Trail geometry for fat bikes- Mtbr.com

# Thread: Trail geometry for fat bikes

1. ## Trail geometry for fat bikes

A recent thread here (http://forums.mtbr.com/fat-bikes/fat...er-774932.html) raised a topic I've been interested in and pondering for a while now, namely, what might be the most ideal frame/fork geometry for a fat bike to be ridden as a trail bike as compared to those more specifically purposed for snow or sand? I'm neither completely naive nor a whiz at issues of frame geometry and how it affects ride quality, but I hope some of the more knowledgable and aware on the board will please give us some numbers and explain how their choices influence the ride. I'd especially be interested in hearing from folks who have designed a custom frame as an alternative to the stock bikes presently available (JN Carpenter, MCS, and Shiggy come to mind immediately in this regard but there are others as well of course). My interest arises from the perspective of snow riding being an unlikely event, and a sincere desire to eventually own a fat bike to be used as an alternative to my Turner 5 Spot for trail riding. We have plenty of rocks and roots here in central NC, and my fat biking experience amounts to one brief ride on a first-generation Pugs.

2. Strange to see that pop up while I have been trying to draw up a frame.

I've done a bit of crude experimenting with a DIY fork which allowed me to play around with the AC (thus changing head angle) and offset.

So long as there is sufficient trail, I prefer a steep HA which I think minimises the heavy steering feel of a fat tyre at low pressure, and is less affected by ruts. Other people have different opinions though.

You may find these useful
Kreuzotter's trail calculator
Yojimg calculator
Bikegeo calculator

I prefer the empirical method of having an adjustable setup so you can test it immediately over the same section of track rather than obsessing over the figures - you can get very similar results with quite varying dimensions sometimes. If you want to try the empirical method take a look at my DIY fork project. It allows enough variation to give you some idea of the direction you want to take your geometry.

Has anyone got a comparison table of the various geometries of existing fatbikes? (and forks)

BTW it's worth considering "flop" in your thinking. A lot of its effect depends on weight distribution.

3. ## Subscribed

I'm just up the road from you in WNC, I also am looking at building a full fat bike as my second bike over the next year or two.

I can say after one ride on my fat front Jones, a design around a larger offset fork (54-56mm) makes a big difference in the steering. I also think not having the longer "snow geometry" chainstays will help the bikes on our trails.

4. I'm no expert, I simply know how to hack together frames, which allows me to try stuff out, and over the years, I've found certain elements I like to keep, where as others, I prefer to avoid.

I wouldn't call my frame tweaked in any way "for fat", it's simply a geometry I've enjoyed for years, built with fat tire clearance.

A high, 13.5" BB is a must for me, I just love it. Others, hate on 'em. I run 180mm cranks, so the high BB helps with that too.

70 deg HTA, on the slack side, works for the way I ride, and helps keep things calm in the rough stuff, stable and stuck to the ground on the high speed sections. I have no love for twitchy thoroughbred race steeds. The whole "I need my 29er to ride like my 26er" thing is lost on me, but hey, if it works for them, great!

Shortish 17.3 chainstays make it climb well and keep the wheel under me, yes, shorter stays do exist, but the soft tail aspect also makes going much shorter tough, and hey, they feel awesome on my Lunch Box so what the heck!

Kinda like a Subway sub, no one eats em exactly the same way, which is why we go there in the first place.

5. Originally Posted by MendonCycleSmith
...A high, 13.5" BB is a must for me, I just love it....
I can see the need for that. I have no problem with "normal" BB heights on other bikes, but I find myself riding the fatbikes through stuff where pedal strike is a nuisance. I've been thinking of using shorter cranks for that reason.

6. Originally Posted by Velobike
I can see the need for that. I have no problem with "normal" BB heights on other bikes, but I find myself riding the fatbikes through stuff where pedal strike is a nuisance. I've been thinking of using shorter cranks for that reason.
Yeah, it's a regional thing for sure. That said, living in the Eastern US, ever since Cannondale brought out the Beast of the East waaaay BITD, with it's 13.5 BB, I've found it to work quite well for me!

7. ## Nice

Thanks for the links to the calculators, they look interesting and informative.

I'm trying to get educated as to all aspects of fat bike geo for trail use because I'm either going to use the acquired information to buy one of the available frames that comes closest, or possibly have one built. But I need to get smart about it first.

