Are wider tyres on performance road bikes really necessary for added comfort?

Discuss light weight issues concerning road bikes & parts.

Moderator: robbosmans

andreas
Posts: 197
Joined: Thu Jun 12, 2014 10:21 pm

by andreas

TheRich wrote:
Tue Nov 17, 2020 9:50 am
My take is that it's more of an argument against 23mm tires than anything else.
No, if you can run a low enough pressure to reach your desired comfort level with 23mm without risking pinch flats, they win on weight and aero (and price, for that matter).
And for people "feeling" a difference in RR that is measured to 0,2W given pressures that yield the same comfort level, or 0-1W given pressures that yield the same deflection level; that's just placebo.

TobinHatesYou
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Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

Talking about rolling resistance really is a red herring. The volume of a 28mm tire can absorb ~2x the amount of impact energy of a 25mm tire inflated to typical pressures.

by Weenie


darnellrm
Posts: 283
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Location: NC, USA

by darnellrm

TobinHatesYou wrote:
Tue Nov 17, 2020 1:07 pm
Talking about rolling resistance really is a red herring. The volume of a 28mm tire can absorb ~2x the amount of impact energy of a 25mm tire inflated to typical pressures.
When inflated to the same pressure, the 28mm tire deflects less ( absorbs less energy ) than the 25mm tire. Not sure what yu are trying to say...

Butcher
Shop Owner
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by Butcher

But when do you set the pressures the same? It seems that the larger the tire, the less pressure you put in. The more weight you have, the more pressure you put in. It's a poor comparison when any test has all the pressures the same, when the tire sizes are not.

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

by Hexsense

darnellrm wrote:
Tue Nov 17, 2020 2:54 pm
TobinHatesYou wrote:
Tue Nov 17, 2020 1:07 pm
Talking about rolling resistance really is a red herring. The volume of a 28mm tire can absorb ~2x the amount of impact energy of a 25mm tire inflated to typical pressures.
When inflated to the same pressure, the 28mm tire deflects less ( absorbs less energy ) than the 25mm tire. Not sure what yu are trying to say...
It can absorb 2x the amount of impact energy before you bottom out on the rim. So you can get away with less pressure without pinch flat. That, while not helping in rolling resistance loss, helps in reducing suspension loss (and comfort, ofcourse).

TheRich
Posts: 840
Joined: Tue Jan 01, 2019 1:36 am

by TheRich

andreas wrote:
Tue Nov 17, 2020 12:31 pm
TheRich wrote:
Tue Nov 17, 2020 9:50 am
My take is that it's more of an argument against 23mm tires than anything else.
No, if you can run a low enough pressure to reach your desired comfort level with 23mm without risking pinch flats, they win on weight and aero (and price, for that matter).
And for people "feeling" a difference in RR that is measured to 0,2W given pressures that yield the same comfort level, or 0-1W given pressures that yield the same deflection level; that's just placebo.
So are the areo and weight differences.

(Some widths may change things like crosswind stability depending on rim width)

AJS914
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by AJS914

Has anyone measured "impact energy" or hysteresis and translated it to watts or a 40km TT time? I know Jan Heine has done roll down tests. There doesn't seem to be any good way to find the tradeoff between hysteresis and aero losses from wider rubber.

For those that love their 23mm tires, are you loving them on your old rims? I think rim width matching counts for something. An 18-19mm internal width rim seems to work exceptionally well with a 25mm GP5000 (which is almost a true to size tire).

The 25mm GP5000TL feels like the fastest tire I've ever ridden. They are mounted on 18mm wide rims. I run 80/85psi.

A long time ago I tried a 25mm GP4000 (a tall 27mm actual tire) on an old school narrow Campagnolo Proton wheel. The big bulb of a tire was a horrible match for a narrow rim. It was imprecise feeling.

DHG01
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Location: Madrid

by DHG01

For those running tubulars or tubeless, one advantage of 25 mm over 23 mm is that, requiring lower tyre pressure, the 25 mm is more likely to seal in the event of a flat.

