question.

Good afternoon everyone.

I am planning to rebuild the front fork and am trying to understand whether I need to get harder springs or not.

I took the bike for a ride around the city and measured the max travel of the fork at 90 mm (125mm max per the spec). I did not hit large bumps but did not try to find a flat road either. Pretty regular city ride.

Are those numbers enough to understand whether the springs are too soft/normal for me or I need to measure something else to make the informed decision ?

Thank you in advance.
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Old November 27th, 2020, 03:39 PM   #2
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are you saying your 35mm from bottom out ?
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Old November 27th, 2020, 06:25 PM   #3
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Quote:
Originally Posted by jrshooter View Post
are you saying your 35mm from bottom out ?
John,

Pretty much, basically that's the deepest the fork compressed over the course of my ride. What I did is -
1 I put the bike on the centre stand.
2 Unloaded the front completely by pushing on the rear.
3 set the zip ties to the lowest where they were touching the dust seals.
4 went for a ride
5 repeated steps one and 2
6 measured the distance from the dust seals to the zip ties - read 90mm
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Old November 27th, 2020, 07:15 PM   #4
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Try maximum braking downhill and hitting some bumps/potholes. Basically simulate worse possible condition.


Hitting bumps while suspension is bottomed-out is very dangerous, especially while in corners or trying to steer. Factory front-end on my pre-gen I can bottom easily under those conditions in S.F. (I'm 80kg). On my new-gen, it's still slightly soft, but doesn't bottom.
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Old November 27th, 2020, 07:15 PM   #5
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not really knowing your sag settings. if i understand correctly your are about where you want to be in fork travel. but i dont know how much preload you have dialed in or compression settings. you defintly dont want to be bottomed out during cornering
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Old November 27th, 2020, 07:51 PM   #6
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On the stock front suspension my ninja used to sag badly when coming to stops. I changed spring, installed emulators and used heavier fork oil and its beautiful now
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Old November 28th, 2020, 10:24 AM   #7
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Quote:
Originally Posted by Ceeloo Yello View Post
On the stock front suspension my ninja used to sag badly when coming to stops. I changed spring, installed emulators and used heavier fork oil and its beautiful now
Its not that bad on the 250H , If I am not mistaken it used EX500 frontend. But I want to see if I can still improve it while I am on it.
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Old November 28th, 2020, 10:26 AM   #8
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Thank you guys for the suggestions. We got good weather today and tomorrow. I will ride it a bit more to test more harsh scenarios
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Old November 28th, 2020, 12:44 PM   #9
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My stock pregen was so softly spring that normal riding on back roads around here would bottom the rear, and a hard stop would bottom the front. I'm only 170 lbs, so I'm not sure who they expected to be riding them. An eBay newgen rear shock ($25 delivered) cured the rear end, and a pair of Sonic springs with their recommended oil level cured the front.
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Old November 28th, 2020, 03:37 PM   #10
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Here are more measurements:

- No load - 25mm
- With me - 43mm
- Normal riding (as in original post) - 90mm max
- Riding over some rough asphalt - few manholes an over train tracks with preloaded front (breaking) - 100mm
- Emergency stopping - progressive breaking to the full stop - the last foot with a bit of a skid - 110mm

So it looks like the emergency braking has almost bottomed it out.
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Old November 28th, 2020, 03:38 PM   #11
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Quote:
Originally Posted by Triple Jim View Post
My stock pregen was so softly spring that normal riding on back roads around here would bottom the rear, and a hard stop would bottom the front. I'm only 170 lbs, so I'm not sure who they expected to be riding them. An eBay newgen rear shock ($25 delivered) cured the rear end, and a pair of Sonic springs with their recommended oil level cured the front.
Thanks Jim, the 250H rear shock looks like the one on the new gen - with a preload. Does yours have a preload ?
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Old November 28th, 2020, 04:14 PM   #12
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I was doing some research , looks like stock EX500 has the rate of 0.585 . The recommended rate for my weight from sonic site is 0.85. That's quite a difference

I feel like I should go for that upgrade.
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Old November 28th, 2020, 05:16 PM   #13
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Quote:
Originally Posted by SibSerge View Post
Thanks Jim, the 250H rear shock looks like the one on the new gen - with a preload. Does yours have a preload ?
They all have a preload. If you're asking if the preload is adjustable, yes it is.
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Old November 28th, 2020, 07:04 PM   #14
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They all have a preload. If you're asking if the preload is adjustable, yes it is.
Yes thats what I meant, sorry
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Old November 28th, 2020, 09:38 PM   #15
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if 58 is your spring, your way under. im 190 pounds and run a 90 sonic spring.
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Old November 29th, 2020, 05:41 AM   #16
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Here's Sonic's suggested spring rate table: http://sonicsprings.com/catalog/calc...pring_rate.php

My 110 lb. daughter rides it more than I do, so I chose the springs as a compromise for both of us. I got 0.70 kg/mm springs. Filled with oil to Sonic's suggested level, they are plenty stiff for me. I can do a stoppie on bumpy pavement an they don't bottom out. I don't remember the % static sag I went for, but I usually try for abut 20%. Of course you adjust that with the spacer length. They supply PVC pipe for making spacers.
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Old November 29th, 2020, 09:34 PM   #17
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Quote:
Originally Posted by Triple Jim View Post
Here's Sonic's suggested spring rate table: http://sonicsprings.com/catalog/calc...pring_rate.php

