Pushing RD capacity - advice please

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GideonReade
Posts: 410
Joined: 4 Jul 2010, 10:46pm

Pushing RD capacity - advice please

Post by GideonReade »

Hi, today's project was to take other half's classic Trek OCLV road bike, which was originally specified for a 1990's elite athlete (I know not who), so 53/42 driving 11-23 8sp. Not ideal for our age, and now we moved up a hill, oops. I must admit, I've not worked on road-spec kit before, except brifters on tourers.

I'm not sure the bikes worth investing too much in, it's quite tired & partly unoriginal. I'm just trying to economically drop the gears. Which I did today, but I miscalculated my purchase, overlooking that I'd left an experimental value in my spreadsheet. Specifically, the bike has a 53T big ring, but I had put in 50T as an experiment, and forgot. So I'm 3T out.

So, we've gone from 53/42 driving 11-23, to 53/38 driving 11-28. BCD is 130, 38T being smallest ring. So biggest sprocket 28, difference 32T. The old Ultegra RD is quoted max 28T sprocket, but difference 29T, there's my 3T error.

Up on the stand it goes ok, and I'm very happy the FD rubs in crossed positions, especially as herself is a bit prone to not noticing them. But, actually, the rear derailleur's contortions don't look very happy. I am seeking advice on the best way to refine and proceed. It needs to not wreck itself if pedalled crossed, noisy is fine. Now, nothing's touching small-small, and big-big isn't hitting a hard stop. But!

I know of three courses of action which might work:
* £: I could buy a budget 50T big ring (£), or a mid-cage deraillieur (££), or a budget 48/36 chainset (£££).
* Free: I could wind in RD H screw disabling the 11. It shouldn't be used with the 38T, and it's very unlikely to be used with the 53T! Obviously this could be unpopular.
* Free: I could try taking 1 or 2 or 3 links out of the chain (I left the old chain on for this option). The RD will be less convoluted in small-small, but, obviously, have to stretch further in big-big.

I'd welcome expert input regarding the positions the RD now adopts - see photos of the crossed positions. The 11-23 is black & dirty, the 11-28 shiny silver. The 38T is, obviously smaller. There's no guarantee the chain was the right length for the old cogs.
Attachments
New, small to small
New, small to small
New, big to big (but with 42T inner on)
New, big to big (but with 42T inner on)
Old, small to small
Old, small to small
Old, big to big
Old, big to big
gregoryoftours
Posts: 2234
Joined: 22 May 2011, 7:14pm

Re: Pushing RD capacity - advice please

Post by gregoryoftours »

Personally I think that it would be kinder to the rear mech to leave the chain as it is. Just avoid the 2 or so smallest sprockets when in the little ring; not gears that are needed anyway.

The mech should have enough tension and cage length to take up the slack for all of the other gears. It's not the end of the world if those gears are used by mistake once in a while anyway, it'll just be a little baggy.

I've run similar setups on old MTBs used as commuter/touring bikes with rear mech cages that ideally would have been just a little longer, but have not caused problems and have shifted fine.

A 53-11 top gear is unnecessarily high really, probably a 50t chainring if available in that BCD would be a relatively cheap way to get a more practical range of gears, and then the mech wouldn't be slack in any combinations either.
Jamesh
Posts: 2963
Joined: 2 Jan 2017, 5:56pm

Re: Pushing RD capacity - advice please

Post by Jamesh »

Dare I say it.....!

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

Cheers James
markjohnobrien
Posts: 1037
Joined: 4 Oct 2007, 8:15pm

Re: Pushing RD capacity - advice please

Post by markjohnobrien »

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

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

Cheers James
That’s what I’d do.
Raleigh Randonneur 708 (Magura hydraulic brakes); Blue Raleigh Randonneur 708 dynamo; Pearson Compass 631 tourer; Dawes One Down 631 dynamo winter bike;Raleigh Travelogue 708 tourer dynamo; Kona Sutra; Trek 920 disc Sram Force.
GideonReade
Posts: 410
Joined: 4 Jul 2010, 10:46pm

Re: Pushing RD capacity - advice please

Post by GideonReade »

Hi all, thanks,

Gregoryoftours - Mostly that's good to hear, but, "avoid top 2 sprockets" just isn't happening unless I wind the H screw right in. My better half has been crossing chains, despite knowing better, for 20 years, so she's not going to stop. Partly a downside of STIs, there's no positional feedback, unlike barends. You're quite right that the 53T is excessive, although I can only drop the FD about 5mm, so a big big ring is mandatory.

