All-road/Gravel bike custom geometry help

[sparky33]

Originally Posted by snguyen268

Do you think I should consider 78mm to 80mm BB drop?

No. 75 is just right for 700c.

[snguyen268]

Originally Posted by sparky33

Either of these geometries looks fine for a road-biased gravel bike. 72…71.7…fine. A roomier front center is useful on a bike this size.

There is a lot to like with T47 because a lot of nice cranks have 30mm spindle.

I like a gravel fit that is a bit less long and low than a road bike, but you do you.

Thanks so much for your input! So if you were to pick between the 2, you would go for the longer TT as well?

Regarding crankset, you know any good 3rd party one (that has a 165mm option) for shimano di2 12-speed drive train? The only option I found so far is Rotor

[Charles M]

DONT TAKE ANY ADVICE....

Go ride a couple of different head angles/wheelbases and answer your own question...

Your weight distribution and riding style will change your mind more than someone else's opinion of what should work... Dont waste your money buying someone else's dream custom bike...

And Rotor are a GREAT option as are Praxis.

[snguyen268]

I have another miscellaneous question for you all:

If you have the choice to have bolt-on mounts for frame bags, would you go for it? or would you stick with velcro straps for simplicity? I know velcro straps can damage paints but does it damage titanium's anodized finish? I don't have plan for extensive bikepacking but would like a small frame bag (2.5L-3L volume) for my >5hrs rides

[sparky33]

Originally Posted by snguyen268

I have another miscellaneous question for you all:

If you have the choice to have bolt-on mounts for frame bags, would you go for it? or would you stick with velcro straps for simplicity? I know velcro straps can damage paints but does it damage titanium's anodized finish? I don't have plan for extensive bikepacking but would like a small frame bag (2.5L-3L volume) for my >5hrs rides

Bolt-on bags are great if you know what kind of bags you will use. Strap on bags are equally useful and easier to take off but require some frame protection tape to avoid damaging the paint, if you care about that.

On my new Breadwinner I went for the 1/2 framebag with bolt-on mounts. Slick. Though it can brush inside of my knees a bit.
Bento-box top tube bags work best when bolt mounted, IMO.

All that said, my favorite 2-3L bag setup is a simple Swift Bandito or Swift Kestrel handlebar bag. It is a simple solution that works perfectly and obviates the need for a frame bag altogether.

[NHAero]

Originally Posted by snguyen268

Snip
Do you think I should consider 78mm to 80mm BB drop?

IMO BB drop should consider the smallest diameter wheel/tire combo you anticipate, and how you ride. I like as much drop as is reasonable on my bikes. My Bingham has 75mm drop and is designed for 650Bx38 tires. In theory, that gives a BB height of (584/2+38)-75=255mm, or just over 10 inches. That's pretty low! In practice, it's a couple of mm higher because the GK slicks measure 332-333mm in radius on the BTLOS rims, not 330mm. For many years I rode the original style Eggbeaters with the Ti axles, which are shorter than the stock steel axles, and provide very good cornering clearance. Recently I switched to Eggbeater 2 pedals with steel axles, and they are wider. For the first time that I can remember, I hit a pedal on the pavement pedaling through a tight turn recently!

My all road bikes are not set up for rowdy off road riding, more for the type of dirt roads we have in New England. So when I ride something like D2R2 I'm a bit more careful than others might be on the bits of jeep road/single track. Usually I have 42mm tires on, so get a bit more BB height.

My Firefly was designed with 78mm drop which in theory gives a BB height of 258mm with 700Cx25 (622/2+25)-78=258. That seems low for a road bike but in practice it measures 265mm. The radius of the GP5000 700Cx25 tire on Easton R90SL rims is 341+mm, and I think the BB drop may be very slightly smaller than what the build sheet shows.

I'm sure that framebuilders know a lot more than I do from a few measured data points what actual BB height will result for a given wheel size and tire size based on the BB drop. And I know that people's opinions of minimum BB height will vary too.

[.RJ]

Originally Posted by snguyen268

2. T47 vs. BSA BB? I am running Di2, which precludes the ability to use 30mm BSA BBs (not enough room for cable routing according to my understanding). Should I go for T47 to have maximum versatility? Any other downsides besides slightly heavier BB and not as common as BSA?

Having done 2 custom bikes with T47, its not a bad solution here, but I do wish I had gone with BSA for at least one of them if not both.

If you are looking at Di2, then shimano cranks seem like they will be forever 24mm spindle so there's no real need to go with a T47 for crank compatability. If you are committed to routing cables/hoses internally then you are kind of forced to go this direction, and with Di2/Hydro its not like you'll ever need to service them, so thats the thing you really need to decide.

[NHAero]

Originally Posted by sparky33

Bolt-on bags are great if you know what kind of bags you will use. Strap on bags are equally useful and easier to take off but require some frame protection tape to avoid damaging the paint, if you care about that.

On my new Breadwinner I went for the 1/2 framebag with bolt-on mounts. Slick. Though it can brush inside of my knees a bit.
Bento-box top tube bags work best when bolt mounted, IMO.

