between sizes: up or down?
 

Edit: I ordered the 53cm Rando frameset with a carbon fork and 650b wheels. but this discussion might still be useful to someone.
I'm looking at a Twin Six Standard Rando as an all-rounder bike. I'll likely take it on more rugged singletrack than I should, but nothing that overwhelms the 43-47mm tires. it will spend most of it's time on roads and bike paths, unpaved whenever possible. Here's a chart I captured from bikegeo.net of my current Traitor Crusade cyclocross bike with a 52cm frame, and the way that I could likely make a 53 or 55cm Standard Rando fit about the same way:The current fit I have is as long and low as I would want any bike to fit. I could stand to raise the handlebar and bring it closer to me.

basically, I can make either fit by using a longer or shorter stem and spacer stack. I also plan to put a PF30 eccentric BB adapter on this bike for a singlespeed drivetrain, which will alter the reach and stack by up to 7mm in any direction but down (look up the Wheels Mfg. EBB instructions to see why that's necessary). so the reach, stack, seat tube angle, and rear-center will be affected based on where the cranks end up. in the end, it's less than 1 cm of adjustment, so it's probably not a big deal.

any reason to chose one over the other?

What does a longer or shorter stem equal? In other words what length?

Because if one COA is using a 80mm stem and the other is using a 110mm. I'm going to tell you the frame using the 110mm is probably the better choice.

Buy based on top tube length, so go big in this case. You can flip the stem if you think the head stack is too high once you get some miles on it, but I think you won't notice.

sorry, but what does COA mean? not familiar with that term as it relates to bicycles. where I live, that stands for City of Austin or Circuit of the Americas.

I am not sure whether it's preferable to use a longer or shorter stem, or if at what point it matters. how short is too short for handling on a road-going bike? too long? it's a bit subjective. it's also possible that a stem length outside of the norm on a conventional road bike is an indication that the rider chose a bike of the wrong size. in my case, I think I could make either of these bikes fit with a 80-100mm stem because the two sizes are not dramatically different.

The ETT on the longer bike is closer to what I have now, but the stack is a lot higher. either one could fit me. the larger one has less standover, but could offer a smoother ride and more room for bottle cages and stuff inside the main triangle. in the end, handling is more important to me. what handling characteristics should I expect from a smaller frame with a longer, higher stem, versus a big bike with shorter, lower stem? the BB, saddle, and handlebar will end up in the same position on each bike, but one will have a longer wheelbase.

Standover doesn't matter. I can't stand over any 29 inch wheeled mountain bike ever made without soft contact due to the sloping top tubes, even on a 15 inch frame. 17-18 inch mountain frames are what fit me, 54-56 road. I am 5'8" with a 32 inch inseam for reference. 20 years ago we thought smaller frames handled better, but the trend has steadily changed to longer top tubes and shorter stems. Longer stem isn't a big deal on the road, but it puts your weight further forward towards the front axle, and that can bite you on trails. 5mm stack height is not a lot of difference.

I am very aware of that. I also don't want a ball-smasher of a bike. there's a difference between no standover clearance and NEGATIVE standover clearance. I think the 55cm frame will have enough clearance to not smash my bits. I might go for the larger one in that case.

COA - Course of Action

Just a general rule of thumb for a Road Bike...I see you are going for an endurance/all rounder...so this may not apply. After purchasing the correct size frame (road bike) and your position is fine tuned...the stem should be between 100mm - 120mm. The idea is if you require a 130mm stem, the frame is most likely too small (should go with the next size up). If you require a stem 90mm or below, the frame is most likely too big (and you should go with the next size down).

What are you trying to accomplish? If you want your bars level or at least close to level, or even higher than the saddle, most likely the larger frame would be the better choice. If you want the bars lower, then the smaller frame would be a good choice. The larger frame will have a slightly longer wheelbase, so it may feel more stable on fast downhills, while the smaller frame may feel more nimble to you.

I went with a larger frame when choosing my Long Haul Trucker, and am happy with the decision, and have been for the past 9 1/2 years of use. I could use their 54cm, and their 56cm frames. I chose the 56, it is comfortable and dead stable with a load at high speeds downhill, speeds up to 45 mph. It has a 90mm stem on it at the moment.

I am trying to accomplish a gravel bike fit that is not a liability on rough terrain when cornering on loose soil for the occasional singletrack ride, more like a CX bike that I have now, but is fairly comfortable for a 100K gravel grind on dirt roads. That is a bit of a contradiction so a compromise will be necessary.

