woodcraft

Pointing to the dynamic relationship between what people will or won't believe and 'the results that experts have found' when those results are, as you say, limited.

Re tire height vs rim width, we have arguments that:
- obviously wider rim makes lower tire
- wider rim makes taller tire
- tire circumference at tread does not change so tire height stays the same
- tire circumference changes slightly at different pressures so tire height also changes with pressure

Campag4life

Hey Dave,
Rule no. 73: After a thread on the internet has run its course, participants emerge from the sidelines and engage in what only can be described as jibberjabber.

Remember, no good turn goes unpunished. Thanks for sharing your experience.

November Dave

As far as aerodynamics go, that's been tested exhaustively by so many entities it's absolutely settled.

As far as the rest goes, if you want to call HED, Damon Rinard, and us having tested at least about 100 different combos and directly measured that tires frequently get taller on wider rims limited, please be my guest. Take November out of it and just leave the other two - Damon is one of the most credible people in the bike industry and HED more or less invented modern wheel aerodynamics.

For me, this is past the point of throwing good time after bad, so I'll take my polite leave now.

redlude97

So another point of data: A gp4000SII 700x25, known to mount wider than spec on a Mavic Open Sport 19mm(15mm internal width), a pretty classic narrow wheel, and a Boyd Vitesse 23mm wide(17mm internal width). I don't have any 25+mm wide wheels for additional comparison. 90psi for both comparisons. I could repeat with a 23mm gp4000s but I suspect the trend would be the same. The answer to where the additional carcass circumference is taken up to get a tire both wider and taller is evident, the bulge at the tire/rim interface is significantly more on the narrower rim. Just think about the two extreme cases, a perfect U shape with the tire casing and a teardrop with an infinitely narrow rim.
Mavic 19mm: 25mm wide and 23mm tall.
Boyd 23mm: 28mm wide and 24mm tall.

Boyd Vitesse 23mm


Mavic OS 19mm

woodcraft

Sorry- I wasn't criticizing your info or expertise. 'Limited' was referring narrower tires being faster only aerodynamically, yet folks tend to take something like that and run with it.

tomato coupe

Can you measure the tire diameter / circumference and / or the rim diameter?

redlude97

couldn't find a fabric tape measure in the house so had to settle for the old school rollout.
Got 214cm and 216cm respectively for 3 measurements for each rim, with an error probably of +/- 2cm

f4rrest

Also, an unused shift cable is an excellent way to measure circumference. Just wrap around tire and measure the gap between the ends and add 2000mm.

Campag4life

Great contribution...thanks redlude and again to November Dave. There have been many great pearls of insight contributed in this thread...mostly from redlude and November Dave who has graciously contributed to share his expertise as a wheel builder.

One of the unexpected byproducts of this thread not expecting an expert like Dave to show up was ask him what I consider to be the most relevant question...in behalf of the forum really....if wheel shopping, what width wheels should we buy? This is a pretty important consideration. Of course in years gone by if buying a road bike or wheels, there was basically one width which I suppose had some variance from mfr to mfr but really it was an outgrowth of a previous era of 'more narrow tires' Now that the industry has evolved to a 25c tire as a nominal tire width selection on a road bike...not just an endurance road bike but even a race bike and what the guys race in the TdF, then stands to reason that based upon the law of proportionality, that rim width may grow too a bit..based upon a shift in trend from 23 to 25mm wide 700c road bike tires. I believe that is what has occurred. But when does one take too much medicine? This was partly the point of this thread. How much does wheel width matter?...say if wanting to ride 25mm wide tires and maybe considering a proportional rim of say 17mm wide versus more traditional 15mm inner flange to flange like on my basic Al Campy wheels?

Dave's response to my question about sweet spot for rim width I believe deserves some further examination. Great insight. Is there an "ideal" inner rim width for ordinary tire sizes we ride on the road?

