AEO

quite the run on sentence.

Wider rims change the profile of the tire. The tire is less able to absorb impacts and is more likely to pinch flat, but what you get in return is better handling in corners and a better aerodynamic cross section.


This is most apparent when you ride a MTB with narrow rims and fat tires, then switch to a wider rim with the same tire. The sidewall is more vertical and rolls less under lateral loads.


To put it simply, think of it like this: Holding a cup by its handle vs. holding a cup from its outside.

Trek760

in my experience only...

My 2011 Mercury S1C 19mm rims vs my new 2012 Mercury S1C 23mm rims. My new wheels are MUCH smoother over bumps, debris and chipseal.

As for scientific stuff... I am a journalist, we don't do math. Just feelings.

bobbycorno

??? Never heard THAT one before. And it's exactly contrary to conventional wisdom.

SP
Bend, OR

AEO

it's specifically a problem when you run tires that are near the lower limits of the rim.
Think about it, all bicycle tires are U-shaped and they don't stretch. What would happen when you pull this unstretchable U-shape by the ends? It flattens out and you have less vertical volume.

wphamilton

Thank you. But the portion due to the greater moment of inertia is only evident during acceleration. If I recall correctly the measurements and equations you showed us only pertained to the inertia, and no other factor of rolling resistance.

The gain in moving the tire's mass two millimeters closer to the center, in my opinion, is insufficient to demonstrate a lower rolling resistance of the tire. I do not want to appear to dispute your claims, but I wanted to note that your test does not seem to support them.

Wouldn't it be fairly easy and inexpensive to simply switch wheels and coast down on a level track?

abstractform20

i can win on both

Nick Bain

Makes more sense than what you dun writed.

Not gonna argue your point becasue it appears as though it has a contradiction and is generally all over the place, NO offense.

WhyFi

...but the most common rim/tire combo (19 and 23, respectively) results in a bulbous cross-section, not a "U" cross-section. Going with 23/23 combo (or similar), results in little loss vertically (if any) with more air volume overall. My front is a 23mm wide rim with a 22mm tire (Conti Attack) - zero pinch flats since moving to the wider rim, despite dropping air pressure by 15 psi, not that anecdotal evidence means much.

Barrettscv 

I’ll add another benefit that a wide rim offers that has less to do with aerodynamics. The benifit is reduced weight compaired to alternative rim and tire combinations.

I ran 700x28 tires on 19mm wide rims for several years. My 220 pound weight and the pot-holed urban roads made this a necessity. The extra air volume of the 700x28 tire improved the ride quality and reduced the risk of pinch flats compaired to a smaller tire.

Recently I started using 700x24 size tires, but wanted to keep the same amount of air volume as the larger tire on the 19mm rim. The 23mm wide Velocity A23 allowed me to run the smaller, lighter and more aero rim & tire combination without much of a reduction in air volume.

The 700x24 now rides like a larger tire, but without the bulk.

RChung

Depends on the magnitude of the difference in rolling resistance. I've seen good results from coasting down a long hallway but it requires either very good balance or a three- or four-wheeled cart. It's easier to use a bike with a power meter mounted on a bike trainer or rollers with a front fork mount.

canam73

You got that one backwards. I agree with Whyfi, that the additional rim width allows for a larger 'loop' of tire profile. Even what we are calling a wide rim is still less than 20mm across the inside. The shape of the profile wouldn't become a U with straight sides until the interior width became 23mm. And it isn't until that point that the profile would flatten as it got wider.

My anecdotal evidence also agrees. I run 23mm tires on my A23s at pressures I would normally only attempt with 25mm tires or wider and have not had a pinch flat.

FLO Cycling

You are correct. There are so many things that can be taken into consideration when you look at the entire system. Rolling resistance is certainly one of the things working against you, but it's very small when compared to aerodynamics.

I also agree with you the a wider rim just feels better. There's no data or calculations I can give you to define my feeling but I personally feel wider rims ride better. To me they feel more stable, they corner better, they are more comfortable and luckily non of those benefits create a reduction in speed. Before starting FLO I rode a 19mm wide wheel and switched to a wider wheel from another company. I was sold immediately. I told my brother when starting our company that when I made the switch from the race wheels I already owned to our wheels, that I didn't want to feel like I was giving anything up (even though we would come to market at a lower price). As a cyclist myself, ride quality and component quality have been a top priority since day one. I knew when we started FLO that wide rims were a must. It is why we spent so much time and money developing custom molds and construction methods to develop wide wheels.

All the best,

Looigi

I'll just mention here that 23mm Mich Pro3s measure a bit over 25mm wide mounted on HED Ardennes rims and a bit under 23mm mounted on normal 19mm wide rims.

wphamilton

This is good to know, especially for those of us who haven't had the opportunity to personally compare. Thanks.

