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Converting 3X10 to 2x10 specific questions
Hey everyone
I'm about to convert from 3 x 10 to 2 x10 with bash ring and have some questions.
Currently have an SLX 24/32/42 crank set and want to go to a 26/38 set up as have check gear ratio charts and this combo should cover all my used ratios.
I can pick up the XT 38T and XT 26T chain rings designed for the 2X 10 cranks.
(38T - http://www.pushys.com.au/shimano-deore-xt-fc-m78...)
(26T - http://www.pushys.com.au/shimano-deore-xt-fc-m78...)
I was wondering has anyone used these chainrings for a conversion before or could recommend a more appropriate brand/store to get a set of 26T and 38T rings from?
My only concern is that the 38T ring appears to have the pin that goes under the crank arm, as it is designed to be an outer ring, will this interfere with a bashring? Is there a reason it cannot be ground off to make room for a bash ring if needs be?
For the bash ring was going to go with the hope bash ring (http://www.wiggle.com.au/hope-bash-guard/) as am confident it will fit, has anyone got any experience with this bash ring? Or could recommend a more appropriate one?
Thanks Chris
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A ring designed to be the outer position will not work well in the middle position ring on a three ring spider. Get a ring that is made for the middle (inside) position. It has that pin to stop the chain jamming between the crank and the ring, so it is an outer ring. SRAM have 38T as they are standard on some Specialized bikes - would suggest you go to your LBS and tell them what you want and get them to order one if they don't have one.
HTH. FWIW.
Don't worry O&S, Chris seems to know what he's doing. The M785 38T ring is designed for a double specific crank, so it does sit in the middle position, and has a pin like a conventional outer ring.
And, to answer the original question, I just checked my XT785 38T ring with a Raceface alloy bash similar to that Hope one, and yes the pin does interfere with the bash. However, it should be relatively easy to drill the pin out from the inner side.
By the way Chris, you know they offer the M785 rings in a 38/24 combination now as well (its the AD version as opposed to the AK you've linked to above) - good for 29ers...
And at the risk of being called unpatriotic, you could pick up those rings a bit cheaper from one of the European online shops, tho' if that's all you're getting, postage might mean there's little in it at the end of the day.
You could also use I think it's Blackspire chainrings, they make a massively wide variety of teeth options and will have the correct rings.
Though I've got nothing against third party chainrings like Blackspire, in this particular application I'm not sure they'd be the best choice. When running a wide ratio double like the OP is planning, the gap of 12/14T between the rings is bigger than the typical 8/10T gap between rings on a triple.
Double specific chainrings are designed to overcome this, and still give reasonably smooth shifting, by having multi-level ramps and pins that extend all the way down to the small ring, to help the chain up that massive gap. Triple chainrings have smaller ramps, and some generic rings don't have ramps at all because they are used in a variety of situations including as single rings.
Take a look at the engineering that's gone into the inside of my M785 38T ring below to see what I mean...
So, I think the best chance of the OP getting smooth shifting is to stick to a matched pair of double specific chainrings like the M785 he's planning to use (and a double specific FD, but I'm assuming he's already thought of that?)
FWIW, I ditched my xt 10s 38/26 rings when worn out, and replaced with slx 9 sp 24 and a Blackspire 36. When i changed i didnt really notice any shifting difference at all, and 36/11 is good for 45kmh on a 29er which is beyond what i will ever need.
the blackspires will also last twice as long as xt rings. I dont mind replacing grannys along with cassettes, i am not so keen on replacing a $70 chainring each time I need to do a cassette though......
Thanks for the info everyone.
I had not really thought about a new FD as thought that most could handle a 12T difference. If I get a new FD do I need to change the shifters as well?
Chris
In my experience a triple FD will work fine in a double application, just wind in the 'H' limit screw on the mech so you don't accidentally try and shift up to the non-existent big ring. However, on both my triple to double conversions I eventually replaced the FDs with double specific ones, more to do with looks than any shifting issues, as the double FDs have a smaller cage which tucks in much more neatly. Some claim the smaller cage also helps with chain retention over rough stuff, and better shifting, but I've not had that experience. And yes, the triple shifters will work fine with a double FD, and newer ones even have a 'mode' switch to change between 2x and 3x operation. In fact, you can't buy a double specific Shimano shifter!
I've been following this thread with interest as I probably only need a 2x10 setup. What I don't understand is the benifit of getting rid of a chain ring. By the time you've put a bash guard on, there would be negligable weight saving. Am I missing something?
Good question! And I can only tell you why I went down that route, as others may have different reasons.
For me it wasn't about weight saving, and in fact as you point out, you still have a front shifter, mech, and a bash in place of the big ring, so you haven't saved any weight!
It was more that I realised I hardly ever used the big ring on my MTB, but did frequently catch it on rocks, logs, and had a couple of nice chainring shaped scars on my calves due to carrying around a spinning saw blade with me! So I checked the gear charts and realised that by replacing the big ring with a bash, and increasing the size of the middle by a few teeth, I'd still have all the gears I needed but have more clearance over obstacles, protection for my drivetrain, less chance of lacerating my leg, and a overall a more simple setup.
It seemed to work pretty well and I didn't notice any real downsides, and so I converted my other bike to the same. When I bought a new Anthem 29er late last year I was pleased to see it already came set up as a 2x10, but without the bash, but that didn't matter as its my XC race bike - and a bash doesn't look cool on a race bike
Pete. Personally I realized that the ONLY reason I ever used my granny ring was because it was available. As soon as I removed it, I just mentally muscled up and pushed harder. (Camelbak climb at Awaba is fine)
I've gone down the 1x9 setup because it just simplifies things. I can run between 8-35km/hr quite easily and up to 40km/hr at a stretch for short bursts.
