Awesome 531 is too flexy for me

So I've been having some issues with grinding vibrations in my transmission, so I took my Mercian conversion down to Brixton cycles to have it checked out. BB problems I thought.

They checked it over to see what the problem was...........turns out there wasn't a problem with anything. I had a chat with the mechanic and he said it was almost certainly the problem was the awesome 531 was flexing so much when I was climbing hills that the chainline was being fucked and causing the grinding. I often have a fairly heavy instrument on my back which makes it worse.

He said try a lower gearing, I run 48/17 so thats not that high, so I tried an 18t cog but it hasn't helped. So it looks like I either put up with it or get a new frame. Balls.
Apparently a 531 track frame would be less flexy as its wheelbase is shorter stiffer (I think)

So for me 531 plus killing puppies = not awesome.

Anyone had anything like this? Any other ways around it?

Use an iPod to drown out the racket.

It doesn't make much noise, just makes it all much harder work. Plus it vibrates right through my pedals which gets fucking annoying after a while

HTFU?

Also, 48x18 doesn't seem that short a gear. Try dropping it to a 19t at the back - spin to win!

It's interesting to hear that your frame can flex enough to mess up the chainline that much. You can normally get away with at least 2mm either side of perfect.

If your frame is flexing that much, i'd recommend getting a new frame.

Yeah use this 'setback' as a chance to 'need' a brand new custom built frame.

I don't like the stink of this.......

try using a smaller chainring and cog, to get a similar GI, (42/16 or something) thus reducing the torque/torsion/twist/rubber duck across your drivetrain. you'll never be wasting money on chainrings and cogs as it's good to have a few, a new frame might be nice but maybe not needed..

I don't think a frame would flex that much, maybe the semi-horizontal dropouts twist more than track ends, but even so..I remain slightly unconvinced.

I don't like the stink of this.......

try using a smaller chainring and cog, to get a similar GI, (42/16 or something) thus reducing the torque across your drivetrain. you'll never be wasting money on chainrings and cogs as it's good to have a few, a new frame might be nice but maybe not needed..

I don't think a frame would flex that much, maybe the semi-horizontal dropouts twist more than track ends, but even so..I remain slightly unconvinced.

It does seem a bit severe. I would go with a smaller chainring and cog... assuming that is the problem, of course.

Wouldn't going smaller increase the torque across the drive train? You're effectively generating more leverage at the cranks...

should I have said torsion?

there is certainly more flex with larger chainrings, enough coupled with a bendy frame will cause the problem, as suggested.

Reynolds 531 seat and chain stays were available in a variety of widths and tapers made with different types of performance in mind.

The thinner versions were flexy by design, while the thickest offered stiffer more responsive rides.

Since this is a conversion, is it possible you're thrashing around on a bike designed for slow comfortable touring?

how heavy are you Dixon ?

Thanks for all the replies, lots of food for thought!
Dylan, I'm 14 stone.

I think that you did mean torsion, as that is more about deflection. I would like to point out, however, that it seems unlikely that it would be chainring flex causing this bike a chainline movement.

Before you start splashing out a load of cash, I'd recommend that you measure your chainline at the cranks and at the sprocket. If you can get these the same, it may be that any deflection of the chain stays while riding will still keep the chain within the +/- 2mm (or whatever) comfort zone to avoid this grinding. Your chainline might be perfect at the moment, but your post doesn't convince me that you've checked every possible factor.

I often have a fairly heavy instrument on my back

Take the grand piano off and see if that helps.

any pics of the bike? that much flexing sounds unlikely...
close ups of chainring/stays etc?

Yeah could be my chainline, it looks pretty straight but I've not measured it.
I'll take some pics tomorrow morning and get them up on here.

I was quite incredulous when the guy told me it was flexing that was causing my problems but hey, he's the mechanic and he seemed very convinced that it was the problem!

also useful to put down your rear spacing OLN as well.

Rear spacing is 126 but it had seemed fine with the rear hub at 120. I have a set of spacers somewhere though, might that help?

will make it worse it the problem is with the chainring grinding on the stays

The grinding is the vibrations caused by the frame flexing and putting the chainline out, not the chainring actually rubbing on the stays!

I think RPM is right and a smaller chain ring will help reduce the problem. You will probably find your bottom bracket is flexing side to side with pedal strokes causing the top and bottoms of your chain ring to move laterally around the bottom bracket, so having a bigger chain ring will amplify this effect on the chain line. (Wish I could be bothered drawing a pic) Getting a smaller chain ring won't reduce the amount of flex in the bottom bracket but it will reduce the effect it has on the chain line so should be worth a try.

Spacing the hub sounds like a good idea.

Where exactly is the grinding coming from? The front or the back?

I don't like the stink of this.......

try using a smaller chainring and cog, to get a similar GI, (42/16 or something) thus reducing the torque/torsion/twist/rubber duck across your drivetrain. you'll never be wasting money on chainrings and cogs as it's good to have a few, a new frame might be nice but maybe not needed..

I don't think a frame would flex that much, maybe the semi-horizontal dropouts twist more than track ends, but even so..I remain slightly unconvinced.

One of the occuring problems that you conversion peps will run into

So I've been having some issues with grinding vibrations in my transmission, so I took my Mercian conversion down to Brixton cycles to have it checked out. BB problems I thought.

They checked it over to see what the problem was...........turns out there wasn't a problem with anything. I had a chat with the mechanic and he said it was almost certainly the problem was the awesome 531 was flexing so much when I was climbing hills that the chainline was being fucked and causing the grinding. I often have a fairly heavy instrument on my back which makes it worse.

having thought a bit more about this, I don't think BB problems have been ruled out (?) because a knackered BB doesn't always show unless it's under load. Quite often you can spin a BB, rock it up and down and all that and it will appear fine, only when you climb a hill or put in a hard standing start will it grumble. If it's a year old cheap sealed BB, then change it. if it's an even older loose ball and axle job then change it.

as always, this is a process of elimination, usually if I ride the bike in question I can isolate the problem better than shooting in the dark on an internet forum.