25mm vs 28mm on aero wheels

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igs417
Posts: 28
Joined: Fri May 03, 2019 3:44 pm

by igs417

Coming from Canyon Endurace CF SL with 28 mm tires on Mavic Ksyrium Elites UST.

Looking for mid depth aero carbon wheels upgrade, disc brake.

Most of the market options in sub 1500$/EUR price range are designed for 25 mm tires (Cosmic Pro Carbon UST, Hunt 50 Aero, DT Swiss ERC 1400, Prime Black Edition 50, Roval CL50). Only options optimized for 28 mm I found are Reynolds AR41/AR41x (very little info on those) and ENVE SES 4.5 AR Disc (far out of the price range).

Should I wait for the market to catch up with 28 mm trend or get something with 25 mm tires? I do 100 km solo rides, road only, but sometimes in poor condition. I've never ridden 25 mm.

I like Mavic Cosmic Pro Carbon UST, as I'm pretty amazed with UST on my Ksyriums, but 25 mm tire width worries me a bit. Should I expect a big impact in comfort if I go with 25 mm?

by Weenie


AJS914
Posts: 3483
Joined: Tue Jan 28, 2014 6:52 pm

by AJS914

Both Farsports and LightBicycle have some wider rims in their catalog now.

The other thing is that putting a wider tire (28mm) on a rim (say 25mm) where it isn't aero optimized is not going to be a big deal for your solo rides. So you lose 5 watts. Big deal. You'll be out on the road for an extra minute or two on your 100km ride.

Also consider that most 25mm tires will actually measure 27-29mm on a wide rim. So if you go buy a 28mm wide rim, the 25mm tire is still the right sized tire. You'd need to find a 30-32mm rim to be aero optimized for your 28mm tire.
Last edited by AJS914 on Sat May 04, 2019 10:32 pm, edited 1 time in total.

Alumen
Posts: 132
Joined: Tue Aug 18, 2015 1:47 pm

by Alumen

I am even considering to go to 23mm from 25mm on my aero wheels...

On aero wheels I would never ever go anything bigger then 25mm though. Regardless of the odd looks with 28mm on aero wheels and that you might loose some watt savings, I just wouldn't like the riding experience of 28mm. Not that I have experience with it, but I think the cornering on speed would just not "feel" great and sharp. Yeah, I know that is subjective, but that is how I have experienced 25mm on 15C aero wheels in the past.
CAAD 13 105 Disc
CAAD 10 2015 R.I.P.

Hexsense
Posts: 935
Joined: Wed Dec 30, 2015 12:41 am

by Hexsense

Compromise,
25c front for aero and handling feel.
28c rear for comfort and rolling resistance.
With asymetric tire size in this way, your front and rear tire pressure can be similar or the same, instead of pumping rear way harder than front because of different weight distribution.

Regardless, External width of at least 27mm is a must. 30mm if possible (Light-Bicycle, Roval, etc.)

dim
Posts: 534
Joined: Fri Oct 13, 2017 11:25 am
Location: Cambridge UK

by dim

igs417 wrote:
Sat May 04, 2019 9:30 am
Coming from Canyon Endurace CF SL with 28 mm tires on Mavic Ksyrium Elites UST.

Looking for mid depth aero carbon wheels upgrade, disc brake.

Most of the market options in sub 1500$/EUR price range are designed for 25 mm tires (Cosmic Pro Carbon UST, Hunt 50 Aero, DT Swiss ERC 1400, Prime Black Edition 50, Roval CL50). Only options optimized for 28 mm I found are Reynolds AR41/AR41x (very little info on those) and ENVE SES 4.5 AR Disc (far out of the price range).

Should I wait for the market to catch up with 28 mm trend or get something with 25 mm tires? I do 100 km solo rides, road only, but sometimes in poor condition. I've never ridden 25 mm.

