TT or regular aero frame?

[shlammed]

How do you figure the geometries are all that different, there is usually about 0.5 degree HTA difference which many times a longer rake makes up for, and many times effective STA's can be had within 1-1.5 degrees of what is considered very mainstream road bike geometry. Granted reach will often be just slightly longer. BB drops will generally be about the same.

So please enlighten me, which geometry numbers are you actually talking about?

Sure, there are extremes in both camps, but looking at the current market as a whole, there is a high degree of overlapping. Especially if you look into brands such as Cipollini.

In fact, a Cipollini RB1000 in size small is about 1,5 degrees STA off of a Planet X Stealth TT-Tri frame in size M, the rest of the figures are practically identical. If you move the seat back about 15mm in the rails in the Planet X Stealth, you've got the exact same fit and the same numbers for handling except a few mm change in seat stay length...

how does front-center change with the two types of bikes? how do the chainstay lengths change between bikes? the weight balance would be the biggest effect on handling, IMO.

I haven't looked at TT bikes recently but I remember they had quite a bit lower bottom brackets too... ~5mm. not that it changes much in terms of how everything works, but it will effect handling a bit. with basic geometry the same length CS wil a lower BB will have more weight on the rear wheel than one with higher BB. sure it wont be much, but the triangles are so small in the back end that a small change can end up being more and more significant.

[Grill]

Ahh... I see... yes, there would definitely be some obvious disadvantages for the everyday-Joe's daily pro peloton rides, no doubt. I was under the misconception that we were talking about casual riders who spend 90% of their saddle time training, either solo or in smaller groups.

And I realize you have spent a great time sprinting out of corners onboard modern TT/Tri-bikes.

Do you actually have experience? Or are you just drawing conclusions upon hearsay?

...TBH, I can admit that pure Tri-frames have one downside, they are built for IM-distances which require a bit of comfort, i.e the old "vertically compliant", which for most of them is in the rear triangle alone. This is not really uncontrolled flex as much as it is a noticeable"softness", think Solace or Roubaix.

It is perfectly detectable in a sprint, but more as the feeling,of an inertia dampener rather than sketchy flexing.

My Shiv has it more than for instance my previous a bit cheaper Planet X Stealth, but on the other hand the Shiv is a way more velvety ride on rougher roads.

But as for cornering confidence and bombing thru hairpins, they're both on rails with very much no influence from flex compromising the handling nor ability for mid-corner line corrections.

So in conclusion, no you won't get Foil or Hi-Mod "snap" or immediate acceleration, but that is about the only downside.

Personal experience with the IA? No, but my mate owns a shop that sells a ton of them. It's a soft bike when compared to the DA, much less the AR.

Have you set up any of your TT bikes with road bars? Because bullhorn position is drastically different than road bar position...

[mattr]

FWIW I once had a road bike with a 72,5 head angle, fork rake to match, 75 seat tube (not really relevant, but what the hell).
Once I'd got all the bits on and the position sorted it was possibly the worst handling road bike I'd ever had. The head angle/rake combination made it feel like it was weaving gently all over the road, and any sort of proper aggressive cornering it would resist, then sort of flop into.

I tried a good selection of new parts, then sent it back, thinking the frame was broken.
Turns out handling like that is "normal", so I rejected the bike and got custom, to match my broken viner. Which until I snapped it had pin sharp handling and went exactly where it was pointed.

The toe overlap (that the head angle/rake was there to fix) never caused an issue, and I'm still riding the same custom frame, 17 years later.

[DMF]

Nowadays BB height will usually be well within the variations of the road bike counterparts. And chainstay length will usually vary within 395-405mm. Front-center of course being a product of reach, STA and rake, but we covered the similarities and dissimilarities there already.

Really though, if you can ride a 73/73 road bike with an inline seatpost and "normal" length stem, you will find that many TT bikes can be made to ride exceptionally well with drop bars and road fit. There is no black magic here, and the numbers do actually add up as well...

[mike]

Get an aero frame unless u are going to do triathlonsn duathlons, or just tting only.

