Pushing RD capacity - advice please

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cycle tramp
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Re: Pushing RD capacity - advice please

Post by cycle tramp »

Apologies , just be checked crank lengths should be 20-21% of your inside leg measurement
It's time to go :-)
GideonReade
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Re: Pushing RD capacity - advice please

Post by GideonReade »

Hi CycleTramp, I suspect you're right, not sure what crank length fitted, any replacement would look for 165mm.

But I'm very unconfident of the smaller chainset approach. It's a 1990s Trek OCLV, top of the line kind of frame. Full carbon. The FD hangs on a little bent sheet tab bonded to the seat tube. The tab has a slot in it. With the 53T outer, the slot has only about 5mm left to go down. It's got much more up. Built for elite legs, I guess.

A 48T big ring is 10% smaller, so if current 53T radius is 80mm (I'm guessing from in bed), that's going to be 72mm with 48T, so the FD needs to move 8mm down, or a gap emerges between ring and FD outer plate...

I'm not a great expert on FDs. Most I have met are band-on so infinite vertical movement. This one isn't. I'm not sure what it's actual range would be, or if other FDs might fit differently?

However, by then, having also changed the RD to increase the tooth difference, we've replaced everything except the ancient RST brifters... How much more is a Sora or Tiagra groupset? The brief is an economical mod, I'm over budget already. 🤔
GideonReade
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Re: Pushing RD capacity - advice please

Post by GideonReade »

Err, it may look like having asked for advice, I'm then resisting a lot of it! Please all be assured I'm taking notice, absorbing lots, and learning things. Our tourers do indeed have much lower gears, largely along lines discussed here!

Fortunately our usual road bike gang rides are pretty flat, until the last climb home, when it's just the two of us.
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Tigerbiten
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Re: Pushing RD capacity - advice please

Post by Tigerbiten »

One option I thought of if you do get a long cage derailleur.
Keep to 53/38 double and drop the 11t sprocket.
Then fit a 32t sprocket to make up the number of sprockets to give you a 13/32 cassette.
It's may be the easiest way to step all the gears down whilst not moving the front derailleur.

Luck ....... :D
cycle tramp
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Re: Pushing RD capacity - advice please

Post by cycle tramp »

GideonReade wrote: 16 Apr 2021, 10:54pm Err, it may look like having asked for advice, I'm then resisting a lot of it! Please all be assured I'm taking notice, absorbing lots, and learning things. Our tourers do indeed have much lower gears, largely along lines discussed here!

Fortunately our usual road bike gang rides are pretty flat, until the last climb home, when it's just the two of us.
Not at all. Most of my advice comes from my own world view (steel frames, front deraileurs with clamp on mounts, friction only gear changes and that sort of thing) and fails completely to take into account things like carbon fibre bike frames with fixed front deraileur mounts, and terrain that the bicycle ridden over.

In regards to the fixed mounting point for the front deraileur, IF it became an issue, it may be worth asking saint john street cycles if they sell some sort of widget that bolts to the carbon frame, and then allows the front deraileur to be bolted to the widget, in a lower position.
It's time to go :-)
cycle tramp
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Re: Pushing RD capacity - advice please

Post by cycle tramp »

Tigerbiten wrote: 16 Apr 2021, 11:23pm One option I thought of if you do get a long cage derailleur.
Keep to 53/38 double and drop the 11t sprocket.
Then fit a 32t sprocket to make up the number of sprockets to give you a 13/32 cassette.
It's may be the easiest way to step all the gears down whilst not moving the front derailleur.

Luck ....... :D
Oh, that is an elegant solution. A 38 chain ring turning a 32 sprocket should give a low gear of about 33 inches... low enough for most unladen bikes to cope with everything but the steepest of longest of hills
It's time to go :-)
GideonReade
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Re: Pushing RD capacity - advice please

Post by GideonReade »

Hi Tigerbiten, that does sound elegant. But having only really fiddled with MTB type cassettes before this case, can I query it?

The 11-28 block I bought for this case, does seem to have all 7 lower cogs assembled onto the assembly bolts. Whereas the MTB cassettes have the lower 3 or 5 or so mounted on a spider: lighter, but fixed. I think you're saying I should be able to get a 32T in the individual pattern, and reassemble my cassette starting from 32T?

And on this 11-28 the 11 isn't part of the bolted preassembly, it's loose, and carries serrations to hold the lockring. I don't recall the next cog down (13T?) having the serrations. Am I missing something? Will that work?
gregoryoftours
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Re: Pushing RD capacity - advice please

Post by gregoryoftours »

GideonReade wrote: 16 Apr 2021, 9:15am How does she feel? She whinges a lot about getting up the hill. Otherwise ok, but on the flat, in the gang, if I'm behind, I often notice use of 42/12 or 42/11. So pushing cruising speed up onto the big ring is probably good.
Does this apply to the revised gearing with 38 small ring and 11-28t cassette, or just the original setup of 53/42 with 11-23 cassette? If just the latter then why not try the hill with 38/28? If that is low enough for her then a 50t big ring will sort out the chain sag, maybe one link removed and all is well. If the new gearing 38/28 isn't low enough then try bigger cassette and long cage mech as suggested on the thread.
GideonReade
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Re: Pushing RD capacity - advice please

Post by GideonReade »

Hi Gregoryoftours, we will find out how 38/28 goes on Wednesday, according to the schedule. I don't know if the 50T will arrive and be on by then, it doesn't affect the low gear test.
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CJ
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Re: Pushing RD capacity - advice please

Post by CJ »

Jamesh wrote: 14 Apr 2021, 9:02pm Dare I say it.....!