I like Mavic Cosmic Pro Carbon UST, as I'm pretty amazed with UST on my Ksyriums, but 25 mm tire width worries me a bit. Should I expect a big impact in comfort if I go with 25 mm?
get 25's and namely Conti GP5000 (I use the tubeless version ... I rate these tyres highly)... they measure approx 27mm on my HED Belgium Plus rims (internal width 21mm and external width 25mm)

on a road bike, I'm not convinced that 28's are better (speed wise) than 25's (yes, 28's are more comfy and good for long rides and if using tubeless, punctures on wider tubeless tyres seal better due to lower pressure) .... but bear in mind that 28's on many rims measure close to 30mm or wider

if you use a gravel bike, or ride on very very poor roads, or don't mind going a bit slower, get 28's (or even better 32's if your frame can fit them)
Trek Emonda SL6
Miyata One Thousand

alcatraz
Posts: 2210
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

The trend is not to go wider because wider is faster, it's to optimize tire pressure for good rolling resistance. If you then weigh 100kg and would bottom out going over bumps then you need a wider tire. If you need a wider tire you need a wider rim to stay aerodynamic.

A 60kg rider riding on above average smooth roads has no reason whatsoever (I think) to go over 25mm wide rims if aerodynamics are a priority.

Besides you can balloon the rear wheel tire a bit without much penalty and going optimal tire width in front.

So ask yourself, what tire width do you need on your front wheel to stay at a tire pressure suitable for the road quality you intend to ride on and pick a rim with that width. If road quality is good you can aim for 95psi lets say, and then if you weigh 85kg including bike that would mean 25mm or 28mm is available to you.

For a 70kg including bike weight the front might be more than enough with 25mm and going wider is going to slow you down.

If you are 90kg and like cobbles or poor road quality riding then an ultra wide rim is right for you. 32mm or so. The optimum tire pressure will then be lower and to not bottom out the wheel you need a wider tire.

igs417
Posts: 28
Joined: Fri May 03, 2019 3:44 pm

by igs417

alcatraz wrote:
Sun May 05, 2019 6:14 am
So ask yourself, what tire width do you need on your front wheel to stay at a tire pressure suitable for the road quality you intend to ride on and pick a rim with that width. If road quality is good you can aim for 95psi lets say, and then if you weigh 85kg including bike that would mean 25mm or 28mm is available to you.
I'm 85 kg rider. Add 8 kg bike and some clothing/equipement, and we're close to 96-98 kg. Roads range from acceptable to poor condition.

I guess 28 mm would be more suitable for me? What's optimal pressure for that? I currently ride 28 mm tubeless at about 80 psi and comfort level is OK for me.

alcatraz
Posts: 2210
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Here is a graph that demonstrates three examples of road coarseness and their air pressure sweet spots.

Image

Poor quality means pressures as low as 65psi.

There is a big gap of optimal air pressure between medium and poor. 60psi vs 90psi so I guess your problem will be to decide what is a good balance for your roads.

In this example they are using a 75kg rider I believe. If you are heavier then maybe you'd want to go up one width. The tire shouldn't compress too much in height which means if you decide on 80psi then you might need a 28c tire ending up at 31mm and thus a 30-32mm wide rim.

Read the full article here:
https://blog.silca.cc/part-4b-rolling-r ... -impedance

You can estimate the air pressure by deciding on a coarseness by looking at the pictures and extrapolating from the graph in this post. Optimum for medium roads with a 75kg rider and 25c conti tires (~27mm) would be 90-100psi. Going on poor condition roads with 100psi increases resistance a lot more than going on smooth roads with 60psi would lose. So the balance of aero vs rolling resistance is not easy to solve without some error. The task is to reduce the error.

igs417
Posts: 28
Joined: Fri May 03, 2019 3:44 pm

by igs417

Interesting notion here: https://www.bicyclerollingresistance.co ... comparison

25mm tire @ 87psi/6.0bar vs 28mm tire @ 81psi/5.6bar = same comfort level (?!) and rolling resistance

I've always assumed that lower pressure equals more comfort per se.

