whats the advantages of deep carbon rims?

BillyMansell

It's the theory that the spoke perpendicular to the road is momentarily stationary, therefore if your speed is X and the speed of the ground is 0 then the speed of the spoke perpendicular to the round must be X-X=0. At the same time, the spoke at the top of the wheel will momentarily be travelling twice your speed of X.

For the whole wheel rim to travel at the same speed as the bike then it would not have to spin.

inseine

nope, only benefit at higher speeds.

What do you mean by higher speeds? You make it sound like air has no drag at all then suddenly the drag arrives at 20mph. There is drag at any speed, it's just that its effects are squared as speed increases so it becomes massively more noticable at speed. I've read plenty of studies that state that aerodynamics are more important than weight even on relatively slow climbs. Of course, we never go really fast on a bike so the effects are never huge.

richh

Nope I still don't get it I'm afraid. The rim is rigid so all places around the rim are traveling at the same speed (although at totally different velocities of course to to the different direction of travel) and that speed is governed by the fact that the tyre is gripping on the road and turning at the same speed as the bike is travelling.

What I can see is that the spokes at the top of the wheel are traveling "into the wind" more than those at the bottom of the wheel (which are moving "away from the wind" and hence would cause more wind resistance, but not that the spokes themselves are travelling faster that you are riding.

I guess I'm looking at it more simplistically than you. If the bike moves 1m over a 1s period, then a single point on the tyre must also have moved 1m in 1s and therefore they are moving at the same speed. As the rim is rigid, if one point moves at that speed, all points must also move at the same speed.

What you're referring to appears to be the relative velocity of various points but all in the direction of travel only, rather than the actual speed of the points.

richh

Anyway, regardless of this, I think the point is that it's the rim end that travels fastest and therefore reducing that by virtue of either a fairing or a deeper rim reduces the area most affected.

What would be interesting (purely for geekiness if nothing else) is to know what proportion of the drag is caused by the wheel actually spinning (and the spokes pushing through the air) vs the bike moving forward (with the additional airflow hitting the spokes, but also the spokes being slightly sheltered by the tyre/rim).

nickel

Carbon will offer huge weight reductions.........for your wallet that is

rogerthecat

I have just purchased a set of carbon deep sections wheels (Zipp), been out for a few rides so far and have found the ride more comfortable, the bike feels more secure when hitting the corners, so far as the speed is concerned, up is slower, down and flat are quicker, (this is compared to Easton EA 90 SLX). The Bling effect should not be understated.

Since this is a beginner forum, may I add when fitting your carbon specific pads use a folded business card and place at the rear of the pad so that the pad is "toe in" when you tighten, this will stop any squealing from your breaks.

Finish on a question: anyone have Zipp Firecrest 303 / 404's? are you using swisstop yellow pads or the grey pads that came with the wheels?

Many thanks

simon_masterson

The usual adage applies: if you have to ask, you probably don't need it.

Really though, whilst I do have my doubts that anyone who is truly a 'beginner' has any need of hardware of that level, nevertheless what I am curious about is carbon clinchers; especially given the durability issues, is there any advantage over tubulars?

rogerthecat

What durability issues do you speak of?

sub55

Down the Road wrote:

Im Bald Ok wrote:

I read somewhere that deep rims start making a difference at 13.5mph. I don't remember where I saw that so take it with a pinch of salt. Maybe someone will come along and elaborate.

Their purpose is to better your aerodynamics. I find as previously said that they spin up slower but will hold a higher speed much better than shallow rims.

They do make a difference in a bunch as you're still taking wind but will obviously make less of an impact compared to riding a TT for example. There's not some magical vacuum pack in bunch racing.

They make a diffierence at over 22 -25 mph. That's why they are used for racing. Other uses are for posing!

Think you're over simplifying that, in terms of time saved , the slower you are the more time you will save.
In terms of watts , the quicker you're going the more watts you will save.

rolf_f

richh wrote:

Nope I still don't get it I'm afraid. The rim is rigid so all places around the rim are traveling at the same speed (although at totally different velocities of course to to the different direction of travel) and that speed is governed by the fact that the tyre is gripping on the road and turning at the same speed as the bike is travelling.

Think about it this way - what speed do you think a point of the tyre is travelling at the exact moment it is in contact with the road surface?

And then think about it this way. A point on the rim that is at the leading edge of the wheel has to get to the trailing edge of the wheel. If you are travelling at a constant speed, for that part of the rim to get to the trailing edge, it will have to be moving slower than the bike. Once at the trailing edge, to get back to the leading edge, it will have to move faster than the bike.

simon_masterson

rogerthecat wrote:

What durability issues do you speak of?

That carbon rims have been known to overheat and soften under heavy braking. Enough that some competitions don't allow them, so says this article...

http://www.bikeradar.com/gear/article/a ... afe-34521/

Granted, I daresay most people won't have that problem, but I'm curious as to why you would bother when you could use a tubular. If you must have wheels that light, why not go for the full monty?

rogerthecat

Thanks for the link an interesting read; I had the option of Clinchers over Tubs, decided on Clinchers, the honest reason was puncture repair, I have been known to be out on my bike for hours on end as have most of us, I carry 2 spare tubes and a repair kit I know how and am quite conversant unfortunately at puncture repair . I am aware that tubs are or at least more puncture resistant, however. Also there was the fear factor never having used tubs before and when spending ££££ on a set of wheels I did not want to end up with a white elephant. The logical option is tubs I guess as they are the lighter wheels set.

simon_masterson

That would be my logic as well in this situation, to be honest.

I admit that as a bit of an eco-mentalist I have a problem with tubulars from the point of view of how wasteful it is to have to throw the whole thing away when puncturing, but nevertheless if I'm going to buy something I consider it better to get the best tool for the job, which is why my assumption would be on tubulars as the better choice since either wheel is a considerable investment...

But nevertheless I can't deny that if I had the money and the bike to match, carbon clinchers might be a tempting prospect. Like I say, it's just the durability that I worry about - both of the rim and of the wheel in a crash - but I daresay by the time I have that kind of cash the scene will have changed anyway!