Do i really need a new bottom bracket?

[BigonaBianchi]

the local bike shop say that to replace my crankset they have to put in a new bottom bracket. The thing is i am not sure thats necessary.

The bike had a campagnolo veloce compact crankset from new. I ripped out the pedal thread on the left crank in cyprus and had no choice but to replace the entire crankset with the only one available at that time, a big heavy FSA double. The FSA did not need a new bottom bracket to fit and work fine.

The FSA is crippleing my hips on climbs and i asked the LBS about fitting a campagnolo triple. They said they cant fit it without replacing the bottom bracket. Given that same bottom bracket worked fine with the origional campagnolo crankset before the FSA was fitted surely it would work ok with a new campagnolo triple crankset?

Thet also say yet another new chain is required. I dontunderstand why i cant just fit a new crankset without a new bottom bracket and new chain.

Are thet right? Am I a nob?

TIA

 

[Sharky]

If you're going from a double to a triple, you'll need a wider bb axle to give clearance for the inner ring. You might also need a new gear lever on the front if it is indexed, to give 3 positions. New chain maybe if the big ring on the front makes the chain too small. Might also need a specific triple front changer to get the increased movement.

I would keep to a double compact and explore a cassette with a bigger cog on it.

Cheers keith

 

[young Ed]

well it depends!
there are different fits or types of BB and thus cranksets
here are the 4 'main' ones

it could be you are asking them to fit a incompatible crankset with your BB? eg:isis on a octalink 2 or whatever
could also be they have found a bit of play in the BB or some grit or whatever making it run rough so it needs replacing for that reason
as for chain it is likely to be a case of wearing components un evenly as in a partly worn chain used on the old crankset and the old cassette will wear new chainrings like hell or an old set of chainrings and cassette will wear a new chain like hell so it is really best to replace whole drivetrain (chainrings, chain and cassette) all at once and together
Cheers Ed

 

[young Ed]

If you're going from a double to a triple, you'll need a wider bb axle to give clearance for the inner ring. You might also need a new gear lever on the front if it is indexed, to give 3 positions. New chain maybe if the big ring on the front makes the chain too small. Might also need a specific triple front changer to get the increased movement.

I would keep to a double compact and explore a cassette with a bigger cog on it.

Cheers keith

would also need a new derailler so in general unless you really want it then best to stay with same amount of chainrings up front and cogs back at the rear as other wise things get complex and expensive
Cheers Ed

 

[BigonaBianchi]

ok..so say i stuck with a compact...i need it to be able handle mountians...cyprus has lots of them...but i want to be able to fly on the flat as well...I dont understand the numbers and how say a 50/34 compares to a 53/whatever?? I want to give my hips a rest on thsoe climbs and maybe even be able to spind instead of grind....i always run out of gears before lighter riders...what ratios should i get do you reckon?

 

[Sharky]

Have a study of a set of gear tables
http://sheldonbrown.com/gears/

The big ring either 50 or 53 is not that much different. A gear of 85" for normal leisure riding should give you all the speed you need with a good cadence. Higher gears might give the impression of going faster, but your legs are probably just going round slower. Downhills at over 30 mph, you are better freewheeling in a tuck position.

At the other end of the scale, you will probably benefit from a bigger cog on the cassette. Study the tables and you can see where all the overlap is in the different gears. With a triple, you get more gears numerically, but it is the two extremes that count.

Other options for improving hill climbing are
- clip less pedals - compulsory
- a lighter bike - minimum luggage, lighter tyres, with front pumped up hard, so no energy lost. Rear slightly softer, so plenty of grip
- technique. Need to experiment with sitting down and high cadence and out of the saddle using power and a bigger gear. Different techniques for different hills.

And if the hill is so steep that your speed drops to walking pace, then walk! No shame in walking, I often do on my single speed bike.

Cheers keith

 

[doog]

If you're going from a double to a triple, you'll need a wider bb axle to give clearance for the inner ring. You might also need a new gear lever on the front if it is indexed, to give 3 positions. New chain maybe if the big ring on the front makes the chain too small. Might also need a specific triple front changer to get the increased movement.

I would keep to a double compact and explore a cassette with a bigger cog on it.

Cheers keith

I agree with this, get them to put a compact double back on (so no change of BB )and get a cassette that will help with your climbing. Ive just replaced a 27-11 with a 30-12 for the big hills. Just needed to adjust the B screw. Technically I will spin out at 33mph at 100 rpm but getting up the steep bits is more important to me than racing down the buggers.

 

[BigonaBianchi]

Thanks chaps

So...

If I got a compact with a 50 big ring and a cassette of 30-12 that would get me up hills easier and still give me a decent speed on the flat without needing new bb shifters or derailers right?

 

[fossyant]

Yup

 

[Sharky]

Before you buy a new crank set - what happened to the old one?
If it was just the pedal thread that went on the LH side, then these people http://www.highpath.net/ might be able to repair it. I can recommend them. I have had two pairs of cranks shortened down to 150mm and both times an excellent job. Short cranks are another topic altogether, but if your cranks are solid and non-fluted, are a possibility.

On the ratios, a 50 x 12 is a massive gear. I use a 50 x 14 on my fixed tt bike and never spin out. Well I did once - 44 mph down the slip road at the start of the Q10/19 course on the Tonbridge bypass!

Good luck
Keith

 

[BigonaBianchi]

Thanks for that link.

Yee olde cranksete is still in Cyprus. I decided to leave it as it was to heavy to fly back without extra cost on baggage allowance. I left the campag bottom bracket cups there as well I think now that I think about it. It was a good idea when I was going to fit a triple. Hey Ho eh lol!

 

[BSRU]

If you're going from a double to a triple, you'll need a wider bb axle to give clearance for the inner ring.

If it is a hollowtech II BB, you just need the right spacers for a triple.

 

[BigonaBianchi]

On the crank length issue mine are 175 which were fitted with bike from New do I just stuck with.them. I always thought shorter cranks were tougher to push??

 

[BSRU]

On the crank length issue mine are 175 which were fitted with bike from New do I just stuck with.them. I always thought shorter cranks were tougher to push??

I have one bike with 170 cranks and two with 172.5 cranks, to be honest I do not notice the difference the 2.5mm makes.

 

[Sharky]

On the crank length issue mine are 175 which were fitted with bike from New do I just stuck with.them. I always thought shorter cranks were tougher to push??

Lots to google on this topic, but crank lengths are only one of the variable factors in the leverage system on a bike. Chain ring size, sprocket size, wheel size and your own legs all make up the leverage system on a bike. When you ride, you change the gear to increase/decrease the load, so if you change one of the other factors (ie shorten the cranks), the point at which you change a gear is just a bit earlier or later. So has no affect on "tougher".

For me, the benefits are being able to raise the saddle by 2cm, thus increasing the distance between the pedal at the top of the circle and the saddle by 4cm! This stops my legs from hitting my chest (stomach) and gives me a much more efficient pedal stroke. I pedal quicker in a lower gear and can pull up with the trailing leg much easier and with more power.

First few rides seem a bit strange, then you can't tell the difference apart from it feeling better.

Not for everybody, but ...... 20 years ago, nobody was using tri-bars.

Cheers keith