SRAM NX conversion

For discussions about bikes and equipment.
RecumbentRide
Posts: 234
Joined: 27 Jul 2012, 9:11pm

SRAM NX conversion

Post by RecumbentRide »

RE:SRAM NX conversion
I plan and converting from my current 3x9 (SRAM hub, hyperglide) Shimano geared setup (Shimano XT derailleurs) to a 1x12 SRAM Eagle NX setup. Using the NX derailleurs, chain & shifter combined with Sunrace CSMZ90 12spd cassette (11-50t). Not yet sure what chainset I'll be going for though.

I presume my existing 9spd hub will be compatible but I'd just like to make sure this assumption is correct. Will I need any other adapters for the 12spd cassette to fit?

The other major question is derailleur clearance. I know some of you have the NX/GX groupset and what I'd like to know is how much rear derailleur ground clearance do you have when you are in the lowest gear, 1st? I ask this as my wheels are 24" which could be a problem. So compared to someone riding 26" (650C+B sizes) I'm losing an 1"-1.5" in ground clearance :shock: I do have the option of going up to a 26 at the back but I rather not have to.

Oh and if you have any comments as to why I'm doing this at all pls keep it to another thread, thanks.
Brucey
Posts: 44521
Joined: 4 Jan 2012, 6:25pm

Re: SRAM NX conversion

Post by Brucey »

RecumbentRide wrote:
I presume my existing 9spd hub will be compatible but I'd just like to make sure this assumption is correct. ...


I suspect maybe not. Here

https://bikerumor.com/2018/06/14/sram-nx-eagle-12-speed-mountain-bike-group-helps-beginners-spread-their-wings/
Image

it says that the cassette fits to 'a standard 10/11s freehub body' by which I think they mean (in Shimano terms) a freehub body which will accept a road 11s cassette. Shimano have been using 'standard' HG freehub bodies for 11s transmissions in two forms;

1) a slightly longer freehub body which is 11s only. This is about 2mm longer than a 10s freehub body and fits 11s 'road' cassettes. You can also use a 10s cassette with this body, using a spacer. These hubs have an even worse dish than 10s hubs and are available (from shimano) mainly in 130mm OLN form. Shimano 'road' stuff is almost completely standardised on this freehub body now; they only list one 'road' hub which doesn't have the 11s freehub body; even Tiagra 4700 now uses a hub with an 11s body, even thought it is still 10s. [However there are lots of third party hubs which are available with an 11s 'road' freehub body and 135mm oln.]

2) a 8/9/10 length freehub body with an 11s 'MTB' cassette. The 11s MTB cassettes have the large sprockets overhanging more to the left, so this 11s cassette can be short enough to fit to a 10s freehub body. These cassettes all have 36T or larger bottom sprockets and (nominally) won't work with 'road' 11s derailleurs.

In a partial volte face shimano have deigned to make just two 11s 'road' cassettes (both in 11-34T only) which have the shorter 10s compatible fitting length. Possibly they did this to allow an easy upgrade path for 10s users; they could go to 11s without buying new wheels.

In the past I've tried to fit a 11s SRAM PG-1130 cassette to a shimano MTB hub and IIRC it wouldn't fit; in shimano terms this cassette seems to be designed for the slightly longer 11s 'road length' freehub body. Maybe others have tried it and can say for sure but I would expect the 12s cassette to be the same.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Brucey
Posts: 44521
Joined: 4 Jan 2012, 6:25pm

Re: SRAM NX conversion

Post by Brucey »

I found this picture of a bike (with bigger wheels) using a GX 12s setup

Image

since the cage is pulled forwards in bottom gear the least ground clearance might be in second gear.

The 50T sprocket has a radius of 101mm (on the pitch circle) and an 11s GX mech (which has a shorter cage) hangs down about 130mm. I guess between guide pulley clearance and the extra length it adds up to about 30mm more, making ~260mm of 'dangle' from the hub centre. This doesn't leave much clearance to the ground if using a true 24" wheel.

