Chainline versus cinch.

9 05 2018

A few years ago, I started running Race Face Next SL, SIXC and then Turbine cranks. The weight and low ‘Q’ factor of the Next are pretty awesome, but I (like others) have had a crank axle insert come loose. Others have had pedal inserts come loose: but, I do have 3 sets on the go which have been fine so far. I am always messing around with things and the shared axle crank interface between Cannondale Hollowgram and Race Face Cinch has had my attention recently. The Hollowgram SI are within grams of the Next SL and may be a reasonable alternative whilst retaining the unbelievable versatility of the Cinch.

A case in point.

The Turbine has a few millimetres greater ‘arm’ offset than the Next SL and I had a use for this. My 44 Bikes ~TNT~ had a Saint crank. The reason was the 83mm BSA shell (mated to a 150mmx10mm thru QR rear hub). There were only so many cranks that were available in this width and this width works well to get short stays and good ring clearance with 3″ tyres. It is a sturdy crank to say the least and the arms are quite bulky. I had been getting some medial knee pain on riding the 44 and I had isolated it to the crank.

On my Vertigo Cycles Kraken, Sean machined a SIXC 83mm crank axle so that the Next SL cranks would fit and work with the 177mm rear end. This used a flipped ring and thus gets a great chainline despite the ‘snow bike’ width rear hub.

A quick note – most geared bike set ups are biased to the smaller rear cogs. This is essentially to get stay/ring/tyre clearances in the manageable bracket. However, there is an argument that the ring should be more inboard at the front for todays gear spreads. Some manufacturers had started to address this when 1x systems became popular, offering aftermarket rings that were spaced to be slightly more inboard than usual.

Then, of course, rear hubs started getting wider and ‘boost’ then ‘super boost’ happened. Sean has been guiding me for years on this sort of thing and the bikes he has built for himself, others and me have often used 150 mm DH rear hubs with either flipped rings on 73mm shells, or ‘normal’ ring position on 83mm shells and as time has progressed and ‘plus’ tyres happened, moved even wider with flipped rings on the 83mm shell equivalent widths and 177mm rear hubs.

Phew.

I had been wondering about converting the 44 to the Cinch system. Interestingly, Race Face – perhaps due to the proliferation of 157mm “super boost” rear hub selection by several manufacturers (very sensibly, I might add – I have been advocate since 2010) – had quietly released a 143.5mm crank axle and also a 149.5mm axle for Next SL. The latter is equivalent to an 83mm BSA shell – the usual standard for a 150/157mm rear end – and had previously only been available in the DH orientated SIXC. The ring would normally be mounted in the inboard biased traditional position.

But you will know that often, direct mount rings can be flipped, if they are round, and there are different offsets of rings. The ‘normal’ is 5 ish mm towards the bike midline. Flipped, it is 5 ish mm outwards Why ‘ish’ ? well, different brands – a list would take too long – use a different offset – from Race Face’s 4.5mm to Absolute Black, Wolftooth and IIRC One Up using 6mm. There are others, but these are probably the major players.

Then there is Boost offset – usually around 3mm less. Soooooo….

If I took the BSA 83mm shell, which utilises the three 2.5mm spacer rings, which normally uses a 149.5mm axle equivalent, bought a 143.5mm axle (designed, most likely, for 148mm rear hubs?), removed 2 of the spacers (take away 5mm of the 6mm difference) and fitted BSA 30mm bb cups, a boost ring (add 2mm back to the chainline which with the shorter axle was 1mm more inboard) and the larger offset Turbines, I reckoned I would get great chainline and get the stay clearance and a slimmer, lighter and therefore more flexible crank on the bike.

In short, it worked.

This stuff is a minefield. I have another bike I want to do something somewhat similar with – my Vertigo Maul. It has a normal 73mm BSA shell, and I am going to use Cannondale Hollowgram cranks with (I hope at least!) a Wolftooth FAT CAAD (listed as -1mm but it seems to be more like +1mm) CAMO spider so that again, I can get a great chainline biased more inboard for the 150mm rear end on the bike.

I have been collecting data on all the different spiders and DM rings around, but the listed offsets are often either hard to find or seem wrong on measuring and thrown together with the different ring mount positions on different brands of cranks, different crank arm offsets and requirement for spacers etc, you need an obsessional trait to try and make it work. My advice? have the bits in hand, measure and then work out if it will fit. The downside is simple – cost.

But, with all the interplay between Cinch kit, Hollowgram and SRAM cranks (which have even more standards for where the ring mounts) you can make an über sweet, bespoke crank work on most bikes and get great chainline.

The bummer is giving myself a reason to pull King BB’s out of frames. Chris King deserve an award for making a bb that is seemingly impervious to scottish weather – no small feat!

Ok – this was probably as hard to type as it was to read and digest. If I have made any mistakes, I will correct them and fire away with questions if you are interested.

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2 responses

16 05 2018
nig3h

Hi,

What BB cups will you be using with the Cannondale Hollowgram crank spindle. I want to set up one of these on my Jones.

Thanks , nige

16 05 2018
velopest

I have 2 sets of the race face bsa 30 on the go. Not heavy use but they are functional. Durability by all accounts though is poor. I’m going to use the wheels manufacturing angular contact bsa 30 on the bike with the Hollowgram- I suspect this will be a bit more durable. I’m using the race face spindle because the bearing seat areas on the Hollowgram spindles is not always set up for external B.B. cups. Some are some aren’t and it seems complicated to work out which are which for some reason!

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