Struggling with sizing!

[bencran]

Hi guys, I know this is a regularly asked question, but I’m struggling!

I was looking at the Trek Emonda ALR 5 and am trying to match sizing to my previous road bike, which was a Planet X RT-58 Alloy - Size 56/L.

Looking at geometry geeks website, I can get a rough match using the 56cm emonda frame, but all sizing charts have me on the 58/60cm frame, which seems a huge jump in size I had in the RT58.

I do think I was at the upper end of the frame size for the RT58, but do not want to make the mistake of buying an uncomfortable bike.

My sizes for info:
Height - 186cm - 6’ 1.5”
Inseam - 85cm - 33.5” (socks)
Arm length - 64cm.

I’m quite long in the trunk and short in the leg for my height.

Any help would be greatly appreciated!

Link to geometry comparison:
https://geometrygeeks.bike/compare/...c-2020-58-cm,trek-emonda-alr-disc-2020-56-cm/

 

[Cycleops]

I’m more or less the same size as you, 6’1 with 33” inseam. My everyday bike is an old Trek with a 56cm frame which is probably not a fair comparison but I find this comfortable although a little small. I generally prefer larger frames and have a 62cm bike I also find comfortable although too big on paper. My preferred size is 60cm.
Its horses for courses and your preferences may be different but I don’t believe sizing to be super critical. You can always mess around with the stem/ bars/saddle to achieve your preferred position. Imho I would say the 58 or 60 would be fine for you.

 

[vickster]

The sizes assigned by the manufacturers don’t necessarily correspond to the same bit of the bike, some use actual or virtual TT, some use ST. Compare all of the dimensions and angles
Or why not ask the Trek dealer And even better, try them out

 

[CanucksTraveller]

It's an often repeated piece of advice, but when in doubt (or when you're between sizes in that overlap zone on the manufacturers' charts), it's more usual to go for the smaller size. You can make a slightly smaller frame comfortable for a slightly larger rider. It's harder to do the opposite and you might always feel you're stretching a bit.

At 6ft 1, (my height) I'd say you're going to be on an L in most makes, or a 56, max 58cm... 58/60 does sound big.

 

[Deleted member 1258]

Look more at the top tube length than the seat tube length, how close is the Trex to the Planet X ?

 

[bencran]

Look more at the top tube length than the seat tube length, how close is the Trex to the Planet X ?

Hi, the top tube is 13mm longer on the trek, which is probably about right and could always be adjusted with a smaller stem.

Thanks for everyone’s replies. I’ve done the digging and looking at geometry, but I guess I’m trying to put my mind at rest.

I think the best bet is probably the 58.

 

[Deleted member 1258]

Hi, the top tube is 13mm longer on the trek, which is probably about right and could always be adjusted with a smaller stem.

Thanks for everyone’s replies. I’ve done the digging and looking at geometry, but I guess I’m trying to put my mind at rest.

I think the best bet is probably the 58.

If the Planet X was a shade small that sounds about right, any way you could sit on the bike before you buy it?

 

[bencran]

If the Planet X was a shade small that sounds about right, any way you could sit on the bike before you buy it?

I think you’re right. The Planet X never felt too small, but I knew deep down that I’d probably be better suited to something with a bit more reach.

 

[Sharky]

If buying online, check out their returns policy.
Wiggle seem to allow returns for bikes.

 

[biggs682]

imho experience planet x are always smaller .
I would say a 58 - 60 would be right as i am 5ft 10" and find 56 - 58 ideal but will adapt to 54 - 60 sizes by playing with stems

 

[bencran]

Thanks guys. Spoke to the shop and they accept returns. Gone for the 58!

 

[Paul_Smith SRCC]

Thanks guys. Spoke to the shop and they accept returns. Gone for the 58!

Hopefully the fact that they accept returns is for reassurance only, the store should be able to help with sizing even if they can't offer a bike fit at the moment. For sure you are not proportionate, your inseam would suggest a 56cm, your height a 58 or even a 60cm, although with your inseam at this stage I'd not be looking that closely at the 60cm.

