Sprockets Top Hat Disc Hub Sprocket Adapter - Best Possible Offset?

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#1
Hi all!

First post. My first and current bike is a 90’s Specialized Rockhopper Comp with a dax F80 kit. I did a couple of stupid things that ultimately destroyed my rear wheel. I’d had an eye on these wheels for I while, and I ordered them this past weekend:

https://www.amazon.com/Ringlé-Rhyno...0098D8T5I/ref=cm_cr_arp_d_product_top?ie=UTF8

In the interest of sparing these wheels from future destruction, I’ve decided to ditch the stock rag joint for a disc hub sprocket adapter. I’ve done a fair bit of reading on the subject, but I’m still not quite sure what to buy.

As I understand it, the following is true:

For a 135mm O.L.D multi speed hub such as the Shimano Deore M525, the distance between the disc rotor mount face and the inner face of the engine sprocket is 17.5mm. However, the maximum distance between the rotor mount face and the inner face of the rear sprocket that can be achieved with a top hat style adapter using a flat sprocket is 15mm. This is due to the location of the spokes.

My questions are as follows:

- Does a 15mm offset place the rear sprocket within the acceptable range of deviation from perfect alignment with the engine sprocket? If so, I think I'll ask the seller of these sprockets to make me a 40T sprocket with a 15mm offset:

https://www.ebay.com/itm/Motorized-...933570?hash=item2a65a4ec02:g:SDYAAOSwJb9WqRXI

- Could perfect alignment be achieved by using a dished sprocket in combination with a top hat style adapter? If so, is such a combination commercially available? I haven't been able to find any such thing :(

Thanks so much for your help! :)
 
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#2
You've read this thread?
https://motoredbikes.com/threads/4-bolt-104bcd-top-hat-for-135mm-o-l-d-disc-brake-hubs.49792/

I asked that same seller on ebay to make a pair of custom top hat adapters for me so I could switch between sprocket sizes using the same adapter, and also to allow me to mount the sprocket on the inside of the adapter to make it effectively dished and get past the problem of the spokes being in the way. We agreed a price and he said it would take two weeks.. and then he didn't contact me again or reply to my messages so I gave up on the dweeb and made my own adapter. :rolleyes:

Actually there is room for about a 17mm offset if you have the right sort of bolts. I think mine was 16mm because of a 1mm dish in the 42T steel mountain bike sprocket. This is only about 0.5mm out of alignment because I made my front sprocket narrower, grinding only the right hand side of it so it was moved outboard. I had to make the front sprocket narrower (0.120") to fit the #410 (1/8") BMX chain anyway. It worked well with this minimal misalignment. You can grind it even narrower and further outboard if you use 3/32" BMX race/ trials chain, like the one by Onza which is a KMC chain so its good single speed chain. Those trials riders obviously have to use a strong reliable chain. Or use 3/32" eight speed chain and don't worry about offset.

I am making a fresh attempt at the rear sprocket setup right now because I have decided to switch to 11/124" (2.25mm) nine speed chain (KMC X9-93) and a multi sprocket stack. Some misalignment won't be an issue with the more flexible multi speed chain, but my two largest sprockets should be within a couple of millimetres of alignment with the even narrower (2.20mm) front sprocket. :)
 
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#4
Bolt Circle Diameter (BCD) obviously affects the size of the hole in the centre of the sprocket. The MBRebel top hat has a 72mm BCD if I recall correctly (IIRC) and 10mm diameter holes, and there must be at least 2 or 3mm of material inside of the holes so the centre hole of the sprocket is probably around 58mm or less.
The spokes will only allow an offset of around 13mm at a diameter of 58mm. The sprocket is thicker than 2mm so perhaps using a file you will be able to make it dished by filing a taper out from the centre hole or file shallow grooves for the spokes to fit into and get some more offset that way.
At 104 BCD (or 90mm centre hole diameter) the spokes will allow an offset of around 17mm, maybe more depending on the exact position of the spokes on the particular wheel, plus another 1mm of dish that's common on mountain bike front sprockets meant to be the largest in a triple chainset.

_20180613_143117.JPG

Yeah I screwed up a bit drawing that but you get the idea. :oops:
 
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#5
About to hijack my own thread here :cool:

Thanks so much for your help guys.

Upon further reading, I think the right move might be to bite the bullet and buy a SBP shift kit. Your thoughts?

Assuming I do go through with it, the question of which kit to buy still stands. Is there a general consensus about which kit is the best? Is the deluxe kit worth the added cost? What are your guys' thoughts?

Oh, and sorry to change gears on you so suddenly (pun very much intended :cool: )
 

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#6
About to hijack my own thread here :cool:

Thanks so much for your help guys.

Upon further reading, I think the right move might be to bite the bullet and buy a SBP shift kit. Your thoughts?

Assuming I do go through with it, the question of which kit to buy still stands. Is there a general consensus about which kit is the best? Is the deluxe kit worth the added cost? What are your guys' thoughts?

Oh, and sorry to change gears on you so suddenly (pun very much intended :cool: )
Consensus on something like that? :p
SBP will make up a custom kit for you if you want to swap out some of the parts for different ones.
I would love to get around to buying a Shift Kit, I have had a bike awaiting one for over a year now, but I haven't stopped working on bike #1 yet, lol! :oops:
I think the deluxe kit has tools that you should really already own if you're a bike fan. I believe you need the HD freewheel, but not the UHD freewheel unless you plan to have multiple front sprockets or some such thing. The UHD freewheel has two bearings like a hub so it can handle the off centre stress far better than a single bearing.

Check out the aluminium spiders! :D
 

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#7
Consensus on something like that? :p
SBP will make up a custom kit for you if you want to swap out some of the parts for different ones.
I would love to get around to buying a Shift Kit, I have had a bike awaiting one for over a year now, but I haven't stopped working on bike #1 yet, lol! :oops:
I think the deluxe kit has tools that you should really already own if you're a bike fan. I believe you need the HD freewheel, but not the UHD freewheel unless you plan to have multiple front sprockets or some such thing. The UHD freewheel has two bearings like a hub so it can handle the off centre stress far better than a single bearing.

Check out the aluminium spiders! :D
Any advantages to going the spider route over a shift kit (barring cost, of course)?

Thanks again for the info!
 

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#8
Any advantages to going the spider route over a shift kit (barring cost, of course)?

Thanks again for the info!
Its just an example of one of the cool parts offered by SBP that could help you create something special and unusual. There's nothing wrong with the kit, but if we all limited ourselves to what's included in the kit all our bikes would be very similar, and in fact the Shift Kit wouldn't have been invented.
The sprockets in the kits are perfectly decent, but they are solid steel and therefore heavy and they are particular tooth counts, even their extra sprockets you can buy are in a limited range of tooth counts, and of course not made to be particularly friendly to a front derailleur.
You can use the SBP alloy spiders to mount standard bicycle sprockets, narrow wide 1x sprockets, alloy sprockets, cheap steel sprockets, sprockets to work well with a front derailleur, sprockets of all different sizes and colours.. :)
 


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