Got Any DH Questions? Ask Them Here

PB Forum :: Downhill
Got Any DH Questions? Ask Them Here
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flag Clarkeh
Posted: Nov 28, 2018 at 23:16 Quote
vydra wrote:
ThunderChunk wrote:

Don't need a 26" fork. 27.5 works fine. I ran one with my 26" wheels for half a season.

Doesn't that change the geometry of the bike though? Or is it such a suddle difference that it doesn’t matter?
Marzocchi forks fit either 27.5 or 26" I imagine the a2c would make a slight difference, but not enough to cause an issue.
flag Loki87
Posted: Nov 29, 2018 at 0:07 Quote
vydra wrote:
ThunderChunk wrote:

Don't need a 26" fork. 27.5 works fine. I ran one with my 26" wheels for half a season.

Doesn't that change the geometry of the bike though? Or is it such a suddle difference that it doesn’t matter?
The only change would be in the BB height due to wheelsize change if the A2C measurement of the fork stays the same (or roughly within the same range). It might be a problem on a frame with lots of travel and a low BB height. Ideally you'd check BB height at full compression and then subtract the change in wheel radius to make sure no ground contact will occur. Also if the BB is already low you might start hitting stuff on rougher tracks.
It really depends on the frame and tracks you ride. For some frames it'll work for some not so much but mostly due to the wheelsize change, the fork should be no big problem given that with most triple clamps there is a small range of adjustment in height possible anyways.
flag tkdbboy
Posted: Nov 29, 2018 at 1:19 Quote
Where on your index finger does your brake lever rest and how much throw does your lever have to lock your brakes?

Is your front and rear brake setup in relation to above equal or not and if so, how does it differ?
flag spaceofades
O+
Posted: Nov 29, 2018 at 7:03 Quote
tkdbboy wrote:
Where on your index finger does your brake lever rest and how much throw does your lever have to lock your brakes?

Is your front and rear brake setup in relation to above equal or not and if so, how does it differ?
I like my finger pretty near the end of the blade, almost at full extension. I like my brakes to work as early in the stroke as possible. I do my best to have the same setup on both sides.
flag apatipsychonaut4
Posted: Nov 29, 2018 at 11:11 Quote
Loki87 wrote:
vydra wrote:
ThunderChunk wrote:

Don't need a 26" fork. 27.5 works fine. I ran one with my 26" wheels for half a season.

Doesn't that change the geometry of the bike though? Or is it such a suddle difference that it doesn’t matter?
The only change would be in the BB height due to wheelsize change if the A2C measurement of the fork stays the same (or roughly within the same range). It might be a problem on a frame with lots of travel and a low BB height. Ideally you'd check BB height at full compression and then subtract the change in wheel radius to make sure no ground contact will occur. Also if the BB is already low you might start hitting stuff on rougher tracks.
It really depends on the frame and tracks you ride. For some frames it'll work for some not so much but mostly due to the wheelsize change, the fork should be no big problem given that with most triple clamps there is a small range of adjustment in height possible anyways.

I use a Marzocchi 380 C2R2 Ti which is 27.5 and never had an issue
flag ThunderChunk
O+
Posted: Nov 29, 2018 at 23:08 Quote
Loki87 wrote:
vydra wrote:
ThunderChunk wrote:

Don't need a 26" fork. 27.5 works fine. I ran one with my 26" wheels for half a season.

Doesn't that change the geometry of the bike though? Or is it such a suddle difference that it doesn’t matter?
The only change would be in the BB height due to wheelsize change if the A2C measurement of the fork stays the same (or roughly within the same range). It might be a problem on a frame with lots of travel and a low BB height. Ideally you'd check BB height at full compression and then subtract the change in wheel radius to make sure no ground contact will occur. Also if the BB is already low you might start hitting stuff on rougher tracks.
It really depends on the frame and tracks you ride. For some frames it'll work for some not so much but mostly due to the wheelsize change, the fork should be no big problem given that with most triple clamps there is a small range of adjustment in height possible anyways.

