SUN xcd and TA 5 vis crank differences

[Xavier Alexandre]

Last year I broke a TA 5 vis right crank arm at the pedal eyelet. I did read that the SUN xcd crank was a suitable replacement so I did order it. I finally came around to replace the old TA crank. The new SUN xcd crank sit 5-7mm outward of the previous crank. Resulting in a wider chainline than previously. Is the SUN xcd crank known to have a different geometry than the TA 5 vis? I guess I should get a shorter bottom bracket to accommodate the SUN xcd? Or could I have made a mistake somewhere in the process?

My next step is to disassemble the crankset again to compare the two crank arms side to side but I did tighten the crank so hard in the hope of closing the chainline gap on the BB that I wasn't able to remove it yet :D

[Justin, Oakland]

I don’t think anyone has ever posited them to be drop in replacements. I would read the manual for the SunXCD and see what BB length they recommend and order appropriately.

-J

[Xavier Alexandre]

That’s indeed what I naively assumed. I did not realize I might have to change my BB. I will order a new one.

Thanks!

[Brad]

You may be dealing with subtle differences in the length of the taper.

  The first thing I would measure is the thickness of the forging close to the taper. 

If the forging is the same thickness then I would start looking at the bottom bracket axle.

You may need to switch out the TA axle for a SUN axle, or vis versa. 

I may be remembering wrong, but I think the TA axles were closer to the Campagnolo spec than to the Stronglight spec, or was that Nervar?

[Igor Belopolsky]

The sunxcd, despite the re-enactment looks, is build for a modern drivetrain, like the velo orange cranks. It’s not a direct copy.

[Xavier Alexandre]

If I change the BB for the recommended one (68/113mm, didn’t check the taper yet, also have to check which thread I have) I guess I should be good and get the classic 43,5 chainline? What would be the difference of a ‘modern drivetrain’?

[Ken Freeman]

I would say, do some measurements before you buy, even if it is from Sun.  I would first remove your crank arms and measure the shell width, the  bb spindle length and the drive side stub length from the drive side edge of the shell.  This last is critical because it alone controls your chainline in the front.  Also measure the corresponding left hand stub length.  Write this all down and check it against your Sun drawing.  I notice it is missing the full set of BB specs.

Then reinstall the crank arms and torque them with a torque wrench so they are equal.  I have a default value I use, but I need to verify it before handing out wrong advice.  Once they are installed and tightened evenly, measure chainline and gently torn the cranks.  We’re looking for whether either of the crank arms is hitting the frame, and if any part of the chainring set or its bolts is hitting the frame.  If the chainline is correct and something is hitting the frame, either the frame has a problem or the Sun is not compatible with your frame.  Both are odd situations, but possible.  

If these “safety checks” all passed, go ahead and measure the left and right Q values and record.  Add them together and recordthat as well.

On Thursday, November 29, 2018, Xavier Alexandre <cuo...@gmail.com> wrote:

If I change the BB for the recommended one (68/113mm, didn’t check the taper yet, also have to check which thread I have) I guess I should be good and get the classic 43,5 chainline? What would be the difference of a ‘modern drivetrain’?

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Ken Freeman
Ann Arbor, MI USA

[Xavier Alexandre]

Thanks! I'm new to this, so all those tips are precious to me. I was naïvely hoping to put this bike back on the road just by switching my broken TA crank arm with the Sun one. I will indeed remove the crank arms again and do those measurements, hopefully tonight if I manage to put the kids to sleep early enough :)

[Brad]

Ken has a very important point.   The people or machines that assemble cartridge bottom brackets make mistakes.   Sometimes what it says on the box isn't what was in the box.    Assymetical spindles sometimes show up where they aren't supposed to be, longer, shorter, etc.  