Now this will not suit everyone. I certainly didn't do it because of weight savings. Saving weight was a slight advantage, but I didn't notice any difference. What I did notice was the 'mental simplicity' of it all! To take this line of thinking any further would have me running SS. Which I'm thinking of trying.
The only downside of 1x9 is when I'm riding on the road downhill and spinning out. Not on the trails.
2009 XTR front shifter & mech anyone? (M970 I think?)
it's about chainline and being able to use the whole cassette with either front rings,
a triple has two problems with using the whole cassette, chainline and chain length.
when you convert from 3 to 2 rings then you solve the chain length issue, you may not solve the chainline problem if you don't use a specific double ring crankset.
some cranksets just work, others are a real PITA to get right for smooth consistent shifting for all gear combos.
You can use spacers, but it may involve some additional thinking, measuring and swearing.
I run slx 3x10 cranks as a 2x10 with bashie I am running 36/28 basicly I just removed the outter ring and locked out the the front mech.
Hey obmal
I was wondering about improving the chainline. I have a giant with the BB71 pressfit bottom bracket and it did not come with any spacers so I cannot rearrange the spacers to improve the chainline. I would only have to move the drive side crank out a mm or so to improve the chainline do you think it is worth getting some spacers and giving it a go?
Chris
Hi Chris,
Sorry, I know you didn't aim that question at me, but there's a lot of confusion out there about chainline, so I thought I'd chip in - feel free to ignore as you wish...
Short answer to your question is - you shouldn't need to change your chainline at all.
Long answer (switch off now if you're not interested in the boring details of chainline
) is ...
The rear chainline (distance from bike centreline to mid-point of your rear cluster) of today's typical MTB with a 135mm rear dropout spacing and ten speed cluster is 47.5mm. Therefore for a 'perfect' chainline with the middle of the cranks lined up with the middle of the rear cassette you'd need a chainline on your cranks of 47.5 too. So how come most modern triple cranksets (including the SLX you've got) have a chainline of 50mm then?
Well its a compromise, and due to a number of factors that push those cranks further outboard than ideal. One is the oversized tubes of MTB frames pushing the front mech out. Another is making room for the outboard bearings of today's bottom bracket designs. And a third is so the chainwheels can clear the chainstays on a wide variety of different frame designs. Out of interest, road bikes usually have closer to the 'ideal' chainline, as they don't have these issues.
Luckily, most bikes not having an 'ideal' chain line isn't too much of an issue, for two reasons. First, the 'ideal' chainline is only really achieved on a single speed or hub geared bike. On a derailleur equipped bike, you'll always be cross-chaining to a lesser or greater extent, depending on what gear you're in. Secondly, the worst issues only arise when using the big chainwheel with the large sprockets, and most of us have learnt not to do this.
Now, to your situation - when you take the big ring off a triple with a 50mm chainline, your front chainline is now the mid point between the old middle and inner rings, so is 2.5mm further in - which is magically - ta da! ... 47.5mm - the perfect chainline! Which incidentally, is why you should be able to use all your rear sprockets with either chainwheel on a double, without any rubbing issues.
So when you convert a triple to a double you've actually improved the chainline, so shouldn't do anything with spacers and the like to change it! Unless... by increasing the size of the middle from 32 to 38 it now won't clear your chainstays, in which case you'll need to space the cranks out until it does. But, just so we're clear, this would be for clearance, and actually makes the chainline worse, not better.
Incidentally, purpose built doubles like the Shimano XT have a chainline of 48.8mm. Again, a compromise as they need to have clearance for a variety of different frames, but only 1.3mm out from that 'perfect' chainline, so not so bad.
Hope that helps...
Thanks Mamil
That makes total sense from what I had been reading on other forums about people converting 3x10 to 2x10 and not having any issue using the whole rear cluster.
Also thanks for the heads up about checking clearance on the chainstay.
Chris
No problem!
By the way, if you did decide to tweak the chainline, I believe the Giants BB shell is 89.5mm, so there's a 2.5mm spacer on the drive side and nothing on the non-drive side to make it up to the standard 92mm width for a BB92 press-fit. So you could ditch the supplied spacer and play around with some 1mm and 0.5mm ones, so long as you kept the total width close to 92mm so the left crank seats properly on the splines. But I think the other issue is that you'd probably destroy the BB cups getting them out - they're only plastic
On the clearance issue - what model bike do you have? I have a 26" Trance and 29er Anthem, and they are both fine with a 38T in the middle position, and in fact could probably take a 40T.
I have recently done the swap from 3x10 to 2x10 ... i did it as never used granny and with the dyna sys 36 at the rear with a 27 front you are able to get up most things .... having said that i can get up all at Kalamunda in big ring (36 teeth) ....
i have still got a 3x10 FD on ... i was thinking that it is the front 780 shifter that only needed to be change (i actually just tweaked the 3x10 shifter to lock out gears), how would a 2x10 derailleur be any different to a 3x10???
I recently changed to 2x10 from 3x9. I left the 3 speed Sram X0 front derailleur on because I didn't think there would be that much difference from one front derailleur to another but the chain was always dropping off the chainrings. I put on a X0 2 speed front derailleur and I haven't had a dropped chain since. The 2 speed one is 2mm narrower than the three speed one. I was skeptical going from 3x9 to 2x10 as I figured 10 cogs would only make things worse, but it works great and I wish I had of done it earlier.