momocycler

Hello all,

So I have one more question/concern about my bike (1985 Miyata Ridgerunner). I measured the frame and it seems to be an 18 inch frame. I am 5'11. Everywhere I look it says that I need about a 22 inch frame or 56 cm road bike or anywhere from 18 to 21 inch mountain bike depending on my inseam length (which I think is 30 inches based on my jeans).

I also read that when adjusting the seat you should be able to almost fully extend your leg with your heel on the pedal (let's call this criteria 1). If you are able to do this by adjusting the seat height, does the frame size matter? Also, you are supposed to be able to touch the ground with the tip of your feet while seated (let's call this criteria 2).

The reason I ask is because it seems like the bike I have is too small for me, but I'm not sure because I can't quite reconcile all these adjustment criteria. I've maxed out the seat height. Currently, I am able to sit comfortable and just touch the ground with the tip of my feet, but at the same time my knee is pretty bent when I put my heels on the pedal. I must be missing something...

I was wondering if I could just get a taller seat (if such a thing exists) that would allow my legs to be almost fully extended when I have my heels on the pedal. Then again, if I make my seat any higher in order to meet criteria 1, I will not be able to meet criteria 2... I'm confused... and I don't want to hurt myself biking... What gives?!

njkayaker

More important than seat-tube length is the effective horizontal top-tube length (HTT).

As you observed, you can move the seat up and down a large distance. It's harder to vary the horizontal distance between the seat and the handle bars.

Note that different types of bicycles and the posture you want to assume also result in different HTT numbers.

The "frame size" is, by custom, the length of the seat tube. When bikes commonly had horizontal top-tubes, this number was somewhat easier to use to compare frames from different manufacturers. Now, with bikes often having sloping top-tubes (at widely different angles), the seat tube number is close-to-useless for comparing.

Being able to reach the ground with your foot (toe) while still seated is not a goal.

The goal is to get the seat height correct (which is basically dictated by leg length).


Seat posts come in different lengths. Modern ones can be quite long.

(There are some kinds of bikes, such as "crank forward" and "city" bikes, where being able to put your foot down is intended.)

JonathanGennick 

I personally would focus on two things: 1) how long the top-tube is, and 2) seat height relative to the bars.

Do not even worry about touching the ground with your feet. I say that, because whether you can touch the ground is greatly influenced by the bottom-bracket height. So you end up conflating two different things when you worry about touching the ground.

How do you feel on your current bike? Do you feel scrunched up? Is your seat high relative to the bars? Going to a larger size frame will tend to stretch you out more, and it will bring the bars higher relative to the seat.

How did you measure your current frame to get that 18 inches?

JonathanGennick 

You might visit salsacycles.com. Click on any of their bikes. Then click on the "Fit Chart" tab. Salsa gives some general ranges for their particular bikes that you might find useful. Just be aware that they are general ranges, and that your body may be built differently, your preferences might vary, yadda, yadda.

FWIW, if I had to guess just from knowing your height, I'd suggest trying a 19" mountain bike, and then give or take an inch in either direction depending upon how you felt about the fit. That's a rough guess. It's just where I would begin. For a road bike, maybe begin at 57mm and go up or down a bit until you dialed in the size that felt the best.

momocycler

Kayaker, "Being able to reach the ground with your foot (toe) while still seated is not a goal." Pheww!! I couldn't quite reconcile those two requirements. I would rather focus on a comfortable ride.

The top tube and the down tube are both 21 inches long. The seat tube is 18 inches when I measure from the intersection of the crank arm and chain ring to the top of the seat post, which is pretty much flush with the top tube. I have raised the seat by 5 inches and I also have another 2 inches based on where the measuring stops. This gives me effectively 18+5+2 inches. The seat is pretty much parallel with the handlebar.

Jonathan, you mention "Going to a larger size frame will tend to stretch you out more, and it will bring the bars higher relative to the seat." I'm guessing the longer the seat tube the longer the top tube... to compensate for the expected longer torso that goes with longer legs. So if my seat tube is too short then my top tube is probably too short too... logical????

