[MMcG]

Just curious as to who developed the "standard" axle to crown height for 29er forks.

It seems that somewhere around there or close to Surlys 468mm axle to crown height (give or take a few mms) is the norm for 29er forks. Was this to "mirror" suspension fork axle to crown heights?

Was it necessary for proper handling of the bigger wheels?

Just curious as to what thinking went into that "standard" fork geometry numbers as it seems many forks are based off of or identitcal to the Surly KM fork numbers.

Yet in some instances, perhaps only on smaller fames, those numbers tend to raise the front end of the bike up quite a bit.

Why wasn't the standard more like the numbers used on the Raleigh non suspension corrected design - or something in between the Raleigh and the KM numbers?

Just curious is all. Especially when I look at the On One Inbred photos I see. I can't help but notice that the front ends on the Inbreds seem pretty tall. Perhaps it is an optical illusion due to the sloping top tube on those frames??

I would love to be able to have an LBS locally where I could grab a Raleigh and take it for a spin and then compare that against an Inbred or Haro Mary for example to see what type of rigid front end works best for me and my riding style.

Just thought I'd throw out this as a topic of further discussion.

Have at it Monkeys!

 

[shiggy]

The KM fork and frame were designed around the only 29" sussy fork of the time - the Marzzochi (80mm travel). It dictated the A-C length and the height of the front end.

 

[MMcG]

thanks, but that still makes me wonder about the others that followed.

Like the new Salsa fork - mimics the KM in every aspect right? Also many others like the Qball fork and maybe a couple more too.

and not to many are shorter than the KM right? The zion is longer, the Niner a lot longer.

I think Kelly had a shorter AC fork for a while though didn't they?

I'm just thinking of the visuals of bikes I've seen online such as Drevil's Matt Chester, JRADS Quiring and a few others with the shorter AC forks and they look really appealing to my eyes. Now whether I'd like the way they ride is another question, but they do look "right" to me to a great extent.

 

[shiggy]

Different sussy forks - even with the same travel - have different A-Cs. Some designers spec for sag, some do not.

The frames with the short A-C rigid forks are not designed to ever be used with suspension. Viva le custom!

 

[Possum]

440mm+/- - non-corrected. "standard" 29"er. offsets can vary with HTA for the builder's preferences on handling

465-470mm+/-, +/-42mm offset - "standard" 80mm sussy-corrected

480-485mm+/-, +/-42mm offset - 100mm sussy-corrected

The above numbers are (decent) approximations of the forks out there, with sag accounted for. They are all approximate, but it should at least give you a ballpark idea of what the frame/fork was designed around.

 

[Guitar Ted]

I've been testing a couple carbon legged forks for review on Twenty Nine Inches and I'll tell ya. These forks are all over the place with different rakes, different axle to crown heights, and then throw in the variance in head tube angles......whew! it can sure be a handful to get a grasp on it all!

I love it, actually. I think that it's opened up the geometry question for debate on 26"ers, too. Look at what Gary Fisher is up to with the Gen II geometry as an example. I think we all got lulled to sleep in the 90's by "Norba Geometry" and we forgot to question why things were the way they were after awhile. 29"ers and DH'ers have re-opened that can-o-worms and I find it fascinating. It sure makes riding a whole new adventure when you slap on a fork with a whole different set of numbers than the fork before it! :biggrin:

By the way, what was the question again.....................:biggrin:

Ahh crap! I'm just gonna hafta go out and ride that other fork again....dang it! :biggrin:

 

[shiggy]

I've been testing a couple carbon legged forks for review on Twenty Nine Inches and I'll tell ya. These forks are all over the place with different rakes, different axle to crown heights, and then throw in the variance in head tube angles......whew! it can sure be a handful to get a grasp on it all!

I love it, actually. I think that it's opened up the geometry question for debate on 26"ers, too. Look at what Gary Fisher is up to with the Gen II geometry as an example. I think we all got lulled to sleep in the 90's by "Norba Geometry" and we forgot to question why things were the way they were after awhile. 29"ers and DH'ers have re-opened that can-o-worms and I find it fascinating. It sure makes riding a whole new adventure when you slap on a fork with a whole different set of numbers than the fork before it! :biggrin:

By the way, what was the question again.....................:biggrin:

Ahh crap! I'm just gonna hafta go out and ride that other fork again....dang it! :biggrin:

Add in that the 26" sussy forks have even more variation in the A-C length and it is really screwball. 440mm has sort of become the "usual" A-C for a rigid fork "corrected" for a 100mm sussy. My 2001 X Fly 100 is ~458 with 20% sag! I was looking a custom fork for my Matt Chester until the Zion 26" fork came out with a 457 A-C and 43mm of offset, matches the Marzzochi Matt designed the frame to use exactly. But Jenson still claims their fork is a replacement for a 85mm travel fork.