36t rear cassette and long cage rear mech???

Cheers James
Well said. Other posters' suggested changes are merely tinkering at the edges. If 42 by 23 was a good bottom gear for an elite athlete, an ordinarily fit rider needs something HALF the size. If you don't believe me, join Strava, ride a steep uphill segment and compare your time with the fastest. if it's better than twice as long you're doing well. Twice the time means you need a gear half the size in order to pedal at the same (presumably most efficient) cadence. QED.

Here's the good news. Eight-speed road rear mechs and cassettes are completely interchangeable with MTB mechs and cassettes, will work fine with your road shifters (but not front mechs), and 9-speed MTB mechs will happily work 8-speed chain, so much lower gears are possible. Even lower is possible if you convert that crank into a triple crank, which can be done by drilling and tapping M6 holes into the crank arms - although the special bolts and spacers are nowadays hard-to-find.
Chris Juden
One lady owner, never raced or jumped.
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elPedro666
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Re: Pushing RD capacity - advice please

Post by elPedro666 »

As mentioned above, so long as your chain is long enough to survive the occasional big/big mistake, a little bit of untensioned rattle an accidental small/small should just serve as a warning to shift rings. Closer ratio rings should help by making the range of the big ring much more usable. I'd gamble you could get at least a passable shift even with the mech sitting well above the ring. Also Sunrace might make a larger cassette without too wide a spread, but I've not researched that properly and do appreciate the desire for close ratios.

Something I do on my own bikes is adjust the front mech so that it starts to rub slightly in the third sprocket, warning you to either click the trim adjustment on the front shifter & pedal harder (if you can see the top ) or be prepared to give up on holding the big ring and shift down!

Mostly I'm posting to say what a lovely frame that is, well worth bending the budget for (2x10 105 is great value ) please feel free to throw up gratuitous extra pics!

I'm a trendy consumer. Just look at my VOG-L09 using hovercraft full of eels.

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elPedro666
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Re: Pushing RD capacity - advice please

Post by elPedro666 »

GideonReade wrote:Hi Gregoryoftours, we will find out how 38/28 goes on Wednesday, according to the schedule. I don't know if the 50T will arrive and be on by then, it doesn't affect the low gear test.
To my mind, unless you live in the flatlands, that's still a pretty mega gear by modern standards - I'm in half-decent shape at the moment* and my 34/30t still gets plenty of wear & tear on it Image

*for a middle-aged rank amateur

I'm a trendy consumer. Just look at my VOG-L09 using hovercraft full of eels.

gregoryoftours
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Re: Pushing RD capacity - advice please

Post by gregoryoftours »

If you do end up going bigger cassette with longer cage mech, any Shimano rear 8/9 speed mech, mtb or road, with suitable length cage will do, and 10 speed road mechs apart from tiagra 4700 which is an anomalous cable pull ratio. MTB 10 speed rear mechs have a different cable pull ratio and aren't compatible. A couple of Dura ace models might not be right either. 9/10 speed mechs I'd probably run with a matching speed chain though in case there is more tendancy to rub with a slightly wider 8 speed chain on a slightly narrower mech cage. I've run plenty of 9 speed chains on 8 speed setups with no problems.
GideonReade
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Re: Pushing RD capacity - advice please

Post by GideonReade »

Thanks for all that guys. Let's see how the current phase goes.
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CJ
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Re: Pushing RD capacity - advice please

Post by CJ »

gregoryoftours wrote: 18 Apr 2021, 5:24pm If you do end up going bigger cassette with longer cage mech, any Shimano rear 8/9 speed mech, mtb or road, with suitable length cage will do, and 10 speed road mechs apart from tiagra 4700 which is an anomalous cable pull ratio. MTB 10 speed rear mechs have a different cable pull ratio and aren't compatible.
To the list of newly incompatible Shimano 10-speed mechs that won't work with their pre-2016 stuff, you need to add the GRX-400 gravel mech, which is basically a Tiagra 4700 with a longer cage. And it's a crying shame this mech won't play with older or fewer speeds shifters, because it has a MUCH longer cage, capable of reeling in a humungous amount of loose chain, that'll cope with even more total difference that their current MTB mechs!

But personally, I wouldn't run 8-speed chain in a 10-speed mech anyway. I think two speeds different is pushing it. If likely to work I would do it, but fit 8-speed or at least 9-speed pulleys. Two reasons: the 8-speed chain is physically quite a lot wider, so there's likely to be a bit of rub in a narrower cage when imperfectly aligned with a sprocket (which happens even in perfect systems thanks to a bit of dirt and cable friction), and because 8-speed indexing isn't as perfect in the first place, so you may need the greater sideways float of the slightly wider pulley bush. And yes, fitting different speeds of pulleys does change the width of the cage.

Going the other way, I found that fitting 10-speed pulleys in the old XT-shadow 9-speed mech I'm using on my gravel/road bike (because the GRX-400 I'd bought won't play with my pre-2016 Ultegra 10-speed STIs!) has significantly improved its shifting precision.
Chris Juden
One lady owner, never raced or jumped.
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