Birdbikes

I'm 5'10 (5'10 1/2-5'11 with shoes) with a 34 inch inseam while wearing shoes, and a 68-69 inch wingspan.

i'm interested in buying an ebike called the radmission from radpowerbikes.


the problem is I have no idea whether to buy the 18 inch mid-step or the 21.5 inch high-step. Can anybody with measurements similar to mine tell me what size bike they would buy? I want to be comfortable with full pedal extension without having to lean forward too far, and also not worry about my knees touching the handlebars.

thank you.

Sonofamechanic 

Best option is to go to your local bike store (LBS) and get their advice on sizing. That said.... I’m similar height with 72 wingspan and 31 inseam...so I’m guessing you have legs where I have arms? . Generally you can more easily adjust for longer legs with seat height on a smaller bike that fits your more ‘normal torso/arm length rather than go with the bigger frame you may not have the arm and torso length to stretch out over.

Iride01 

I can't tell you what size because even among the same brand of bikes, you might be a M for one model and a ML for another model of their bikes. Or a 56 cm in one and 59 cm in another.

Unless you have your own personal experience to go by, then go by what the manufacturer recommends for that model and the recommendations of those that can actually see how you fit on that model bike.

Usually most people can go a size up or down from their perfect size.

GamblerGORD53

I would get the bigger one and get bars with more sweep. Straight ones are horrible for discomfort.
These boutique bikes are really bad at providing size measurements.

Moisture

You would need a long seat tube and a pretty short reach, stem and top tube. Id suggest going for the bigger size and probably changing to a shorter stem.

cyccommute 

I wouldn’t say a “medium” in any brand. Maybe a medium large but far more likely a large. Start at a 58cm and go from there. Contrary to most people’s thoughts on bicycle frame sizes, a 58cm in on company is pretty close to a 58cm in another company. Their geometries aren’t that much different. The seat tube might not measure 58cm but measured to the virtual top tube (imaginary horizontal top tube) most every company has the same size bikes.

TiHabanero

Unfortunately you have the dreaded short torso longer leg syndrome. Tough to fit you on anything production. I suggest you contact the manufacturer and ask them directly what they recommend. Midstep or highstep frame.
Initially I had posted they do not post geometry, but I had not scrolled down far enough on the page. After looking at what they post it is apparent to me that you need the highstep frame. Stem or bar change may be needed.

ARider2

It's fine to go to your LBS for advice about sizing as long as you're up front about your plans to purchase online rather than from them. Some LBS will assemble and tune a bike and can offer this service if you're not going to build it yourself.

Trakhak

Ballet toe shoes? "Kiss"-style platform shoes? Your inseam measurement in shoes is irrelevant. One bike sizing method I know of stipulates measuring inseam barefoot, using a book or equivalent held horizontally and mashed up to the bones of your crotch, preferably with an assistant doing the measurement. Your correct measurement is likely as much as 2 to 3 inches shorter, and correct frame size might be somewhere around 56 or 57 cm, center to top. A bit larger for low- to moderate-effort cycling, maybe.

Wanderer

It's a hard stretchover if you buy a bike too big!

Fredo_Adagio

You need to go to your local bike shop and actually try riding different size frames for the bike that you want.

When I bought my most recent road bike, a Trek Emonda, I brought my old bike with me to the bike shop and told the staff to match the fit. The mechanic told me that the 2020 model had Trek's H2 fit and would require a smaller frame size to match my old bike. The 2021 model had Trek's H1.5 fit and could match my old bike with the frame size recommended by the standard size guide. The problem was the minimum stack height of the handlebars, which was too high for the 2020 model. If I had bought the 2020 model, I would have needed to get a smaller frame and swap the stem for a longer one to achieve the desired reach dimension.

I've been playing these games with my Specialized Shiv triathlon bike. I bought the frame that was recommended by the standard size guide, but I had to switch to a longer stem, which required replacing the brake and shift cables with longer ones. I also switched to shorter crank arms, which required changing the bottom bracket and chainrings.

wphamilton

54-56 frame, depending on how you like to set up.

Birdbikes

I have a 34-35 inch inseam while wearing shoes and a 68.5 inch wingspan (i'm roughly 177cm and 178 cm with shoes). how does that affect reach?


my understanding is, I will have to raise the seat higher on a bike to get full pedal extension. That means I will have to lean forward more correct? The higher the seat goes, the higher the reach to the handlebars?


that means I need something like an 18 inch medium hybrid instead of a 20 inch large right (trek fx1 as my example)? But then, since I have a smaller bike, wont my knees end up hitting the handlebars or making me feel cramped due to my longer legs? Plus the handlebars are probably lower on the smaller frame making me have to lean more?


so wouldnt it actually be better to get a large and just get a shorter stem? I dont understand why everything I read says its better to get a smaller bike when you have long legs but short arms.

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GamblerGORD53

I don't think you are too far off normal. But yes I agree with what you are thinking.
Get a shorter stem and bars with more rise and further sweep back. Straight MTB bars are awful anyway.
Way too many do the opposite and end up with a giraffe stem. Makes no sense.

Moisture

I would look into a large or maybe even an XL bike and look into getting a short stem.

With your legs at full extension, you'll need a pretty short reach to feel more or less comfortable. It'll obviously raise your centre of gravity and make it more difficult to achieve a somewhat more comfortable riding position with your handlebars level with the saddle.

