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tires sizes, my head is spinning.

Old 04-02-15, 10:28 AM
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tires sizes, my head is spinning.

Hey kids!
looking for some advice here. I am interested on a dynamo hub for my road bike, the bike its set up with 27" tires. Nowadays looks like 700c is the standard. If I go head an buy a new 700c wheel already built with a dynamo hub can and should I be able to fit it on my bike?
My bike is a 1981 Peugeot P8 (I know its not a Px-10) carbo-lite 103 tubing

Thank you.

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Old 04-02-15, 10:51 AM
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Depends. What kind of brakes do you have? The 27" is slightly smaller than the newer and more common 700c rim. The quick and easy fix is to buy some long reach caliper brakes, Tectro makes some. You may just need them for the rear wheel.
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Old 04-02-15, 11:05 AM
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Leebo flipped it .. The standard tires and rims meet at is the tire bead seat diameter.. 27" its = 630mm, 700c its = 622.

An International agreement was reached so tires from one country fit rims from another .. tires bear marking saying metric width too .

8mm difference in diameter '/, 2 = 4mm radius.. that is how far down your brake pads must reach towards the axle, to hit a 700c rim..

given the bead seat of the tire is on the inside of the rim at roughly the middle of the brake track..

Last edited by fietsbob; 04-02-15 at 11:12 AM.
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Old 04-02-15, 11:52 AM
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Yes, but you need your brake pads to be approximately 4mm lower. Can you do that? If not, you will also need new brake calipers.
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Old 04-02-15, 11:58 AM
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Or a drop bolt if one is available for your brakes...
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Old 04-02-15, 12:06 PM
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If you did buy a newer bike, you could always have the dynamo hub installed on a 700 rim along with new spokes.

Last edited by JerrySTL; 04-03-15 at 07:32 AM.
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Old 04-02-15, 01:37 PM
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Oh snap, always hated math. I have one bike converted from 27 to 700c. A little room for bigger tires.
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Old 04-02-15, 02:50 PM
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The short answer: Yes, you can fit 700c wheels on your bike.

And now for the fine print:

1) As mentioned above, your brakes will need an additional 4 mm of reach for 700c wheels. If your brakes don't have 4 mm of pad adjustment available, you need to replace the calipers or use offset brake pad holders.

2) Most new wheels use freehubs and cassettes rather than freewheels. 7-speed and higher cassettes are commonly available, but you'll need something compatible with the shifters and derailleurs on your bike. Assuming your P8 uses friction shifting -- as opposed to indexed shifting where each click on the shifter is exactly one shift -- you can probably run a 7-speed cassette without compatibility problems.

3) Your frame dropouts may be spaced at 126 mm, a little narrower than the current 130 mm standard. Not a big deal. You may be able to slide a 130 mm wheel right in. You can also "cold set" the frame to permanently respace it.
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Old 04-02-15, 03:28 PM
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Originally Posted by SkyDog75
The short answer: Yes, you can fit 700c wheels on your bike.

And now for the fine print:

1) As mentioned above, your brakes will need an additional 4 mm of reach for 700c wheels. If your brakes don't have 4 mm of pad adjustment available, you need to replace the calipers or use offset brake pad holders.

2) Most new wheels use freehubs and cassettes rather than freewheels. 7-speed and higher cassettes are commonly available, but you'll need something compatible with the shifters and derailleurs on your bike. Assuming your P8 uses friction shifting -- as opposed to indexed shifting where each click on the shifter is exactly one shift -- you can probably run a 7-speed cassette without compatibility problems.

3) Your frame dropouts may be spaced at 126 mm, a little narrower than the current 130 mm standard. Not a big deal. You may be able to slide a 130 mm wheel right in. You can also "cold set" the frame to permanently respace it.
Points 2 and 3 above only apply to rear wheels, and a dynamo hub is on the front. So if you are only putting a front on you should be good, if you have the reach with your brakes. But even that is easy and cheap enough to replace if necessary. There are medium and long reach calipers that will work. Tektro brakes are pretty good and really cheap, in fact you may be better off with them than with what you already have.

And since you didn't ask, let me recommend the B&M CYO Premium for the light. It throws off a lot of light where you need it most. This is what I use, along with the Shimano 3N72 dynamo hub laced up to 26" mtb rims. I built a matching rear just because I could, but I didn't really need it. I didn't have any of the rear wheel issues you would have.
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Old 04-02-15, 10:50 PM
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As an alternative, any competent bike shop should be able to build you a wheel with a 27" rim and a dynamo hub. 27" rims are much less common than when I was learning to build wheels, but they are still out there.

Universal Cycles will build a wheel from parts they stock. I found these pretty quickly:
Universal Cycles -- Shimano Nexus Sport Dynamo Hubs
Universal Cycles -- SunRingle CR-18 Rims
According to their calculator, this would cost you about $175 plus shipping.
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Old 04-03-15, 05:51 AM
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Thank you all for the fantastic advice. I will definitely look into this considering the information received here on this forum.
Much appreciated it.
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Old 04-03-15, 05:56 AM
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If there's any visible space on the brake arms beneath the pads it will likely be a simple fit with minimal brake adjustment.
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Old 04-17-15, 06:14 AM
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Thank you! I got the 700c wheel built with the dynamo hub in it and works good. The only thing is bothering me now is that I have a 700 front wheel and a 27" rear wheel. I will save some cash to get the matching wheel in a near future. Thank you for all the advice.
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