rosstheboss
Retrobike Rider
I've got a 2000ish Trailstar and need to know what size BB axle to use. I've got some RS7s to go on it (square taper) and tried fitting them with a 107mm BB to no avail or am I being a nob, please let me know.....
DMR Trailstar BB help needed...Perry?
- Thread starter rosstheboss
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icantthinkofausername
Senior Retro Guru
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I think some of the Trailstars had BMX BB's but I couldn't really tell you anything more useful! There is a couple of chaps with DMRs so hopefully they will offer something more constructive than the above!
rosstheboss
Retrobike Rider
It a normal 68mm bb shell, just need to know the right axle length....or what I'm doing wrong!
at one point i put my rs7s on my blue one with a 110mm . the cranks had a 4 arm spider ( the one without any granny ring threads ) and a stainless ring in the middle position . it was a while ago and i cant remember if the chainline was any good or not . i usually use a 113mm or 116mm . my cream one usually has bmx cranks on it so chainline is adjustable although i recently changed these over to some square taper cheapies . this is of course all single speed with a dmr hub
ill get the tape measure out in a min and see whats what
ill get the tape measure out in a min and see whats what
i reckon mine currently has a 113mm
i missed the bit where you used a 107mm . pop that in and put the cranks on . get a straight edge and run that along the chainring to the cassette or sprocket at the back . i use a tape measure held against my freewheel tooth and line it up against the chainring
pictures make this easier
. this isnt a dmr but the principal is the same , this bike was nearer and i can take the chain off easily . im also doing this one handed and its dark so the pics arnt great
ignore the chain
this one is likely what you will end up with , the gap on the left is large as the chainring is too far in . hold the straight edge away from the ring and measure the gap as its parallel . double this number as the bottom bracket remains even , ie if its got a 110mm and you need an extra 3mm get a 116mm as 3mm is lost on the other side , if you went for a 113 you would only gain 1 1/2 mm either side
what it should look like is this , the straight edge runs along the ring . although ive taken the photo along the outer of the ring as its easier to see . correct chainline is against the teeth . next time i take the cranks off ill be cutting off that extra lump of chainguide
you have to put the straight edge along the chainring , if you do it sprocket tooth to ring tooth in the shortest points you have no reference . you can use string if you have it . you can pretty much guarantee string is straight when pulled taut
for gears go for middle - middle . if you have 3 chainrings its the middle chainring . if you have 9 speed its 5th gear . if your using a double ring and 8 speed you will need to go from the center of the 2 rings and the center of the cassette , between 4th and 5th gears
i missed the bit where you used a 107mm . pop that in and put the cranks on . get a straight edge and run that along the chainring to the cassette or sprocket at the back . i use a tape measure held against my freewheel tooth and line it up against the chainring
pictures make this easier
. this isnt a dmr but the principal is the same , this bike was nearer and i can take the chain off easily . im also doing this one handed and its dark so the pics arnt great ignore the chain
this one is likely what you will end up with , the gap on the left is large as the chainring is too far in . hold the straight edge away from the ring and measure the gap as its parallel . double this number as the bottom bracket remains even , ie if its got a 110mm and you need an extra 3mm get a 116mm as 3mm is lost on the other side , if you went for a 113 you would only gain 1 1/2 mm either side
what it should look like is this , the straight edge runs along the ring . although ive taken the photo along the outer of the ring as its easier to see . correct chainline is against the teeth . next time i take the cranks off ill be cutting off that extra lump of chainguide
you have to put the straight edge along the chainring , if you do it sprocket tooth to ring tooth in the shortest points you have no reference . you can use string if you have it . you can pretty much guarantee string is straight when pulled taut
for gears go for middle - middle . if you have 3 chainrings its the middle chainring . if you have 9 speed its 5th gear . if your using a double ring and 8 speed you will need to go from the center of the 2 rings and the center of the cassette , between 4th and 5th gears
rosstheboss
Retrobike Rider
Thanks for the detailed info Perry, it will come in very handy! The problem I'm having is when I tighten the crank bolts up the drive side crank won't go round, although DMR used to recommend a 108 axle for singlespeed...... :cry: The axle doesn't seem to be long enough to stop the crank binding on the BB face.... :?
