I need some pictures to better understand this ;)

Regulation 14 here:
https://www.cyclingtimetrials.org.uk/articles/view/11

Unenforceable.

Just like the previous exception rules, all the rider has to do is move.
It says nothing about the pad positioning itself.

Unless they have a bunch of photographers and judges on route to try and catch you, it is a meaningless rule with huge ambiguity.
You will now once again have to check in to scrutineering with both person and bike present and not just get the bike approved which was the whole idea of dropping the examinations for exemptions and just allowing a choice of one or the other.
Powers that be again having a rule that is stupid, ambiguous and achieves nothing.
What sort of idiots run these shows?

I'm guessing mfgs will see this as a rider issue, not a bike issue. UK TTers will just end up riding larger frames to get the reach.

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

Hi Steve-


The UK office might have some people familiar with it, but (without speaking for everyone in Waterloo either) it's the first I've heard of it.


What's "normal"? Below I've modified one of my graphs from the padXY thread...anonymized, data shifted to account for elbow position on pads (several assumptions baked into that shift, but reasonable ones I think), reversed the X axis to line up with the CTT graphic you linked to....(0,0) is frame stack and reach, and that line is 30mm away from and parallel to a theoretical 73deg head tube angle aka the steering axis in that same CTT graphic:




If I'm correctly understanding your concern, everyone left of that line falls afoul of the 3cm rule. I suppose an argument could be made, that since there are almost 2x as many riders on the wrong side of that line as the right side (per the CTT rule), that there's a "norm" with respect to fit that lies somewhere a little further left of CTT's arbitrary line.

Here's the thing, though...however they got to those positions, those are their positions relative to what they're riding right now...and that includes the spatial relationship between their pads and the steering axis. Maybe they like the combination of fit and handling and power output that goes with their position, maybe they don't, but for my purposes, "normal" includes everyone on that graph, right where they are....and the steering axis, right where it is relative to them.


I'd be happy to review whatever substantiating information or data CTT has to support this rule. In the last couple years the UCI saw fit to eliminate what many considered to be similarly arbitrary restrictions on rider position...it would be interesting to know why CTT thinks theirs is not only worthy of retention, but increased enforcement.

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Carl Matson

Thank you Carl for that very detailed response. As you can possibly imagine, the debate here in U.K. TT is getting rather heated.

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Developing aero, fit and other fun stuff at Red is Faster

The answer to this is really very simple.
The first race where this is strictly enforced, nobody who falls foul of the rule enters the race, but instead hands the organiser a letter stating that the existence of this rule is why.
Money talks, simple as that.

Thanks, Carl, that is very useful information.

The rule has existed for quite some time, and appears to have originally been driven by concerns about the superman position and safety. However, it doesn't actually prohibit the superman position, it just means you need a custom frame to achieve it, but I've only heard of one person using a custom frame to do that in a CTT event. So it really comes down to a belief that we need to limit how far forward people go for safety reasons. I'm not aware of there being any justification at all for the choice of 3cm from the steering axis as a sensible safety limit, however we're now in the situation where the burden of proof would probably be on anyone wanting to change the limit to something else. The appetite for enforcement arose from a complaint at this year's National 10 mile championships regarding 2 of the top 3 riders being clearly outside 3cm by one interpretation of the old version of the rule. There has for years been a vocal minority complaining about this rule not being enforced, and as the rule exists, it doesn't seem unreasonable that CTT would want to enforce it, as they have no power to remove or change it, only a motion at the AGM can do that, and it would need >66% support from district representatives, who indirectly vote according to the preferences of individual clubs. It was the process of a motion being raised by a district and getting a large enough vote at the AGM that resulted in the ambiguity being eliminated this year, so CTT could reasonably argue that they are just doing what the riders want, though it's unclear to what extent district representatives actually seek to capture the opinions of riders and vote accordingly, there is no formal process in place to ensure that happens. A survey on the UK TT forum suggested most respondents are opposed to the rule.

But what is clear is that we are stuck with the rule for 2017 as there is no mechanism by which it can be changed or eliminated till next year's AGM, and in any case, it's not clear that an attempt to change or eliminate it would achieve a large enough vote to succeed. There have been several unsuccessful attempts to change the rule in recent previous years.