I know there are a variety of opinions regarding chainstay length and I understand the overall concept of what happens as they get longer or shorter. What are anyone's thoughts on optimal dimensions for trail riding? Given the limitations imposed by the tires, seat tube, and front derailleur, what is the actual measurement of the shortest practical chainstay...and then what is the sweet spot for a bike that will still negotiate terrain well without feeling like a truck?

I also get it about BB height, and I like the geo of my 5 Spot. Actually, I recently set it up with a 650b wheel on the front, which raised the BB and I accommodated it with no trouble. So I'd favor something with a 13-13.5" BB I guess.

Thanks, and keep it coming.

8. ## Jugsley

This is what I did with my Pugs. The truss fork made a huge difference in the way the bike handles and brakes.

9. Originally Posted by Tripower
This is what I did with my Pugs. The truss fork made a huge difference in the way the bike handles and brakes.
Do you find the NuVinci step-less gears useful on a fatbike?

10. Originally Posted by GrahamWallace
Do you find the NuVinci step-less gears useful on a fatbike?
Yes.

11. Originally Posted by Tripower
The truss fork made a huge difference in the way the bike handles and brakes.
Could you elaborate?

I kinda miss my NuVinci'd Pugsley (I didn't sell it out of disgust, I sold it because my best friend lusted after it).

12. Originally Posted by Drew Diller
Could you elaborate?

I kinda miss my NuVinci'd Pugsley (I didn't sell it out of disgust, I sold it because my best friend lusted after it).
I did not like how much the Pugsley fork flexed during braking. The flexing of the fork during downhill braking caused the front of the bike to start "bouncing" if the brakes were not modulated properly.

Rock crawling is much easier with the truss fork (at least for me). Again, because of the reduced flex. The steering is much nibbler and quieter (if that makes any sense). The front tire eases in and out or corners much smoother than before. The truss fork did change the geometry a tad so that might be the reason.

Although the Pugsley fork was not that bad, I am just use to riding bikes with truss forks.

13. Originally Posted by MendonCycleSmith
I'm no expert, I simply know how to hack together frames, which allows me to try stuff out, and over the years, I've found certain elements I like to keep, where as others, I prefer to avoid.

I wouldn't call my frame tweaked in any way "for fat", it's simply a geometry I've enjoyed for years, built with fat tire clearance.

A high, 13.5" BB is a must for me, I just love it. Others, hate on 'em. I run 180mm cranks, so the high BB helps with that too.

70 deg HTA, on the slack side, works for the way I ride, and helps keep things calm in the rough stuff, stable and stuck to the ground on the high speed sections. I have no love for twitchy thoroughbred race steeds. The whole "I need my 29er to ride like my 26er" thing is lost on me, but hey, if it works for them, great!
Your geometry preferences sound very close to the fatbike I home-built. I took an old OX-II steel hardtale, added a old manitou I fork modified for fat use, and then re-built the rear triangle for fat clearance and also at hight needed to keep the HTA at 70° (and keep fork trail from getting too high) while using the uber-tall front suspension. I didnt think through the implications on BB height when I built it and wound up up around 14" BB height (zero BB drop measurement). It felt really wierd to be so high-up the first couple times I rode it but it slowly became familiar and comfortable. Responds well to shifting of bodyweight side-to-side in order to keep it going strait on loose/narrow snowtrails and it has massive amounts of pedal clearance for riding through deep snow and mud ruts. Downside is that saddle is so tall that it is a bit hard to get up on to get going after I have flounder or stopped on loose snow or to quickly get enough momentum to keep ballanced if I need to get start on a loose uphill. It is also a long way to fall off from so high up & harder to just put down a foot to stab when needed. I might next try limiting the suspension travel slightly to bring the front end down a bit, maybe rework the rear triangle. Good to hear that 13.5" BB height works well for you, small reduction from current 14" height might make a difference.

14. Originally Posted by Tripower
I did not like how much the Pugsley fork flexed during braking. The flexing of the fork during downhill braking caused the front of the bike to start "bouncing" if the brakes were not modulated properly.

Rock crawling is much easier with the truss fork (at least for me). Again, because of the reduced flex. The steering is much nibbler and quieter (if that makes any sense). The front tire eases in and out or corners much smoother than before. The truss fork did change the geometry a tad so that might be the reason.