[Xavier Alexandre]

I was finally able to take some measures:

• BB shell: 68mm
• BB spindle length: 116mm
• Side stub length from edge of the shell, drive side and non drive side: 24mm
  
• Spacer on the drive side: 2.5mm

I also looked at a few differences between the Sun xcd crank arm and the TA 5 Vis one. The external shapes near the rotor are quite close but the internal shape are indeed quite different. In particular the 'hole' start a few mm deeper on the TA. Also the hole is .2mm narrower on the Sun XCD one. Those two things explain the chainline difference with the same BB. Also the Q factor is gonna be around 12-15mm wider with the same chainline due to the difference in the arm shape.

I will indeed need to change the Bottom Bracket. The Sun diagram above recommend a 113mm one but I might be tempted to try a 110mm one first as I had a bigger than 1.5mm difference with my previous chainline on the 116mm BB.

[Ken Freeman]

Good job, that tends to explain the excessive Q! 

Well, what's the difference in arm height above the table between the TA and the Sun?  That difference is the amount you would need to shorten the BB spindle on each side.  You are limited in how low the Q can ultimately be, by the chainring distance from the center plane, but also by the clearance from the end of the crank arm to the chainstay.  I am comfortable with as little as 5 mm.

That said, I generally don't compromise the chainline measurement unless there is a really strong reason.  While many of agree on loving low Q, it's not a strong enough reason.  And if your width comparison is evidence, your actual TA Q should have been around 141 mm.  146 mm is wider, true, but still pretty darn narrow.

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[Ken Freeman]

From this point on, there might be some trial and error ... 

[Xavier Alexandre]

I will target a normal chainline between 43 and 44 mm and the Q factor is gonna be what is gonna be. I don't have strong opinions on the ideal Q factor for me and as you mentioned it is gonna be on the low side anyway. I will switch from a FSA Bottom Bracket to a Shimano UN55 so trials are gonna be less expensive than with FSA.

[satanas]

Bear in mind that the 110mm Shimano UNxx BBs are 3mm longer on the LHS - they are asymmetrical, unlike 107, 113, 115 & 118mm. The RHS of a 107 UN55 is the same as a 107, while the LHS is the same as a 113; chainline will be the same with 107 and 110, but the LH crank will stick out more with 110. Most 110mm cartridge BBs are like this as people seem to have mostly copied Shimano. :-(

Later,
Stephen

[Xavier Alexandre]

I had of course no idea. This is super confusing. I will need some time to wrap my head around this since I was indeed planning to buy an UN55 110.

Thanks for the heads up.

[Stephen Poole]

If you use a 1.5mm spacer behind the RH cup, a 110mm UN55 can be made to be symmetrical; why Shimano make them longer on the LHS is beyond my comprehension. (122.5 & 127.5 are also asymmetrical, but longer on the RHS, which makes more sense with older triple cranks.)

Later,

Stephen (who usually likes 107mm better)

On Sat, 1 Dec. 2018, 00:59 Xavier Alexandre, <cuo...@gmail.com> wrote:

I had of course no idea. This is super confusing. I will need some time to wrap my head around this since I was indeed planning to buy an UN55 110.

Thanks for the heads up.

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[Kieran J]

I did not know this! Very odd.

KJ

[Alex Wetmore]

0.2mm difference in square taper size is the difference between two almost but not quite interchangeable square taper standards.  Check Sheldon Brown's website for the details, but it's something to be aware of when buying a new BB.

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From: 65...@googlegroups.com <65...@googlegroups.com> on behalf of Xavier Alexandre <cuo...@gmail.com>
Sent: Friday, November 30, 2018 4:43:27 AM
To: 650b
Subject: Re: [650B] SUN xcd and TA 5 vis crank differences

 

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[Xavier Alexandre]

My LBS had a Shimano UN26 in 110mm. As mentioned above, it is indeed asymmetric. Thanks for warning me, I would have been very confused otherwise. I did measure 20.8mm from the shell to the right spindle and 22.5mm to the left. And yes, I did measure a totale spindle to spindle length of 111.3 instead of 110.

A slight issue I had is that without any spacer there would remain a gap on the left, so the minimum shell size is more 70mm without any spacer. Without any spacer, the big chainring was too close (1mm gap) to the chainstay anyway so I did add to the right the 2.5mm spacer I had from the previous setup.