My 110 lb. daughter rides it more than I do, so I chose the springs as a compromise for both of us. I got 0.70 kg/mm springs. Filled with oil to Sonic's suggested level, they are plenty stiff for me. I can do a stoppie on bumpy pavement an they don't bottom out. I don't remember the % static sag I went for, but I usually try for abut 20%. Of course you adjust that with the spacer length. They supply PVC pipe for making spacers.
Thanks Jim, that does help. I sent them a question regarding what spring rate I need for my bike. Waiting for the answer now but based on their charts it looks like 0.85 should be the right spring for me.
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Old November 29th, 2020, 09:43 PM   #18
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Quote:
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if 58 is your spring, your way under. im 190 pounds and run a 90 sonic spring.
John is that for track or street riding?
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Old November 30th, 2020, 07:34 AM   #19
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John is that for track or street riding?
track
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Old November 30th, 2020, 10:20 AM   #20
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Quote:
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track
Thanks for confirming.
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Old February 4th, 2021, 06:38 AM   #21
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I decided to go with 0.80 springs from RaceTech, Racetech were more expensive than Sonics but SonicSpring's shipping charges to Canada were crazy. At the end RaceTechs turned out to be cheaper delivered.

While I am doing springs and seals I decided to add the emulators as well. Although not cheap people praise them so much I decided to pull the trigger. One rod has been drilled already so there is no way back .

We will see how this works out when the snow wears off.
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Old February 4th, 2021, 08:01 AM   #22
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Woohoo!!! I have similar set-up on my track-bike. You're really gonna love the transformation!
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Old February 6th, 2021, 07:33 PM   #23
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Woohoo!!! I have similar set-up on my track-bike. You're really gonna love the transformation!
I truly hope for that !

I finished rebuilding both sides today. Now I have to reassemble and align everything.

I measured the travel while the spring was not in the tube and it measured about 115mm with the damping rod spring being unloaded.

So apparently my emergency brake test I did in the fall was bottoming them down.

Stock spacers gave me 18mm preload which is in the middle of what Racetech specifies. I put them in, once I measure the static sag I might adjust them but it seems to be good start.

Even with the tubes being off the bike and trying to load it with both hands I can feel the difference in the spring rate. Not sure if I can easily tell that the emulators are working, though
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Old February 9th, 2021, 08:25 AM   #24
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The front is all back together. The race sag is at 28mm now. Do you, guys, think it's a bit on the shallow side for the street riding ?

I will probably test it in spring and then cut the spacers a bit. The static Sag is 18mm.

I was only able to roll in the garage as the rest of the surface is covered with snow and ice, Canada eh ? But I can totally see the difference already. The bike does not dive as much when stopping.
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Old February 9th, 2021, 10:55 AM   #25
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Personally I'd leave it. You tend to hit bigger bumps and potholes on streets and can use a little extra travel.

Having adjustable damping really helps dial it in!
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Old February 9th, 2021, 11:34 AM   #26
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Personally I'd leave it. You tend to hit bigger bumps and potholes on streets and can use a little extra travel.

Having adjustable damping really helps dial it in!
Thank you for the feedback Danno, I will keep it as is then. I need to take the second stage of my M license course in spring so I need to have the bike ready , once thats done I can play more with the settings and adjustments

I have dropped the rear end yesterday to lubricate all the bearings and stuff.
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Old March 9th, 2021, 04:28 PM   #27
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We got really warm weather today - 10C (50F for US folks) So I took the bike for a spin. Good news , nothing fell apart on the ride after me overhauling both the front and the rear

Seriously though, to be honest I lack experience to provide good judgment of what has changed but here are my observations that you might be able to help me to interpret.

1. The bike now "hugs" the road. It's follows the contour of the surface and does not float like it used to be. From the comfort prospective it's worse from the control perspective it's great. It feels more predictable now. I got the same feeling that I had when I replaced the stock Sachs struts on my BMW 328 with Bilstein HD. I wanted to puke in the beginning because on a road that is a tiny bit wavy up and down it was creating the rocking motion that made me want to puke Cannot blame the car it was just following the road.

2. The dive has significantly reduced.
3. I was not able to bottom it out while doing the controlled emergency brake. I compressed it pretty hard. I know because I lost the rear end and it swayed a bit. The forks went only about 75% in, The front end did not skid ! Before the change my front end would always skid in this case as I was (as I found out later) completely bottoming out the forks. And I cannot blame it on the better traction as the ground is still near freezing temps now and when I was testing it before the ground was way warmer.
4. I feel the steering is more predictable now.
5. Riding in normal conditions the forks wend down to 6cm max (out of 11 available - about 55%). It used to be 9cm which was is 85%.


I set my emulators towards the higher preload. I might want to try to unload them just a bit. Will see, I think I will ride it for a bit and then play with it. I want the weather to warm up a bit so the oil is warmer.

Overall I think it's great and I am happy for spending that money. I should have done it earlier, but how would I have known
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