2017 MX Suspension advice

[C5tor]

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.

 

[Philip]

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.

 

[Philip]

I added the specs to the 1st post:
Factory developed Redshift MX suspension shim stack specs (UPDATED)

 

[TCMB371]

Stock valving is trash. Get that bike revalved and it'll be way better.

 

[Judaslefourbe]

You can also swap the link for a steeper curve on the shock.

 

[C5tor]

You can also swap the link for a steeper curve on the shock.

Any recommendations on what link to try?

 

[Philip]

An MXR rocker, links, and shock?

 

[snydes]

FYI we found out MX/MXR shocks are not interchangeable without modification to the subframes for reservoir clearance due to the upper shock mounting points being machined in the bulkheads at different locations.

 

[Judaslefourbe]

You don't need to change the shock. Just use the MXR link. It will fit in 99% of cases.

 

[C5tor]

You don't need to change the shock. Just use the MXR link. It will fit in 99% of cases.

Well, that is a good start, but I’m pretty sure Liquid doesn’t have any suspension links listed for sale. Anyone know if the MXR link was a stock part for some other bike?

 

[snydes]

Well, that is a good start, but I’m pretty sure Liquid doesn’t have any suspension links listed for sale. Anyone know if the MXR link was a stock part for some other bike?

You probably did, but be sure to check with @ayden_kry first. I don’t think they have their entire Alta inventory listed on eBay.

 

[ayden_kry]

If anyone is interested I just made a listing for them Alta Motors TRILINK, 74MM, CNC, LOADED MXR/EXR | eBay

 

[#76]

@C5tor

What did you end up doing in this to get it sorted?.

 

[C5tor]

@C5tor

What did you end up doing in this to get it sorted?.

To eliminate the skid mark, I ended up adding a link to the chain. This moved the wheel back a bit, and eliminated the rubbing. It also allows you to mount wider tires, since the swingarm widens out farther back.

I frankly can’t remember if I ever swapped out the link for an MXR one. I definitely ordered one, just don’t remember if I actually ever swapped it out!