Dave wrote:
18 seems enough for most road tires up to 28 actual. 21 sure seems better for a 32mm wide "28mm Conti GP4000" than 18 does, but the "28mm Conti GP4000" is also wider by a good bit on the i21 rim than it is on the i18 rim. And as tires get wider, I and many (most?) propose that tires should be wider relative to the rim, for both the suspension that you generally want when you're using really wide tires and the rim protection that you want/need when using really wide tires, really wide tires generally being more likely to be used off the beaten path. That's why we think an i21 (or i21.5 as in the case of one of our current favorite rims) is as ideal as you'll get for 700c tires from say 24 actual to somewhere around 40 actual. You're looking for different tire profiles along that range.

With an eye toward proportionality, my point all along about any anticipated free lunch of the trend toward wider rims is...when is rim width too wide for a given tire? This is why I asked Dave...a man who knows having experienced probably every wheel/tire combo out there.

This begs the following point that Dave touched upon. More isn't necessarily better. When is rim width too wide for a given tire width? I mean, some are running some very wide rims on 23 and 25mm size tires. Is this good for example?
I have beat the drum of wide rims are heavy. Of course carbon lessens this dynamic...or the downside of it. Not so much with wide Al wheels which can get up in the 1700 gram range based upon profile/height.

But what is the other downside of very wide rim with 23/25mm tire? Dave mentioned rim protection which is true. But goes full circle back to tire design which is part of the controversy why some haven't been able to wrap their mind around why a tire can be taller on a wider rim. The tire sidewall profile loses it arc and why it stands taller on a wider rim.
Is this good or bad? Well, it maybe good for tire side wall rigidity...yes wide wheels add air chamber volume...a tire become a tad taller...but the tire itself can lose its 'suspension effect'. Why is that? Because a straighter side wall doesn't flex the same as a more bulb shaped tire. Look at the tire shape in the picture. The bulb shape of a tire 'by design' is created for suspension effect i.e. vertical forces are attenuated by the sine of the tangent to the arc along the sidewall. A more vertical sidewall of mounting on a wider rim, a tire loses an increment of this suspension effect. Dave mentions this and therefore further word of explanation. This in part explains what many report when it comes to handling with wider rims...a more telepathic steering response. This stands to reason. But with that, there is some loss of suspension when going to a wider rim because the sidewall will be more vertical and of course most of us go to a wider tire in the first place for a more compliant ride ergo, greater suspension effect.

So there are many considerations at play. I have mentioned, I like my current road bike combo of 25c tire with 15mm inner flange width. Likely 17-18mm inner flange width based upon Dave's recommendation would be more 'ideal' for a 25mm tire it seems for reasons now discussed. But, there are many even wider rims out there you guys are running with 25mm wide branded tires. Point being, wider rim 'in the extreme' isn't necessarily better. The relationship between tire width and rim width emerged from exhaustive trial and error 50 years ago. It probably still applies today other than rims are now moving toward being proportionally wider to mate with wider tires which likely have grown also due to advancement in tire technology as well....lighter, supple and durable wider tires.

Dreww10

I've run 20.5, 24.4, and 29.4 mm rims over the last few years, in that order. I can't emphatically state that wider is faster or more comfortable, however, there are two key benefits I've found:

- The wider the rims gets, the easier it is to get the tire on and off....with the 29mm rims, I can peel the tire off and re-install without a tire lever
- I can go for days without checking tire pressure, letting them drop down to around 80 psi, without any noticeable loss in speed (and I'm 175 lbs.)

The 25mm tires on the 29mm rim do feel a little more "sure" around corners - with 25's on the 24.4 rim, there's still clear deformation of the tires at the ground at 100psi, whereas the wider rim displays no deformation at all, and I'm sure that's where the cornering feel comes from.

Racing Dan

Its a misnomer claiming the tyre gets "taller" on certain rims. Obviously it does not. The wheel diameter stays the same no matter what rim the tyre is mounted on. If it didnt stay the same, the carcass and tread would either have to stretch or contract, to get to a different diameter. Why would it do that, outside of normal pressure related stretch

Campag4life

I hope you mean... 'in your opinion'. Are you a wheel and tire expert? Dave from November is and rejects what you wrote.
Good of you to return to the thread however...lol.