36er chaps, we have a few bikes with MTB gearing, up to 34 anyways. But this bike needs to run in road gangs, it can't have huge jumps between gears, that makes matching pace really tough. And it's only got 8speeds. As it happens I did todays ride on a 3x8sp 11-32 tourer, as I needed a bit of cargo (loose tea!), and was struggling with pedalling to slow or too fast. Completely regearing the topic bike to a modern standard like 2x10sp is probably no cheaper than buying a secondhand replacement bike.
mcshroom
Posts: 175
Joined: 30 Aug 2011, 12:00am

Re: Pushing RD capacity - advice please

Post by mcshroom »

I'd say it will be fine as it is. The small gears will be noisy with the lack of tension, but it's not that dramtic an issue.

A simple fix would be to get an 8/9sp MTB rear mech with a longer cage, or something like a current Sora/Claris road mech. It'll index fine with the shifters, and then should have the capacity for the whole system.
cycle tramp
Posts: 3479
Joined: 5 Aug 2009, 7:22pm

Re: Pushing RD capacity - advice please

Post by cycle tramp »

How does the cyclist of this bike feel about the gear ratios?

Given that the 38 x 11 gear produces a gain of some 96" (which if peddled at a rate of 2 rotations per second would produce a top speed of over 32 mph) is the large chainring ever used?

If the low gear of 38 x 28 is enough for the area around which the cyclist cycles, why not use the existing rings of 42 tooth and 38 tooth chainrings on the chainset with the 42 taking the place of the outer 50 tooth ring?
It's time to go :-)
iandusud
Posts: 1577
Joined: 26 Mar 2018, 1:35pm

Re: Pushing RD capacity - advice please

Post by iandusud »

On one of my bikes I run a 10 speed Ultegra short cage mech with 50/34 chainset and 11-32 cassette. It works fine. However if you use the small chainring with the smaller sprockets the chain will go slack. Of course there is no need to use these combinations and even if you do it is not an issue.
GideonReade
Posts: 410
Joined: 4 Jul 2010, 10:46pm

Re: Pushing RD capacity - advice please

Post by GideonReade »

Thanks CycleTramp and Iandusud,

The 42 outer idea is interesting, although only a 10% step... Almost a mental inversion of approach, rear for coarse, front for fine. I could foresee some confusion. But unfortunately I also think that the now available maybe 5mm of downwards adjustment for the FD would leave it flying well above the 42T big ring. I could be wrong about that. It wasn't designed for us oldies!

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.

Your 10sp is 37T difference isn't it? Wow. Although I guess that's well in the compact double era. And if you're careful to avoid crossover... Clare isn't.

It might sound like I'm dissing my better half. But TBH I find myself that the on my one (Ergopower) bike with no visual or tactile feedback of chain position, I'm also somewhat prone to crossover. Not a problem with bar ends or STIs with visual indicators. This ole bike has RST STIs without indications.
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freiston
Posts: 1500
Joined: 6 Oct 2013, 10:20am
Location: Coventry

Re: Pushing RD capacity - advice please

Post by freiston »

You could increase the capacity of the RD by extending the hanger - £4.99:

https://www.sjscycles.co.uk/gear-spares ... -extender/
Disclaimer: Treat what I say with caution and if possible, wait for someone with more knowledge and experience to contribute. ;)
the snail
Posts: 333
Joined: 5 Aug 2011, 3:11pm

Re: Pushing RD capacity - advice please

Post by the snail »

freiston wrote: 16 Apr 2021, 1:04pm You could increase the capacity of the RD by extending the hanger - £4.99:

https://www.sjscycles.co.uk/gear-spares ... -extender/
That won't increase the capacity - it will allow a larger sprocket. The OP needs a mech with a longer cage. Personally I'd try it as is, I've run set ups like that before. If it's noisy in small/small then that tells you to change gear. If it doesn't work, then a new derailleur is probably the best/cheapest option.
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freiston
Posts: 1500
Joined: 6 Oct 2013, 10:20am
Location: Coventry

