Mini-Fat: anyone riding a Specialized GC 20x4?

Has anyone built a mini-fat MUni with the Specialized Ground Control 20x4 tire?

The tread pattern looks good and you would end up with a pretty aggressive tread pattern, 24" diameter and 4" of cushy tire. Assuming the build wasn’t too heavy that sounds like a bouncy good time.

The tire was made for the kids Fatboy 20, which appears to be a high-spec miniature fatbike. The tire is available for $40 USD

I would be curious to hear the thoughts of the collective and I am a bit surprised nobody is talking about this tire on here.



Cannot comment on the 20" version but it exists also in 24x4.0 & 26x4.5 !

I have a friend who has one on his Surly Conundrum 24 build but I have not had the chance to ride it yet. However the tread looks good and it is an appreciated tire in the fatbike forums too.

My daughter rides the Fatboy 20 pictured above so if you need any measurements, please let me know.

There’s a shop near me selling a complete 20" fat for $200… it has sooooo crossed my mind. Looks really fun for rock gardens.

I ran the 24 x 4.0 on the Conundrum for a bit. Almost all of the use was at so it was on wooden obstacles, but not on dirt.

It was bigger and bouncier than the 3.0 Intense that it was replacing. Like the 26" fat tires it also autosteered. It had too much grip at times when I was trying to ride skinnies or needed to pick a line between obstacles. I’m happier with the 3.0 in those situations.

Other than that negative trait, shared by most fat tires, it rode well. It didn’t have the rollover capability of a 26" fat, but it definitely got hung up less than the standard 24 x 3.0.

The weight change between the full downhill tire and the Ground Control wasn’t noticeable as good or bad. The sidewalls are definitely thinner than a full downhill tire, but they are better than many tires available in the 29" size.

I’ll probably go back to it as some point. It’s a good tire, but since I have a 26" fat, I don’t have a huge need to keep it on the 24 right now. Then again, since reading this thread, I may have to throw it on again and give it another run.

If only changing out a downhill tire wasn’t such a beast…

Just for the sake of curiosity I would be interested in the overall diameter and width at the widest point.

I’m pretty busy until mid-April but after that I might get bored and want to build myself a minifat.

Too bad there aren’t fat 22s.

Sorry if this is a dumb question, but what is an appropriate frame for the 20x4? I assume the tire could be put into a 26" Hatchet frame or one of Jacob’s frames, but that’d leave a lot of clearance (6") between the tread and the underside of the frame. Also, fat frames tend to flare out toward the crown … and in towards the hub. Would a 26" fat frame be too narrow at the point where the 20x4 tire passes?

The Nimbus Oregon frame stays wide all the way down with just a little tapering. I’m running a 26x3.8 Surly Nate currently with more than enough room for a fatter tire. I’m not sure about the Hatchet, but the Oregon seems like it would easily take a 20x4 wheelset.

The bottom width of a Fat frame will depend on the hub width:

  • with a 125mm hub, it will be almost straight all the way and the fat tire will go in okay inflated (this is the case of the Oregon & Hatchet)
  • with a 100mm hub, you will have this narrowed down section to reach the hub squarely and you will have to check how high does the transition happens (this is the case of the Surly Conundrum and a Flansberrium)

However, there exists a few 20" frames that can fit such a big tire like the Sun XL uni with its 4" tires and maybe the infamous Mongoose Squid.

The easiest fix would be to use the 20" Club monster as a starting point.
But this Uni is heavy at 7.7kg.

I posted some pictures in another Thread, but here are some of my Mini-Fat.

This thing is a blast, can’t say how it compares to a smooth tread, and I haven’t ridden it much in the snow, but on the beach it’s a beast, plenty of tread and grip to ride on the canted surface of the beach, and I was even able to ride out into the shallows (ankle height, if that), though that stopped quickly as I didn’t want my shoes wet.

That looks pretty fun

It does look like fun :D. The tire fits really nicely in the Sun frame, but that rim is just asking to be alloyed with some drillium.

Honestly hadn’t even thought about drilling the rim out to lighten it… (psst. it’s for sale if anyone want’s to take that upon themselves :stuck_out_tongue: )

So, has anyone built a uni and ridden with this tire yet?
“Accidentally” got my lbs to order one for me yesterday :roll_eyes:
Today I ordered a single wall 60mm inner width rim and a Kris Holm Spirit hub for this little project. This is also going to be my first frame with machined bearing clamps!
There shouldn’t be problems with 100mm hub and 20x4 tire, right? At least 26"/80mm rim with 4.7" tire has been great fun with a regular width hub. It feels way more natural than a 125mm hub with fat tire. Somehow my knees end up further away from the tire with a narrower hub…

I think you would be fine with a 100mm hub, as long as your frame has clearance for 4". As mentioned earlier in this thread, Flansberrium and Surly Conundrum both
used 100mm bearing pitch with no problems (others might have more input). You fabricate your own frames, yeah? I’d be interested in seeing your progress and your bearing holders! I don’t have any experience with this tire in particular, but none of Specialized tires have been a real turn-off. I think, even for a kids bike marketed tire, it probably is spec’d pretty good.

Here is a good image from issi pedals that shows why pretty well:

Looks like this is the same as the club(UK) version.

Oh, that is good to know. I somehow missed that they used 100mm too.

Yes, I have made multiple steel frames (latest one in freewheeling topic) and I’m going to use steel for this one too. I have also made some fiberglass prototypes (going for carbon fiber when I get inspiration for that). But after trying alloy frames I have realized that frame weight is really insignificant for my unicycling. :frowning: Weight of the wheel affects handling a lot more…

And about this tire. Only thing that I’m worried about is that it is 72tpi. But thread pattern seems promising, so I decided to try this one and see how it feels.

When I first started to think about a unicycle that I could easily carry when hiking (and ride some interesting sections) with my non uni’ing friends, Veetire Mission Command (20x4.0, 120tpi) was a strong choice in my mind. Then I realized how slippery that tire looks in pictures. I may still buy that one at some point to see if it is.