Help With Gear Ratios and Cassettes Please

[Witterings]

Totally new to and trying to understand this so any kid glove help would be appreciated.

I currently have a 29er running 39/27 on the front and 12-36 cassette and am only just able to cope with some of the hills around here, if I buy a gravel bike that's 48/32 and 11-32 on the back ... I'm guessing this is going to be quite a bit harder to pedal going up them hills ... am I right??????

If so and I'm struggling can I just change the cassette on the rear to say an 11-42 and if the new bike has say Tiagra or 105's do I have to use specific cassettes or any that have the ratio I'm looking for ??

I did find Bikecalc.com, is this a good site to use or are there better ones ... any help much appreciated!

[[XAP]Bob]

Sheldon Brown's gear calculator is your friend.

As is a little knowledge:
Gear inches = Chainring tooth count / Sprocket count * wheel size.

[fastpedaller]

Can you get the gravel bike with a triple chainset? A 28/38/48 chainset will give you the lower gears without the need for huge sprockets on the back, and possible be easier to change gear as well.

[thirdcrank]

... If so and I'm struggling can I just change the cassette on the rear ...

It's not quite as easy as that. The biggest issue is that your rear mech will have two capacity limits. One is the size of the biggest sprocket it can accommodate and the other is the total tooth difference ie the difference between smallest chainring plus smallest sprocket AND biggest chainwheel plus biggest sprocket, although there's waggle room eg you are unlikely to use biggest chainwheel and biggest sprocket together. If you haven't got the instructions for your rear mech, you should find the data here:
http://si.shimano.com/?FOLDER%253C%253E ... =iS193Zw#/

There can also be problems with the front mech in connection with the angle at which the chain enters the cage. eg it may be a lot higher with a large sprocket

[Brucey]

'it depends'.

If you buy a gravel bike then it will presumably come with 2x10 or 2x11 (road style) STIs and since these are the single most expensive part of the bike you are pretty much stuck with them, or have a large bill to face for new ones. Getting a bike with 3x gearing from the start will solve this but otherwise you probably need to

a) get a super-compact double chainset (budget option here is from Spa cycles, and is actually a converted triple) and
b) find some way of getting an RD to handle the bigger sprockets you want.

Shimano cater poorly for these needs but you may be able to get some satisfaction by using a hanger extender to increase the biggest sprocket that can be used. Since these gizmos are cheap (pennies on ebay) I'd certainly try that first, even if I thought it might not actually work.

If the total capacity of the RD isn't quite enough then you can ask yourself if the chain running slack in the small-small combinations is a big deal or not; I think 'not'. Remember that you have cause to be optimistic in this regard, because shimano's specifications include what should definitely work, which by definition does not exclude a load of things that might work OK.

FWIW RD-5800-GS will work with tiagra 10s or other road 11s and (with the right chain and cassette) I have seen this mech both cope with sprockets of ~42T teeth and shift nicely on the smaller sprockets (even though it is miles away from the latter) once fitted with hanger extender. The arm length of this RD is about the same as other RDs that shimano claim at least 5T more total capacity for.

cheers

[Witterings]

Hmmm ... some of the answers have gone a bit over my current level of knowledge if I'm honest.

I spoke with the retailer yesterday and they said that a Tiagra can go to a 11-34 on the rear which is the lower of the 2 models and with the 105 version if they swapped it from new it'd probably only be about another £35 to put an Ultegra derailleur on the rear which again would allow me to go to a 11-34 ... I'm not convinced though that a 32 front and 34 rear combo though is going still going to be an awful long way from the 27 front 36 rear I can get on the 29er????

Th retailer felt that a gravel bike may be easier to ride on hills than a 29er so would compensate to a dehree but I can't see it'd make that much difference.

Certainly a 3x may well address the issue but does anyone know if this can be run with the standard 105 or Tiagra on the rear??? If so it's probably something else they'd be able to do for a relatively small cost from new.

Also will a hanger extender be compatible with either the Tiagra or or 105's and if so any idea what the max I could go to on the rear would be with one??

The retailer has also said I can take a bike out for an extended trial and suggested I take mine up to them, go cycle some nearby hills on that 1st and then take the demo bike out and see how much difference I noticed.

[iandusud]

The retailer is quoting Shimano's specs when he says that the Tiagra rear mech can cope with a largest sprocket of 34t. However I use a Tiagra mech on my tandem with a 12-36 cassette with no problems at all, so I would say that this is definitely an option. I would suggest that you take up the offer of an extended ride. The gravel bike will certainly feel different to you 29er and you will be able to assess whether or not the gearing is suitable for your needs.

It might be worth checking to see if the chainset on the gravel bike will accept smaller chainrings.