From the point of view of riders who have to comply with CTT rules, there is very little downside to frames simply being much longer than they currently are in general. For example, the Shiv TT is one bike that is quite helpful for compliance, as the stack doesn't increase as the reach gets longer with increasing frame size. Some people are buying second hand P4s, but they aren't easy to get hold of. So the question is why are frames getting so short for a given stack? I guess the downside of making them longer would be the increased amount of carbon used, so a longer frame will cost more and be heavier, so if the rest of the world doesn't agree frames need to be longer to give safe handling, the UK TT market probably isn't big enough to cause any accommodation by global manufacturers. I've argued for some time now that it would be better if we used either triathlon or UCI rules to ensure availability of compliant bikes, with relaxations where appropriate, e.g. doing a 12 hour TT with UCI restrictions on water bottles would be a bit silly IMO, but never additional restrictions that can make bikes designed for those rules unsuitable for UK CTT events. But there are some people who see no problem with having to go to a small custom frame manufacturer if you want to ride in a TT. And of course many of the people on the right of your line are delighted to make things difficult for their competitors on the left of the line. If you have limb/body proportions that make it really easy to comply, you get a competitive advantage by forcing some of your rivals to adopt a position that doesn't suit their limb/body proportions.

Thanks Carl. I can hit my fit numbers on a medium SC (as would be expected of someone 5'11"), but in order to not contravene the 3cm reg, I'd need the stack of a medium with the reach of an XL. Not ideal.

Carl, nice piece of data processing. From your database, is it possible to tell

• Primary competition mode olympic tri / IM tri / TT, also amateur / elite
• Whether these riders would be UCI compliant (bar end data, also saddle . . .)
• Whether riders have the "right size" bike i.e does frame size concur with your expectation from pad XZ data

There's a huge spread of reach there, really curious as to whether it's rider morphology, race discipline or bike fit.

Further to Steve's comments : The argument that seems to be put out there is that to much weight over the front of the bike is unstable / dangerous even if your position is not that stretched. An example of this is the National 25mile champ Ryan Perry. His position seems fairly standard and a long way from a superman position. However the bike he rode last season (Boardman TTE) is difficult to comply to the 3cm rule on (which is ironic what with Boardman being an icon of the UK time trial scene). If this were true then a number of bike manufactures suggested fit ranges are unsafe. Of course there is no proof of this just a surmising that it might be dangerous. Personally in the age of deep wheels enough weight over front wheel is beneficial.

You're very welcome.


Don't know about our competition, but we went where the fit coordinates were/are. Since our process, as laid out by Slowman many times, starts with the front of the bike (in this case the cockpit) and works backwards, frame geometry that allows for our desired cockpit (range) solution - while maintaining good handling characteristics and meeting stiffness goals, etc etc - is one of the results...not one of the inputs.

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Carl Matson

dontswimdontrun wrote:

Carl, nice piece of data processing.

Thanks. In the context of that padXY thread it was just my take on how Dan was classifying people and in particular looking for a reason why some folks were categorized as one thing but pictures of them seemed to tell a different story.



in order:

• no...though having that sort of "3rd axis" information was suggested a couple times in the padXY thread. I agree it would be interesting, but it wasn't info Dan was asking for.
• nope, at least not based on that particular database...all it has is padXY...a few folks added just enough brand and frame size info for me to back out what I did
• no again...at least not from a bike design perspective...like I said, I take that point cloud pretty much at face value. granted, there are probably going to be some padXY points which simply aren't feasible to reach with a given design without adding weight/complexity/additional sizes/different geometries/etc. why those folks are outliers could be due to having the wrong size bike, or a really poor/inappropriate fit, or some unique morphology (or pathology).

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Carl Matson

Not speaking for the whole industry here, but the fit ranges aren't suggestions...by design (and that can be intentionally or incidentally...even accidentally?) they're what is available to the rider/fitter/coach, allowing for solutions to the wide variety of fits that are out there...a universe of fits that seems to have a center of gravity somewhere beyond what CTT thinks is appropriate.

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Carl Matson

That's not what I meant by question 3, it's not whether you've got the geometry "right" (FWIW the last road bike I bought was a 5500 when there was no H2 or H3), but whether these riders had chosen the best size in the range for themselves. I now realise that there's more info in the graph than I thought - it's extrapolated elbow position referenced to frame stack/reach as zero/zero, hence the intercepts at 30mm and 100mm. So, we have total pad stack of between 30 and 170mm. 30mm is a challenge to achieve, but 80 is a doddle and 100+ seems gratuitous to me. So where would we be if people chose a size larger, or in some cases two? From Trek geometry tables, TT frames gain 20mm in reach with 25mm in stack, so one size moves the steer axis 27mm and would bring the CTT legal proportion to well over half. Road frames it's 5mm reach for 20mm stack, so one size would be 11mm or so. You can design the locus of the stack/reach curve, but not which point on it people choose. What do you see as normal or correct for cockpit dimensions - brochure pictures don't often show huge stacks. Is there a point at which you think "Eeuuuuw"? I appreciate it's easier to "correct" a bike that's too small than too large.

