steel frame comparison ?

If the frame is exactly the same then no I don't think so but if one has a different tube shape or wall thickness then it could make a difference.

I have an original inbred (boggo steel) and an 853 with the same design. Can't tell the difference. Nice sticker though.

If the 725 is thinner tube walls then it will bend slightly more. This is possible because 725 is stronger so you can use thinner tubes.

But if both tubes are the same thickness the only difference is that the 725 is stronger in a crash

All steel is the same stiffness

The more bendy one will bend so little it makes zero difference beyond placebo. In fact even an aluminium frame won't bend that much less.

The only useful bend you get is through the tyres and to a lesser extent the saddle.

Reynolds 725 is a chro-moly steel, as is 4130. Unless the 725 tubes are butted and of significantly different diameter, then apart from a couple of hundred grammes, I doubt you’d notice the difference.

725 starts life as 4130 and then gets heat treated to make it stronger. So unless the 725 starts out with more butting / thinner walls it’ll essentially be the same weight as 4130. Probably not worth paying a huge amount extra I don’t think.

On my Marino frame I did pay for 725 over 4130 but it wasn’t much more expensive and the frame is still heavy so I suspect they’ve used the same tube profile as they would have done with 4130. Should be strong though 🤷‍♂️

in this instance the 4130 is far more expensive than the 725 option.

“ The more bendy one will bend so little it makes zero difference beyond placebo. In fact even an aluminium frame won’t bend that much less.”

See my post on the recent hardtail thread. Bad science.

Also, Ton is a big bloke - that much force and leverage will make a frame flex far more than a smaller rider will.

“ in this instance the 4130 is far more expensive than the 725 option.”

It really comes down to specifics - the exact frames and tube butting make a difference. I’d get the cheaper one!

The more bendy one will bend so little it makes zero difference beyond placebo. In fact even an aluminium frame won’t bend that much less.

The only useful bend you get is through the tyres and to a lesser extent the saddle.

You need to think 3D not 2D

Ampthill's right on the materials stuff. 725 vs non-HT CrMo can influence the finer points of tube spec but when comparing 2 different brand's bikes it's more likely the basic tube sizes and fit/geo are going to be more influential in the ride, especially for a big guy.

@jameso I think in part I learnt from you. Am I correct in remembering that the first Croix De Fer was 4130 as you wanted thicker tubes for stiffness when loaded? So there wasn’t any point using 725

I’d buy the one with geometry closest to your current ideal.

if it's designed and made well you may notice a difference. if it's a cynical marketing ploy, then no you won't! How much is the price difference?

in this instance the 4130 is far more expensive than the 725 option.

That's an easy decision then - go for the potentially stronger, possibly lighter 725 and take any 'steel is real' gain that there is it isn't.

You need to think 3D not 2D

I very much think 3D. And the very last thing you want for handling and response is a chassis that twists.

This is where I've told a CAD engineer to think 3D isn't it : )

What I'm getting at is that a steel frame can bend/flex/twist to the point where it's really not placebo, they can bend too much for some riders - as you say sometimes

the very last thing you want for handling and response is a chassis that twists.

IMO too much twist isn't good but too much stiffness isn't all good either. Depends whether you're Chris Hoy or a 50+ year old audaxer. There's a range that works for different riders and uses and it's subjective. But I don't think stiffer is better in the way the bike industry generally presents if we're talking about rigid bike framesets. I don't believe the human body works well with totally rigid tools for something like a bike frame, or only in fairly extreme cases.

ton
Full Member
in this instance the 4130 is far more expensive than the 725 option.

Is that the Surly tax?

The one that’s a nicer colour will ride better

Am I correct in remembering that the first Croix De Fer was 4130 as you wanted thicker tubes for stiffness when loaded? So there wasn’t any point using 725

Sort of, it was 520 crmo for cost / keeping it simple reasons and it was more oversized in the 2 main tubes than some for a bit more stiffness. 9-6-9 tubes, pretty common spec, not particularly thick. It wasn't that light, about the same as a Surly equivalent but stiffer for the weight. 725 could have saved ~100g maybe. The stiffness was for avoiding the shimmy I'd felt on lighter tubed frames esp with a basic load on but it was very early days in my loaded bike riding experience. Plenty of audaxers are happy on lighter-tubed frames with big Carradice saddle bags but I wasn't keen on how bikes like that felt at times.
TBH my tastes have mellowed a bit since, I might do it differently now and I've got more of a taste for how a slimmer tubed bike can ride as long as it's not loaded in a way that makes it inclined to wobble at speed.

Surly tax Vs Spa cycles is just what I was thinking 🙂

The fancier steels are basically allowing thinner tube walls and shorter butts / longer thin sections without denting or fatigue / buckling failures.

Surlys don't have a reputation for breaking, and I'd imagine the thin bits aren't very thin as they litter them with lots of braze on bosses.

And I'm not entering the stiffness vs handling debate.....

Surlys don’t have a reputation for breaking, and I’d imagine the thin bits aren’t very thin as they litter them with lots of braze on bosses.

That's it, they're not particularly oversized so they can use thicker wall tubes without being excessively heavy (ok, that's up for debate for some..). Tough and trad-looking frames that aren't too stiff, it's not a bad way to do it.

edit to add, @ampthill fwiw I got a good reminder of the principles and how it applies to bikes from Scot Nichol's essay series .. partly because I was fairly hopeless with formulas as a Mechanics and Physics student :/ http://www.strongframes.com/more/metatllurgy-seven-part-series

What I’m getting at is that a steel frame can bend/flex/twist to the point where it’s really not placebo

I don't think it can, but I have no evidence apart from empirical. It will flex more than aluminium but it will flex a very very small amount.