Although the Pugsley fork was not that bad, I am just use to riding bikes with truss forks.
Stock pugsley front end geometry is 70.5°HTA (447mm fork A-C), 43mm rake producing around 84mm of fork trail. I am curious how much your truss fork differ from this to produce the handeling you prefere. Any percieved loss of strait line stability for staying on narrow loose snow trails?

15. The stock geo on my Carver is 69.5 with a Pugs fork and an Endo. I am using an Enabler and a BFL which I figure jacks up the front end at least an inch and a half or so, resulting in a 68 degree HTA give or take. I would not want it any steeper. For summer use I am running a 100mm 29er fork which results in about the same or maybe a hair slacker - perfect IMO for everything, but it's purely a matter of taste and personal preference. I much prefer the more relaxed handling on all conditions.

16. Originally Posted by Tripower
Although the Pugsley fork was not that bad, I am just use to riding bikes with truss forks.
Did you use the 100 or 135 mm Pugsley fork?

17. Originally Posted by GrayJay
Stock pugsley front end geometry is 70.5°HTA (447mm fork A-C), 43mm rake producing around 84mm of fork trail. I am curious how much your truss fork differ from this to produce the handeling you prefere. Any percieved loss of strait line stability for staying on narrow loose snow trails?
Tracks better with the truss fork.

18. Originally Posted by rasse1977
Did you use the 100 or 135 mm Pugsley fork?
135mm offset

19. Originally Posted by Velobike
I can see the need for that. I have no problem with "normal" BB heights on other bikes, but I find myself riding the fatbikes through stuff where pedal strike is a nuisance. I've been thinking of using shorter cranks for that reason.
I found that the wide BB shell increases pedal strikes. Hit more things on the edges of the trail and the pedal is lower when the bike is leaned. Have had adjust my riding style a bit (for the tire differences, too).

Anything below 12.5" is a low BB to me. Prefer 13.0". 180-185mm cranks.

20. Originally Posted by Tripower
This is what I did with my Pugs. The truss fork made a huge difference in the way the bike handles and brakes.
I'd love to hear more about the new fork. I've had some latent Jones lust for a while, but never made anything happen. I could probably justify the cost/hassle to repurpose my Pugs with a Jones fork...

Did the truss fork raise the front end? Can you describe the handling differences?

Thanks for sharing...

21. It is really hard to explain. It rides very similar to my spaceframes except the Pugs is not as rigid in the rear.

If you are ever out in my area, you are more than welcome to take it for a spin.

22. Any idea of what the AC dimension is on the truss fork? (Axle to the crown race landing)

23. GrayJay' try a seat dropper seat post. I have a KS i900 R and I also have 27.2mm dia model to get around the very reasons you've noted, albeit not in snow. Wouldn't be without them now.

Al.

24. AC on Jones fork...435? Seems like I came across that figure while poking around Jeffs site...
one of the reviews?

Tripower...were you able to install the Jones without any changes to the headset? I also
assume that the headtube length can not exceed that of the Jones bike for his fork to be
installed...shorter is ok...can use spacers?

25. Originally Posted by Sand Rat
AC on Jones fork...435? Seems like I came across that figure while poking around Jeffs site...
Thanks, I was guessing between 430/440 from looking at pics.

26. Originally Posted by Sand Rat
AC on Jones fork...435? Seems like I came across that figure while poking around Jeffs site...
one of the reviews?

Tripower...were you able to install the Jones without any changes to the headset? I also
assume that the headtube length can not exceed that of the Jones bike for his fork to be
installed...shorter is ok...can use spacers?
I used the "special" Jones headset. The Pugs headtube is the same length as the Jones.

27. Originally Posted by Tripower
I used the "special" Jones headset. The Pugs headtube is the same length as the Jones.
What size Pugs do you have?

28. The Sandman frames are designed specifically as trail riding machines or "fully killers", though they also handle excellently on (and win) snow races. I've only had the chance to ride mine on snow once in the past year. It's been trails, mud, leaves, rocks and roots all the time for me and I love it (even with endomorphs front and rear).

29. Originally Posted by vikb
what size pugs do you have?
20"

30. Originally Posted by Orkje
The Sandman frames are designed specifically as trail riding machines or "fully killers", though they also handle excellently on (and win) snow races. I've only had the chance to ride mine on snow once in the past year. It's been trails, mud, leaves, rocks and roots all the time for me and I love it (even with endomorphs front and rear).
The geometry info on their site seems to be limited. I can't find the HT and ST angles...am I missing it?

