Sturmey Archer R-SRF 3 BMX jump bike Question

[ClappedOut]

Looking at a 20inch wheel to a 24 and swapping the three speed over-is it just a spoke calculator and am I better off using the original bike rim or a replacement. Is there any specific Spokes for the hub or just the correct diameter stainless and length with spoke washers
https://www.sheldonbrown.com/wheelbuild.html the guide I plan to use.
Any advice appreciated

Thanks

[rogerzilla]

How many holes does the hub have?

[jb]

How can you use the original rim if your swapping it for a 24? Is there some misunderstanding here?

[ClappedOut]

I have a 36h 20inch rim with a 3speed hub and all the controls on its way for little money, compared to buying new with all the controls.
The bike is 24 inch rim with free wheel currently.

So I could take the hub out of the 20 inch existing rim and take the 24'inch rim off bike and re lace with new Spokes.

Or.

I could keep the single speed rim off the bike and get a new rim.

A friend thinks they have a silver 24 inch mountain bike rim they are going to check, if it is OK this would be a cheap way to keep original bike wheel.

What I asked badly is are bmx and mountain bike Spokes a different thickness to a shopper bike?

Will the hub I have coming take mountain bike thickness Spokes or will I need thinner Spokes to fit hub?

If hub needs thinner Spokes will the spoke nipples be compatible with a BMX or mountain bike rim or does the rim need replacing

Just trying to get my head round hub, spoke, nipple and rim compatibility without all the parts here yet.

[PT1029]

The majority of spokes used are the same thickness, 14g/2mm thickness. Other thinner/thicker spokes do get used but are less common.
Wait for your wheel to arrive, and check if the spokes are 2mm thick, and then do the same on your 20" wheel.
Most mountain bikes use the standard 2mm spokes. The SA hub may well need different length spokes from the existing hub used in your 24" wheel.
There is a chance the shopper SA hub spindle might not be long enough for a 135mm mountaing bike frame. SA axles come in a variety of lengths, including long enough for 135mm frames.
As someone said, check the spoke count on the hub. Some shoppers have less than 36 spokes due to the small wheel size.

[rogerzilla]

I was just checking you weren't lacing a 36h hub to a 28h rim (more common in smaller wheels). It's possible by skipping holes, but the spoke calculations are beyond me.

[ClappedOut]

Thank you for the advice the Stumley archer hub was very cheap, I will offer up the parts before committing to doing it.

Having only aligned built wheels and last seeing a old elswick hopper 3 speed in the 1990's all a bit cloudy.
Plus other than I believe SA built in Taiwan now I haven't seen a current model in the flesh yet.

[Sid Aluminium]

Shouldn't need spoke washers as the RSRF3 hubshell has nice thick, modern alloy flanges.

[Sid Aluminium]

I'm guessing the RSRF3 will be plenty wide. Might be too wide, depending.

Fun facts: The rotary shift SA 3s have solid axles without passages or cutouts. They have 3/8-26 axle threads (!), have different cable pulls and require unique C30 shifters.

[ClappedOut]

Thank you for all the help and replies, I found a website BMX Museum and it seems popular

https://bmxmuseum.com/forums/viewtopic.php?id=304579

It may be that it will or won't work on the frame we have, but the idea of a simple 3 speed hub means 33% lower gear for hills and bridges and 33% higher for more speed. I believe second is 1:1.

[rogerzilla]

There was a BMX version of the AW once, I believe, although it may only have been for the US market.

SA hubs, with their flattened axles, may not appreciate being jumped. The axle is just the right way around to bend. All the shells are the same width, so 135mm spacing leaves a huge vulnerable overhang on each side; a frame and hub with not much more than 110mm spacing would be better.

[ClappedOut]

There was a BMX version of the AW once, I believe, although it may only have been for the US market.

SA hubs, with their flattened axles, may not appreciate being jumped. The axle is just the right way around to bend. All the shells are the same width, so 135mm spacing leaves a huge vulnerable overhang on each side; a frame and hub with not much more than 110mm spacing would be better.

Thank you for info I paid £32 so I would be happy to build a bike around the hub, if needs be I would be happy to source another frame etc.
Naively I thought a solid axle would be stronger and didn't consider internals for BMX could be different.

My son has a BMX as well as this jump bike, I wonder if a 26inch mountain bike type frame with cx gravel tyre would be better.

I know very little about the modern stumley archer, my only experience of the AW is in shopper bikes and old town bikes the old guys seemed to ride decades with next to no maintenance.

My goal is a 3 speed bike for 9 Yr old with mild country lane ability and if he jumps off a curb height it survives 6 inches in air max.

Thank you for guidance.