Gear Ratios

[steveindenmark]

Regardless of how many times I read articles on this matter I struggle to understand it.

I am not a strong climber and prefer to spin up mountains.

I have a choice of 2 cranksets.

48 X 32T or 53 X39T

Which would be more suitable for me?

 

[Lozz360]

48 x 32t. Less teeth on the front means lower (easier) gearing.

 

[flake99please]

48/32 would better for 'spinning' up the hills.

 

[bpsmith]

Therein lies the problem for anyone not understanding the concept.

Travelling 36.7 inches per pedal stroke sounds worse than 40.5 inches. What a lot of people don’t follow up with is that, the further you travel per stroke, the more effort is required.

The downside of a smaller inner ring, is the relatively smaller outer ring that goes with it. You gain on an easier gear on the hills, but you lose out on the bigger gear on downhill or the flat. Depends if the trade off suits your riding.

Personally, I would go part way and opt for a Compact 50/34, although I do note that there are only 2 choices in this question for some reason.

 

[flake99please]

Ive edited my earlier post, as i believe the OP is referring to the crankset tooth counts only. I was initially confused by the 53 x 39T & 48 x 32T, where it should have been written as 53/39 & 48/32.

 

[bpsmith]

I’ve got you, I hadn’t thought about that angle.

Don’t think you needed to amend your post mind you, as it was well explained. I was just referring to other places where they don’t put it in the same way as you did.

 

[steveindenmark]

Thanks for the replies guys. As you can see already it is a complicated subject and I appreciate your help.

Here is the situation I have at the minute.

I have a Genesis Croix de fer 20 and I expect to be going up some very big mountains next year. I want to be able to spin up the mountains and cruise on the flats. Going at any great speed is not important and I rarely use the last 2 rings on my rear cassette.

My CDF has a 53/34T chainset and 11-34T, 10sp Cassette. It has BSA 68 standard Road bottom bracket.

My thoughts were to change the rear cassette to an 11-36 and change the crankset to either an FSA 48/32T or an FSA 53-39T with an FSA bottom bracket and a Wolftooth Roadlink.

I understand that this will lose me speed on the flat. but again I spin on the flat as well and rarely use the last two rings on the cassette.

Would it be advisable just to change the rear cassette first and see how that goes, before messing about with bottom brackets and cranks?

Is this the way to go or are there other alternatives.

 

[Ajax Bay]

the further you travel per stroke, the more effort is required.

No. It's only more effort if the rider pedals at the same cadence. Pedalling a 40" gear at 72rpm requires the same 'effort' (power) as in a 36" gear at 80rpm.

it is a complicated subject

Steve - it really is not - and my recommendation to you is to fit the 48/32 crankset.
Most of your riding will not be up hills and most will not be batting along at 35kph+. But there will be hills to climb and you will have to make a judgement of how low a gear you need to get up the steepest hills that you are not prepared to walk up. And you need to factor in the effect of fatique after 14 days on the road. On the plus side you will be fitter and stronger by next summer.
For your long rides, any time you are going over 30kph is the opportunity to take it easy. A high top gear will allow you to pedal downhill and achieve super speeds, but this capability is not necessary, it's just for fun. Most of the effort you put in at those speeds is frittered away on air drag.
So here's an estimate for you.
To get up the hills you need better than 1:1 gearing. So the 32t chainring driving a 34t sprocket. On a 700 wheel that will give you a 28.6" gear for getting up hills. At the other end the 48t driving an 11t sprocket gives you a 117" gear (far longer than necessary) and would allow you to pedal happily along (at 90rpm cadence) at 53kph.
An 11-34 cassette like this one.
Have a look at this (set up for 48/32 and an 11-34 cassette. You can alter the parameters on this to your heart's content.
http://www.gear-calculator.com/?GR=...19,21,23,26,30,34&UF=2240&TF=90&SL=2.6&UN=KMH
Personally I would probably ditch the 11t sprocket and replace it with the 12t (they don't make 12-32 or 12-34 cassettes for some unknown reason). This will still allow me to pedal at 90rpm at 50kph - more than enough. Remember the greater the range of the cassette, the wider the gaps between each gear ratio, and this is a disadvantage.

