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Track Cycling: Velodrome Racing and Training Area Looking to enter into the realm of track racing? Want to share your experiences and tactics for riding on a velodrome? The Track Cycling forums is for you! Come in and discuss training/racing, equipment, and current track cycling events.

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Old 02-07-17, 07:48 PM   #1
lean88
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Why disc wheel for the sprinter?

Hi guys my first post.
i asking why a disc, and you hear, is more aero and is more stiff, ok but is more heavy too.
and as why know aero is more important in the front wheel but in the rear not much (and hear... but in pro level...) ok you have that small aero benefit, but sprinting is that, pure aceleration, and a more heavy wheel is slower for aceleration.

i make my test in the 250m track using 2 heavy covers for my training 30mm alloy rear wheel.
the test 500m TT standing start.
the result: 1s slower in the aero but heavy set. and you feel that extra watts needed for aceleration (after that aceleration point is more easy to mantain the speed for the rotational inertia, but i dont care im a sprinter )

i know a good disc is not too heavy but is more heavy than a good 60mm deep rim.
and a 60mm deep with 28 spokes is stiff ok.

so is not better a light option? FOR SPRINTING. NOT LONG DISTANCE NOT TRYA.

sorry for my english
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Old 02-08-17, 06:43 AM   #2
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Track cycling is limited by the 6.8kg rule. At lower level, it probably isn't checked but at world cup level every bike is weighted. Also top level disc are not too heavy. The campagnolo disc is 825g for the rear and 800g for the front so 1625g for the set. Each mavic comete disc is 980g and the io is 750g so 1960g for the double comete set and 1730g for the comete+io set. New corima disc and 5 spoke wheels are 1270g (rear disc), 1000g (front disc) & 870g (5 spokes) so 2270g for double disc setup and 2140g for disc+5 spokes.

For comparison, I am currently building up a set of wheels with 88mm chinese rims, cx-ray spoke and 24/20 Dt swiss track hubs and they will weight around 1850g.
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Old 02-08-17, 08:44 AM   #3
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I think lean88 is confusing a disc wheel with aero wheel covers that are attached to normal spoked wheels.

Like this:

Zipp 900 Disc Wheel - Wheelbuilder.com

vs:

Aero Disc Covers - Wheelbuilder.com
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Old 02-08-17, 10:31 AM   #4
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thanks guys,
Carleton i know the diference, meaby i dont wrote correctly.

Godsight thanks for the info. you are comparing top disc vs chinese rims.

but what if you use a wheel more lighter than a disc?

for example
rear mavic comet 980g. (the best in the market) shop.mavic.com/en-int/comete-track-rr0719.html

vs.

rear mavic cosmic ultimate 40mm deep, 695g. shop.mavic.com/en-int/cosmic-ultimate-rr0819.html

almost 300g! you feel that in aceleration
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Old 02-08-17, 10:55 AM   #5
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almost 300g! you feel that in aceleration
It takes VERY little aero advantage to easily make up for the difference in 300g would make in acceleration.
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Old 02-08-17, 10:58 AM   #6
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A lot of events are determined by how fast you can go, and how long you can go that fast for.

Acceleration happens before that - and for a much shorter period of time.
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Old 02-08-17, 11:54 AM   #7
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A lot of events are determined by how fast you can go, and how long you can go that fast for.

Acceleration happens before that - and for a much shorter period of time.
got your point, but in team sprint and mach sprint aceleration always matters, and more watts you need for aceleration more tired you are for the rest.

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It takes VERY little aero advantage to easily make up for the difference in 300g would make in acceleration.
understood, but that dont hapens in my test of standing starts.

meaby a compromice solution is the top disc wheel. good weight and aero.

But if you cant affort a expensive top disc (like me now ), which is the best and cheaper second option?

Carleton: i dont have money for a casco warp, i use a skate tipe of helmet, you got my point im looking for an option against disc
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Old 02-08-17, 12:04 PM   #8
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almost 300g! you feel that in aceleration
It depends! The acceleration of a wheel itself depends on the moment of inertia of the wheel.

You can compare weight (or mass) if it's at the same place in the wheel.
So, using 400g tires instead of 100g tires would just be silly. And it's intuitive.

But the moment of inertia depends on the mass and the distance away from the axel. The further away, the more acceleration is affected. Heavy rims matter more than heavy hubs.

And since a disc (a proper disc, not a spokes wheel with a cover) doesn't need the extra structural support on the rim for spoke nipples, the mass at the edge of the wheel can be reduced.

TLDR: mass alone doesn't determine acceleration.
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Old 02-08-17, 05:01 PM   #9
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It depends! The acceleration of a wheel itself depends on the moment of inertia of the wheel.