Campag4life

You should qualify what you mean by no deformation. Tire contact patch by definition is tire deformation. Without, you wouldn't stick to the road very well and psi would be prohibitively high. I believe you are speaking of propensity for the tire to deform laterally. Yes, but this is a tendency and not absolute. All tires will flex laterally when cornering. But do agree it stands to reason that a wider rim is a broader platform to brace the tire against lateral acceleration in a corner. Makes sense. Point is, then what is the downside from drinking so much Koolaid aka when is wide too wide?...a question I posed earlier in the thread. Dave from November responded. Rule of thumb for a 25mm tire is generally no greater than 18mm wheel width.

We talked about wheel weight of course and you mentioned something also implied ability to mount tires easier. This has a companion dynamic, easier for tires under pressure to blow off the rim. Years ago there was a rule of thumb for tire width relative to rim width in large measure for this reason. It was always suggested that tires be wider than rims. This is due to the security of the bead under pressure. A wider tire...stresses on the bead due to constantly changing tire forces, place the bead laterally against the flange of the rim with more or less pressure. With a rim wider than the tire, there is some loss of bead retention...because these stresses are directed more radially to keep the tire bead seated. Dave from November may even have a rule of thumb for tire width versus rim width...part of the calculus being the safety component of keeping the tire seated firmly on the rim. This is part of the consideration for rim width. More isn't necessarily better and can in fact be worse.

Racing Dan

lol all you want. Circumference and diameter of the wheel is directly related via pi, as you know. If the the tyre gets "taller", the implication is that the wheel diameter is bigger as well. For that to happen the circumference needs to be longer. Say the tyre gets 1mm "taller". That is the same as +2mm on the wheel diameter and 6.3mm on the circumference. Why would you believe the tread/carcass elongates 6.3mm because you put the tyre on a different width rim. Makes very little sense.

Campag4life

It makes little sense 'to you'. I explained why 'twice' in this thread. If you can't accept it, that's ok. Just responding to your false assertion that tires don't inflate to larger diameter on a wider rim. They do. Same tire material. Just like air volume increases with same tire on wider rim, a wider rim changes 'effective' tire diameter in cross-section which projects the tire contact patch radially farther away from the rim. Makes perfect sense to me.

Racing Dan

Prove it by measuring the circumference of the same tyre mounted on a 15c and a 19c rim with a tape measure.

Racing Dan

If anything happens at all, the wider rim should result in a smaller diameter, not bigger.

Sy Reene

Did you read posts #154 and #157 above?

Racing Dan

Yes, both seem highly inaccurate.

Sy Reene

oh okay. And of course we've all decided that the chart in the OP of this thread, done by HED cycling and created from plaster casts they made of their various rims/tires, is also completely inaccurate.

Racing Dan

I have no idea what you "decided". Im not accusing anybody of anything. Im just posting my assertions, same as every body else. All Im asking for is an accurate measurement of the circumference of the same tyre on different rims. Not plaster casts or +/- 2cm roll outs or parallax error prone measurements with a ruler.

noodle soup

Some people still deny climate change.

Racing Dan

Yeah, but flo Cycling has the opposite conclusion. According to Flo the wheel diameter becomes smaller (lower tire height), not bigger, on a wider rim. It cant all be true at the same time. Something is up with either the measurements, the model explaining it or borh.

FLO Cycling - Why Do You Use Less Tire Pressure for a Bigger Tire or Wider Wheel?

Also there is still the issue of explaining how the tyre becomes "longer" or "shorter" when you mount it on a different width rim.

Sy Reene

It seems you're suggesting that tires have no elasticity?
Here's my experiment and anyone can do this at home (no need for different rims)..
Same tire on the same rim. Inflated to 15psi, 24mm height and width. Inflated to 90psi = 26mm height and width. IOW, Tires do stretch.
A wider rim describes a larger diameter circle for a tube to inflate within, which means a size increase for both width and height.

Racing Dan

Im not suggesting tyres have no elasticity. In fact I suggested the Exact opposite in a post further up. Still I would assume the elongation of the tyre is proportional to the pressure, not the width of the rim.