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Fore/Aft weight?

1340 Views 9 Replies 4 Participants Last post by  ward
Been reading and looking at posted vidieos; as I am a fat bike wannabe, there are a few questions.

What kind of fore/aft weight balance is typical? I ask this because I have read that some have made note that the front tire will want to skid under low traction conditions; due in part to light weight over wheel?

Why the slack HT angles? I understand their use for FS, but to my knowledge, all forks are rigid on fat bikes. Does it have anything to due with an 'attack angle' for soft conditions?

I ask this because the best way to travel over soft surfaces is to be 'even footed'. That being the case, it seems having a near 50-50 split would be a good starting point.

I respect that fat bikes are the way they are for a reason, but why? Surely they have not been developed without thought to this concept.

Any comments would be welcome!
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I'm not convinced about slack head angles either.
All the fatbikes I have ridden were set up with a pretty standard ~40/60 front and back weight distribution just like a regular bike. To achieve anything else (like 50/50) would make the geometry of the bike pretty weird, like employing super long chainstays, or a triathalon seatpost angle, or some odd fork geometry that could lead to toe overlap. The bikes handle well as they are, probably because they borrow so heavily from the tried and true fit of regular mountain bikes. There probably aren't a lot of situations where a 50/50 weight distribution would outweigh (no pun intended) the odd handling that would be introduced by designing a bike like that, for vast majority of riders anyway.

The place the weight distribution question comes into play is the fact that you need the ability to move your weight around on the bike to put traction where it is needed (extra weight), or put flotation where it is needed (lighten that end of the bike). Having a bike that's not overly long in the cockpit allows you to achieve this body english imo. Sitting on the nose of the saddle and leaning your upper body forward can get the weight closer to 50/50 if you are on a dicey surface, but sometimes you want some extra traction in back and want the front tire to ride on top of a crust so you sit back on the saddle and put your body upright. This can change from pedal stroke to pedal stroke and you may even find yourself rocking to coax your progress forward. But in the end being able to ride a normal-fitting and neutral-handling bike is the most important.
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For soft sand, works well to hedge the balance rearward, increasing forward (and uphill) traction and enhancing the float of the ft. wheel/tire. Also put's you in a better position to react (and not end up over the bars) when the ft. tire drops into an unexpected soft spot or hole. I use a shorter stem for sand only rides and scoot the seat back a bit too. In the soft stuff the ft. tire has marginal cornering traction anyway, because of the surface. Like TSCheesy says, you've got to move around on the bike on those surfaces to make the bike do what you want it to. I run my saddle just a hair low to free me up a bit for this.... move a little forward and weight the outside to "carve" a turn... like a skier. I also like wider handle bars now... I think they give me better leverage over that big 'ol tire, helps me weight the outside of the ft. end too. For a dirt ride on a FB, a longer stem, little lower bar height, and scoot the seat forward a little might be in order. As far as slacker HT angles go, I like 'em on 29er's, which basicly FB's are. Let's you push that ft. tire forward for clearence of the peddles and a suspension fork, if you chose to use one. also feels safer on soft, sandy or snowy downhills.
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When I played around with half fat on my 29er, I found the steering and handling I liked best was when I had it set up with a steep headangle (home brewed adjustable fork allowed this).

That was with drop bars which gave me more positions than flats. Also wasn't ridden in snow because I had my Pug by then.
Thanks everyone!

My thinking was revolving around the measurements taken from my 26er and wondering how close it is to alowing a fat tire without overlap; real close! From there I was trying to use those measurements to design a 'dream bike'. In doing so I was forgetting what I was doing to my own question. I was increasing the front center verry little in relation to the rear; which increases the weight over the front greatly. Thanks Tscheezy for correcting my stuck in a rut thinking!

Ward; thanks for your input; you have given me feedback on unasked questions. durring your vidieos and others I keep looking for information as to what the sand is doing under the tires, that and how much sidewall flex there is, hard to come to any conclusions. Having grown up within walking distance from the ocean, I think I can read the condition of the sand itself fairly well.