31. Originally Posted by vikb
The geometry info on their site seems to be limited. I can't find the HT and ST angles...am I missing it?
Same with Fatback.

If anyone knows the figures post them up, I'll put them on the comparison list I've made up with trail and flop calculated.

32. Originally Posted by Tripower
This is what I did with my Pugs. The truss fork made a huge difference in the way the bike handles and brakes.
That is one good looking bike right there
*Motorman seal of approval*

33. The geometry info on their site seems to be limited. I can't find the HT and ST angles...am I missing it?
I can't seem to find the angles either, only the measurements (in the PDF).

34. ## Ti Fatback

I've just given my Ti Fatback a complete run through all of the local trails that would matter to me and I'm pretty happy with it as a trail bike. Most notably was a certain rocky uphill switchback that I cleaned cleaner than any bike I've owned. With my angle finder I'm measuring between 69><70 degree HTA. Also enjoying the slack head tube for some sandy downhill areas I frequent.

My 2007 Wildfire was always a competent trail bike for me, can someone enlighten me what this "snow geometry" is all about? I haven't noticed anything lacking in cornering ability in either fatbike I own compared to my 29r. I've read some of the other threads, most of them lack detail, except Velobike's. Not criticizing, just trying to understand as I've been riding Fatbikes all year round for five years without issue. I also ride a 29r and a cross bike.

35. Originally Posted by Steve Balogh
I've just given my Ti Fatback a complete run through all of the local trails that would matter to me and I'm pretty happy with it as a trail bike. Most notably was a certain rocky uphill switchback that I cleaned cleaner than any bike I've owned. With my angle finder I'm measuring between 69><70 degree HTA. Also enjoying the slack head tube for some sandy downhill areas I frequent.

My 2007 Wildfire was always a competent trail bike for me, can someone enlighten me what this "snow geometry" is all about? I haven't noticed anything lacking in cornering ability in either fatbike I own compared to my 29r. I've read some of the other threads, most of them lack detail, except Velobike's. Not criticizing, just trying to understand as I've been riding Fatbikes all year round for five years without issue. I also ride a 29r and a cross bike.
not to question the validity but are you saying the fat was just as capable as the 29r over the same terrain??

36. Originally Posted by Orkje
The Sandman frames are designed specifically as trail riding machines or "fully killers", though they also handle excellently on (and win) snow races. I've only had the chance to ride mine on snow once in the past year. It's been trails, mud, leaves, rocks and roots all the time for me and I love it (even with endomorphs front and rear).
What rims/hubs do you use?

37. Originally Posted by Tripower
I did not like how much the Pugsley fork flexed during braking. The flexing of the fork during downhill braking caused the front of the bike to start "bouncing" if the brakes were not modulated properly.
I am happy you wrote this, because this is exactly what I am experiencing ever since I got my Surly Big Dummy, and this is definitely annoying. Actually the only annoying thing about this great bicycle.
So, according to this, a fork exchange might help.
Regards, Phil

38. ## Yes

Originally Posted by nvphatty
not to question the validity but are you saying the fat was just as capable as the 29r over the same terrain??
Yes, I was quite surprised - I believe the large front tire is giving the stability going over a few
rocks. But being able to do the turn as tight as I did really surprised me. When I get a chance, I'll post a video (need to trim it down). Granted, on a good day the 29r should go up faster, but a lot of times things get baked and that section gets loose. With a fatbike I'm less likely to be walking. Makes me wonder if I should get a pair of Schwalbe 2.35/2.4's for the 29r. Using Nobby Nics right now.

Also, measuring around 73 degrees on the seat tube angle.

39. New to this whole fatbike thing, just built up a size small 170mm 9zero7 about 3-4 weeks ago. Took it out for my 2nd singltrack ride yesterday, have to say it is quickly becoming my favorite ride. Handles unbelievable in the tight and twisty sections, even with 170 bars. Running XTR 1x9, HD's on RD's non drilled, the only con as of now are the climbs and i think that's more because of my conditioning and not the bike. I can hammer into the curves and berms and the bike just rails them with out tapping the brakes. The geometry of this bike just feels right for singletrack.

