700 x 28... I don't think so

[Johndec]

Am I missing something here? I always assumed the 23, 25, 28 whatever related to the width of the tyres. I got some Vittoria Rubino Pro 28's today from one of the usual suspects in the UK. Whacked them on a cheapo ride to the pub/shops bike I got from Reid to replace the horrid Kenda tyres that it came with. After being rather pleased with myself for not buggering up any tubes fitting the tyres, I noticed that they didn't look much wider than the 22mm tyres they replaced.

A quick measure with my digital calipers showed them to be an average of 25.4mm wide (exactly an inch in the old money). A long way short of 28mm. I also measured the 23mm GP4000s on my Colnago, the average was 23.7mm. My Olmo with 23mm Vittoria Diamante Pros was 24.1mm.... All tyres were at 100 psi for the comparison.

I did notice that the rolling circumference is slightly larger for the 28m tyres, 2150mm compared to 2130mm for both the 23mm tyres (measured with a dress makers tape under no load, subtract bit for tyre drop under my weight).

Huh?

[open roader]

I had a similar experience with Schwalbe Ultremo ZX clinchers in a 25mm size which mounted onto Eurus 2 way fit rims ( a 20.5mm wide rim) at only 23.8mm which is only 95.2% of specified width but not as far out as your 90.7% discrepancy. How wide are the rims you have these fitted to?

[rkelsen]

Isn't it the height of the tyre, measured from the bead seat to the outside of the tread?

[Johndec]

OK, as soon as I posted the above post, the little wheels in my tiny mind started turning. Rim width, you idiot... The no name Chinese rims on the Reid are only 18.6mm wide (measuring the brake pad width) which is 1.2mm thinner than the Braccianos on the Colnago and 1.6mm thinner than the Fulcrums on the Olmo. Put the 28mm tyres on the Fulcrum rims and they would be damm close to 28mm.....

[bigfriendlyvegan]

Sheldon answers all http://sheldonbrown.com/tire-sizing.html#isoetrto" onclick="window.open(this.href);return false;

[Nobody]

My understanding is 25 and 28 are pretty much the same size, just for different rim sizes. Put a 28 on a 15mm inner rim and it should be closer to 25mm. Put a 25 on a 19mm inner rim and it should be closer to 28mm.

[Carriage]

Forgive my ignorance Johndec, but what's wrong with the Kenda tyres? I don't have experience with any others.

[ozdavo]

Widths are nominal only and actual width will vary model to model. Also they will often stretch from new 1-2mm or more.

[rkelsen]

what's wrong with the Kenda tyres? I don't have experience with any others.

Try some better brands and then you'll know.

[MichaelB]

Widths are nominal only and actual width will vary model to model. Also they will often stretch from new 1-2mm or more.

Nailed it in one !!!

[foo on patrol]

OK, as soon as I posted the above post, the little wheels in my tiny mind started turning. Rim width, you idiot... The no name Chinese rims on the Reid are only 18.6mm wide (measuring the brake pad width) which is 1.2mm thinner than the Braccianos on the Colnago and 1.6mm thinner than the Fulcrums on the Olmo. Put the 28mm tyres on the Fulcrum rims and they would be damm close to 28mm.....

Just read this thread and was going to say, if, you have narrow rims then they will pull in narrower.

Foo