On a thread some time ago, I had this conversation with Tom A about lower BB bikes and lower Cda. His view was that moving the rider down in the space had almost no impact on Cda. Basically you're just putting an extra cm of frame inside the dirty air around the rider's legs/body which if I recall correctly he felt would be close to negligible. Not sure if it really is or now. Would be interested in hearing Damon's views as Cervelo no longer has to market its high BB decision and in fact, going lower than most of the competiton should be able to explain the reasons why...maybe it is handling, maybe it is aero.

When we discussed this some time ago (the high BB on the older Cervelos) Rappstar felt that it was because the low BB would result in a really short head tube if the goal was the get the rider low enough. Of course, that we with traditional headsets and stems, so different picture on front end air flow compared to the new gen of superbike designs. The new designs allow you to go with taller head tube and get the same relative pad placement.

Its one of those things that I think you'd have to test for to really get and answer. I doubt it would end up being more than a few seconds over a typical TT. Still most every race vehicle tries to get low for aero considerations, so it doesn't seem like a bad idea for bikes.

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Styrrell

Well it took a long time but I was finally able to masterbate to this thread.

I'm certain I don't understand, but you're welcome I guess?

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Styrrell

Hey Ted. Was wondering if you got the drinking problem under control?




( This is a movie joke not an addiction joke so everyone get some control.)

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customerjon @gmail.com is where information happens.

Hi Dev,

I'm impressed someone's actually studying the geometry tables!

To answer your questions, we lowered the BB in recognition of the leadership triathletes are showing in trending toward shorter cranks. It also reduces aero drag. The old P-series Cervelos had higher BBs (generally 60mm of drop) because TT specialists were using longer cranks at the time, and pedaling through roundabouts and corners, so needed the clearance. It's taken a while, but since Jim Martin's studies in 2000 and 2001 (and other subsequent studies) athletes have slowly begun to choose shorter cranks, making a lower BB practical for a production bike. We didn't want to go too low though, so settled on 75mm as a current optimum. Now you have one less excuse not to get back on a Cervelo. ;-)

The longer 399mm chainstays are for better shifting as you mentioned (the component companies actually publish a 405mm minimum), and also for brake / chain ring packaging. The right rear brake shoe nut now misses the small ring, so it can open wider, making the P5 compatible with all (including wider) wheels.

Proposing to change the chain stay length actually started a big discussion inside Vroomen White Design. We did a quick survey, measuring actual weight distribution of a bunch of different riders on their own bikes, and the related changes in weight distribution as each rider rider moved between their natural riding postures. From memory, the weight distribution change due to the new chain stay length is less than 2%. In comparison, the weight distribution change due to hands on base bar versus in the aero position, etc. was typically 10% or so, up to 25% for some riders with extremely different positions. Naturally the variation across individuals was a bit greater than that.

In many ways this survey was an extension of the Cervelo RS project years ago, when we actually had ride test frames made in the proposed geometry. These frames had horizontal dropouts about 4cm long(!) to really play around with how chain stay length affects handling. Wish I could get you on one - by using the quick release, in a few seconds you could be riding chain stays anywhere between 380 and 420mm! Each extreme feels a tiny bit different, but all settings rode well. Without looking, practically no test riders could tell which extreme they had just tested.

Cheers,

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Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)

Ha! Yeah not quite there yet. Still can't get over all the bad things that happened on the raid over Macho Grande. ;)

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Hans Bielat
TorHans LLC Co-Founder, Owner, Chief Innovation Officer
http://www.torhans.com

Your the man.

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customerjon @gmail.com is where information happens.

Hi Damon,

Your points actually corroborate well with the Kuota Kalibur that I had some time ago....if I recall correctly 72 mm BB drop, and 39.9 cm chain stay. Handling was fine...pretty well in the same range as the P5. My Kalibur was actually the best handling bike (for tri position) through technical terrain that I have ridden over the last decade (Kestrel 200, Softride Solo, Litespeed Tachyon, Cervelo Soloist, P3SL, QR Lucero, Kuota Kalibur and Kestrel Airfoil).

I'm generally checking head tube length, head tube angle, front centre, BB drop and chain stay length of pretty well every bike that comes out more out of interest related to how you guys design things. If I look at all of that, I get a good appreciation for not just potential fit, but how this bike will ride "in space". I can place the saddle more or less wherever I want over the BB (stack and reach tables are useful, but I guess I was looking at geometry charts before Slowman started stack and reach).

Anyway, good move on the lower BB height and longer chain stay. I hope more vendors go this route. Looks like this bike would ride nicely on the descents at IM France or Alpe d'Huez tri :-)

Hi Damon, hi Dev,

thank you, Damon and all Cervélo colleagues, for this IMHO superb bike and you, Dev&Damon, for these interesting geometry related insights.

With 194cm (76kg 42yrs) I am happy using a 2008 P2C size 61cm for 40K triathlon bike splits the last 3 years:
http://forum.tour-magazin.de/...=2540737#post2540737
Work allows only for limited training (ususally less than 4000km per year) nevertheless my personal record for the bike split is getting closer to the one hour mark,
i.e. last year 1:01:27 (39,4 kph avg. on the bike plus some transition).

