Disc brake rotors as spoke protector discs?

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crg
Posts: 99
Joined: 11 Oct 2021, 10:33am

Disc brake rotors as spoke protector discs?

Post by crg »

Note: added later

My RD came perfectly setup and with a spoke protector. Chain never slipped while shifting into the lowest gear. Chain slipped twice when going thru potholes and over bumps and the spoke protector saved the rear wheel.

Metal (and plastic, as well) spoke protector discs for freehubs are not easily available in India.
C​​​​​an I use disc brake rotors as spoke protector discs?

If yes, have the following questions.

1. Should I use centerlock or 6-bolt rotors?
​​2. ​​​For a 11-36T cassette, diameter of 36T cog is 150mm (6 inches).
Is it better to use 180mm or 203mm rotors?
3. Should I attach the rotor to the spokes or the 36T cog?
4. How close to the 36T should the rotor be to prevent chain derailment?

​​​​​​​Thanks
Last edited by crg on 30 Jan 2023, 1:45am, edited 1 time in total.
richardfm
Posts: 963
Joined: 15 Apr 2018, 3:17pm
Location: Cardiff, Wales

Re: Disc brake rotors as spoke protector discs?

Post by richardfm »

If you adjust the low limit on your rear derailleur you won't need a spoke protector.

Edit
I doubt if brake rotor would fit over the freehub

Edit Again
Can you order one from AliExpress? There are plenty of plastic ones on there. Do metal ones exist? I have never seen one.
Last edited by richardfm on 29 Jan 2023, 7:53pm, edited 1 time in total.
Richard M
Cardiff
Bmblbzzz
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Location: From here to there.

Re: Disc brake rotors as spoke protector discs?

Post by Bmblbzzz »

I'm not sure it would work either, but how about asking this lot for a source of spoke protectors?
https://groups.google.com/g/bangalore-bikers
cycle tramp
Posts: 3482
Joined: 5 Aug 2009, 7:22pm

Re: Disc brake rotors as spoke protector discs?

Post by cycle tramp »

... its a nice idea, but a spoke protector sits between on the rear hub and has a massive circular hole which the freewheel thread fits through and is then screwed into place by the freewheel (or locked in place with a free hub).

..having seen the mechanical engine-you-at-ee which exists in India, if it can't be found, I suspect someone can make it. Providing that the spoke protector doesn't catch the chain on the most largest sprocket then something like a circular metal or plastic lid of a sweetie tin would serve.. you've just got to cut a circular hole in it

P.s. if I send you one, can you send me a working Morris Oxford :-) if not I'll settle for a tuktuk
It's time to go :-)
crg
Posts: 99
Joined: 11 Oct 2021, 10:33am

Re: Disc brake rotors as spoke protector discs?

Post by crg »

richardfm wrote: 29 Jan 2023, 7:33pm If you adjust the low limit on your rear derailleur you won't need a spoke protector.

Edit
I doubt if brake rotor would fit over the freehub

Edit Again
Can you order one from AliExpress? There are plenty of plastic ones on there. Do metal ones exist? I have never seen one.
1. See note.

2. Hence my query here. 6-bolt rotor does. Not sure about centerlock rotor.

3. AliExpress, and similar sites, cannot deliver to India.
Bmblbzzz wrote: 29 Jan 2023, 7:45pm I'm not sure it would work either, but how about asking this lot for a source of spoke protectors?
https://groups.google.com/g/bangalore-bikers
Unavailable online. Will try.
cycle tramp wrote: 29 Jan 2023, 9:24pm ... its a nice idea, but a spoke protector sits between on the rear hub and has a massive circular hole which the freewheel thread fits through and is then screwed into place by the freewheel (or locked in place with a free hub).

..having seen the mechanical engine-you-at-ee which exists in India, if it can't be found, I suspect someone can make it. Providing that the spoke protector doesn't catch the chain on the most largest sprocket then something like a circular metal or plastic lid of a sweetie tin would serve.. you've just got to cut a circular hole in it

P.s. if I send you one, can you send me a working Morris Oxford :-) if not I'll settle for a tuktuk
6-bolt rotor fits thru the freehub. Not sure about centerlock rotor.

Getting custom made is inexpensive but the the time and effort involved is just not worth it.

Tuktuks ... as many as you want. New is about £1500 to 2000 each. Used ones much less. But shipping and certification will probably be more than the cost of a new one. Unless of course you have an estate where certification is not required.
NickJP
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Location: Canberra, OZ

Re: Disc brake rotors as spoke protector discs?

Post by NickJP »

All the frisbees for spoke protection I've seen are a) not flat but dished, so that the frisbee clears the freewheel/cassette cogs, and b) are much thinner at their mounting point than the ~1.8mm thickness of disc rotors.

Also, a lot of modern cassettes, particularly those with a large cog of 34t or bigger, overhang their mounting point on the inside. That is why HG 11-speed MTB cassettes (and the largest Shimano HG road cassettes) can fit on a narrower freehub body than smaller 11s road cassettes, because the larger cog size can take advantage of the additional clearance provided by the bracing angle of the spokes at the larger diameter.
crg
Posts: 99
Joined: 11 Oct 2021, 10:33am

Re: Disc brake rotors as spoke protector discs?

