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  1. #1
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    Fatbike design and evolutionary changes needed...

    I'm eagerly anticipating the On-One fatbike because it seems to be close to what I want. That On-One are promoting it as a rock-crawler is a plus.

    But it has prompted some idle thoughts about some things that could be improved on fatbikes.

    1. Fork ends: there is so much grip in a fat tyre that forkends that were evolved to deal with skinny tyres are not really suitable. The extra grip is twisting the forks. I think we need a move to through axles to unify the structure more. This need will become more apparent as fatbikes get used more on hard surface trails.

    2. Geometry: my experiments with steeper head angles while preserving a reasonable trail have me convinced that this is the way to go. This also means the head of the bike is raised or lowered less during low speed turning which may be of some advantage in snow - I haven't tested that. A nimble bike is always an advantage at the low speeds used in lumpy ground.

    3. Front dropout widths: we are now getting tyres that are fatter than the usual 100mm OLD on the front. The easy cure is to go to 135mm and use a rear hub or special front depending on the fork. My limited experience with 135mm front OLDs (Surly offset fork, Salsa Enabler) is that there is a fair bit of squirming going on when the brakes are used heavily (hence point 1). At the moment it's possible to squeeze the fatter tyres into a 100mm fork, but maybe we need a front new standard such as 110mm or 120mm. Short as possible being the better to reduce potential for flex.

    4: Rear dropout width: Currently the offset 135 is the most useful setup, but this creates potential problems with wheel builds. Unfortunately once we go for a symmetrical wheel build we lose the ability to use hub gears. I suspect that changes here have to come from the hubgear manufacturers rather than the frame builders. The only 170mm hubgear is the S-A and with only 3 speeds it is too limited a range for most people.

    5. Tyre widths: I'm convinced that a minimum of 6" is necessary for real progress in soft going.

    6. Suspension: As tyres get fatter, pressures have to drop and then we get the inevitable pedal bob. Combine a fat tyre with suspension and you have some interesting dynamics. Suspension damping combined with lower profile tyres may become necessary so that most of the suspension movement is in portion of travel controlled by the damper. I'm sure once the downhill boys wake up to the grip advantages of fat tyres we'll see some rapid advances in this area.
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  2. #2
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    I have not noticed fork/hub twisting. A fork with forward opening dropouts negates hub movement under braking, especially when used with a good internal cam QR skewer (Shimano).
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  3. #3
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    In my opinion, the offset rear is not a good design. Having the wheel/hub centered under you is important...despite what has been debated over and over. Offsets are fine for dirt or snowmobile trails, but if you are in tough snow conditions, handling suffers...especially when you come over-center with your weight. Just my experience....that is why I got rid of my pug and bought a fatback.

  4. #4
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    Quote Originally Posted by sevenpedaler View Post
    In my opinion, the offset rear is not a good design. Having the wheel/hub centered under you is important...despite what has been debated over and over. Offsets are fine for dirt or snowmobile trails, but if you are in tough snow conditions, handling suffers...especially when you come over-center with your weight. Just my experience....that is why I got rid of my pug and bought a fatback.
    A far as weight distribution goes, having the tire contact patch on the centerline of the BB/steer tube/rider is what matters. That can happen with an offset frame/fork (and does with the Pugs) or a symmetrical frame/fork.
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  5. #5
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    Quote Originally Posted by shiggy View Post
    I have not noticed fork/hub twisting. A fork with forward opening dropouts negates hub movement under braking, especially when used with a good internal cam QR skewer (Shimano).
    I think relying on a 9mm or 10mm QR axle is asking a lot considering it was designed for much lighter use. I'm convinced what I'm feeling is down to the axle being inadequate for the loads under heavy braking. I noticed it immediately when I put on the Enabler, and to a lesser extent with the Pug offset 135mm fork. The squirming effect was much less with my 100mm OLD forks. (I'm not talking about axles being popped out of dropouts but flex). We're putting motorcycle level grip loads through an assembly designed for a 1900s gentleman's bicycle.

    Quote Originally Posted by sevenpedaler View Post
    In my opinion, the offset rear is not a good design. Having the wheel/hub centered under you is important...despite what has been debated over and over...
    The point of the offset is to allow you to use a 135mm hub. Its offset matches that of the frame so that the wheel does align with the centreline of the bike, ie centred under you. Thus it should have no negative effect on handling. Until we get wider gearhubs, it's the best solution available.
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  6. #6
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    Quote Originally Posted by Velobike View Post
    I think relying on a 9mm or 10mm QR axle is asking a lot considering it was designed for much lighter use. I'm convinced what I'm feeling is down to the axle being inadequate for the loads under heavy braking. I noticed it immediately when I put on the Enabler, and to a lesser extent with the Pug offset 135mm fork. The squirming effect was much less with my 100mm OLD forks. (I'm not talking about axles being popped out of dropouts but flex). We're putting motorcycle level grip loads through an assembly designed for a 1900s gentleman's bicycle.
    I started out with the Hadley QR's that came with the hubs, but they couldn't keep the wheels in place for trail riding. I kept having disc rub problems, realized I could fix them by opening the QR and letting the wheel drop back into place. Hadley QR's are external cam, and seem to have a narrower cam than some. I replaced the front with a shimano internal cam QR and stopped having issues. The back is now a bolt-on, and stays put as well. I think that thru axle hubs would be a good feature for fatbikes, especially as they move into suspension and higher loads/speeds.

