Struggling w/ Frame Size: 23" vs. 21"

Reactor · Jul 23, 2005

Aepheme said:
Hi! I had a quick question...

I've done some MTB riding before, but not a whole lot -- always been waiting until I had the money to buy something more than $200. Well, now I have that money, and I think I'm going to buy the "Specialized Rockhopper". My local bike shop has it for $500, and it seems like a good average-budget bike.

I'm not sure which size to get: I'm somewhere around 6'4" (plus or minus an inch depending on who's measuring), with an inseam of about 36" (+/- 0.5").

One guy at the bike store said I should go with the 23" and the other guy said the 21". I'm not exactly sure what to go with! The hard part is... I can't ride both, because they don't carry the 23" (and I don't think many stores do).

Any suggestions? Is there another measurement I can take that might help me decide which one fits better? I hate to buy blind. Thanks for the help!

A lot is based on feel. You really need to sit on the bike, and see how it feels. Pant's inseam isn't reliable, it has to be properly measured. You might be a 38" or even larger measured from the bottom of your stoking feet to your crotch. I'm going to assume you gave the "pants" inseam, and that your riding inseam is about 38".

In many ways the length of the top tube is more inportant than the size of the seat tube. See how your body is positioned when the seat is at the proper height. For you that's going to be about 31-33" from the pedal at the lowest position to the top of the seat. Depending on the saddle and crank, that should be 6-9" of seat post showing.

You should be able to pedal with a slight bend (20-30 degrees) in your leg with the pedal at it's lowest position. Your hips shouldn't rock when you pedal, and you should be able to stand up and slide off the back of the seat if you have too. Wear the shoes you are going to use riding.

When you sit on the bike make sure you're not having to support too much weight on your arms. If you do you'll get tired on a long ride and have back pain. You also don't want to be sitting bolt upright. If the seat height is even an inch or too off the bike can feel totally different. Make sure it's right, before you decide.

Without seeing you and the bike I can't really say for sure. My guess is have to say you are probably in the grey area between sizes and could probably ride either one with the right combination of seatpost and stem. Frame geometries vary so the seat tube size isn't always a good indication of size. If you feel cramped, or you're sitting bolt upright on the 21" you need to try the 23", if they don't have it in that model, try another with a similar geometry. Make sure it's right, have them swap the stem if they have to. If you have the seat post all the way up, you want the larger size.

Get the most experienced person at the bike shop to help you. The bike shop won't intentionally steer you wrong, they don't want an unhappy customer, but like everywhere else they get busy, and not all sales people are created equal.

If it helps I have a 32-33" pants inseam (34-35" leg), and ride a 19" bike and 20.25" bike and both work. The 19" bike feels a little small but it's an XC race bike, and feels perfect when I race. The larger bike is a trail bike, and feels perfect riding technical stuff, and on all day rides.

Wumpus · Jul 23, 2005

Aepheme said:
When you look at a "well fit" bike in a profile view, what should the vertical drop be between the top of the seat and where the grips are on the handlebar?

I like for my bars to be level with the top of the seat. Taller folks can get away with a little more drop(2 to 4").

You can raise the bars with some spacers under the stem (if the steerer tube is long enough), a riser bar(1 to 2") or get a stem with some rise.

One other thing to check is the standover height. Make sure you have a little extra room if you have to bail in some technical terrain.

Reactor · Jul 23, 2005

Aepheme said:
Reactor -- Thanks a lot for your comments! I didn't expect such a thorough analysis so quickly; I'm incredibly impressed with this forum...!

You're absolutely right -- I probably am between sizes. I wish I could check out any bike with a 23" frame, but the manager of the bike store said he's only had to order one of those over the past several years. Doesn't seem like a size they keep in stock.

I rode the 21" around for a while this afternoon, and I felt that the seatpost was raised unusually high. I felt like I was putting extra pressure on my hands since my center of gravity was higher than it should've been. Is that are proper analysis? Could that be solved by a 23"? It could just be because I haven't gotten the hang of distributing my weight across the bike. (Although, I'm only 170, so it's not like I have a ton of weight to control).

When you look at a "well fit" bike in a profile view, what should the vertical drop be between the top of the seat and where the grips are on the handlebar?

I mean, I guess it's going to vary depending on...actually, there are too many variables to consider here. Mountain bike sizing is so complex! It's almost like trying to find a well-fitted suit.

It's exactly like buying a suit, because you're going to "wear" it for hours at a time. Typically on a xc bike the seat should be about the same as the handlebar to maybe an inch or two above it. On a trail bike the opposite is generally true. If your drop or rise is much more than this the bike is probably the wrong size, and you're going to impact the bike's handling because of the change in weight distribution.

If your seat is too high, it will force you to put more weight on the bars. If your hands/wrists/arms hurt in the parking lot, the bike is not going to work on long rides or off road. There are a couple of ways to fix it, get riser bars, get a stem that raises your bars higher, or get a different bike. If you get the 23" bike the front of the bike will be higher as well as the seat tube, it will change your riding position the same as dropping the seat on the current bike by a couple of inches, except you'll be able to pedal efficently. The bike will also be about an inch longer.

