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Replacement Crankset Concerns
#1
I bought a new Carrera Subway 2 hybrid from Halfords about 7 weeks ago. Last week my left crank fell off! I was surprised I hadn't noticed it getting loose during the ride. The bolt is partially de-threaded (may have happened while working loose) and Halfords said the bottom bracket may have also dethreaded, but they are not sure yet. As the bike is new and came from the factory with the cranks attached, I guess there was some assembly fault. I took it in this weekend and they have agreed to repair it for me. They have ordered a new crankset and said they will see if it needs a new BB too. I was shocked that all this was needed just because the crank came off!

The current crankset is a Truvativ Isoflow 42/32/22 175mm, but they said that they don't sell those. The replacement on their system is a Romax Tracer RBR544 42/32/22 170mm. After returning home and looking up both cranksets, I have a some concerns/questions. I am a novice to bike maintenance but keen to learn and would be grateful of advice.

Firstly, is the 170mm or 175mm measurement the length of the crank? And will the 5mm reduction in length on the Romax make much difference? I presume I will have a less power? (or torque?) I don't think I like the idea of that...

Secondly, is the Romax Tracer an equivalent spec replacement for the Truvativ Isoflow? From a quick search it seems to be a cheaper product.

Finally, I have read that it is better to have a higher cadence, and I may not be pedaling right, but I have felt on this bike that I would prefer a higher ratio lowest gear and I find that I don't often use more than the bottom few gears. I noticed that there is a Truvativ Isoflow 48/38/28 175mm. The 48 teeth will give me a max ratio of 8.5 rather than the 7.4 I've had so far. The problem is I don't know how this will 'feel'. Will it make much difference? Will it be too much? I guess at least I won't be in bottom gear all the time. N.B. The cassette is 11/32T.

I did ask in the shop if it would be possible to get a crankset with more teeth. They mentioned that I may have get a longer chain too. Will the bigger Isoflow 48 fit my bike? Will I have to replace other parts too? e.g. the front derailleur. Do you think this is worth doing this or should I stick with the original ratios and learn to pedal with a higher cadence? perhaps I should have bought a road bike after all Smile

Sorry for the lengthy question. Thanks in advance for advice.
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#2
whoops! sorry for posting in the wrong area.
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#3
170 vs 175 - it depends how fast you move your feet. The shorter the cranks; the higher the cadence you'll be able to achieve.

22/32 allows you to climb walls...... 28/32 allows you to climb really steep hills. Either will take you up anyplace an automobile will go.

You will need a longer chain with 48. You maybe able to just add a few links that your LBS has left over.....

On my hybrid, I switched from a single 44T with a 14-34T freewheel to a 48/38/28 triple with a 13-28T freewheel. I pedal on the slower side too; and I was maxing out with the 44/14 combination.

The 48 will fit fine. I wouldn't worry about the relative supposed quality. The front derailleur may have to be moved upward - no big deal.
Nigel
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#4
Thanks Nigel. Very useful.

(06-06-2011, 02:42 PM)nfmisso Wrote:  22/32 allows you to climb walls...... 28/32 allows you to climb really steep hills. Either will take you up anyplace an automobile will go.
I very rarely need to climb anything that can be considered a hill. I commute to work on the flat mostly, so I'm not too warried about the higher gears.

(06-06-2011, 02:42 PM)nfmisso Wrote:  On my hybrid, I switched from a single 44T with a 14-34T freewheel to a 48/38/28 triple with a 13-28T freewheel. I pedal on the slower side too; and I was maxing out with the 44/14 combination.
Playing with http://www.sheldonbrown.com/gears/, it seems that your upgraded bottom gear ratio is the same as my pre-upgraded one i.e. 7.2 (I'm assuming u have 26" wheel radius and 170mm crank). However, with the combination I'm planning to upgrade to, my bottom gear ratio would go up from 7.2 to 8.5 i.e. an 18% increase. I have 24 gears. 3rd from bottom will have the same ratio as your upgraded bottom gear and my pre-upgraded bottom gear. So, I effectively get 2 extra bottom gears by upgrading. This sounds about right to me in theory, but I was wondering what you think when I put it in that context? do you think it might be too much?

