Toroidal v non toroidal rims

forestnot1

Are toroidal rims worth so much more than non toroidal?

What are the benefits/negatives?

ugo.santalucia

In essence yes... both modelling and wind tunnel show the air flow is much improved for toroidal rims. In real life they also handle cross winds a lot better...

So, yes, if you really need to have deep carbon rims, get some good ones

forestnot1

Ah right ok. Was looking at planetx 50s as they are on offer at the moment, only really for crit racing and the odd road bike tt.

I'm fairly lightweight at 63kg so maybe they're not the best idea?

ugo.santalucia

forestnot1 wrote:

Ah right ok. Was looking at planetx 50s as they are on offer at the moment, only really for crit racing and the odd road bike tt.

I'm fairly lightweight at 63kg so maybe they're not the best idea?

Planet X use a wide range of rims and you never know what you get. The older type 50 are quite thin and V shaped... the 52 carb-alloy rims are very V shaped, you can almost use the edge to slice a potato... but the 45 are reasonably wide and less V shaped.

forestnot1

I was looking at the pro carbon 50s http://www.planetx.co.uk/i/q/WPPXCAR700 ... et-no-logo

Maybe I should be looking at the ct45s at £200 more

Grill

Actually no according to Paul Lew. The RZR 92 and current series of Aero wheels (the 90 is faster than the Element*) test as fast or faster than Zipp*.

Here is the RZR 92 data which shows it is faster than 808's and the 808+Sub 9 disc (you'll notice the 808+disc is faster than the RZR 92 + disc which is likely due to toroidal discs having better performance at yaw).
https://www.reynoldscycling.com/uploads/RZR92_Executive_Summary.pdf
http://www.reynoldscycling.com/uploads/RZR_A2_Windtunnel_Aero_Principles_rev1_low.pdf

*yaw dependant, but then again every manufacturer can claim to have the 'fastest wheel' when they speak of a specific yaw.

forestnot1

I presume reynolds are v shaped?

Grill

Indeed.

cswitch

I've have Reynolds 46 and HED Jets (the current wide rim type). They both were fast but the HED's virtually steer themselves straight in high crosswinds - quite a strange sensation and hard to explain but they are very good in windy conditions. Having said that the 46 were also not that bad in high winds.

Bar Shaker

The reason for the advantage of Toroidal rims is in the trailing edge of the wheel. A V shaped rim works best on the front section but at anything other than perfect 'straight ahead' airflow, the air will stall over the sharp leading edge. The drag from this stalled air will more than eliminate any gains from the front of the wheel.

In the real world, there is always some yaw and the airflow is never from straight ahead, unless on an indoor track.

The purpose of using a deep carbon rim is to remove the fastest part of draggy spokes, from chopping through the air. The spokes are travelling forward at twice the wheel speed at the top of the rim, so exhibit the square of the drag increase, compared to the centre of the wheel. If the rim shape is aerodynamic, or even just aero neutral, this is an advantage over the spoke ends that it replaces.

This is why deep section rims can let the rider hold a higher speed for the same power.

If you get rid of all of the spokes, as in the case of a track 'disc' wheel, you have the least draggy wheel of all.

I have often thought there is mileage in aerofoil shaped spokes, but no one has done it yet.

Grill

You should probably have a read...
http://www.reynoldscycling.com/downloads/DET%20White%20Paper%20Full%20Version-final.pdf

ai_1

Bar Shaker wrote:

The reason for the advantage of Toroidal rims is in the trailing edge of the wheel. A V shaped rim works best on the front section but at anything other than perfect 'straight ahead' airflow, the air will stall over the sharp leading edge. The drag from this stalled air will more than eliminate any gains from the front of the wheel.

In the real world, there is always some yaw and the airflow is never from straight ahead, unless on an indoor track.

The purpose of using a deep carbon rim is to remove the fastest part of draggy spokes, from chopping through the air. The spokes are travelling forward at twice the wheel speed at the top of the rim, so exhibit the square of the drag increase, compared to the centre of the wheel. If the rim shape is aerodynamic, or even just aero neutral, this is an advantage over the spoke ends that it replaces.

This is why deep section rims can let the rider hold a higher speed for the same power.

If you get rid of all of the spokes, as in the case of a track 'disc' wheel, you have the least draggy wheel of all.

I have often thought there is mileage in aerofoil shaped spokes, but no one has done it yet.

The advantage is not just in eliminating the spokes. I't also eliminating the relatively square edge provided by a shallow rim which presents a bluff trailing edge on at the front of the wheel and a poor leading edge at the back of the wheel.

Bar Shaker

Grill wrote:

You should probably have a read...
http://www.reynoldscycling.com/downloads/DET%20White%20Paper%20Full%20Version-final.pdf

I wish I hadn't, Grill. You could power slide a bus through the holes in that work.

I stopped reading when I got to "Yaw for a cyclist is the same as yaw for an aircraft with one key exception: for the cyclist, the bearing and heading of the bicycle must be identical. If they are not, the bicycle is skids out of control. Despite this difference, the yaw component does exist for a cyclist, though it can only be experienced in a wind tunnel. The reason for this is that in the wind tunnel, yaw and relative wind are the same."

Utter rubbish.

ai_1

Bar Shaker wrote:

Grill wrote:

You should probably have a read...
http://www.reynoldscycling.com/downloads/DET%20White%20Paper%20Full%20Version-final.pdf

I wish I hadn't, Grill. You could power slide a bus through the holes in that work.