    Quote Originally Posted by sevenpedaler View Post
    In my opinion, the offset rear is not a good design. Having the wheel/hub centered under you is important...despite what has been debated over and over. Offsets are fine for dirt or snowmobile trails, but if you are in tough snow conditions, handling suffers...especially when you come over-center with your weight. Just my experience....that is why I got rid of my pug and bought a fatback.
    As long as the forces remain centered and symmetrical, there is no issue. If you have an offset build and the wheel or frame is flexing out of line, then you will have issues because the forces will no longer be in line.

    Symmetry is overrated.
    Attached Thumbnails Attached Thumbnails Fatbike design and evolutionary changes needed...-img_1792s.jpg  

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  7. #7
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    VB: like your thoughts.

    #1 Fork ends - would never consider nothing less that a 20mm through axle
    for a custom fork

    #2 Geo - My current thinking is 71.5* with a A/C of about 425mm and offset of 45,
    gives somewhere in the area of 75mm trail, if I remember correctly. What is your
    thinking about what would be ideal?

    #3 Front Dropout width - If you plan for those 6" tires seems like you would need
    something like 170mm width? Am I right in thinking that forks this wide would tend
    to flex more easily? Perhaps with a 20mm TA or larger combined with an short A/C
    with heavier gauged tubing and shaped legs, flex could be managed? Is not fork flex
    less needful in a fat bike fork for comfort anyway, so why not take advantage of the
    tire cush and make a trade?

    #6 Suspension - Baloons for tires and a suspension fork make for some interesting
    choices. Seems like your idea of low profile tires must be the path for the future if
    wider tires are to be produced.

    Standover Height - One of my personal quibs with fatbikes, it is higher than needed with
    any frame size. Again shorten that A/C measurement AND run that top tube through a split
    down tube, each would connect to the headtube in the reverse present pattern.

    Why, since all fatbikes presently produced are full rigid, why the long A/C as in a suspension
    fork? Sure, some have stuck on a suspension fork and are happy with it, and the frame design
    easily accomedates this move. However, if frames were designed with a low BB height and
    steeper headtube angles, and then if someone wished to add a suspension fork, would this not
    then move the effective BB height and headtube angle into an acceptable range for the intended
    purpose?

    With proper planning of construction, could we not then get a little more of having our cake and
    eating it too?

  8. #8
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    Given my experiment with a 69 degree head angle with a suspension corrected rigid fork, and then an unknown degree head angle with a Lefty, I'm going to agree that a slightly steeper angle is good for fatties.

    That said, if you steepen to an extreme, suspension fork legs tend to bind more, don't they? I'm no expert here so I'm asking more than stating. I like the idea of a 3.5" linkage fork for fat tires - put some condoms around the pivots and enjoy some long lasting function in mucky / cold conditions.
    Disclaimer: I run Regular Cycles (as of 2016). As a profiteer of the bicycle industry, I am not to be taken very seriously.

  9. #9
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    Quote Originally Posted by Velobike View Post
    I'm eagerly anticipating the On-One fatbike because it seems to be close to what I want. That On-One are promoting it as a rock-crawler is a plus.

    But it has prompted some idle thoughts about some things that could be improved on fatbikes.

    1. Fork ends: there is so much grip in a fat tyre that forkends that were evolved to deal with skinny tyres are not really suitable. The extra grip is twisting the forks. I think we need a move to through axles to unify the structure more. This need will become more apparent as fatbikes get used more on hard surface trails.

    2. Geometry: my experiments with steeper head angles while preserving a reasonable trail have me convinced that this is the way to go. This also means the head of the bike is raised or lowered less during low speed turning which may be of some advantage in snow - I haven't tested that. A nimble bike is always an advantage at the low speeds used in lumpy ground.

    3. Front dropout widths: we are now getting tyres that are fatter than the usual 100mm OLD on the front. The easy cure is to go to 135mm and use a rear hub or special front depending on the fork. My limited experience with 135mm front OLDs (Surly offset fork, Salsa Enabler) is that there is a fair bit of squirming going on when the brakes are used heavily (hence point 1). At the moment it's possible to squeeze the fatter tyres into a 100mm fork, but maybe we need a front new standard such as 110mm or 120mm. Short as possible being the better to reduce potential for flex.

    4: Rear dropout width: Currently the offset 135 is the most useful setup, but this creates potential problems with wheel builds. Unfortunately once we go for a symmetrical wheel build we lose the ability to use hub gears. I suspect that changes here have to come from the hubgear manufacturers rather than the frame builders. The only 170mm hubgear is the S-A and with only 3 speeds it is too limited a range for most people.

    5. Tyre widths: I'm convinced that a minimum of 6" is necessary for real progress in soft going.

    6. Suspension: As tyres get fatter, pressures have to drop and then we get the inevitable pedal bob. Combine a fat tyre with suspension and you have some interesting dynamics. Suspension damping combined with lower profile tyres may become necessary so that most of the suspension movement is in portion of travel controlled by the damper. I'm sure once the downhill boys wake up to the grip advantages of fat tyres we'll see some rapid advances in this area.


    1. Funny. You are the only person to ever suggest this. I see no issue what so ever. Thru axel unnecessary.

    2. Steeper head angle. I'll disagree again with this. I'd even suggest slacker.

    3.135mm works fine. No new standards when you don't need them. And its' a pain in the ass for everyone from fork makers, brake makers, and hub makers. 135mm works just fine.

