All-road/Gravel bike custom geometry help

[madsciencenow]

To the OP, curious how tall you are. I also noticed the stack and reach numbers and based on your saddle height you have really long arms and maybe torso? I use the same numbers on my road and gravel bike for stack and reach and I'm 172ish cm tall. My saddle height is always set around 69.3 cm and saddle to bar drop is about 4-5 cm. I know this doesn't tell the whole story but your numbers seem even more extreme than mine by an appreciable amount. Seems like you are going to have be in a pretty aggressive position relative to your height which you may or may not find you like for gravel riding. Not sure you'd find a bike you could rent to get your numbers but might be worth trying before having a custom frame made and then finding out you hate the position.

[snguyen268]

Originally Posted by madsciencenow

To the OP, curious how tall you are. I also noticed the stack and reach numbers and based on your saddle height you have really long arms and maybe torso? I use the same numbers on my road and gravel bike for stack and reach and I'm 172ish cm tall. My saddle height is always set around 69.3 cm and saddle to bar drop is about 4-5 cm. I know this doesn't tell the whole story but your numbers seem even more extreme than mine by an appreciable amount. Seems like you are going to have be in a pretty aggressive position relative to your height which you may or may not find you like for gravel riding. Not sure you'd find a bike you could rent to get your numbers but might be worth trying before having a custom frame made and then finding out you hate the position.

So I am 172cm tall, 83cm inseam, 62cm arm length, 137.5cm total body length. Not sure where these numbers fall on the distribution but my fitter said I have longer arms than average?

The geometry of the gravel bike copies over my current road bike set up (is that sufficient? or I need to search for a gravel bike with that geometry?). What I mean is that the saddle to handlebar reach on my road bike is the same as shown in the geometry and the stack is the same as well. The only difference is that reach is 378mm on my road bike + 120mm stem while it is 403mm reach + 100mm stem on the "longer" version of gravel bike. I honestly have been surprised by how aggressive my position is but I haven't felt
major discomfort on ~4hrs road rides. Not sure if that is of any value? Do you think I should still consider going less aggressive? I am planning to do more 5-6 hrs ride this summer to make sure there is no problem but I feel like it's hard with really long rides to know if some soreness is just inevitable or indicative of wrong-fit? For the records, though I have felt some soreness on my back at times during my 4-6 hours ride, the sensation goes away if I just get off of the saddle and stretch for a couple seconds and I have never finished a ride with back pain.

Originally Posted by fredd

As for the crankset, I'd go with Ultegra over the Rotor. Yes the Rotor is lighter and arguably looks nicer, but Shimano rings shift significantly better than Rotor ones IME. And Rotor's 4 bolt spider won't really take Shimano rings, which is deeply annoying.

Perfect! Yeah, I should just stick with ultegra. I have never used Rotor crankset before so good to know about the shifting experience. I was just on a weight-weenie mode for the past couple days looking at Rotor but I don't think it's worth the $500-600 extra.

[madsciencenow]

Originally Posted by snguyen268

So I am 172cm tall, 83cm inseam, 62cm arm length, 137.5cm total body length. Not sure where these numbers fall on the distribution but my fitter said I have longer arms than average?

The geometry of the gravel bike copies over my current road bike set up (is that sufficient? or I need to search for a gravel bike with that geometry?). What I mean is that the saddle to handlebar reach on my road bike is the same as shown in the geometry and the stack is the same as well. The only difference is that reach is 378mm on my road bike + 120mm stem while it is 403mm reach + 100mm stem on the "longer" version of gravel bike. I honestly have been surprised by how aggressive my position is but I haven't felt
major discomfort on ~4hrs road rides. Not sure if that is of any value? Do you think I should still consider going less aggressive? I am planning to do more 5-6 hrs ride this summer to make sure there is no problem but I feel like it's hard with really long rides to know if some soreness is just inevitable or indicative of wrong-fit? For the records, though I have felt some soreness on my back at times during my 4-6 hours ride, the sensation goes away if I just get off of the saddle and stretch for a couple seconds and I have never finished a ride with back pain.

First, I misread your saddle height (I saw 65 rather than 73 ish cm). Second, my arm length is 66 cm so even longer than your arms. After looking again at your spec I think the only big surprise to me is the bar to saddle delta. If you are comfortable with what you have then I'm not sure I'd make huge changes. When I had my gravel bike and all-road bikes built, I was asked about going less aggressive on both reach and drop. I thought about this but decided against it as I have issues with getting weight shifted onto my lower back which is what would have happened with the suggestion to shorten reach and increase stack. I'm an n=1 so don't base your decision on what worked for me but I think you will be ok, based on what you shared above. Would be interested in what others have done with road set-up versus gravel/all-road.