Agreed, totally silly. Choke up when being examined and then go back to whatever is normal after.

The rule applies whilst competing. This is not supplanting the UCI reg, CTT is separate and not the UK's UCI franchise. The issue Steve is seeking counsel on is whether the rule is compatible with the geometry of mainstream competition machinery. The merits of (in)accurate enforcement during the race vs the systematic gaming of a pre or post race check is a different, though equally valid topic.

So somebody slides a little forward to power up the short hill and they get disqualified?
This is all so stupid.
Continual video footage and examined after the race?
How the flaming FRuck are you going to accurately judge this 3cm rule on a moving cyclist?
Is everybody going to be made to put a bright yellow flagging line projecting upwards from their stem so some single hour trained marshal can disqualify you for your gross insafety.

If I set myself up to ride a TT safe and comfortable, I am illegal in wheelbase length, total of my bike in front of the BB, where I sit in relation to the BB, the angle of my armrests and now if I head to the mother country you can throw in this new abomination.

The only reason TT setups become dangerous is because of having to comply with moron rules.
Too short front centres, too short wheelbases, flat bars that offer no support and you have to sit on the last inch of seat with your centre of gravity forward to make any power.

To everyday public, a tri bike and a TT bike are the same.
All these extra rules for cyclists doing TT are ridiculous.

I still don't think that graph has enough info to do what you're asking...as Slowman and others pointed out in the padXY thread, there are a host of other factors that go into determining whether a person's fit is appropriate...padXY isn't enough.


I don't pass any judgement on normal/correct/eeuuuw. I'm not a fitter...and I don't really think the fitter's job is to pass aesthetic judgement per se, either...it's to find the position which best suits each individual's needs. For my purposes that point cloud simply is. ..and my job is to try and influence the design process such that we end up with a product that lets the fitters (and DIYers) do their job and find that happy place wherever it is in that cloud.

Long & low looks are great for marketing brochures...reality occupies a much larger space. If Dan and the FIST army succeed in their quest to consolidate & shift that cloud, I expect our bike designs will follow suit.

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Carl Matson

Carl, I don't know how easy this would be for you, but do you already have something that can take padXY and determine the largest SC that can accommodate that? I was just wondering what the level of compliance with the 3cm rule would look like if everyone was riding the largest possible SC for their co-ordinates.

I drew a diagram to look at where the elbows would be for what I regard as a "normal" setup, with a flat 100mm stem, aerobars above the base bar, and forearms positioned on the pads where mine have the widest part of the forearm, and it resulted in 4-5cm being a normal sort of place for the elbows to end up. To get safely inside 3cm looked like it would need the norm to shift to what is currently around the shortest end of commercial stem ranges, 70-80mm. The SC is very good in this respect, providing short stems, but that only works if the frame has enough reach to compensate.

I have thought of one reason why people who don't have to comply with CTT rules might prefer longer frames - I find toe overlap to be a problem on some occasions when manoeuvring around at low speed.

Is there a specific reason why Trek's approach with the Madone of having two fits for each size can't be applied to the SC - is it just the lower sales volume of the SC making it infeasible?

Sliding tends to be on the saddle (Tony Martin, Contador etc) but the rule does apply for the whole of the ride.
UCI limits saddle position and bar reach, so people will as you point out be hanging off the front of the bike.
CTT regs do not limit forward position of the saddle, nor the forward reach of the bars, except relative to steering axis. This actively encourages longer wheelbases. It seems we are laying the same accusation that bikes may be too short for perfectly reasonable positions (obviously there is still the condition of being unreasonably stretched, which we wish to discourage).
Further searching here, largely untainted by any influence of UK TT scene, brings up several pieces by Dan Empfield.
1) What Size? Part 2 (2015) Shows that various elite athletes from triathlon and cycling skin the pad reach/stack cat with different size frames and stems.

His own recommendations for front centre (cautioning against too much weight on the front wheel) would put me on a Medium SC, the larger of two possible sizes for me. It would be a bit of a struggle to get pad stack low enough, but I'm currently right on CTT's other bar position reg, pads >80% of saddle height.

Part 1 of the article contained the following wise words:
[Fit calculators] are very precise. They are solving a fit problem.

What they are not doing is solving a handling problem.

Let's work through the handling problem now.

I am a guy with few and basic needs. On my road race bike, beyond the mechanical aspects (shifting, braking), and contact point comfort, and assuming my fit coordinates are achieved, my primary concerns are:

1. Is the bike stable at all speeds in all positions, including a tuck?
2. Is the bike's handling pleasing when I'm out of the saddle?
3. Does the bike corner and descend well?"

