Compact cranks 50/34 question

^ I wasn't going to suggest that as I don't want a puppy killed on my conscience :)

Not looking good.....i could just use a band on below the braze on?....Not ideal.

I thought the aim of the CX70 was to go lower/deeper.....ie closer to the chainrings.

The CX70 I would suggest (having never handled one) has the cage profile modified so it follows the curve of smaller chainrings, as you said. But, I feel sure, for the bottom pull that the rest of the mech is standard Ultegra.

Two main reasons make me say this .. A cross bike will be made with smaller chainring sizes in mind so extending the links doesn't add value only flex and Shimano will want to make the smallest change they can to sell another product without incurring tooling cost.

If you have enough room a band on below could be an option .. I personally don't think you'll have enough room and the band will want to be where the braze on is, seeing as you're only 3mm away from the correct position.

I think that this is going to be sub-optimal.

You've probably bought the parts now, but I'd suggest going back to the 50T at the front, and then a long cage rear mech and a bigger block.

There's a difference between the 'bouncy' cadences at your slow-twitch ceiling on the flat, and the kind of fast-twitch stuff that kicks in on fixed descents.

My max speed was just over 35mph, so my max cadence was around 170rpm, with Sade-like levels of smooth operation (not Marquis De).

Not all of us have NASA-grade bearings in our joints, like you ;)

That said I do enjoy the transition from "arg.. Don't like this" to the point at which everything relaxes and the purple curtain descends when descending fixed.
It normally kicks in for me when I finally convince my brain that slowing down /stopping would be a lot worse than embracing the washing machine :)

@marxist_vulcan - I may be mistaken, but I'm sure I've seen an adaptor somewhere (possibly DIY/custom-made) that you can attach to a braze on mech, essentially extending the mounting slot downwards. I'd ask around, have a look on the usual forums (e.g. weight weenies), etc.

@dan - it's a lot more effort doing it with a freewheel, hit about 185rpm today, but couldn't sustain it for as long as would do on fixed (assisted drive, init).

BMMF...cheers!

Though i don't ride fixed these days....coming down hills terrified me....i suppose a lack of control.....and don't know the RPM but lots on a steep hill......scared me shitless at times......i got better but always used my front brake to modulate my speed a tad.

Funnily enough, I've just decided to rejig the set up on my fancy pants bike to be 46/34. I was going to opt for 44, but remembered to check mech/bottle boss clearance, and - allowing ~2mm per 1t - realized a 44t would need extra faff, much like your own situation. I had about 7mm of room for manoeuvre, so went for a 46t, which ideally would involve an 8mm change. Close enough.

Funnily enough, I've just decided to rejig the set up on my fancy pants bike to be 46/34. I was going to opt for 44, but remembered to check mech/bottle boss clearance, and - allowing ~2mm per 1t - realized a 44t would need extra faff, much like your own situation. I had about 7mm of room for manoeuvre, so went for a 46t, which ideally would involve an 8mm change. Close enough.

Have you got a 46T yet?.....if not buy mine and i will get a 50T.....Mine is a Shimano CX 70 bought for £32.99....on my bike but not used apart from putting the chain on the bike.

Yeah, already bought. Thanks for the offer though.

I was not aware of the 1T=2mm rule, thanks BMMF.

Funnily enough, I've just decided to rejig the set up on my fancy pants bike to be 46/34. I was going to opt for 44, but remembered to check mech/bottle boss clearance, and - allowing ~2mm per 1t - realized a 44t would need extra faff, much like your own situation. I had about 7mm of room for manoeuvre, so went for a 46t, which ideally would involve an 8mm change. Close enough.

46? Really? This interests me..

46? Really? This interests me..

As mentioned above...i've got one and want to offload it...cost me £33.....but if i put it on ebay....i get him by fees from ebay and paypal......14%!!.....So £26 posted....if you are interested......its a bargain as it is new and unused....the BCD is 110.

46? Really? This interests me..

Well, I'm not racing, but it's the summer/fast bike, and I know what kind of speeds/terrain will generally be involved. I use a 12-23, with 1t increments from 12 to 19, and want a good chainline. The centre gears are 16/17, so 71" and 75.5", and I'll happily cruise along on those in the summer on the flat (solo or group) at 19-23mph - that's my starting point, and the rest falls into place.

I'll still be able to brute force climbs in the big ring if I feel like it, but if not, I'll make ad hoc decisions when I'm getting towards the crux, with the intention of avoid any overt cross-chaining, which I fucking hate. In this instance it will be either:

• I can muscle through it, dropping down to 46/19 (63.6") if necessary.
  
• I'll 'heart & lung' it instead with a largest gear of 34/14 (63.8").
  
  

For most of my riding, the little ring won't see much use, but the 46t will give me something like my fixed gear/nice chainline experience, with subtle added modulation possibilities.

46/12 will be enough to get myself up to 50mph on ski ramps, or as fast as my cornering ability allows on more twisty/curvaceous descents. TBH, the 12t is likely to see as little action as the 23t.

That's the long and short of it.

Makes sense, I guess you are happy spinning at higher rpm's too - so if you ever find yourself 'undergeared' on a shallow descent in a group you can compensate, whereas I could not. Or something.

^^ no I'm quite happy with 50/34 on both bikes at the moment - but thanks for the offer