At what rim depth do benefits kick in at realworld speeds?

Bobbinogs

A query in the RBA forum has made me think about the aero benefit of rim depth. Basically, there are a couple of us looking for a little oomph when it comes to riding flatter/draggy sections where a light weight rider will often struggle to match the bigger power boys when travelling around the 20s. Climbing wheels will typically be 24mm - 30mm so the question would be, has anyone managed to detect a definite speed attainment and holding benefit from deeper section wheels and is there a magic figure (in depth) as to when that usually kicks in?

FWIW, I have ridden with 30mms and didn't really detect anything over the 24mms I compared them with. However, I did start to notice crosswinds a lot more and would therefore be hesitant about switching to 50mm. So just trying to work out if there is a benefit to be had and whether something like 40mm or 45mm might be a sweetspot, etc.

Oh, there is no way in a million years I could afford ultra expensive wheels so please don't recommend solving any crosswind issues by buying some Lightweight jobbers, etc.

drlodge

Have just received a set of "BORG50" tubeless wheels from the Cycle Clinic, as I see 50mm as a good all round aero wheel. 30mm-40mm won't provide much benefit whereas 70mm-80mm is getting deep for cross winds.

Tried them out last night and was very pleased. They're a toroidal section rim so less affected by cross winds. Reasonable cost too.

drlodge

viewtopic.php?f=40042&t=13020726&p=19922788&hilit=BORG50#p19922781

fenix

I used to have 50mms but with the winds that we were having at the start of the year I've gone shallow rims.

Train harder and save your money I think.

ugo.santalucia

Modern rims as low as 30 mm... look carefully and you will find fewer PROs using 50-60 mm rims these days, compared to 5 years ago

drlodge

Depends what you want to use the wheels for Bobbinogs. For proper all round use I would probably go for 35mm, but my wheels are to be used in the dry and hence when the weather's fine, so I shouldn't run into strong winds.

Are these wheels for a "summer" bike, or one that'll be used all year round?

Its a trade off between good aero and side wind disturbance.

Bobbinogs

Thanks chaps, (Borg are an interesting option particularly given Malcolm's service). I probably should have mentioned these wheels would be for summer usage but I am trying to avoid the "what wheels" type of debate as I figure it probably is of more use to determine what are the main features I want from the wheelset (as in, "must be 40mm or 50mm") and then look in RBA for the options with the right features. I think you are right about the trade off between good aero and sidewinds which is why I trying to work out what the sweetspot is, without ending up with just another wheelset that is not that different from the ones I have already.

I do get the "train harder" thing, btw. It is a fair comment but I wanted this thread to be less about me/a rider's fitness and more about the experiences of riders with rim depth variations.

Anonymous

Less deep front wheel would solve the wind issue whilst giving max overall aero advantage wouldn't it?

Guessing this severely limits choice of wheelsets though.

jgsi

It's not having 60mm rims that bllks my racing up... but still wouldnt like to part with them.... even if current twittrati style opinion says they are old fashioned.

ugo.santalucia

JGSI wrote:

It's not having 60mm rims that bllks my racing up... but still wouldnt like to part with them.... even if current twittrati style opinion says they are old fashioned.

You only see sprinters using them, while 3-5 years ago everyone was on them

simon_masterson

Anyone can benefit from deep rims, but even if you're riding at TT speeds, the benefit is mainly noticeable in TT terms. And if you get your front tyre width wrong, you're throwing away speed. They make a nice noise and feel fast, but get some aero kit and narrow bars too.

bendertherobot

I've been riding 60mm this week. I'd probably go for 50mm given the choice but, quite honestly, I've been as fast (if not faster up hills) and quite noticeably faster on the flats etc.

Point of reference is how much they are better than my existing Fulcrum Quattro 35mm (1750g).

I've done some hills today in spinny gears and noticed no obvious weight drawbacks (they are 1800g ish).