    4. Agree, but mostly disagree. Loss of gears? Tell that to the Pugsley. Or my 9:Zero:7 offset which works great as is...I could run gears up front no problem, but choose not too. Tell that to Moonlander. Some sacrifice...but not much.

    I only agree because as I'm looking to experiment with things like 38mm wide 29er rims in the rear, 47mm 26" rims, etc.. they don't like the offset. Which sucks. Because I don't like 170mm hubs...but I see the point now. Next bike probably will just because I like to tinker. But my favorite hubs won't be 170mm anytime soon either so we'll see. Rims however...

    5. 6" will be fun, but for a select niche of terrain. Think we'll see a front for sure. Hell I'll want one for fun. But haven't found a need for wider than my 3.8's I'm running now. Plus in rear you'll have to go long chain stays or a jackshaft...neither is a good idea. If you really want bigger...just do it right and go Hannebrink. Works awesome and great company. Bonus: You have an electric option that is best in that field. Seriously. Give Kane a call. Great guy.

    6. DH? They actually went the other way...used to have a few 3.0 tires (which were the early fat bike tire pre-Surly Pugsley world) and such. Yet guess what? Some run as small as a 2.35". Why? Every second counts. Same reason a 29er DH may exist, but no one is placing on one.

    Suspension: Will agree. Wrote a bit on Fat-bike.com (Write there as "Sevo")on the very issue that we'll see tire size decrease to 3.2-3.3" area on narrower rims when suspension comes around. Low profile I agree will be a must. Larger tires however will be counterproductive.

    Even with smaller tires with low profiles we'll have a whole new slew of problems arise. Which once again will point towards smaller tires.

    Do agree that Shiggy's rig is probably where we'll see a lot of people going. The general public can't convince their significant other they have a bike that is only good for snow and sand, which means they'll start setting 'em for year round use. Which is another reason you'll start seeing some narrower tire options.
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  10. #10
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    there really is no downside to a thru axle or 360 dropout besides weight and cost... seeing as we are talking aboot $2000 30lb bikes, i think that is a non issue.

    as for the new standard of front hubs, i never support new standards in the bike industry unless it is a huge improvement. please don't encourage these kind of cash grabs.

    side note, i have a BFL on a RD in my 100mm fork. all i have to do is remove my caliper (but i'm used to that coming from my lefty) clownshoe fits through the dropout, but i would have to deflate the tire and would require more clearance than my pugs fork could handle. easily fixable but a bit of a nuisance
    your 29er may float over roots and rocks, but my superlight 26 just plain floats

  11. #11
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    Quote Originally Posted by juansevo View Post
    1. Funny. You are the only person to ever suggest this. I see no issue what so ever. Thru axel unnecessary.
    2. Steeper head angle. I'll disagree again with this. I'd even suggest slacker.
    3.135mm works fine. No new standards when you don't need them. And its' a pain in the ass for everyone from fork makers, brake makers, and hub makers. 135mm works just fine.

    5. 6" will be fun, but for a select niche of terrain. Think we'll see a front for sure. Hell I'll want one for fun. But haven't found a need for wider than my 3.8's I'm running now. Plus in rear you'll have to go long chain stays or a jackshaft...neither is a good idea. If you really want bigger...just do it right and go Hannebrink...
    1. Maybe I'm the only person who's tried 5 different forks on the same afternoon.

    2. My preference for steep HAs is a result of experimentation - with rigid forks. Agree that slack HAs are required to allow a telescopic fork to work properly - they stutter with a steep HA. It's about time we had a decent linkage fork.

    3. I'd be perfectly happy with a 135mmm through axle front hub, but narrower would be lighter and stiffer.

    5. I want to ride on a select niche of terrain. That's the point of a fatbike surely. Plenty peat bogs around where I live. The Hannebrink looks like a bodge made up of available parts rather than an evolved product. I've done enough riding on small wheels offroad to have serious doubts about small wheels capacity to keep going when faced with large obstacles.
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  12. #12
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    VB has obviously been thinking and experimenting with these ideas for some time.
    As a 260lbs+ rider, I agree that front through axle forks are stiffer and prevent Qr/dropout issues.

    I do not ride front QR forks off road at all now.

    Rear frame width would probably be best at 170 OLD . It does give the possibility for symmetrical builds and (potentially) 170mm IGH hubs with LOTS of gears.
    Would be best to have bolt through axle as well or Maxel type set up.

    Until then an offset adapter would be appreciated

    VB makes an excellent point about low profile rubber. This is exactly what has happened in cars with wide rubber and low height ratios. There would of course need to be wider (TA) suspension forks

    Geometry , I will not comment on as I generally prefer slack
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    When I9, Hope or Hadley make a 170 hub with high engagement points, I would consider a symmetrical frame, otherwise I personally see no need to switch from my Pugsley. Geometry is a personal thing- I would hate to see all fat bikes follow the same standard, because they are all ridden in different conditions and terrain.

  14. #14
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    Quote Originally Posted by Dr Feelygood ! View Post
    ...Geometry , I will not comment on as I generally prefer slack
    I can understand that. A slack HA with a long travel telescopic fork becomes very steep under heavy braking, so slackness is necessary with a telescopic fork to allow for this (as well as function).

    A steep HA frame requires either a rigid fork, or a linkage fork with compensating linkages.
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    Tyres...

    I often think about them.

