Anyone here know the BCD of an old SR Royal chainring?

I don't have the crankset here so I can not take an image of it. It's an SR Royal and I wonder if the BCD of that stayed the same over the years. It has 2 laurel leaves with an oval with SR inside another oval with ROYAL in that oval ubder the oval with the SR in it. Does anyone here know what the BCD was on those cranksets?

Cheers

On 7/26/2019 1:15 AM, Sir Ridesalot wrote:
I don't have the crankset here so I can not take an image of it. It's an SR Royal and I wonder if the BCD of that stayed the same over the years. It has 2 laurel leaves with an oval with SR inside another oval with ROYAL in that oval ubder the oval with the SR in it. Does anyone here know what the BCD was on those cranksets?

Cheers


Royal series, which are cold forged, were made in several
versions, 144mm, 130mm, 110mm.

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971

On 7/26/2019 1:15 AM, Sir Ridesalot wrote:
I don't have the crankset here so I can not take an image of it. It's an SR Royal and I wonder if the BCD of that stayed the same over the years. It has 2 laurel leaves with an oval with SR inside another oval with ROYAL in that oval ubder the oval with the SR in it. Does anyone here know what the BCD was on those cranksets?

Cheers


Why not measure and do math?

If n = number of bolts, d = distance between bolt hole centers
cosine in degrees

BCD = 2*sqrt((d*d)/(2*(1-cos(360/n))))

On Friday, July 26, 2019 at 4:11:32 PM UTC-4, ERSHC wrote:
On 7/26/2019 1:15 AM, Sir Ridesalot wrote:
I don't have the crankset here so I can not take an image of it. It's an SR Royal and I wonder if the BCD of that stayed the same over the years. It has 2 laurel leaves with an oval with SR inside another oval with ROYAL in that oval ubder the oval with the SR in it. Does anyone here know what the BCD was on those cranksets?

Cheers


Why not measure and do math?

If n = number of bolts, d = distance between bolt hole centers
cosine in degrees

BCD = 2*sqrt((d*d)/(2*(1-cos(360/n))))

Ah, because the crankset is not HERE with me? Hard to measure something when it's miles away.

Cheers

On Friday, July 26, 2019 at 1:57:37 PM UTC-7, Sir Ridesalot wrote:
On Friday, July 26, 2019 at 4:11:32 PM UTC-4, ERSHC wrote:
On 7/26/2019 1:15 AM, Sir Ridesalot wrote:
I don't have the crankset here so I can not take an image of it. It's an SR Royal and I wonder if the BCD of that stayed the same over the years. It has 2 laurel leaves with an oval with SR inside another oval with ROYAL in that oval ubder the oval with the SR in it. Does anyone here know what the BCD was on those cranksets?

Cheers


Why not measure and do math?

If n = number of bolts, d = distance between bolt hole centers
cosine in degrees

BCD = 2*sqrt((d*d)/(2*(1-cos(360/n))))

Ah, because the crankset is not HERE with me? Hard to measure something when it's miles away.

Cheers

The diameters are pretty easy to tell on a double - if you have a 144 the smallest small ring is a 44 tooth. a 130 is a 39 and the 110 a 34 though I think that you could probably mount a 32 with careful bolt symmetry.

As you can see, over the years people have used lower and lower gears so that while they actually climb slower they can retain that speed longer over progressively steeper terrain.