Incidentally I'd spring the extra for a GX chain; it has a better hardening treatment on the pins and it isn't much more money.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
RecumbentRide
Posts: 234
Joined: 27 Jul 2012, 9:11pm

Re: SRAM NX conversion

Post by RecumbentRide »

Brucey wrote:I found this picture of a bike (with bigger wheels) using a GX 12s setup

Image

since the cage is pulled forwards in bottom gear the least ground clearance might be in second gear.

The 50T sprocket has a radius of 101mm (on the pitch circle) and an 11s GX mech (which has a shorter cage) hangs down about 130mm. I guess between guide pulley clearance and the extra length it adds up to about 30mm more, making ~260mm of 'dangle' from the hub centre. This doesn't leave much clearance to the ground if using a true 24" wheel.

Incidentally I'd spring the extra for a GX chain; it has a better hardening treatment on the pins and it isn't much more money.

cheers


I'm going to be optimistic and reckon the derailleur will probably be vertical on gears 3 or 4 so I might just get away with it :roll: , one other thing I've got fairly fat tyres which gives me a bit more clearance. Only one way to find out for sure :)
RecumbentRide
Posts: 234
Joined: 27 Jul 2012, 9:11pm

Re: SRAM NX conversion

Post by RecumbentRide »

Brucey wrote:
RecumbentRide wrote:
I presume my existing 9spd hub will be compatible but I'd just like to make sure this assumption is correct. ...


I suspect maybe not. Here

https://bikerumor.com/2018/06/14/sram-nx-eagle-12-speed-mountain-bike-group-helps-beginners-spread-their-wings/
Image

it says that the cassette fits to 'a standard 10/11s freehub body' by which I think they mean (in Shimano terms) a freehub body which will accept a road 11s cassette. Shimano have been using 'standard' HG freehub bodies for 11s transmissions in two forms;

1) a slightly longer freehub body which is 11s only. This is about 2mm longer than a 10s freehub body and fits 11s 'road' cassettes. You can also use a 10s cassette with this body, using a spacer. These hubs have an even worse dish than 10s hubs and are available (from shimano) mainly in 130mm OLN form. Shimano 'road' stuff is almost completely standardised on this freehub body now; they only list one 'road' hub which doesn't have the 11s freehub body; even Tiagra 4700 now uses a hub with an 11s body, even thought it is still 10s. [However there are lots of third party hubs which are available with an 11s 'road' freehub body and 135mm oln.]

2) a 8/9/10 length freehub body with an 11s 'MTB' cassette. The 11s MTB cassettes have the large sprockets overhanging more to the left, so this 11s cassette can be short enough to fit to a 10s freehub body. These cassettes all have 36T or larger bottom sprockets and (nominally) won't work with 'road' 11s derailleurs.

In a partial volte face shimano have deigned to make just two 11s 'road' cassettes (both in 11-34T only) which have the shorter 10s compatible fitting length. Possibly they did this to allow an easy upgrade path for 10s users; they could go to 11s without buying new wheels.

In the past I've tried to fit a 11s SRAM PG-1130 cassette to a shimano MTB hub and IIRC it wouldn't fit; in shimano terms this cassette seems to be designed for the slightly longer 11s 'road length' freehub body. Maybe others have tried it and can say for sure but I would expect the 12s cassette to be the same.

cheers



Well, done some further research and nearly everywhere is saying they are compatible on the MTB side but not for the road hubs. See here, here and here as one example. Fingers crossed :)
Brucey
Posts: 44521
Joined: 4 Jan 2012, 6:25pm

Re: SRAM NX conversion

Post by Brucey »

RecumbentRide wrote:
Well, done some further research and nearly everywhere is saying they are compatible on the MTB side but not for the road hubs. See here, here and here as one example. Fingers crossed :)


One of those links is the one that I linked to above and it clearly says 10/11s freehub body, not 8/9/10/11s body which would be correct for shimano 11s MTB hubs. Another is based upon the announcement of the parts only. The other one says 'the 11T only just engages with the freehub body splines'. When I tried a SRAM 11s MTB cassette it 'only just didn't engage' but it fitted fine on a 'road' body. I'd have got maybe one turn on the lockring with the MTB body, tops.... Anyway if MTB 'yes' and road 'no' that doesn't even make any sense, not from the POV of freehub body length; 11s shimano road hubs have a longer freehub body than 8/9/10/11s shimano MTB hubs, and as I mentioned I have failed to be able to fit even a SRAM 11s MTB cassette to a shimano MTB hub, because the freehub body simply wasn't long enough.

