Gearing

Quoted post said:

Originally posted by Chris Bryson
Hi
can anyone help with a tech questions regarding gears.
I have a peugeot professionnel which I only use for excercise, its in mint condition , a bit dated but is does for what I want. I am getting on in years and have difficulty getting up hills.
The current gearing set up is 52/42 front and shimano hyperglide 13-23 on the back. I have ridden the bike with a 52/38 front and can get up hills OK but the back mech is too short to make full use of the 38 front ring. A 28 tooth back ring with a 42 chainwheel gives the same theorectical gearing so should do the same job. The back mech is a short cage shimano rx100 am I better changing the back cassette and keeping the 42 chainwheel which is generally ok or using the 38 chainwheel and changing the back mech. The problem I have is I can,t find out if the RX100 back will cope with a 28 tooth back sprocket.
The obvious answer is sell the bike and buy a new one with a triple but I dont have that sort of cash and could not justify the £700 odd for a new cannondale or similar.
Any help will be much appreciated

Here is a blurb from:
http://www.bikepro.com/products/rear_derailleurs/shimroad_rder.html

SHIMANO RX100 REAR DERAILLEUR
The low cost, high quality replacement changer for your bike. It has, however a number of features that the more expensive ones have. Like the Dura-Ace rear, there are adjustments for return spring tension, B-Tension adjustment, high and low gear adjustments, and a convenience adjuster for cable slack. Installation and cable fastening are done like the DA rear, with a 5mm allen wrench. The body is made of aluminum and steel, while the pulley cage and bolts are made of steel. The pulley cages are made of plastic with a polished steel bushing to revolve on, while thin steel caps keep dirt out of the whole mechanism. The cage is fashioned to prevent spoke damage in an overshift. The RX100 weighs 279 grams. The maximum rear sprocket for this derailleur is 28 teeth, while the minimum is 12 teeth. The greatest difference in size between the two front chainwheels can't exceed 13 teeth and the Total Capacity for this derailleur is 28 teeth. Right between the DA and the Ultegra.

By the sounds of it you'd be best off with a 39/52 or 39/53 and a 25-12 cassette (both combos should be readily available) and I think these would match the specs of the derailleur

Quoted post said:

Originally posted by Chris Bryson
Hi
can anyone help with a tech questions regarding gears.
I have a peugeot professionnel which I only use for excercise, its in mint condition , a bit dated but is does for what I want. I am getting on in years and have difficulty getting up hills.
The current gearing set up is 52/42 front and shimano hyperglide 13-23 on the back. I have ridden the bike with a 52/38 front and can get up hills OK but the back mech is too short to make full use of the 38 front ring. A 28 tooth back ring with a 42 chainwheel gives the same theorectical gearing so should do the same job. The back mech is a short cage shimano rx100 am I better changing the back cassette and keeping the 42 chainwheel which is generally ok or using the 38 chainwheel and changing the back mech. The problem I have is I can,t find out if the RX100 back will cope with a 28 tooth back sprocket.
The obvious answer is sell the bike and buy a new one with a triple but I dont have that sort of cash and could not justify the £700 odd for a new cannondale or similar.
Any help will be much appreciated

Something does not compute... A 52/38 and 13/23 needs 24 teeth of wrap. I don't know of any shimano RD that won't wrap that much. Even an 8 speed DA which is speced for 26 teeth of wrap will actually wrap 32. The RX-100 was speced for 28 tooth wrap capacity. Maybe your chain is too long, and you shouldn't be in the small/small either. I don't know of any shimno road RD that won't handle a 28.The RX-100 certainly will.

Hi
Just to say thanks to everyone who replied. I changed the cassette to a 12*28 and kept the 52*42 chain rings, everything works fine and it goes up hills like a dream, its like a new bike.

Chris, just a point of note, Im glad that u decided to go for the new cassette as it gives u a much lower gearing than the change of front chainring would. A gearing of 38x23 gives a ratio of 44.6 gear inches, while the 42x28 gives a ratio of 40.5 which is significantly lower. If u wanted to go lower again im quite sure with the correct chain length (and possibly avoiding extreme gears) u could run the 38 with the 28 rear sprocket to get up those really steep hills.

Right drewjc. If the OP continues to have trouble with hills, go for a 38 up front... although the ratio are not significantly different, I find a smaller chainring is much easier on the legs...

Quoted post said:

Originally posted by Powerful Pete
... although the ratio are not significantly different, I find a smaller chainring is much easier on the legs...

And how can that be if the gear inches are the same??