28 mm dekk, 105 regelen og hjulsett,

As a rule of thumb, the wider you go, the deeper the wheel has to be to get the airflow to remain reasonable.

ie 23mm tyre = 45mm minimum depth

25mm tyre = 60mm minimum depth

In case anyone is interested, the technical reasoning behind this is as follows.

When air is moved out of the way, it is initially positively pressured so it will behave very predictably. When you try to move the air back to where it started, you have created a vacuum and in there you get random movement which causes vortices and increases drag. If you move the air back slower (ie make the profile longer) you will reduce the chance of the air going chaotic. When you have a wider rim, you are moving the air further away from it's start position so you have to compensate with a longer chord (deeper rim).

The technical term (in Europe) for it is alpha critical angle.

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Ensure the minimum rim depth is as follows:
23mm tyre -> 45mm minimum rim depth
25mm tyre -> 55mm minimum rim depth
28mm tyre -> 80mm minimum rim depth

The following is a simplified answer so it's not 100% correct but you'll get the idea.

NACA 0024 is deciphered as follows

00 - indicates it's a symmetrical aerofoil with no camber
2 - multiply by 10% gives you the maximum width, in this case 20% of the chord length
4 - multiply by 10% gives you the position of the maximum width, in this case, 40% of the chord length.

On a bike tyre and rim, the position of the maximum width drops as a percentage as the rim gets deeper so it's not a linear arrangement. This must be considered in conjunction with the major (and Huge) difference that the wheel is rotating.

The aerodynamics are not linear and there is a bit of empirical testing in there.

Stemmer at felg bør være bredere ja, denne videoen forklarer det hele.


Vær obs på at vi her snakker om 28 mm faktisk bredde, ikke nødvendigvis oppgitt bredde på dekket.

Er også i stuss over at flere av produsentene anbefaler bredere dekk enn felg, f.eks. Zipp anbefaler 28mm på 303s, som er 27mm ytre bredde.

Hvordan er det med 105 %-regelen og kjøring på grusveier? Er det trygt med litt bredere felg enn dekk på grusveier av OK kvalitet, eller risikerer man å å skade felgen på div grus?

Nei, ser ikke for meg noe problem med dekk som er like brede som felgene, men mer usikker hvis felgen henger 1-2 mm utenfor på hver side. Noen som har erfaring med dette?

Virker logisk for meg at felgkanten blir noe mer eksponert for løse steiner etc. når dekket ikke dekker hele felgbredden (...)

Kan det være at fordeler med lavere rullemotstand eller andre ting trumfer aero?