[roubaixtuesday]

My experience of fitting a cassette beyond the nominal design capacity. It worked just fine until the chain wore out. The chain extender gizmo remains in place though I've since reverted to an 11-32 cassette, with no problems.

viewtopic.php?f=5&t=113182&p=1110987&hilit=Roadlink#p1110987

The offer to try out sounds sensible. You can probably use the method I did to get to 40T rear if you need to, though i think cassettes start to get expensive at some point as they get larger?

[Brucey]

Certainly a 3x may well address the issue but does anyone know if this can be run with the standard 105 or Tiagra on the rear??? If so it's probably something else they'd be able to do for a relatively small cost from new.

converting (even from new) from 2x to 3x is the sort of job that ought to be cheap but it leaves either you paying for a new set of STIs or the retailer carrying shop-soiled stock (the 2x STIs that were on the bike) that they cannot sell at full price. And the labour of course. Whether it actually works or not depends on the details of the cassette and chainset used vs the (actual not specified) capacity of the RD.

Also will a hanger extender be compatible with either the Tiagra or or 105's and if so any idea what the max I could go to on the rear would be with one??

The Tiagra RD-4700-GS model actually has the same length arm as the RD-5800-GS so ought to have a similar capacity. However the latter has a 'long tooth' guide pulley and that seems to be important.

The way the hanger extender works is fairly crude; it simply pushes the mech downwards so that it clears the biggest sprocket. Despite clever springs etc in the double pivots of the RD, this of course increases the gap between the guide pulley and the smaller sprockets. For many years the most positive shifting was usually obtained by making this distance small, and anything that increased this distance just made everything worse and was to be avoided.
However I was amazed when I saw a hanger extender being used to convert a bike with RD-5800-GS to an 11s cassette with a 42T bottom sprocket; that it shifted on and off the 42T sprocket was no surprise but the thing that made me look twice was that the shifting on the smaller sprockets was just as good as ever, even though the guide pulley was now a long way from the sprockets.
I think that this is because of the (further improved over previous iterations of HG) relationship between the chain and the sprockets (clever ramps and hooks on the sprockets, that engage with the chain in specific ways) and that the guide pulley on the mech has longer than normal teeth that impose themselves on the chain. I expect this setup to be sensitive to the exact design and type of cassette and chain, and for all know it may not work anything like so well once the parts are a bit worn; but it can work really very well indeed when the parts were new.

You can get some idea if a hanger extender conversion is going to work simply by screwing the B tension screw in so that the mech is much lower than normal, and trying the shift on the small sprockets. If the shifting goes to pot then a hanger extender probably isn't going to work either, not with that mech/chain/cassette type, anyway.

cheers

[NetworkMan]

Hello again,
A bit off topic but if you aren't completely wedded to a Gravel Bike you might perhaps consider a British Traditional Touring Bike (Brittob perhaps?). I find mine (fitted with those Vittoria Hyper tyres) excellent on gravel and it has low gears by virtue of the triple chainset. AFAIK most Gravel Bikes come with a compact double chainset which I suspect will put the most used gears at one end of the small or large ring, whereas with a triple they can be arranged to be in the middle of the middle ring. This also means you get gears from slightly easy to slightly hilly without even leaving the middle ring.
Two makers/suppliers that I know of offering Brittobs with flexible gearing choices - triples where you can choose chainrings and cassettes are Thorn in Bridgewater, Somerset and Spa in Harrogate, Yorkshire but there may be others I don't know of.
If you like the idea and you want disc brakes you might look at the Thorn Club Tour and the Spa Wayfarer.
I see that Thorn are actually selling the Club Tour as a Gravel Bike so they must agree with me
https://www.thorncycles.co.uk/bikes
Spa are rather more restrained in their advertising:-
https://www.spacycles.co.uk/m1b0s21p386 ... S-Wayfarer
Don't be put off by the steerer sticking up above the stem, they leave it long so you can get the bars right and then cut it off shorter if you want.
Spa will certainly offer test rides and I expect that Thorn will too.

If you like the idea, I expect that others on here may well come up with some other suppliers/makers.
Spa offer their Elan which is even nicer in some ways but it's only in Titanium and much more expensive than the Wayfarer.

[Witterings]

Hello again,
I find mine (fitted with those Vittoria Hyper tyres) excellent on gravel

I fitted those on my 29er last night as don't have a gravel bike yet but have a charity ride coming up I a couple of weeks ... am taking them out this evening for a proper test to see what I think of them although initial impressions just taking it a couple of hundred yds down the road I didn't really notice that much difference from what was on there apart from noticing every bump in comparison.

Be interesting to see how I get on with a 20 mile ride this evening.