Gravel / Gravé / Gnarmac / Groad / ATB

I'm trying to!

Can't help thinking that the manufacturer must know something I don't though

Add stem length into the equation and I'll bet you'll find controls are there or thereabouts equal

I agree entirely - I ordered the large based on the TT, stack and reach

Why TT? the Reach is more accurate and any TT measurement should be ignored.

Doesn’t TT length also take into account ST angle and therefore saddle setback relative to bottom bracket? Something reach ignores completely, no?

TT measurement should be ignored taken into consideration along with all the other relevant data

Ed pls. People like to sit down sometimes

But a bike fit centres around the BB. Your saddle position is fixed in relation to the BB, which is why reach and stack are a better metric for frame sizing.

ST angle doesn’t really have a bearing on anything fit-wise, your saddle position is still set in relation to the BB.

I’m guessing TT measurement for sizing is basically a throw back to when all road frames were horizontal TT and 73/73, which then got carried over as “ETT” when compact frames came in, but as geometry has evolved it’s no longer that simple.

ST angle doesn’t really have a bearing on anything fit-wise, your saddle position is still set in relation to the BB.

This.

The only thing ST angle is important is for those who need the saddle further/nearer to the BB, which can be remedy by simply looking at the seat angle and Reach together.

I’m guessing TT measurement for sizing is basically a throw back to when all road frames were horizontal TT and 73/73, which then got carried over as “ETT” when compact frames came in, but as geometry has evolved it’s no longer that simple.

Zing.

your saddle position is still set in relation to the BB

And this should, in theory, be constant among all my bikes of different types?

Take two frames with the same reach - but different seattube angles and toptube lengths, and you could easily find that you can make one fit you and not the other.

Fit is all done relative to the BB, yes. But if the ST angle dictates whether you can or can't be in the correct position relative to the BB then it becomes important.

Very much this. If a frame has a long reach, but very low stack, and modern slacker geo (eg 68/73) and you need to run the bars high, by the time the bars are at the correct height the reach has reduced considerably. So reach, stack, ett and ht are all important IMO.

Which is what I found on an XL Stache, with its tiny head tube. On paper it fitted, but by time bars were at right height, it was way too short.

As I understand it, yes.

From what I’ve learned talking to bike fitters, in relation to saddle position, there is an objective optimal position based on your bio-mechanics.

The geometry of the frame should put you in the “correct” type of position for the intended type of riding.

“Cockpit” is more of a preference, there’s no ‘optimal’ in the way there is for saddle position. It’s a trade off of reach/comfort/aero/steering etc. etc.

Makes sense, I jammed my saddle forward a while back to compensate for too much reach and that caused a lot of other issues. My mountainbike has been very comfortable from the get-go, so I'll have a good look at the saddle position on there to get some cues for my other bikes.

(I've decided to not buy a new frame / bike before having done a bike fit, but realistically that's still a year out as my student budget doesn't allow for it.)

Yes, however if you says, have a TT bikes, then it gonna be a little different.

Makes sense, I jammed my saddle forward a while back to compensate for too much reach and that caused a lot of other issues.

When it come to bike fit; saddle to bb distance is the first thing to sort out, then everything fall in place (get correct stem length, handlebar, pedal position etc.).

As you found, moving saddle make issues worse than shorten the stem to reduce the reach.

I just went to have a look over the Arkose before ordering. There is a huge difference between the medium and large. Previously thought I might be between L and Xl but I think I may be going for a shorter stem on the L

I reckon these are pretty good value:

https://www.planetx.co.uk/i/q/CBPXTEMV3RIV1700BW/planet-x-tempest-rival1

Especially now that the new model is thru axle and has rack and guard mounts

They’re banging out some major deals at the moment. They’re also doing the ‘space chicken’ (open UP knock off thing) in 700 and 650 builds with rival 1 for the same money.

Yeah I do quite like the Space Chicken

That’s probably wise re: fit and buying a new frame.

You can have a fairly decent crack at a basic fit yourself, especially if you’ve got a home trainer you can put the bike on. I vaguely remember the GCN video on bike fit to be not terrible.

If you’ve got a bike that feels good - make sure you note the measurements before you start messing with it.

Really good ratio price/build !

That Space Chicken carbon frame with Force 1 & 650B for £1599 seems a steal!

I'd rather go for Vitus Substance CRX.

Back to my geometry question - I was just looking at the Arkose and
I'm now thoroughly confused - it's beyond me what some manufacturer's
thinking is here.

For my height (181cm) they suggest a size large for the Arkose-
eff.top tube of 578mm, stack of 607mm and reach of 398mm!

Whereas Vitus suggest a medium - eff.top tube of 545mm, stack of 568mm
and a reach of 371mm

That's an insane difference?

Seems so - with respect to Vitus that's a pretty small frame for a 181cm rider imo. If correct (the web info may be wrong etc) that's less reach than a small Arkose.

I'm 184cm and I did the Arkose geo / frame design for Pinnacle, I ride a L with an 80 or 90mm stem. The sizes are 10-11mm reach apart with even reach and stack gaps so you could ride a M as long as the saddle-bar drop didn't get too much for you.

Reasoning for the long-ish geo or the general layout (398mm reach for a L) is that long stems don't have a place on an off-road bike imo, but the Arkose is part road bike and I want some weight on the front wheel in corners and the stem can't get too short without losing that road bike handling feel. So an 80-90mm stem works well and the slightly longer reach the bike has always had is based on that. The head angle isn't as slack as some since slack head angles also push the f wheel fwd beyond the bar and can cause a vague cornering feeling due to weighting imbalance - unless countered with a longer stem... and a long stem and slack HTA feels wrong to me.

The stack is higher because I think the hoods default position of a race bike doesn't help on a gravel bike, if the bars set up a bit higher you're more likely to use the drops more often. Using the lower drop position for descending off road is illogical I know, as is riding a bike like this at speed off-road ... but it's fun if the road / off-road mix and ability is about right.

Prob a bit long-winded there but if I couldn't justify the numbers...

In short, it's not meant to be a road bike as in a trad road fit, so no need to refer to trad road sizing to size up an Arkose or any other similar bike.

My Secan fork was in the recall.

Does anybody have a tapered, thru-axle, flat mount disc fork I could buy? (Bonus points if it has mounts and stuff, so it’s still useful after the replacement fork arrives)

Would very much like to ride my bike!!

Not cheap but https://www.planetx.co.uk/i/q/FOSEGV2/selcof-carbon-gravel-fork