To an extent on a Trek Emonda ALR 5 the saddle height needed to achieve the correct leg angle will probably have the most influence on the size frame needed. The old school theory of inseam x 88.3% gives a starting point for saddle height with neutral ankling, over the years I have noticed this is the most accurate with size 41 feet; again assuming neutral ankling I'd normally expect to see that equation under read for larger feet and vice versa ( I have bike fitted for years)

Ankling Leg angle and position over bottom bracket.
​

Note I highlighted starting point, ankling, cleat positioning, muscle groups, personal pedalling style, shoe size and type to name some of the considerations all influence leg angle and the saddle height to help achieve that. At 186cm - 6’ 1.5” tall I have assumed you have a larger than size 41 feet, your inseam @ 850 x 88.3% = 750mm saddle height, as mentioned I'd expect that to under read given that I have assumed a larger foot size, so you can see I have used 770mm for both the 56 and 58cm on the BikeCAD drawings I composed for each, both would work at that saddle height with margin to raise and lower on each size, so your theory of going with a 58cm is probably ; the 770mm height I have used is of course still a guesstimate. If you have the correct bike fit on your current bikes you should be able to measure the 'saddle height' and 'setback' then cross reference that to both sizes.

56cm 58cm
56cm morphing to 58cm with the same saddle height and setback

During the Covid Pandemic bike stores are open but not fully, those that offer bike fitting will not be doing them if their local restrictions dictate that they shouldn't be; but if you are confident that your current set up is good then using your current bike fit data will be of value to them in helping you choose the correct size.

 

[bencran]

Thank you so much for your reply. Absolutely amazing insight.

just for reference I have size 44.5 feet!

Unfortunately I haven’t had a chance to actually visit the shop and bought purely on previous sizing.

It arrives on Friday, so fingers crossed the calculations were right!

 

[SkipdiverJohn]

The old school theory of inseam x 88.3% gives a starting point for saddle height with neutral ankling, over the years I have noticed this is the most accurate with size 41 feet; again assuming neutral ankling I'd normally expect to see that equation under read for larger feet and vice versa ( I have bike fitted for years)

Ankling View attachment 568663 View attachment 568666 Leg angle and position over bottom bracket.
​

@Paul_Smith SRCC for saddle height what's your opinion of the relative merits of the Lemond formula + crank length vs the Richards Bicycle Book 1.09 x inside leg regardless of crank length?
I'm 5' 11 1/2" with a 33 1/2" leg and size 10 feet. Normally I'm riding in pretty stout footwear with thick soles if that makes any odds. I don't wear cycling gear. If I use the Lemond method, it says my saddle height should be 36 1/4" on 170mm cranks. The Richards method gives the saddle height as 36 1/2".
I only ride old-school bikes and my default initial set up is 36 1/2", then I try a tweak and see if it helps. Different bikes are set to slightly different heights, but all are between 36 1/2"and 36 3/4", these numbers having been arrived at by trial and error. My default frame size I seek out is 23"-23 1/2" when purchasing, although have got a 22 1/2" 531 Raleigh which fits fine, but the bar height is at the safety limit..
As you may deduce from some of my postings I am something of a bike fit sceptic, I have never had one, and personally doubt one would offer me much. In your defence I will say though that all your conclusions posted on CC always seem to be arrived at after some diligent consideration and there is a lot of logic behind it.

 

[vickster]

@IanSmithCSE, for saddle height what's your opinion of the relative merits of the Lemond formula + crank length vs the Richards Bicycle Book 1.09 x inside leg regardless of crank length?
I'm 5' 11 1/2" with a 33 1/2" leg and size 10 feet. Normally I'm riding in pretty stout footwear with thick soles if that makes any odds. I don't wear cycling gear. If I use the Lemond method, it says my saddle height should be 36 1/4" on 170mm cranks. The Richards method gives the saddle height as 36 1/2".
I only ride old-school bikes and my default initial set up is 36 1/2", then I try a tweak and see if it helps. Different bikes are set to slightly different heights, but all are between 36 1/2"and 36 3/4", these numbers having been arrived at by trial and error. My default frame size I seek out is 23"-23 1/2" when purchasing, although have got a 22 1/2" 531 Raleigh which fits fine, but the bar height is at the safety limit..
As you may deduce from some of my postings I am something of a bike fit sceptic, I have never had one, and personally doubt one would offer me much. In your defence I will say though that all your conclusions posted on CC always seem to be arrived at after some diligent consideration and there is a lot of logic behind it.

Think you’ve tagged the wrong chap