2017 MX Suspension advice

C5tor

Chief Comedic Instigator
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1,200
Location
San Ramon, CA
#1
Question for you suspension gurus out there, since suspension is one of those subjects that make my brain bits all confused.

Well, it appears my son has been landing the MX a bit hard. We had mostly been riding trails and hills, which the 4CS suspension handled quite well. But now that he is hitting the MX track and starting to hit some pretty big jumps, the rear tire is starting to hit the rear fender on the MX. It didn’t help that the new Battlecross X40 tires I put on the bike are considerably taller than the Pirelli Scorpions that were on it previously. The bike already has a stiffer rear spring than stock (a 65 N/mm). But I wasn’t expecting him to start rubbing the rear tire, given he only weighs about 140 lbs with gear.

Short of revalving the shock (which I maybe will have done this summer if I have some money), I would assume my choices are to crank up the preload on the spring, and increase the low speed compression. Is that the correct action? I will definitely be resetting the sag, as he is heavier now than when I got the bike, but really hadn’t expected his light weight to affect the bike much, especially with the heavier spring.

Also, anyone know of a good suspension shop in the SF Bay Area that knows 4CS suspension? I’d rather deal with a local shop if possible, rather than ship the suspension out and not have the bike for a month or more. We use these bikes almost every weekend, and it would be very traumatic to not be able to ride for an extended time. It has been our only outlet during the lockdown.

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Philip

Administrator
Staff member
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3,314
Location
Lake Havasu City, AZ
#2
Nah, that's not much rubbing here. Nothing on the fender. Just add 2 links to the chain and move the wheel back 5/8" to reduce the rubbing.

But if not the rubbing but the bottoming is your main concern, I am going to post a link to the Alta 4CS factory revalve specs out in the open. It has been years and years since anyone was actively revalving 4CS suspensions, so it is no longer the trade secret that it once was.
 

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