TobinHatesYou
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Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

darnellrm wrote:
Tue Nov 17, 2020 2:54 pm
TobinHatesYou wrote:
Tue Nov 17, 2020 1:07 pm
Talking about rolling resistance really is a red herring. The volume of a 28mm tire can absorb ~2x the amount of impact energy of a 25mm tire inflated to typical pressures.
When inflated to the same pressure, the 28mm tire deflects less ( absorbs less energy ) than the 25mm tire. Not sure what yu are trying to say...

I didn’t say same pressure, I said typical pressures. A 28mm tire at 65psi can absorb roughly 2x the energy of a 25mm tire at 85psi before bottoming out.

maxim809
Moderator
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by maxim809

AJS914 wrote:
Tue Nov 17, 2020 7:23 pm
Has anyone measured "impact energy" or hysteresis and translated it to watts or a 40km TT time? I know Jan Heine has done roll down tests. There doesn't seem to be any good way to find the tradeoff between hysteresis and aero losses from wider rubber.
I see why you are asking as it's an interesting question. The best real-world study I've seen that captures hysteresis effects on different tarmacs, and translates to lost watts is Silca's RR/Impedance blog post. By now, all tire nerds have likely seen this.

However, I have not seen any study that specifically quantifies impact energy swept across various tire widths of different PSI across different tire/rim width combos. Silca's study focused mainly on 25mm's.

The Silca Blog Post we all know and love: https://blog.silca.cc/part-4b-rolling-r ... -impedance

My takeaway is to run the highest PSI possible for your given system weight (using Silca's PSI calculator), but leave a comfortable margin of headroom so as to not exceed that breakpoint pressure. And each of us have to find for ourselves where that breakpoint is, because we live and ride in different conditions.

For my weight, for how & where I ride, my sweet spot is 90±3psi on 25mm's in dry conditions.

My opinion is this whole thing is a lot like trying to pick the perfect mattress... Some people like it firm, others soft, others somewhere in-between still. And we all sleep differently so there is no one-mattress-fits-all.
AJS914 wrote:
Tue Nov 17, 2020 7:23 pm
I know Jan Heine has done roll down tests. There doesn't seem to be any good way to find the tradeoff between hysteresis and aero losses from wider rubber.
On a related note on roll-down tests... Not sure what Jan's tests looked like, but there are Youtube and Bike Magazine testers who have conducted their own home brew roll down tests. It's important to note that unless the roll down is conducted on a Half-Pipe, the tests are flawed from the perspective of testing Crr & aero. Most tests I've seen will conduct the roll-down on a downhill that ends in a flat course, and measures the final speed or distance traveled. This approach is only an exercise in physics, and not testing for the effects of Crr & aero themselves. A half-pipe should be used instead. OR, a better approach is providing more inputs to refine the data via RChung.

In-Depth explanation of why Half-Pipe vs Flawed Downhill Rolldown: https://www.cyclingapps.net/blog/how-fi ... down-test/
Currently building a: Basso Diamante

neeb
Posts: 728
Joined: Tue Jan 27, 2009 8:19 pm

by neeb

Ideally we should be talking about tyre volume when mounted rather than nominal tyre width. Internal rim width affects this just as much as tyre "width" marked on the tyre. The difference between a 23mm tyre mounted on a 15mm rim and on a 19mm rim is more than the difference between a 23mm and 25mm tyre mounted on the same rim.

Maybe we should be measuring tyre width as the distance between the beads when the tyre is unmounted and squashed flat. I guess if tyre widths were specified that way, you could easily calculate tyre volume when mounted using that figure combined with internal rim width (assuming a given pressure).

It's funny that as internal rim widths have been getting wider, so have tyres. You could argue it should be the other way around - as rims get wider internally you should fit "narrower" tyres to maintain the same volume, with the advantage that the shape is better (less "light bulb") for the same volume.

I like 23mm tyres on 19mm internal rims. On narrower rims I'd run 25mm tyres for better handling/comfort and 23mm for speed, this compromise being imposed by the rim width. The wider rim means less compromise. I'm light though - if I was heavier then 25mm on 19mm intermal (with a correspondingly wider external diameter for aerodynamics) might be better.

