Psykal

Hi all,
I'm an amateur road-biker looking to get a titanium frame after 7 years with a Giant TCR. Also, having moved regions in France, I am in gravel friendly terrain now and am trying to get a custom frame with a Chinese manufacturer (shortlisted Waltly and XACD). I speak sufficient Chinese to pull off the conversation if necessary but wanted to get my design validated by some of you who have clearly more experience with this than I have. I'd really appreciate your feedback and advice on the dimensions/geometry. I am 167cm with 82cm inseams and am going for a generally more uptight ride position.

Some additional questions:
1) BB Shell Size: I have an Ultegra groupset that I intend to install on the bike. Is 68mm the recommended size for this?
2) Head Tube Size: Roadbikes generally have 36mm diameters - would you recommend a different size for gravels? If so any recommendations on the head set? Ritchey?
3) Dropouts: I have only ever known QR style dropouts on road bikes. Are there advantages to the 142X12 thru axle?

Any feedback on whether I am messing this up will be appreciated.

Psykal

Oops, it appears I cannot upload images as a newbie. I'd be happy to send it over privately if someone would like to take a look at the drawing.

unterhausen

Welcome to the forum. Sorry for the anti-spam limits for new users. What you can do is upload your pictures to an album in your gallery and we can post them here for you if you let us know.

I would get through axle right now because that's what the industry is doing and it's just easier. People will argue for advantages, but that's the main advantage I see.

I would get a tapered head tube if it's offered. There are a lot of 1 1/4" forks, but it might be easier to get a head tube for 1 1/8" to 1 1/2". There are many options, so who knows what those builders will work with. Maybe just straight 44mm. This link shows what is possible:
https://www.paragonmachineworks.com/...-titanium.html

Depending on your tube sizes, T47 might work best, particularly with big tubes. Again, it depends on the builder. They may have an easier time with 68mm. I'm not sure what alternative bb sizes your ultegra cranks will work with, but 68mm and T47 will work.

Psykal

Thanks a lot for the advice unterhausen . I have uploaded the image to my gallery as well. I appreciate your help in posting it to the thread.

unterhausen

voilà

unterhausen

I would go for a 395mm A-C fork, it's the most common size for this kind of bike. The dimension you give is not A-C. A-C is the hypotenuse of the 45mm-388mm triangle. Many gravel forks now have 55mm rake. With a head angle that slack, you are going to be happier with 55mm rake.

Do you anticipate doing a lot of descending? Or even just steep hills? I would consider a shorter stem and longer top tube.


What size tires are those?

blakcloud

I am questioning your top tube length and stem length for your height. From the numbers you gave, you have extra long legs for your height and that would mean a short torso. Basically for your height I am not convinced that an essentially a 54 cm frame is the right size for you.

Your head tube length is also on the aggressive side and maybe that is what you want a race style gravel bike. If you are looking at more endurance fit, I would rethink that one.

Are you copying the stack and reach of your Giant? Once you get that sorted why don't you just copy the geometry from someone like Moots or Lynskey? Don't try to re-invent the wheel when there are so many good gravel bikes you could just copy.

For bottom bracket, T47 would be my choice. Thru axles would just be a given with disc brakes. Third Shimano GRX would be my group choice.

That is just some food for thought. If you do follow through with this endeavor please keep posting because I am sure others will be interested in the process and your final build. Good luck.

scubaman

With the caveat that I've never designed a bike frame: designing for an Ultegra crank (=68mm bottom bracket shell width) seems like it might limit your maximum tire size, because the chain ring(s) and the crank arms need to clear the chainstays. Perhaps others here could advise?

Psykal

Thanks blakcloud. Actually, yes, good food for thought - no point in copying the TCR for a gravel geometry. Let me look up Lynskey and Moots. Also good advice on the frame - I struggled a bit with my TCR in the beginning with the seat height and the handles, I suspect that I know why now.

dwmckee

I have owned two Ti bikes now and spent a lot of money on them. My advice for gravel riding is that carbon frames beat the heck out of Ti in every way except for lifetime durability. And as far as I am concerned I do not want to be riding the same bike in 25 years, I want to change with the times and be riding the latest and greatest, not a 25 year old throwback. I have no problem at all replacing a carbon frame after 7 or 8 years of great service.

Parkyy16

As others have pointed out, you'll get more fork options by going with a 44mm head tube. Unless you have a specific fork in mind(Ritchey forks for example), go with a 44mm for versatility and upgradability. T47 is also a good advice as you can use the "stiffer" cranks made for the pressfit bottom bracket as well as the Shimano cranksets. Expect a bit higher BB costs if you go with T47.

As for the geo, The angles look decent(depending on what type of trail you're on), but the stack seems pretty aggressive. If you know that you're comfortable with that much bar drop, no issues with that geometry. I would personally make the stack a bit higher, more similar to an endurance bike, and adjust the reach a few mm back to make it the same fit overall. EDIT: Holy hell, just saw your body measurements. You've got some looooong legs. I'm 175cm with 81cm inseam and I was told I'm slightly above average on leg length. Which means you'll likely need a reach of 370 or lower to make sure the bike fits. I'd get a bike fit before ordering your frame with a body proportion this far out of norm.

435 chainstays is a good "all-rounder" length. You can have them put in sliding dropouts and you can adjust it as you need from 430 - 450. BB drop seems good, reach seems good. For the fork, you could get a slightly longer and more offset fork(ENVE G fork, Rodeo Spork, Whisky, etc). That'll make your trail a bit shorter, so you get a bit livelier front. I prefer 60 - 68 trail, any more feels a bit sluggish from my personal experience. You can adjust trail with tire size, so if you get it within a ball park of the tire you think you'll use and you should be okay.

So... to summarize, this is what I would do(ST and HT angles adjusted for the type of riding that's available around me. If you're near more intense gravel, you can slacken the head angle and adjust other things as needed.)
- Change HT to 130 or 135mm for a stack of 555-565ish
- Change HT to a 44mm tube
- Change bottom bracket from BSA to T47
- Request a sliding rear "dropout" for adjustable chain stay length to be adjustable between 430 - 450mm
- 74° seat tube angle, 71.5° head tube angle
- ENVE G Fork(395mm axle to crown, 50mm offset), resulting in 63mm trail

rm -rf

Will you have toe overlap?

I have a custom Ti frame that was made for all-day road riding and for gravel roads. The designer wanted to have minimal toe overlap, but I told him it wouldn't be a problem. So I got more of a road bike geometry that I like.
The toe overlap is fine, most of the time, but not good at all on steeper gravel roads and other slow speed situations where I need lots of steering input. I have to be very careful, and I still bump the side of the tire sometimes.

It's never been a problem when riding on roads, unless the grade is extreme on a climb.

Chilepines

There are a lot of variables in frame design so too many things to respond to in a totally custom frame.

Your reach of 388 is really long for someone of your height. 375 is more typical for a 50-52 cm frame. And then a stem length of 100 mm is, I think, going to be way too long.

Of course a lot depends on the terrain you ride. In New England (where I live) the gravel roads tend to be steep and descents are fast, so when I get a new frame it will have slacker HTA than my current 70 degree (which is already slacker than the vast majority) and I'll go with 50 mm offset fork. I'll increase reach 10 mm from current as well and go with a shorter stem. BTW - I'm same height as the OP and my stack is 573. If you want a more upright position (which I think you do on a gravel bike) you'll want a taller stack.

shelbyfv

This is good advice. Since you are asking these questions on the internet you probably shouldn't be winging it.