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kgt
Posts: 7827
Joined: Sun Jun 18, 2006 10:29 am
Location: Athens, Greece

by kgt

So... "If you want to go as fast as possible, choose your required comfort level and pick the smallest tire that can provide that comfort for you."

dcorn
Posts: 322
Joined: Thu Oct 05, 2017 4:21 pm
Location: NoVA

by dcorn

Who cares what the wheel is 'optimized' for? I've been riding with 32mm hutchinson tires on my Reynolds Strike 62mm aero wheels. They only have a 17mm inner width and the tire actually shrinks down to 30mm wide, but it is nice and comfortable. I'm a bit over 90kg and I run 80psi tubeless. I've raced the bike a few times, no issues. Yes, the tire 'light bulbs' out a bit so maybe I'm losing a few watts, but I'd rather not beat myself up on crappy roads and not have to worry about dodging rough patches or hitting dirt a bit.

If you want something wider, Light Bicycle has a 46mm deep rim with a 23mm internal width that will certainly be optimized for a 28mm or wider tire. I'm waiting on my set of 46 x 21mm wheels from them. Much cheaper than any of the big name brands.

joshatsilca
Posts: 20
Joined: Thu Feb 21, 2019 4:52 pm

by joshatsilca

igs417 wrote:
Mon May 06, 2019 6:33 am
Interesting notion here: https://www.bicyclerollingresistance.co ... comparison

25mm tire @ 87psi/6.0bar vs 28mm tire @ 81psi/5.6bar = same comfort level (?!) and rolling resistance

I've always assumed that lower pressure equals more comfort per se.
There is a fomula for calculating this based on something called 'casing tension'. Larger tires at the same pressure are stiffer, though our testing has shown that as the object you are impinging the tire with gets smaller, the stiffness begin to approach each other.. so the larger tire can be stiffer when loaded against a flat surface and slightly less stiff against a small bump. We have an entire blog post on this: https://blog.silca.cc/part-2-tire-stiff ... er/harsher

The rule of thumb is that for equivalent stiffness you need to reduce pressure by 2-3% for each mm larger your tire measures.. so in this case, say we lower 2.5% per mm x 3mm and we get 6.0 becomes 5.6bar

Josh
Owner of SILCA
Check out my Tech Blog: https://blog.silca.cc
Stories of the Tech behind the Tech: https://marginalgainspodcast.cc

willmac
Posts: 159
Joined: Thu Aug 25, 2016 11:33 am

by willmac

I’d throw another comment to this one and that’s tubeless vs clinchers. I have both clincher and tubeless GP5000’s. I run the clinchers at 85psi and tubeless at 75 and both feel pretty similar in terms of both speed and comfort. The thicker sidewalls on tubeless most likely needs looking into in a similar way as to what Silca did with clinchers but the thicker sidewalls on the conti’s definitely makes them behave differently to what the clincher version does.

Etienne
Posts: 195
Joined: Tue Aug 23, 2005 11:41 am
Location: France

by Etienne

willmac wrote:
Thu May 09, 2019 10:30 am
I’d throw another comment to this one and that’s tubeless vs clinchers. I have both clincher and tubeless GP5000’s. I run the clinchers at 85psi and tubeless at 75 and both feel pretty similar in terms of both speed and comfort. The thicker sidewalls on tubeless most likely needs looking into in a similar way as to what Silca did with clinchers but the thicker sidewalls on the conti’s definitely makes them behave differently to what the clincher version does.
Do you ride the clinchers with butyl or latex innertubes ?

willmac
Posts: 159
Joined: Thu Aug 25, 2016 11:33 am

by willmac

Butyl. I don’t have the patience for dealing with latex inner tubes plus the fact that latex and carbon is not a good mix unless you have discs.

by Weenie


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