Slater Mobster AM 24" build- Mtbr.com
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  1. #1
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    Slater Mobster AM 24" build

    I haven't seen many discussions about the Slater Mobster 24" FS frame so I took a bit of chance in buying one. It was one of the few bikes I could find frame/shock only for under $1k that would grow to fit 26" wheels. I had many nice parts around so was really set on frame only. I know what people will say about the frame/single pivot suspension design, but hold your commentary on that ;-)

    I called BJ at Slater bikes in Colorado and after some discussion, I realized this was as close to the geometry and sizing I wanted in a frame only option as I was going to find. It can be built as a DH rig with up to a 170mm (not a typo!) fork or as more of an eduro rig with a 140mm (what I am opting for). The specs state a HTA of 64 degrees, I think that is with a 160mm fork, so it gets less slack with a 140mm fork. As luck would have it, he had a scratch and dent special for me, $500 with headset, seat collar and a very entry level shock (with 150mm of rear travel, again, not a typo). Normal price is $950, I bit at the offer.

    The frame arrived and the scratches and dents are hard to even see. But one negative was a needed to get both the BB and the head set chased and faced to remove excess paint. +$50 from local mechanic, no big deal but never have had to do that on a new frame before.

    The build: I had a set of 24" Alienation Malice wheels laced to 28h Novotecs that I had bought and built up a while ago, they were under $150 all in. I decided to improve on the drive train i had kicking around, so spent $60 for an XX1 gripshift 11 spd, $50 for an NX 11 spd deraileur, and used a newish XT cassette kicking around. I decided to buy the Trailcraft 152mm direct mount cranks because I am not impressed with the Suntour Xeron that I bought for my daughter's bike (can't get the chain line to work...). For fork, I found a used Manitou Mattoc Pro 26" with 140-160mm range and got that for $250 (it has the IRT option added which is a bonus for tunablity). The Mobsters that Slater showed me built up all have 27.5" forks (!), he uses the Suntour Aoins because Suntour will valve them for lightweight riders for no cost when ordering them. So I figured going with a 26" fork would keep the front down a bit for the more all around riding my son will be doing. I finished it out with some carbon bars off ebay ($15), a nukeproof stem ($10) from some closeout sale last year and a nice set of Deore brakes I had from a take off a few years ago (love the adjustability of these for small hands and the ability to make them grab at the start of the stroke). I also found a 27.2" carbon seat post for peanuts and then hit up my local shop for a really nice specialized xs seat they had from a takeoff (more than I wanted to spend unfortunately).

    Initial impressions and tuning: Can't find my luggage scale, but it's definitely not heavy. Think the Fat Albert and Hans Dampf tires are beefy but heavy and the XT cassette is a tank. Will look for the scale to get a total weight. This is a 26" frame no doubt! So if you have 24" wheels on it, you will have a longer wheel base. It's about 3.5" total additional wheelbase compared to his pretty compact 24" hardtail he is using now, but that thing has a pretty steep HTA and is smaller overall. No big deal in my book, we're likely to be doing mostly either smooth flow or more traditional straight on steeps. When I had everything on the frame, it was clear we would need to do some suspension tuning. The BB height is an issue out of the gate with 24" wheels. Since I don't want 160mm of front travel and don't really care about the full 150mm in the rear, I can get it to where I think the BB is low enough with 24" wheels. I dropped the Manitou fork to 140mm and then messed around with the IRT adjustment and the air pressure and just increased sag a bit so the axle to crown height dropped a bit more. Same thing on the back, the cheap shock is at least a dual air design and so I was able to get pretty decent sag combined with good rebound control. Again, I think that reduced effective travel to around 130-135mm in the rear, but that lowered the BB below the axles even a bit more.