I can get either of those bikes to fit with the handlebar above or below the saddle without resorting to weird stem dimensions. either of them will fit me in a trainer. The real questions are:

• wheelbase difference of 10mm, is that a lot?
• front-center is where the wheelbase difference lies. toe overlap and weight distribution are affected
• exposed seatpost—more seatpost=smoother ride most fo the time. does 2cm of seatpost allow enough extra flex that I'd notice?
• stack—I like the aesthetics of a level stem and fewer spacers, but I won't like that determine what frame I buy. I should ignore it, actually.
• trail: how much does 3mm difference in trail make? probably not a lot. either way, the new frame has more trail than my old one—which equates to more stability at speed, correct? trail is still a bit mysterious to me.

I was thinking about drop bar bikes I've owned in the past: 54cm Salsa Vaya had a very long wheelbase and I thought it handled like a school bus—in a bad way. I used it like a gravel/CX bike on singletrack and roads of all sorts and it never felt fun to me. no surprise, it was designed to be loaded down and ridden for days on end as a tourer.
The next bike was a 52cm Soma DCD and it was a ton more fun for my riding. I went through the same dilemma between the 52 and 54 frame. I choose the 52 and put a pretty tall stack of spacers under the stem. I think I had a 90mm stem on it, but I am not certain of how it fit compared to what I have now. I do recall BAD toe overlap on this bike with 35mm Cross Boss tires, so I think I should avoid a bike with a front-center this short. I should have gotten the 54 DCD.I'm looking at the 52 & 54 Rando to see what is somewhere between the DCD and the Vaya above. Here are what I think of the relevant numbers:

https://cimg7.ibsrv.net/gimg/bikefor...d0f181f097.png
Looks like the reach and stack on either Rando could work for me. I am worried about the short front-center on the 53, but maybe that's silly. Note that the Rando will have a EBB. that will move the BB drop, reach, and stack by up to 7mm, which is not a lot.

Based on that sentence alone, I would be inclined go with the smaller of the two, though the reach of both are shorter than your Crusade. If you are really worried about overlap, go with the 650 rims, it would be even more nimble as well. If you could ride them both it would be easier of course. I'm sure that isn't an option though.

I didn't see it mentioned anywhere, so how tall are you? I'm going to guess, based on their sizing chart that you are 5' 9".

I'm 5'9", barely. I think there's a bump on the top of my skull that makes me that tall. so I would be on the very bottom end of the size of rider who would fit on a 55cm. I also can't reach my toes to safe my life, so I always end up on smaller frames and even with short stems so the bike it not too stretched out. with a 55cm frame, I don't think I'd feel comfortable with anything longer than a 80mm stem, so that would be a limiting factor.

hold up, let me be rational here. all this started because I want to put tires bigger than 35mm on a gravel bike and my current CX bike has that limit. when I am done, I will have spent over $1500 in order to go from 35mm tires (which actually measure to more like 38mm) to a bike that can fit 40 or 42mm tires. is this a worthwhile purchase for 5mm of extra tire space? Holy moley, I feel silly.

You keep talking about not liking being stretched out, and you feel you will be limited to a short stem on the 55. What does that tell you?

Well, if you want to be rational I can't help you. I like spending other people's money. :innocent: If you do decide to buy a new bike, I would still lean towards the 650 wheels. I like them, especially on smaller frames. I have them on a 56 cm Long Haul Trucker and have been very happy with them, still am. Zero overlap issues, strong, and they make the LHT more nimble than the 700s.

For Gravel I wouldn't want to bother. I used to run 45's on my Cross Check to ride mountain bike trails, but outgrew that stunt mostly. If you are going to ride Emma Long, tubeless 42mm tire will be a noticible improvement, but still extremely limiting. If I can't or don't want to ride something on 35's, I jump to 2.2's or bigger. I remember riding the Northeast Texas Trail on 45's because I knew it wouldn't be a technical mountain bike trail. By day 3 I was wishing I had left the Hookworms on the Fargo due to the chatter on the unimproved sections.

That's fair. I feel limited by 35s but I don't think 42s would make a huge difference. my mtb always has 29x2.3–2.4 tires on it, and a suspension fork. so I am never under-biked IMO on that.

The other option is to get the new Rando with 650B wheels, which would allow up to 47mm tires. that might be just enough to not suck on dirt but still be fun on roads.

I am also entertaining the idea of a Van Dessel WTF, which has room for 29x2.1 tires. that might be overkill and encourage me to ride places that are silly.