What size of a road bike frame

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Artur

New Member
Hello to all bicycle enthusiasts.

I am planning to build a endurance bike, based on a basic aluminium frame. Its Brand-x Rd 01 frame available on Wiggle or Chain Reaction half price right now. Its 122 euro. The frame is made of 6061 triple butted aluminium and has a carbon fork.

As this is going to be my first road bike I has no experience in sizing a frame. This is why I would like to ask you to help me to decipher a frame measurements before I make an order.

I'm 175 cm or 5 foot 9 and my inside leg is 84 cm or 33 inches.
I have to choose between 54 or 56 frame.

Geometry:
Seat tube - 54 is 500, 56 is 520
Effective top tube - 54 is 547, 56 is 558
Head tube - 54 is 145, 56 is 160
Head angle - 54 is 73°, 56 is 73°
Seat angle - 54 is 73,5°, 56 is 73°
Reach - 54 is 384, 56 is 385
Stack - 54 is 551, 56 is 565
BB drop - 54 is 65, 56 is 65.

How would you characterize those frames based on the measurements, and which size will be right for me.
Last to say I will not be using this bike for any competitive riding. I want to ride solo first before I am confident enough to join some club. I am planning to do 50 k distances.

Thanks for reading

Artur
 

Sharky

Guru
Location
Kent
You really need to find a dealer who will let you have a test ride.

In my case, also 5 ft 9 ins. In the old days would ride a 23 in frame which would be 58cm. But current bikes are 56cm and one a 54cm.

So no real help, sorry. Just go and try a few.
 

CanucksTraveller

Macho Business Donkey Wrestler
Location
Hertfordshire
It's so hard to know for sure if you've not sat on one, and all makers are different in how they size frames.

I tend to err on the smaller if I'm between sizes, I'm just over six feet and that's on the cusp of M/L and L for Giant, and between L and XL for Genesis, to use two examples. I find the lower of both are the more comfortable, if I go larger I find it feels like a "stretch" to the handlebars and I don't enjoy that feeling.
 
OP
OP
A

Artur

New Member
When I measured my inside leg I was surprised of an outcome. Usually when I buy trousers even 32 is to long.
First I used a book to make a measurement but I seemed not accurate. Eventually I used builders level. Tried few times - 33 inches.
 

Cycleops

Legendary Member
Location
Accra, Ghana
If you have a 33" inside leg you should be safe with the 56, especially if it's a sloping top tube. You can adjust reach with the stem. If you have long legs you may have longer arms too.
I prefer a bigger frame to smaller but we're all different.
 
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How tall are you? Stack and reach are the key measurements for comfort and efficiency. A size 54 with those measurements will give a ‘base’ fixed frame stack and reach ( the figures quoted) which would work for someone of about 5 ft 7 - 5 ft 11. You could then fine tune it with steerer cuts / stem spacers / stem lengths to make it how you want it. I’m 5ft 11, and those are pretty much the figures that work for me, with a 100mm stem, and 2 x 5 mm spacers on a low rise ( 9mm ) headset top cap and the steerer cut flush with that height.
 

wafter

I like steel bikes and I cannot lie..
Location
Oxford
If you are unable to try before you buy then I would go for the smaller 54cm frame. For 5ft 9” you have quite long legs and therefore a shorter torso, you may be overreaching with the larger frame.
+1 on this, generally speaking.

OP; I'm similarly proportioned (around 177-178cm and 83-84cm) and both my current road bike and its likely gravel replacement are / will be "medium" frames at "53cm" and "54cm" respectively - although bear in mind that at best these numbers show only one part of the puzzle. Frame reach on each is quoted at 389 and 385mm respectively, while stack is 560 and 593mm respectively.

Interestingly for the sizes you quote, the reach is only 1mm longer for the L (385mm) over the M (384mm) but the stack is considerably higher on the L (565mm) v. the M (551mm). The seat angle is less on the L model, suggesting that the effective total distance from seat to bars might actually be a little less on the large frame, given the minimal additional frame reach.

On frame specs alone the medium frame has a stack/reach ratio of around 1.43 while the large has a ratio of 1.46; putting them both in "endurance road bike" territory, although on paper the large is more "relaxed" than the medium.

It's a bit of an odd one. Conventional wisdom suggests that those with relatively long legs go for more endurance-proportioned frames with larger stack/reach to accomodate the shorter torso, and usually for any given geometry a smaller frame is the way forward as (minimum insertion lengths permitting) pushing the seat higher on a smaller frame to get more stack is more versatile and has fewer knock-on effects than shortening the stem on a large frame to reduce reach.

All that said the slightly steeper seat angle on the smaller frame will potentally mean a longer effective reach (seat to bars) on the Medium frame than the Large (potentially a bad thing if your proportions mean you're limited on reach), but it will also give you more horizontal displacement between the seat and crank centre for a given seat height; which might help reduce knee pain (I have to have my seat set pretty far back, possibly because of the angularity caused by my leg length). Also the lower stack of the medium frame will mean more drop between the seat and bars on the smaller frame, all things being equal (although could could flip / replace / space the stem to gain stack in this area).

