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Frame Size - Top Tube Height

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Frame Size - Top Tube Height

Old 06-28-13, 09:13 AM
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Frame Size - Top Tube Height

Hi all, new to the forum...

After noticing the other thread on top tube height with respect to frame size etc. I did not want to stir the pot here, but I wonder about this issue as well.

I am in the market for a new bike (dual sport) having been out of biking in any meaningful way for about 30 years (age 53). At about 5'5" my choices in frame size are limited. I'm looking at a Marin San Rafael with either a 15" or 17" frame. At 17" when I flatfoot both sides the top tube is "right there" but when on the bike riding, it does not feel too big at all. The 15" give me extra top tube clearance but requires that I extend the seat tube quite bit and just seems small.

The "top tube" rule of thumb would suggest I go for the smaller frame and one of the key points of rationale, if I understand it correctly, is that when stopping, or in a panic stop, you would stradle the top tube and would need that extra clearance.

I'm just wondering, when stopping do you folks generally straddle the top tube and put both feet on the ground in most cases? I know when I used to bike I would typically leave one foot on a pedal, stay in the saddle, and balance with my other foot on the ground. This avoids the top tube clearance issue. Also, in a panic am I likely to hop off the saddle and stradle the top tube? Again, this would not seem to be a natural reaction for me.

Would appreciate your views.
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Old 06-28-13, 10:38 AM
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Originally Posted by tripod
Hi all, new to the forum...

After noticing the other thread on top tube height with respect to frame size etc. I did not want to stir the pot here, but I wonder about this issue as well.

I am in the market for a new bike (dual sport) having been out of biking in any meaningful way for about 30 years (age 53). At about 5'5" my choices in frame size are limited. I'm looking at a Marin San Rafael with either a 15" or 17" frame. At 17" when I flatfoot both sides the top tube is "right there" but when on the bike riding, it does not feel too big at all. The 15" give me extra top tube clearance but requires that I extend the seat tube quite bit and just seems small.

The "top tube" rule of thumb would suggest I go for the smaller frame and one of the key points of rationale, if I understand it correctly, is that when stopping, or in a panic stop, you would stradle the top tube and would need that extra clearance.

I'm just wondering, when stopping do you folks generally straddle the top tube and put both feet on the ground in most cases? I know when I used to bike I would typically leave one foot on a pedal, stay in the saddle, and balance with my other foot on the ground. This avoids the top tube clearance issue. Also, in a panic am I likely to hop off the saddle and stradle the top tube? Again, this would not seem to be a natural reaction for me.

Would appreciate your views.
if it were me, I'd go with the larger frame size. If a bike feels small to you now, it will never feel "right". And the bigger frame will allow the bars to be higher.

When I stop, only one foot goes down, and the other stays clipped. I only take both feet out and stand flat-footed when waiting for a train to go by or something like that.
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Old 06-28-13, 12:48 PM
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Hi, such a bike that fits should have plenty of top tube clearance, rgds, sreten.
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Old 06-28-13, 09:58 PM
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Yeah, go with the bike that feels best -- you'll ride more!

Some would say it doesn't matter at all, but it WOULD if you couldn't put both feet down when straddling.... If the bike feels good, and is easily adjusted to your body, then the standover can be disregarded (it's only a starting point, anyway).

Both feet on the ground at a stop? Only see kids and rookies do that, and then only until they learn they need that other foot up to re-start.
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Old 06-29-13, 06:02 AM
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Thank you for your comments.

It was interesting, I went into my LBS yesterday and tried out a 17" frame again and, as I noted before, I can flatfoot when straddling the top tube but the bar is right there. As it turned out they also had a 15" in stock, the smallest frame for this model, so I tried that. Mathematics would suggest that I should have about 2" clearance. Nope, the stand over height is virtually identical.

An interesting observation on the smaller frames is that their geometry is limited by those things that remain static, in this case the front wheel. Regardless of the size of the frame, as a minimum the front end of the top tube needs to be above the front wheel and fork (naturally). On a 17" frame on this model the front of the top tube is about as low as it can go. Moving to a 15" frame, the only real change is that the back end of the top tube is lower to reach the 15" point on the seat tube, the front of the top tube can't go any lower, so the top tube has more of a backwards slope.