40. ## Mukluk Ti Geometry Works For Me

I've been riding a Mukluk Ti for a few weeks now, primarily on out local trails in the San Diego area. The geometry is very different from my other bikes, but it hasn't been seen as a hindrance; only something different.

My Ellsworth Id was infamous for it's high bottom bracket, but that gives it lots of trail clearance. It is a bit harder to get on and off the saddle, not quite as stable in the switchbacks, and seems to have the weight aft, making it one of my harder bikes to keep the front end down while climbing. My Santa Cruz Superlight (26" version) is well balanced and FAST on smooth trails, but quickly hits its limits when the going gets rough. It's not twitchy, but you get the sense that you are riding it close to its limits. My Santa Cruz VP Free feels incredibly stable at speed in the rough and is relatively easy to climb, thanks in no small part to its longer wheelbase and slack head angle. 7" of travel front and back probably doesn't hurt in that aspect either.

The only real issue with the Mukluk is its weight and resistance to acceleration. At a steady speed, I don't notice the weight, but try racing that bike against a friend and I feel every ounce. Take it on a long trail ride, and I'm ready to keep going. I have gotten used to the handling, love climbing up steep sections with the additional traction and balance that the wheelbase provides; and am blown away by the stability the bike has at slow speeds, in trackstands, and around switchbacks. While stable at high speed, the rebound from the tires makes for some interesting trajectories when the going gets rough. I've subsequently removed the big chainring to provide more clearance over rocks because I just don't ride the bike that fast and I'm getting more comfortable dropping over ledges.

Ultimately, I guess I'm trying to say there is probably no "perfect" geometry that sets a fatbike up for trails instead of snow. The sweet spot for fatbike geometry is probably pretty wide and you can learn to overcome any deficiencies by just getting out and riding! The Mukluk is currently my bike of choice as I continue to expand its range.

41. I put Jeff Jones Loop H-bars on my Pugsley which moved the grips back far enough I need a setback post to get the effective TT I need. In the process I am creating a cockpit and weight bias similar to a Jones spaceframe.

Jeff Jones Spaceframe - a set on Flickr

Then I plan to ride them back to back on the same trails and see what's what.

No specific expectations or theories....just figure it will be a fun experiment.

42. Will be interested to hear your thoughts. As I'm now on a Jones SS and am thinking of a 1x full fatty.

43. Originally Posted by nitrousjunky
Will be interested to hear your thoughts. As I'm now on a Jones SS and am thinking of a 1x full fatty.
Is your Jones a straight up 29er or a half-fat?

44. Originally Posted by vikb
Is your Jones a straight up 29er or a half-fat?
half-fat with the Jones 50mm rim and a Nate.

45. Originally Posted by Tripower
This is what I did with my Pugs. The truss fork made a huge difference in the way the bike handles and brakes.
Pretty cool combo and great creative thinking to get there.

I love my truss fork.

46. Originally Posted by nitrousjunky
Will be interested to hear your thoughts. As I'm now on a Jones SS and am thinking of a 1x full fatty.
Just had a look at the Geo charts for my 18" Pugs vs. the Jones....numbers below are Pugs/jones:

HT angle: 70.5/70.0
Fork Offset: 43mm/55mm
ST angle: 72.0/72.0
Wheel Base: 42.6"/42.0"
Eff TT: 23.4"/23.0"

47. Originally Posted by vikb
...Then I plan to ride them back to back on the same trails and see what's what....
No specific expectations or theories....just figure it will be a fun experiment.
That's the sort of experiment I like to see.

48. Originally Posted by vikb
I put Jeff Jones Loop H-bars on my Pugsley which moved the grips back far enough I need a setback post to get the effective TT I need. In the process I am creating a cockpit and weight bias similar to a Jones spaceframe.
No specific expectations or theories....just figure it will be a fun experiment.
When I first setup my fatbike and rode it on loose snow trails, #1 problem I had was that the front end would wash-out in loose snow and it was difficult to keep it going strait on narrow, loose snow trails. By trial and error I figured out that setting it up to distribute more weight on the front tire really helped to reduce wash-out and improve stability on loose snow. In my case, I moved the saddle + bars forward from my usual riding position and it helped tremendously.