Shouldn't we be selecting tyre volume and wheel width at least to some extent according to our individial weights?

TLN
Posts: 224
Joined: Wed Jul 12, 2017 4:50 pm

by TLN

sigma wrote:
Sun Nov 15, 2020 9:08 pm
In the Chicago area, when I am back, the road conditions resemble the cobblestones of Europe. I use the widest tire I can fit on the lowest pressure. A hardtail mountain bike would be a better choice for sure.
Lol. Can confirm : )

I found out two things surprised me:
1. I found that Strada Bianca 30c on Trek Domane (with read isospeed) felt very fast. I was riding that bike for an hour or two. Way faster then I anticipated.
2. I found that SL5 Tarmac Disc with 17c internal rims and 25c tires feels way worse than Allez Sprint with 21c tires and 26c wheels (measured 29). Everyone is saying that alu is harsh, but those two bikes were felt pretty close to me.

It seems that it comes down to where compliance comes from. My goal is to have wider rim (21+c) with supple tires but pretty stiff and racy frame. That way I can tune level of compliance with tires/pressure and still maintain better grip with bigger tires. ALl that adds some weight, but being a heavier rider I don't care as much.
His: Specialiez S-Works Tarmac SL5 Disc.
Hers: Cannondale Synapse HM Disc

sigma
Posts: 260
Joined: Mon Apr 02, 2018 4:12 am

by sigma

TLN wrote:
Fri Nov 20, 2020 1:46 am
sigma wrote:
Sun Nov 15, 2020 9:08 pm
In the Chicago area, when I am back, the road conditions resemble the cobblestones of Europe. I use the widest tire I can fit on the lowest pressure. A hardtail mountain bike would be a better choice for sure.
Lol. Can confirm : )

I found out two things surprised me:
1. I found that Strada Bianca 30c on Trek Domane (with read isospeed) felt very fast. I was riding that bike for an hour or two. Way faster then I anticipated.
2. I found that SL5 Tarmac Disc with 17c internal rims and 25c tires feels way worse than Allez Sprint with 21c tires and 26c wheels (measured 29). Everyone is saying that alu is harsh, but those two bikes were felt pretty close to me.

It seems that it comes down to where compliance comes from. My goal is to have wider rim (21+c) with supple tires but pretty stiff and racy frame. That way I can tune level of compliance with tires/pressure and still maintain better grip with bigger tires. ALl that adds some weight, but being a heavier rider I don't care as much.
You know I am starting to draw the same conclusions about the importance of the wheel inner rim width and tire combination taking strong precedence over the bike frame. Some of my older bikes had only room for super narrow wheels and tires by today's standards, but from this point on, it's 30 minimum for me. I will check out the Strada Bianca - my old Domane is rim so I am not sure it will clear it (i run 28s now), so thanks for the suggestion. I do find the isospeed to be quite effective - my original Domane was the rear only, but a Chicago parks and recs worker armed with a rolling leaf blower sent that bike to an early grave, so Trek replaced it with the last rim version which has isospeed in the front and rear. It's great - I have taken it to Europe and on Ride the Rockies and I really enjoyed it.
S-works Tarmac SL6
S-Works Venge
Factor VAM 02 disc
Trek Domane 2016 SLR
Open U.P. gravel 2016
Factor One rim v2
Factor LS in progress
Cannondale Black Inc Scalpel 2017

MikeD
Posts: 390
Joined: Thu Dec 11, 2014 9:55 pm

by MikeD

Yes, it's the best, cheapest, most effective way to make a bike ride more comfortably; but the caveat is lower tire pressure is necessary. Use one of those 15% tire drop calculators to get a ballpark tire pressure.

by Weenie


whosatthewheel
Posts: 122
Joined: Sun Jun 12, 2016 1:35 pm
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by whosatthewheel

Why do you need comfort?

I do understand if you are into long distance... Audax or you want to do the TCR, but for your average weekend ride, why do you need extra comfort? It's not an Audi, it's a race bike...

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