    I've lived with tyres for all purposes, I feel people will be making a mistake should they think "Fatter is better" In actual fact, for our fatties, 4" is about right. Why, because the forward resistance it causes is negligable, i.e. it pushes very little wave in front of it at the front contact point. Going to 6" wide increases this forwad contact wave or resistance. Now, having said that, I too, would like more floatation, how is this achieved? Simple, larger diameter, by doing this, one creates a bigger foot print when the tyre is deflated. Remember, a tyres width is fixed, the length of it's foot print however, is only limited by its side wall height and diameter. So if we had a 4" tyre with a 4" side wall that was 32 inches in diameter we could let it down to say 4 / 5 PSI and get a foot print that was say, 14 inches long by 4 inches wide, this would give us 56 square inches per wheel of ground contact space and only be displacing 4" of snow / mud at it's front contact point. Now lets say my bike and I have a combined weight of 230 Lbs and we assume 75% rear and 25% front load share. (This is just a guess BTW !) The back wheel will be carrying 172.5 Lbs and the front 57.5 Lbs it'll mean the rear has a ground contact loading of 3.08 Lbs per square inch and the front 1.02 Lbs per square inches. Make sense?

    On hard track or asphalt, wider, lower profile is better,particularly when coupled to high horsepower and torque, but that's a whole story of its own!!!

    Have a think about snow skies as opposed to snow shoes...........

    Comments?????

  16. #16
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    Quote Originally Posted by alanm View Post
    ...I too, would like more floatation, how is this achieved? Simple, larger diameter, by doing this, one creates a bigger foot print when the tyre is deflated....
    I agree.

    That's another valid way to get what I'd like - more flotation. The larger diameter would have benefits in the rolling resistance too.

    There would be construction difficulties - such as how to fit the rest of the bike between the wheels.

    However there is already a 36" wheel bike getting around, so nothing impossible there. It would also mean that problems with chainline on extra wide tyres would be obviated.



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  17. #17
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    HArdest ride on my fat

    Quote Originally Posted by Velobike View Post
    I'm eagerly anticipating the On-One fatbike because it seems to be close to what I want. That On-One are promoting it as a rock-crawler is a plus.

    But it has prompted some idle thoughts about some things that could be improved on fatbikes.

    .....

    2. Geometry: my experiments with steeper head angles while preserving a reasonable trail have me convinced that this is the way to go. This also means the head of the bike is raised or lowered less during low speed turning which may be of some advantage in snow - I haven't tested that. A nimble bike is always an advantage at the low speeds used in lumpy ground.
    ......
    For those that need to tweak HA:

    Cane Creek Cycling Components :: Components :: Headsets

    My new Fatback has the slackest HA of any bike I've own. So far in both sand and snow it works better than anything I've tried. Descending is fantastic. I've never ridden one, but I know a couple of guys who years back purchased a crossbike with a seriously steep HA and they could not control them in sand.

    "Low speed, lumpy ground" - Glad I read this, trying to decide where to ride today, now I know where to go, and see how the Fatback handles a really ugly section of trail - sharp LH turn on a steep hump. I'll answer back on this one later.

  18. #18
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    Quote Originally Posted by Steve Balogh View Post
    ..."Low speed, lumpy ground" - Glad I read this, trying to decide where to ride today, now I know where to go, and see how the Fatback handles a really ugly section of trail - sharp LH turn on a steep hump. I'll answer back on this one later.
    I'll be interested in your findings.

    On the 24 hour I did recently the Pugsley was quite tricky and didn't handle as well as one of my bikes bike with the steeper head angle on the same sections.

    Of course, HA isn't all there is to this. The HA and the offset combine to determine the trail and there's various combinations that will result in the same trail figure. For a given trail figure I prefer the steeper HA.

    On the other hand, I've heard there have been some papers that claim that none of this really matters and we humans simply adapt to what we are riding. (I don't have a reference unfortunately - maybe someone can point to it).
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  19. #19
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    Quote Originally Posted by deuxdiesel View Post
    When I9, Hope or Hadley make a 170 hub with high engagement points, I would consider a symmetrical frame, otherwise I personally see no need to switch from my Pugsley. Geometry is a personal thing- I would hate to see all fat bikes follow the same standard, because they are all ridden in different conditions and terrain.


    Hadley do make a 170 hub. The US Fatback hubs have been made by Hadley, exclusively for Fatback, from the get-go.

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    Also, Paul is supposed to be eventually making a 170 rear hub that will be using I9 freehubs.

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    Quote Originally Posted by Velobike View Post
    On the other hand, I've heard there have been some papers that claim that none of this really matters and we humans simply adapt to what we are riding. (I don't have a reference unfortunately - maybe someone can point to it).
    Just look up "unrideable bicycle"
    The stability of the bicycle

    I first read this in "Bicycling Science" by DG Wilson. There is a lot of information in there, and some mathematical models of handling/stability. I took what I recall was the "stability number" equation, and graphed it - trail vs head angle. an 80 degree head angle always required the least trail to achieve the same stability number. Recumbents I built with this head angle worked very well - but I found I needed to run narrow handlebars so the force/feedback felt right.

    A better system of analysis was Bill Patterson's "Lords of the chainring" class materials from CalPolyTech. The math was simplified from the models used for aircraft. Calculations require knowing the center of gravity of the bike as well as the radius of the tire profile - among other factors. He doesn't give you a perfect number to work to, but the system lets you compare things and decide what range of values you like.

