Mountain Bike Reviews Forum banner
1 - 11 of 11 Posts

·
Uncle
Joined
·
4,388 Posts
Discussion Starter · #1 ·
Was milling through my parts bin earlier today, and came across a KM fork: A-C 468mm, 43mm offset. Comparing to a common 100mm 26" fork, we're talking about 7-12mm shorter A-C & an extra 5mm of offset.

I think I'm going to give this fork and my 650b wheel a try on my Access 26" (71* HTA @ 475mm A-C) bike just for kicks, to see how it effects the ride characteristics. If you've done something similar, post up what you found in doing so.
 

·
NedwannaB
Joined
·
12,791 Posts
Thaaaaaat's it!

Entrenador said:
Was milling through my parts bin earlier today, and came across a KM fork: A-C 468mm, 43mm offset. Comparing to a common 100mm 26" fork, we're talking about 7-12mm shorter A-C & an extra 5mm of offset.

I think I'm going to give this fork and my 650b wheel a try on my Access 26" (71* HTA @ 475mm A-C) bike just for kicks, to see how it effects the ride characteristics. If you've done something similar, post up what you found in doing so.
You're looooooooosing it now. :eek:ut: But yeah let us know how it rides. :thumbsup:
 

·
Uncle
Joined
·
4,388 Posts
Discussion Starter · #5 ·
Man, can't a guy experiment a little? :D

650B front / 26" rear for now. The Access frame won't fit a 650B wheel. My goal is to figure out a proper feeling geometry without investing in a bunch of 650b spec'ed parts. I have a bike that will accept 650b rear, but I don't have such a wheel at this time. My big concern is with the fork offset, and I'm working under the assumption that the sweet spot is somewhere in the 42-45mm range. If this fork / wheel combo supports this assumption, then I'll likely invest in a rear wheel and an appropriate fork. I'm happy to try both wheels on this bike with my Vanilla fork (still a great fork, btw), but I need more assurance that I'll be able to get the trail issues worked out. Thus the experiment.

@ Jeff: Dude, I lost it long ago. How is your sanity holding up with all this B-craziness?
 

·
www.derbyrims.com
Joined
·
6,766 Posts
In general terms, increased fork axle offset makes steering quicker, less a2c makes steering quicker, bigger wheels makes steering slower.

The lower a2c fork would closely counter the higher axle of the 650b wheel to minimize head angle change. The bigger front wheel will still have a little slower steering. The increased fork offset would make steering slighlty quicker.

The net changes should handle about the same. The tighter handling from fork dive while cornering will be lost.
 

·
Registered
Joined
·
9,598 Posts
JMac47 said:
Wheel fiddling helps keepb my sanity with all the teenage girl craziness running rampid around my house!! :p
Too funny.

I live with my girlfriend (we are both divorced) and she's got two teenage girls. Some nights it is just me with Laura and Kim and Krista and the garage and work bench/bikes/tools are my refuge!!! :thumbsup:
 

·
NedwannaB
Joined
·
12,791 Posts
Oh yes.....

MMcG said:
Too funny.

I live with my girlfriend (we are both divorced) and she's got two teenage girls. Some nights it is just me with Laura and Kim and Krista and the garage and work bench/bikes/tools are my refuge!!! :thumbsup:
Can you say female DYNAMICS? heh heh j/k ladies. :D

Now back to topic at hand, B craze. I'm expecting another Neo today to set up my back wheel. Then see just what is needed to adjust rr shock for clearence. Plenty of room around stays and braces, just tight on the rr cable boss on seat tube in full compression. At 140ish #'s, I could just put a little more air in it and would probably be fine. :cool: BB is a tad taller then I'd like but se la vee.
 

·
Uncle
Joined
·
4,388 Posts
Discussion Starter · #10 ·
derby said:
In general terms, increased fork axle offset makes steering quicker, less a2c makes steering quicker, bigger wheels makes steering slower.

The lower a2c fork would closely counter the higher axle of the 650b wheel to minimize head angle change. The bigger front wheel will still have a little slower steering. The increased fork offset would make steering slighlty quicker.

The net changes should handle about the same. The tighter handling from fork dive while cornering will be lost.
That's pretty much what I was thinking, Derby. LOL @ the fork dive comment. Will probably get around to trying it out this weekend.

While we're going through the wheel war games, give me your thoughts on this if you don't mind:
2005 Rockhopper with 26" wheels, 70* HTA, 73* STA, 38mm offset. If I swap both wheels to 650b, I will end up with 4mm of additional trail (going from ~82mm up to ~86mm). This sounds like a lot to me, based on the measurements I come up with for bikes that I know fit me and ride well. Any thoughts?
 

·
www.derbyrims.com
Joined
·
6,766 Posts
Entrenador said:
That's pretty much what I was thinking, Derby. LOL @ the fork dive comment. Will probably get around to trying it out this weekend.

While we're going through the wheel war games, give me your thoughts on this if you don't mind:
2005 Rockhopper with 26" wheels, 70* HTA, 73* STA, 38mm offset. If I swap both wheels to 650b, I will end up with 4mm of additional trail (going from ~82mm up to ~86mm). This sounds like a lot to me, based on the measurements I come up with for bikes that I know fit me and ride well. Any thoughts?
Here's my math based on measured wheel sizes. The 650b wheel dimensions are about 3.8% greater than 26 inch with the same tire casing and knob heights ( http://forums.mtbr.com/showthread.php?t=442924 )

82mm * 1.038 = 85.17mm

Added steering trail due to a bigger wheel radius doesn't slow steering as much as the same increase in trail to the smaller wheel (think about much smaller wheels with increased trail).

The bigger mountain wheel's steering response is slowed and stabilized, in small part due to increased trail, but more by the added weight to rim and tire (think about a 650b mountain wheel vs. a road bike wheel somehow mounted to the same bike - they both have the same ~700mm diameter and the same trail).

The overall handing response feel on smooth pavement or hardpack converting a 26'er to 650b front and rear feels like about a half size bigger frame size without changing wheels, like the wheelbase was stretched 1/2 inch longer - but it wasn't. The smooth surface handling change is nearly all about changing the direction of both wheels' inertia.

The 1/2 inch higher BB of a 650b converted 26'er raises the seated weight center only about 1.2% (for me, a 6 foot rider having about 42 inch high weight center when seated), not much as a handling factor. Without raising the BB and weight center, for a 200 lb rider like me, it would be similar in handling change as adding 32.38 oz (2.02 lbs) water in a water pack. The higher weight center is 1.2% more stable, but 1.2% less nimble.
 
1 - 11 of 11 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top