All-road/Gravel bike custom geometry help

[.RJ]

Originally Posted by snguyen268

In other words, my thinking of chainring size is more to fine tune the gear ratios in the middle rather than to achieve a higher max/min gear ratio, if that makes sense.

It does make sense, given the drag that the 10t ads, to size the ring to stay out of that.

But I wouldnt compromise anything else to get there. If your builder is using a chainstay yoke that will do a lot to get tire/chainring clearance.

[snguyen268]

Yeah for sure, completely agree with you there. I am planning to keep my 425mm chainstay with 45mm tire clearance. We are definitely going to use a chainstay yoke in this case, which will clear 46T comfortably. My builder is just a bit unsure about 48T, we will test fit during the build. I was just surprised and never thought it would be a challenge given that carbon bikes can easily clear 50-52T chainrings + 425mm chainstay + 45mm clearance these days. But I guess metal tubing does not permit a more complex shaped chainstay like carbon does.

[bmeryman]

Just got caught up on this thread; you're taking a really thoughtful approach to this and there's been a lot of great commentary and suggestions as well! I have a couple thoughts to add:

I'm also running a 46t front ring, but with an XPLR 10-44 cassette. I did consider the full mullet setup, but I found the gearing jumps a bit too big for my preference. I will say that I'm primarily riding on pavement or dirt roads, so I don't mind foregoing the low-low gears. Same as you did I picked my chainring based on what would keep me in the middle of the cassette most of the time.

Forgive me if I've overlooked it, but have you considered a UDH rear dropout? I think that's a nice option for futureproofing, especially if you're going to be in the Sram ecosystem.

I'll be following this thread more closely now; I'm working on a similar design and we've got similar fit goals. Let me know if you need to need to test fit/performance on any of our roads up here in VT - I'd be happy to show you around!

[.RJ]

Another option for you could be to use a boost (148x12) rear hub.

I dont know how much that really the other factors of the design, but it would allow you to push the chainring/chainline out 3mm and give you more clearance. Your wheelset would be an oddball @ 100/148 instead of 100/142, so you'd either have a pain upgrading or selling down the road, but its an option.

[snguyen268]

Originally Posted by bmeryman

Just got caught up on this thread; you're taking a really thoughtful approach to this and there's been a lot of great commentary and suggestions as well! I have a couple thoughts to add:

I'm also running a 46t front ring, but with an XPLR 10-44 cassette. I did consider the full mullet setup, but I found the gearing jumps a bit too big for my preference. I will say that I'm primarily riding on pavement or dirt roads, so I don't mind foregoing the low-low gears. Same as you did I picked my chainring based on what would keep me in the middle of the cassette most of the time.

Forgive me if I've overlooked it, but have you considered a UDH rear dropout? I think that's a nice option for futureproofing, especially if you're going to be in the Sram ecosystem.

I'll be following this thread more closely now; I'm working on a similar design and we've got similar fit goals. Let me know if you need to need to test fit/performance on any of our roads up here in VT - I'd be happy to show you around!

Yeah, I am planning on using UDH on my frame given that it seems to be the new standard for the forseeable future. Will take the chance to try out the Transmission system as well to see how it is. I was definitely considering XPLR as well but ended up choosing a full mullet setup for more versatility (with my calculations, the gear jumps likely won't bother as much as the gear ratios fall close to most of my most heavily used gear ratios).

Thanks mate! I will hit you up if I get a chance to go up that way this summer, definitely want to do some riding up that way for sure.

Happy to chat/bounce ideas abt your build as well. I often find myself going in circle when thinking abt my build on my own so trying to bounce it off people here has been very helpful For a question I asked earlier in the thread, are you planning on T47 or BSA for your build?

Originally Posted by .RJ

Another option for you could be to use a boost (148x12) rear hub.

I dont know how much that really the other factors of the design, but it would allow you to push the chainring/chainline out 3mm and give you more clearance. Your wheelset would be an oddball @ 100/148 instead of 100/142, so you'd either have a pain upgrading or selling down the road, but its an option.

That's an interesting thought that I haven't considered, will look into it more. My current plan is to keep my current wheelset which is 100/142 so it might complicate it a bit and I'd probably favor the "easy-to-replace" aspect of 100/142 for now.

[bmeryman]

Originally Posted by snguyen268

Happy to chat/bounce ideas abt your build as well. I often find myself going in circle when thinking abt my build on my own so trying to bounce it off people here has been very helpful For a question I asked earlier in the thread, are you planning on T47 or BSA for your build?

I've been back and forth on T47. I'm open to either, to be honest, so I may lean on the builder's expertise/recommendation. I'm happy with BSA and I'll probably stick with BSA if I choose to route the rear brake hose externally around the BB, but I am a bit intrigued by fully internal brake routing in which case I'd go T47. I already have BSA BBs for virtually every spindle, so it'd be nice to save a bit and not buy another part.

