Quantcast

How slack is too slack?

in the trees

Turbo Monkey
May 19, 2003
1,210
1
NH
I've been doing some upgardes in the off-season and had some questions regarding head angle. What's an ideal angle range for DH? I'm running 26/24 (used to run 24/24, so I know this may be the issue) on a hardtail and it looks real slack. Can anyone tell me what angles they're running on rigs? Thanks.
 

draco

Monkey
Mar 5, 2003
126
0
Roche-STAR
67 was like the standard for DH head angles. 66 was a lil slacked, 65 was way slack, and 64 was, wrong bike. 68 was nimble, for maybe a tighter course, and 69 is like, DJ street hardtail .

so anything past about 65 is bad. at least, thats when you get into acceclerated wear and tear on fork bushings, seals, crowns, etc.
 

draco

Monkey
Mar 5, 2003
126
0
Roche-STAR
easy. its all in relation to the ground. so flat, is 0, and vertical, is 90. typically measured on a bike with some form of a protractor/level/auto/thingy. you can actually use a protractor and a ruler and figure it out.
 

JK:UK

Chimp
Apr 17, 2004
79
0
UK
so is the angle the angle the forks stand at off the ground.

trying to figure out my 888 8" on bullit (M) angle
 

Kornphlake

Turbo Monkey
Oct 8, 2002
2,632
1
Portland, OR
to measure the angle you'd need to drop a plumb bob from the bottom of the headtube while the bike is standing vertical (like it would be if you were riding it) Measure the distance from the bottom of the head tube to the spot where the plumb bob pointed on the ground. Then do the same thing from the front axle to the ground. Subtract the second measurement from the first and call this A. Now measure the distance between the two points on the ground, call this B. Now recall that A^2+ B^2=C^2. C^2 is the axle to crown distance more or less, you can calculate it or measure it (I'd do both to verify my tape measure and calculations are at least in the ball park) Finally to find the headset angle you have to find your scientific calculator and input tan^-1 (B/A)= and that is your head angle as long as your calculator is in degrees mode. You can check this by using Cos^-1 (C/A)= or Sin^-1(B/C)= That's how I'd do it anyways, since my protractor isn't big enough to rest on the floor and reach all the way up to the fork leg. I have a neat little angle finder that looks kind of like a curved bubble level but I don't trust it to be very accurate. They also make a type of protractor that has a bubble level mounted in a wheel with the angle graduations marked all the way around, you line up the edge and spin the wheel until the bubble is level and read the angle, again I don't know that I'd entirely trust the accuracy of the bubble level though, at least not to more than a degree or so.

Note: I use the ^ symbol to denote the power of a term for example c^2 would equal C squared or C*C. It is pretty standard notation to me and most others here, but not all of us are engineers here.
 
Oct 27, 2003
59
0
Madcity Wisconsin
I think it all depends on rider style and skills. For me personally i would never want a bike that had slacker than 66 degrees unweighted. For me i like it in the 68-67 range for most my riding, but if i stickly raced dh i would perfer a 66 degree headangle, you can get all your weight over the front wheel and dig that mofo in, i feel plenty stable with that setup too with a good bb height.

I say use your muscles to get through rock gardens, and finese the bike through, that is the fastest and most rewarding way.:)
 

Zoso

Monkey
Jan 31, 2003
212
0
Seattle
66 (unweighted) seems to work well for me. Any slacker than that would seem like over kill unless you ride really steep stuff.

The easiest way to measure it is to go to your local shop and ask them to do it for you. Most decent shops have a Park HA measurement tool that has a magnet that sticks to the head tube and a guage that will tell you your exact head angle. Easy, simple, accurate.
 

in the trees

Turbo Monkey
May 19, 2003
1,210
1
NH
I measured last night - 65 on the nose. Still feels slack to me. I forgot I could throw in a set of e-13 reducers to help with head angle. I'm gonna try that before I rebuild my rear wheel.

Yes, JD a Monster T handling the bumps up front.:D
 

MMike

A fowl peckerwood.
Sep 5, 2001
18,207
105
just sittin' here drinkin' scotch
Originally posted by Kornphlake
to measure the angle you'd need to drop a plumb bob from the bottom of the headtube while the bike is standing vertical (like it would be if you were riding it) Measure the distance from the bottom of the head tube to the spot where the plumb bob pointed on the ground. Then do the same thing from the front axle to the ground. Subtract the second measurement from the first and call this A. Now measure the distance between the two points on the ground, call this B. Now recall that A^2+ B^2=C^2. C^2 is the axle to crown distance more or less, you can calculate it or measure it (I'd do both to verify my tape measure and calculations are at least in the ball park) Finally to find the headset angle you have to find your scientific calculator and input tan^-1 (B/A)= and that is your head angle as long as your calculator is in degrees mode. You can check this by using Cos^-1 (C/A)= or Sin^-1(B/C)= That's how I'd do it anyways, since my protractor isn't big enough to rest on the floor and reach all the way up to the fork leg. I have a neat little angle finder that looks kind of like a curved bubble level but I don't trust it to be very accurate. They also make a type of protractor that has a bubble level mounted in a wheel with the angle graduations marked all the way around, you line up the edge and spin the wheel until the bubble is level and read the angle, again I don't know that I'd entirely trust the accuracy of the bubble level though, at least not to more than a degree or so.

Note: I use the ^ symbol to denote the power of a term for example c^2 would equal C squared or C*C. It is pretty standard notation to me and most others here, but not all of us are engineers here.



...or you could spend $9 at home Depot and get one of these...
 

