Deep carbon rims - optimum depth if speed is the main target

daniel_b

Evening all,

I'm always on the lookout for something to upgrade, and my Foil is my current focus.

It's running circa 1550g Mavic Cosmic 50mm Exalith wheels, but I have been in touch with Scribe wheels, and it looks like they could either build a pair of 50s which would save around 120grams, OR build a pair of 65s for about 10g less.
I would opt for a set with no branding.

I have the CR1 for climbing routes, so not worried about making it a 'non climber' but part of me is not sure what it would be like in the cross winds - I'm not a big or heavy rider.

Another option would be 50/65 which weighs in at 1487g, though I suspect the difference visually would annoy me a bit - here's a foil with that setup:



The Mavics could then find a home on the TT bike I still need to build.

Be interested to hear opinions and experiences.

N0bodyOfTheGoat

If speed if your aim, isn't it rim depth and aero efficiency what you need, rather than saving the weight of a Snickers Duo?

Sounds like you really need something like 85mm, but then they could be a real handful in wind, which we seem to be getting a lot of over the last few weeks.

DeVlaeminck

There's no real answer to the question as there is always a trade off between weight, cost, aero, susceptibility to side winds etc .

I mean theoretically a rear disc and tri spoke is likely to be pretty fast but ... The 50/65 combo looks ok - for me if the mismatch rim serves a purpose it's fine but I'd be ok on a deeper front than that 95% of the time and if you've got another bike anyway.

super_davo

Have a watch of the Hambini Aero bike wheels video (early Hambini, before he got all sweary). The main thing I took from it was that the core advantage of deep wheels is lowering the amount and speed of the airflow through the spokes which cause "chop" and therefore drag. You get the same effect, to a degree, with wider wheels.
Once you watch that, you'll end up wanting the widest set of 50-65 wheels you can get.
Which seems to be what most of the high end aero bikes are shipping with these days, and also what pro's are using.

fenix

I don't think it's just depth it's design too. Mate was out on his 404 Firecrest for the first time yesterday and it was very windy. He had no problems.
My old 50mms were a pain in the wind.

If it were me I'd not be keen on deep rims on a climbing bike.

daniel_b

N0bodyOfTheGoat said:

If speed if your aim, isn't it rim depth and aero efficiency what you need, rather than saving the weight of a Snickers Duo?

Sounds like you really need something like 85mm, but then they could be a real handful in wind, which we seem to be getting a lot of over the last few weeks.

LOL, good point, but I always like a 2 for 1 if I can get it :-)

Also found out that the Cosmics actually weight in at 1650g, so like for like would save a not inconsiderable 220g, but even 65's would save over 100g, so a nice bonus.

It's not a climbing bike perse, even though it does climb ridiculously well imho, and to be fair, if I am saving weight, I can't see how that would be a negative.

The reviews I have seen of they're various wheelsets seem to be fairly positive, not seen any mention of struggling in strong winds.

I've certainly had no major issues with my Cosmics, although can't recall whether I have been out in gusty conditions or not, but no 'hair raising' moments spring to mind, and as far as I am aware they are a fairly old design, with nothing paricularly modern about them.

They also can fit 'race' bearings, which are meant to be a bit smoother, but less weatherproof - but as I try to avoid the rain on this bike, reckon it could be worth the risk, such as it is.

@Superdavo - will try and find the Hambini vids you speak of.

super_davo

This is the Hambini video in question https://www.youtube.com/watch?v=BUih_emc54M.

There is a more recent version covering all things aero, but this just focuses on wheels. Well worth a watch before you splash out £1k plus on aero wheels!

daniel_b

Cheers SD, some viewing for later - much appreciated.

EDIT: Just watched it SD, very educational, thanks for posting :-)

ugo.santalucia

I've always been reluctant to get deep wheels in fear of looking like a slow idiot with deep wheels. Now I am a bit quicker than I used to be and I've realised I don't actually need them to keep up in the "fast ride"... it's good to get a good workout for your pain a chocolat and anything that saves me watts, would "make me fat" so to speak. Obviously, if I was racing time trails I would have a different perspective...