Now I wonder if/how much a P5 instead of a P2 helps for the "below 00:59:59 on the bike split" quest... really 30sec or more?
Beside motivational effects of new material, of course! ;-)

a) The P2C 61cm is setup with a 1cm spacer and 10cm stem (Vision Sizemore plus Vision basebar and R-bends -> approx. 17,5-18cm drop from saddle to the bar.
As per geometry table a 61cm sized P5 front with the low bar and no spacer results into similar or even few mm higher stack (due to lower BB), correct?
Then, x-low bar with 1,5-2cm spacers sounds odd to me...

b) Given the length of my legs, I would be interested to continue using 175mm cranks, hoping the 15mm lowered BB does not interfere/hamper?
Instead I would expect better handling in steep/sharp curves, though pedalling has to stop earlier in wider bends, I guess ...

c) The P2C (61cm) weighs in at 8.1kg with pedals, polar speed&cadence sensors and the bottle cage ... can I expect a similar low weight from a P5?
A friend has a 58cm P4 that is quite "heavy", but perhaps that is also due different components, i.e. SRM wattmeter, HED instead of Zipp wheels etc.

And finally, when can we expect P5 delivery in good old Europe? My usually well informed Cervélo dealer vaguely refers to May? Uuh ...

Hoping above points are of interest to some of the taller/larger athletes in this forum ...

Many rgds, Hart

Hi Hart,

Congratulations on your excellent performances! Thanks for riding a Cervelo, and for considering a new one.

Aero benefits will be quantified in the white paper I'm currently writing. Probably available in the next weeks, since I'm traveling at the moment.

For size, please just let me know your arm pad stack dimension from your current bike. Measuring instructions and pictures are in the PDF (available on the Cervelo P5 web page) here:
http://www.cervelo.com/files/stackreach.pdf


For crank length, you can keep the 175s of course, and as you mention, be careful not to pedal too deep into the sharpest corners. I suspect most are not in danger of striking a pedal, since many road bikes are within a few millimeters of the P5's bottom bracket height, but just ease into it to discover your own limits. More info on crank length can be found here in slowtwitch, and I've also written an answer to that question on the Cervelo web site as well:
http://www.cervelo.com/...e/crank-length/2954/

I don't have visibility into delivery schedules. Please just have your dealer confirm with his distributor. It's possible I might see him later this week. I'm guessing he might speak German, and the German speaking Cervelo folks arrive here in Fuerteventura for Brain Bike in a few days.

Cheers,

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Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)

Hi Damon,

Thanks a lot for answering all the questions in this thread. It's great. One more for you.

Is there any chance that the X-Lo will have future modifications to allow it to be reach adjustable? It allows going super low but without being able to adjust the reach it makes it of questionable value, no? I would like to use it, but cannot because the reach would be too short.

One more thing. My 2005 Soloist had 70 mm BB drop, yet the P3SL and subsequent Cervelos were 60 mm drop. The Soloist also had a very similar chainstay length to the new P5 (I believe it was around 40 cm).

A quick note of appreciation for Gerard's posted comments and all your responses to the numerous P5 queries - besides the great Cervelo products, this is yet another reason why I ride Cervelos.

Also, a public thank you to Jakub Macel in Cervelo's Customer Service department for managing my crash replacement after a difference of opinion with a Mack truck and a stop sign at IMC. Terrific service through the entire process.

Looking forward to riding the P5.

Cheers, Brian

Thanks Brian. I also really appreciate our staff, Jakub especially!

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Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)

Hi Dev,

That's right, the P5's 75mm of drop is a whopping 15mm more (lower BB) than the P3SL's 60mm, but only 5mm more (lower BB) than classic road bikes. So we've lowerd the BB "a lot" from the P3/P4 era, but not actually by an extreme amount compared to many, many road bikes.

Cheers,

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Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)

not as pretty as the p4, but the numbers are so sick.

Having read thru the whole thread but not found any information I would like to ask how I will be able to shift gears with DI2 on the handle bars, which from my point of view is the main reason having a DI2 Dura Ace on a Tri-Bike. I have not noticed any possibility on the Magura Brakes

It can be done very easily if you take some time and look around. Be creative and find a solution as I know many people that have hacked the Di2 and put buttons wherever they want them. There are also other options that are standard from Shimano. Can be a lot smaller in my opinion which I have seen people do already. Sprinter options can be used as well and they say in conjunction with main shifters but I have seen other again to this without using the main shifters.




Stop looking at the tree as there is a forest behind it.

Thank you for that. My first thought was the same, but this means a "fiddled" solution. My question is more... why does Cervelo and Magura not come up with something "more professional" introducing it as DI2 Tri-Bike ?!

Professionals I guess do not want shifting down at the brakes. They want it at the shfters but you do not have to fiddle to much to make this work.

 
Thanks for going to 75mm drop. I hope more manufacturers copy you and go down to 75mm but ideally 80mm. For a tri bike, I don't see any reason to not go to 80mm. Its not like we are pedaling through corners anyway, and the handling benefits really are nice with the bigger drop from the BB. My Airfoil pro is 70mm and I've been bugging Harad to go lower for some time :-). I'd like to see 80 mm BB drop and 40 cm chainstays as the standard on tri bikes (but that's just me) :-)

Wise words..... since I am not a professional but willing to pay top money I expect them to put much more love and attention into such detail. Snifff.... Well looking forward fiddling ones again.... :o)

Or just go without the Magura's and run Di2 with a different brake. There are a few out there that you could use now and some in developement.

because somewhere in the cost/time/benefit analysis they decided to release the p5 rather than work di2 buttons into the magura brake levers.

maybe one day a fully integrated solution will exist.

the fiddling is pretty easy though =)

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