So on my recent Wales C2C on my loaded Niner with a Rotor 46/30 and 11/42 cassette I found myself running out of gears, especially on the 20% gradient climbs. My one pet hate is having to grind up a climb at 50 RPM as I find it fatigues the legs. On my MTB I run a 34/24 and a 11/42 and that enables me to keep the legs spinning at a high cadence even on the really steep stuff.
I actually looked at how many times I made use of the 11/46 combo whilst cycling and concluding it was maybe used a handful of times on steep descents. Seems really pointless to me to have those gears as they just don't get used when riding a loaded bike.
So what I want to know is whether there is anyway of being able to run an MTB 36/26 c/set on my Niner RLT Steel and if so what would I need to do to get it to work with the Ultegra shifters.
I had an XT triple for a little while on my Vaya. The problem isn't with the shifters, but getting the bottom bracket and crank axle lengths correct - I had to put a spacer on the axle to make it work. IME the front mech ratio is close enough/the same between mtb and road, unlike the back end. I used an XT front mech, which you should be able to pick up very cheap these days (I have a few knocking about if you need). A road front mech might not like the smaller rings.
The problem isn’t with the shifters, but getting the bottom bracket and crank axle lengths correct
That was my thought as the spindle length is longer on the MTB than the Road?
Would it be possible just to change the chainrings?
Would it be possible just to change the chainrings?
46/30 is the lowest ratio that you can get.
I had a XT crankset with 36/20 front and 11-36 on my Reilly Gradient for Torino-Nice worked perfectly and could still hold 18-19 mph on the flat.
Don't worry about axle length, BB shell on frame is same whether road/ gravel/ MTB, wither 68 or 73mm, so if you run MTB cranks, you just need MTB bottom bracket.
and could still hold 18-19 mph on the flat.
That's my point. Much better to have the gears for the hills instead of the flats and descents.
Don’t worry about axle length, BB shell on frame is same whether road/ gravel/ MTB, wither 68 or 73mm, so if you run MTB cranks, you just need MTB bottom bracket.
So basically replace the current road BB in the frame with an MTB one and then I will be able to fit the XT chainset?
@scud I appreciate you have done this, but when i had a Ridgeback road tourer, it came with a mtb chainset and that had a approx 10mm spacer on the DS to take ip the extra width of the chainset axle. I cant remember what BB it had im afraid, so it may be the road/mtb difference.
Regards
Ian
The BB shell width doesn't change - probably 68mm, so you just need an XT BB (as Scud says) and use the correct amount of spacers as normal.
Going the other way is where you might run into problems (i.e. fitting your Rotor chainset to an mtb) as narrower Q factor may interfere with chainstays.
Ok, i understand now. I had thought the only difference between a road and a mtb HT2 BB was the amount of thread in each cup, not the actual amount of cup that was proud of the shell.
Thanks for bringing me up to speed
Ian
I thought fitting the chainset was the easy part. Getting a way to shift it is where it gets tricky. Either the mtb mech doesn't play with the road shifter, or the road front mech won't swing out far enough forthe mtb big ring
I use 26-38 or 30-42 MTB doubles on my gravel bike, have done for years. They've pretty much stopped making anything in that range now.
One day Shimano and SRAM might wake up to the fact that gravel bikes are not all for racing 200 miles in Kansas. I had fairly regular opportunities to talk to Shimano about this from ~2008/2009 onwards (Croix de Fer V1 on 50-34, always was daft really) but now I think they simply don't get it, they don't seem to be able to grasp how to market anything that isn't racing derived. Ramble over.
Middleburn and Sugino options are worth looking up.
I thought fitting the chainset was the easy part. Getting a way to shift it is where it gets tricky. Either the mtb mech doesn’t play with the road shifter, or the road front mech won’t swing out far enough forthe mtb big ring
Bar end shifters solve that. Not everyone likes them but if your bars aren't roadie low so you can stay in the drops most of the time and the bars have some flare, they work well. tbh I prefer them over Shimano STIs these days.
Middleburn and Sugino options are worth looking up.
Middleburn Duo is practically perfect for this. Unfortunately, also very expensive!
Middleburn Duo is practically perfect for this. Unfortunately, also very expensive!
Expensive, but not a part you wear out either. The Incy Spider they made was also really good.
Got to agree with @jameso Currently on a 3x9 on the gravel bike and hardly ever use the big ring.
Crunching the numbers for GRX double and it looks like I'd be forever switching chain rings.
One of the other tricks is the 105 triple with the outer ring removed, replaced with a chainguard or maybe some 3D printed tab covers like XTR M985s had. See a few audxers using those.
Easier to get the same ratios from Sugino RD2 chainsets that Spa Cycles sell - loads of choice.
https://www.spacycles.co.uk/m8b0s109p0/Drivetrain/Chainsets
I have a 34-48 on my road bike and though it's a lugged steel frame and fork with a bit of flex, the chainset feels fine on it. I don't miss the HT2 stiffness at all. Might be different if fitted to a really stiff carbon bike with stiff wheels. Bonus is BBs last forever unlike HT2.