When you hop off the saddle and straddle the top tube, particularly on a small framed bike, you are about/at least, halfway along the top tube towards the headtube. So, the 2" difference in frame size results in a difference in standover height of less than an inch. Honestly, I didn't notice any significant difference. As this is the smallest frame in that model, if I was to live by the 2" clearance rule I would be out of luck. My choices would be limited to going with a model with smaller wheels or riding sidesaddle.

Based on all of this I am now more convinced than ever that the 2" rule of thumb is just that, a way to get the ball rolling, a starting point, particularly for the smaller framed bikes for shorties like me.

The 17" frame feels right. I'll go with that.
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Old 06-29-13, 10:31 AM
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I'm just wondering, when stopping do you folks generally straddle the top tube and put both feet on the ground in most cases?



that is how I try people on bikes to find best size to Buy.. Stand over height,
is the clearance under You standing over the bike, flat footed.

in the case of the pictured bike it is the middle of the top tube ..

Seat tube length is called 'size' but it is shorter .. as you see, because of the slope..

Then, stem swapping gets the Reach dialed in .

Its Up to You, whether, riding the Bike, you stop with a foot on the pedal..


I did straddle the Top tube to hold up the bike, while using the Drive through ATM

Last edited by fietsbob; 06-29-13 at 10:39 AM.
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Old 06-29-13, 01:28 PM
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Hi,

Shorties should buy bikes based on smaller wheel sizes, it is that simple.

Forget 28" 700C bikes, go 26" MTB wheel size, or even 24"/ junior wheel size.

A 700C front wheel is simply too big for any sort of decent geometry.

FWIW standover with one one foot on the ground is near identical
to both on the ground, foot on a pedal makes no real difference.

rgds, sreten.

Last edited by sreten; 06-29-13 at 01:37 PM.
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Old 06-29-13, 05:04 PM
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Thanks but I'll stick with the 700C bike.

You and I will simply need to agree to disagree on the importance of the stand over height rule of thumb. I feel it's a starting point and you feel it is more than that. Works for me...

Last edited by tripod; 06-29-13 at 06:05 PM.
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Old 06-29-13, 07:22 PM
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Originally Posted by sreten
700C front wheel is simply too big for any sort of decent geometry.
I'm sure Chris Sugai of Niner Bikes (they make 29" MTB's, he's a co-founder and 29er fanatic, also about 5'5") would be enlightened, should you tell him that. His business AND his passion is based on the same wheel size -- OHH, the HUMANITY......!

rgds, DX.
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Old 06-30-13, 04:44 AM
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Originally Posted by tripod

Thanks but I'll stick with the 700C bike.

You and I will simply need to agree to disagree ....
Hi,

We don't disagree. You have already pointed out the front height
limits of 700C wheels, so for people below a certain height 700C
wheels are not a good idea, whatever the stand over height is.

I was being general, regarding smaller people, I was not
implying that 700C wheels are too big in general for 5'5".

e.g.the front end of this "Medium" :

https://www.walmart.com/ip/GMC-Denali...edium/16203487

looks identical to the "Large" version :

https://www.walmart.com/ip/GMC-Denali...Large/12080282

Standover height clearly doesn't tell the whole story here ....

rgds, sreten.
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Old 06-30-13, 05:46 AM
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Originally Posted by sreten
Hi,

We don't disagree. You have already pointed out the front height
limits of 700C wheels, so for people below a certain height 700C
wheels are not a good idea, whatever the stand over height is.

I was being general, regarding smaller people, I was not
implying that 700C wheels are too big in general for 5'5".

...

Standover height clearly doesn't tell the whole story here ....

rgds, sreten.
Agreed, there are many other factors to consider.
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Old 06-30-13, 05:51 AM
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Go out and read about fitting, and don' limit your reading to the Internet. There's a lot more to it than standover, and even wheel size.
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