40mm rims v 50mm rims

redvision

My best bike currently has 40mm rim wheels and whilst I wasn't that impressed with them to start with, the more I used them the more I grew to love them and appreciate the difference deeper rims can make.

Anyway, I have been toying with the idea of a new bike, with emphasis on aero as I plan to do more tt's this season, whilst also getting back doing a few road races, but now have a lower budget so thinking about changing parts on my current bike instead - ie putting on some aero bars and possibly changing the wheels for some slightly deeper ones and keeping my current wheelset for more undulating/ hilly events and training.

I remember hearing arguments claiming 40mm rims don't offer that much aero benefit, although from my experience they do, but I have struggled to find a comparison between 40mm and 50mm.
So i'm wondering if anyone on here has both and can offer a comparison? Main questions being do the 50mm rims make a significant difference to speed (on flat roads) over the 40mm? And, from your experience, are they worth the extra money?

Thanks

timothyw

The trend is clear, deeper is more aero - https://www.hambini.com/testing-to-find-the-fastest-bicycle-wheels/

But personally I wouldn't bother going to 50mm, I'd go all the way to 60mm.

In fact I did.

Advantage of 60mm is that it's still easy to get 80mm inner tubes for them without having to muck about with extenders etc....

I've never owned 40mm rims, but do have some 32mm rims, and yeah, they're faster.

Whether they're worth it depends on how much you want to spend and which wheels you go for.

I'm tight so built my own using cheap chinese rims.

redvision

Thanks for the quick response.
I know there are clear aero benefits with deeper section wheels but didn't really want to go to 60mm as 50mm would be just that bit more versatile.

I guess I'm just trying to weigh up whether there would be much of a difference to the 40mm rims I have now. It seems such a small height difference but if the 50mm would bring a significant difference in performance/ speed then i guess it would be worth the expense.

w00dster

I have 40mm, 50mm and 65mm. The 40mm are great year round wheels, they get used more often than any of my others.
My personal opinion from lots of riding, but no scientific testing is that 40mm offer very little aero assistance, 65 are obviously better, but then they are heavier as well. My 65s notice the wind, it can be uncomfortable on some fast descents when the wind is up.
Would I spend the money going from 40s to 50s? Nah, I’d do what Tim recommends and look at the 60/65mm. Is there a “significant” speed advantage over 40mm rims? No. There is an advantage but it’s not going to turn a slow rider into a fast rider. Your probably talking at the most about 10 watts difference.

arlowood

According to the Hambini data a set of Enve 40mm wheels requires 189 watts to maintain 30km/h. No Enve 50mm wheels for comparison unfortunately but 4 other 50mm brands required 186 watts to maintain the same speed. So you benefit by around 1.6% in power output by switching from 40 to 50mm. Rims ranging from 58 to 65mm were only marginally better than the 50mm rims tested

Might not mean a great deal in the real world but I'm sure the psychological benefit of deeper rims could be worth the outlay.

redvision

Thanks Arlowood, that's really interesting info.

I know the deeper wheels would probably bring the psychological benefit - I have a set of fulcrum quattros which only have a 35mm rim yet they feel noticeably faster than my fulcrum 7s.

Actually thinking of going down the carbonzone route now. Given my uncertainty I figure trying a set of deeper rims from them for a third of the price to the ones I was considering has to be worthwhile.

step83

timothyw said:

The trend is clear, deeper is more aero - https://www.hambini.com/testing-to-find-the-fastest-bicycle-wheels/

But personally I wouldn't bother going to 50mm, I'd go all the way to 60mm.

In fact I did.

Advantage of 60mm is that it's still easy to get 80mm inner tubes for them without having to muck about with extenders etc....

I've never owned 40mm rims, but do have some 32mm rims, and yeah, they're faster.

Whether they're worth it depends on how much you want to spend and which wheels you go for.

I'm tight so built my own using cheap chinese rims.

Valve extenders were the bane of my life till I found out Decathlon have 80mm valve tubes in stock, will take up to a 28c as well.

On mine I can only comment between two extremes, 25mm and 66mm. Obviously the 66 feels much faster, I would say defiantly on the flat or a decent they are, certainly not a climbers wheel though

singleton

I had 40mm rims on my old bike but when I bought the replacement I went with 50mm.
Not sure if they're any faster - but they look better.

darrell1967

On mine I can only comment between two extremes, 25mm and 66mm. Obviously the 66 feels much faster, I would say defiantly on the flat or a decent they are, certainly not a climbers wheel though

Why aren’t they a climbers wheel?

darrell1967

On mine I can only comment between two extremes, 25mm and 66mm. Obviously the 66 feels much faster, I would say defiantly on the flat or a decent they are, certainly not a climbers wheel though

Why aren’t they a climbers wheel?

timothyw

Well, presumably because they are heavier than a shallow rimmed climbing wheel designed for minimal weight.

There will be a crossover point at which the hill is steep enough that a lighter wheel would be better, although there are a lot of factors, and weather conditions on the day will affect where this crossover is.

Shallow climbs are still quicker on heavier aero wheels.

thecycleclinic

Deeper genreally offer lower aerodynamic drag but inevitably cross wind stability is affected. 50mm deep seems to be a good compromise.

88mm deep rims are a handful on a windy day.

neilr4

I went the chinese route (CSC) and purchased a set of full carbon 60mm with U-shaped rims and the highest spec hub 2 years ago for crit racing (480 euros delivered) and they've been great except when the wind gets to gale force 5 the front wheel can get caught in the wind so I purchased a 35mm which I swap out when the wind picks up and no drop in speed that's noticable compared to the 60mm. I use 30mm aluminium wheels during the winter (32 spoke DT swiss 240 laced to H plus son rims) but when I switch to carbon wheels my ave speed increases by 3-4 kph for the same watts. I've never ridden expensive carbon wheels (zipp, enve etc.) so can't compare but at 480 euros for a set I can afford to crash them.