    Most modern bikes are just "rule of thumb" cut/try, but they do work. But look at how 29ers had to evolve their own "rules" - and we're doing the same now for fatties.
    This isn't a "you're doing it wrong" topic.

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  22. #22
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    Today's ride

    Quote Originally Posted by Velobike View Post
    I'll be interested in your findings.

    On the 24 hour I did recently the Pugsley was quite tricky and didn't handle as well as one of my bikes bike with the steeper head angle on the same sections.

    Of course, HA isn't all there is to this. The HA and the offset combine to determine the trail and there's various combinations that will result in the same trail figure. For a given trail figure I prefer the steeper HA.

    On the other hand, I've heard there have been some papers that claim that none of this really matters and we humans simply adapt to what we are riding. (I don't have a reference unfortunately - maybe someone can point to it).
    OK, tried a couple of trails today:

    The one hump I spoke of, the Fatback cut through it like a hot knife through butter. Some other sections that have small steep hills with almost total switchback turns, I could cut the corners better than any bike I've owned. Same story with a second trail I rode today, the odd weather we had unfortunately attracted "pizza cutter" riders who took to the mid-winter thaw and really hacked up several trails - today those frozen ruts created a ton of stutter bumps on many climbs and descents. All worked well on the Fatback.

    I find this interesting what you are saying because a couple of friends of mine bought a once popular cyclocross bike that had a steep HA. Wasn't long before they sold them. When riding them through sand they were difficult to control. But I'm thinking why the MFG did that might be related to what you are saying.

    I seriously made an effort to make my Fatback fail, but nothing worked. Perhaps the terrain you ride is way different from mine. The only other place I could possible test your idea here is a vacant field near my house, extremely bumpy, and requires riding through thick field grass as well.

    When Greg set me up the frame, he made a last minute decision to put me in a bigger frame, I'm using a 20 instead of an 18, with a 110 stem and a Moots bar with an 8-degree sweep. This is the largest frame I've ever owned, I've taken to it quite quickly. I have a short inseam, but a long torso. The bend in the top tube and the slack HA is what makes this frame work for me.

  23. #23
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    Quote Originally Posted by wadester View Post
    Just look up "unrideable bicycle"
    The stability of the bicycle...
    I'm familiar with that one. Also Wilson, Sharpe and others. My favourite was the work of Tony Foale - unfortunately I loaned his book out many years ago and never got it back.

    I gave up on trying calculations and moved to an empirical method - there's too many variables for me to digitally calculate even if I take my shoes off for larger numbers (even in binary ), so an adjustment of a few degrees here and a inch or so there is the way I work now.

    Weight distribution is important too. The large variation in tyre profiles available of a fatbike throw a bit of randomness into the mix too. Then there's the profile problem - the shape of the same tyre on a 100mm rim and low pressure is widely different from it on a narrow rim and a slightly higher pressure.
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    Quote Originally Posted by shiggy View Post
    I have not noticed fork/hub twisting. A fork with forward opening dropouts negates hub movement under braking, especially when used with a good internal cam QR skewer (Shimano).
    I hate to say that I have noticed some twisting in the fork of my Mukluk under hard braking and I'd likely attribute it to twist in the hub/fork juncture. I switched from the stock skewer and it definitely helped, but even before I read this post, on my ride yesterday I had an instance going into a dirt corner hard under braking where I got a good bit of flex... enough to make me think about it. And this wasn't on a steep or rocky trail. Just a level trail on good, tacky, Midwestern dirt. In fact, attached is a photo from the ride...
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    Quote Originally Posted by Velobike View Post
    I'll be interested in your findings.

    On the 24 hour I did recently the Pugsley was quite tricky and didn't handle as well as one of my bikes bike with the steeper head angle on the same sections.

    Of course, HA isn't all there is to this. The HA and the offset combine to determine the trail and there's various combinations that will result in the same trail figure. For a given trail figure I prefer the steeper HA..

    Anyone have input about good range of fork trail to use for fattbikes? Looks like a pugsly uses about 82mm and 907 about 85mm. Any thought about effect of trail above/below this range?
    I threw together a random collection of parts and had >110mm of trail. It was way,way too much and had horrible wheel flop and very quirky, unpredictable steering. I re-worked the bike for 90mm of trail (71degree HTA) and it is much better now. Just wonder how a much lower trail figure like 60-70mm might feel on a fatbike.

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    Quote Originally Posted by mgersib View Post
    I hate to say that I have noticed some twisting in the fork of my Mukluk under hard braking and I'd likely attribute it to twist in the hub/fork juncture. I switched from the stock skewer and it definitely helped, but even before I read this post, on my ride yesterday I had an instance going into a dirt corner hard under braking where I got a good bit of flex... enough to make me think about it. And this wasn't on a steep or rocky trail. Just a level trail on good, tacky, Midwestern dirt. In fact, attached is a photo from the ride...
    I wonder if it more about the torsional stiffness of the fork rather than the fork/hub interface since the forks are WAY wider. It is one of the things I thought about when I drew up the fork for the On-One fat bike (that now rusty one). I was surprised about how light the unicorn fork I am using is.
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    Quote Originally Posted by shiggy View Post
    I wonder if it more about the torsional stiffness of the fork rather than the fork/hub interface since the forks are WAY wider. It is one of the things I thought about when I drew up the fork for the On-One fat bike (that now rusty one). I was surprised about how light the unicorn fork I am using is.
    I suspect it's a combination of forces. I notice it most on the Enabler which is a symmetrical 135mm fork, and to a lesser extent on the 135mm offset Surly fork.