I stopped reading when I got to "Yaw for a cyclist is the same as yaw for an aircraft with one key exception: for the cyclist, the bearing and heading of the bicycle must be identical. If they are not, the bicycle is skids out of control. Despite this difference, the yaw component does exist for a cyclist, though it can only be experienced in a wind tunnel. The reason for this is that in the wind tunnel, yaw and relative wind are the same."

Utter rubbish.

I haven't read the link yet, but based on that quote it's definitely not written by an aerodynamicist. It's very badly written and unless I'm misundertanding it, it's nonsense. What is "relative wind"? Yaw is simply the angle in the horizantal plane at which the airsteam encounters the object. The inclusion of the terms bearing, heading, yaw and relative wind in the above snippet seem like confusion. Significant sustained yaw as experienced by a bike only occurs with aircraft due to sideslip. e.g. an uncoordinated turn.
Perhaps I should go read the link before criticising further. Maybe there's an explanation!

cycleclinic

I have to say now I have read the link it does not make much sense to me either. Confusion of terms is the main issue.

My own experience of "toriodal" rims is they work well in a side wind compared to a similar depth V. I have ridden mine in some pretty strong winds and the bike did not feel out of control or overly twitchy.

Grill

Makes perfect sense, but this might help if you're having trouble:

http://www.reynoldscycling.com/reynolds/news/Worlds-Apart-the-Wind-Tunnel-and-the-Real-World

That white paper was written by Paul Lew. Perhaps not the most eloquent, but there's no one I'd rather have in my corner (okay maybe Simon Smart but it's a push) when it comes to aero wheels.

ai_1

Grill wrote:

You should probably have a read...
http://www.reynoldscycling.com/downloads/DET%20White%20Paper%20Full%20Version-final.pdf

I started reading but after a few pages the use of imperial units of measure along side SI units started to make me feel ill. I'll return for another look after I recover. Seriously, what's with stating lift and drag in pounds, the moment in Newton-meters, chord in meters, circumference in inches, and speed in mph and feet/sec? It also refers to angular wheel velocity in mph which is not angular velocity, it's just velocity.
However, to be fair, aside from my objection to unit mixing, what I've read so far seems mostly okay. I'm curious to see where they're going with this.

I'd also like to know what sort of CFD modelling they did. CFD gets abused a lot! Very often you'd be as well off painting a pretty picture based on your expectations as believing the output of a CFD model. The results are massively influenced by the assumptions made to apply a solvable mathematical model, the choice of mesh, and sufficient convergence checking of the solution. You can't solve any aerodynamic problem using the actual governing Navier-Stokes equations since they're not solvable. You have to make assumptions appropriate to the problem at hand and use those to simplify the equations. Badly chosen assumptions can produce massively inaccurate results. Thankfully they also did tunnel testing so that should have identified any major flaws in the CFD work.

Bar Shaker

I have no trouble with the concepts. I have a pilot's license and am a keen sailor, so yaw and 'apparent' wind are very familiar to me.

There is much missing from the paper. eg, were the wheels rotating at the bike speed being represented, or were they stationary? From the test equipment photos, it looks like they were stationary, which turns all of the data into junk.

Statements such as "At an angle of zero degrees yaw and relative wind are identical. For all other angles where the cyclist is moving forward into a head wind (as long as the head wind velocity is greater than zero), the yaw angle is greater than the bearing (course direction), but it is less than the relative wind." actually mean nothing.

Another gem is this..."Once the cyclist is riding with a tail wind, net wind is zero or less, the wind direction has lost its significance, and there is no possibility for the wheel to generate forward thrust. The chart below shows how yaw in the wind tunnel translates into real world relative wind."

So, if I am riding at 30kph with a tailwind from my 5 o'clock of 10kph I experience no 'lift' from the wheel?

The graphs are also interesting in that they show the Reynolds RC(?) wheel to be amazing but don't explain why the Reynolds Assault is so dire. The Assault is a wheel that I quite like.

The whole paper is quackery that hopes to bamboozle the uneducated reader (I am not saying that's you, Grill), into accepting the findings without questioning them. There is much to question and even more to doubt!

ai_1

Bar Shaker wrote:

I have no trouble with the concepts. I have a pilot's license and am a keen sailor, so yaw and 'apparent' wind are very familiar to me.

There is much missing from the paper. eg, were the wheels rotating at the bike speed being represented, or were they stationary? From the test equipment photos, it looks like they were stationary, which turns all of the data into junk....

....The whole paper is quackery that hopes to bamboozle the uneducated reader (I am not saying that's you, Grill), into accepting the findings without questioning them. There is much to question and even more to doubt!

I'm also very familiar with the concepts having done a MSc in aerodynamics. Although it was 9 years ago and I don't work in the field, I just dabble a bit these days, so I'm a bit rusty. I agree it comes across as an oddly constructed document that seems to have the intention of confusing readers while convincing them to trust the conclusion. Put it this way, it certainly wouldn't pass muster as an academic paper.

Grill

The Assault and Strike use a blunted shape as opposed to the DET on the Aero and RZR line (wide into V) which would explain the difference. He talks about the benefits here: https://www.youtube.com/watch?v=ceNJIHyErZc

Paul does have a tendency to misuse words (or at least the meaning might be clear in his head but isn't clear to others) as pointed out in this ST thread: http://forum.slowtwitch.com/forum/Slowtwitch_Forums_C1/Triathlon_Forum_F1/Reynolds_58/72_Review_P4803369/

Of course from a TT standpoint any deep front wheel is good in low wind out and backs races. I'll be aero testing at some point this year with the RZR 92 and probably an 808 to see if there's any noticeable difference.