Raised BB, head angle, Vanilla RC...

[keen]

  My 2001 Way Big Disco Monkey has a Marzocchi Z1 fork which has lifted the front end 1.5". Running a stock length rear shock (8.25") my head tube angle is 68 deg. vs. stock which is 70.5 deg. The raked head angles cause slower steering (chopper effect)Maybe I could get used to it? any opinions on a 68 deg. angle?  I was considering going to an 8.5" Fox Vanilla RC which would bring my head tube angle up to 70 deg. which in turn would raise my BB height. Would a raised BB cause a stability problem? I looked @ quite a few pic's of K2's running long travel forks w/ Vanilla RC's- how are they doing? Thanx

[GET]

I lot of the riders who post here seem to like the slacker steering angle (68 degrees).  I happen to like more precise steering (~70 deg.).  We have some tight twisty singletrack.  Someone calculated (or measured) that an 8.5" i-2-i shock raises your center of gravity less than an inch (~5/8", as I recall).  If stand-over clearence is an issue, then that might be a reason not to go with it.  However, IMHO, the stability change is not going to be nearly as noticeable as the handling change due to the longer fork.

[jimbo]

From RC at Mountain Bike Action

http://www.mbaction.com/qanda.asp?curpage=100

Q. Hey RC - Is there such a thing as a preferred BB height? I’m riding a bike right now that has a 12.5” BB. If I look at new bikes, should I look at taller BB’s; say C-dales Jekyll’s, which adjust from 12.9 – 13.5”? Or would a 12.5” Stumpjumper be a better fit? Although I like the idea of say, another ½” to 1” of clearance to increase the odds of avoiding trail rock, I’ve got a concern about going higher. I’m a 5’11” long legged creature who has to have high seat height for proper leg extension. Sitting on my seat, I can barely touch the ground with my shoe tips. If I go to a 13 – 13.5 BB, doesn’t it stand to reason that, assuming the same leg extension, my seat height would be another ½ to 1” higher from the ground. Wouldn’t this be a big problem since none of my starts could be in a seated position since my feet wouldn’t be able to touch the ground? Also, what does that additional height do to my center of gravity in tight, technical, maybe upright, terrain? Something? Nothing? Thanks for taking the time to answer. Sam

sbattaglia@stayner.com - 6/4/01 9:37:33 PM



A. Sam, Bottom bracket height is all about a secret ratio between wheelbase and rider height. Raising the bottom bracket adds ground clearance, but at some point, it causes the bike to bounce over bumpy ground because the center of gravity is too high in relation to the wheelbase. The longer the wheelbase of your bike, the higher your bottom bracket can be and still rool smoothly over the earth. Too low and the pedals will bash into rocks and logs--and dig into the ground while you are pedaling out of corners. 11.5 inches is about as low as you can get away with on a typical hardtail and 12.5 to 13 inches is about right for a 4" travel dual-suspension trailbike. Specialized opted for a low, 11.5 inch bottom bracket height on its line of FSR XC suspension bikes and this single feature has bred complaints from many owners. You really don't need to touch the ground--keep your feet up and you will be better balanced. Get a seatpost QU clamp and lower your saddles for tricky downhills. RC

[slowride]

My comment would be that the raising, etc should only be noticeable when the bike is unloaded (ie, when you're not on it). I don't know what kind of sag is appropriate for the Marzocchi you have, but in general there should be some sag there. Not to mention the fact that when you're actually riding, the head angle would probably be constantly variable due to the fact that the length of the fork is always changing as it compresses and decompresses to absorb the bumps.

2 degrees is pretty small. Go out and ride the bike, and if it feels just awful to you, then think about doing something to fix it.

[numbnuts]

I think i am one of the slacker angle lovers, currently running a shorter than stock rear shock and a 100mm fork on a medium Evo. I think a lot depends on your riding style, I ride a lot of technical singletrack and don't feel any lack of control. I also ride some real steep rocky stuff with drop offs and roll offs, nothing massive but I find that I have more control and confidence in those situations. I am actually desperate to get a 5" fork but will try and get one that will adjust for long climbs.
Re BB Ht, Lots of people are running the 8.5 RC and loving it so unless you've got ridiculously short legs it should be a sweet set up, probably the optimum all round set up for that frame. I nearly always drop my seat for steep stuff also. Remember you are going to have a lot more [and better quality] travel also, compared to a Noleen anyway. [smiley=nod.gif]

[jimbo]

What kind of shorter rear shock are you using?

Me and 2 other buddies run Psylo SLs.  We ride all kinds of terrain so it's nice setup the fork for the terrain.  

[dmc]

I'm running a 125mm Vanilla R on the front and a 200mm Vanilla RC on the back and I find it fine, I have found that on tight single tracks around the side of hills that I do hit my pedals a bit more with the shorter shock but overall it is a much better bike, Your head angle shouldn't be to much of a problem as you will be running more sag with a long travel fork than on a shorter one, I like the way my bike goes up hills more now than before as with the negative travel from the sag the front is alot smoother (but the 50mm stem makes keeping the front down a prick). If you have a 8.5 RC you will want to run more sag so it shouldn't be to much of a change in the height of BB. dmc

[keen]

  I measured my BB height 14 1/8"- Z1 wedge, 8.25" rear shock. I mocked up an 8.5" shock/ fixture for testing purposes ( broom stick mounted @ 8.5") head angle went from 68 deg to 70 deg., BB height went to 14.5". riding impressions: 68 deg. steering is a bit floppy, slower steering w/ an impression that downhill rides would be handled better.  70 deg. fast percise steering, downhills would be a little tougher due to the touchy steeing. Wheelbase w/ an 8.25" shock is 45"- yes long due to the extended length of the Z1 fork. 8.5" shock brings the wheelbase to 44.5" ( I think stock is 44.6" )

[numbnuts]

JIMBO, i have a van r on the back, I got from ebay and am not sure of size, supposed to be 8 i-i. All I know is it works great.
DMC
I am encouraged about the reports of the fox van r fork, I have heard others say that it doesn't alter the geometry as much as other 5" forks. I agree about the shorter stem being a bitch uphill, BUT it feels sweet going down or off stuff.

If I can get a deal on the psylo SL I jump on it, I seem to remember that Jimbo "stole" his.

I have a week of riding and partying in NC over Easter, so I can't buy anything until I've paid off those debts.  [smiley=upset.gif]

[RED5]

Bike as setup for most of my riding right now is 7.875 Fox RC on back with a Psylo 125mm up front with a 24" rear wheel. Gives me about a 67% HT and I love it.

I tried the 8.5 RC and couldn't stand the HT angle when I ran a 26" rear tire. With the fork and rear shock raising my BB up I felt the bike was to unstable, especially on high speed descents. With a 24 it was alright but still not what I was looking for.

[numbnuts]

RED5, what kind of riding are you doin, general trail stuff or mostly downhill, cos that bike sounds like it'll flip over if you try and ride uphill ! Do you use the travel adjuster on the psylo much?

[RED5]

I pretty much do everything on my Evo with the 24 on it. But your right the headangle can make it a chore to climb with, especially on most real steep or loose rocky climbs. The offset to that is the 24 climbs easier. Overall, it suits me pretty good. However, for XC I only use the 24 on the shorter rides 10-12 miles. For the the longer ones I tend to use the 26.

As for the Pyslo, I had the travel adjuster and got rid of it. For me it felt like it made my climbing harder, like the front end was trying to plow into the ground. I use and standard setup set at 125mm. Like lock outs I find it useless.