    A large diameter through axle clamped in the fork legs is going to have 2 benefits, firstly to eliminate any axle flex, and secondly as a result of the clamping to stiffen up the fork.
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    Interesting thoughts VB.

    I'd say that your needs are about as niche as they come, and you'd be best served (on most of them) by simply going custom, instead of asking the industry to adapt to your whims.

    Nothing wrong with your whims, but even you can see that they go against the grain of what most are using and asking for.

    Like yours, my whims are non-standard in many ways. I've asked some of the biggies to consider my preferences in the past, and then, after I got the idea that they had no interest, I just went custom. Works for me.

    YMMV.

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    Well;

    I think the front thru axle idea is particularly keen. For all the reasons stated, it seems to me to be a natural. If many if not most 2-9ers are going that way... is it not a Fatbike natural? Once someone makes a real suspension fork, it would seem to be almost obvious. Shouldn't be very hard to accomplish at all in the time being on any given CroMo fork.

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    Quote Originally Posted by shiggy View Post
    I wonder if it more about the torsional stiffness of the fork rather than the fork/hub interface since the forks are WAY wider. It is one of the things I thought about when I drew up the fork for the On-One fat bike (that now rusty one). I was surprised about how light the unicorn fork I am using is.
    Yeah... I wonder what a QR15 interface would feel like. I bet that change alone, with the same fork legs, would get us the necessary stiffness. The reason I believe it's the hub/dropout interface is because there have been two instances where, after either going through a cross-rut, or making an aggressive move with the bars, I have actually had the hub move slightly in the dropouts. It was the initial reason for my skewer switch from the stock Salsa model on the front-end of my Mukluk.

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    Quote Originally Posted by Velobike View Post
    A large diameter through axle clamped in the fork legs is going to have 2 benefits, firstly to eliminate any axle flex, and secondly as a result of the clamping to stiffen up the fork.
    #3 = Takes more time to swipe! Which is why I prefer bolt-ons.

    Less worry over safety, stronger, and more apt to stay mine.

  32. #32
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    Quote Originally Posted by mgersib View Post
    Yeah... I wonder what a QR15 interface would feel like. I bet that change alone, with the same fork legs, would get us the necessary stiffness. The reason I believe it's the hub/dropout interface is because there have been two instances where, after either going through a cross-rut, or making an aggressive move with the bars, I have actually had the hub move slightly in the dropouts. It was the initial reason for my skewer switch from the stock Salsa model on the front-end of my Mukluk.
    MG: I hear ya. I have felt some strange sensation in the front end of my Muk too. Even had the hub shift in the drops once. This is also on dry trail.

    Of course, we are putting a lot bigger footprint on the ground resulting in a lot more traction than our 29"ers have. Something has to give if the tire sticks better, ya know? It's like a football player on Astro-turf. The foot sticks like glue but the knee will give out when the guy gets tackled.

    You are familiar with the old, larger axle caps once tried on 26"ers. Specialized does this with their OS-28 end caps. I feel it helps a lot, and feels about the same as a 15Qr, to my mind. It could be a way to go to keep QR's and get rid of the funky feel.

    In the end, I think a thru-axle would help, but I am just suggesting that QR's may not have to go if they are used with the over-sized axle end cap concept. That said, Maxles are so easy to use, why not, right?

    As far as the rest goes, I see a bit slacker head tube angles being far better in loose stuff, and can be done to handle just great for trails. This past weekend's ride on snow really dialed me up to why slacker is better for the loose stuff.
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    Quote Originally Posted by Guitar Ted View Post
    You are familiar with the old, larger axle caps once tried on 26"ers. Specialized does this with their OS-28 end caps. I feel it helps a lot, and feels about the same as a 15Qr, to my mind. It could be a way to go to keep QR's and get rid of the funky feel.

    In the end, I think a thru-axle would help, but I am just suggesting that QR's may not have to go if they are used with the over-sized axle end cap concept. That said, Maxles are so easy to use, why not, right?
    I agree. I have front QR hubs with 25mm faces. Makes a noticeable difference in a sussy fork.
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    Quote Originally Posted by shiggy View Post
    I agree. I have front QR hubs with 25mm faces. Makes a noticeable difference in a sussy fork.
    I've been thinking while reading this thread and after years of riding Mag 21's and then 28mm Sids flex what flex? I suppose it's all relative.
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  35. #35
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    Quote Originally Posted by mikesee View Post
    ...you'd be best served (on most of them) by simply going custom, instead of asking the industry to adapt to your whims....
    I'm not so much asking the industry to change as trying to predict the direction it will move in.

    As for custom, you're probably right. My liking for steep HAs is not going to go down well with a market that believes slacker head angles are the go - and they're right if they fit a telescopic fork. The slacker HA is needed as the travel of telescopic forks increase. Thus the benefits of a steep HA can only be got with rigid or linkage forks.

    BTW if we have the same trail figure on 2 bikes (assuming everything else on the bikes is identical), one steep, the other slack, the one with the steep HA will flop less at low speeds (think climbing on lumpy stuff) and be less inclined to get deflected by edge impacts (not so easily unsettled by ruts).

