On the cusp road bi...
 

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On the cusp road bike sizing: size up or size down?

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I'm in the market for a new (endurance geometry) road bike. Will hopefully get enough time on one to have a confident view of fit, but on many size guides I'm in the overlapping section between medium and large, and one of my favourite on paper options (Scott Addict 30) seems to be in very limited supply.  So I might not get much chance to properly try it out if I go down that route.

So if there's any doubt - is bigger or smaller the safer option?

My instinct was smaller, based on mtb experience and knowing a friend who spent 6 months to decide his Canyon was too big. But a quick chat to a shop suggested the opposite based on a big difference in headtube length between sizes on the particular frame we were discussing.


 
Posted : 23/07/2023 2:59 pm
 poah
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I'd go down with a longer stem or find a different bike. That being said have actually tried said bikes?
how much you looking to spend?


 
Posted : 23/07/2023 3:13 pm
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Medium to large reach looks to be 390.9 vs 394.3, same length supplied stem (103), stack 572.4 vs 594.3, according to https://geometrygeeks.bike/bike/scott-addict-30-2022/ .

So large would put you in a slightly less aggressive position, which may help any existing back weakness. At the cost of 20mm less exposed post and potentially less aero.

https://www.scott-sports.com/global/en/product/scott-addict-30-bike-red has a size guide, based on a few questions it asks you.


 
Posted : 23/07/2023 3:24 pm
leffeboy reacted
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Down. Longer stem puts more weight over the front wheel and handling is better. Sometimes it’s a brand thing. You might be between sizes on one and bang on for another.  If the headtube is too short, look for another model/brand. Because handling is geometry.


 
Posted : 23/07/2023 3:33 pm
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I would size down but as above, watch the head tube length - although if endurance geometry should still be fairly big I suppose.


 
Posted : 23/07/2023 3:35 pm
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When sizing down do check how close to the limits of the seat post you get as well.


 
Posted : 23/07/2023 3:44 pm
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3-4mm on reach isn't going to make the difference so choose on stack or how high you want the bar to be. 100mm stem is pretty short for a road bike so adding 10mm there will be fine if you want more reach to the bar on either size.


 
Posted : 23/07/2023 3:53 pm
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have actually tried said bikes?
how much you looking to spend?

I'm looking to buy on Cycle2Work and my company has a £2.5k limit. It's the Halfords scheme, which bike shops don't really like, and many charge a surcharge even on full price bikes due to the extortionate commission (can't really blame them).

I don't mind topping up by £500 or so in cash though most places (officially at least) don't allow that. Have heard from one off the record that they'd "find a way".

In any case, I'm fine with mechanical 105 so don't really need to spend much more. Would most likely want a wheel upgrade, but happy to take something lower spec and add that later. I did note that Ribble sell an upgrade from their base Mavic wheels for the same price you can buy those wheels outright elsewhere.

So I'm after someone with that Scott (in stock, so I can actually see and sit on it - not just orderable) and who takes Halfords vouchers. Which narrows the field a bit! I'm in London and the closest I've found so far is Bristol, and a few others up North.


 
Posted : 23/07/2023 4:09 pm
 Jamz
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Go down a size, 100%. If the 594cm stack figure is correct for the larger size then that's pretty damn tall for a road bike. Very easy to make a smaller bike taller/longer but it doesn't work the other way round. In my experience, you have to be careful about going too high with the bars on a road bike - you lose all the feeling/confidence in the front end when cornering, and it also gets a bit weird when climbing out of the saddle. If you are comfortably seated on a road bike, then there really shouldn't be any strain on your back, even with a low front end - your pelvis should be able to rotate forwards so that you can keep a straight back and comfortable weighting split between bum and hands.


 
Posted : 23/07/2023 4:15 pm
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Be wary of toe overlap if you're sizing down. I got caught out with this and had to buy another frame!


 
Posted : 23/07/2023 4:29 pm
 poah
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look at the geo and try some bikes that are local to you with similar geo to see how they are.


 
Posted : 23/07/2023 4:41 pm
dc1988 reacted
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You can make a small bike slightly bigger, making a large bike smaller tends to affect the handling. Shorter stem etc makes a responsive front end a lot twitchier

Personally if the either size doesn't fit I'd walk away and find one that does


 
Posted : 23/07/2023 5:03 pm
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You can make a small bike slightly bigger, making a large bike smaller tends to affect the handling. Shorter stem etc makes a responsive front end a lot twitchier

Not really, within reason anyway.  Using a 90mm stem in place of 100mm and shorter reach bars (as I do) makes little difference and the difference it does make it all forgotten after the first 10 miles.  My bike fits perfectly using 90mm stem and 70mm reach bars with a 150mm head tube and 53.5 top tube.  Yes I could use a frame that is 51.5 top tube, 150 head tube and use a 110mm stem but that frame probably doesn't exist.

Yes putting on a 60mm stem may have an impact but if you are putting on a 60mm stem you have the wrong size bike, just as it you are putting on a 150mm stem and a massive seat post.


