Slightly smaller inner chainring?

Manc33

I have got a "Prowheel Ounce" triple chainset that is 30/39/50T and want to make it a 28/39/50T, can you just buy any 28T inner chainring for a triple with 5 bolts and it will fit?

I don't even know what to look for. :oops: All I know is those are the cheapest of the chainrings. Front mech is a Tiagra/R443 so the 22T difference should be fine. My bike would have a massive gear range with a 28T. Will shifting on the front be worse because of it being a 22T difference not 20T?

Would end up with a lowest gear of 0.88 and highest the same as now, 4.55. 8)

Monty Dog

For a road triple, 30t is about the smallest you can fit - you need to know/measure the bolt circle diameter for your chainring and see what is available. Spa Cycles have a good range. Measure the distance between two adjacent bolt centres and use the following:

http://sheldonbrown.com/cribsheet-bcd.html

mercia_man

The outer rings of road triples are 135 or 130 BCD, depending whether you have Campag or Shimano type. But the inners of all the ones I've used are 74 BCD, the same as the old mountain bike triple inner and the same as most modern touring chainsets. It means you can use a little ring as small as 24 teeth (as I do), 26 or 28.

You do have to make sure your front mech will cope. My Campag Centaur triple can cope with a 48 big, 24 little set-up, despite this being over the quoted capacity.

Spa Cycles sell huge range of Stronglight and TA 74 BCD rings from 24 up.

Manc33

Going off the outer bolts its a 130 BCD.

Inner bolts = 44mm x 1.701 = 74.844

So the inner ring BCD is 74. Does Sheldon Brown mean you can measure outer and inner bolts and the "x1.701" works for both? The guy was a human dynamo when it came to bike knowledge.

I get confused because road chainrings are 5mm nearer the frame than on a MTB but the spacing is the same between the rings.

I mean what if there was a MTB 28T inner ring and the BCD matched, it would fit? Not that I am after a MTB one I just wondered.

mercia_man

You've established you have a Shimano type road triple chainset. The same 74 BCD inner rings fit five-arm mountain bike, road triple or road touring chainsets. It will take as small a ring as 24.

Just order a TA or Stronglight 74 BCD 28 ring from Spa Cycles, Wiggle etc and fit. Front changing will be the same as before but you will have the lower gearing you desire on little ring. You will have to take chainset off to fit it.

Manc33

Luckily they had the exact one (74 BCD, 5 hole, inner, 28T) in the clearance section:

http://www.spacycles.co.uk/products.php?plid=m2b0s185p0

I guess its not gonna be a TA or Stronglight but what do you want for £5. 8)

"6061 alloy chainrings with ramps and pins (on middle and outer rings). As used on our Spa Cycles chainsets."

It'll do, its rare I use that ring anyway.

There's a hill near me, 600M @ 10% gradient and I can't even get up it in one go on my current setup (30F/32R). Judging from that, just how weak am I? I have been managing to do that same route every day though and seem to be knocking about 9 seconds off (a 26 min ride) each time. 3 more months of that and I might be able to blast up it on the middle ring standing up.

How the hell people cope on setups like 39/50T with a max sprocket of 25T on their cassette I have no idea. I am in that gear on the shallow gradients like 2% or 3%. In fact 39F (my middle ring, a small ring on a double) and about 25R is the gear I am in most of the time on the flat, THAT is most road bikes "lowest" gear. Either people have got legs like fleas or I am pathetically weak.

desweller

Well, 26 minutes is more of a warm-up than a ride. Does that answer your question?

Monty Dog

I would add that most road front triple mechs have a capacity of 20 teeth - i.e. large - small. You may experience chain rub on the inner ring and smaller sprockets, so best avoided.

mercia_man

The more you practise hill climbing, the better you will become. And the lower your gears, the easier it is. Spinning quite quickly in a low gear is the best way to climb all but the shortest hills. It means you can pace your efforts. Trying to power up longer hills standing on the pedals in a high gear will use up your energy reserves quickly.

Manc33

Using up my energy reserves takes no time on that hill. It goes up, has a flat bit, then goes up. Its average gradient is 10% but the flat bit means the 2 hilly parts are probably 12% or 13%.

I estimate then, I can only do about 250M at a 12% gradient with 30F/32R (0.93) on a 23lb bike with 100PSI in the tyres. Its inconceivable to most people here but thats my "fitness" level at the moment.

From how tiring it is I would say me going up there is equal to a 20 mile ride (from doing them in the past and now this). Doing the hill climbing to me is making me fitter than when I was doing 20 miles every day. That is my heart rate gets up to max, so I am forced to adapt. When I do a 20 mile ride, taking say 1hr 40 mins, my heart rate never goes above 160.

To me a 5 mile ride in the wind can equate to a 10-15 mile ride in non windy conditions. I have even set off on a ride and come back home because of the wind. If I have to pedal downhill, I come back home lol. It is serious graft biking in the wind, any distance. :oops:

Manc33

Turns out the chainring is a Stronglight after all. 8) For £5 I expected some unbranded steel thing.

Last time I took triple chainrings apart, there were 10 spacers between all the rings. This Prowheel Ounce was as simple as it gets, there are no spacers.

Had to use both arms and legs to undo the 8mm crank bolt. Granny ring went on easily.

Got the mandatory cut on top of my hand. :roll:

Front mech has no problem with it, changes just the same as when it was a 30T.