 

[steveindenmark]

My CDF already has that Tiagra 11-34 cassette. Wouldnt changing it to an 11-36 make spinning easier or is the difference too small to notice?

With regards to the chainring. What would the difference be between the 48/32T and the 53/39T

 

[MacB]

53 x 11 gives 130 gear inches
39 x 34 gives 31 gear inches

48 x 11 gives 118 gear inches
32 x 34 gives 25.4 gear inches

Those are based on a 700x32 tyre and as you can see you gain more at the bottom than you lose at the top, as a %age. Worth checking that your existing deraillers will cope with the new set up.

 

[swansonj]

I endorse the "think through the consequences of not having a gear as extreme as you'd really like" approach.

Not having a top gear as high = having a bit of a rest and only going at 30 mph instead of 35 mph

Not having a bottom gear as low = spending far more effort than you want struggling up hills, knackering your knees, depleting your energy stores, and probably weaving all over the road and having more difficulty keeping your front wheel on the ground.

 

[Ajax Bay]

Changing to a 36t largest sprocket would have two effects/impacts.
1) It will give you a gear which is 6% lower so for a given hill this would allow you to pedal up at a higher ratio and higher cadence (spinning) and achieve the same speed (so at the lowest speeds - stay balanced).
2) Your rear derailleur will be at or beyond the limit of its capacity - you don't want the complication of the wolftooth link (or similar). And you don't need it with a choice of a smaller pair of chainrings.
By going to a 32t small chainring you have already gained far more (32t versus 39t implies a gear ratio gain (for going up hills) of 18%). If you go for the 48/32t crankset, I do not think you need the 11-36 cassette. The penalty is wider ratio between the gears as you shift in the middle of the cassette - a disadvantage for the ride you plan.
Going to a 48/32 crankset will mean you need to lower your front derailleur a bit, but the 16t difference between 48 and 32 is 'standard' for a normal FD (cf 50/34 or 52/36 cranksets) and the shifting should be fine. If your seat tube fitting is 'braze on' check you have the range to drop it (?3mm).
I'd just go for the 48/32 although frankly if you're going to keep the 11t smallest sprocket you could even consider a 44/28 (probably not available at a sensible price). My focus would be on the cassette. You have said that you rarely use the smallest two sprockets. Get rid of the 11t and have the small sprocket run as 12, 13,14 by a bit of customisation. I did exactly this for the Mille Pennines, which went up Hardknott Pass (at the 200km point) and up Rosedale Chimney (at the 770km point) -see link. (NB the hills you're heading for are not that steep; they're long, and you may also have long stretches into a headwind.) I swapped my 12-27 cassette for a 11-30. But I then swapped the 11t for a 13t to give me a 12,13,14-30. On the cranks I swapped out my 30t (NB triple) for a 28t. This double action meant I was getting a gear 12% lower - 2/5ths from the chainring swap and 3/5ths from the cassette change.

 

[steveindenmark]

Getting up hills as easily as possible ids the aim of the exercise. Top speed on the flat is of no interest.

So as I see it now.

Forget the Wolftooth link.
Keep the rear cassette as 11-34T.
Change the BB to the required FSA BB
Change to the FSA 48/32 Crankset.

Bearing in mind it has a Shimano BB at the moment and I do know which FSA BB I need. Is there anything else I need that goes along with the BB that I need to buy?

 

[Ajax Bay]

No. Bear in mind the FSA crankset may be compatible with whatever Shimano BB you have on now.

 

[steveindenmark]

No. Bear in mind the FSA crankset may be compatible with whatever Shimano BB you have on now.

No it isnt. I have checked that already. I checked it with Genesis and FSA.