Specialized Sirrus 1988
09-24-20, 02:59 PM
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Specialized Sirrus 1988
Does anyone know the clamp size for the front derailleur, because I currently have a shimano 105 clamp on derailleur, but I bought a braze on shimano 600 one to replace it in the future. Would the 105 derailleur state it somewhere because I've tried measuring the circumference and end up getting a measurement of 3 5/8 inches. Which means the diameter is 29.32cm and I know that isn't one of the normal tube sizes.
09-24-20, 03:13 PM
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That model looks pretty normal. Is it possible your initial measurement for circumference was 2mm off? You multiply 28.6 x 3.14 and get 89.8, which is very close to your 3 5/8 circumference measurement. 28.6 would be the size I'd expect.
09-24-20, 03:14 PM
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some times the diameter is printed on the inside of the FD clamp like so....
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09-24-20, 10:53 PM
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Most likely your Sirrus' seat tube is the old road-bike standard of 28.6 mm. The size should also be stamped on the inside of the clamp, as seen above.
But I have a question.
Why did you buy a braze-on front derailleur as a backup for a clamp-on one? If the frame doesn't have the required tab on the seat tube, the new derailleur won't go on the bike. If it does, how does the clamp-on that's on the bike now even work when it's sitting that low?
I'm really confused...
--Shannon
But I have a question.
Why did you buy a braze-on front derailleur as a backup for a clamp-on one? If the frame doesn't have the required tab on the seat tube, the new derailleur won't go on the bike. If it does, how does the clamp-on that's on the bike now even work when it's sitting that low?
I'm really confused...
--Shannon
Last edited by ShannonM; 09-24-20 at 10:57 PM.
09-25-20, 01:28 AM
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Most likely your Sirrus' seat tube is the old road-bike standard of 28.6 mm. The size should also be stamped on the inside of the clamp, as seen above.
But I have a question.
Why did you buy a braze-on front derailleur as a backup for a clamp-on one? If the frame doesn't have the required tab on the seat tube, the new derailleur won't go on the bike. If it does, how does the clamp-on that's on the bike now even work when it's sitting that low?
I'm really confused...
--Shannon
But I have a question.
Why did you buy a braze-on front derailleur as a backup for a clamp-on one? If the frame doesn't have the required tab on the seat tube, the new derailleur won't go on the bike. If it does, how does the clamp-on that's on the bike now even work when it's sitting that low?
I'm really confused...
--Shannon
https://www.universalcycles.com/shop...p?category=530
You might also want to get digital caliper, very handy for measuring many things around a bicycle.
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09-25-20, 02:26 AM
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Lots of manufacturers make adapters to attach a braze-on FD on a frame without the braze-on fitting. Quite a few in this list. Make sure you get one for a 28.6mm ST.
https://www.universalcycles.com/shop...p?category=530
https://www.universalcycles.com/shop...p?category=530
I do remember wondering why all front derailleurs weren't made like that, since it would simplify all sorts of supply issues and would seem to have zero downside. One derailleur, buncha clamps, easier and cheaper for everyone from Shimano headquarters all the way down to the wrench at your local bike shop.
--Shannon
09-25-20, 03:08 AM
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Lots of manufacturers make adapters to attach a braze-on FD on a frame without the braze-on fitting. Quite a few in this list. Make sure you get one for a 28.6mm ST.
https://www.universalcycles.com/shop...p?category=530
You might also want to get digital caliper, very handy for measuring many things around a bicycle.
https://www.universalcycles.com/shop...p?category=530
You might also want to get digital caliper, very handy for measuring many things around a bicycle.
09-25-20, 08:39 AM
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btw OP we are going to need pictures of the Sirrus so get to posting or use the gallery 
09-25-20, 09:54 AM
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I was able to figure it out by taking off the derailleur and seeing the model number. The pdf that came up said that this model had the clamp diameter 28.6 so thank you all for your help. And I put a picture on my gallery because I don't have enough street cred yet to post pictures in fourms. The paint still looks good, but the only problem is rust on the top tube cable guides which I'll probably repaint.
