Compass tires actual size

[jambee]

I just got back from my LBS and figured, I'll use their fancy measurer device to check out if my new 700x44mm Compass tires really inflate to that size.
Rim is Pacenti SL25.
PSI is 35.

I was surprised to see that the tire measured at 40mm! Now I'm curious what my 700x38mm measured at.

This being said, I love these tires dearly and can not be happier with what Compass is putting out lately. I'm just curious if anyone was actually able to measure 44mm on them Snoqualmie Pass.

[p nut]

How long were they on the bike before the measurement? They tend to grow after a few days.

[spoonrobot]

They tend to grow after a few days.

False. They will expand with miles, not with time. However, they will not expand 10% (4mm), at best you can expect 1-1.5mm of additional width as the tires break-in through riding.

Compass tires are almost always going to be smaller than the listed size.

[ColonelJLloyd]

False. They will expand with miles, not with time. However, they will not expand 10% (4mm), at best you can expect 1-1.5mm of additional width as the tires break-in through riding.


Agreed.

Compass tires are almost always going to be smaller than the listed size.

It is dependent on inner rim width and to lesser degrees psi and whether tubeless or tubed. Casing strength likely also plays a factor (speaking of tires in general).

One data point: Compass SBH (48-584) measure 47mm on Pacenti PL23 (i18) and 51.5-52.0mm on Velocity Blunt SS (i26.6), both with tubes.

[jambee]

Well, the Pacenti rims they are mounted on are 20mm inner width.

Like I said, I'm not disappointed or anything....I figured the crowd here will find this data point interesting.

[Luwabra]

Great info thanks.. was wondering what they inflate to new. What tire is this and standard or light casing?

[p nut]

False. They will expand with miles, not with time. However, they will not expand 10% (4mm), at best you can expect 1-1.5mm of additional width as the tires break-in through riding.

Mr. Heine shows 2mm growth (over a few days, no mention of miles, by the way). And says even more with EL (6mm growth [10+%]).

"Mounted on a 23 mm-wide rim, the tire measured a little over 49 mm. In the two days since, the tire has “grown” by 2 mm. The “Extralight” tires tend to stretch even more, so when used with wider rims, they’ll probably be close to the anticipated 54 mm."

https://janheine.wordpress.com/2015/06/09/compass-tire-prototypes-really-big-tires/

[Mark McM]

As noted above, rim inside width will affect inflated tire width (which makes sense, since the rim forms part of the pressure chamber). Therefore, the labeled tire size must assume a specific rim inside width.

Here's an article on the ETRTRO sizing system (as used for bicycle tires):

https://en.wikipedia.org/wiki/ISO_5775

From the article:
The inner width of the rim on which the tire is mounted should be about 65% of the tire's nominal section width for tires smaller than 30 mm and 55% for those larger.


An ETRTO labeled width of 44mm assumes a rim inner width of 24.2mm = (0.55 x 44mm). Since the Pacenti SL25 has an inner width of 20mm, you should expect a tire labeled 44mm to have an actual mounted width of about 4mm less, or about 40mm. For an actual mounted width of 44mm, the tire should be mounted to rim with an inside width of about 24mm.

[merckx]

A pair of Barlow pass (38c) standard casing mounted to 17mm rims measured 36.5mm with no miles. Inflation pressure was 50 psi.

[ColonelJLloyd]

Jan had this to say this morning on the 650b list. I don't think this is out of context in any harmful way, but if anyone objects I'll delete the quote. I'm not going to speculate on what he meant by "in the two days since", but he did not say that he didn't ride on the tires in those few days. Notice he mentions mileage below, but not time.

There isn't a huge conspiracy about mis-labeling tires. And by now, Panaracer has plenty of experience how to make wide, supple tires. Compass tires came out pretty much as expected. The explanation why tires vary from their labeled size are much simpler. Tire size depends on a multitude of factors:

- rim width
- tire pressure
- mileage (most tires grow as they get ridden)
- whether you mount them tubeless
- casing material, with more supple casings stretching a bit more. So a Compass Extralight typically is a tad wider than the Standard casing.
- where on the tire you measure. It's rubber, not a precision-machined piece of metal!
- variation within one production run (small) and from one run to the next (a bit larger)
- even the temperature, with rubber actually contracting as it gets hotter.