[DMF]

I would certainly agree that a TT/Tri frameset for a road bike build isn't a completely worthwhile endeavor... Although I do fancy putting in an opposing response to all this BS about TT/Tri bikes having this and that awkward geometry when it in fact simply isn't true...

It's not the handling, nor the fit, nor the geometry that makes TT/Tri bikes a lesser choice. Those issues are today nothing but myths (though there was some truth to it 15 years ago). It is however the weight penalty, the inability to have the popular sit-up-and-beg fit, and the sluggish acceleration that holds this choice back...

Each to his own though, lets not forget there are som very serious aero differences between an IA and an AR or a Shiv and a Venge..

[continuum]

+1 for regular aero frame, TT's geometry is uncomfortable

[kgt]

Sorry but Shiv's geometry is not similar at all to even an agressive road frame like RB1000.

Stack and reach are not comparable since the position of the rider's body is (and must be) rather different on a tt bike.
Compare st angles (77° vs 73.5°) or chainstay length. A 4° variation in st angle or a 10-15mm difference in chainstay length is huge.

[stanseven]

Coming from someone who's spent many a day pouring over geometry charts, especially on TT/Tri bikes, and who has used several TT/Tri bikes for road bikes, I feel like I've got to put in a word about some of the myths here regarding steep angles, unmaneuverable steering characteristics, etc...

First of all, lets assume a size L road bike that is geometry wise very much in the middle of the field. This would be a 73 degree STA, 73 degree HTA, ~380-390mm reach and 43mm fork rake...

Now, just because the Specialized Shiv Tri numbers happens to be handy in my head... A size M with the setback seatpost (that comes with the frame) gets roughly a 74.5 degree STA, has a 72,5 HTA with a 45mm fork rake and a 405mm reach...

The Shiv has a 77 degree STA

[DMF]

Well yes, technically speaking. But the proprietary seatpost has a 12,5mm setback, which for most seat heights put the actual rail clamp center at a little less than 76 degrees to the BB. This could also be turned around, effectively making it just slightly over 78 degrees. And then there is a 37,5mm setback seatpost that does the same trick.

So in reality you could have approximately 74, 76, 78 or 80 degrees STA. Never 77, even if the actual seat tube is 77 degrees...

[davidalone]

you 'CAN' ride a TT bike with dropbars in a road race. you just have to have the morphological proportions to have a good fit on board when you put drop bars on it. handling will be 'abit' different ( depending on the frame) but if you ride it often enough should be okay.

a good number of ITU triathletes do this ( this is draft legal triathlon, mind) and is pretty much like a road race, with maybe just a tad bit less aggression. that being siad, it's certainly not ideal and i's not something I would do.

[Marin]

Almost all of the aero is in the rider: Position, helmet, gear.

The bike part is mainly front wheel, bars, forks, front brake & cables.

Last is the frame.

[kgt]

+1

also:
- a tt frame's torsional stiffness will not be that great.
- its narrow headtube-fork will not be that stiff.
- its handling will be not that confidence inspiring.
- it will suck on sidewinds.
- it will not feel that great when riding out of the saddle.
...and many many other compromises that really do not worth it.

[dunbar42]

One more consideration is where you ride. If you have long, uninterrupted straight stretches of road to ride than a TT bike could have some appeal. Around here it's absolutely awful for TT bikes since you have to get off the aero bars and onto the base bar every time you need to slow down for a stop sign, red light, other riders, joggers, cars trying to hook/cross you etc. An aero road bike with clip-on aero bars will get you darn close (20-30w) compared to an aggressive TT fit. I can definitely see the appeal of TT bikes if you like going fast and can get down in the aero position for 10-15+ minutes at a time. To make an analolgy, a TT/Tri bike is a drag racer and a road bike is a sports car. Drag racers excel in a staight line but show their shortcomings in the corners.

[addictR1]

thanks guys for all your input... i never plan on putting a road bar on a TT frame.. that would just look odd.

guess i'll have to test ride my friend's propel and see what the hype is all about...