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Change in drivetrain possible?

Old 01-20-18, 01:56 PM
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Paravia
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Change in drivetrain possible?

I have a Genesis Croix de Fer with Tiagra 4700 (50/34 front, 11-34 cassette).

I need to replace the cassette (worn) but the supplier is out of Tiagra 10sp 11-34, however they have the same in 11-42.

I am getting old and would surely enjoy the 42 when climbing (of course at a price of harsher shift changes). My question is, can I just replace the cassette? Will it shift to 42? Do I need to replace anything else (chain etc.)?

Sorry I am not a beginner really.... yet here you have it a beginner's question
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Old 01-20-18, 02:12 PM
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Shimano's web site lists the max rear cog diameter as 34T.


Can't wait for a few more product cycles until some one comes up with the new idea of more then 2 chain rings. Andy
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Old 01-20-18, 02:26 PM
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I would think that 11/34 cassettes should be easy to find. My go-to source for things like that is Niagara Bicycle. Just be sure the number of cogs matches up with what you have now. I'd check my chain for wear too - my normal philosophy is to install a brand new chain to go with a new cassette.

I wouldn't bet on switching to an 11/42 cassette without having to make a bunch of additional changes. You will definitely need to replace your chain with a new, longer one and I wouldn't bet on your existing derailleur and maybe even shifter working with that big of a cassette change.
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Old 01-20-18, 02:37 PM
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In Cassettes , steel is all the same only the finish differs.. the one by cranks craze ah spawned things like that 11 by 42,

but that wont be plug and play substitute for a 34t..

a triple crank with a 22 or 24t granny gear will be a more reasonable change.. I got a decade on tours with one ..
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Old 01-20-18, 02:43 PM
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I am replacing my 10-sp 114 links chain (worn) and front cogs (50T is worn badly) so I decided to add a new cassette as well (although it appears to be okay-ish), sadly my supplier has everything in stock but the 11-34 cassette. Now surely I could find it elsewhere but that would mean two purchases/deliveries/S&H etc. which is annoying to me. Hence the question if I can replace the 11-34 with an 11-42 (which has intrigued my lazy legs ) but if you say it won't work I will leave the old one in place for the time being.

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Old 01-20-18, 03:08 PM
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You would need to get a derailleur capable of handling the 42 tooth AND get a longer chain of course. I might note that Andy's comment about a "new idea of more than 2 chainrings was sarcastic. Of course triples have existed for a long time, and as you are finding out a so-called compact crankset does not work for everyone. Unfortunately changing to a triple at this point is prohibitive, as you would need a new crankset/BB, left shifter and possibly front derailleur.

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Old 01-20-18, 03:34 PM
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I have no desire to change to a triple (EWW), I am quite happy with 50/34 and 11-34 BUT since I was shopping I thought it'd be fun to try a larger cassette. My rear derailleur is this, and the specs as you can see say "Total Capacity: 39T (front double)" so in my naivety I thought maybe it'd work with 40 (?)
(I re-read Andys post.. now I get the sarcasm, didn't get it before thought he was serious).

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Old 01-20-18, 04:22 PM
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You of course have every right to not want a triple, but EWW is not a very convincing reason. Compact doubles were mainly created so people could have (semi) low gears and still have a racy look, and for manufacturers to save some money and reduce inventory complexity.
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Old 01-20-18, 04:30 PM
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I owned a bike with a triple in the past, totally redundant just more weight to carry. I have the same ratios now (actually more) with a compact double, easier/quicker to use and to maintain, so I don't see the point of a triple.
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Old 01-20-18, 07:02 PM
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I have only an 8 speed cassette with my triple. In spite of that, when I compare our two drive trains I come up with 16 useable different gear ratios on my bike, compared with 14 on yours. That's not even considering the less than useful 50-11 on yours compared to my 48-12, or the fact that a triple has a much more comfortable transition between chainrings, and operates most of the time as a double.
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Old 01-20-18, 07:15 PM
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Originally Posted by Paravia View Post
I owned a bike with a triple in the past, totally redundant just more weight to carry. I have the same ratios now (actually more) with a compact double, easier/quicker to use and to maintain, so I don't see the point of a triple.
Then you had the wrong combination of rings on the triple with the cassette you are using.

