Doge

Lab equipment only would tell us about the tire. I don't see too much in the lab that tests the entire system.
Best for that is many runs on in the real setup.

Doge

Everyone knows disc brakes have an aero disadvantage.

Abe_Froman

I disagree. We're talking about a few watts...heck maybe A watt difference. You can't test that on a bike on the road.

And really...it is not that complicated....there are only two aspects that need to be examined. Rolling resistance, and aerodynamics. Aerodynamics can be tested WAY more accurately in a wind tunnel than you could ever hope for on a bike.

Rolling resistance - same. Far greater level of accuracy. Though I do acknowledge that there are questions about how well lab tests simulate asphalt. Still.....I'll take the lab test on a roller over anything measured on a bike.

Edit: Here is an interesting read: https://flocycling.blogspot.com/2016/...ire-study.html

To sum up...they say 25mm GP4000iis is 0.39 watts faster than 23mm GP4000iis...taking into account both aero and rolling resistance. In my world, that translates into "who the **** knows." So take the more comfy tire

A side not though...they did run both tires at the same pressure. I'd like to see the test re-done with a pressure difference between the two. But if you go by the bikerollingresistance measurements...no matter what way you cut it the overall difference is going to be +/- A watt or so.

Doge

Wind tunnels provide repeatable tests. They don't deal with multi-axis, side to side movement, changing rider position, bumps, gusts from random angles and the recovery/getting back on course.

All-else-equal thing does not work with for wheel testing as all else isn't equal. Rider changes, so the jarring and vibration changes and that affect the rider position and affect rider confidence, which changes their position. That is hard to figure in the lab. Wind gusts move the rider off course, bumps and holes move the rider off course and they need to correct and the mass affects that. One tire will absorb the hits better, the other will move the rider more. Increasing width by a mm increases rotating wheel mass by ~25g. I think it is closer to a total system difference of 10W, but I'm not alone in doing things to save a watt here and there.

woodcraft

At that weight & pressure, what's the point of 25s?

fietsbob

Getting expensive wider tires after reading the VBQ articles, sold by the guy who publishes the magazine that carries the test?

Abe_Froman

See my link above in the edit....0.39 watt difference between sizes. IE....exactly the same, or within the margin of error of testing, I'm sure.

Regarding course correction loss and weight..I'll defer to you...though I find it somewhat implausible that those differences could be measured, much less felt on a bike. I don't race...though I did just do my first cyclocross race yesterday

asgelle

Rolling resistance tests (roller or on road) provide the parameters for slip. Wind tunnels provide data on rider position, and different wind angles. Getting back on course (as you say) is the same as side to side motion. It's up to the user to apply the model correctly.

woodcraft

I doubt that that's what motivates Doge...

Doge

Contact patch? There is no issue. They are faster.

These tires have 100PSI reported by the pump. They the first two measure within 1mm width of each other - both are 25mm. The 3rd is 27mm. All 3 have latex tubes. The lighter color easily - easy to feel - has the most give. It is the one ridden at 120PSI sometimes. Even on rough roads is gives. The bigger tire at the end of the video is stiffer. It feels and is much slower at the same PSI. The rider and bike go 1 mph or so slower with this tire at the same PSI.

It is ridden at about 70PSI because it is ridden where give and sidewall strength are more important.

HTupolev

It's a suspicion based on the data that's been published pertinent to suspension loss. Silca's data shows suspension effects kicking in by 110PSI for a much heavier rider (190lb bike+rider) on 25mm GP4000SII on very good asphalt. BQ's data shows them kicking in between 90 and 100 PSI on 25mm Corsa CX on the concrete surface at Marymoor Velodrome. And for a lighter rider, those effects likely kick in at lower pressures.

Sure, but if all the values that you try are in a range which allows a problem to occur, you're not going to isolate that by doing more tests within that range. My understanding is that you think you're looking here:



And I wonder if what's happening isn't actually more like this:

Doge

I can be. Front and rear wheel travel in different amplitude SIN waves - the side to side movement and if there are no disruptions energy is preserved.

