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Replacing Chainset due to thread problems
#1
Hi,

I'm new to this forum and bike DIY generally so apologies in advance if this has been covered elsewhere etc.

I have a 2006 Giant OCR3 with a TruVativ Touro, 30/42/52T chainset. Last year I replaced the existing pedals which was fine on the one side, however, it turned out that the thread on the second one had essentially fused with the crank arm. With lots of effort and two pedal wrenches later I managed to get it off with half of the thread left. I managed to make do with this position over the winter, however, now the pedal has come away and basically the crank need replacing.

I am happy to do this replacement however, I am now entering the world of chainset ratios, BB cartridges etc. etc. and I am finding "too much" information on the internet which is in places contradictory. I could replace the chainset with another one of the same size, or even the same model, however, I noticed that this ratio seems to be associated with beginner models and that 30/39/50 seems more common in the next level up. If I were to replace with a different ratio such as this what would be the implications in terms of knock on jobs - ie. would I have to replace derailers, adjust the chain and so on? Also, the original specification just says I have a BB cartridge attached to the chainset, would this also need to be replaced when I do the work? There is no particular noise etc. from the bike, it was running perfectly (aside from only having one pedal attached!) so maybe these would not need to be replaced at this time.....

If I stay with the same 30/42/52 ratio I will probably go with the Shimano 2303 but if adjusting to the 30/39/50 is not going to cause too much further work then I would probably go with the Shimano Tiagra 4500 range 30/39/50. I mainly ride on roads in the UK so no major hills etc. and I use the bike for Triathlons.

Any advice and thoughts would be gratefully received. I am looking to do all of this work for below £100 but if I can marginally improve performance of the bike at the same time then I would rather do this.

Thanks in advance
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#2
Same thing happened to me, except that the pedals were installed crossthreaded by the LBS that I bought my bike from and went unnoticed until I went to clipless pedals that were installed at another LBS. My bike is a Giant Defy, which is the replacement for the OCR, and it came with an FSA Omega crankset (same chainrings as yours) where the drive side crank was the one that was rounded out by the pedal. I was able to get around 300 miles on the crank after the clipless pedals were installed and I had to replace the crank. Anyway, to make a long story short, I ended up replacing just the crankset and bottom bracket and went to the Shimano Tiagra. I haven't had any issues since then and I really like the difference in the Tiagra crankset over the FSA. It feels much stiffer when going over bridges and what we call hills in Florida.
HCFR Cycling Team
Ride Safe...Ride Hard...Ride Giant
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#3
John, thanks for the reply, it was the drive side on mine too and I also only noticed when converting to clipping pedals. I think I'll go for that option too, if it's good enough for Florida, it'll be good enough for this corner of England!! Thanks again
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#4
You shouldn't have to change any derailleurs if you change chainring size. You will have to move the front derailleur up or down depending on the new configuration. If you go with larger rings you would need a longer chain. There is nothing beginner or advanced about chainring sizes, it all depends on the conditions you ride in. since you're in flat conditions, the lager rings would enable you to hit a higher top speed as long as your legs and body can produce the power required to get there Big Grin
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#5
you also need to watch out for your chainline when renewing chainsets, not all sets are the same so unless you replace with the same make, it is possible to find that your new one is in a different position to your old one and you cannot set up your FD properly, you may even need to change your BB axle.

Unfortunately, you do not find this out until you have completed the set up.
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#6
The bike shop that replaced my crankset only replaced the BB. I also had a 30/42/52 chainring setup on the FSA that stripped and the Tiagra is a 30/39/50 setup. The only thing that they did was readjust the FD because of the difference in size of the large chainring. They used the same chain and FD. I have no problems with shifting, chain skips or anything that is related to changing a crankset. Since the crankset was replaced in December, I have put over 500 miles on the bike.
HCFR Cycling Team
Ride Safe...Ride Hard...Ride Giant
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#7
Cheers guys, I'll have to see how it goes then once the chainset arrives. You can maybe look forward to questions on adjusting the FD in due course....... Haha thanks again for all you inputs.
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