2) In between bike sizes? (2010) An earlier call for a larger rather than smaller frame.
" It's typically better to ride a tri bike with a stem 2cm or 3cm shorter than what you'd ride on your road bike, though a lot of bike manufacturers don't realize that. So, me, I ride a 12cm stem on my road bike, a 9cm stem on my tri bike, and both bikes handle very nicely and as they should."
"I think you can see, then, that the trend today is to buy the larger frame, if you're in between sizes. Even if you're spot on a particular size, consider whether the next size up might not work better for you."

3) Steering geometry for tri bikes (2004) A much earlier call for longer front ends.

To me it seems there is common ground on what makes bikes stable and safe (and the converse), and from the dates of these articles it is not a new phenomenon of the latest frame geometries. CTT rule was brought in for 1998 season.

And for those of us at the taller end of the spectrum?
There are no larger sizes.
Armrest length rules are far too short, just putting clipons on my standard road bike setup and sliding my seat a little forward of where I normally sit at 10-12cm behind the BB, with no shifters on the bars will push me right up to the edge of the rule.

The rules are a joke and need to changed.

It is impossible for me to adhere to this 3cm rule in any practical way.

So-called superman positions are not dangerous, short wheelbase, short front end, non supporting seating on bikes with gross weight balance problems are the cause.
And it is moronic rules that create this.
Remove the restrictions and let us all ride safe and equal positions.

Imagine if the now common trend in MTB to move to very short stems and longer wheelbases was ruled against?
MTB is so much safer now than in it's beginnings with horrible short geometry and small wheels.
Cross country rigs now eat up country that was once the preserve of downhill only bikes.

Why is there a need to stifle road TT geometry?
This is the cheapest change you can ever make to a production bike, just change the geometry.

UCI rules are just dumb.
You cannot run a rim wheel and fit a cover, but you can pay five times as much and run a solid disc.
How does that equal the playing field?

Nobody on tri bikes are falling off because they are unsafe, so this line of reasoning is simply untrue.
Under UCI rules, there are still smaller people effectively running superman positions, if this is so unsafe why are they still allowed?


UCI and now this idiotic 3cm thing are just so far down the silly scale it's not funny.

Well...I think this is pretty close in terms of how large the CTT elbow position compliance windows are for each size SC...it works for my coordinates (I wouldn't be legal on a medium, but would make it on a large). Mind you, we're back in terms of padXY now...not elbowXY...my assumptions (elbowX vs padX in particular) are still baked in...and the axes are flipped back to the convention from the padXY thread so we're looking at the right side of the bike.



And then, just for fun(??), I came up with a formula which you can use to check any elbowXY against any given frame geometry for CTT compliance...

[ETA: removed it...thinking i found an issue or two...then figured it was OK, so it's back...for now]

If your elbowXY satisfies the following inequality AND that bike can actually accommodate the coordinates (padY especially...but padX could be an issue as well), you should be OK with respect to this particular rule:

elbowY < -TAN(head tube angle in radians)*(elbowX-frame reach) + 30*TAN(head tube angle in radians) + frame stack

where elbowX is padX (either pad center or back of pad works) minus the distance from there to your olecrenon process, and elbowY is same as padY

[disclaimer! I don't know what sort of tolerance the CTT commissaires allow on their measurements, so this should only be used as a sanity check...not as "proof" of compliance] It's also possible someone will check my work and discover it's flawed...so watch for edits :-)

Steve Irwin wrote:

Is there a specific reason why Trek's approach with the Madone of having two fits for each size can't be applied to the SC - is it just the lower sales volume of the SC making it infeasible?

I imagine that's part of it. There's also the UCI's commercial availability clause to consider. Have to make most of a size run in H1 to accommodate the team anyway, so why not offer it in another color & spec or two. Outside of the pro road racing world there aren't quite as many mega-drop laid-out customers...hence H2.

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Carl Matson

Cool, more data :)
Some observations:

• Taking the pad Y against frame size stack data, your chart shows Treks are engineered for pad stack delta 65-175mm, so there's no-one above that range and a handful that are below the lowest value.
• Only two riders need an XL to get the required padY, four require an XS and for a further four even the XS is too tall.
• Size Large should be on the line with elbow at 640/425, your CTT line goes through 640/485, so elbow to pad centre is 6cm? That's certainly less overhang than I choose, and I think Steve too.
• With that elbow offset, pad reach of ~500mm is likely to exceed UCI bar reach, difficult to make assumptions of arm length vs padY, maybe slight +ve trend? Plenty of this dataset is outside UCI too.
• Admit I'm a bit confused by the mid pad / pad range / full range terms, note that the XL cut-off (short) ties in with the shortest full range number.

For completeness the full quadrilateral of pad adjustment for each size with "CTT line" across the middle would show how the riders fit in (or don't).