Post by crg »

NickJP wrote: 30 Jan 2023, 3:44am All the frisbees for spoke protection I've seen are a) not flat but dished, so that the frisbee clears the freewheel/cassette cogs, and b) are much thinner at their mounting point than the ~1.8mm thickness of disc rotors.

Also, a lot of modern cassettes, particularly those with a large cog of 34t or bigger, overhang their mounting point on the inside. That is why HG 11-speed MTB cassettes (and the largest Shimano HG road cassettes) can fit on a narrower freehub body than smaller 11s road cassettes, because the larger cog size can take advantage of the additional clearance provided by the bracing angle of the spokes at the larger diameter.
Good points Nick.
Mine is a 9-speed cassette on a 11-speed hub and requires a 1.85mm spacer.
Perhaps I can use the disc as the spacer!
Of course, need enough clearance from the derailleur.
re_cycler
Posts: 214
Joined: 13 Dec 2022, 7:18pm

Re: Disc brake rotors as spoke protector discs?

Post by re_cycler »

richardfm wrote: 29 Jan 2023, 7:33pm If you adjust the low limit on your rear derailleur you won't need a spoke protector.

Edit
I doubt if brake rotor would fit over the freehub

Edit Again
Can you order one from AliExpress? There are plenty of plastic ones on there. Do metal ones exist? I have never seen one.
A fine example of a metal spoke protector to be seen on this just posted Viscount bike for sale.
viewtopic.php?p=1752424#p1752424
gregoryoftours
Posts: 2234
Joined: 22 May 2011, 7:14pm

Re: Disc brake rotors as spoke protector discs?

Post by gregoryoftours »

I'd have to try it to be sure but I can't imagine a disc rotor to be suitable even if it was possible to fit. I'd expect a derailleur/chain that came up against it to get snagged in the gaps between the rotor spokes and get pulverized, probably taking the wheel spokes too!
gregoryoftours
Posts: 2234
Joined: 22 May 2011, 7:14pm

Re: Disc brake rotors as spoke protector discs?

Post by gregoryoftours »

Amazon India has plenty of spoke protectors that are freehub wheel compatible.

https://www.amazon.in/s?k=spoke+protect ... _sb_noss_1
crg
Posts: 99
Joined: 11 Oct 2021, 10:33am

Re: Disc brake rotors as spoke protector discs?

Post by crg »

gregoryoftours wrote: 31 Jan 2023, 9:33pm Amazon India has plenty of spoke protectors that are freehub wheel compatible.

https://www.amazon.in/s?k=spoke+protect ... _sb_noss_1
Why not add freehub to the search, check if it really fits freehubs and 36T cassette and then post the results here?
gregoryoftours wrote: 31 Jan 2023, 9:29pm I'd have to try it to be sure but I can't imagine a disc rotor to be suitable even if it was possible to fit. I'd expect a derailleur/chain that came up against it to get snagged in the gaps between the rotor spokes and get pulverized, probably taking the wheel spokes too!
Please try on a stand and post here.
gregoryoftours
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Re: Disc brake rotors as spoke protector discs?

Post by gregoryoftours »

crg wrote: 1 Feb 2023, 11:33am
gregoryoftours wrote: 31 Jan 2023, 9:33pm Amazon India has plenty of spoke protectors that are freehub wheel compatible.

https://www.amazon.in/s?k=spoke+protect ... _sb_noss_1
Why not add freehub to the search, check if it really fits freehubs and 36T cassette and then post the results here?
gregoryoftours wrote: 31 Jan 2023, 9:29pm I'd have to try it to be sure but I can't imagine a disc rotor to be suitable even if it was possible to fit. I'd expect a derailleur/chain that came up against it to get snagged in the gaps between the rotor spokes and get pulverized, probably taking the wheel spokes too!
Please try on a stand and post here.
That's a bit of a weird reply. My post wasn't supposed to be snarky. I linked to the spoke protectors that I found on Amazon India because you said that you couldn't find them easily available in India. The ones that are designed for freehubs are described as such. They are the ones that have a bigger hole and clip to the spokes. I don't know if they'll be big enough for 36t sprockets or not.

Maybe having found some spoke protectors that are easily available in India you can research them yourself a bit to see if they are suitable.

I don't think that disc rotors are suitable for the job at all, especially seeing as proper spoke protectors are easily available, but if you want to try them go ahead.
PH
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Re: Disc brake rotors as spoke protector discs?

Post by PH »

A disc rotor is unsuitable whether it fits or not, mainly because you're looking for a solid smooth surface between the chain and RD, and the spokes. A rotor is likely to catch one or the other and make it worse.
I like them on a derailleur bike, as a last stop protection if something goes wrong, but as already said, if the chain is routinely coming off, bumps or not, there's something wrong with the adjustment.
crg
Posts: 99
Joined: 11 Oct 2021, 10:33am

Re: Disc brake rotors as spoke protector discs?

