Replacement Crankset?

[ex passenger]

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

Sorry for the lengthy question. Thanks in advance for advice.

 

[ex passenger]

Sorry folks - novice here - I have confussed everyone by getting high and low gears the wrong way around. How embarrasing!

Here is a corrected version:

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 at the weekend and they have agreed to repair it for me. They will order 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, will the 5mm reduction in crank 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 top gear and I find that I don't often use more than the top few gears. I noticed that there is a Truvativ Isoflow 48/38/28 175mm. http://www.sheldonbrown.com/gears/ tells me 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 top gear all the time. N.B. My 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?

It seems that with the 48T chainring I'm considering upgrading to, my to gear ratio would go up from 7.2 to 8.5 i.e. an 18% increase. I have 24 gears. 3rd from top will have the same ratio as my pre-upgraded top gear. So, I effectively get 2 extra top gears by upgrading. I imagine this to be about right, but I was wondering what others think? 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

As I'm not too concerned with the low gears because I rarely go up any hills, 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.

Sorry for the lengthy question. Thanks in advance for advice.​

 

[ex passenger]

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

 

[arallsopp]

It should be fine, and if not, its their issue. AFAIK, the only difference between 8 and 9 speed up front is the width of the derailleur cage (unaffected by the cranks) and (potentially) the spacing between the rings. I shouldn't think there'd be any problem really.

The shortened cranks will reduce the leverage, but probably also encourage you to spin faster. Given most people pedal slower than advised (mashing) this is probably a good thing. 175mm cranks are standard, but you might find something shorter actually keeps you in the power band for longer. Its quite easy to over-extend.

In short, fear not, try it out, and if it sucks moan at them until they solve it

 

[gds58]

I would definitely advise against accepting a cheaper option of chainset/cranks from Halfords. I know for a fact that they routinely stock a nice SUNTOUR triple chainset which will be an equally good quality replacement for your damaged Truvativ. I have personally never heard of this other make that they are offering you so I would steer clear of it. It may well be a perfectly good chainset but why accept a cheaper option on the bike for no returns to you.

Check out this link below for the Suntour chainset I referred to on Halfords website:

http://www.halfords.com/webapp/wcs/..._productId_158394_langId_-1_categoryId_165545

I hope this helps!!

Graham

 

[Bensbikespares]

The crank will fit and work fine, It's only you need to know the gear speed stuff at the back. so it will be fine