fltche1

Just out of curiousity how difficult and how expensive would it be to change out the crankset on my PR-10. I have the 42/52 Stronglight and I want something geared lower as I live in an area where hills are prevelant and i would like to explore more areas more than just the mostly flat area where I currently ride. Would it be easier for me to change the chain rings themselves?

Grand Bois

The PR10 never got the 122 mm BCD Stronglight 93. It's probably a 49D, in which case chainrings should be no problem.

We need a picture of the crankset.

rhm

But the answer is probably here:

Red Clover Components - Red Clover Components - Bicycle Triplizers and Chainrings

fltche1

Will this be sufficient?

I am thinking that if I replace the 42t chain ring down to a lower tooth gear it would give me a good enough range to be able to tackle what I am doing. Between the 52t and a lower I would have enough variety in the gears I would get the climbing ability I am looking for while keeping my speed.

juvela

hello fltche1,

if you wish to keep the same outer the smallest inner that was offered is 38t (some have found 37t but these seem to be quite rare).

if a person wanted to get cute there is a stronglight outer adaptor c/w which bolts on to the 49d arm and is drilled to accept model 99 inner c/w's which go down to 28t. it is part nr. 490T, is rare and would be difficult to source. perhaps Mel Pinto may have some in the warehouse...



launch was ~1977.

alternately, you could go to a t.a. cyclotouriste pattern set of chainwheels which will bolt right on to your existing crank arm. it this pattern every size from 26t-60t is offered.

Ex Pres 

I would say this is your answer

eschlwc

what tooth count is your largest cog on the rear cluster? if not 28t, a new sunrace freewheel will be the easiest, cheapest, and most satisfying modification you can probably make.

fltche1

The rear is as follows, 24-21-18-16-14-13. IRD makes a freewheel that I was considring but I figured that adjusting the chainring would have more impact than adjusting the gearing on the freewheel. I could be wrong in my thinking though. In my current riding, when I pair the 18 rear and 42 front... I am maxed. If I go really hard I can do the 21 rear and 42 front. I am usually running about 18 mph on the 18 rear and 42 front. This PR is still a racer... I am not.

dddd

Not all of this makes sense to me. What is "maxed" when in the 18 or 21t rear cog?

To get the same benefit as you could get by using a 28t in back, you would have to drop seven teeth in front.

fltche1

It means the gears I have selected/the chain on. So for instance, on a slightly hillish terain if I have the chain on the 42t chainring and the 18t cog of the freewheel, that is the maximum amount of power I can handle for sustained periods of my rides which consist of 13 miles If I am on the 42t chainring and the 21t cog of the freewheel I can only sustain it for short intervals because my legs are going to be found by some pedestrian or bicyclist unlucky enough to find them on the path after I have keeled over and died .

If I am understanding you correctly... I should change out my freewheel before I change out the chainrings?

The rear is a 126mm hub which is standard I believe. IRD make a nice set with a tooth range of 13-32 for not a lot of money. Or a search for a suntour 6 speed would not be out of the question as my front deraileur is a suntour...

Something along these lines?

https://www.ebay.com/itm/SUNTOUR-free...4#ht_37wt_1359

non-fixie 

Think in percentages: a four-tooth drop in the front (from 42 to 38) is a 12.5% change in gearing, a four-tooth increase in the rear (24 to 28) will give you 16.6%.

juvela

tip -

in case you should have occasion to order a 49d chainwheel it would be wise to advise seller that you have a late type set with allen key c/w bolts. the manufacturer changed the set over from hexhead c/w bolts to allen key ~1973. the bolt holes in the c/w's are smaller for the hexhead bolts than they are for the allen key.

eschlwc

non-fixie nailed it.

adding teeth in the rear makes a greater impact on lower gearing.

i have two ird freewheels, but the only advantage i've seen over the sunrace options is the stealthy coasting. if you don't use a bell to pass peds, the ird's stealth can be a detriment. (the sunrace 'click' is a nice warning to peds.)

so, if your rear derailleur can handle it, get a shiny new sunrace 28t fw from ebay. if you buy a 5-speed, send a note to the seller specifically asking about the color, as sometimes they feature a shiny one, but they mail an ugly, black one with writing on the largest cog. the 6-speeds aren't as susceptible to this issue. but you can probably remove the cog writing with acetone if you're stuck with one of those ugly ones.

fltche1

I read an article on gearing and walked away with bigger gears on the freewheel and smaller gears on the crankset = climb hills. smaller gears on the freewheel and bigger on the crankset = harder to pedal but more speed. I saw the percentages and understood enough to know what they were but not how to calculate them or which would have a bigger impact. And for me thats when I wave my little white flag hoping for reinforcements.

fltche1

ANd the rear deraileur is the simplex its either the prestige or the criterium and im fairly certain its the criterium which can handle a max cog size of 34 teeth.

fltche1

Defiant Freewheels, 7, 6, and 5 speeds

The IRD freewheel is even on sale....

jimmuller 

Changing both FW and small ring is a belt-and-suspender approach. You don't have to do both unless you can't get what you want with just one change. But non-fixie did nail it - 1 tooth is a bigger deal when you change from 24 than when you change from 42.

