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advantages of correct size frame

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advantages of correct size frame

Old 02-13-17, 05:12 PM
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advantages of correct size frame

Hey so what are the advantages of having the correct size frame over using a long stem and high seatpost.

As far as I see if im 5" 10" but can reach the pedals fine on a 19" road frame with an extra long seatpost and mtb stem.

Is there something in missing?
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Old 02-13-17, 05:23 PM
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Top tube length will be short but some folks like it that way. Frankly I have a hard time getting bars high enough even when the frame is my size.
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Old 02-13-17, 05:29 PM
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1-If you need a seatpost or stem in an unusual dimension, you have fewer available choices.
2-Since huge seatposts and stems extrude into empty space with no triangulated support (unlike frame tubing), they need to be built quite beefy. Since an undersized bike has a lot more stem and seatpost than a correctly-sized bike, they can end up heavier even if the frame is lighter.
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Old 02-13-17, 05:36 PM
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also without changing stem would a bike designed for relaxed drop bar geometry have racing geometry on an undersized frame as its lower or is there more to geometry than that?
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Old 02-13-17, 06:13 PM
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Originally Posted by flik9999 View Post
also without changing stem would a bike designed for relaxed drop bar geometry have racing geometry on an undersized frame as its lower or is there more to geometry than that?
The geometry is based primarily by the head tube angle and wheelbase. Ride height is determined more by wheel size and bottom bracket location, which cannot be too low if you don't want your pedals to hit the ground. A frame with "relaxed" geometry will have more trail in the fork, which increases stability, and a longer wheel base, which slightly reduces handling, as the farther away the rear whee is from the front one, the more movement it takes for the front wheel to move the rear wheel. More trail means that rolling resistance will have more leverage to pull the wheel straight as the bicycle moves, less trail has the opposite effect.

Racing geometry means a steeper head tube angle, with less trail. This reduces steering effort, and increases response. On the negative side, it can make the ride twitchy, or cause wobbles at high speeds if the wheel is out of balance, not trued properly, or if there is any misalignment. The shorter wheel base in a racing frame allows the rear wheel to react more quickly, with less movement of the front wheel.

Always try to get a frame which fits, you will get the best performance and ride quality for your body size.
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Old 02-13-17, 06:15 PM
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The wheelbase will be shorter (usually), causing toe overlap.

Is it snowing there too?

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Old 02-13-17, 06:17 PM
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Would you buy a pair of shoes in size 7 if you wore size 10?
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Old 02-13-17, 06:43 PM
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Originally Posted by zonatandem View Post
Would you buy a pair of shoes in size 7 if you wore size 10?
^Exactly. Frame fit is extremely important. You can usually fit a couple of sizes, but once you go outside of those it will be a terrible ride, no matter how long your stem and seat post. I'm the same height as you OP, and there's no way I would ride a 19' frame. Just remember, these forums see a lot of bikes for sale that were bought by someone who hoped they could get away with a frame that was too big or too small, and ultimately decided it wasnt gonna work after riding it for a while. Save yourself the headache and buy the correct size.
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Old 02-13-17, 06:56 PM
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To add to this, smaller size high end frames may well be built using lighter gauge tubes or in the case of carbon frames using less material. Small frames are designed for smaller, lighter riders and may not be up to the demands put on them from taller, heavier riders. As well, longer seatposts, stems and wider handlebars increase the stress that bigger riders put on their bikes. Professional riders often ride frames that are much too small for them, a good example of this was Ryder Hesjedal who rode a bike a couple of sizes too small for him in order to achieve a better aerodynamic position because of his height. However, as a pro he never had to buy a new bike because it broke during a ride and he had multiple bikes each year at his disposal. Every year, he would have been given new bikes from the current model year so he never was riding a bike more than 1 year old

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Old 02-13-17, 11:36 PM
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With compact frame sizing, the reach will generally feel too low even when the bike is the correct size.

The usual solution is to install a stem riser and install the stem on top of it and then the bike feels safe to handle.

I've done that modification to all my bikes.
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Old 02-14-17, 12:23 PM
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Frame size isn't that big a deal if you're only going to poke along at 10 to 15mph. Things start to change over 20mph. And, if you're on a too small bike on a long steep downhill, watch out for speeds over 30mph. It can become very frightening on a too small frame. So generally speaking, IMHO a larger frame is better for higher speeds and big downhill runs.
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Old 02-14-17, 04:46 PM
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I'm not an expert in geometry, so I'm just logically musing about this topic. If you get a frame that is significantly smaller than what you should ride and compensate it with a very long stem, wouldn't the weight distribution front to back get significantly changed. I would think that more of the mass of the body would be pushed towards the front. I know that because of the STA, some of the mass will be moved back, but generally if you need say a 170mm stem on a small as compared to say a 100mm stem on a bike that fits, overall the mass of the body is shifting forward.

I would think that this will affect the handling. If there is too much weight at the front of the bike, this would make braking on decents pretty unsettled.

Also the handling of a bike with a very long stem as compared to a 100mm +- stem... would that have an effect on how the bike feels?

I'm only talking out loud here, I have no real knowledge as to if any of these things are significant. I do see a lot of top riders choose a bike that seems to be smaller than what their height would suggest.
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Old 02-15-17, 01:20 AM
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Bike fit is a game of millimeters - I've seen and experienced the difference a 2mm adjustment in stem height can make. So why would you subject yourself to fitting a bike to your body that's INCHES out of whack? 1 inch =25.4 mm. That's a Lot of adjustment! The top tube+stem difference between my wonderfully riding last bike and my better-riding present bike is 9mm, and that 9mm put the present one into "perfection" territory.
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Old 02-15-17, 04:16 PM
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I've got bikes that are 20", 21", 23" and 25" and I ride them all...but, being stretched out on a large frame stops being fun after a while but I do like the way the big frame floats along the road. . On the other hand, riding in the drops is way more comfortable and I have better overall control on the 21". My 23" road bike has aero brake levers and riding on the hoods is the most comforatble riding position for this bike.
In all cases, you play with the head tube, seat post and seat angle to get them adjusted (game of mms--amen) "just right" for you.
For me the only non-starter would be a frame that was too small where I felt cramped.
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Old 02-16-17, 12:52 PM
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It's better to have a bike slightly too small than slightly too large because you can always increase saddle height, crank length, stem length, stem height, angle, etc.

Meanwhile, Mark Cavendish has a bike 3 sizes too small and he just get's a longer stem to accommodate. He doesn't seem to have much problems.
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