So id look more into a tall stack figure unless you're okay with your handlebars being well below your saddle height and a relatively short top tube/reach length. Look for a bike with a sloping top tube.

Kapusta

This^^^

I'd go for the bike with the proper reach, and if you need to raise the saddle and bars, just do it.

Iride01 

Well I wasn't talking specifics for the OP, maybe I should have specified that. All of the size I mentioned were not intended to be recommended sizes.

However I won't disagree that you could try to figure out the imaginary seat tube length by your method. Some manufacturers even show that in the bike geometry tables. But for a long time we've known that sizing a bike by the seat tube measurement isn't the perfect way to tell.

Arguably I will agree that it gives a decent basis to pick a bike. But probably no more than going by anything else. I rode bikes that ran the gamut from 64 cm frames to 56 CM frames during my adult life. Most years 35+ spent on a 64 cm, most miles on a 59 and 60 cm, and currently on a 56 cm bike. All comfortable for the riding I was doing at the time on them. I'm 5'-11" with a 34.5" inseam.

Also, when the manufacturers list their bikes in letter sizes you can't do an imaginary seat tube length if the mfr doesn't tell you it in their geometry tables. IE. Look at this TCR Advanced SL

https://www.giant-bicycles.com/us/tc...sl-disc-1-2021

They don't draw the imaginary horizontal top tube or even give a measurement that will suggest the imaginary seat tube length. Yet here we are, looking at a M (medium) size frame that the manufacturer say might be the one for the 5'-10" OP. As with many bikes people fall in the overlap of bike sizing. And even when they don't, a size bigger or smaller probably isn't going to be bad for most.

Iride01 

It's not your arm and leg length that mean anything. It's your experience or lack of that should be telling you you need to go and sit on and ride the bikes to get an idea what you might like.

You could go and do a bunch of online calculators and figure out stuff. But if you don't even know which type of fit, upright, aggressive or very aggressive, will be comfortable then what will a calculator do for you? It'll just make you more confused IMO. You'll still be in the dark and gambling with any purchase.

Don't spend your wad on your first bike or even the first two or three bikes. Buy something you can get some experience on for what currently feels comfortable to you. Once you've ridden a while your impressions and perceptions of what fits you will change. Maybe even the style of riding you do will change.

Personally, IMO, I wouldn't buy a bike thinking I'm going to ride some off road and some pavement. You'll probably seldom go off pavement. If you do, then get two inexpensive bikes. One for off road and one for pavement. A bike that can do both does one or both things poorly.

Moisture

You might want to look into a bike designed around drop bars as a flat bar conversion candidate. You'll get the seat tube length you need, but with the short reach and top tube of a drop bar bike.

DaveSSS 

Your height to inseam ratio is not that extreme. Inseam should be measured from floor to firm crotch contact in bare feet. I have an inseam/height ratio of .49. I have no trouble fitting stock frames with a 100-110mm stem, even with a -17 (horizontal) stem because I can tolerate a saddle to bar drop of 10cm. On a road bike, the drop more than doubles with my hands in the drops.

blamester

It's not always as simple as a shorter stem. Because that changes the handling and weight distribution.
You might find that when you look over your shoulder you steer in that direction and swerve out into the road. Or you can't ride comfortably one handed for instance.
Or how it can change how you pull the brake levers.
Best like mentioned above is to get a cheap bike and work from there. Stems are cheap and threadless are a godsend for experimenting.
The fit will also change as you get fit.
I have tried to make the wrong size bike fit me and ended up with too many compromises.

cyccommute 

Every road bike I’ve ever owned was a 58cm. I bought one on sale that was 56cm and regretted it from the moment I bought it. It felt cramped from the get-go. I never rode it all that much because it just felt too cramped. I passed on a 60cm touring bike because it felt too tall. I’ve owned 39 bikes (half road bikes) and never found that I could vary the size much on either mountain or road bikes.

The current touring bike I own is marked as “58cm” but the seat tube doesn’t measure that. However, the other parts of the geometry are similar to all my other road bikes.

Sonofamechanic 

I dont think it was the height to inseam ratio that threw respondents as much as it was the arm reach being less than the height—that is where a shorter top tube might really be beneficial—you can only shorten the stem by so much before your steering gets quirky.

Trakhak

Not to worry: that's his height in shoes, presumably, since that's how he measured his inseam, so both figures are, to put it politely, suspect.

wphamilton

Because the reach is more sensitive and it needs to fit, first and foremost. As you mentioned, just raise the seat if you need to.

Leaning forward more, yes you can set up a smaller frame more easily for the more aggressive riding positions. You're not forced into that kind of setup. Even if you raise the saddle two or three inches it's trivial to move the bars up, if you really need to and haven't gotten weird with the seat post (I've seen some riders with their saddle way up, legs fully straight and tiptoeing at the bottom of the stroke. I caution to avoid that).

I'm the same size as you, about 33-34 cycling inseam* but with longer wingspan (the more typical 70-71 inches). My 3 bikes are 54, 55, 56.5 set up for various positions and all 3 are comfortable. Smaller than 54 would be cramped (reach) and anything 57 or larger would be way too big.

* I don't even recall it exactly, because other than adjusting the seat post it's really not that important. I do the saddle by by sitting on it and adjusting to the legs, so I don't really even need it for that.