The question really is, is that enough? The traditional way to compute gears was wheel diameter times the ring size divided by FW cog size. For any precision that matters you can use 27" as the wheel size. Bikes geared like yours have a low of about 47", quite high. In the old days a "sport bike" might have a low in the upper 30's. For the hills around here I prefer lower 30's, like 32 or 33. There are times I wish for something lower, like when I grinding up a 10% grade for 1 mile or a 20% grade for even 1/4 mile. It really depends on your hills.

juvela

the criterium rear mech has a largest cog capacity of 28t. it also can wrap 28t. these numbers are the same as for the prestige.

John E

True.

50-38/14-28 would work and provide a significantly lower bottom gear than he currently has. 48-38/13-28 would retain a 100-inch top gear, equivalent to 52/14.

dddd

If a 28t freewheel can first be installed, perhaps an adjustment to the bike's fit parameters can allow a more-effective "stand and climb" position at the handlebars, i.e. a more-forward positioning of the bars and saddle, so might allow more force to be delivered to the pedals without undue knee-joint stress. This has been my recipe for getting vintage road bikes with limited gearing up all of our steep hills, but works best with larger-sized frames where a wildly long and/or tall handlebar stem won't so much be needed.

This one gets by with it's original double chainset and only a five-speed, 13-24t freewheel, yet I can comfortably go up a 20% grade on it for perhaps a full minute or two before having to begin weaving my way further up the road.

davester

This is confusing. To reach 18 mph with an 18-42 you would need to spin over 100 rpm. If you're going 18 mph you would generally be in the 52t chainring, not the 42. Are you mixing up the 52 and 42? Go look at a gear calculator and figure out what gearing you'd like and work from there. This one is nice: Mike Sherman's Bicycle Gear Calculator

It sounds to me like your best bet is to change the chainrings as originally suggested because you aren't using the top range of gears. Changing only the freewheel will still keep you with the same set of top gears and will widen the steps, not a desirable thing in general. Your current low gear is 46", which is definitely too high for hill climbing for most folks. Even going to a 38T inner will only get you down to a 42" gear and changing only the freewheel will only get you down to a 40". If I were you I'd see about changing to TA cyclotouriste rings and get something like a 32-49 up front. That'd give you a 35" to 99" gear range which would probably be much more useful while keeping your closely spaced freewheel. If you wanted to go even lower then you could switch out the freewheel.

Bear in mind that my suggestions are made not knowing whether your derailleurs can handle this range, though I'm guessing they can.

fltche1

I can upgrade the rear up to a 28 and be well within any deraileur limits. If I start changing the chainrings I will have to be careful. going to a 32-49 would be over my chain wrap limits. I could do a 32-42 and be close to max capability of my deraileur when it is paired with a 14-28.

dddd

Only you will be able to say just how much lower that your bottom gear ratio needs to be.

Can you simply estimate for us a % change you think you will need?

How much clearance do you measure between the smallest cog and the inside of the frame?

Perhaps a seven-speed freewheel like a 13-28t will allow both lower gearing and nice, tight ratio gaps?

Consider a modern chain with any switch, but that old Stronglight crankset is, unfortunately, spaced for the wide, clunky chains of old. I would bend the small ring's teeth very slightly toward the big ring so as to use 7.1mm (8sp) modern chain.

I myself hate riding bikes with old, wide, clunky, squeaky (lube-needy), heavy, inflexible, friction-plagued "bushing"-style chains!

BTW, a Sunrace freewheel and KMC X-series chain could be bought for 30 or $40.

fltche1

Fixed the post to reduce confusion. What I meant by that was my chain wrap limits.

fltche1

as far as the percentage goes.... if I could get my low end down to about 35-40 on the gear inch chart in the calculator provided I think I would be ok. If I swap out to a 30/40 chainring it will drop my gear inch chart down to a 33 which I think would be pretty good.