 
Posted : 24/07/2023 6:18 am
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Disagree with the 594mm being too tall/affecting handling, I'm 5'11" and ride a variety of bikes ranging from about 590mm stack to just over 600mm, can honestly say I've never felt them lacking in confidence, surely if you're cornering at speed you're not going to be sat upright in the saddle?

I DO agree with the sizing down comments though, my bike with taller headtube is also the longest bike I own and even with a 100mm stem I've had to compromise saddle position to get a comfortable reach. I've tried 90mm on a previous road bike and I guess for my weight/position/riding style it eas the tipping point for handling, got a bit speed wobbly on fast descents and a bit light on seated steep climbs.

Flipping the stem up buys you 20mm or so extra stack and you get used to the looks, I don't notice it any more and haven't been laughed out of any group rides so it's obviously not as glaring a faux pas as I first thought. Same for those bars with the additional 20mm rise.

Finally, in my experience of low back issues, I think I've noticed that reach can be more of a problem than drop, my back doesn't seem phased with a 30-40mm difference in bar+saddle heights but excessive reach seems to cause more issues.


 
Posted : 24/07/2023 7:59 am
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Not really, within reason anyway. Using a 90mm stem in place of 100mm and shorter reach bars (as I do) makes little difference

I think stem length is proportionate to bike size, sounds like you're on a smaller bike than the OP?


 
Posted : 24/07/2023 8:01 am
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Have a look at crank length, that can be an item that changes between sizes.

I'm 5'10" and on the boundary line too. I sized up to a 56 rather than down to a 54 but then running a shorter stem and 170mm cranks than stock on the 56. I like the slightly taller head tube and marginally longer forward wheelbase, but it's more parts to change and fiddle with to get the same fit as I'd have had on the recommended smaller size, worth it IMO. YMMV of course.


 
Posted : 24/07/2023 8:11 am
 Jamz
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Disagree with the 594mm being too tall/affecting handling, I’m 5’11” and ride a variety of bikes ranging from about 590mm stack to just over 600mm, can honestly say I’ve never felt them lacking in confidence, surely if you’re cornering at speed you’re not going to be sat upright in the saddle?

Didn't say that 594 would be too tall or that it would affect handling, only that it was quite tall for a 56 frame - I would expect a 56 to have a stack around 2 cm shorter than that. My aim was simply to point out that going too tall at the front will affect the weight distribution of the bike and therefore the handling. This will obviously vary from person to person depending on their body proportions. Newbies often get it into their heads that they need a taller front end for more comfort, but it doesn't always work like that, and sometimes you sacrifice handling for comfort.

For reference, I'm 179cm and like a pure road bike to have a stack around 550-560cm - but I also have a shorter torso and longer arms than average, so my centre of mass naturally falls quite far towards the rear of the bike. I run a decent amount of saddle to bar drop to offset this. My touring bike has a stack of 590cm, which is fine on a touring bike, but it doesn't feel anywhere near as good as the lower stack bike on descents and fast corners.


 
Posted : 24/07/2023 8:42 am
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Having had a look at the bike in question, I’d be asking the bike shop what they can do with regards to a longer stem.
Looking at the pictures the cables are hidden. I’d be seeing what can be done.

Anecdotally a couple of years ago I was in the same position, wanted an S-Works Tarmac SL7, test rode it in my size, was too small so wanted to try with a longer stem. They wouldn’t swap out the integrated stem/bar combo for me….and that was a £12k bike. I went down the road and bought an Emonda SLR and Trek were more than happy to customise it exactly as I wanted.

Smaller / longer is very personal. I’ve always liked smaller road frames. But we are all different, I’ve always preferred racey geometry so not really had any issues. But I’d be recommending visit a bike shop and trying things out if possible. Don’t just get the bike because it’s on Cycle2Work, get the one that fits you.


 
Posted : 24/07/2023 8:53 am
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I'd agree with selecting an alternative model which has the exact geometry you need.

But I'd also agree with going for the smaller frame, if you had to choose between those.

I'm not so expert as some here, but with road bikes I've found shorter bikes are more fun and engaging most of the time. Longer ones feel more confident at speed and can maybe be a bit more comfortable over the miles.

Did you rule out Boardman BTW? If you've in the Halfords scheme, their bikes tend to be on the relaxed side of sporty, well-specced and good value.


 
Posted : 24/07/2023 9:04 am
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Having had a look at the bike in question, I’d be asking the bike shop what they can do with regards to a longer stem.
Looking at the pictures the cables are hidden. I’d be seeing what can be done.

Changing the stem with hidden cables is trivial, they just route underneath it in a channel. Likewise, modern headset spacers split in two, so you can adjust the stem height easily.

They wouldn’t swap out the integrated stem/bar combo for me….and that was a £12k bike.

I can sort of see why, lot more work to swap bars out and they can probably sell the bike easily anyway.


 
Posted : 24/07/2023 9:10 am

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