With this 110mm BB and the 2.5mm spacer I got the same chainline as previously with the same ~3/4mm gap from the big ring to the chain stay and with the same front derailleur setting. I took the opportunity to measure it though, and it seems my chainline, as set now and as set previously, was in fact around 41.5mm. It was running fine previously so I think I will let it like that for the moment.

If I manage to put the children I will try a quick test ride. Thanks for the help!

Xavier

Left gap remaining on the left with the UN26 without any spacer

Chainring to chainstay gap without any spacer

Measuring the chainline

Measuring the chainline is a pain

[Yellowsheep]

T.A. pro vis uses an ISO taper bottom bracket spindle and the Sun xcd uses a JIS taper bottom bracket spindle.  ISO and JIS are NOT the same.  Using crank arms for a different spindle taper will result in different chainline measurements:

https://www.sheldonbrown.com/bbtaper.html

[Brad]

The angle is the same on JIS and ISO square tapers, the length of the taper is different.  

The major differences in "antient" times between Campagnolo, Stronglight and TA cranks was in the extractor thread [J.A. Stein is your go to].   Nervar used the same thread as Campagnolo and Sugino Mighty imitated Campagnolo.  

[Yellowsheep]

Yes angle is the same but length is different so chainline is effected.  The important thing to identify is what taper a crankset is.  For example, TA cranks made prior to late 80's was JIS taper (which is older French taper).  TA stopped producing cranks for a while so when they began making cranks again, they retooled their machinery and made cranks with ISO taper.  So TA crank vintage will determine it's taper and the necessary BB taper.  That said, mixing crank taper and bb taper is not a problem as long as you adjust for the chainline differences as per Sheldon Browns article above.

[Yellowsheep]

Correction from above:   "Yes angle is the same but length is different so chainline is effected"....should read "  Yes angle is the same but thickness is different so chainline is effected". 

[Stephen Poole]

On Fri, 13 May 2022, 02:12 Yellowsheep, <yellow...@gmail.com> wrote:

 ...That said, mixing crank taper and bb taper is not a problem as long as you adjust for the chainline differences as per Sheldon Browns article above.

^ Whilst this is usually true there are some combinations that do not work. For instance, M737 XT cranks (JIS) will bottom out on Dura-Ace 7410 "JIS short taper" BBs; the shoulders at the ends of the tapers indent the inside edges of the crank arms. And at least some Phil Wood JIS BBs have had rather large tapers, so Campag/ISO taper cranks may not go on as far as one might like.

Proceed with caution...

Later,

Stephen

[Eric Hounshell]

Stephen, interesting what you say about Shimano BB asymmetries. I have tried to find this info systematically presented but failed. Do you have a good source that I can save for reference?

-Eric

[Joel S]

I would like to know more as I am considering a double with XCD arms and TA rings.  It is one of the few ways I can get the compact doubl3 I want, 40 or 42/28.  

On Tuesday, May 10, 2022 at 6:31:56 AM UTC-4 Brad wrote:

[Joel S]

   I have a TA Zephyr which has straight arms.  I also have a Sugino which flares quite a bit outward.  I am considering the XCD with TA 5 vis rings.  I am wondering about  the Sun XCD and if it  has a straight arms? I have decided on a double which they recommend a 113 BB.  

[Stephen Poole]

Re UNxx BBs: I do not have an academic citation available for lengths, sorry. What I said was based on past experience but since most of these BBs are now obsolete and unavailable I don't have samples to measure. It's also IMHO not worth getting bent out of shape about fractions of a mm of difference, something people have done here in the past; it only has to be close enough to work(!), and one can always use spacers to move things laterally.