You need a couple of redundant gears so you don't get in the "magic place" of by the time you complete a double shift to the big ring, you've lost so much speed you have to shift back to the small ring.
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Old 01-20-18, 07:39 PM
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Originally Posted by Paravia View Post
I owned a bike with a triple in the past, totally redundant just more weight to carry. I have the same ratios now (actually more) with a compact double, easier/quicker to use and to maintain, so I don't see the point of a triple.
If you were seriously considering an 11x42 cassette, then a triple combined with a more closely spaced cassette is anything but redundant.

The closer spacing of the two larger rings is a major plus as is the ability to have a very low low gear without going to a dinner plate size largest cog and the huge gearing gaps those cassettes provide.

The weight penalty of the triple is negligible, certainly no more than that of having a 42T cog.
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Old 01-20-18, 08:28 PM
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[QUOTE=Paravia;20121222]I have no desire to change to a triple (EWW), I am quite happy with 50/34 and 11-34 BUT since I was shopping I thought it'd be fun to try a larger cassette. My rear derailleur is this, and the specs as you can see say "Total Capacity: 39T (front double)" so in my naivety I thought maybe it'd work with 40 (?)
(I re-read Andys post.. now I get the sarcasm, didn't get it before thought he was serious).[/QUOTE]


Sorry to not be more obvious. But after 45+ years in the trenches the marketing cycle repeats itself more then once.


Having come from 5 rear cogs and no shift gates/lift pins and bushinged chains we learned to shift both ders or we went home when it got real. Andy
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Old 01-20-18, 08:50 PM
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Originally Posted by Andrew R Stewart View Post
Having come from 5 rear cogs and no shift gates/lift pins and bushinged chains we learned to shift both ders or we went home when it got real. Andy
Isn't it ironic that after the development of shift gates, pins, shaped teeth and shaped front derailleur cages that have made front shifting so much better and more reliable than it ever was in the past, the current fad is to discard all of these improvements and use a single chainring?
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Old 01-20-18, 09:00 PM
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Originally Posted by Paravia View Post
I owned a bike with a triple in the past, totally redundant just more weight to carry. I have the same ratios now (actually more) with a compact double, easier/quicker to use and to maintain, so I don't see the point of a triple.
Could you please explain that for me?

A typical road triple would have 52/39/30 chainrings. A similar typical compact double would be 50/34. With a smaller big ring and a larger little ring, how could a compact double have more gear ratios?
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Old 01-21-18, 06:39 AM
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Originally Posted by Retro Grouch View Post
Could you please explain that for me?
I had a bike with a triple in the past, 50/39/30 front and 12-25 rear. This gave me 27 sp with a range of ratios from 4.17 to 1.20.
The 'compact' double I have now has 50/34 front and 11-34 rear, so the ratios are 4.55 to 1.0. So I go faster and climb better. I find 2 cogs at the front easier to use. It weighs less (not that I care) etc. That's what I meant with redundant.
Maybe shifting is more jumpy but I really never notice because where I live is so hilly I often have to do 4-5 shifts in two seconds.
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Old 01-21-18, 06:48 AM
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It doesn't have to be a Tiagra cassette. Any 11/34 10 speed Shimano type cassette will work, such as SLX, XT or even Sram cassettes.
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Old 01-21-18, 08:15 AM
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Originally Posted by dsaul View Post
It doesn't have to be a Tiagra cassette. Any 11/34 10 speed Shimano type cassette will work, such as SLX, XT or even Sram cassettes.
+1

I'll wade into this and comment that a 34-42 is extremely low, too low for a road bike. You're giving up good cog spacing to achieve insanely low gear inches. Gear inches you ask? (You say you're not a newb but here's a link to a very useful site that lets you calculate drive train specifics)

BikeCalc.com - Bicycle Gear Inches Chart

If you were going to try for lower gears I'd point to a 12-36 cassette, I saw sram at least makes that ratio. That 11 tooth cog is almost worthless now, I think if you put a 36t cog on back the RD definitely won't be able to take up extra slack in 34-11.