    If anyone wants a cheap way to experiment with this, just make a DIY fork which allows you to adjust various factors, and thus simulate the various HAs on a frame.
    Last edited by Velobike; 01-17-2012 at 01:37 AM.
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    I understand the effects of offset and trail very well, and I too have an adjustable offset fork to play with.

    I've experimented bunches, and my conclusion is a virtual mirror image of yours: More. As in, I always want a higher trail number than the industry is willing to offer. Anything less than 90mm and the bike feels sketchy to me. 100 or so feels just about right, and 110ish is positively divine.

    I'm often told by low-trail/steep HTA proponents that 'if I lived and rode at X' I'd want things different, and almost invariably when I go to visit and ride those places that turns out to not be the case. Often emphatically so. More often than not I've found that these folks are just parroting others, and have never experimented for themselves.

    To each their own, though.

    MC

  37. #37
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    Quote Originally Posted by mikesee View Post
    ...I always want a higher trail number than the industry is willing to offer. Anything less than 90mm and the bike feels sketchy to me. 100 or so feels just about right, and 110ish is positively divine...
    Oh, I'm not making myself clear. We're in accord over trail. I like heaps of trail too, just have a different way of getting it.

    This is done on a bike with a steep HA by having the appropriate fork offset.
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  38. #38
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    I too believe that float and low rolling resistance can be had when increasing rim size.
    This effect has been observed by many when going from 26" to 29" with an other identical rim and tire. A 2.5" increase in rim size gave a significant advantage, especially over loose sand an snow, but also over rocks. Asphalt, the most likely condition for a taller rim to do well, offered the least if any improvement.

    That's why I posted earlier that the ultimate fat bike will have taller rims, and I proposed the same rim standard I proposed years ago for XC. 698mm bead size, where 29" has 622mm, and 26" and fatbikes have 559mm.
    Existence of 36" bikes (90cm tall wheel) without toe overlap, more than decent singletrack handling and outrageous roll-over ability (up-stairs) suggest that a 698mm rim with 4" fatty (just around 90cm as well) would be well rideable. the contact would be stretched out, the hotspot of surface pressure reduced. On top of this, it's known that a large rim diameter for a given tire cross-section will allow for lower tire pressures. Yes, at the cost of increased risk of hitting rims. Which immediately seems to be overcome with a slightly more "blunt" rim profile. 29"ers hit rims relatively often, but the snake bikes this produces is surprisingly low. More, softer hits?

    Depending on someone's prime riding style, the super-large fatty wheels will be a blessing or downring limiting. Every wheelsize is a compromize, but for every given terrain there is a sweetspot somewhere. IMO, for skinny tire XC, the ideal wheel size is the largest that doesn't compromize rider fit. Even tiny tiny women win WC's on 29" wheels. They are not disadvantaged, even on the challenging, steep and winding tracks of world cups.

    Only one effect I worry about with super tall fatty wheels is the knife-in-butter effect. Low-speed resistance when trying to steer the front wheel. A longer contact patch, after all, is like a taller knife being stuck into butter and then twisted, it's harder to do. I now realize as I white this, that the larger rim will have the tire sink in less deeply also, meaning less snow or sand to be shoved to enable a turn.

    Off-topic:
    Really out there: I am think of a chainless (and cardan-less) drive system to elinate all known issues with those in terms of space and performance. It would be based on magnetic interaction. Less likely to be useful for fat bikes I realize, due to the tall tires them selves. A crankset lined with magnet, and a rim or tire lines with magnets. these interact losslessly, acting as 2 virtual cogs. It would add weight, but also drop weight. Hubs would be front hubs only. No chain or cassette. But magnet on rim or tire, and a rather unique gearing above the BB. I have yet to research how much torque would make the practicle setup slip. It's not near infinite like a chain. But of course there are ways to increase torque from the bike's side while keeping the wheel somewhat light: multiple magnet cogs sharing the torque. Tell me it'll never happen. Maybe it's even been done before I brainfarted it first.

  39. #39
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    Quote Originally Posted by Guitar Ted View Post
    MG: I hear ya. I have felt some strange sensation in the front end of my Muk too. Even had the hub shift in the drops once. This is also on dry trail.

    Of course, we are putting a lot bigger footprint on the ground resulting in a lot more traction than our 29"ers have. Something has to give if the tire sticks better, ya know? It's like a football player on Astro-turf. The foot sticks like glue but the knee will give out when the guy gets tackled.

    You are familiar with the old, larger axle caps once tried on 26"ers. Specialized does this with their OS-28 end caps. I feel it helps a lot, and feels about the same as a 15Qr, to my mind. It could be a way to go to keep QR's and get rid of the funky feel.

    In the end, I think a thru-axle would help, but I am just suggesting that QR's may not have to go if they are used with the over-sized axle end cap concept. That said, Maxles are so easy to use, why not, right?

    As far as the rest goes, I see a bit slacker head tube angles being far better in loose stuff, and can be done to handle just great for trails. This past weekend's ride on snow really dialed me up to why slacker is better for the loose stuff.
    I like the idea of running a MAXLE-type of setup... Might be the ideal scenario for a fatbike rigid fork, with a solid-clamping skewer.

    And I like your ideas about slacker HT angles too, especially as we venture into 'suspension for fatbikes' territory. It totally makes sense to me for a number of reasons.

    Good stuff...

  40. #40
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    Quote Originally Posted by mikesee View Post
    I understand the effects of offset and trail very well, and I too have an adjustable offset fork to play with.