HTFR

Monkey
Aug 20, 2002
413
0
Chelsea, Quebek
Originally posted by MMike
...or you could spend $9 at home Depot and get one of these...
or you could save 9 bucks and gas money and do a simple calc and learn something:D .

oh and kornflake you can also use cosine law

c^2=a^2+b^2-2abCos(C')
but then you have to solve for C'
 

MMike

A fowl peckerwood.
Sep 5, 2001
18,207
105
just sittin' here drinkin' scotch
Originally posted by HTFR
or you could save 9 bucks and gas money and do a simple calc and learn something:D .

oh and kornflake you can also use cosine law

c^2=a^2+b^2-2abCos(C')
but then you have to solve for C'
As I already know how to do those calcs, I'd rather save the time and effort. not to mention, you will likely get a more accurate result by measuring directly.
 

jimmydean

The Official Meat of Ridemonkey
Sep 10, 2001
40,574
12,803
Portland, OR
When a company posts a bikes geometry, it must be the frame without fork. Because the RMX with a Jr. T (170mm) is listed as having a HA o 66.75, then the RMX Pro with 888 (200mm) as the same head angle.

Now if the 888 jacks the front up as bad as some say, plus adds 30mm of travel, then the "effective" head angle (not listed, but what I would gues you would notice) would be diiferent. Sure looks different in the pics.

The reason I ask is I rode an RMX yesterday and fell in lust! But I don't like the way the Jr. T feels. They didn't have the pro in stock, so I couldn't compare the 2 together. My fear would be the angle that felt so good with a bad fork would be crushed with a great fork that was too tall.

Man, this sucks!
 

BlackDiamond

Chimp
Jan 25, 2004
71
0
Rancho Cucamonga CA
Originally posted by Kornphlake
to measure the angle you'd need to drop a plumb bob from the bottom of the headtube while the bike is standing vertical (like it would be if you were riding it) Measure the distance from the bottom of the head tube to the spot where the plumb bob pointed on the ground. Then do the same thing from the front axle to the ground. Subtract the second measurement from the first and call this A. Now measure the distance between the two points on the ground, call this B. Now recall that A^2+ B^2=C^2. C^2 is the axle to crown distance more or less, you can calculate it or measure it (I'd do both to verify my tape measure and calculations are at least in the ball park) Finally to find the headset angle you have to find your scientific calculator and input tan^-1 (B/A)= and that is your head angle as long as your calculator is in degrees mode. You can check this by using Cos^-1 (C/A)= or Sin^-1(B/C)= That's how I'd do it anyways, since my protractor isn't big enough to rest on the floor and reach all the way up to the fork leg. I have a neat little angle finder that looks kind of like a curved bubble level but I don't trust it to be very accurate. They also make a type of protractor that has a bubble level mounted in a wheel with the angle graduations marked all the way around, you line up the edge and spin the wheel until the bubble is level and read the angle, again I don't know that I'd entirely trust the accuracy of the bubble level though, at least not to more than a degree or so.

Note: I use the ^ symbol to denote the power of a term for example c^2 would equal C squared or C*C. It is pretty standard notation to me and most others here, but not all of us are engineers here.
Holly crap!! I just eyeball it. LMFAO!!
 

BlackDiamond

Chimp
Jan 25, 2004
71
0
Rancho Cucamonga CA
Originally posted by Zoso
66 (unweighted) seems to work well for me. Any slacker than that would seem like over kill unless you ride really steep stuff.

The easiest way to measure it is to go to your local shop and ask them to do it for you. Most decent shops have a Park HA measurement tool that has a magnet that sticks to the head tube and a guage that will tell you your exact head angle. Easy, simple, accurate.
Yea, I like his idea!! ;)
 

fonseca

Monkey
May 2, 2002
292
0
Virginia
Originally posted by jimmydean
When a company posts a bikes geometry, it must be the frame without fork.
Most companies post geometry using a fully or mostly built bike, including a fork and wheelset with tires at the least. That's how you get wheelbase measurements, BB and TT height, HT and ST angles.

Turner, for instance, uses a Fox fork on a lot of frames for their measurements, something you need to consider when looking at their charts, since with some other SC forks you will end up a degree or more slacker.
 

zedro

Turbo Monkey
Sep 14, 2001
4,144
1
at the end of the longest line
Originally posted by MMike
As I already know how to do those calcs, I'd rather save the time and effort. not to mention, you will likely get a more accurate result by measuring directly.
spoken like a seasoned engineer.....whos probably had his share of calculatory mishaps;)

but ya, taking one direct measurement is better than taking two or 3 then using a formula....more independant measurements=less accuracy
 

zedro

Turbo Monkey
Sep 14, 2001
4,144
1
at the end of the longest line
Originally posted by JK:UK
yeah i know...but which angle is it?just between vertical and the angle your forks are at?
the horizontal (axle to axle! ground has to be level) and the fork axis. Doesnt matter really, its all relative. If you measured 25degrees, everyones gonna know you meant 65 degrees.
 

Zoso

Monkey
Jan 31, 2003
212
0
Seattle
Originally posted by ViolentVolante
that tool doesnt even exist, at least not one made by Park
It may not be made by Park, but it was blue so I just assumed. Anyway, it DOES exist because I used it a few weeks ago to measure mine. Just because you've never seen something doesn't mean it can't exist. As we all learned from philosophy class, that's a fallacy of ignorance, which is an invalid argument.

And as far as the magnet thing goes, it didn't stick to MY headtube, but it does have a magnet on it (for when steel was the popular material back in the day I think).
 

Jm_

sled dog's bollocks
Jan 14, 2002
18,739
9,459
AK
I find that the slacker your headtube gets, the bigger front tire you need to keep from washing out, and then all of a sudden you are running a 2.8 or 3.0 and everybody is pedaling past you. 67 is just about right for everyone, give or take one degree. Going anything more than that, and you'll suddenly need a super-sticky large tire, or you'll be way to steep.