Author Topic: Non standard triple chainset  (Read 3393 times)

Re: Non standard triple chainset
« Reply #25 on: 26 August, 2014, 08:12:07 pm »
Wow, everyone has an opinion on gearing  ;)

I've linked to it before but take a look at Wilko's bike.

But if you look closely you'll see that the inner ring is unusable - the bottom of the dérailleur cage would foul the chain in the smallest chainring, with most of the rear sprockets.

Its the third most talked about subject in cycling.

Second is "Which is the worst hill?" and first is 'Jam or cream first on a scone?"

Re: Non standard triple chainset
« Reply #26 on: 26 August, 2014, 08:14:17 pm »
...But if you look closely you'll see that the inner ring is unusable - the bottom of the dérailleur cage would foul the chain in the smallest chainring, with most of the rear sprockets.
As yes but ... allow for the fact that in the photo the cage is in the big ring position - over the inner ring, it would drop a bit. Then factor that he uses this machine with different wheelsets and I imagine with different rear clusters (still larger sprockets) and if low gears are wanted (touring for example) it needs only to work with say the two largest sprockets on the inner ring and it's viable, non? Hence also, the custom extra long rear mech cage, so it doesn't self destruct if he accidentally goes 'big-big'!


pdm

  • Sheffield hills? Nah... Just potholes.
Re: Non standard triple chainset
« Reply #27 on: 30 August, 2014, 05:13:21 pm »
zigzag:
To get back to your question about "spinning out" at speed. 2p worth.

I think the way to work it out is to consider how fast you actually want to go at your preferred maximum cadence.

For example, I am most comfortable at 90-100rpm but I can spin 120rpm downhill without too much trouble - faster is difficult with heavy legs!
Uphill, I can usually do about 15kph at 4% - 34 inches at 100rpm - or 11kph at 6% - 29 inches at 85 rpm. (~230W - I am not a racer!).
Level about 32kph - 78 inches at 100rpm (also ~230W)
Downhill depends on how steep and how fast I want to go. 120 inches at 120 rpm gives almost 70kph (180W and -8%) - plenty fast enough.

Hence my choice of a set of ratios from ~29 to ~120 inches.
With a triple in this range (53/39/30,12-27) the steps are approximately: 117,108,100,94,87,83,79,73,67,64,60,54,49,42,37,33,29 inches. 17 effective steps on 3 chainrings.
With an 11 speed compact double in this range (50/34,11-32) the steps are approximately: 120,110,101,94,88,81,78,75,69,64,60,53,47,42,38,33,28 inches. Also 17 effective steps on 2 chainrings. So far, it seems that the double shifts better and getting the right ratio is easier than on the triple.

With such a similar set of rations, the compact double seems, to my mind, the better choice.

Re: Non standard triple chainset
« Reply #28 on: 01 September, 2014, 04:03:55 pm »
At the other end of the spectrum, I’m most comfortable at about 65 rpm.

This equates to 18.5 mph in 99 inches ( Top at 195 W ); 16 mph in 85 inches ( cruising at 130 W ); 8 mph in 42 inches up a 10%; 5 mph in 24 inches up a 15% ( 320 W ) and 4 mph in 22 inches up steeper.

zigzag

  • unfuckwithable
Re: Non standard triple chainset
« Reply #29 on: 17 September, 2014, 12:40:46 pm »
went for the standard set of rings 52-42-30, as larger than 42t middle rings aren't available. i'll see how i get on :)

zigzag

  • unfuckwithable
Re: Non standard triple chainset
« Reply #30 on: 04 December, 2014, 01:26:01 am »
a quick update. i've converted my bike to triple, keeping the same 7 speed setup*. chainset is 10sp 105 with 52/42/30 rings, rear mech 10sp 105 medium cage, front mech 9sp 105, chain 8sp. shifts very well, only there's a slight chain rub at the extreme combinations (which signals the need to change a gear).
this triple setup is around 160g heavier and more embarrassing, but will provide a wide range so i can both ride steep hills and do tt's (quite looking forward to the first one!). you lose some, you win some!

* to downgrade to 10 speed, i'll just need to change the levers, chain and cassette which are waiting in a spares box