[mstateglfr]

Originally Posted by snguyen268

Thanks so much for pointing out about the stack/reach. It definitely seems extreme to me as well (based on my research comparing these designs with stock-geometry race gravel bikes). Those numbers came from my current fit on my road bike where reach is 378mm (running 120mm stem) and stack is 532mm (stem is slammed on 15mm top cap). According to my fitter, I have relatively long arms, can rotate my pelvis forward and keeping my back flat so he thought longer reach/lower stack works very well for me. Do you think it's a good idea to reduce these numbers even though they feel comfortable for me on the road currently?

Oh I see, so stem is 100mm on this new build instead of 120 on your current bike, and reach is therefore increased on the new bike.
Hey if it works then it works. You are very flexible and/or have a long torso and arms.
Everyone is different, so getting a bike fit and custom bike is exactly why its so cool that everyone can be different and have a bike that works for them.


Just wanted to make sure the outlier number(reach) was pointed out. Sounds like its on purpose so cool.

[snguyen268]

Originally Posted by madsciencenow

First, I misread your saddle height (I saw 65 rather than 73 ish cm). Second, my arm length is 66 cm so even longer than your arms. After looking again at your spec I think the only big surprise to me is the bar to saddle delta. If you are comfortable with what you have then I'm not sure I'd make huge changes. When I had my gravel bike and all-road bikes built, I was asked about going less aggressive on both reach and drop. I thought about this but decided against it as I have issues with getting weight shifted onto my lower back which is what would have happened with the suggestion to shorten reach and increase stack. I'm an n=1 so don't base your decision on what worked for me but I think you will be ok, based on what you shared above. Would be interested in what others have done with road set-up versus gravel/all-road.

Thanks for sharing! What size bike are you riding? Yeah I am curious what others have done as well. I have been riding this set up since October and will continue to do it for the next few months to make sure when my gravel bike goes in production, I won't have any regret about the position. Honestly, I have been playing devil's advocate and try to find flaws in my position because I am not trying to emulate the pros but so far the more aggressive position my riding position becomes, the more comfortable I feel (started with ~40mm spacer and 90mm stem, now down to 0mm spacer and 120mm stem). Not sure if that makes sense at all?

[snguyen268]

Originally Posted by mstateglfr

Oh I see, so stem is 100mm on this new build instead of 120 on your current bike, and reach is therefore increased on the new bike.
Hey if it works then it works. You are very flexible and/or have a long torso and arms.
Everyone is different, so getting a bike fit and custom bike is exactly why its so cool that everyone can be different and have a bike that works for them.


Just wanted to make sure the outlier number(reach) was pointed out. Sounds like its on purpose so cool.

Yeah exactly, the 20mm was essentially move from stem onto top tube. I agree about the coolness of custom because if I go stock bike, I would have to get like a size 56 in some brands for the reach but stack will be too tall. Really appreciate you taking the time! I am very grateful

[CAAD]

Originally Posted by snguyen268

Thanks so much! Have you found a terrain where you feel a bit "underbike"? What tire width do you often runs on your bike? I plan to do 35-38mm for most of my riding.

I run 40c Conti Terra Speed tires. The bike is exactly what I was going for. Lots of road sectors where I'm at to get to the gravel. Most of the chunky stuff isn't terribly long in duration and the bike handles it just fine. Depending on the route 70ish miles or so I'll bring a small CamelBak and 2 bottles, never have to stop. Had a DT cage on my checkpoint, never liked it, a stainless Arundel cage couldn't hang on to a bottle when things got rowdy.

[snguyen268]

Originally Posted by CAAD

I run 40c Conti Terra Speed tires. The bike is exactly what I was going for. Lots of road sectors where I'm at to get to the gravel. Most of the chunky stuff isn't terribly long in duration and the bike handles it just fine. Depending on the route 70ish miles or so I'll bring a small CamelBak and 2 bottles, never have to stop. Had a DT cage on my checkpoint, never liked it, a stainless Arundel cage couldn't hang on to a bottle when things got rowdy.

Perfect! Thanks!!! I am gonna be doing a lot of roading riding too so I definitely want to make sure my new bike doesn't feel too sluggish on the road. I am riding mostly in northern New England so gravel can vary quite a bit from dirt trails that I can comfortable ride my 28mm road tire on to fire roads with lots of loose gravel so I want to take that into account as well. It's a tricky balance I guess

[madsciencenow]

Originally Posted by snguyen268

Thanks for sharing! What size bike are you riding? Yeah I am curious what others have done as well. I have been riding this set up since October and will continue to do it for the next few months to make sure when my gravel bike goes in production, I won't have any regret about the position. Honestly, I have been playing devil's advocate and try to find flaws in my position because I am not trying to emulate the pros but so far the more aggressive position my riding position becomes, the more comfortable I feel (started with ~40mm spacer and 90mm stem, now down to 0mm spacer and 120mm stem). Not sure if that makes sense at all?