When I rode for an hour yesterday, everything seemed fine and I was pretty comfortable, but I did feel like my legs just were not stretching enough. So I found myself often standing on one side to get a stretch. I do also feel a little scrunched up, but I feel like I could address that issue by changing my handlebar to a drop bar one of those specialty/triathlon type bars. Basically, any type of bar that would stretch me out some more. My main problem comfort wise is that I feel like my legs want to stretch a little more. Getting a longer seat should help, right? Is that possible?

njkayaker

This is why you don't need to put your foot down:
https://sheldonbrown.com/starting.html

Don't worry about the down tube measurement.

Here's a picture. The toptube is fairly horizontal.

https://www.google.com/imgres?imgurl=...ed=0CD4Q9QEwBQ

It sort of works that way.

One issue might be is that, if you need the seat very high, you might not be able to raise the handle bars enough to match.



Do you have a LBS (local bike shop) that you use? It might make more sense to talk to them about basic fitting since they would be able to see you and your bike together.

JonathanGennick 

I should add some caveat about the above being true for a given frame design. A larger Rockhopper will stretch you out more than a smaller Rockhopper. But if you change frame designs too, then all bets are off. I've an 18" Fargo frame with a shorter top tube than my 17" Rockhopper frame, for example.

I should also add that sizing trends change over the years. I see a lot of older mountain bikes with long stems and shorter top tubes than what is common today. You can't compare an 18" frame from 15 years ago with an 18" frame from today. They may or may not fit the same.

I tend to agree w/njkayaker. It probably is worth your time to visit a couple of bike shops and seek some advice from people who can see you on the bike.

ddez

Also make sure when you are raising your seat post that you dont extend it past the safe mark(line inscribed on post) thats put there so you dont over extend it. It must be in the seat tube a certain amount.

momocycler

Thanks all for the feedback. I'll be stopping by a LBS tomorrow.

longbeachgary

It's too small.
Today's conventional wisdom is that you can get a bike to fit with a long seat post and a long stem - that's why today's bikes come in only a few sizes (small, medium, large and extra large) while older bikes came in a dozen different sizes. I don't believe that this is true - IMO changing the stem changes the handling.

Buzzbait

Remember cajone clearance. Don't go too big on a mountain bike. You need clearance when standing over the top tube. Maybe 3 inches or so between your cajones and the tube. Any less and bailing out could be very painful.

LesterOfPuppets

I don't think I've EVER bailed out straddling the top tube on my MTBs. Regardless, I like my frames kinda small.

OP, don't worry about criteria #2.

OP, there's no way I'd be happy riding the gnar on an 18" bike with a 30" cycling inseam. Of course, 15" MTBs in the mid 80s would have super short top tubes, so those would suck too. Your bike would be perfect for fire road biking, or even slick tire road rider, I'd imagine. Longer seatpost in there and perhaps a longer stem if you're not stretched out enough for road position.

njkayaker

It's likely it is a bit small. It is also what he has.

knobster

I love this one:

The Flying Leap is a less common, but equally poor technique, consising of running alongside the bicycle then jumping up onto the saddle. This is sometimes done by riders in a hurry, but it is dangerous and inelegant.

Inelegant? We do this in cyclocross all the time! Maybe that's one of the reasons why people think the sport is goofy.

LesterOfPuppets

Doh, I've been improperly mounting my bike for years. I use the cowboy technique about 90 percent of the time. Guess I better not gain any weight or all my wheels will die

njkayaker

It would seem that cyclocross is the exact opposite of "elegance".

Keep in mind that Sheldon Brown is addressing beginners. A fair number of beginners (including the OP) are not even aware of Sheldon Brown's preferred method. And, what ever method they choose to use, they should be aware of this method.

LesterOfPuppets

OP, got any pics of current setup?

Al Criner

Your pants inseam is not your "bicycling" inseam, that is a different measurement. I am wearing some jeans with a 30" inseam, I measured my pubic bone height at about 33.5" (85cm).

Loose Chain

Dudes, mtbs are sized differently from road bikes. A 56cm/22inch road bike is roughly equal to a 17-18 inch mtb.

Your pants inseam has nothing to do with bike sizing. I see homeboys all the time in pant on the ground, with about a 14 inch inseam.

Your saddle height is adjusted per:

.883 X PBH = SH

Where PBH is your pubic bone height measured by sliding a book tight into your crotch while against a wall in bare feet, mark the wall and measure.

SH is the resulting saddle height measured from the center of the crank to the crown of the saddle along the seat tube.

This gets you in the ball park.