Fat Bikes / Fatbikes

Fat front Jones...

1x1

Cheers.

The Jones is a 29" rear, the 1x1 a 26"?

I think those two examples have proven what I thought about the proportions of the 26" rear being a better match for the fat front, even though the outer diameter of the 29" matches more closely.

Yeah i was kinda worried about how much a fat front would jack up the headtube etc but I noticed the other day while riding with my mate on his Orange 5 that my frame/forks were a good bit steeper than his anyway and he seemed to be managing so would slackening my angles really matter so much?

Looking at the Surly site, the current 1x1 headtube angle is 71.5, the Pug and Moonlander are 1 degree slacker at 70.5 and the Krampus is a further degree slacker at 69.5.

The Krampus is supposed to be more aggressive than the full fat Pug and Moonlander so not seeing why they've gone slacker with it :S

Any maths geniuses that can work out what difference a fat wheel/tyre/fork will make to my headtube angle if I find a2c sizes etc?

The Krampus is supposed to be more aggressive than the full fat Pug and Moonlander so not seeing why they've gone slacker with it

Head angle is just one variable in the steering equation, the Krampus has a 48mm fork offset compared with 43mm on the Pugsley and Moonlander, which still leaves it with a bit more trail, but then it has a longer top tube so for a given fit it would take a shorter stem, which will quicken it up a bit. The different cross section of the tyres will also affect the camber steer. You can't look at one variable in isolation and make judgements about the way a bike will handle.

Any maths geniuses that can work out what difference a fat wheel/tyre/fork will make to my headtube angle if I find a2c sizes etc?

It doesn't actually take a genius, it's fairly simple trigonometry.

For a quick and dirty estimate, it takes about a ¾" lift of the head tube to slacken the head angle by 1°.

Sticking a complete Pugsley front end on a 1x1 will lift the front by about 1" (2.5" increase in rolling diameter, ¼" shorter fork), so around 1°20' change in angles

I think my current fork will be closer to the 80mm sus corrected version (it's an older, v brake only era 1x1 f&f) so the Pug fork is longer (447mm a2c v my 413mm) according to surly site plus my very quick n dirty calculation using the diameter of a 29er tyre (I couldn't find 26" fat) had it at 46mm/1.8" of lift on the headtube. Which is gonna be more significant.

I presume you used the 'fork length' measurement off the 1x1 frameset geometry page?

If you goto the forks page there's a 100mm corrected and an 80mm corrected version of the 1x1 fork. The fork length on the frameset page is the A2C of the 100mm version.

I'll measure my fork in the morning to be sure but I don't have much tyre to steerer bottom clearance so presuming my fork is closer to the 80mm version.

I presume you used the 'fork length' measurement off the 1x1 frameset geometry page?

Yes, and the tyre diameters off the respective geometry charts.

Triton have started their sale all ready and almost all of their bikes, including 2014 fat bikes from Salsa and Surly, are reduced.

Yes, and the tyre diameters off the respective geometry charts.

Hadn't seen that.

I've also now found a site quoting the external diameter of the 26" tyre I'm using (Conti RaceKing 2.2) as 685mm which is slightly bigger than the tyre diameter used/quoted on the 1x1 geo page.

So, taking the tyre diameters and fork lengths and doing my calculations again now I'm more awake it's looking like a 61.5mm lift. (27.5mm difference in wheel/tyre radius and 34mm longer fork).

3/4" = 19.05mm, 19.05 goes into 61.5 3.22 times so 3.22 degrees of slackening. That's too much eh?

It's too much unless you have extra fork offset to keep the trail down. You can use this calculator to get any of head angle/fork offset/wheel diameter/trail from the other three.

Standard Pugsley trail is 85mm, putting a Pugsley front end on your 1x1, assuming 3° change in head angle, you'd have 103mm of trail. At the moment, you have 76mm

Done some more googling and there doesn't seem to be much that's shorter than the surly forks and the only forks I could find with more offset were a fair bit longer.

I may just settle for wider tyres on the stock 1x1 f&f. I reckon I can fit in at least 2.4" and still leave plenty mudroom.

didnt 1x1 have clearance for 2.75"

didnt 1x1 have clearance for 2.75"

Current model states 2.8". I can't see me getting anything that big in mine. Not on the wide trials rims anyway.

There's a lot of chat about cutting the brake mounts off to make more room for tyres/running 24" wheels with ultrawide tyres but I don't want to go that way.

Edit: have just bought a used 2.7 Big Earl off retro bike so will see if that fits anything.

For the sand in Dubai?

Yours?

I wish!

nice build/write up, reminds me of those pre-electric Hanebrinks

http://www.instructables.com/id/EXTREME-FAT-TIRE-BICYCLE/

Another early Hanebrink bike

I rented one of those in 2000 in Les Menuires. They were called BDD - bicycle de descente- no drivetrain, drum brakes, good fun. I can't find much about them online though.

Grrr, 2.7 Big Earl is a) not all that much wider than the 2.2 RaceKing it replaced and b) rubbing the booster on my HS33 at one side at one point of rotation.

Maybe I do need a fat bike after all!