Arm shape/thickness/bend matters in two ways:

1. It will affect Q factor

2. It might affect FD clearance to the inside of the crank arm; old TA and Stronglight 49D cranks were notorious for lacking this

40x28 or similar is easily achievable with 50.4BCD cranks, but also with other cranks that have or will accept subcompact spiders like 110/74 (Sugino OX series, Dixna La), 110/58 (Middleburn with Incy spider), 104/64 (many MTB cranks and some modern road cranks), Rene Herse, etc. Most subcompact cranks however don't come with rings smaller than 46x30, even if smaller ones might fit. Double MTB cranks - a critically endangered species - will often accommodate much smaller rings, but at the expense of a much higher Q factor, typically 168mm+ for current cranks. It's not easy to get MTB sized rings and a road Q factor.  :-(

Later,

Stephen

[John Hawrylak]

Joel

You might want to look at the Sugino TD-2 with pantograhed TA rings at Spa Cycles in UK.   50-28 available with a 153mm Q for about $145 shipped to USA

SPA CYCLES TD-2 Touring Double Chainset with custom TA chainrings | £100.00 | Drivetrain | Chainsets | Spa Cycles

You trade off some Q for $$ vs a Rene Herse crank (143 Q)

John Hawrylak

Woodstown NJ

[Stephen Poole]

The TD-2 cranks have 110BCD; this is stated clearly in Spa's description. A 28T inner ring is not possible with a 110BCD crank unless it has a smaller bolt circle for a triple inner...

* The smallest normal ring that will fit is thus 33T, available from TA

* Praxis Works make 48x32 sets that fit 110BCD cranks but require the ends of the spider arms to be relieved for the chain to clear

* BikinGreen sell 48x31 and 46x30 sets for either normal 5 bolt or Shimano 4 bolt 110BCD cranks, but they work by using smaller diameter bolts and offsetting the teeth inwards to gain chain clearance at the spider; they're usually available on eBay

It's also worth bearing in mind that the commonly recommended (and cheap) Stronglight Impact aka Sugino XD cranks typically have a Q of 160+mm, versus ~140 for Dixna, ~142 for RH (depending on the spindle chosen), 145 for OX, 151 for GRX, etc.

Later,

Stephen

[Eric Hounshell]

Is a Stronglight Impact the exact same crank as a Sugino XD? I would love to have a spreadsheet of all the crankset truths.

[Stephen Poole]

On Tue, 17 May 2022, 21:09 Eric Hounshell, <ehoun...@gmail.com> wrote:

Is a Stronglight Impact the exact same crank as a Sugino XD?

^ So many people have claimed in the past. Photos seem to prove it.

Later,

Stephen

[ThermionicScott]

I've bookmarked the Wayback Machine's copy of an old Harris Cyclery blog post where they measured a bunch of UN54s.  You can work out the amount of asymmetry with some simple math:  http://web.archive.org/web/20101022002409/http://blog.harriscyclery.com/relative-chainline-bottom-brackets/

- Scott in Cedar Rapids

[Mitchell Gass]

On Tuesday, May 17, 2022 at 4:09:17 AM UTC-7  Eric Hounshell <ehoun...@gmail.com> asked:

Is a Stronglight Impact the exact same crank as a Sugino XD?

The XD has a hidden chainring mounting bolt behind the crankarm, and the Impacts I've seen do not. I prefer the latter, because it's easier to install chainrings (the hidden bolts are fiddly), and there's a wider selection of replacement outer chainrings where the anti-chain-dropping pin is in the right place.

Mitchell Gass

Berkeley CA USA

[njh...@gmail.com]

Spa Cycles sell their own badge-engineered version of both the Sugino Alpina2 and XD2 cranks at a really good price (STG30 for the crankarms without chainrings). I have both the genuine Sugino and Spa cranks, and they're the same forging, the only difference being that the Spa item doesn't have the Sugino crown stamped into the back of the arm near the pedal thread.

If you want a low Q crank for small chainrings with a wide choice of chainrings available, the Sugino OX 110/74 crank has a claimed Q-factor of 145mm. Here's an OX801 crank setup with TA 39/26 chainrings. The photo also shows the Sugino adapter for lowering the front derailleur beyond the maximum adjustment available natively with the "braze-on" derailleur attachment:

Nick