[snguyen268]

Originally Posted by bmeryman

I've been back and forth on T47. I'm open to either, to be honest, so I may lean on the builder's expertise/recommendation. I'm happy with BSA and I'll probably stick with BSA if I choose to route the rear brake hose externally around the BB, but I am a bit intrigued by fully internal brake routing in which case I'd go T47. I already have BSA BBs for virtually every spindle, so it'd be nice to save a bit and not buy another part.

Ya, I was back and forth (still a little bit) but ended up going with BSA per my builder's recommendation as we are routing hydraulic hose outside BB. I just hope that BSA will not become an obsolete standard in the next 15-20 years

[.RJ]

Originally Posted by snguyen268

That's an interesting thought that I haven't considered, will look into it more. My current plan is to keep my current wheelset which is 100/142 so it might complicate it a bit and I'd probably favor the "easy-to-replace" aspect of 100/142 for now.

A lot of hubs can be "boosted" with a spacer for the rotor and re-dishing the rim, too. You would need a 'boost' chainring to compensate in theory, but I have run many non-boost offset chainrings on 'boost' frames with no problems at all. It may be hard to find an offset chainring if you are using a 1x road group, I dunno.

Its not quick swap, but, it also doesnt turn your wheelset into a paperweight if you upgrade either.

[snguyen268]

That's a nifty trick. I haven't read up much on boost frame so will definitely read more into it to see if it makes sense here for me. Thanks so much for your insight.

[maslow]

I’m in the pretty much the exact same boat as you with a custom build and I’m deliberating over the HT angle/fork rake and resulting trail. I feel your pain and understand you just want to get it right first time.

One would like to think that if you have had a conversation with the frame builder and given them a clear brief of what you want the bike to do then really they should be able to advise what will/wont work for your case use. I’m assuming you’re talking Firefly/Seven/Bingham/Desalvo etc then I think you can rest assured they’ll do their job and nail the brief.

IMO I’d opt for the T47 bb shell. You can still fit a 24mm spindle crankset if needs be.

[snguyen268]

Originally Posted by maslow

I’m in the pretty much the exact same boat as you with a custom build and I’m deliberating over the HT angle/fork rake and resulting trail. I feel your pain and understand you just want to get it right first time.

One would like to think that if you have had a conversation with the frame builder and given them a clear brief of what you want the bike to do then really they should be able to advise what will/wont work for your case use. I’m assuming you’re talking Firefly/Seven/Bingham/Desalvo etc then I think you can rest assured they’ll do their job and nail the brief.

IMO I’d opt for the T47 bb shell. You can still fit a 24mm spindle crankset if needs be.

Yeah you spoke my mind accurately I assume youYes, it's a I do have full faith in my builder but you know that sense of doubt/uncertainty when it's only a pdf till you get to finally ride the bike?

Is there a particular reason why you favor T47? Most of the resources I have come across only mentioned the advantages of T47 when it comes to a carbon frame or Ti frame with full internal routing (for me hydraulic cable is routed outside of BB)

[Alistair]

Originally Posted by snguyen268

Is there a particular reason why you favor T47? Most of the resources I have come across only mentioned the advantages of T47 when it comes to a carbon frame or Ti frame with full internal routing (for me hydraulic cable is routed outside of BB)

The other benefit is flexibility - you can use everything from Shimano spindles to 30mm spindles. And retain a decent size bearing while you do it. Does that actually matter in practice? Not really.

[.RJ]

Originally Posted by snguyen268

Is there a particular reason why you favor T47? Most of the resources I have come across only mentioned the advantages of T47 when it comes to a carbon frame or Ti frame with full internal routing (for me hydraulic cable is routed outside of BB)

A few things - builders like them because it gives more surface at the BB to weld tubes to, making fabrication a little easier. They've become pretty commonplace on new bikes, so if/when you need a new one, it wont be hard to find say, a dub crank T47 BB. And long term, they're as future proof as you'll find for different cranks/groups.

[maslow]

Originally Posted by .RJ

A few things - builders like them because it gives more surface at the BB to weld tubes to, making fabrication a little easier. They've become pretty commonplace on new bikes, so if/when you need a new one, it wont be hard to find say, a dub crank T47 BB. And long term, they're as future proof as you'll find for different cranks/groups.

This ⬆️

[snguyen268]

Originally Posted by .RJ

A few things - builders like them because it gives more surface at the BB to weld tubes to, making fabrication a little easier. They've become pretty commonplace on new bikes, so if/when you need a new one, it wont be hard to find say, a dub crank T47 BB. And long term, they're as future proof as you'll find for different cranks/groups.

That's exactly was what I gathered from reading as well, especially the "futureproof" aspect given prevalence of T47 in virtually any newly released bikes nowadays. I also saw articles on the larger surface area for welding. However, my builder was more of a BSA proponent given that it has been around since forever and accommodate both 30mm and 24mm spindle cranks. Then the reverse question becomes, when do you favor BSA over T47? Seems like never?

Of course, it's probably a gamble either way given one cannot predict the future. I just wish that there was just one standard for BB to make life easier for everyone