Mountain Bike Reviews Forum banner
1 - 12 of 12 Posts

·
Some Assembly Required
Joined
·
4,063 Posts
Discussion Starter · #1 ·
I was czechen out the latest issue of Decline & saw the DT Swiss advertisement with the star ratchet hub & my brother, a mechanic, asked me why don't they build hubs with a sprag instead of star ratchets & pawls. He explained they were bomb proof, instant engaugement & most importantly CHEAP! Anyone ever tried a sprag application that you know of ??

O'yeah......Merry Christmas !!!!!
 

·
Some Assembly Required
Joined
·
4,063 Posts
Discussion Starter · #3 ·
shiggy said:
I would need to know what "sprag" is first.
I did a search on sprags & found lil' to nuthin' of a definition of sprag. However, my bro says it's a oneway clutch that freewheels one way & engauges the other. He says automatic transmissions in cars & trucks have'em in them.
 

·
Formerly DMR For Life
Joined
·
989 Posts
hes reffering to sprag cluthes
From http://www.renold.com/Renold/web/si...chFreewheels/Sprag_Clutch_Index.asp?menuID=21
Sprag Clutch Freewheels
A Sprag Clutch is a free-wheel device having an inner race, and an outer race either of which can be the input or output member. The input member can be arranged to drive the output member in a chosen direction and permit the output member to over-run in the same direction.

In general, Sprag Clutches are able to transmit greater torques, within given overall dimensions, than other types of free-wheel device.

....i'm not sure why they don't use them...i would guess that there would be maintenance issue that might not make it as reliable

possibly weight issues as well
DMR
 

·
Premium Member
Joined
·
48,238 Posts
shiggy said:
I would need to know what "sprag" is first.
Looked it up.

Interesting. I wonder about how well they would last in the grit and contamination of bike use. Roller clutch hubs and freewheels have been tried many times and touted as "bomb-proof" only to fail quickly in real-world use.
 

·
Registered
Joined
·
99 Posts
sprags wont work well without lubrication

as a transmission builder,i can tell you sprags are really strong and engage instantly.
2 problems for bike use are 1 you need constant clean lubrication 2nd would be high amount of drag when coasting
 

·
Dr Gadget is IN
Joined
·
2,393 Posts
Weight vs strength

Sprag or roller clutches are really good things - but they put one heckuva radial outward load on the races. All the car/heli applications have super duty steel races to take the load. They work by wedging the roller between the races when loaded in the drive direction.
 

·
No Justice = No Peace
Joined
·
1,512 Posts
Silent Hubs

I seem to recall some so called "silent hubs" from the 80's that used a sprag system. I can't rememeber who made them. Seems to me that they would be un neccessarily heavy and, as stated, difficult to lubricate. The up side might be that catastrophic failure would leave you with a fixed gear instead of none at all.

Just trying to be optimistic here....
 
1 - 12 of 12 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