There is of course more to it than that; there is the matter of spoke clearance and this will be worse with a 130mm OLN hub than a 135mm OLN hub. Regarding spoke clearance you can compare an 11s cassette with a 12s one.

11s is 10 x 3.9mm = 39mm total RD throw

and

12s is 11 x ~3.6mm = ~39.6mm total RD throw

so from the POV of spoke clearance there isn't going to be much in it, even if the sprockets are the same size (which they are not). Anytime you have a larger big sprocket you get more clearance to the spokes for free, because of the angled spokes.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
RecumbentRide
Posts: 234
Joined: 27 Jul 2012, 9:11pm

Re: SRAM NX conversion

Post by RecumbentRide »

You are obviously far more technically adept than I. BUT I've not found anywhere which says a Shimano 8/9/10spd HG MTB freehub won't work / accept a SRAM NX 12spd cassette. But one thing that may be a spanner in the works is I've somehow assumed my hub is MTB so that's something I need to check and upgrade if necessary.
Some videos which I found helpful are here and here.

Regarding the spoke clearance that one went over my head a bit, sorry :(
Brucey
Posts: 44521
Joined: 4 Jan 2012, 6:25pm

Re: SRAM NX conversion

Post by Brucey »

in fairness the SunRace 12s cassette may not be exactly the same length as the SRAM NX one where it fits onto the freehub body either; here you have a fourth party's version of a third party part to fit a shimano hub. There's no published standards for the shimano HG spline or freehub body, so other people's versions of it are an approximation to it of one kind or another; I'm surprised there are not more problems with mismatches between different parts made by different people.

The only thing that gives me some hope that you are going to be able to fit this cassette onto an 8/9/10/MTB11 freehub body is a mention in one link that the SRAM NX 12 cassette 'needs a spacer' on an 11s freehub body. If so, this means it ought to be in with a chance of fitting on the slightly shorter freehub body with no spacer.

The width calculations are simply based on the pitch of the cassette x the intervals (n-1) . If you assume that the smallest sprocket is in about the same position at the RH end, the width calculation tells you how much further leftwards (or not) the largest sprocket is likely to be. Whether the RD hits the spokes or not depends on the RD, the spokes, and (because the spokes are angled from the vertical) how large the sprocket is.

FWIW if it doesn't fit there are some options e.g.

1) different freehub body
2) machining back the shoulder at the LH side of the freehub body (effectively making the splines a bit longer)
3) -which only applies to cassettes with an aluminium central carrier- you can shorten the central part of the cassette slightly.

I think the SRAM NX cassette can't be shortened as per c) but I'm not sure about the SunRace one.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
RecumbentRide
Posts: 234
Joined: 27 Jul 2012, 9:11pm

Re: SRAM NX conversion

Post by RecumbentRide »

Okay so I'm going to be running the SRAM NX 12spd setup and I'm looking for a single crankset that will allow me to swap in different chainrings which obviously need to be 12spd compatible. I'm hoping to start with a 46 tooth chainring which I believe will cover most bases i.e. single day rides & loaded touring. Though I'd still like the option to be able to use a slightly bigger or smaller toothed chainring if needs require. I've no idea where to start with this and I'm not looking to spend too much, somewhere in between budget and high end.