I run an xt touring triple on a Kona rove Al
I needed to move the 2.5mm spacer from nds to D's to get alignment right for front mech
Other than much more usable bike
I am still not understanding whether I can fit a 2 * 11 speed XT chainset to the 68mm PF46 frame. I know I can get a hope PF46 BB for a 68mm shell, but the
states that it gives you an assembled width of 91mm which according to the spec foot notes is a road c/set spindle length.
But if I then look at the Shimano Shimano Spec it seems to state 89.5mm, 92mm is MTB.
SO it is all rather confusing.
Another thing to consider is if you can get the front mech low enough for the smaller chainring size. I was considering sticking a mtb chainset on my gravel bike but the front mech is already about as low as it will go so I'm stuck.
Looking at it from the other end: what about a 46 or 50 cassette?
But yea, the big S are missing out on decent doubles.
Another thing to consider is if you can get the front mech low enough for the smaller chainring size. I was considering sticking a mtb chainset on my gravel bike but the front mech is already about as low as it will go so I’m stuck.
I have enough downtube and can drop the mech 25mm, but I have decided to take a gamble and have bought an XT 36/26 c/set, new BB and a XT front mech. I bought the mech as the Ultegra one I have will obviously be curved for road size rings so not sure it would work with an MTB chainset.
PF46 Spec
states that it gives you an assembled width of 91mm which according to the spec foot notes is a road c/set spindle length.
But if I then look at the Shimano Shimano Spec it seems to state 89.5mm, 92mm is MTB
92mm is for Shimano asymmetric PF with a 41mm ID BB shell - different to PF46 BB shells.
Shimano PF41 std symmetric BB is 89.5mm or 104mm, with a 2.5mm spacer on the DS.
The 91mm dimension for PF46 you linked to is across the outside of the cups. Measured across the cups Shimano std PF or HT2 is 96mm - that's the dimension you need for a Shimano non-boost MTB chainset.
There's a 96.5mm wide BB for 24mm axle in that PF46 pdf - but it's for 73mm BB. For an MTB crank in a 68mm shell it would have to accommodate 3 spacers. I doubt it will as that reduces the depth the cups are pressed in.
Shimano BB shell spec is +/- 0.5mm tolerance so 96.5mm is ok if your BB is 68mm or a tad under.
Do Hope have a PF46 for 68mm shell that gives a 96mm outside width total?
Both the Wheels Manufacturing and Hope BBs will give you an outer face measurement of 90.5mm and 91mm respectively with a 68mm shell. Basically it is 5.5mm out, so can I just use spaces on the crank axle to effectively widen the c/set and provide the correct chainline?
Wheels Mfgt do provide a kit which enables you to pack out the bearing cups from the frame
but as you mention, this will reduce the amount the cups are then pressed into the frame.
I run a 26 36 chainset on my gravel bike. I use a spa cycles subcompact which is around £90 with bottom bracket. This is that chain line, works with my Tiagra front much but needs a threaded bottom bracket.
Basically it is 5.5mm out, so can I just use spaces on the crank axle to effectively widen the c/set and provide the correct chainline?
I don't know tbh. I think the Hope and Wheels Mfg BBs you mention must be for road PF? If you added spacers to the MTB axle the bearings may not be sitting on the right part of the axle, could end up with some play / poor fit.
Might be better to ask if the Hope or Wheels Mfg BB cups are compatible with 2.5mm spacers each side?
A shimano HT 2 axle is uniform along its length Id and od
I'd have no issues spacing the axle.
I would be very reluctant to space out a press fit
A shimano HT 2 axle is uniform along its length Id and od
It's 24.0mm at the bearing fit point but 23.8mm in the centre section - whether that matters I'm not sure, depends on how the PF46 BB and spacers line up bearings and axle.
I would be very reluctant to space out a press fit
Same here if the cups weren't deep enough to account for it. I don't know what BB shell ream depth is compared to average cup depth or the Wheel Mfg cups.
It’s 24.0mm at the bearing fit point but 23.8mm
Not on the ones im looking at but may be older models.
It’s 24.0mm at the bearing fit point but 23.8mm in the centre section – whether that matters I’m not sure, depends on how the PF46 BB and spacers line up bearings and axle.
That's a very good point. All I can do is see where the bearing point is on the c/set axle as otherwise like you say the bearings will not run on the bearing part of the c/set axle.
Might be better to ask if the Hope or Wheels Mfg BB cups are compatible with 2.5mm spacers each side?
Wheels mfg do sell the spacers that sit between the cups and the frame specifically for a Specialized frame that has a 61mm shell. I pinged them an email to get their thoughts.
10s XT double and 11s road have that 0.2mm difference but 11 or 12S MTB may have changed. If so that should mean spacing them out is ok at least as far as axle-bearing location.
11 or 12S MTB may have changed. If so that should mean spacing them out is ok at least as far as axle-bearing location.
Ok. The c/set is 12 speed so I will check it with a vernier gauge.
It did also get me thinking that as the frame is a PF30 it could be possible to get it converted to T47 and then you can run a threaded BB and space out like Shimano do with their threaded BBs
I just wanted to post an update on this in case others were considering it. I had no issues at all getting this to work. I fitted a Shimano SLX 36/26 c/set and used a band clamp SLX front mech. I fitted a Wheels Manufacturing 68mm BB shell and then used spacers on the 24mm axle to get the chainline correct.
Shifting works perfectly and if I am honest it works better than the old Rotor 46/36 c/set I had on there before.