Dished outer chainrings on Shimano Tiagra Crankset?

[oldcarltonfan]

I’m currently using a Tiagra compact crankset with a 9 speed rear cassette (12 to 25) and thought I would try a 46T outer chainring as I seldom need the smaller of the rear cogs when on the outer chainring.

Therefore I fitted a 46T Stronglight but discovered that when on the inner chainring the chain now caught on the riveted-on shifting ramps of the new outer chainring from the 7th rear cog outwards. I then spotted that the original 50T Shimano outer chainring was very slightly dished outwards. After some trial and error I eventually fitted a 0.6mm custom made shim fitted between the spider arms and the new outer chainring, this keeps the chainrings close enough to avoid trapping the chain between them, but nearly cures the problem (cog 1 to 7 now usable on rear cassette when on inner chainring, but 8th still catches slightly, clicking on the outer chainring's shifting ramps, I don't care about 9th as smallest cog to smallest chainring looks like a strain on the chain anyway)

So experts of Cycle Chat, I have the following questions:


1. Does anyone make a 46T outer chainring compatible with a Shimano Tiagra compact 110 BCD that is slightly ‘dished’ outwards to restore full usage of my rear cassette whilst on the inner chainring? I have searched the internet and failed to find anything.

or

2. Could I just drill out the rivets on the shifting ramps on the outer chainring and if so what would the effect be on shifting? (I presume minimal as I jury-rigged the new outer on backwards to try and it all appeared to work!)

or

3. Could I use a hydraulic press or similar to dish the new chainring slightly, if so any tips?

or

4. Does anyone have a better answer?

Thanks

 

[sparrow101]

i had a similar problem when i changed from a tiagra chainset (9speed) to a r700 chainset(10speed), i was unable to use the two smallest cogs when on the inner chain ring.

I had a 10 speed chain lying around which i fitted and it solved the problem as its slightly thinner

 

[Crackle]

TA chainrings may well solve your problem. I had problems with Stonglight chainrings on Shimano but the TA works a treat. They do a number of different rings and you'll need to find the one you need on their website before seeing who has it in stock.

Edit: Make sure it says outer.

 

[oldcarltonfan]

Sparrow101 and Crackle,

thanks very much for the input. I will start looking at TA chainrings and if that doesn't work I can invest in a 10 speed chain. Am I alone in finding a compact 34/50 a bit odd to use? I sat down and did some maths and a 34/46 with a 12/25 cassette seems to fit my general riding needs as I don't need the ultimate top speed any more and I can use the outer ring more. Its just a shame I can't get it to work yet!

oldcarltonfan

 

[Crackle]

No you're not: My outer is currently 46 and I've a 49 in the box if I need it. A 46 outer is good for 28mph at my maximum cadence or a bit more. Does me fine.

 

[oldcarltonfan]

28 MPH sounds about right. I checked on the Sheldon Brown calculator and I reckon at maximum cadence I could just achieve 30MPH. Given that I cruise around at 15 to 20 MPH +/- wind, I don't think it will be a problem, I quite like freewheeling down hills anyway!

I'm glad that someone else has done the same thing, I checked around a bit on-line before I changed and couldn't find much info.

thanks again for the advice.

oldcarltonfan