Alternatively (... and ideally) if there was some way I could use my current XT Hollowtech 2 crankset with just a 46T chainring (would need a 12spd compatible chainring of course, would I get away with an 11spd one) and remove the inner 2 chainrings and front derailleur. Would this be possible I wonder?
RecumbentRide
Posts: 234
Joined: 27 Jul 2012, 9:11pm

Re: SRAM NX conversion

Post by RecumbentRide »

Brucey wrote:in fairness the SunRace 12s cassette may not be exactly the same length as the SRAM NX one where it fits onto the freehub body either; here you have a fourth party's version of a third party part to fit a shimano hub. There's no published standards for the shimano HG spline or freehub body, so other people's versions of it are an approximation to it of one kind or another; I'm surprised there are not more problems with mismatches between different parts made by different people.

The only thing that gives me some hope that you are going to be able to fit this cassette onto an 8/9/10/MTB11 freehub body is a mention in one link that the SRAM NX 12 cassette 'needs a spacer' on an 11s freehub body. If so, this means it ought to be in with a chance of fitting on the slightly shorter freehub body with no spacer.

The width calculations are simply based on the pitch of the cassette x the intervals (n-1) . If you assume that the smallest sprocket is in about the same position at the RH end, the width calculation tells you how much further leftwards (or not) the largest sprocket is likely to be. Whether the RD hits the spokes or not depends on the RD, the spokes, and (because the spokes are angled from the vertical) how large the sprocket is.

FWIW if it doesn't fit there are some options e.g.

1) different freehub body
2) machining back the shoulder at the LH side of the freehub body (effectively making the splines a bit longer)
3) -which only applies to cassettes with an aluminium central carrier- you can shorten the central part of the cassette slightly.

I think the SRAM NX cassette can't be shortened as per c) but I'm not sure about the SunRace one.

cheers


Thank you for your detailed response. I'm confident at this stage it will work out fine as plenty of other folk seemed to have converted successfully who were in my position.
Brucey
Posts: 44521
Joined: 4 Jan 2012, 6:25pm

Re: SRAM NX conversion

Post by Brucey »

RecumbentRide wrote: .....Alternatively (... and ideally) if there was some way I could use my current XT Hollowtech 2 crankset with just a 46T chainring (would need a 12spd compatible chainring of course, would I get away with an 11spd one) and remove the inner 2 chainrings and front derailleur. Would this be possible I wonder?


there is no reason why you couldn't use a single chainring on your extant chainset. You don't say what your bike is but your username is a bit of a clue. On most recumbents the issues surrounding chainsets are different from other bikes. One of my criticisms of 1x transmissions is that the chainline is terrible; however it is often far less terrible on a recumbent, because the chain run from the last guide is usually a fair bit longer than the chainstay length on a standard bike.

The cheapest way forward is to use a single chainring (your extant big ring?) and to retain the FD as a fixed guide if you need to. So-called narrow-wide (NW) chainrings are designed for 1x use and have benefits on conventional bikes; it is not clear to me that you will get benefit on a recumbent in the same way. NW chainrings were pricey but they are becoming more of a commoditised item. Obviously you can only buy even-toothed NW chainrings and do note that the makers concentrate on the smaller sizes such as MTBers would want. 46T would be a 'very large' NW chainring. AFAICT 12s chains are a similar internal width to 11s chains, so 12s chain ought to run OK on a 10/11s chainring, or even a worn 9s one (suck it and see?). What it won't do, if 12s chain is slightly narrower, is derail easily from one chainring to another. Since you don't want that to happen, this ought not concern you unduly.

[ there is normally about 0.2mm difference between the internal width of a chain and the thickness of the teeth on a chainring. Some of this clearance is to allow for dirt (eg in MTBing) and some of it is there to allow the chain to derail from one chainring to another in a double or triple setup. The biggest single change in chain internal width occurred when 9s chain came out; many chain makers list this (and 10/11s models) as 11/128" chain rather than 3/32" chain. I've tried using 9s chain on much older chainrings and some shifts (notable the downshift from the middle ring of a triple) were dreadful. I''ve also reduced the width of a nominally 1/8" chainring until an 8s chain was a snug fit on it (for a 1x setup), and this (the chainring teeth were about about 2.2mm wide, far wider than most nominally 3/32" chainrings) caused the chain to become extremely resistant to falling off (in road use). Had it been a MTB things would have been different I am sure; any amount of dirt would have provoked chainsuck.]

