Chain speed a cassette type

[widelyawake]

I have just bought an old racing bike. It has a back wheel on which there is a five speed freewheel. I would like to replace the wheel with a new cassette wheel but I am not sure what kind of chain / cassette is compatible with the crank. If someone knows how to measure a chain and therefore know what number of speeds cassette to buy it would be greatly appreciated.

Andrew

[1FJEF]

Bicycle Chain Sizes

Determining chain sizes is a function of learning how to measure a bicycle chain width, both internal and external, and the bicycle chain pitch. These three elements together describe a bicycle chain size and give you the information you need to buy a new one.

My old (1984) touring bike has 126mm rear drop outs & six rear cogs, but uses a 1/8" chain which is fairly unusual.

1. How to measure bicycle chain width- INTERNAL WIDTH is the main thing.
There are 1/8" (3.175mm) and 3/32" (2.38mm) width bicycle chain. Sizes refer to the distance between the two inner plates. (I-W)



Something better than a tape measure would be a good idea.

If you measure the rear drop outs to get OLD you will hopefully get 125-126mm which will often spread to 130mm without too much fuss (like cold setting the frame). 130mm OLD wheels are common, if your chain is the common 3/32" you should be just fine.

Is the wheel diameter an issue? Is it set up for 27" (630mm)? What size in mm is on the tire? You need to make sure the brakes will adjust 4 or 5mm down to go from a 27" to a 700C.

[DaveM]

You're going to have to get a new chain to suit whatever cassette you get, so the question is will the new chain fit on your front chainrings ok. The answer is "probably", but hard to be sure.

On a 5 speed, the rear spacing on your frame is probably 120mm. To go up to 7 speed, you'll have to spread it to 126, to go up to 8 speed or above, you'll have to spread to 130. This should be ok on a steel frame, but spreading a full cm may take more force than you want to do by hand every time you take you wheel on or off. May want to get the frame cold set by a shop.

Next question is if you have a 27" wheel or 700. There are not a lot of 27" inch wheels with a cassette hub, but you may be able to find something. As 1FJEF notes, you can switch between 27 and 700, but there are some considerations to check first.

The big question is - what are you trying to achieve? More gear choices, stronger axle, just a cooler looking new wheel?

[widelyawake]

Thanks for the replies 1FJEF and DaveM

@1FJEF the chain is indeed IW=3/32 and the dropouts are 125mm - what do you mean by and OLD wheel? - do you just mean to find a second hand wheel somewhere. I measure a wheel radius of ~31.5cm so I assume its a 700C 622mm
wheel.

@both I would like to buy a new wheel mainly cause the old one has glue on tires which aren't very cost effective when flats come around.

In summary I think that if I get a wheel with a 700C tire, freewheel with 6 or 7 speeds and an appropriate chain I should be fine. or ...

Andrew

(01-21-2013, 12:41 PM)DaveM Wrote:  You're going to have to get a new chain to suit whatever cassette you get, so the question is will the new chain fit on your front chainrings ok. The answer is "probably", but hard to be sure.

On a 5 speed, the rear spacing on your frame is probably 120mm. To go up to 7 speed, you'll have to spread it to 126, to go up to 8 speed or above, you'll have to spread to 130. This should be ok on a steel frame, but spreading a full cm may take more force than you want to do by hand every time you take you wheel on or off. May want to get the frame cold set by a shop.

Next question is if you have a 27" wheel or 700. There are not a lot of 27" inch wheels with a cassette hub, but you may be able to find something. As 1FJEF notes, you can switch between 27 and 700, but there are some considerations to check first.

The big question is - what are you trying to achieve? More gear choices, stronger axle, just a cooler looking new wheel?

[DaveM]

OLD means "over locknut dimension". This is the standard measurement for the space in the rear end of the frame. Note that you have to measure between the <i>inner</i> surfaces of the dropouts (or the ends of the "locknuts", not the end of the axle, on the rear wheel.) If you have a spacing of 125, you are good to put anything up to a 7 speed without a problem, and only a few more mm to go up above that.

If you have sew-ups (glue on tires) I'm pretty sure you have 700 size wheels. I don't think there's any such thing as 27" sew-ups. Dealing with a flat on the road with sewups isn't that bad actually. You carry a spare tire with you. If you get a flat, your tear off the flat tire, put the new one on, pump it up and ride. You have to be careful cornering on the new tire because it isn't glued on, but the pressure will hold it on well enough for cautious riding. Sew ups also ride better than "clinchers". However, gluing on a tire is a PITA and if you get a flat, fixing the popped tire is a big pain or buying a new one every time is expensive.

If you go 7 speed, I'd recommend a 7 speed cassette. Cassette hubs have a lot stronger axles than freewheel hubs. Cassettes have to get replaced more often than freewheels, but you're not buying the whole mechanism each time. But a 6 speed freewheel (or your current freewheel) will work fine on a new wheel. Get a new chain if you get a new gear cluster (one appropriate for the number of gears). It should work fine with your crank.