A very common question in our Bike Bible Facebook Forum is how to get the right setup for the right gears for climbing hills, for example for those of us like here at BBHQ that struggle a little to get up the climbs who are looking to invest in a 32t rear cassette – how do we go about this? Do we need to make changes to our current setup? Do I need a longer chain? All very valid questions that we hope to address here for you in this guide!
Firstly there are not many differences in the set up needed for larger gears between road and MTB bikes, the principles are exactly the same the more teeth the cassette has on the rear and the fewer teeth on the front chainring enables the rider to spin their legs faster/easier than a set up with fewer teeth on the rear and larger on the front, simple maths of it dictate this. If you are riding a fixie that has 10t rear cog and a 10t front chainring – your wheel revolutions will equal one turn for every one full revolution of the front cog – but if you increase either cog you get less or more for every revolution- so the smaller the front and larger the back the more turns is needed by the front to complete one full revolution of the rear…with us so far? Simply put divide the number of front teeth on the chainring by the number of teeth on the rear cassette to get a number – so a 52t front chainring teamed up with a 32t rear cassette would have a number like 1.62 – this is the number of times the rear wheel would complete one full revolution for every full revolution of the front chainring. So using that calculation on paper it looks harder to get up a climb using a compact chainring of 36t with a 32t cassette as you would need to turn the pedals 1.12 times to get one full revolution of the rear wheel, so not very energy efficient but it it easier on the legs! Now at this point we could get massively technical and get into revolution and distance traveled – but as that is very technical and very long winded we will save that for an article all on its own!
Top Tip – Remember the simple calculation to work out the best gear ratio for your style of riding – A: The number of teeth on the front chainring – B: The number of teeth on the cassette sprocket equals the number of revolutions of the wheel per full revolution of the cranks so – A/B= C.
So when it comes to setting up your bike ready to take a new cassette there a a few things you need to keep in mind. Firstly when it comes to your existing rear derailleur – it may not be suitable for the job in hand! Some bikes more so in the world of 10 speed groupsets will only come with a short cage rear derailleur, which although will work with a 32t cassette – its not designed to and you will find yourself both indexing the gears a lot more often, and replacing expensive parts quicker due to the strain that it puts on both the derailleur itself and the cables and shifters. So to save yourself some money and a whole heap of time in the long run – plus a lot less hassle trying to get it to work we would and so do bike manufacturers (we recommend listening to the manufacturers as they handle your warranty!) to invest in a medium or long cage rear mech. Relatively inexpensive if you shop around for a deal with some 105 ones coming in under £30 with a good offer from retailers. Also consider if you are upgrading to a larger cassette is you may need to check your chain length, to avoid undue pressure on all components involved you may need to add some links or more preferable upgrade the chain to allow for the change. Keep in mind to not cross the gears – by this we mean going big ring on your front gears and big ring on the back – this puts undue pressure on the chain and derailleur meaning that it is liable to bend or stretch meaning indexing or at least keeping the gears indexed is near impossible.
Now you have your rear cassette in place or are looking at them you may also want to consider your crankset. Most bikes on the market unless its a TT bike or set up for racing will more than likely come already equipped with a compact chainset, a compact being usually for a double crankset 50/34 (50t big ring 34t small ring) it might not sound like a lot dropping down from a 52/36 or a 53/39 set up but it can make all the difference if tackling a prolonged gradient. Before shelling out a large amount of money on a new crankset we would advise to consider your riding style and terrain you usually ride on, if you only hit the climbs once or twice a week and the remaining on flat fast rides is it worth the large investment in a new crankset? Unlike the rear cassette change that offers the ability to still push hard if you invest in the right cassette (like SRAM PG1130 32/11 cassette) changing the chainsets will be more noticeable on the flat, so always consider what style and type of riding you are more likely to be doing and set the bike up accordingly.