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 Post subject: Stevens Volt TT Frame?
PostPosted: Sun Nov 04, 2012 7:47 pm 
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Joined: Tue Mar 20, 2007 5:56 pm
Posts: 980
I posted a question on slowtwitch but got no response.....probably not the most popular Tri frame...

Has anyone had one? Comments good or bad? Any comments about sizing? I can't find any numbers for the stack height of frame...

Thanks!


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 Post subject: Stevens Volt TT Frame?
Posted: Sun Nov 04, 2012 7:47 pm 


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PostPosted: Sun Nov 04, 2012 8:32 pm 
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Joined: Wed Jun 22, 2011 9:39 pm
Posts: 123
Well you can just about do it with a bit of trigonometry using their geometry chart.

No user info here, just a bit of critique of the design, looks a bit bodged together using some strange ideas. I think there are more aero solutions out there for the same money (only prices i found were €2750 for frameset.)
EDIT(excel error before!): stacks are 518,532,550,570,595 approx

My gripes with it are the top-tube headtube interface, its a mess to generate drag, the rear mounted brakes leave a messy cable routing in the air, and the curved fork blades extend the leading edge into the clean air.
Personally i don't get the angled seat tube design, but i guess that could be forgiven.

My favourite TT bikes at the moment are (uci legal versions) :- Canyon speedmax, bmc tm01, speedconcept 9.9, P5, Scott Plasma3
a good tririg omega with good routing will be a better front brake than the TRP rear mount brakes. (data here http://www.tririg.com/articles.php?id=2 ... hite_Paper" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;)

OR nosecone shiv for uci illegal if you can find one.

Obviously getting a frame to fit is the best, then getting an aero one is important!


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PostPosted: Mon Nov 05, 2012 1:38 pm 
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Thx for the info. The front end of the bike reminds me a lot of the Specialized 'Transition' design....but no idea if that is a good thing or a bad thing.
I did actually own a Speed Concept 9.9 briefly, but it was the wrong size. I may buy another, but was browsing around to see if something 2k cheaper would fit the bill.... :)


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PostPosted: Mon Nov 05, 2012 6:12 pm 
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Joined: Mon May 30, 2005 7:13 am
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I think the best price on a frame "comparable" to the SC for sure would be the Felt DA4; also the scott plasma premium pointed out by the other poster can be had at a pretty good discount, around $3K for a new frameset.

The other frame I noticed recently at a great price point was the Focus Izalco at Excel Sports. They only have a size small, but Walser essentially allowed Focus to mass produce one of his designs. Its not quite one of the recent superbikes but even Gerard has stated it stacks up well to the P3.

I personally would skip the Stevens. The Scott can be had for the same price and its truly proven.


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PostPosted: Mon Nov 05, 2012 6:21 pm 
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NGMN wrote:

I personally would skip the Stevens. The Scott can be had for the same price and its truly proven.


From a price perspective, I was looking at some of the new Stevens Volt frames showing up on ebay for around 1300 US...


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PostPosted: Mon Nov 05, 2012 7:22 pm 
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Nevermind...

$1300 is a pretty hard to beat price point. At that price, I'd be less inclined to steer you away. I'd go with the Focus I mentioned personally, but that may not fit you with a stack of ~480 and reach of ~400


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PostPosted: Wed Nov 07, 2012 1:55 pm 
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Fair enough that is a challenging price point, 2nd hand cervelo P3s go for around £1000 or ~$1600 in the UK at the moment.
I just guess I'm talking about frames based on personal experience, have ridden my p3 for 6 seasons now and love it, but had the opportunity to do a side by side test on a speed concept 9 and shiv with nosecone, setting them up exactly the same as my p3 with the same wheels, components, etc and was losing around 10-12W to the speed concept and ~15W to the Shiv (errors ~+/-5W, 4 repeats for each). I'm generally looking to podium at my TTs so that big a gap thanks to the frame alone is bugging me a little!