You can compare weight (or mass) if it's at the same place in the wheel.
So, using 400g tires instead of 100g tires would just be silly. And it's intuitive.

But the moment of inertia depends on the mass and the distance away from the axel. The further away, the more acceleration is affected. Heavy rims matter more than heavy hubs.

And since a disc (a proper disc, not a spokes wheel with a cover) doesn't need the extra structural support on the rim for spoke nipples, the mass at the edge of the wheel can be reduced.

TLDR: mass alone doesn't determine acceleration.
^^ This and the fact that once you get over 40kph, aero trumps weight every single time.

You might look at a match sprint and see the acceleration part, but facts are that modern sprinting with bigger gears and endurance leaning riders going long mean that there is very very rarely a 100-150m sprint to the line any more. I'd even go out on a limb and say that rarely even happens at club level any more.

Then take into account that rotational mass argument. That 700g rear wheel may sound light. But in actual fact it probably has a super light hub and lower spokes. What does that mean? That means the rim is heavy and all that mass is out at the rim, just where it isn't wanted. That makes it slower to accelerate. On a disc wheel, that 870g is spread right through to the hub, not localised around the rim. In essence I very much doubt that you will notice a big difference physically (note mentally is different). When you got up to speed, especially up around 60kph I bet you do notice a big difference in the wheels.

Finally look at events like TT. How long is the acceleration phase up to 40kph? For me, I can get over that fairly easily within 100m. For a kilo, that's less than 10% of the event where acceleration matters vs 90+% where aero matters.

If that acceleration phase is killing you so much that you consider an aero spoke wheel to be better, then there's no doubt that fitness is your issue, not wheel selection. Never underestimate just how fit you actually need to be to be a sprinter
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Old 02-08-17, 06:18 PM   #10
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Also road deep section wheels are generally shallower and lighter than track deep section wheels. The Zipp 808 track set is 1805g, the 404 track set is 1655g. Since track cycling has no crosswinds (except some outdoor shallow track) and no rule limiting the depth of a wheel (road are limited to 65mm IIRC), track cyclist can go for bigger aero gains than road cyclist.

In sprinting, top speed is more important than acceleration. And top speed is limited by aero drag, not weight.
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Old 02-08-17, 10:45 PM   #11
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A few things to take note of:

1) Aero wheel covers are not legal for track use.

2) The weight at the RIM is what matters when it comes to acceleration. A disc wheel has it's weight distributed more evenly than a spoked wheel. A heavy disc can have a lighter "rim" than a spoked wheel that weighs less.

3) Wheel stiffness also matters, and most discs can me made stiffer than a spoked wheel. A wheel that is light but flexes can waste as much energy as it takes to accelerate a heavier wheel.

4) Aero is more important than weight, even in an event as short as the 500m. 1/3 of the event is spent accelerating, 2/3 is spent battling the wind. Even the 250m the aerodynamics are more important because the whole event (times portion) is spent at speed.
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Old 02-08-17, 11:28 PM   #12
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..................

1) Aero wheel covers are not legal for track use.

................................
In the USA wheel covers are allowed for Cycling USA races per rule 1I1(b) --- [http://www.usacycling.org/usa-cycling-rule-book.htm]

There may be no protective shield, fairing, or other device on any part of the bicycle, which has the effect of reducing air resistance except that spoke covers may be used.

If you do not live in the USA maybe your cycling body also has a similar rule.

Occasionally I see riders with wheel covers but as noted in other responses I do not believe they provide any significant benefit.
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Old 02-12-17, 09:13 AM   #13
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Originally Posted by Hrothgar42 View Post
It depends! The acceleration of a wheel itself depends on the moment of inertia of the wheel.

You can compare weight (or mass) if it's at the same place in the wheel.
So, using 400g tires instead of 100g tires would just be silly. And it's intuitive.

But the moment of inertia depends on the mass and the distance away from the axel. The further away, the more acceleration is affected. Heavy rims matter more than heavy hubs.

And since a disc (a proper disc, not a spokes wheel with a cover) doesn't need the extra structural support on the rim for spoke nipples, the mass at the edge of the wheel can be reduced.

TLDR: mass alone doesn't determine acceleration.
This is an interesting discussion. Curious if anyone can theorize how this consideration runs for a tri-spoke (or five-spoke) vs, say an 88-mm spoked rim...
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Old 02-12-17, 12:31 PM   #14
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You might have to talk to Tom Compton at Analytic Cycling for this one. But I'm also going to say it depends on the rim and the tri spoke. Corima trispokes have shallower rims than the HED/Specialized, and the HED trispokes are much lighter than the Specialized ones. You're going to have to pick which apple and which orange you want to compare.
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