    I've experimented bunches, and my conclusion is a virtual mirror image of yours: More. As in, I always want a higher trail number than the industry is willing to offer. Anything less than 90mm and the bike feels sketchy to me. 100 or so feels just about right, and 110ish is positively divine.

    I'm often told by low-trail/steep HTA proponents that 'if I lived and rode at X' I'd want things different, and almost invariably when I go to visit and ride those places that turns out to not be the case. Often emphatically so. More often than not I've found that these folks are just parroting others, and have never experimented for themselves.

    To each their own, though.

    MC
    Mike, do you mean for snow bikes, or bikes in general?

    I have experimented with HTA/offset/trail/front center and know what I like for my riding style, at least for dirt, mud...
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    VeloBike:

    Put me down as one who has misunderstood you, I too assumed that you wanted a lower trail number.

    Are you then trying to get the control you desire by moving the axle back towards yourself, putting
    more weight on the front wheel, while not changing the trail number too much? In order to do that you must decrease the fork rake some, correct? This in turn, make toe overlap more likely, right? Something some try not to have when sawing on the bars, picking your way slowly about.

    Question:

    If the above is correct, why not figure how much ETT length you need for a given HTA and fork figures, just short of toe overlap, then add the reduction to the stem length to obtain your fit? Seems like I read
    somewhere that the two are not quite the same when applied. Did not understand though.

    With the former example, the fork would transmit a more direct, rougher feel than the latter, if that matters.

    Any corrections to me would be welcome.

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    One reason I suggested this is because my present 1989 26er (no FS) has a short TT and a long stem. I have done some rough measurements and with a fork to accept a 29" tall tire, it looks like a close fit.

    The BB and stays would have to be reworked though.

    Also, would I be correct to assume you have tried different bar widths to gain proper control?

    While that short TT and long stem work fine, I find myself longing for a longer TT and shorter stem, which is the direction frames in my size have taken sense '89. (about 1.5"+)

    Just a thought for your consideration in your pursuit.

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    If you take 2 bikes with the same wheelbase and riding position, then the one with the steep HA will need a longer top tube, hence a shorter stem to have the bars in the same place relative to the rider and front wheel.

    Most of what I have come to believe is needed with HAs and trail is as a result of experiments and modifications I made to motorbikes in the 70s to try to get them to handle at high speed on rough dirt roads. I lived on the edge of the desert in Oz and hundreds of miles to the next large town). Back then the standard Japanese motorbike had really dodgy handling, and we needed fast bikes simply to get anywhere. Ironically none of my mates believed my findings although they were quite happy to admit that my bikes handled better than theirs - they thought it was down to the suspension units which admittedly were nonstandard.

    This gave me the base for when I started to fiddle around with bicycle geometry.

    However, in the 80s, Tony Foale did a series of very interesting experiments on the same thing, and basically confirmed for me I was on the right track. He also points out the disadvantages of the telescopic fork - "The only drawback noticed – juddering under braking – is a consequence of the poor structural integrity of the telescopic fork as a type."

    If you click the link, you'll end up on his site, and there's lots of great resources there.

    BTW a very simple trick to increase trail if you have a telescopic fork is to pull off the lowers and replace them with the fork crown reversed. The fork looks the same to the casual eye, but because the crown is reversed, you have reduced the offset by twice its offset, and thus moved the vertical line dropped from the axle to the ground further back from the line drawn through the steering head to the ground - ie increased the trail. Obviously whether this does any good depends on the geometry of your bike and your forks construction (and at your own risk etc etc), but it is an easy thing to try. (I suspect this may not be so easy to do on the current batch of forks)
    Last edited by Velobike; 01-18-2012 at 07:22 AM.
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    How about using a 20mm thru axle. If I remember correctly isn't the spacing on them already 110mm rather than 100? It would stiffen things up enormously and there are already maxle offerings to make pulling your wheel not much harder than a standard QR. Redesign the fork slightly for the 10mm wider width replace the drop outs with pipes for the thru axle (threaded on one side for the maxle) and we're ready to ride.

  45. #45
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    Quote Originally Posted by woodi2259 View Post
    How about using a 20mm thru axle. If I remember correctly isn't the spacing on them already 110mm rather than 100?...
    Using an existing standard like that makes sense. I've been looking at 110mm hubs because I'm planning a new fork. I'd prefer a simple clamp on the fork - the time difference in removal would be minimal.
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    Looks like salsa already makes a thru axle rigid 29er fork. All they need to do is reshape the legs a bit to accommodate wider tires and I think it just might work well. Salsa Cycles | Components


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    Thanks for the referance to Tony Foale VeloBike, have read some of his work before, good for a re-read.

  48. #48
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    Quote Originally Posted by Sand Rat View Post
    Thanks for the referance to Tony Foale VeloBike, have read some of his work before, good for a re-read.
    Yeah, he did far more elegantly than I did.

    I like the bit where he gives the bars a knock at high speed to see if he could instigate a wobble. I've been spat off one of those R75/5s at speed and there's no way I'd be daft enough to try that on one of them in unmodified form.

    Still, it's a pretty good indication of the benefits.
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    VB

    Rode a R75/7 for many years, once hit a 6" deep X 18" sharp pot hole at about 55mph...never fazed
    the bike, my AMF built Sportsters...would hate to think.

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    How about accommodation for a kickstand?

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