A gust (not smooth breeze) of wind will require the cyclist adjust. That wind moves the rider off course. If they did nothing they would be on a new vector. So to return to course, that takes energy. It takes more energy on a heavier bike/wheels.

A rock or a pot hole also jar the bike off course. OR even wee small pebbles. This takes the bike off course too, and requires correction. If the suspension absorbs the bumps the rider has a better ride and there is more loss in heat in the tire. If the suspension is stiffer, well other things are absorbing the heat, and the rider may change position - which changes everything.

Abe_Froman

And a heavier bike/wheels is more difficult to blow off course. I don't see this as having a real effect one way or another.

Doge

I may try lower PSI. As my lab rat is now at college, it is hard to test and he's kinda over it and things are not so serious anymore. I'll see if he's up for a Thanksgiving test. The weather matters too. So we'll have to do 6 or so runs.

This is a video of 4 tests posted many times. The actual recording is a pain, but we likely have about 50 or so tests like this. Different tires and wheels etc., up hills. In general I think the TT @ 120 and race around 105-110 for those silks work well, they are not Corsa Cx. We too run front PSI near rear PSI.

Wind is roughly the same. Position changes at the same spot. Thinner tires get the appropriate higher pressure by a measured cross sectional area relative pressure.

asgelle

I'm still waiting for you to tell us how much more energy. If it's 0.00000001 J, do we really need to care?

Doge

Rim profile being the largest part of the gust equation, not mass for going off course.

And the pot holes?

Abe_Froman

The tire is not going to change the profile of your rim...

And potholes...sure bigger the better .

Doge

This is a thread the OP started about performance. If you're into just tooling along and don't care about which is faster I think this is the wrong thread.

Did you see the HR differences for the same power in the video?
I like to test whole systems and not isolate one part because as I posted, change one part and other things change.
Rather than figuring Joules, I hope time works. I think choosing between the top tires/pressure etc matters about 5 sec in 30 min. Choosing between a top wheel setup and an average road cycling set would be about 1-2 min in 30 min.

asgelle

And you say those factors you list affect performance. So the question is how much? How much aero can I sacrifice for a benefit in recovery from side gusts?

Doge

Yes - I told you in the last reply to you what a wheel difference makes - several seconds over a similar quality one.

The gusts - 2-3 higher HR beats (similar to what was seen in the video) from your core controlling a larger profile rim.
Depending, those 2-3 beats can be sacrificed without loss of speed, sometimes they cost speed. It depends on how close to the limit you are. But they are reflections of energy being used and they do add up.

Abe_Froman

Again...if you do the math (or have bikecalculator.com do it for you...), that's 3 watts. There's no way you can say what is causing 3 watts of difference from one run to the next. 4 degrees F in ambient temperature can cause that discrepancy, FFS.

Doge

Don't you wish you had my eye?
This is the kind of thing bike calculators give you.
Capture.JPG

Abe_Froman

I'm not sure what you're getting at....

asgelle

That's the integrated effect of all factors. I'm asking specifically about those not included in rolling resistance or drag.
Post hoc ergo propter hoc. How do you know the change in heart rate is due to engagement of the core. How do you know it isn't an emotional response to the wind gust or any other factor?

Doge

That when I see real rides of riders going very fast, even out and back to minimize hill issues, wind issues etc, that they do way better than calculators. Or it takes much less power to go fast.
That 32.2mph run above was closer to 300W not 610W. If I put the parameters into a bike calculator I get high W for speeds that are done all the time.

I have found through testing, my riding and talking to other riders that there are energy/fatigue cost from equipment. It is pretty well accepted that higher profile wheels are not good on gusty days.

If they were faster I'd think they'd be used - sometimes anyway. But they are known to be slower. Exactly why they are slower, I don't know. But I do see increase in HR. And a 15mph gusts will spit packs. Is it because the rider can't handle the beast and they are scared, or is it because for some reason it takes more energy to handle them - or both. I just know they turn out to be slower in some conditions. Would I be afraid of using the same the track, no. I don't know how wind tunnels have tested that. But riders know that. I've at least seen something in HR.
The similar approach is applied to tire pressure, drive train, weight etc. In the end seems the calculators are generally beat by an mph or so.