So, you use wider bars and a shorter stem for sand; must keep that in mind! By the way, what chaingring and cogs do you find most useful for sand? Thinking about a 1X10 setup with 11-36 out back; and a 26 in front. I would rather short myself on the top end than the bottom as my style is not built around a need for speed.

My dream bike was looking more like a CX than a MTB; my understanding has been shifted. If and when, I want to take full advantage on the nearby Oregon dunes.

Again thanks everyone!
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Oregon Dunes... now your speaking my language! I'm about 9hrs away. Planning to get down there ASAP! This was in July of '09, my only trip down there so far. Also my first attemt at filming (a re-edit for sure).
This was on my first FB w/ LM's & a custom frame. "Cockpit" is lower and the BB is a little higher like an XC bike... which I prefer for mountain dirt & singletrack. Kind of cool 'cause I can compare ... and the Fatback is much better in the sand. Can't wait to get it down there! Hopefully Spring or early Summer. As far as gearing... I LOVE to climb things so I run a 20 tooth low up front on a regular old triple (only used the big ring twice... kinda scary going that fast on this big 'ol thing...) w/ standard 11-34 on both bikes. Hoping they'll (the Forest Service) will continue to tolerate us in the non-motorized areas down there... there are no laws against it (yet) but some of the trails that access the open dunes from the road do say "no bicycles". They know about our bikes, I've talked to the local ranger's a couple of times. There's only a few of us attempting "big sand" rides right now... in they're own words "if there were hundreds of you, we'd have to take a look at it". I did cross path's w/ a "sierra clubish" fella... he was not at all happy w/ me leaving a tire track out there. If it get's real popular, I expect we'll eventually have some conflict and get somewhat "regulated". That said, I spent ALOT of time pushing &carrying the bike around out there in the really "big sand"... doesn't bother me a bit 'cause i'm a hiker too, but it's not for everybody. Folks that don't like to dismount and hike-a-bike probably aren't going to love this as much as I (we) do so I don't think we'll ever see big number's of FBers out there... not like in the motorized area anyhow. If they do regulate us, it would be nice to get some FBer's at they're meetings and try to get some bicycle legal corridors. If we don't show up, for sure the equestrians, and the "foot traffic only" crowd will surly toss us out. Keep me posted on your adventures down there when you finish your bike.

See you in the sand, Cheers!
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Sand Rat said:
durring your vidieos and others I keep looking for information as to what the sand is doing under the tires, that and how much sidewall flex there is, hard to come to any conclusions.
Add to that that no one runs the same pressure front and rear, and the sidewall flex would not tell you anything anyway.

If you want to maximize your chance at success on really soft surfaces, get 100mm rims. Period. They are no guarantee that you will stay on top, but they make a bigger difference than anything else on the market.
Ward; thanks for the Vidieo!

A few years have past sense I have been to the dunes, (2 hours away) a little dirt bike riding with my sons or just out in my sons SUV. My thoughts are that it is best to stay away from those areas if one is to safely enjoy the dunes on a bicycle. Looks like you found a good spot!

A sister of my wife and her family were there many years ago on their quads when another rider on a quad came over the crest of a dune in a jump and landed upon her; compound leg fracture!

I am not against some regs to promote order and safety; just as long as they are kept open for enjoyment. Here in the hills on BLM land it is dificult to find a place to shoot due in large part they are also used as a dumping ground for trash and stolen cars. A few ruin it for the many.

Must keep an ear open as to any moves to form policy on the dunes.
tscheezy If you want to maximize your chance at success on really soft surfaces said:
DITTO, There's nothing like 100mm's! My hunddies are undrilled and way heavier than my 65's and way out perform them in the soft stuff!! I don't care what anybody says, when it comes to soft snow,sand pea gravel or etc... if you want to negotiate these things and peddle through 'em, get some 100mm's! "period"!

Right on tsc, cheers!... In the mountains tonight, watchin' it snow... finally!

If your engineering minded, draw a cross section and do the math... it's easy to see why they work so well.
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