All that said, my favorite 2-3L bag setup is a simple Swift Bandito or Swift Kestrel handlebar bag. It is a simple solution that works perfectly and obviates the need for a frame bag altogether.

Agree with Sparky about small handlebar bags, I have the Almsthre bag that is similar to the Bandito on my Bingham and Firefly. I opted for bolt-on bosses for a TT bento on the Bingham but found that when standing up I rubbed on even a small one. For trips I use a larger bar bag that still doesn't require any support structure (Orucase Smuggler XL, 4.5L).

[sparky33]

Originally Posted by Charles M

[SIZE="4"]
And Rotor are a GREAT option as are Praxis.

Those Praxis cranks are nice.

[benb]

Last time I worked on a custom bike design the guy who helped me was Asian descent. His bikes were similar reach/stack ratio as we're talking about here and we definitely talked about this as I'm almost the complete opposite. I'm all legs.

If you trust your fitter I bet both will work fine. I think the one thing is you might be out on the extremes enough you really want to nail this bike and make it a keeper, as it might have limited audience if you want to sell it. Of course that would depend on where you live. If it's that specific and you're really confident you're going to nail it then maybe it's the time to really make it your dream bike?

I'm 12cm taller and my saddle height is 6-7cm higher and yet the 2nd of these two bikes isn't that far off the reach I could use. But I couldn't ride it without an absolutely insane stem, as I'd probably be looking at 15cm+ drop the way it's setup, and because my torso is short and I like to keep my arms bent I tend to favor lower drop as I still have a pretty low torso.

I went through this twice and it would still make me super nervous doing it again. I didn't buy the bike last time, but I do think they had it right. If your proportions are in the middle of the bell curve maybe all this feels easy, but when you're not it's a nervous process.

[snguyen268]

Originally Posted by NHAero

IMO BB drop should consider the smallest diameter wheel/tire combo you anticipate, and how you ride. I like as much drop as is reasonable on my bikes. My Bingham has 75mm drop and is designed for 650Bx38 tires. In theory, that gives a BB height of (584/2+38)-75=255mm, or just over 10 inches. That's pretty low! In practice, it's a couple of mm higher because the GK slicks measure 332-333mm in radius on the BTLOS rims, not 330mm. For many years I rode the original style Eggbeaters with the Ti axles, which are shorter than the stock steel axles, and provide very good cornering clearance. Recently I switched to Eggbeater 2 pedals with steel axles, and they are wider. For the first time that I can remember, I hit a pedal on the pavement pedaling through a tight turn recently!

My all road bikes are not set up for rowdy off road riding, more for the type of dirt roads we have in New England. So when I ride something like D2R2 I'm a bit more careful than others might be on the bits of jeep road/single track. Usually I have 42mm tires on, so get a bit more BB height.

My Firefly was designed with 78mm drop which in theory gives a BB height of 258mm with 700Cx25 (622/2+25)-78=258. That seems low for a road bike but in practice it measures 265mm. The radius of the GP5000 700Cx25 tire on Easton R90SL rims is 341+mm, and I think the BB drop may be very slightly smaller than what the build sheet shows.

I'm sure that framebuilders know a lot more than I do from a few measured data points what actual BB height will result for a given wheel size and tire size based on the BB drop. And I know that people's opinions of minimum BB height will vary too.

Yeah that makes sense. Is your all-road bike a Firefly? That's actually what I am working on right now. I live in MA so most of my riding will be here around Boston and in northern Maine (D2R2 is definitely an event I am targeting to do in the future). If you have any words of wisdom when it comes to bike geometry design for the kind of riding we have here in New England, I would love some insights.

Originally Posted by .RJ

Having done 2 custom bikes with T47, its not a bad solution here, but I do wish I had gone with BSA for at least one of them if not both.

If you are looking at Di2, then shimano cranks seem like they will be forever 24mm spindle so there's no real need to go with a T47 for crank compatability. If you are committed to routing cables/hoses internally then you are kind of forced to go this direction, and with Di2/Hydro its not like you'll ever need to service them, so thats the thing you really need to decide.

Thanks for the insights! Yeah I am still kinda on the fence because I see that there are some 3rd party cranks for shimano that uses 30mm spindle so I just need to decide how important it is for me to not have the option to run 30mm spindle with internal di2 routing. Any downside to T47 that you have experienced that made you wish you had gone for BSA?

Originally Posted by NHAero

Agree with Sparky about small handlebar bags, I have the Almsthre bag that is similar to the Bandito on my Bingham and Firefly. I opted for bolt-on bosses for a TT bento on the Bingham but found that when standing up I rubbed on even a small one. For trips I use a larger bar bag that still doesn't require any support structure (Orucase Smuggler XL, 4.5L).

Thanks for the rec! I do plan to have bolt-on bosses for a TT bento box. Maybe I should just stick with that and add a handlebar bag if I ever need it. It's just that the thought of having a small frame bag that sits neatly within the main triangle is aesthetically attractive to me haha

Originally Posted by benb

Last time I worked on a custom bike design the guy who helped me was Asian descent. His bikes were similar reach/stack ratio as we're talking about here and we definitely talked about this as I'm almost the complete opposite. I'm all legs.