Compliance whether longitudinal or lateral comes from the tyres, which is to be expected considering how much softer a rubber compound with air in it is compared to a metallic tube irrespective of what metal it is made of.

You will not notice any difference. Too many other variables between 2 different frames made by different brands. Wheels will make more difference.

You can feel a difference between steel and al , but you need to equalise other variables so try a vintage Guerciotti vx. a similar slim tube steel frame. You'll also get a pretty good insight into how a very bendy frame affects handling , especially if you're 6 foot plus (apparently, as I'm not).

Different steels, not so much, that's down to other parameters

All else being equal between the frames I’d take 725 over 4130. Especially if the 725 is cheaper.

There are bigger things to think about though - mainly frame geometry and built. On a hardtail whacking a set of bigger volume tyres most like makes more difference to comfort for example. My steel frame also has a 2.6” back tyre on it so it’s the most comfy hardtail I’ve ever had.

@nickfrog I don't mean this to be a 'how hard do you ride?' line but there really is quite a bit* more flex in some frames than others. I have some bikes that can have shimmy induced with a certain load on the bar and others that are almost impossible to repeat that with. Shimmy is flex coming from quite small forces, riding can put much higher forces into a frame.

Compliance whether longitudinal or lateral comes from the tyres,

Vertically, yes it's mainly tyres and seatpost (the other current steel bikes thread got into this) but it changes when the bike is leaned over or loaded with opposing bar and crank forces. @chiefgrooveguru described it well in the other thread, how the lateral loads or twist affect an MTB frame. That's what I meant about thinking 3D, a frame being far stiffer in the vertical plane than in others. Wheels and tyres will flex at angles too but that doesn't 'save' the frame from flexing.
The same thing is happening on a road bike, road bikes can go thinner on the tube specs than MTBs and have less tyre give.

*Agreed that it's really hard to put numbers to all this, even if I did know what I was doing with the maths at that level. A very complex situation to model. I wish I was as smart as mick_r because he won't get into all this : ) but I do find it fascinating, partly as it's an area that isn't all engineering or all wafty-design. It's empirical as you say, sensing and trying to separate out influences and trying to test with non-equal samples. Loads of bad science pitfalls. Loads of marketing BS attached to it.

Just thinking about my alloy road bike vs my new carbon gravel bike - when on the turbo trainer putting a hard effort in the bb on the alloy ones flexes a surprising amount. The carbon one is much more overbuilt in that area and very little side to side flex.

Yet when out  riding on the road the carbon one is more comfortable over broken / vibratey surfaces.  Broadly the same tyres at 90psi - so not much tyre give there. So material and design can make a surprising difference.

Is that the Surly tax?

it is indeed......... to the sum of £700

i have been a longtime surly fan. owned 7 or 8 over the years. but i am afraid i wont be owning another.

I’ll read the article later Jameso

My thoughts are……

When the bike is upright and hits a bump the seat post, fork and bars might bend enough to help reduce the force you feel. The first aluminium bike I road had a really fat seat post and it was harsh sat down . This was when we thoughts 30 psi was a low pressure. I bought similar bike with a 27.2 seat post and it felt as comfy as the old steel bike. The frame doesn’t bend enough vertically to reduce reduce the force

Frames clearly flex when forces are applied out of the plane of the frame. Stand next to your bike holding the saddle and bars. Press down with your foot on the pedal nearest you. The bike flex’s easily. It’s obvious that frames flex in use, just not within their plane

But I have no idea whether that’s a good or a bad thing

Pick the back wheel up of a steel framed bike by the saddle and drop it and the frame will spring as the wheel hits the ground. An alloy frame won't do this to the same degree. A steel frame seems to dampen the trail chatter for me, which makes them more stable at speed, than an alloy frame. Sorry for going off topic.

On a touring bike, forks and saddle are everything.
(And the Spa own-brand saddle is brutal).

Otherwise it's as dc1988 says.

If you are really interested in the materials and not just the sticker then surely you need to be looking at the make up/butting of every tube? I have seen many a frame proudly sold as some fancy model with gas pipe seat stays etc.
Also bear in mind that many a modern steel frame is capitalising on the legend of steel. Eg my Cotic X was sold as having all sorts of wonderful properties inherent with steel. Well it rusts and like railway lines it's heavy and unresponsive. However my 1983 531c frame and fork Raleigh rides beautifully.
Old good quality steel road bikes are mostly nice. Gas pipe isn't . A full 853 will be nice made today. Something with girders won't.

@ton - I really like the D’Tour I bought from Spa, does all the stuff I wanted from it and was cheaper than an equivalent Surly.

Tube set comparison with my wife’s old 26”LHT, the 725 D’Tour has smaller OD tubes that sounded thinner when flicked and has more tactical reinforcement gussets on it.

The LHT seems to use burlier tubing overall, whilst the design of the D’Tour seems a bit more thought out. Both ride really well, no downside I can see at all from the D’Tour handling or frame stiffness being impacted as the design/geometry are nice.

I could rell my 531c was slightly more compliant laterally at the BB than my handbuilt Columbus SLX (internal rifles at BB and fork tube). Changed the cheaper bike to 653 and that was much closer to the SLX. 531c main tubes with 753 rear triangle.

You don't see many 753 or TSX frames these days as they were very thin. My builder refused to use TSX. PS both bikes are like magic carpets to ride, yet climb really well. Both over 30 years old.

Depends whether you’re Chris Hoy or a 50+ year old audaxer.

Speaking as a middle aged audaxer, I do find my 531c Thorn wonderfully comfortable on long rides. It's not too clever when loaded with panniers on a twisty descent though.