49. Originally Posted by GrayJay
When I first setup my fatbike and rode it on loose snow trails, #1 problem I had was that the front end would wash-out in loose snow and it was difficult to keep it going strait on narrow, loose snow trails. By trial and error I figured out that setting it up to distribute more weight on the front tire really helped to reduce wash-out and improve stability on loose snow. In my case, I moved the saddle + bars forward from my usual riding position and it helped tremendously.

The key word is "loose" snow trails which means flat in practice. The new setup on my Pugsley is for riding steep rocky dirt trails with lots more traction than loose snow. When your front wheel is 1'-2' below the back wheel there is a lot of weight on it even with a rearward saddle position. Heck my butt will likely be hanging way back over top of the rear tire like in the photo above.

I've got zero concerns about my front wheel washing out. It rarely snows on my part of the island.

Going uphill the rearward saddle position facilitates lofting the front wheel over obstacles and the loop h-bar has about an 8" spread between front and rear hand positions so you can shift weight forward on steep climbs to keep the front wheel planted.

50. vikb- I bet one thing that is going to stand out, is the difference in steering between the 2 different fork offsets.

The greater offset of the Jones fork makes a big difference there IMHO.

51. Originally Posted by nitrousjunky
vikb- I bet one thing that is going to stand out, is the difference in steering between the 2 different fork offsets.

The greater offset of the Jones fork makes a big difference there IMHO.

Yes absolutely. I noticed that on last night's ride. Having said that the difference wasn't huge in practice. It's most noticeable at walking speed when you are picking your way through a tech section.

It's also the one thing you can't change easily on the Pug without getting a Jones truss fork [I heard he wasn't selling them a la carte??] or getting a custom fork built.

I'm not sure at medium speed I noticed the steering differences much, but I need more time to evaluate it.

From a macro perspective we agreed both bikes felt very similar on the trail.

I liked having a Nate on the rear of the Pugs and wouldn't switch to a 29er wheel.

I also need to spend more time on the Jones by myself so I can tweak the bars/saddle position to my liking [5'11"] vs. just riding it the way my friend [5'6"] has it setup.

Forgetting the Jones for a second I'll say that this new rider position is really fun on the Pugsley vs. my usual more centered XC oriented position - at least on our steep technical trails.

52. He does however have the unicrown fork listed individually on his current price sheets. However it probably would be cheaper to have a custom fork built so you could still run the Pugs wheel.

Also for those interested in the Jones fork numbers, the axle to crown of the unicrown fork is listed as 441mm with 55mm offset.

53. Originally Posted by nitrousjunky
He does however have the unicrown fork listed individually on his current price sheets. However it probably would be cheaper to have a custom fork built so you could still run the Pugs wheel.

Also for those interested in the Jones fork numbers, the axle to crown of the unicrown fork is listed as 441mm with 55mm offset.
Good catch...one of my favourite features of the Pugs is the swappable wheels. I wouldn't give that up.

54. Originally Posted by vikb
Just had a look at the Geo charts for my 18" Pugs vs. the Jones....numbers below are Pugs/jones:

HT angle: 70.5/70.0
Fork Offset: 43mm/55mm
ST angle: 72.0/72.0
Wheel Base: 42.6"/42.0"
Eff TT: 23.4"/23.0"
Just ran the figures.

If the Jones fork is 435mm A/C against the Pugs 447mm, then the effective HA of your Pug becomes 71.1º.

The standard Pug is trail 86mm and flop 27mm. With the Jones fork it becomes trail 69mm and flop 21mm. (The Jones fork on the Jones is trail 76mm, flop 25mm)

(Assumption tyre diameter = 740mm.)

55. Originally Posted by Velobike
Just ran the figures.

If the Jones fork is 435mm A/C against the Pugs 447mm, then the effective HA of your Pug becomes 71.1º.

The standard Pug is trail 86mm and flop 27mm. With the Jones fork it becomes trail 69mm and flop 21mm.
Do you have those numbers for the Jones bikes?...sorry if I missed it...numbers have been flying around this forum fast and furious lately!

56. Originally Posted by shiggy
I found that the wide BB shell increases pedal strikes. Hit more things on the edges of the trail and the pedal is lower when the bike is leaned. Have had adjust my riding style a bit (for the tire differences, too).