I have ridden my MChester with a KM fork (~10mm longer) and it was OK. With the Zion fork it rides smooth and quick and it is nearly same feel as with the sussy.

Hard to imagine what the near random fork lengths do to production frames.

 

[el-cid]

Look at what Gary Fisher is up to with the Gen II geometry as an example.

I wonder what inspiration or influence Keith Bontrager had on this latest project. I love the handling of my '97 Race Lite with the Judy fork with the KB crown and long-ass stem. KB seemed to be one of the truly innovative guys in the industry and could have went so much further with the influx of Trek $ if they hadn't decided steel hardtails weren't in vogue . A different discussion for a different day I guess.

 

[shiggy]

I wonder what inspiration or influence Keith Bontrager had on this latest project. I love the handling of my '97 Race Lite with the Judy fork with the KB crown and long-ass stem. KB seemed to be one of the truly innovative guys in the industry and could have went so much further with the influx of Trek $ if they hadn't decided steel hardtails weren't in vogue . A different discussion for a different day I guess.

What KB was doing with the Race and Race Lite frames was pretty much the opposite of the Genesis/G2 concepts.

Short front-centers and long stems to weight the fork and make it more active. Reduced fork offset to increase trail for stability on descents and minimize the effective trail reduction when on soft terrain (the tire contact point moves forward when on soft surfaces. This increases the effective fork offset and reduce the trail. When the trail approaches zero the steering becomes unstable).

 

[MMcG]

Hey Shig - can you throw up some visuals for us on the Bonty frame and fork concepts vs. the Fishers.

And what's the scoop with the Genesis 2 deal?

 

[shiggy]

Hey Shig - can you throw up some visuals for us on the Bonty frame and fork concepts vs. the Fishers.

And what's the scoop with the Genesis 2 deal?

It may take a while. Remind me if I do not do it in a few days.

G2 is meant to quicken the steering feel of the Fishers. The long TT, "normal" trail of G1 is very stable in a straight line and on descents but can be sluggish in the twisties.

G2 shortens the TT slightly and increases the fork offset (reduces trail). The bike reacts quicker while the still-long TT maintains most of the stability at speed.

The old Bontrager concept was the long trail in the steering gave the stability while the short TT helped keep the agility.

 

[Guitar Ted]

The reason for the longer top tube/ front center on Genesis versus Bonty geo is to keep you from going OTB as much. Believe me, I took some doosies over the bars on my '96 Race. That bike was a single tracking demon though. I guess it's part of the reason I went to 29"ers, getting dumped over the front end one too many times.

 

[shiggy]

The reason for the longer top tube/ front center on Genesis versus Bonty geo is to keep you from going OTB as much. Believe me, I took some doosies over the bars on my '96 Race. That bike was a single tracking demon though. I guess it's part of the reason I went to 29"ers, getting dumped over the front end one too many times.

My preference is the moderate length TT/long stem model. The front-center of all my mtbs (except the Coiler), two 29ers and three 26ers, are within an inch or so of each other.
Endos are a non-issue for me with 26 or 29 inch wheels. It happens occasionally but only when I do something stupid.
Been riding the same basic fit since 1986. For the first ten years my TTs were considered "long". For the past ten many call them "short."

 

[MMcG]

Shiggy - is your TT length preference also impacted by your use of the dirt drop bars? Or would you ride the same tt on your bikes if you were using flat bars or risers? Just curious of thsoe bars impact things a bit (or is the impact more in stem length/rise?).

 

[shiggy]

Shiggy - is your TT length preference also impacted by your use of the dirt drop bars? Or would you ride the same tt on your bikes if you were using flat bars or risers? Just curious of thsoe bars impact things a bit (or is the impact more in stem length/rise?).

The bar choice has nothing to do with it.

 

[MMcG]

Gotcha - thanks.

 

[El Caballo]

Short front-centers and long stems to weight the fork and make it more active. Reduced fork offset to increase trail for stability on descents and minimize the effective trail reduction when on soft terrain (the tire contact point moves forward when on soft surfaces.

I've never liked Genesis Geometry for that reason...not enough weight on the front. And the Bontrager short TT/long stem, as mentioned, causes the endo problem.

The other way to get more weight forward, of course, is to make longer chainstays. My BM Flyer has bizarre geometry by normal standards (19" chainstays*, 72 HA, ~71 STA, 55mm stem). The end result is a quick-steering bike that has good weight distribution, but can climb seated and doesn't want to endo when I sneeze. It really opened my eyes to reality vs. conventional wisdom regarding frame geometry.

I give up a little bit of ease in manualing, but I'll worry about that the day my upper body is 1/5 as worked as my legs at the end of a ride.

(*Yes, I posted previously that the BMF had 18.25" chainstays. I was wrong...it's 19".)

 

[Changleen]

Interesting thread for a bunch of freaks.