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Olympia Cycle & Ski, 1813 Portage Ave

Friday, October 14, 2011

A word about FAT tires

We know we've been posting quite a bit about fat tire bikes recently, but we've been building a lot of them up (relatively speaking at least) for customers in preparation for winter and it's what's on our minds, so here's some more info:

Actually, this is in response to some questions we've been getting about the brand new Big Fat Larry 4.7" tire. Specifically, will it work in a Puglsey or a Mukluk, which until now our customers have been using with the under 4" wide Larry and Endomorphe tires.

Here's what we know so far

First, the summary - It looks like you can use the new Big Fat Larry tires in the rear of either the Pugsley or the Mukluk (the two fat tire models we currently carry) with varying degrees of chainline adjustments, and certainly with the soon to arrive Moonlander with no adjustments.  The Big Fat Larry fits fine in the front forks that come stock with all of these bikes with no adjustments.

Note that we talk about Larry tires below, but if you're using Endomorphe's in the rear instead of Larry's you can refer to the Larry measurements because the tire width between the two tire models is negligible for our purposes here.

Note also that our observations below were made with tires all pumped to about 15 psi.

If you have a Surly Moonlander (and you don't, because there are only two coming to Winnipeg before Christmas, and the guy typing this has his name on one, and the shop manager is getting the other, but don't worry, more should be available for order shortly thereafter) you can fit any fat bike tire and rim combo, so if you plan to get yourself a Moonlander (a) talk to us about it now so we can make sure you're next in line, and (b) surf over to something more interesting because you have no worries here.

If you have a stock Surly Pugsley with Large Marge or Marge Lite 65mm rims you can run the Big Fat Larry's with what appears to be no chain rub (based on our experimentation in the bike stand - real world results may be a bit different).  The chain will come close to rubbing but looks to be okay.  You may want to use a spacer to push your crankset driveside out a bit more (if that's an option for you) and/or get rid of your smallest cog and space the rest of the cassette outboard a bit to make sure there's no rub though.  Your tire width should increase from 89mm if you're using a Large Marge/Larry combo to 97mm if you move to a Large Marge/Big Fat Larry combo.

Unfortunately we can't tell you how a Big Fat Larry looks on a Rolling Darryl 82mm rim yet because we don't happen to have any Rolling Darryl wheels built up in the way they are required to be dished to sit properly in a Pugsley.  However, we do know that a Big Fat Larry / Rolling Darryl combo yields a 100mm wide tire according to our unscientific back-of-the-shop study, so we're only talking 1 1/2 mm per side (3 mm in total) between this combo and the Big Fat Larry / Large Marge combo we tested above. If we're reading this right it indicates to us that you may only need to lose 1 more cog in order to run Big Fat Larry's and Rolling Darryl's on your Pugsley, if that.

FYI, Surly's blog states that using the Big Fat Larry's with the Large Marge rims (let alone Big Fat Larry's and Rolling Darryl's) will cause you to lose the use of a few cogs.  We disagree, for now, but again we haven't tested the set up in the real world.

If you're riding a Salsa Mukluk you probably already have an 80mm or 82mm rim because that's how most of them shipped.  If you're running an 82mm rim like a Rolling Darryl with a Larry tire the resulting width looks to be approx. 97mm (coincidentally that's the same as the Big Fat Larry / Large Marge combo) which will rub with the chain when you're shifted into the largest 4 gears on your rear cassette and your granny gear.  Of course the 2012 Salsa Mukluk 3 (the model we're using for this test) comes out of the box with chain rub issues in the two largest cogs (more about that here) so our hope is that if you use a fat tire specific crankset like the Mr Whirly Offset Double or maybe the E 13 that comes spec on the 2012 Mukluk 2 you may only need to give up the same cog or two in the rear to use the Big Fat Larry.  If you happen to have built up your Mukluk with Large Marge rims you should be able to use Big Fat Larry tires and have pretty much the same results as with the stock Larry / Rolling Darryl combo because both combinations yield the same 97mm width.

Clear as muddy snow?  If you have any thoughts to share, if you think our measurements are way off, or if you want to congratulate us on such great investigative journalism, feel free to email us at editor(at)  We're aways happy to post added info / corrections here.