Cross wind wise they aren't brilliant but they are very acceptable (and it's been very windy today).

There was this study, which I hope to unpick.....http://www.cyclist.co.uk/in-depth/1467/ ... eight-rims

akh

Swiss Side publish some interesting data on their website. They don't just give the savings for riders averaging pro speeds either.

According to the link below, if you can average 35 kph (21.75 mph) for 40 km, a set of their 48.5mm deep wheels will increase your average speed to 36 kph (22.37 mph.), saving you 1 m 54 s (@ 180 W).

All else equal, with the 62.5mm wheels, you'd average 36.01 kph (22.43 mph), saving you 2 m 4 s.

http://www.swissside.com/hadron-ultimate-launch/

bendertherobot

Anecdotally, I'd be inclined to agree. It just seems easier to get them to maintain a speed. It's also interesting, in my case, just how much faster 60mm seem to be than 35mm. So if I were coming at this from 20-24mm wheels I'd be seeing some real differences.

sloppyschleckonds

60mm

bendertherobot

So, I should try and keep mine then?

ugo.santalucia

bendertherobot wrote:

Point of reference is how much they are better than my existing Fulcrum Quattro 35mm (1750g).

the quattro is not an aerodynamic rim by modern standard... it's the shape more than the depth

bendertherobot

Indeed. And I'll be incorporating that into the review as well. It's surprising just how easy moving 1800g is when they're aero.

I say surprising. It's not really, just makes you unlearn a few things that you had no reason to believe in the first place.

I did try to rope Professor Brian Cox into this one but apparently he's busy.....

drlodge

Sounds like you're after the same wheels that I was, and I ended up with the Borg50. Not sure if it was Malcolm or DCR wheels that could build 34, 50 and 60 or a mix hence 38:50 or 50:60

cycleclinic

I don't do a shallower clincher rim. there is no point. With a clincher the shallower rim is not much lighter and the 50mm rim I use is barely affected by crosswinds any way, as would all rims with a similar profile. Roval use a rim that looks so similar it come from the same factory so crosswind performance is all down the the profile. Most of the aero gain comes from the front wheel so going shallower defeats the point entirely. Shallower rim for all round use I dont think works either as I have shallower tubular rims on one bike (actually two) and I am no quicker but these wheels are properly light though.

I can't believe Mavic are still peddalling the myth that rim mass makes a difference. It is so marginal it is irrelevant. Go shallow for short punchy climbs well they need to do the math on this. On short punchy climbs the speed can be quite high so aero effects still dominate.

One day everyone will come round to my way of thinking.

So it must be DCR that does the split option I will leave that to him.

mrb123

drlodge wrote:

Sounds like you're after the same wheels that I was, and I ended up with the Borg50. Not sure if it was Malcolm or DCR wheels that could build 34, 50 and 60 or a mix hence 38:50 or 50:60

DCR does 38s and 50s in his carbon clinchers.

drlodge

Must have been DCR then, he does a 38mm "yellow jersey" rim, 50mm "green jersey" and says he also has a 60mm rim with 100g penalty.

The 50mm toroidal rim from TCC is great for my needs. 60mm would be getting a bit deep.

zoomer42

On a good day with little wind, the first time get up to around 22mph+ using 50's it does feel like its just that bit easier staying there.

Definitely had a few hairy moments with cross winds, but they are few are far between.

savethemamil

FLO Cycling have done several studies of the benefits of different depths of aero rim versus a standard box section. http://www.flocycling.com/aero.php. They have a table showing the time benefits over 40k with constant power. There is a meaningful benefit even for their 30mm rim, which has no crosswind problems, and their 60mm and 90mm give progressively greater gains.

rolf_f

savethemamil wrote:

FLO Cycling have done several studies of the benefits of different depths of aero rim versus a standard box section. http://www.flocycling.com/aero.php. They have a table showing the time benefits over 40k with constant power. There is a meaningful benefit even for their 30mm rim, which has no crosswind problems, and their 60mm and 90mm give progressively greater gains.