Post by crg »

gregoryoftours wrote: 1 Feb 2023, 7:48pm
crg wrote: 1 Feb 2023, 11:33am
gregoryoftours wrote: 31 Jan 2023, 9:33pm Amazon India has plenty of spoke protectors that are freehub wheel compatible.

https://www.amazon.in/s?k=spoke+protect ... _sb_noss_1
Why not add freehub to the search, check if it really fits freehubs and 36T cassette and then post the results here?
gregoryoftours wrote: 31 Jan 2023, 9:29pm I'd have to try it to be sure but I can't imagine a disc rotor to be suitable even if it was possible to fit. I'd expect a derailleur/chain that came up against it to get snagged in the gaps between the rotor spokes and get pulverized, probably taking the wheel spokes too!
Please try on a stand and post here.
That's a bit of a weird reply. My post wasn't supposed to be snarky. I linked to the spoke protectors that I found on Amazon India because you said that you couldn't find them easily available in India. The ones that are designed for freehubs are described as such. They are the ones that have a bigger hole and clip to the spokes. I don't know if they'll be big enough for 36t sprockets or not.

Maybe having found some spoke protectors that are easily available in India you can research them yourself a bit to see if they are suitable.

I don't think that disc rotors are suitable for the job at all, especially seeing as proper spoke protectors are easily available, but if you want to try them go ahead.
I first check Amazon India and all online stores in India, before looking outside. Your suggestion about searching on Amazon could've been phrased better.
Since proper spoke protectors are unavailable, I started looking at alternatives.
PH wrote: 1 Feb 2023, 8:54pm A disc rotor is unsuitable whether it fits or not, mainly because you're looking for a solid smooth surface between the chain and RD, and the spokes. A rotor is likely to catch one or the other and make it worse.
I like them on a derailleur bike, as a last stop protection if something goes wrong, but as already said, if the chain is routinely coming off, bumps or not, there's something wrong with the adjustment.
The chain doesn't routinely come off. The two times it came off, I was not shifting.
RD came perfectly setup from the manufacturer, based on the shifting for almost 2 years. Nothing to do with my skill in adjusting the RD, since there was no need to adjust.
The rotors have different patterns and it is something to be aware of.
I have no compulsion about using rotors, other than the ease of obtaining them.
gregoryoftours
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Re: Disc brake rotors as spoke protector discs?

Post by gregoryoftours »

You're not going to get rotors to work. A rotor will always be manufactured pancake flat. That means even if it's the right thickness to replace a spacer behind your cassette, there will not be enough clearance between it and the biggest sprocket for the chain to engage on the largest sprocket. You can't space it any more because your cassette will then be spaced too far out and your cassette lockring will not engage the threads. A centerlock rotor is also not usable. Even if the hole is the right diameter (which I don't know without looking) the middle of a centerlock rotor is several mm too thick to be usable on a freehub.

If somehow it was possible to stamp an offset into a rotor and mount it behind the cassette, the design of rotors is such that a chain would get tangled/snagged into the gaps and jam, and the combination of a hard steel rotor and chain snarling up behind the cassette would probably cause more damage to the bike than a chain jam alone.

Your best bet is to measure the driveside hub flange diameter on your rear wheel, and see if the attachment clips on any of the freehub spoke protectors sold via Amazon India will fit that diameter. (The clips fasten the protector to the hub flange, not the spokes generally, I had forgotten this point). The protector also needs to match your spoke count so that the spokes don't interfere with clip engagement.

It may be possible to get one with a large enough outer diameter to cover a 36t large sprocket, but even one that is borderline in size will prevent the chain jamming down between the spokes and the back of the cassette which is where the real damage is done so it would definitely be worth trying.

Just because your gears have worked fine for all of this time doesn't mean that the low limit is necessarily adjusted correctly, or hasn't gone out of adjustment, or any other number of issues could be contributing to the problem. The gears can operate perfectly and be perfectly indexed even if the low limit screw is misadjusted to the point where it is no longer doing its job, and you'll only find it's not properly adjusted when the chain jams down the back of your cassette or the rear spokes eat your rear derailleur.

The low limit screw on a rear derailleur should be set such that a very small amount of extra resistance is felt when changing into bottom gear as the derailleur butts up against the limit screw. Too much and the shifter internal is strained when set to bottom gear, and/or you'll have difficulty changing to/staying cleanly in low gear. Not enough and there can be just enough play or flex in bottom gear that the derailleur can end up hitting the spokes in some circumstances.

To check the low limit, shift gear into the biggest sprocket. Push the parallelogram body of the derailleur toward the wheel. If it moves even a little before you feel it butt up against the low limit screw then the limit screw is not set correctly.

Worn sloppy derailleur pivots, loose hub bearings can also result in the derailleur hitting the spokes.

If the overall wheel spoke tension is insufficient then the wheel can deflect sideways enough over rough ground/cornering that a correctly limited derailleur can still come into contact with the spokes. Same is true for a warped wheel. The alignment of the derailleur also wants checking regularly to see that it or the mounting hanger aren't bent so that the derailleur may hit the spokes. These are issues worth looking at as well as considering a spoke protector as a protector is really a last resort when all other reasonable steps have been taken.
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