AEO

yeah, the difference is negligible and you'd really only run into that sort of problem if you tried using a 20mm tire.

Shroomy

Wow, You guys really seem to get into it with these forums... geez

AEO

yeah, read the sticky at the top, that should give you a clue as to how asinine some of these threads can get.

StanSeven

So 2mm difference overall. That wouldn't seem to affect the sideshape enough to make any difference in pinch flats then

FLO Cycling

Our contact patch test was to determine if in fact the wider rim created a shorter and wider contact patch. In the end it did. In theory this should lower the rolling resistance but... as I mentioned above, we do not have accurate data yet comparing the actual rolling resistance values. That is something we can definitely look into. Coasting down a track could in theory work, but I think there are too many uncontrolled variables in doing that to produce an accurate result.

All the best,

RChung

Accuracy isn't so much the issue, it's precision. Having said that, if you're careful the precision can be reasonably good (CV ~ 1%).

FLO Cycling

Care to describe how you would control the test/other variables?

RChung

Sure. However, it depends on the size of the effect you're trying to measure, the test venue you have handy, and equipment you have available (or can get). Here are four:

1. If you have a calibrated power meter and either a trainer or a set of rollers with a front fork mount, the easiest fastest way is to do a test like this: https://biketechreview.com/tires/roll...75-roller-data
There have been validation tests showing that smooth roller tests correlate well with outdoor field tests (that is, if tire A has lower rolling resistance than tire B on rollers, then A < B for field tests on real roads). The protocol isn't hard but you do need a calibrated power meter.

2. If you have a power meter but you don't have a trainer or rollers (or you want to estimate both the aero drag and the rolling resistance drag) you can either do Virtual Elevation testing or else classic regression testing for aero and rolling drag. These methods are usually used for estimating aero drag but Crr falls out of the solution as a by-product.

3. If you don't have a power meter there are still a couple of possibilities. If you have a way to record moment-by-moment speed (such as with something like a Garmin head unit) and a speed sensor, and have a wind-sheltered road with a known elevation drop, you can do this:
https://forum.slowtwitch.com/cgi-bin/...590389#3590389
You'll need a wind-sheltered venue since variable wind will add noise. If you don't know the true elevation change, you can still determine the difference in Crr between two tires but you won't be able to estimate their absolute magnitude.

4. If you don't have a power meter or a way to record moment-by-moment speed, you can still exploit the relationship between rolling resistance and slope: rolling resistance scales exactly like slope. This is the way some HPV guys have tested rolling resistance: they build a small ramp and roll their vehicle down a long hallway. This works better with a vehicle with three (or four) wheels since the speeds are very low so balance becomes an issue for bikes. Here's an example of one such test; the page is in Dutch but you can Google Translate it: https://wimschermer.blogspot.com/2010...e-and-rim.html
A method similar to this was used to test both aero and rolling drag for racing wheel chairs.

These aren't the only methods. There are some pretty crappy methods out there that give poor precision but these are a few about which I have first-hand knowledge. As I said, it depends on what you have available to you. If you take reasonable amounts of care you can get reasonably precise results. A CV of 1% means, for example, that you could distinguish the difference between two tire/rim setups with Crr = .005 and .0051 with a fairly large amount of confidence.

However, to be honest, I'm guessing you won't try any of these, and you just asked your question because you thought "there are too many uncontrolled variables to produce an accurate result" and you hadn't expected that anyone had spent any time or effort thinking about how one might actually do a careful experiment to achieve high precision.

frenchyge

The 27% increase in rim width only shortened the contact patch by 2.9% (@120psi), so the theoretical reduction in rolling resistance is half of that (1.45%). I think *that's* roughly the size of the effect they'd be trying to validate.

The rest of the responses are drifting away from any 'science' related to wider rims in favor of commentary on comfort, handling, pinch-flat protection, etc. If you run a tire at lower pressure, of course it's going to feel more comfy. You can buy new wheels to let you run that lower pressure without pinching, or just buy wider tires for a lot less.

Bob Dopolina 

Rollers? Hallways?

I applaud the efforts and they may be useful in looking at tire compounding but I remain skeptical that any of these methods, no matter how carefully designed, controlled or executed can take into account tire deflection on an irregular surface. This is where the real world differences appear in terms of rolling resistance because it is about materials and construction.

Do you have links to tests like these that also do not involve a human being in the system?

Paul01

WARNING: This is purely subjective and not scientific at all.

I find the 25mm rims with 25C Gatorskins tires at 115 psi much more comfortable than the same tires on 19 mm rims with the same 115 psi.

Handling seems about the same.

Rolling resistance seems about the same.

YMMV.