Changing big chainring, advice needed!

[328isport]

Hi all,

I'm currently running a mid 80's Campag Super Record set up, 7 cogs on the back, and 42/52 on the front, however my old bike had a 53t chainring and I'm finding I prefer that.

So I picked up a NOS Royce 53t chainring, but this is where the questions come in, as it's important to me that everything works perfectly.

Chain first up, I assume to keep everything the same as it is currently all I need to do is run one extra link right? I'll be fitting a new chain with the ring anyway.

Will I need to do anything with the front dérailleur? as logically with the slightly larger diameter chainring I assume it should be moved slightly up, but I guess there's a certain tolerance.

I picked up a tool today for the chainring nuts so that should make that bit easy.

 

[TGR]

I think you do not have to do anything - if you are lucky.

The rear mech should cope with the larger ring - if not, then shorten the chain but I would imagine that it should be fine. Link removal would really only result if the original chain was fitted with minimal tolerance at the rear mech. (this is hard to explain)

The front mech MAY need raised - again wholly dependent on the tolerance it has been set with at the moment.

I would be interested to hear if you do have to adjust anything - for my future plans.

Richard

 

[pigman]

I
I would be interested to hear if you do have to adjust anything - for my future plans.

Richard

every case is different. Whether the OP does or doesnt need to adjust does not mean that you automatically follow.

My opinion is that if it needs no adjustment, then it wasn't set at the optimum height for the current 52 ring

 

[TGR]

I agree, but i could not work out the mathematics of what adding one tooth to chainring would do do the diameter.

Perhaps some mathematician could provide the figure - i cannot imagine it being very much more than 1mm.

Richard

p.s. i left school toooo long ago!

 

[bodrobert]

The distance between the pins of the chain is 1/2". It means that the circumference of the chainring (measured at the center line of the chain pins) is:
52 * 1/2" = 660.4 mm
53 * 1/2" = 673.1 mm

It must be divided by 2* pi to get the half diameters (radius):
105.16 mm
107.18 mm

The difference is about 2 mm. You must raise the front derailleur about 2 mm.

 

[TGR]

Congrats for that, i could never have done that.

Richard

 

[328isport]

Cheers Robert, any words of wisdom in regards to the chain length?

 

[bodrobert]

I think that you could leave the chain length as is. One tooth difference (which takes only a half, because the chain wraps around only the half of the chainring) means a half link of the chain, it does not really matter.
Check the length of the chain on the largest-largest combo (without the rear derailleur) and you must have an extra link if you pinch it with your fingers.
http://sheldonbrown.com/derailer-adjustment.html#chain

 

[328isport]

Excellent thanks Robert! Very interesting that, I almost wonder if there's a bit of riding style involved in chain length, reason being I'd never, ever go Large/Large as its not a gear that would be of use on the road, out of my 7 cogs I only really use the 4 smallest on the larger ring before dropping onto the smaller one.

However! On the smaller ring I'll run down to the second smallest cog quite often (one cog off the small/small combo which allegedly you should never do) as this is a good road gear, with decent pick up and reasonable speed, it also allows me to then switch onto the large ring from there without a huge step up in ratio and only one change needed on the shifters rather than up on the large ring then down on the cassette to get back to a sensible ratio.

Given this I'd say I'm much more likely to suffer from a chain too long than a chain too short, and actually a slightly short chain may mean I could eliminate chain droop altogether.

Of course I'm not willing to test this and will no doubt set the chain to the length mentioned by the experts anyway!

 

[hamster]

Don't go too short. While it's not something you would knowingly do, it's at the moment when the guy with the black Range Rover is trying to kill you that you shift down instinctively. That's when a short chain will stuff the rear mech straight into the wheel. If you are lucky it's a new wheel and mech. If you are unlucky it's a trip to hospital as well. Short chains are dangerous, long chains are not.