Anything below 12.5" is a low BB to me. Prefer 13.0". 180-185mm cranks.
I concur with this for XC ish FBing. In fact, last time I rode w/ Shiggy, I smacked a pedal so hard it through me over the bars (I think he might have just barely caught it on video). It was a super skinny, "raw" desert trail and the rock was hiding behind sage brush. Sometimes our tires have to roll over rather than squeeze through obsticals as well. Never the less, love riding mine year 'round. My "custom" is basically a 29er hardtail built wide enough for FB tires/rims and spec'd for the Maverick. Not only higher at the BB, but lower in the "cockpit" as well. Maybe a little to much weight on the front end for optimum snow & sand riding, but just right for the trail! (and it does fine on the soft stuff too). I believe the Mav is a big part of it's "all 'round" success.

57. If you are not snow riding and would rather not haver the strong tracking/stability of the stock pug setup, you could use a fork bending jig to add a bit more rake to the pugs CrMo fork legs, bring the pugs fork trail more inline with the jones setup.

58. Originally Posted by GrayJay
If you are not snow riding and would rather not haver the strong tracking/stability of the stock pug setup, you could use a fork bending jig to add a bit more rake to the pugs CrMo fork legs, bring the pugs fork trail more inline with the jones setup.
The Pugs fork seems really beefy I'm not sure how successful modifying would be. I'm also not sure it's that important. I noticed more precision on the Jones at very slow speeds where wheel flop is more of an issue on the Pugs, but I didn't at moderate speeds. That's just an early assessment, but so far I wouldn't spend a lot of time/\$\$ to change the Pugs. I may build up enough reasons to do so with more riding of both bikes....hard to say at this point.

59. Originally Posted by vikb
The Pugs fork seems really beefy I'm not sure how successful modifying would be. I'm also not sure it's that important. I noticed more precision on the Jones at very slow speeds where wheel flop is more of an issue on the Pugs, but I didn't at moderate speeds. That's just an early assessment, but so far I wouldn't spend a lot of time/\$\$ to change the Pugs. I may build up enough reasons to do so with more riding of both bikes....hard to say at this point.
As you percieved, effects of fork trail are sensitive to speed. It is a bit road-centric but a good basic explanation of the handeling characteristics of trail is over at; Spectrum Cycles | Geometry

60. An observation - we can obsess too much about geometry, because at the end of the day, if it's possible for a human to ride a unicycle, then a few degrees of HA or mm of trail on a bicycle isn't going to make anything unrideable.

However I do like to know the geometry of bikes I like riding, and they usually turn out to be similar. It makes it easy to reproduce a pleasant ride when I build my next bike (n+1 rule). In my various (rough) experiments with differing geometries, there has never been anything I couldn't ride. Usually the differences are only obvious in tight tracks with irregular surfaces (technical).

I am unlikely to be doing high speeds though - I'm generally riding at an all day pace.

It's the high speed bits that can be the problem - an off can have serious consequences. Things that cause me bother are ruts and large loose rocks. My ideal geometry will stabilise quicker than I can react.

61. Originally Posted by GrayJay
As you percieved, effects of fork trail are sensitive to speed. It is a bit road-centric but a good basic explanation of the handeling characteristics of trail is over at; Spectrum Cycles | Geometry
Bicycle Quarterly has had numerous bike geometry articles over the last few years. Well worth the investment in back issues if you want to geek out on bike handling.

Bicycle Quarterly: Home

62. Originally Posted by nitrousjunky
He does however have the unicrown fork listed individually on his current price sheets. However it probably would be cheaper to have a custom fork built so you could still run the Pugs wheel.

Also for those interested in the Jones fork numbers, the axle to crown of the unicrown fork is listed as 441mm with 55mm offset.
See the thread below. I took a few measurements on the Jugsley.

http://forums.mtbr.com/fat-bikes/geo...ks-775465.html

Jones does sell the truss fork seperately when he has extras in stock.

63. any thoughts on how trail (edit: as in the ground) angle affects things? we can get the same trail etc by differing head angles/offsets, and weight distribution can be moved around with stem length within reason...so what effect does angle of the ground have on things? any?
thinking in terms of pure geometry i cant immediately think of one - trail is trail no matter how it is achieved and on what angle of ground - but seat of the pants wise i'm thinking there is...?