Were frame proportions comparable I'd say the medium would be the dead-cert, but given the weird relationships in this case I'd say there are possible plus points for the large too.

Do you currently have a bike? Best thing I can suggest is to take some reach and stack measurements off that / play with it to try and replicate the setup you'd get on either frame. Outside of this, if you had to make a call based on specs alone I'd suggest that the safest bet is probably the medium frame... FWIW.

Good luck :tongue:
 
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vickster

Legendary Member
Similar proportions to me, I’m maybe half an inch taller and my legs a bit longer. All my bikes are 54cm effective TT with 100mm stem. And slight layback on the seat post. I prefer to go smaller if between sizes
 
OP
OP
A

Artur

New Member
How tall are you? Stack and reach are the key measurements for comfort and efficiency. A size 54 with those measurements will give a ‘base
+1 on this, generally speaking.

OP; I'm similarly proportioned (around 177-178cm and 83-84cm) and both my current road bike and its likely gravel replacement are / will be "medium" frames at "53cm" and "54cm" respectively - although bear in mind that at best these numbers show only one part of the puzzle. Frame reach on each is quoted at 389 and 385mm respectively, while stack is 560 and 593mm respectively.

Interestingly for the sizes you quote, the reach is only 1mm longer for the L (385mm) over the M (384mm) but the stack is considerably higher on the L (565mm) v. the M (551mm). The seat angle is less on the L model, suggesting that the effective total distance from seat to bars might actually be a little less on the large frame, given the minimal additional frame reach.

On frame specs alone the medium frame has a stack/reach ratio of around 1.43 while the large has a ratio of 1.46; putting them both in "endurance road bike" territory, although on paper the large is more "relaxed" than the medium.

It's a bit of an odd one. Conventional wisdom suggests that those with relatively long legs go for more endurance-proportioned frames with larger stack/reach to accomodate the shorter torso, and usually for any given geometry a smaller frame is the way forward as (minimum insertion lengths permitting) pushing the seat higher on a smaller frame to get more stack is more versatile and has fewer knock-on effects than shortening the stem on a large frame to reduce reach.

All that said the slightly steeper seat angle on the smaller frame will potentally mean a longer effective reach (seat to bars) on the Medium frame than the Large (potentially a bad thing if your proportions mean you're limited on reach), but it will also give you more horizontal displacement between the seat and crank centre for a given seat height; which might help reduce knee pain (I have to have my seat set pretty far back, possibly because of the angularity caused by my leg length). Also the lower stack of the medium frame will mean more drop between the seat and bars on the smaller frame, all things being equal (although could could flip / replace / space the stem to gain stack in this area).

Were frame proportions comparable I'd say the medium would be the dead-cert, but given the weird relationships in this case I'd say there are possible plus points for the large too.

Do you currently have a bike? Best thing I can suggest is to take some reach and stack measurements off that / play with it to try and replicate the setup you'd get on either frame. Outside of this, if you had to make a call based on specs alone I'd suggest that the safest bet is probably the medium frame... FWIW.

Good luck :tongue:

Thank you for that analysis.
 

steveindenmark

Legendary Member
I am 5'9"and ride a size 50 frame. How you sit on a frame is a purely personal thing Go to a bike shop and sit on a lot of different bikes to work out an average. Some bike shops have a stand over measure as a basic guide. Dont listen to people telling you the size of frame you need. Go and do it yourself before parting with your money.
 

vickster

Legendary Member
I am 5'9"and ride a size 50 frame. How you sit on a frame is a purely personal thing Go to a bike shop and sit on a lot of different bikes to work out an average. Some bike shops have a stand over measure as a basic guide. Dont listen to people telling you the size of frame you need. Go and do it yourself before parting with your money.
A 50 top tube? The smallest (XS) Croix de fer has a 52.4 TT according to the Genesis geometries
 

wafter

I like steel bikes and I cannot lie..
Location
Oxford
Thank you for that analysis.
No worries - sorry it wasn't more conclusive! It started out as "get the medium frame because" and as I read through the specific frame specs some of my reasons disappeared :tongue:

Looks like a decent frame for a budget build; half tempted to buy one myself and migrate the bits from my knackered Giant.. that said I think that would tip the Mrs over the "bikes in the kitchen homicide threshold
A 50 top tube? The smallest (XS) Croix de fer has a 52.4 TT according to the Genesis geometries
I'd guess seat tube - my medium-framed Boardman is defined as a "53cm" from the seat tube; while the top tube is 55.5cm.
 

steveindenmark

Legendary Member
A 50 top tube? The smallest (XS) Croix de fer has a 52.4 TT according to the Genesis geometries
I have 8 bikes and the CDF does not get used that much. Even then the stem has been changed for a vey short tilting stem. I think it is a 52 frame. It was so cheap it was worth a gamble.
 
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