    Initial ride impressions: We haven't taken it out far or on anything crazy aggressive yet, but I'm pretty impressed with the ride and in particular how well the suspension works for him. The cheap stock rear shock has a lock out lever and I watched him click that into place, stand up and crank up a really steep section with only minimal movement in the rear suspension. Definitely no bob, so at least for the long uphill segments, having the lockout should temper the admittedly primitive rear suspension design. The front suspension height is perfect, he was never close to pulling up the front wheel. I think what is effectively a 26" wheel base out behind him negates that. And he was really comfortable standing and cranking up, the bike fits him well. We haven't been on anything steep with switchbacks to check its handling there, I am guessing he will have to learn how to muscle through that sort of terrain with the longer wheelbase. Overall it climbs way better than I expected, I had some worries here as I built the bike up in the stand. Heading down he was really comfortable, that is where the geometry really shines. The fork is tuned well for drops that are 1-2 stairs in height (6-12") and when he is going down it just looks like the geometry was made for that direction.

    Next steps: Because of the geometry and how I have it set up, it really needs a seat dropper. He hasn't used one before and it's going to be hilarious watching him try to learn how to use it, but he's going to need this for any sustained climbing. I still have to play around more with the rear suspension and measure how much travel he is using. I may also start looking for a used rear shock as an upgrade (it's 190mm x 50mm so I should find used options). I may pull the Manitou apart and try a few other tricks I've read (dropping to 2.5w oil instead of 5w) to try to get a bit more low speed sensitivity. But I also need to just get a better grasp of the 3 dials on the right side of the fork and how they interact with each other (I've never used a Manitou before).

    Cannot seem to get most pics to upload right now, here's a one in the front yard to give a sense of the bike.

    Slater Mobster AM 24" build-slater-mobster-2.jpg
    Attached Thumbnails Attached Thumbnails Slater Mobster AM 24" build-slater-mobster-6.jpg  


  2. #2
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    Wow man, that looks awesome. Sounds like a fun build for sure. That's a sweet deal for 500$. The pic is at an angle, but it almost seems like the kid is almost game for the 26" wheelsize (tho it seems to fit today for sure). How tall is he? That's the one nice thing if he is inbetween sizes. You can drop some money on this nice build, ride the 24" for a season and then bump to the 26".

  3. #3
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    Thing actually looks kinda beast. Does it sit in its suspension with a bit of sag?

  4. #4
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    A bit more tuning of the suspension, with sag around 25-30% it gets him in a good position and with an ok BB height. He definitely will need a dropper post, going to look for one today to order. In order to get his feet on the ground when his butt is on the seat, which I think is a necessity for technical trails, the seat has to be pretty low. It is then way too low for sustained pedaling while seated (too much knee bend). If i had designed this frame, i might have thought about lowering the BB a hair. But i might not say that once i see him on a rough trail using 60% of the travel.

    As for 26” wheels, he’s probably close to tall enough. The issue is that is a big wheel to steer and he’s just gotten comfortable maneuvering the 24” wheel.

  5. #5
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    Good thinking on not pushing too much wheel on him too soon. I think a lot of people are doing just that, for whatever reason... probably for better roll over and because bigger has 'just got to be better', but I think the positives in most cases might be outweighed by the negatives. Especially when a kid hasn't really mastered handling a bike in the first place. To me it's kinda like moving a kid past a study subject when they're floundering. It's not necessarily gonna get better by skipping ahead.

    It's cool that you can put the 26's on the same bike, that way he knows the fit of the frame and it's not like 'everything' changes. It's the same familiar bike, now with bigger faster wheels.

    I agree, the BB looks really high, but like you said, running a bit of sag ought to help, and that bb is going to come down quite a bit when he's blowing through the travel.

  6. #6
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    Thanks! I was really curious how this was going to turn out. Looks great, love that color. Unfortunately I want/need to run a Machete JUNIT 24 fork. I'll have to email BJ, but my gut tells me the A2C on the JUNIT will be too short. I had forgotten it's a 27.2 seat tube, too. That really limits dropper options.

  7. #7
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    Great build! Let me know how the dropper works out and if its worth it!

  8. #8
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    That looks awesome!