Do a search on this forum, I can't find it now but every month this same question pops up. Lots of good info around.
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Old 01-21-18, 09:02 AM
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Originally Posted by Paravia View Post
I had a bike with a triple in the past, 50/39/30 front and 12-25 rear. The 'compact' double I have now has 50/34 front and 11-34 rear, so the ratios are 4.55 to 1.0. So I go faster and climb better.
Again, fine that you made a choice for yourself, but:
1. Apples to oranges - a triple can of course have an 11-34 cassette, and the low would be lower. Or achieve the same low with a 30 and have smaller jumps.
2. You don't go faster with a 50-11, unless you are wasting energy fighting air on a downhill. Anyone who finds a 1:1 low gear insufficient (as I do as well) is not going to spin out a 50-11 on the flats.
3. Shifting between chainwheels on a compact usually requires multiple shifts. In any case it's better to anticipate and shift several rear cogs at once when making a large transition than to try to match gears when rapidly changing speed.
4. Getting a wide range with a compact means larger jumps in both chainwheels and cassette than with a triple. If that does not bother you that's fine, but it's a simple mathematical fact.
5. A properly adjusted triple shifts smoothly and predictably, and the derailleur only has to deal with two chainwheels at a time.
6. You're right - the weight diff is inconsequential, even if you're hauling the bike up stairs - especially as one may need a smaller cassette.
In today's market the only advantage that I see to a compact is a wider available selection of bicycles. I suspect the used market for triples will improve as a result.
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Old 01-21-18, 09:49 AM
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Tiagra 4700 is still available as a Tripple, not that it is the answer to the OP's question.
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Old 01-21-18, 01:50 PM
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I ended up ordering the same front cogs (50/34) and the same cassette (11-34)!
What confused/intrigued me was that the cassette (Tiagra CS-HG500) - which is part of my Tiagra 4700 drivetrain - is being offered with 4 options, including 11-42, from the sale page, so I thought maybe they were freely interchangeable. Now I know, I guess, that my derailleur won't reach 42T.
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Old 01-22-18, 09:10 AM
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I see that you've found a matching cassette, but if you decide to look for a lower gear ratio, there is a way to make it work.

https://www.wolftoothcomponents.com/...ducts/roadlink

This will allow your rear derailleur to be spaced away from the hub so that you can use a larger rear cog. This does not increase the chain wrap capacity of the derailleur, only spaces it away so that larger cogs can be used.
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Old 01-22-18, 09:34 AM
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Thanks for the link, bookmarked for future upgrade! Although it says "10s Cassette Compatibility: 11-42: Not supported" I guess I can always find an 11-40.
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Old 01-24-18, 03:26 AM
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Originally Posted by Paravia View Post
Thanks for the link, bookmarked for future upgrade! Although it says "10s Cassette Compatibility: 11-42: Not supported" I guess I can always find an 11-40.
Right, the wolftooth roadlink will not support an 11-42 cassette. It will work with an 11-40 cassette, but you can only have a 12 tooth difference between the front chainrings, ruling out a 34-50 compact double with a 16 tooth difference between its chainrings.

You could, however, look into a wolftooth tanpan, a device allowing you to use a mountain bike rear derailleur with road levers like your Tiagra STI levers.

You can use one, but you have to stay within the total capacity of the derailleur you want to use. You mentioned above that your Tiagra derailleur has a total capacity of 39. That number is different to the number of teeth on your largest cassette cog (you thought that it corresponded to the 40t cog on the 11-40 cassette). To calculate total capacity you can use the following equation:

Large chainring teeth - small chainring teeth + large cassette cog teeth - small cassette cog teeth.

Long story short, with a tanpan you can run a 34-50 compact double with an 11-40 or 11-42 cassette, provided you have the right derailleur. Some XT derailleurs would be okay, such as the trekking derailleur (Shimano XT RD T8000? Maybe also the Deore trekking derailleur?). The XT trekking derailleur has a total capacity of 47 teeth and it's a 10 speed component, so it will play together with Tiagra components nicely.

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