Author Topic: 73mm Bottom Bracket  (Read 2017 times)

Tayo

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73mm Bottom Bracket
« on: April 22, 2021, 01:45:55 PM »
I'm about to order a Thorn Mercury but I'm a little put off by the apparent lack of quality 73mm bottom brackets available. They seem to be a bit of a weak link when compared to the quality of the Rohloff and Son hubs on the same machine.

I'd be grateful if anyone who has/had a 73mm bb can recommend a long-lasting unit or at least one that doesn't fail after a few thousand kms.

I've done well with 68mm  UN55 bb's on other bikes but it seems the 73mm variety isn't readily available.

I'd buy an outboard/external bb for ease of access  but unless they've upped their longevity I'd stick with square taper.

Thanks
« Last Edit: April 22, 2021, 01:58:28 PM by Tayo »

PH

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Re: 73mm Bottom Bracket
« Reply #1 on: April 22, 2021, 04:32:52 PM »
This IRD Defiant has a ten year warranty
https://www.sjscycles.co.uk/bottom-brackets/103-ird-defiant-qb95-jis-english-thread-sealed-cartridge-bottom-bracket-68-mm-shell/

It's multi purpose, comes as standard as 68mm but cups available to convert to all sorts including 73mm
https://www.sjscycles.co.uk/bottom-brackets/french-ird-bottom-bracket-conversion-cups/

I currently have two, the only problem with them is they look too bling to hide away!  I wish I'd bought a couple more, the price has gone up a chunk since I bought mine.  Time will tell if they were worth the money. 
Although less common, I'm not sure 73mm ST is going to disappear, Shimano's newer UN300 comes in several 73mm axle lengths.  What's more likely is that they'll get downgraded as their better chainsets don't use them.  if you can find one in the axle length you need, Tange Seiki have a good reputation, though i don't think I've used one. 
An EBB frame is of course more future proof than a standard one, to make it compliant with another system (Maybe something yet unknown) would just require a different insert.

Tayo

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Re: 73mm Bottom Bracket
« Reply #2 on: April 22, 2021, 08:02:37 PM »
Thanks Paul.

Good call on that IRD. See what you mean regarding its aesthetics too, but unfortunately out of stock in the required(?) 107mm length.

They have a Tange Seiki in stock
 
https://www.sjscycles.co.uk/bottom-brackets/tange-seiki-ln3922-73-mm-jis-english-square-taper-bottom-bracket-107-mm/

but I've no knowledge that it would be any kind of upgrade in quality to the VP unit

https://www.sjscycles.co.uk/bottom-brackets/vp-bc73-107mm-bc13724t-unit-price-us304pc/
 
that Thorn has pencilled in for me.

Other than that there's a First DX.  I know Spa use First in some of their bikes so maybe it's worth a punt.

https://www.sjscycles.co.uk/bottom-brackets/first-dx30-73-107mm-bc13724t-unit-price-us485pc/

And that's your lot!
 :-\
« Last Edit: April 22, 2021, 08:06:11 PM by Tayo »

PH

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Re: 73mm Bottom Bracket
« Reply #3 on: April 22, 2021, 08:21:07 PM »
but I've no knowledge that it would be any kind of upgrade in quality to the VP unit
If that's what they fit, I'd go with it, they're not the sort of people to penny pinch on a three grand bike, if they fit it it'll be because they think it suitable.
When it dies, as they all do, you can decide if it represented good value or if you're looking for something better. Or you could buy an IRD, when they come back in stock, and leave it on the mantlepiece till needed, it is a thing of beauty.

JohnR

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Re: 73mm Bottom Bracket
« Reply #4 on: April 22, 2021, 09:35:34 PM »
I was told that the 110 parts are also acceptably close and would note that the eccentric bottom bracket shell can be moved laterally by a mm or so within the frame to achieve the desired chainline.

John Saxby

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Re: 73mm Bottom Bracket
« Reply #5 on: April 23, 2021, 02:02:09 AM »
Depends how much you want to spend, but suggest check the offerings from Chris King, Phil Wood, and SKF.  The latter is recommended by Jan Heine of René Herse Cycles.

Danneaux

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Re: 73mm Bottom Bracket
« Reply #6 on: April 23, 2021, 04:54:04 AM »
Quote
...suggest check the offerings from Chris King, Phil Wood, and SKF.
+1 on Phil Wood. I have over 75,000mi/121,000kms on three Phil internal units and have never had a problem. Phil was my maker of choice when replacing the original Shimano Deore OBB/EBB unit on my Nomad, trouble-free since installation to date.

Best,

Dan.

PH

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Re: 73mm Bottom Bracket
« Reply #7 on: April 23, 2021, 09:04:17 AM »
I was told that the 110 parts are also acceptably close
On a Shimano 68mm, the 107 and 110 offer identical chainline, the additional 3mm is all on the non drive side, I'd assume it's the same on the 73mm but haven't checked. 
I've never heard an explanation for this, I'd be interested if anyone has got one!
I agree with your other point, the chainline is fine tuneable with the same BB, as well as some offsetting of the insert, there's the Rohloff supplied washers for the chainring and you can also get BB washers to shift the drive side out a mm or two. I prefer a wider Q in order to not clip my heels on the chainstays, so use a 118mm BB and the chainring on the middle position, with a guard in the outer. This has other advantages, but they're secondary to getting the position and chainline correct.

Tayo

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Re: 73mm Bottom Bracket
« Reply #8 on: April 23, 2021, 12:18:50 PM »
Brucey (natch) did the graft and published his findings over at CUK.
https://forum.cyclinguk.org/viewtopic.php?f=5&t=105385   

531Colin has info re. 73mm on the same thread.

It looks like IRD 107 and 110 share the same measurement (20.5mm) on the drive side too.
https://www.interlocracing.com/shop/product/ird-qb-95-bottom-bracket-4057?search=bottom+bracket

Quote
This IRD Defiant has a ten year warranty
https://www.sjscycles.co.uk/bottom-brackets/103-ird-defiant-qb95-jis-english-thread-sealed-cartridge-bottom-bracket-68-mm-shell/

It's multi purpose, comes as standard as 68mm but cups available to convert to all sorts including 73mm
https://www.sjscycles.co.uk/bottom-brackets/french-ird-bottom-bracket-conversion-cups/
   

Are both left and right cups easily removed on your Defiant? I'll look into converting one to 73mm if they are. Reason for asking is that I've read that the drive-side cup on other IRD models is impossible to remove without getting physical with it.
« Last Edit: April 23, 2021, 04:42:42 PM by Tayo »

PH

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Re: 73mm Bottom Bracket
« Reply #9 on: April 23, 2021, 08:20:03 PM »
Are both left and right cups easily removed on your Defiant? I'll look into converting one to 73mm if they are. Reason for asking is that I've read that the drive-side cup on other IRD models is impossible to remove without getting physical with it.
I'd read similar, but the cups came off both mine reasonably easily by hand, just used a cloth for grip, about the same force as a tight screw top jar.