Fat-BoB Trailer v2.0 (aka Crisco Bob)

Back in March I shared my exploits in getting a Bob Trailer to work with a Fat-Bike. That article mainly focused on how to modify the yoke of the trailer to work with Robert Axle Project extended (Bob compatible) rear thru axles. You can read about that here – https://fat-bike.com/2017/03/how-to-make-a-bob-trailer-work-with-your-fat-bike/. After we posted the article, one of our reader’s comments was, “What about a fat tire for the back of the Bob?” As you can see (below), Fat-Bob v1.1 was not very fat in the rear, so we went back to the fat-dash bike dot com deep thinking chamber and started to puzzle together a solution. This article is going to mainly focus on how to get a fatter tire to fit on old Bob.

Fat-Bob v1.1 – (standard rear tire)

I remembered that, last winter, the folks at Burley had us test out a fat tire kit for their flat bed trailer that utilizes the same diameter wheel as the stock Bob rear wheel (16″). So we asked Burley to send us one of those tires and we mounted it onto the stock Bob wheel. It wasn’t an easy tire swap, because I don’t think the tire, on my second-hand Bob, had ever been changed, since the day it left the factory a long time ago, but thanks to the power of gnome-skull and my kung fu grip, the new 16 x 3″ tire was mounted onto the stock Bob Trailer wheel.

Fat Bob v2.0 : aka Crisco Bob

The new tire combination easily fit between the sides of the Bob’s rear stays, but the tire rubbed, because the new tire is too tall (not too wide). And I mean it was really close. So close, that if you ran the rear wheel all the way at the very end of the trailer’s horizontal drop outs, with one third of the Q/R hanging out of the back of the drop, it would just clear. So close, but I knew that a rear wheel, that’s just barely clamped in the trailer drops was never going to be reliable for heading into the back country. All I needed was a longer set of Horizontal drops or….drop out extentions!

I contacted Tom Koren, the owner of Fatdapter to see if he could design and machine a part that would extend the dropout to accommodate the new fatter tire. I sent Tom a rudimentary drawing and after a little brainstorming, I dropped the trailer off with him and he went to work designing our dropout extender.

Tom sent me a couple of renderings and then had a set 3D printed. With just a small tweek in the fit Tom then machined a few sets.

3D Printed Dropout Extentions

Tom wanted to have two attachment points to hold the D/O Extender to the drop out, so he drilled and tapped a hole in the trailer’s rear stays and used a common braze on bolt to keep things (field serviceable). After a quick coat of rattle-can paint, he installed them as you see in the pictures below. (click any picture to enlarge)

I imagine that this is a little like what it was like to build a fat-bike before 2010. The tire clearance is a generous quarter of an inch all the way around. I’ve ridden this version of the fat-bob , loaded with everything that I need for an overnight on gravel and then on Kettle singletrack and the thing rides like a regular bob on the back of a mountain bike…..which is to say, spectacular! The Bob has a 70 pound weight limit and a warning label that we should have read, before we tried to give Dustin a ride in Puck’s Trailer up at Levis a couple weeks ago.

Dustin & Puck – Puck’s Bobzilla Trailer

Puck’s Trailer is a whole ‘nuther story. He bought a kid’s Mongoose Fatty and replaced the trailer’s rear end by removing the stock rear stays and welding the severed Mongoose fork onto the trailer swing-arm. We’re planning a Puck vs. Gomez trailer shoot-out on a trip to Michigan, the first weekend in August. You should come with! Puck is going to regail us with his adventures with Bobzilla for years to come and who wouldn’t want to be part of the rich mosaic of those stories? So you should really come with.

Crisco Bob and my goat, Seth, attached to one of the top 3 fat-bikes that I’ve ever ridden, the Corvus from Fatback Bikes.  #shakennotstirred

So to summarize for those that want to modify a Bob Trailer like Crisco Bob :

Extended Bob Axles from – www.robertaxleproject.com

16 x 3″ Tire – www.burley.com

Dropout Extensions – www.Fatdapter.com



About Gomez 2576 Articles
Just an old cat that rides bikes, herds pixels, ropes gnomes and sometimes writes stories. I love a good story.


  1. Did you ever do a video of a trip with these fat-bob’s? Have you tried any other modifications/adaptations? It would be really cool to see a video of the fabrication of the front fork to the trailer suspension and how the for/trailer brake was hooked up to the bike as well.

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