Me gotta ? regarding frame geometry

[Carbon_Angus]

If you have a head tube that is XC (like on the *57, EVO and carbon bikes)  and put a 5 inch fork on it.....will it be the same (handle) as a 5 inch fork on a more slack head angle???



I know the head angle will change in refernce to the wheel axle, but the "frame" geometry doesn't change, right?



I guess what I am getting at is if I wanted to put a five inch fork on one of my k2/Pro~Flex steeds, it would NOT handle as well as a tirade or some other bike with a slacker head tube angle.



My only experience has been on my Oz with 4 inches, my 857 with 3 inches and and the x~link and a Trek Liquid with 5 inches.



as most of you know I just do xc stuff and try to stay in one piece while riding [smiley=laughing.gif]



[smiley=beer.gif]

[Frankd3000]

It HAS been a year with it's fair share of injuries, hasn't it?

To answer your question; yes, the slacker headtube angle will ride with a slower steering feel, because it is. While the frame geometry WILL change the angle of the seat tube and the rest of the frame, this won't play a role in steering. They (the rest of the frame) can be anything and they won't affect the steering of the bike (okay, except maybe wheelbase).

The simple fact of the matter is that when you make the front of the bike higher, thus reducing the headtube angle, you slow down steering response.

The only way to counter-act this is by raising the rear of the bike also. This would help to re-gain some of the lost frame geometry/headtube angle. The pros of doing this are mainly increased BB height and potential for more travel. The cons are higher center of gravity and less stand-over height.

I'm going through all of this right now with Frank. It's been very educational.

[shovelon]

And don't forget your shock and fork balancing. Sure the front will be higher. You can adjust this with less sag on the rear and more sag on the front.

And a good number of forks these days have adjustable travel. My Psylo and Maverick have a 2 inch drop for climbing. But on the descent, with some front braking there is some fork compressing. So in most cases, when I care most, I am riding in the same geometry the bike was designed with. But what a difference in performance.

Terry

[Matno]

Actually, raising the front end only does throw your weight back somewhat. That can lead to "unweighting" your front end, which makes steep climbing difficult. On the other hand, it makes descending nice... To compensate, you can put your seat slightly more forward, but then you shorten your effective top tube length. I guess that's the biggest difference between a frame designed for the slacker head tube angle and one that's not. Now, whether or not it's big enough for you to notice or care is completely subjective! I would have to ride a LOT more bikes than I do to be able to say things like "the 69.5 degree head tube angle felt slightly more stable than the 70 degree setting..." I still think that magazine reviews are mostly subject to interpretation and how a bike feels to you is all that matters.

[Sprucey]

I think you will find it fine.

Different fork manufacturers have different length forks (crown race to axle) for the same travel.

I run a 120mm Marzocchi Marathon SL coil (which is a long fork) on my Oz with no problems. All I have done is fitted a shorter stem to make up for any slower steering (110mm to 90mm).

The Oz was designed in 97/98 when head angles were generally steeper than is the fashion on bikes designed today. I think all you are doing is making the bike more like today's modern free ride bike in feel.

matno is right - there is no such thing as free lunch. You get bettre stability and performance on the technical downs but it requires more finesse on the steep technical climbs 9although most modern forks have some sort of lock down / shortening mechanism anyway.

Sprucey

[jimbo]

Modifications outside the original design parameters can have some interesting results.  As long as the modifications are not extreme most riders just naturally adapt to it.



I added a Psylo to my K2 Evo.  Bike seem to work fine in all the travel modes.  I bought a new Gemini with 7 inches of travel front and back.  Took a couple days of riding to get use to the bike. Rode the Gemini for several months.  Decided to ride the Evo and immediately noticed that I felt like I was too far back on the bike through the downhill berms.  I had to purposely shift my weight forward to plant the front tire throught the turns.  Like Matno said the bigger fork shifted my weight further back.  I had naturally compensated for it without realizing it when I only had that bike.  The Gemini was designed for the longer fork so the riding position is more neutral.  Switching between the bikes was the only way I noticed that.



On the other hand my buddy just put a 6 inch travel Chubby DH on his K2 Disco Monkey.  That sucker weighs something like 8 pounds.  He has no problem with the front end lifting on steep climbs.  He did mentioned that the rear of the bike feels noticibly flexy with his cross country rear wheel.  Putting on his freeride rear wheel balanced the bike a little better.  It's no wonder on the stiffness descrepancy, the stantions on the Chubby is 36mm!!!