I am trying to find a crankset that fits a very specific set of criteria, and was wondering if you might be able to help.

The key requirements are:

160mm length (would consider 165, but no longer)
Light
Pressfit GXP BB
Compatible with 28t Rotor QX1 ring (76 BCD)
Aluminium
Flat surface - not machined grooves like most of the Rotor cranks
(these last two requirements are to provide compatibility with this 4iiii PM: http://4iiii.com/product/precision/

Does such a thing exist?

Will consider swap for an almost new 175mm SRAM XX1 Crank with unused 32t ring (Pressfit GXP).
Or you could just make me an offer...!

Any deore would fit. You could order a set of xt cranks at 165?.

Your srams would be snapped up on singletrack sales. And then order a new from chainreaction.

Chris

Thanks Chris, but I think the XT M785s are 104/64 BCD, whilst the Rotor QX1 Ring is 76mm.

I wish I could find such a simple solution (XT's are a great, proven crankset), but I have been chasing my tail on this for ages!

Maybe get some 'normal' cranks with 104bcd and use AbsoluteBlack oval rings (they go down to 30t) http://absoluteblack.cc/oval-104bcd-chainring.html

Many thanks - that looks like a good option.

Maybe get some 'normal' cranks with 104bcd and use AbsoluteBlack oval rings (they go down to 30t)

Thought they only did 32 + 34t?

s8tannorm wrote:Thought they only did 32 + 34t?

Oh yeah, oops. I'm sure there's more oval rings coming on the market from other people. New trend innit.

Apparently they have a 28t ring coming soon.

I'm really chuffed with Q-Rings; use them on the road bike, but front shifting can be a pain in the ass, and for that reason I didn't bother with them on the MTB. However when I'm running a 1x (or SS) setup, they feel great and I can't think of any reason not to use them.

I'm going to get an Absolute Black 32t ring once my current one is worn out. I'm intrigued.

I like the Absolute Black oval. Used to use a BETD Goldtec oval one but the AB is so much nicer

I can't get my head around the concept of an oval ring on a singlespeed

Ian wrote:I can't get my head around the concept of an oval ring on a singlespeed

What like where the chain either jumps off the rings or it suddenly tightens up and stops?

*I know that's pretty poor english, but meh

The effective ratio of the ring changes as it rotates - I get that (just), so that for a 32t ring, you're varying between 30 and 34 teeth (effective).

But, is half of the circumference of an oval (i.e. the bit where the chain wraps round) always the same value if you start measuring for any given point around an oval? Is the rate of increase of one axis matched to the rate of decrease of the other axis, as the crank rotates? If it is, I guess it'll work, but I just can't visualise it.

I believe chain tension does alter but it's only a small amount, so doesn't cause any issues ... similar to having the usual tight - slack spots in a chain.

Many, many moons ago, I used Shimano Biopace rings. Rather than having even pressure all the way around the ring, the was a slack spot that allowed for faster movement through the stroke. When I got to the sweep through the bottom or top of the stroke, I had added foot-speed to push through these areas. Loved those rings...was disappointed to learn Shimano discontinued them. I'm presuming the modern take on 'em is somewhat similar.

Greetz

S.

The circumference of the chain ring with the chain on will always be roughly similar.

If you draw a circle then put a vertical line through it, then draw two ovals that overlap one in each direction you'll be able to eyeball it.

Then again you may be out riding a bike!

ianfitz wrote:The circumference of the chain ring with the chain on will always be roughly similar.

If you draw a circle then put a vertical line through it, then draw two ovals that overlap one in each direction you'll be able to eyeball it.

Then again you may be out riding a bike!

Ah, gotcha cheers. I haven't really looked at them particularly closely I must admit. My latest chainring I've just purchased is a stainless steel surly one without any fancy oval-ness or thick-thin-ness!

I'm sure I read somewhere that the old Shimano bio pace (which I had on my very first mtb) actually made your pedal stroke worse. The current batch of oval rings are orientated round 90 degrees from the old bio pace.

Interesting about the "worse" pedal stroke. I was on a road bike and for the majority, it was flat road riding. When spinning at 80rpm or higher the power probably wasn't even, but then again, you're just turning it over at that speed. I noticed it more when I was 65rpm or lower - I'd get to the top of the oval and it would feel like a free fall pushing downward. Perhaps that's what was off-putting to a lot of folks. Using a straight push-pull technique (as opposed to an even-pressure circular motion) worked well for me during slow rpm.

Never got to try Biopace on a MTB...my Cadex came with Suntour XC Pro rings...almost 20 years ago now. Where did the time go? :)

Greetz

S.

Yeah Ian, I had biopace on my Muddy Fox Courier. Piece of crap.

Seems to be like Vege/Marmite...love it or hate it. *laughs* @MB - you shouldn't be so harsh on your MFC though.

Greetz

S.

General description of what Biopace did - as distinct from current offerings - is detailed here: http://en.wikipedia.org/wiki/Biopace

For all that I said up there about it making things worse, there is some evidence that biopace does provide a performance benefit here: http://blog.artscyclery.com/general/shi ... ity-study/

I rode on a Rotor ring back last year and I can't say I noticed the increased/ decreased load in the power stroke on a per revolution basis, but when I'd finished the ride my legs did feel a bit different to normal. But, to be honest, as a singlespeeder, riding gears was a funny experience on it's own - never mind with wonky rings

Scattamah wrote:Seems to be like Vege/Marmite...love it or hate it. *laughs* @MB - you shouldn't be so harsh on your MFC though.

Greetz

S.

True man, It was a great bike, it has a plastic disc wheel cover on the back wheel. Poor Man's Tioga Disc Drive.

Biopace worked a bit if you rotated the rings clockwise. You'd still knacker your knees, it just took a bit longer.

Q Rings are great, I've got them on my road, CX and mountain bike.

ianfitz wrote:The circumference of the chain ring with the chain on will always be roughly similar.

If you draw a circle then put a vertical line through it, then draw two ovals that overlap one in each direction you'll be able to eyeball it.

Then again you may be out riding a bike!

or look see this uTube vid you can see the rear mech jockey wheels dont bob indicating the chain is pretty much constant tension

https://www.youtube.com/watch?v=A0_6AZOsLcU