64. Originally Posted by dRjOn
any thoughts on how trail angle affects things? we can get the same trail etc by differing head angles/offsets, and weight distribution can be moved around with stem length within reason...so what effect does the trail have on things?
primarily effects handling characteristics, i.e. side-side transitions like the following examp>>>
A bike with lots of trail will be directionally stable. It will tend to go straight and be easy to ride hands-off. It will not have its direction changed by every tiny bump in the road. Such a bike will take more physical effort to steer than a bike with less trail.
A bike with only a little trail will be livelier (some would say “squirrellier”). It will take very little effort to change its direction whether that effort comes from your hands on the bars or from a bump in the trail, road etc.

65. Originally Posted by dRjOn
any thoughts on how trail (edit: as in the ground) angle affects things? we can get the same trail etc by differing head angles/offsets, and weight distribution can be moved around with stem length within reason...so what effect does angle of the ground have on things? any?
I have puzzled over that too. I think weight distribution has a considerable bearing on the effects of trail and flop, so when we shift our weight back on the bike on a hill maybe what we are doing is preserving our CoG position relative to the front wheel to keep the correct loading on it.

I have also been trying to work it out for the effects of ruts, eg does where the side of the rut comes into contact with the wheel mean the effective trail and flop have been changed? It would explain how some ruts can throw you quicker than you can react.

I can't think of a reliable test though.

I think I need some body armour for further research.

66. Originally Posted by Velobike
I can't think of a reliable test though.

I think I need some body armour for further research.
seems appropriate

67. Here's my "XC" or "trail" fat bike. Nothing new to most of you, but for those who haven't seen it: I had it custom built specifically for riding year round here in the north west- single track, jeep trails, no trails, sand, snow... I wanted this bike to be able to thrive no matter where it ended up. It can't match my Fatback for snow or sand performance (though it does just fine in those conditions) but that's the trade-off. Kind of like a stock jeep can go "Jeeping" just fine, but can't match the modified, "trailered in" rock crawler for all out 4x4 performance. Or an all mountain ski that handles everything you can throw at it, but tough to match the performance of a powder only ski in deep powder.

Like Shiggy said on page one, a higher than "snow bike" BB to give it more clearance and get you up on top of that big fat machine (as opposed to down inside it) and give you some command over it. My BB on this bike is 13 1/4" off the ground (about 1 1/4" drop). Raising the BB also effectively lowers the "cockpit" position as far as the rider is concerned. The front end on this bike was spec'd for the Maverick which, preloaded, has an A to C of approx. 180mm so, even though it has a shorter than "snow bike" HT, it sits just about as high off the ground as my Fatback. It's the higher BB that lowered the "cockpit".

With the fork pre loaded it's HT angle is approx. 70.5* and it's CS's are 17.5". It's made of Easton ALU tubing and has been rockin' and rollin' all over the Northwest for going on 4 years now. It rides like a hardtail 29er w/ allot more footprint and the ability's of high floatation if needed.

I'm convinced that the Maverick has allot to do with it's success out there, and for sure with it's ability to keep up with reg. mtb's.

Bottom line: This is my favorite bike EVER!! It get's ridden more than any other bike I've ever owned! I can't begin to tell you how much fun I've had on this bike. And Ton's of stories about it continuing on when the other bikes on the ride were "shouldered". I'm thinking about building a set of Salsa Gordo 29er's (35mm) for it before summer to have as an option when riding buff or tech. single track.

Anyhow, this is my idea of an "all terrain", pedal powered machine.

<a href="https://www.flickr.com/photos/[email protected]/6344311485/" title="FILE0037 by wardee61, on Flickr"><img src="https://farm7.staticflickr.com/6058/6344311485_465721ea2b.jpg" width="500" height="375" alt="FILE0037"></a>

68. This thread has given me pause to consider my headtube length necessary to install a
Jones Truss fork...may limit my position on the bike, have to do some more drawings and
see what there is to see. (1/2 scale) Using a small pugs as a base point.

Very interesting to hear the comment from Vikb and the position offered by the loop bars,
and how he liked it.

That the greater offset of the Jones gave an improved feel of control at walking speeds, falls
right into my aim point.

And thanks Ward for giving a detailed description of your bike, what your plan was, and how
sucessful it turned out.

All of what has been said here has been said elsewhere from time to time, but it is always good
to see it more clearly brought together in one place, plus hearing it again makes things 'click'
sometimes. For me, this thread has been a great help.

Be good to see a detailed description on the new On One Fat bike, when it is ready.

My thanks to all, and to twangcat for starting it all.

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