I think the idea with the stevens and transition head tube was that the air is dirty coming of the back of the stem as its more or less squared off by the clamping bolts so you need to fill the low pressure gap behind it to reduce drag. However they chose to also put the cable stops here which is causes the gap to be a bit big (eyeball aerodynamics) which I think will give the air enough time to angle inwards and hit the top tube face square on like its a wall. I think one of the design considerations will have had to be that by using standard stems rather than frame specific ones like on the plasma and shiv etc. is that they don't know the exact shape and size of the rear end of the stem so had to give extra space for it, to minimise compatibility issues. Whereas if you make a specific stem to morph into the top tube then you can smooth all this out and remove quite a high drag area. the alternative appears to be the aero rear sections of the sky aerobars to fill in the gap with a carbon "fairing".

have look at the CFD from cervelo the blue area behind the stem is what I'm talking about. (cervelo fully expect you to put a toptube bag/box there to fill the area. they even advise that this is good practise!)
Image

Focus cronos are very nice bikes too. :)


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PostPosted: Wed Nov 07, 2012 2:11 pm 
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Good info, thanks.
I wonder what 10 watts translates into time wise for a half ironman (90km)?
Also.....that 10-15 watt difference.....is that only in a very specific wind direction?
If yes, I'm assuming that the -average- wattage savings is going to be considerable less when in real world situation where effective wind angle is constantly changing?

The Focus looks nice but it is a little too long/low to fit me.

Cheers


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PostPosted: Wed Nov 07, 2012 2:36 pm 
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Tests were powermeter data tests using golden cheetah software and its aerolab function to work out CDA. It was a a still day, the anemometer I "borrowed" from work was registering less than 1mph, FYI I was testing at 25mph. So I guess they are only relevant to 0 yaw, as thats the only direction the bike would see (assuming I was riding in a perfectly straight line...)

regards to a 70.3 it depends on you Cda and target speed. as its a cubic relationship between speed and power at any given Cda.
A few quick calculations using some standard information (rather than specifics) suggests about 0.5kmph increase at about 40kmph speeds. Which is small but not insignificant. or roughly 1min30 over 56miles at same average speeds. [edit: in perfect conditions]
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PostPosted: Wed Nov 07, 2012 2:43 pm 
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Cool, thanks.
Over 90km in a 70.3 event I tend to average somewhere around 36km/hr. So might see less speed increase, but over a greater period of time, so maybe more time savings... :)

Good chance I'll end up with another speed concept 9 since I know exactly what size frame/stem setup will fit me well. I have no shops nearby that stock specialized bikes. I'd probably fit on their new tri specific Shiv in a medium, but not sure, and hate to spend that kind of $$ ordering online if not sure..

Next decision is Stinger 9 front and rear, or a rear disc... :)


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PostPosted: Wed Nov 07, 2012 3:34 pm 
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Nothing like the sound of a disc... :) although they really aren't much faster than a stinger 9.

at 36kmph in the same Cda ranges its about 7-8 w for a 0.5kpmh rise so probably 0.6-0.7 kmph rise. Which is more like a 2min saving (ideally).


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PostPosted: Wed Nov 07, 2012 8:01 pm 
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Always go for a disc, unless the race won't allow it.

Nice work on the field testing machinenoise!


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PostPosted: Wed Nov 07, 2012 10:05 pm 
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Location: Shetland, Scotland
Rule of thumb puts 10w (tested saving measured at 30mph) as giving about 1s per km in a TT.
That holds roughly true for the normal TT speed range.


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PostPosted: Wed Nov 07, 2012 11:35 pm 
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Yeh sounds about right, was going for a practical number of 12-15seconds over a 10mile TT at my race speed ~29mph

Also works out at about 2/3rds of the ideal system numbers I put up above, which is probably in the right ball park.

It was a complicated afternoon I can tell you! getting two other people to bring their prize tt bikes and let me rearrange the setups and take saddles on/off and srm on off was a bit of a nightmare! kudos to them! Both were using integrated aerobars, so i called that part of the frame setup FYI, as they come as part of the frameset integrated unit. I had USE TULAs on the P3. Error bars still bit large for my liking though!


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PostPosted: Wed Nov 07, 2012 11:44 pm 
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Machinenoise wrote:
I had USE TULAs on the P3. Error bars still bit large for my liking though!


The fact that you had Tula's on the P3 makes the data that much more impressive for the SC and the Shiv. Thats a slippery bar.

The SC bar could be a bit more slippery with the handholds cut flat I'm thinking.


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Posted: Wed Nov 07, 2012 11:44 pm 


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