If you trust your fitter I bet both will work fine. I think the one thing is you might be out on the extremes enough you really want to nail this bike and make it a keeper, as it might have limited audience if you want to sell it. Of course that would depend on where you live. If it's that specific and you're really confident you're going to nail it then maybe it's the time to really make it your dream bike?

I'm 12cm taller and my saddle height is 6-7cm higher and yet the 2nd of these two bikes isn't that far off the reach I could use. But I couldn't ride it without an absolutely insane stem, as I'd probably be looking at 15cm+ drop the way it's setup, and because my torso is short and I like to keep my arms bent I tend to favor lower drop as I still have a pretty low torso.

I went through this twice and it would still make me super nervous doing it again. I didn't buy the bike last time, but I do think they had it right. If your proportions are in the middle of the bell curve maybe all this feels easy, but when you're not it's a nervous process.

Yeah I am definitely nervous about this process because I have never thought that my fit position is that extreme. This is where I will just have to have full faith on my fitter/builder as he is very experienced. This is my dream bike and one that I will keep no matter what so for sure I just want to make sure it fits me (with the ability of adjusting for small changes in the future)

[.RJ]

Originally Posted by snguyen268

Any downside to T47 that you have experienced that made you wish you had gone for BSA?

A bit part of it with a steel bike is aesthetics - it looks a bit out of place - and with my customs I've asked for external cable routing so routing the rear brake through the DT and the T47 shell makes servicing a pain, but eventually going to a hydro brake will make that a non issue. I built it with paul cable brakes because thats what was available in 2021 when I built it up.

[snguyen268]

Hi all,

I have a bit a down time so I find myself back working out my bike build and have a couple things that I would like to pick your brain on:

1. Drivetrain selection - Currently I am between 3 approaches. Let me know which way you think I should go with?

a. Use my current Ultegra di2 12-speed (50x34 + 11-34). Pro with this is that saves me on cost but limitation is gear range off-road

b. SRAM 1x Mullet (46 + 10-52 Eagle). After doing some gear ratio calculation, this combo will have all the gear ratios that I use most frequently on my current Ultegra setup so road riding shouldn't be an issue. The bonus is the lowest gear will be sub 1:1, which will be useful for off-road. The cons here is of course, cost since I will have to get everything and that will really max out my budget. Any other downside of going 1x Mullet for road riding that I have not thought about?

c. The future GRX 12spd Di2. The hope here will be to emulate the SRAM 1X Mullet while keeping some current Ultegra parts (assuming cross-compatibility, which is not a given).

My build is planned for later 2024 so I have time to mull over and potentially wait for the new GRX, if it is gonna be released by then. But some SRAM discounts right now are pretty tempting...

2. Is it worth it to invest on a pair of hand-built wheels? Originally I was not factoring in wheels into this built (planning on using my current pair of wheels, which is 44mm deep, 21mm internal width, and can take up to 42mm tires so definitely capable for off-road riding). However, after talking to a wheel-builder, I start to fancy the idea...Not sure if it is worth it? It will definitely put me way over budget...

3. When doing a fully custom build, where do you prioritize spending money? Frame vs. Components vs. wheels. Where would you rank these 3 groups of items in order of priority. Right now, I am going all in on the frame (i.e. getting all the bell and whistle that I want, not necessarily need). Then using the remaining of my budget on Ultegra or Force/XX1-level components and neglecting the wheels. But should I prioritize wheels over components?

4. I have modified my new bike geo design a bit. The changes here compared to the front page is slightly slacker HT angle (71.5 instead of 72), increased fork offset (52mm instead of 50). The result is about 4mm increase in front-center/wheelbase. You all have any thoughts? Does this design strike a balance for mixed road & off-road riding? Or it goes too deep into the off-road geo now?

Thanks so much!

[snguyen268]

Getting closer to getting all the parts for my build and trying to make up my mind on some decisions. Hope you guys have some insights to share

1. On drive train selection, I am pretty set on doing a SRAM 1x mullet with 46T + 10-52T using the SRAM Transmission. The rationale here is I calculated gear ratio of my current setup on my road bike to figure out what are my most heavily used gear ratios for specific terrains and found that 46T + 10-52T combo will offer all of my favorite gear ratios and some more on the low end, which is exactly what I am looking for. Is there anything else I should consider? Anyone has experience with using SRAM Transmission yet on a gravel/road bike? If so, what are your thoughts? If 1x MTB mullet is a bad idea, what alternative system I should look into?

2. I am still back and forth about whether it is a good or bad idea to go with T47 BB (over BSA)? T47 seems to gain popularity recently so maybe it's here to stay for a long time? Since BB is not a changeable part of the frame, I just hope to go with one that is relatively "futureproof"

Thanks a bunch!

[KonaSS]

Nothing is future proof. But of the 2 choices, I would say BSA has the most staying power.