    Sent from my Pixel 2 using Tapatalk

  9. #9
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    Rad!

    Good job.

  10. #10
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    A few updates...
    BrandX dropper from CRC is only $109 on sale and comes in 27.2 diameter. Only drawback is it comes with a lever designed for a cross or gravel bike. But it is compatible with one of the aftermarket horozontal levers, so add $50 for that.

    Climbing is really amazing. I took him on a short trail yesterday that has two really steep sections and he powered up them with no problem. One section has loose rocks and he could never get it with his hard tail. His face lit up when he realized he could do it on this bike...

    Still tuning suspension but had him on some 18-24” drops that he launched at speed and it sure was smooth on the landing. Also had him do a huge set of stairs to watch rebound and tweak rapid fire small bump handling.

    A bit of squeaking noise in either the rear shock or one of its pivots. Annoying, have to figure this out, but realize this stock shock may be something i should upgrade.

    Still haven’t weighed it, but I’d say its 26 lbs, maybe 27 lbs.

  11. #11
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    I finally took him out on a proper trail, for reference you can look up “Raging River” on Trailforks or Strava. We hit Upward Mobility for the climb, 3 miles and about 1.1k feet of climbing. Then we took Poppin Tops upper and lower and then Flow State upper and lower.

    Climbing- the gearing is perfect and he was consistently pedaling in 2nd or 3rd gear. I am really impressed with this cheap shock, we didnt put it into lock on the climb because there were some rocky and rutted sections on the climb. Any fear I had of this geo not being great for climbs is gone. Front tire was always on the ground and he navigated all the ruts well on the climb. The dropper post (arrives today) will be welcome, he stood a lot on the climb because the seat is so low to enable him to get the feet down flat.

    Descending- upper Poppin Tops is a short black diamond with some table tops at the start and then a few swooping berms going into steep sections with air ramps on the way out. Then the remaining 3 sections are mostly high speed flow trails w ramps liberally scattered. The bike really handles well across all these types of terrain. On the flow trail he was taking speed into ramps and stumps and as rode on his back tire i could see the suspension moving well as he launched and landed. On the lower part of Flow State there are successive tight bermed turns and no doubt he has some work ahead to learn to get thru those turns at speed. I think the long wheel base is the culprit here but he was getting used to it by the last few turns.

    Overall- He said he felt he could go twice as fast as any other bike he’s ridden (all hard tails admittedly) and told me he felt very comfortable letting go of the brakes and launching ramps at speed. From behind he looked like one of my adult friends, not a little kid getting squirly. I think the frame is a solid option for $950, a steal for the discount i got. I also cannot say enough about the Manitou fork. He’s well under 100 lbs but with some careful tuning i got it to use most of the travel on big landings but still have decent small bump performance. The key is lots of sag and low air pressure. I am going to rebuild and drop from 5 wt oil to 2.5 wt oil to see if that adds a bit more suppleness.

  12. #12
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    A year later and now my son has been on this bike with 26" wheels for about 6 of the 12 months since buying it. It is insane how well it has worked for him, he's hit Big Bear, Mt Bachelor and Timberline for lift riding as well as a summer in the Hood River area and it's been wild to see him progress. Once we moved up to the 26ers it looked more like a small adult bike and worked much better on speedy and bermy runs. Anyone thinking 140mm is too much suspension for someone this size, I would say think again.
    Today we hit the same local trail as last May, at Raging River in the Seattle area, and it's chock full of ramps and doubles that give adults a challenge. The bike allows him to just manhandle the trail. Only complaint now that he is a bit heavier is the rear shock. Will try to give it some more air in both chambers but also at that point where I may spring for a Fox or RS and send it off to be revalved. Also, the stock 190mm x 50mm stroke shock seems about 5cm too much stroke for when he really lands hard and has the seat all the way down (we could hear some tire to seat contact), so may shorten to 45mm if possible. He will be on this thing for at least a year more so worth a bit of investment.

    Slater Mobster AM 24" build-quinn.jpg

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