It sounds like you need the 23" bike The shop probably doesn't carry them because your bigger than 98% of the people they deal with. It's a vicious cycle, tall people don't ride because they can't find the right size bike, and shops don't carry XL bikes because tall people don't ride...

hooples3 · Jul 23, 2005

reactor is on point with his advice, I couldnt have said it better myself
I am 6'3" and ride a 20" specialized Hardtail. I have a 33"-34" inseam .. the bike feels just a little big for me. i will add that I have a 120 mm stem as well. Personally I would test out the 21" and see if your comfortable, as lonmg as you dont feel squished you will be fine

Reactor · Jul 23, 2005

one more thing...

You'll notice Hooples3 and I ride the same size bike, he's 4" taller than me but we have about the same inseam. I've got very long legs and arms, so I'm comfortable on the same size bike. Your inseam is 2-4" longer than ours, you need at least the 21".

See if the shop will change out the stem on the 21" bike or the handlebars before you give up hope. They won't be able to put on spacers because the fork's steerer tube is already cut, but if they have an unassembled bike in the back they might assemble it for you with the full compement of spacers, or swap the forks. Then you can figure out if you need the bars lower and they can cut the steerer tube to the right length.

If it still doesn't fit, you need the bigger bike.

Wumpus · Jul 23, 2005

I'm 6'3" with a 38" true inseam(pants is around 35 to 36").

Took a few quick measurements off my bike:

Standover 33.5"
TT(horizontal) 23.5"
Steerer(which can help raise the bars) 7"

It seems close specs to the 23" though my TT is shorter I also run a relatively long 130mm stem.

Mine measures 20" from the BB to the top of the seattube, but I wouldn't pay too much attention to that as it is a full custom.

Reactor · Jul 23, 2005

One last thing. If you have them order the 23" bike, make sure they don't cut the steerer tube on the bike until you come in and get a chance to test ride the bike and get the handle bart into a position you like. The shop can use spacers and a compression bolt to mount the bars/stem. For testing purposes they can then move spacers from below the stem to the top to adjust the bar's position. Once it's where you want it, they can cut the steerer and put in a star nut.

JRB · Jul 23, 2005

I will just say, not knowing if it were said. Too small really sucks. Too big sucks, and is dangerous. Not seeing the specs, 23" seems big for your height. That said, ride them both. A little longer stem and a set back post may make the 21" the right bike. Shops will usually swap new parts for similar quality parts of a different size as needed. Good luck.

BigMike · Jul 24, 2005

23" is a HUGE frame. like everyone else has said, if you can get the shop to order it for you to try, definantly try both.

BUT, if they make you pay for it before they will order it, be wary. Find out exactly what their return policy is, and tell them strait up that yuo just want it for testing purposes.

Wumpus · Jul 24, 2005

Aepheme said:
I don't know if this is good or bad....

After hearing Wumpus' dimensions and getting Reactor's opinion -- I was pretty confident that a 23" would be the way to go.

But BigMike and Loco's comments made me slightly less confident! I'll have to put some more thought into this...

Loco decided to give an opinion without bothering to check the specs. :nuts: He thinks that all my bikes are too big (for him

).

JRB · Jul 24, 2005

Wumpus said:
Loco decided to give an opinion without bothering to check the specs. :nuts: He thinks that all my bikes are too big (for him ).

Just saying to be careful of too big.

Reactor · Jul 24, 2005

loco said:
Just saying to be careful of too big.

In all honesty it's really difficult to help with fit issues over the internet. Anyone in this thread could get you fitted for a new bike in about 5 minutes in person, and could make sure it was right. Over the internet there is some guess work involved no matter how good you are about supplying information.

BigMike · Jul 24, 2005

Reactor said:
In all honesty it's really difficult to help with fit issues over the internet. Anyone in this thread could get you fitted for a new bike in about 5 minutes in person, and could make sure it was right. Over the internet there is some guess work involved no matter how good you are about supplying information.

bingo. ask the people in the shop. If they won't help you, find a new shop

N8 v2.0 · Jul 31, 2005

I'm 6'4 and I am comfortable with a 21". For me a 23" would be way to large for my style of riding...

JRB · Jul 31, 2005

So it feels too big, and doesn't ride right??? That doesn't sound like the right bike. I bought mine too big, first off. I immediately replaced it. Oh well, good luck.

Changleen · Jul 31, 2005

I have always been a fan of 'smaller bikes and put the seatpost up if you need to' probably because of my BMX background. 23" is HUGE! 6'4" isn't ridiculous tall. My housemate is 6'2" and he rides a Specialized 'medium' frame. Provided the TT length is decent, a smaller frame is far more versatile and looks better too!

Struggling w/ Frame Size: 23" vs. 21"

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