Actually I have signed up for a 10 TT at Mallory Park, but I suspect I will look less of a slow idiot with shallow wheels... I don't think I'm going to trouble the 21 minute guys with or without aero gains...

Back to your case... you want to replace a pair of 50 mm wheels with another pair of 50 mm wheels which are allegedly 100 gram lighter... it seems a lot of money for a minute gain (minute is less than marginal)

daniel_b

I've been guilty of doing that as well, ie I buy really nice kit, and then won't wear it until I get to x amount of power or watts per kg, but what i have found is, that if I allow myself, or treat\indulge myself if you like, to use the better gear, this in turn seems to motivate me to work harder, and I seem to become faster - could well be a simple placebo effect, but just telling my own personal experience.

No I wasn't looking to replace with 50\50, that was the last and least likely option.
Initially 65s were the choice, but after posting on here, viewing videos & reviews, and posting on the Foil facebook page, I think I will settle on 50\65 with race bearings.

It's not just to save a bit of weight, well it will be 160g which isn't inconsiderable, but will also then mean the cosmics can move onto the Exocet 2 framset I have for an age but never gotten around the building - a trickle down of sorts.

It's also not the weight gain I am after perse, that is a bonus, I'm hoping the aero gain on a chanride will inprove speeds\reduce watts required.

Combined with a Berk saddle, I think (though I will check) that should get it down to around 6.9kg.

ugo.santalucia

... and yet there aren't many out there in deep aero wheels, tribars, pointy helmets and skinsuits who can beat Alf Enger's 49:24 on a 25 mile course...



If I manage to clock a long 23 minutes on a 10 TT I might think about aero as the next move... so it probably won't happen...

daniel_b

Talent, skill and strength beats all - the rest of us try and make up for\minimise\hide\accommodate those deficencies in whatever ways we can!

I'm also going to be intrigued to see how the Foil will do versus the TT bike on a 10 or even 25 miler.

me-109

ugo.santalucia said:

... and yet there aren't many out there in deep aero wheels, tribars, pointy helmets and skinsuits who can beat Alf Enger's 49:24 on a 25 mile course...



If I manage to clock a long 23 minutes on a 10 TT I might think about aero as the next move... so it probably won't happen...

Classy. LF hubs for stiffness. QR levers horizontal. No tape on the bar tops. Skeleton drilled calipers. Not sure if the lack of lever hoods is deliberate or just cheapie sign-of-the-times components.

ugo.santalucia

Were rubber hoods around in the 70s?

johngti

I'm seriously thinking about reducing my already shallow 38mm carbon wheels for something shallower. Not being particularly flush, I only bought Zuus wheels which are nice and still going strong but even 38s were very sketchy in the wind a couple of weeks ago. Alloy and shallow might be heading my way soon.

arlowood

Have a look at this report from Hambibi looking at the power demands to maintain either 30km/h or 50km/h with different depth carbon wheelsets.

https://www.hambini.com/testing-to-find-the-fastest-bicycle-wheels/

His objective was to look at the performance of wheels from different manufacturers but the overall results are quite revealing. So at 50km/h the main differences in power demand are seen at the extremes of his testing regime i.e. with rear disc wheels at one end and the 38-40mm rims at the other. In between there doesn't appear to be a huge difference in power demand between 80mm and 50mm rims.

So the actual benefits of switching from a 50mm to a 65mm wheels may be more psychological than physical.

ugo.santalucia

arlowood said:

So the actual benefits of switching from a 50mm to a 65mm wheels may be more psychological than physical.

Never had any doubt about it. The all rims aero profile thing has been pumped like hell to sell upgrades. It was an easy area to target, as thanks to in mould technology, making massive rims which are reasonably light is easy enough.
Half of the customers go on to ride with their core body at a 45 degree angle, when not greater...

simon_e

arlowood said:

So the actual benefits of switching from a 50mm to a 65mm wheels may be more psychological than physical.

Yep.

When Flo published their figures the difference between 30mm and 60mm in controlled conditions was a lot smaller than I expected.

In the real world, in anything but a solo race/TT situation, it's completely irrelevant (and anyway would be far outweighed by the much greater differences in position and clothing).