Slacker head angle as well. It definitely improved handling for me. Higher BB to clear rock gardens and slacker angles, big improvement.
flag JRavoth
Posted: Nov 30, 2018 at 8:05 Quote
ThunderChunk wrote:
Loki87 wrote:
vydra wrote:


Doesn't that change the geometry of the bike though? Or is it such a suddle difference that it doesn’t matter?
The only change would be in the BB height due to wheelsize change if the A2C measurement of the fork stays the same (or roughly within the same range). It might be a problem on a frame with lots of travel and a low BB height. Ideally you'd check BB height at full compression and then subtract the change in wheel radius to make sure no ground contact will occur. Also if the BB is already low you might start hitting stuff on rougher tracks.
It really depends on the frame and tracks you ride. For some frames it'll work for some not so much but mostly due to the wheelsize change, the fork should be no big problem given that with most triple clamps there is a small range of adjustment in height possible anyways.

Slacker head angle as well. It definitely improved handling for me. Higher BB to clear rock gardens and slacker angles, big improvement.

Higher BB sucks, way harder rail corners, and stability decreases at high speeds and through the rough stuff. Clearance doesn't matter as much on a dh rig anyway.
flag Loki87
Posted: Nov 30, 2018 at 8:30 Quote
JRavoth wrote:
ThunderChunk wrote:
Loki87 wrote:

The only change would be in the BB height due to wheelsize change if the A2C measurement of the fork stays the same (or roughly within the same range). It might be a problem on a frame with lots of travel and a low BB height. Ideally you'd check BB height at full compression and then subtract the change in wheel radius to make sure no ground contact will occur. Also if the BB is already low you might start hitting stuff on rougher tracks.
It really depends on the frame and tracks you ride. For some frames it'll work for some not so much but mostly due to the wheelsize change, the fork should be no big problem given that with most triple clamps there is a small range of adjustment in height possible anyways.

Slacker head angle as well. It definitely improved handling for me. Higher BB to clear rock gardens and slacker angles, big improvement.

Higher BB sucks, way harder rail corners, and stability decreases at high speeds and through the rough stuff. Clearance doesn't matter as much on a dh rig anyway.

Yup, higher BB sucks.
Also it's not really true in general. It'll become higher relative to before BUT the smaller wheels will drop it again,probably more than it was raised by the fork. And the HA and BB height only change if the forks A2C is longer which may or may not be the case depending on the forks you compare.
The only way to know for sure is to measure the components and existing system and do the math or to simply try it.
flag ThunderChunk
O+
Posted: Dec 1, 2018 at 21:48 Quote
It depends on the frame. My gambler with 26" wheels had a BB height of around 340mm. That's freakin low. Riding gnarly tech was scary because of all the pedal strikes and I would hit the bash guard. Switching to a 27.5 fork gave me just enough clearance to avoid pedaling strikes and hitting the BB.
flag vydra
Posted: Dec 6, 2018 at 19:30 Quote
Lets suppose that I put a 180mm fork on a 200mm DH bike. Would the geometry support this?
flag lifted-d
Posted: Dec 6, 2018 at 19:43 Quote
vydra wrote:
Lets suppose that I put a 180mm fork on a 200mm DH bike. Would the geometry support this?
big single replacing a dual crown? just find the axle to crown heights and compare, one inch is approx 1 degree.
flag Tripmo
Posted: Dec 6, 2018 at 20:57 Quote
ThunderChunk wrote:
It depends on the frame. My gambler with 26" wheels had a BB height of around 340mm. That's freakin low. Riding gnarly tech was scary because of all the pedal strikes and I would hit the bash guard. Switching to a 27.5 fork gave me just enough clearance to avoid pedaling strikes and hitting the BB.

I am riding a Gambler 10 from 2013 (26" frame). My BB height I ride with is 345mm, had so many pedal strikes already, lol. But I love the low feel setup. So good when you downhill.

Only 2 weeks ago I hit a rock and now my bottom of frame got a paint chip out of it.....
flag jamieridesbikes
Posted: Dec 7, 2018 at 13:45 Quote
lifted-d wrote:
vydra wrote:
Lets suppose that I put a 180mm fork on a 200mm DH bike. Would the geometry support this?
big single replacing a dual crown? just find the axle to crown heights and compare, one inch is approx 1 degree.
200mm DC forks usually have the same axle to crown as a 180 SC.
flag Cdmc2002
Posted: Dec 16, 2018 at 11:35 Quote
Hey what’s a good sub 100 set of DH bars that you guys would recommend, currently running a Truvativ holzfeller DM stem of that means anything to anyone

 


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