It doesn't appear to be a 'standard box section' that they are comparing their aero wheels with; it is a 32 spoke Mavic Open Pro with round spokes. For this argument we'd really need the comparison to be a realistic box section alternative like a Campag Neutron with low count bladed spokes. Probably the 30mm rim won't actually give much meaningful benefit over the more appropriate shallow rim. As it is, you get to save 60 seconds or so in 40k over the 32 spoke rim with the 60. I think I'd perhaps be interested in that if I was TTing but I can't say I would otherwise. The test is also theoretical based on a single front wheel in a wind tunnel so hard to say what the 60 seconds might be in the real world.

jdee84

I have a set of Mantel 50mm carbon clinchers using them it does seem a lot easier to hold speed around 20ish on the flat or slightly draggy sections. Haven't had any real trouble with side winds felt a slight push at times but the previous dt swiss alloy wheels with a 25 - 30 mm v shaped rim would really catch the side winds.

drlodge

Lets face it, deep carbon wheels are just the business, they look great and sound terrific. I don't actually care if they improve my performance or not, as I'll be too busy looking good.

BTW I agree with the comment above about being able to hold a high speed (> 20mph) more easily. But it could be that stuff that was injected into the tyres - you know, that placebo effect stuff.

CHRISNOIR

drlodge wrote:

Lets face it, deep carbon wheels are just the business, they look great and sound terrific. I don't actually care if they improve my performance or not, as I'll be too busy looking good.

Very much this. Cosmic Carbone wheels have actually made me slower as I'm spending half the ride trying to clock myself in shop windows ("Damn, Chris. You look good...").

ugo.santalucia

Rolf F wrote:

savethemamil wrote:

FLO Cycling have done several studies of the benefits of different depths of aero rim versus a standard box section. http://www.flocycling.com/aero.php. They have a table showing the time benefits over 40k with constant power. There is a meaningful benefit even for their 30mm rim, which has no crosswind problems, and their 60mm and 90mm give progressively greater gains.

It doesn't appear to be a 'standard box section' that they are comparing their aero wheels with; it is a 32 spoke Mavic Open Pro with round spokes. For this argument we'd really need the comparison to be a realistic box section alternative like a Campag Neutron with low count bladed spokes. Probably the 30mm rim won't actually give much meaningful benefit over the more appropriate shallow rim. As it is, you get to save 60 seconds or so in 40k over the 32 spoke rim with the 60. I think I'd perhaps be interested in that if I was TTing but I can't say I would otherwise. The test is also theoretical based on a single front wheel in a wind tunnel so hard to say what the 60 seconds might be in the real world.

In a wind tunnel drag test the shape and number of spokes are almost irrelevant... they do matter in real life aerodynamics though

mfin

drlodge wrote:

Lets face it, deep carbon wheels are just the business, they look great and sound terrific. I don't actually care if they improve my performance or not, as I'll be too busy looking good.

CHRISNOIR wrote:

Cosmic Carbone wheels have actually made me slower as I'm spending half the ride trying to clock myself in shop windows ("Damn, Chris. You look good...").

Remember that whilst in your own minds you look good so you might have the self-image thing you like, to non-cyclists who'll never notice the wheels you'll just be another bloke parading about in spandex. A good amount of other cyclists might also see you and think "look at that plonker riding deep sections" ...only joshing, but I bet it is true.

thegreatdivide

drlodge wrote:

Lets face it, deep carbon wheels are just the business, they look great and sound terrific. I don't actually care if they improve my performance or not, as I'll be too busy looking good.

BTW I agree with the comment above about being able to hold a high speed (> 20mph) more easily. But it could be that stuff that was injected into the tyres - you know, that placebo effect stuff.

All of this. I look and sound the business on my 404's (that's what I tell myself).