That is how you get different people measuring the same tire models and getting different sizes. The Snoqualmie Pass 700 x 44 mm tires that measured 36 mm clearly weren't seated correctly (the molded line didn't show above the rim), but others report anywhere from 40 to 42 mm for brand-new tires. I got 42 mm on the standard version with tubes. If you mount the Extralight tubeless, you'll probably get 44 mm.

Just as an example, my Rat Trap Pass Extralight measured 52 mm on my Firefly when mounted with tubes, and 54 mm when mounted tubeless. The labeled size is 54 mm. The Switchback Hill is 48 mm with tubes and 50 mm tubeless. If I were to make a new mold, I'd call them a 50 mm tire, rather than 48. But even so, it's within 4% of the labeled size.

There is a simple reason why tires usually are narrower, rather than wider, than the label says: If somebody buys a tire that is wider than advertised, it may rub on the frame. That is a real problem. On the other hand, if a 54 mm tire really is 2 mm narrower than expected, you'll never notice until you measure them with a caliper. The Switchback Hill being 2 mm wider when you run them tubeless hopefully isn't a big deal: If your bike has clearance for that large a tire, you probably have a little extra room.

Mr. Heine shows 2mm growth (over a few days, no mention of miles, by the way). And says even more with EL (6mm growth [10+%]).

"Mounted on a 23 mm-wide rim, the tire measured a little over 49 mm. In the two days since, the tire has “grown” by 2 mm. The “Extralight” tires tend to stretch even more, so when used with wider rims, they’ll probably be close to the anticipated 54 mm."

https://janheine.wordpress.com/2015/06/09/compass-tire-prototypes-really-big-tires/

[Lovetoclimb]

has anyone had a similar experience with their 32mm width tires? I would like to use them on a bike but only if they will be around 30mm with inner tubes. Probably mounted on H Plus Son Archetype rims or something very similar ...

FWIW on that same rim and bike a 32mm Conti Gatorskin measures right at 32mm, but its the height of the tire that seems to be the limiting factor with the front Campag brake caliper.

[p nut]

Jan had this to say this morning on the 650b list. I don't think this is out of context in any harmful way, but if anyone objects I'll delete the quote. I'm not going to speculate on what he meant by "in the two days since", but he did not say that he didn't ride on the tires in those few days. Notice he mentions mileage below, but not time.

Oh, I'm sure any type of force induced on the tire will help it to stretch. I wasn't implying riding does NOT impact the growth. Just clearing up that time also has an effect.

And, really, who puts on some brand spanking new tires and doesn't go for a ride??!! :)

[ColonelJLloyd]

has anyone had a similar experience with their 32mm width tires? I would like to use them on a bike but only if they will be around 30mm with inner tubes. Probably mounted on H Plus Son Archetype rims or something very similar ...


Just mounted some new Stampede Pass ELs on hard ano TB14s. They measure 30.5mm with Vittoria 25-28mm latex tubes. I suspect they'll end up plumping out to 31mm to possibly just shy of 32mm.

And, really, who puts on some brand spanking new tires and doesn't go for a ride??!! :)

Word.

[donevwil]

My:

- Low mile (~200) Compass Snoqualmie Pass 44s measure 40mm wide on 23mm rims (Synergies),
- Medium mile (~800) Compass Barlow Pass 38s measure 36.5mm on 24.5mm rims (A719),
- Low mile (~100) Compass Stampede Pass 32s measure 30mm on 25mm rims (HED+),
- Hi mileage (~3000) Grand Bois Cypres 32s measure 32mm on 25mm rims (HED+).

All standard casing.

[merckx]

has anyone had a similar experience with their 32mm width tires? I would like to use them on a bike but only if they will be around 30mm with inner tubes. Probably mounted on H Plus Son Archetype rims or something very similar ...

FWIW on that same rim and bike a 32mm Conti Gatorskin measures right at 32mm, but its the height of the tire that seems to be the limiting factor with the front Campag brake caliper.

Stampede Pass EL's on TB14 rims measure 32mm after some miles beneath them. I usually run 55/50 psi.