Arguably on a recumbent with a 1x setup you don't need any lateral clearance worth speaking of; indeed if you can't get a NW chainring in the right size, you could try filing a 1/8" chainring or 3/32" SS chainring and using that perhaps.

If you have to change chainsets, I'd suggest buying whatever one which allows you to most easily buy the chainrings you want to use. However there is an additional point, which is that many recumbent riders prefer to use shorter cranks. Since not all cranks are available in short lengths and/or can be shortened, this may influence your choice.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
RecumbentRide
Posts: 234
Joined: 27 Jul 2012, 9:11pm

Re: SRAM NX conversion

Post by RecumbentRide »

Wow you are indeed a mine of information, thank you. I don't have the resources to file down existing chainrings. What I'll probably do is look for 10/11spd chainrings as you suggested. I have seen this mentioned elsewhere so believe it's indeed a solution.

Incidentally on a slightly different topic have you see the Archer DiX. Way too expensive for me but interesting and I guess should have seen it coming :)
RecumbentRide
Posts: 234
Joined: 27 Jul 2012, 9:11pm

Re: SRAM NX conversion

Post by RecumbentRide »

So-called narrow-wide (NW) chainrings are designed for 1x use and have benefits on conventional bikes; it is not clear to me that you will get benefit on a recumbent in the same way. NW chainrings were pricey but they are becoming more of a commoditised item. Obviously you can only buy even-toothed NW chainrings and do note that the makers concentrate on the smaller sizes such as MTBers would want. 46T would be a 'very large' NW chainring. AFAICT 12s chains are a similar internal width to 11s chains, so 12s chain ought to run OK on a 10/11s chainring,


Where I'm now having a problem and there isn't a lot of information out there is trying to source a chain wheel for my crankset Shimano XT FC-M771 to replace the 48 Tooth 9-Speed Chainring 104 BCD. I'm sure I've seen somewhere that my current 9spd crankset setup is compatible with the 10 and possibly 11spd but I'd rather not take the chance and I'd like to have a 11/12spd chainring on standby. You are so damn right about "that the makers concentrate on the smaller sizes such as MTBers would want" grrrrr!!
So if I'm correct I'm looking for a chainring that's compatible with Shimano Hollowtech 2 which is 46/48t 104 BCD and I'm not having much luck online. Can't believe how much time I'm spending on this arrghhh :cry:
RecumbentRide
Posts: 234
Joined: 27 Jul 2012, 9:11pm

Re: SRAM NX conversion

Post by RecumbentRide »

aha SJS cycles may just turn out to be my saviour they have an amazing selection as it turns out :lol: madly.
Brucey
Posts: 44521
Joined: 4 Jan 2012, 6:25pm

Re: SRAM NX conversion

Post by Brucey »

RecumbentRide wrote:Wow you are indeed a mine of information, thank you. I don't have the resources to file down existing chainrings. What I'll probably do is look for 10/11spd chainrings as you suggested. I have seen this mentioned elsewhere so believe it's indeed a solution.

I would try the 9s big ring in the first instance; it might work well enough for you to at least make a good decision about the size based on experience.

Incidentally on a slightly different topic have you see the Archer DiX. Way too expensive for me but interesting and I guess should have seen it coming :)


I hadn't seen the Archer D1x and I too guess that I should have seen it coming. It does rely on the mech being spring loaded though, hence they say it won't work with a Rohloff or a Pinion, not without 'serious hacks'.

Battery life seems a bit short; I wonder if they will offer a remote battery pack option?

I would guess that with a bit of development it ought to manage a front derailleur instead, but there are complications to be overcome; a modern RD is a much easier thing to control.

I wonder if an improved softare release might include an optional overshift function?

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Post Reply