Re: Pushing RD capacity - advice please

Post by freiston »

the snail wrote: 16 Apr 2021, 1:20pm
freiston wrote: 16 Apr 2021, 1:04pm You could increase the capacity of the RD by extending the hanger - £4.99:

https://www.sjscycles.co.uk/gear-spares ... -extender/
That won't increase the capacity - it will allow a larger sprocket. The OP needs a mech with a longer cage. Personally I'd try it as is, I've run set ups like that before. If it's noisy in small/small then that tells you to change gear. If it doesn't work, then a new derailleur is probably the best/cheapest option.
This is the time that the small print in my signature comes in to play - thanks for the correction :)
Disclaimer: Treat what I say with caution and if possible, wait for someone with more knowledge and experience to contribute. ;)
TheBomber
Posts: 520
Joined: 16 Feb 2020, 8:18pm

Re: Pushing RD capacity - advice please

Post by TheBomber »

To add to the areas already well covered above:
I could try taking 1 or 2 or 3 links out of the chain
Agreed. That chain looks long to me and could easily cope with at least one link pair removed. Always check on the stand that you haven’t gone too far as that will lead to a catastrophic failure, but basically the chain can run in a straight line from the bottom of the chainring to the top of the guide pulley (the upper one on the derailleur). It might be noisy there but that might encourage Clare to shift to a more drivetrain friendly gear anyway, no?
Partly a downside of STIs, there's no positional feedback, unlike barends.
You can get visual indicators for STIs - they go in the cable where it pops out the side of the STI. I could send you a 10 speed one (PM me) that you’d have to mark up with tape/paint/whatever to indicate where the nasty cross chain gear is.

Are you now committed to the 11-28 block? A surf of the web is likely to reveal Shimano compatible ones by brands such as Sram or BBB that might start with a more suitable 12 or 13T sprocket.
I'm not sure the bikes worth investing too much in, it's quite tired & partly unoriginal.
If the frame is suitable for Clare then your mods are likely to be worth pursuing. Any secondhand bike is likely to come with issues of its own while your choice in new ones is currently heavily restricted by supply problems.
GideonReade
Posts: 410
Joined: 4 Jul 2010, 10:46pm

Re: Pushing RD capacity - advice please

Post by GideonReade »

Thanks TheBomber. I've kept it on the old chain for now (>0.5 <0.75 wear) specifically so I can muck about with the length without worrying about making stiff links. Once it looks right I'll trim the new chain to match.

Well, I've no other use for that block, although it could be used next time a hack needs an overhaul. TBH I was so chuffed to actually find it I snapped it up - been looking for a while. I do agree that starting at 12 or 13 would be even better. A cursory search though didn't turn any up; I guess 8 speed is a less diverse universe than it was, now it's so downmarket (we have, err, six 8speed bikes 😁). Anyway, let's stick with 11-28 and see how we do.

I'd never heard of the inline indicators - what an obvious idea. Let me see if she's interested. Unfortunately on her 9 speed tourer, someone, that is to say me, already put noodles on the gear cables, to make room for a bar bag. But no such issue on the subject bike, and it's due new gear cables anyway.
cycle tramp
Posts: 3479
Joined: 5 Aug 2009, 7:22pm

Re: Pushing RD capacity - advice please

Post by cycle tramp »

GideonReade wrote: 16 Apr 2021, 9:15am Thanks CycleTramp and Iandusud,

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.
H'mmm.... I'm not wholly surprised. Even a 38 chainring turning a 28 sprocket, produces a 38" inch gear, which is kind of heroic (my smallest gear when I was touring on my 3 speed worked our at 39" and I had to make some considerable effort to get up some hills). You may make the cyclist happier if the current chainset was swapped for another chainset with smaller chainrings... but there may be another advantage by making this choice - a chance to look at chainsets with an appropriate crank length. It used to be that the recommended crank length was some 20% of the riders' leg length (with some modifications depending on foot size). However this has been forgotten by bike manufacturers and most modern bikes are fitted with either 170 mm or 175 mm cranks regardless of the frame size. Fine if you are an average size man, less good if you are smaller than average lady. If you Google Mike Burrows Crank Length, he's done some rather thought provoking experiments based on the subject.
It's time to go :-)
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