Sizing for me generally runs between a 52 and a 54 for US makers (think SL6 or an older S6Evo. I had a Moots RSL in a 52 that worked very well for me. I also had a number of Serottas mostly in the 54 size range) and 51.5 F8 or 48s/50s for C60. The challenge I bump into with factory bikes is the stack is more than I want on the larger options mentioned or the reach is a bit less than I'd like on the smaller sizes. This said, I can ride stock bikes from most manufacturers with no problem. On the custom bikes I own the ETT is 55.5 with saddle to bar drop being around 5 cm. If you PM me I can send you some CAD files. I may have also posted the files in the custom bikes section but I don't recall.

[jds108]

55cm is a lot of top tube for somebody of your height. And as others have said, that headtube is quite short for a tt of that length (applies to both of your drawings). This could be the correct TT + HT dimensions for you, impossible to know. I'm 5'10" (178cm) and ride 55 or 56 TT bikes. (and one with a 57 TT and a shorter stem which feels fine)

It sounds like you're able to get long and low and if that's the case, then perhaps it's spot on!

Comparing the ride between the two drawings - I don't see a whole lot of difference there. I think most folks couldn't differentiate a 71.7 vs 72 degree steerer, at least I don't think I would.

With tires that big, I'd suggest you think about lowering the BB a little bit.

[snguyen268]

Originally Posted by jds108

55cm is a lot of top tube for somebody of your height. And as others have said, that headtube is quite short for a tt of that length (applies to both of your drawings). This could be the correct TT + HT dimensions for you, impossible to know. I'm 5'10" (178cm) and ride 55 or 56 TT bikes. (and one with a 57 TT and a shorter stem which feels fine)

It sounds like you're able to get long and low and if that's the case, then perhaps it's spot on!

Comparing the ride between the two drawings - I don't see a whole lot of difference there. I think most folks couldn't differentiate a 71.7 vs 72 degree steerer, at least I don't think I would.

With tires that big, I'd suggest you think about lowering the BB a little bit.

Thanks so much for your input! I honestly share the same feeling because that makes me feel like I will be riding a size 56 bike, which is something I have never though about. At one point, I even thought my current size 51.5 bike is "large" for me, let a lone a size 56. This aspect of thing is something I will rely on my bike fitter. What's on my mind to decide is steering responsiveness/stability, general stability on vs. off-road, i.e. whether to place some of the reach into the stem or top-tube. I also agree that I likely won't be able to tell the difference. I think that adjustment was made when I want to increase the ability of the bike to handle rougher gravel without losing its road-feel. Does that make sense? If you have any advice here, I would greatly appreciate it.

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

[Davist]

I'm about the same size.. I pick #2 I think bigger front center and shorter stem works better for off road.

some thoughts, I like a bit more stack on the gravel bike to look around on trails. If you're super flexible then probably not an issue, but if you get into more rugged terrain it may help.

Even if you think you'll be running 35-38 try to design with 45-50 clearance, I continue to get wider. (went from 35 to 43 on 700c and have 47-2.1 on 650) there's not much of a penalty in my opinion with the quality of tires now.

Finally get some fender mounts, makes my winter road riding better!

[snguyen268]

Originally Posted by Davist

I'm about the same size.. I pick #2 I think bigger front center and shorter stem works better for off road.

some thoughts, I like a bit more stack on the gravel bike to look around on trails. If you're super flexible then probably not an issue, but if you get into more rugged terrain it may help.

Even if you think you'll be running 35-38 try to design with 45-50 clearance, I continue to get wider. (went from 35 to 43 on 700c and have 47-2.1 on 650) there's not much of a penalty in my opinion with the quality of tires now.

Finally get some fender mounts, makes my winter road riding better!

Perfect! Thanks so much for your input. Seems like #2 is the more optimal route to go based on people's suggestion. How much more stack would you recommend? Another 5-10mm? Yes, I am designing the bike to take 700c x 45mm or 650b x 53mm because for sure on off-road-heavy rides I likely will prefer the comfort of wider tires.

[Davist]

mine's probably 25mm higher stack and about 1/2 that in reach shorter overall. I can fit my 43 GKSS under fenders (I hate "swamp butt" )

[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.