Anyone else have a hybrid with this sort of gearing? i.e.
chainset 48/38/28T, cassette 11/32T, 26" wheels, 170mm crank

If I'm not very interested in the high gears, do you think it will be ok? or is there other factors I'm overlooking? Any advice gratefully received as I can't really try before I buy.

Many Thanks, Paul.
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#5
(06-06-2011, 07:33 PM)Apprentice Wrote:  ........I very rarely need to climb anything that can be considered a hill. I commute to work on the flat mostly, so I'm not too warried about the higher gears.........

Paul; I think that mean "lower" gears - which are used going up steep hills. Higher gears are used going down and on the flats.

Given that you have mostly flat ground; I suggest you look at a double with 52/39 instead of the a triple. On my commuter I have 52/40 with 14-34T; on another bike I have 53/39 with 13-23T. Our tandem has 54/44/28 with 12-30T.
Nigel
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#6
(06-06-2011, 08:02 PM)nfmisso Wrote:  Paul; I think that mean "lower" gears - which are used going up steep hills. Higher gears are used going down and on the flats.
Thanks Nigel. Whoops! As I say, I'm quite new to this! In that case please swap 'low' and 'high' in my previous posts.

(06-06-2011, 08:02 PM)nfmisso Wrote:  Given that you have mostly flat ground; I suggest you look at a double with 52/39 instead of the a triple. On my commuter I have 52/40 with 14-34T; on another bike I have 53/39 with 13-23T. Our tandem has 54/44/28 with 12-30T.
Why would a double to be preferable to a triple? If I did change to a double, wouldn't I have to change the front mech too?
Thanks,
Paul
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#7
double: weight, cost and generally taller (faster) gears.

On my commute, I never use the 40 tooth chainring, just the 52. In the near future, I'll be swapping the 14-34T freewheel for a 13-28T. That jump from 34 to 24 is too much, and 52/28 is fine for the tiny hills that I encounter
Nigel
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#8
Halfords say they are planning to replace the original Truvativ Isoflow 42/32/22t on my Carrera Subway 2 with a Truvativ S650 48/38/28. My only concern is that they said this is a 3 x 9 speed crankset and my bike is a 3 x 8 speed. They told me that it will work fine.

Anyone know if this will work or not? Can you just replace an 8 speed with a 9 speed? What is the effect?
What is the difference between an 8 speed and 9 speed crankset?

Appreciate your help.
Paul
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#9
Paul; it will work fine. The 9 speed crankset may or may not have the chain rings a fraction of a millimeter closer together.
Nigel
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#10
Hi All, I thought I would update you on how this worked out. Halfords replaced my original original Truvativ Isoflow 42/32/22t crankset on my Carrera Subway 2 with a Truvativ S650 48/38/28 about 6 months ago now. I have been very pleased with it. Commuting to work I mostly use the 2nd highest gear on the flat. The highest gear is excellent for downhill - and when the wind is behind me! Overall, it feels a much better range of gears for me.

Nigel, thanks for your advice. It was very helpful.
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#11
Very cool, Paul! We're glad it worked out for you and that you reported the results! Hang around, bro. It gets better!

A little 'insider' into my thoughts for All -
I think that the current trend to Triples on road bikes is cool. It gives 'old' mountain bikers, like me, another familiarity point when crossing back over. And in the hills of North Arkansas, I can sure put some spin into a 30 - 28 to get me up a 3/4 mile long, 14% grade. That's 30 little ring / 28 big cog. I run 30/39/50 with 11-28 out back.

If we forget the "old mountain bikers" and want to ride recreationally - charity rides, weekly club rides, etc - the new compacts are a pretty good idea, too! Get more people on a bike is my motto. Smile

oh c^ap.... I think my frozen pizza set off the smoke alarm.. brb...
Wheelies don't pop themselves. (from a QBP fortune cookie)
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#12
Glad all turned out for ya Paul!!!


How did that pizza turn out Rob?? Tongue lol
Good maintenance to your Bike, can make it like the wheels are, true and smooth!
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