23mm GP5000 too narrow for 19mm inner rim?

Jul 17, 19 17:58

Post #1 of 17 (4086 views)

Just getting into the time trial world and have a small TT event coming up. My bike came with cheap Maddux RS 3.0 wheels which I have measured at about 24.3mm outer rim and 19.2mm inner rim. These wheels have a set of Vittoria Zaffiro clincher tires in 25mm and inflated to about 85-90psi, the size is about 26.5mm. Now according to most compatibility charts, 25mm shouldn't be used on 19mm rims. I thought I could get some marginal gains by getting a pair of the GP5000 (clinchers) tires and keeping the wheels the same for now - upgrade later. I thought of going 23mm in the front and 25mm in the back, but I'm not sure if that 23mm would fit and if I am sacrificing aero gains any.

Thoughts?

Re: 23mm GP5000 too narrow for 19mm inner rim? [Cane89] [ In reply to ]

Jul 17, 19 18:28

Post #2 of 17 (4058 views)

23mm GP5000s fit very well on my wheels, which are 21mm internal diameter. Maybe I’m misunderstanding the question but I don’t think there’s any way the 23s are too narrow for your wheels.

Re: 23mm GP5000 too narrow for 19mm inner rim? [Cane89] [ In reply to ]

Jul 17, 19 20:09

Post #3 of 17 (4003 views)

Cane89 wrote:

I'm not sure if that 23mm would fit

Why wouldn't you think the 23mm would fit? You want the rim to be at least 105% of the tire width for optimal aero gains. Your current 26.5mm wide tire on 24.3mm wide rim is not ideal. I have mounted 23mm tires onto 25mm and 26mm wide rims without any issue.

Re: 23mm GP5000 too narrow for 19mm inner rim? [RichardL] [ In reply to ]

Jul 17, 19 20:32

Post #4 of 17 (3982 views)

Ahh, so the outside rim being at least 105% the tire width (inflated im assuming)...That would mean ideally you want the inflated tire measurement slightly less than the out rim width? So say the 23mm I inflate and it balloons to 24.5mm, while not technically ideal (99%), it would be more 'aero' than the current set up I have which you mentioned is a 26.5mm tire on a 24.3mm outside rim (92%).

Also, I'll probably drop the pressure on the tires too. Maybe see how 80psi is. I'm pretty light at 145lbs.

Re: 23mm GP5000 too narrow for 19mm inner rim? [Cane89] [ In reply to ]

Jul 17, 19 20:37

Post #5 of 17 (3979 views)

Cane89 wrote:

That would mean ideally you want the inflated tire measurement slightly less than the out rim width?

Exactly. You want your measured tire width to be slightly less than the outer rim width. Inner rim width is irrelevant when talking about aero.

Re: 23mm GP5000 too narrow for 19mm inner rim? [Cane89] [ In reply to ]

Jul 17, 19 20:47

Post #6 of 17 (3971 views)

Your wheel is not aero period. What tyre you put on it will be of little significance in regards to aero...

Re: 23mm GP5000 too narrow for 19mm inner rim? [Shambolic] [ In reply to ]

Jul 17, 19 20:51

Post #7 of 17 (3966 views)

Shambolic wrote:

Your wheel is not aero period. What tyre you put on it will be of little significance in regards to aero...

True, its a pretty basic wheel, but I should be able to at least decrease rolling resistance by swapping out tires.

Last edited by: Cane89: Jul 17, 19 20:52

Re: 23mm GP5000 too narrow for 19mm inner rim? [Cane89] [ In reply to ]

Jul 17, 19 20:52

Post #8 of 17 (3963 views)

Rolling resistance yes. Aero no...

Re: 23mm GP5000 too narrow for 19mm inner rim? [Shambolic] [ In reply to ]

Jul 17, 19 20:53

Post #9 of 17 (3961 views)

Shambolic wrote:

Rolling resistance yes. Aero no...

I'll take what I can get for now :P Until I get more $$ and get more serious into the sport

Re: 23mm GP5000 too narrow for 19mm inner rim? [Cane89] [ In reply to ]

Jul 17, 19 20:55

Post #10 of 17 (3956 views)

I wouldn't get to technical on it but a 23mm 5000 should be fine and a good option

Re: 23mm GP5000 too narrow for 19mm inner rim? [RichardL] [ In reply to ]

Jul 18, 19 1:55

Post #11 of 17 (3864 views)

RichardL wrote:

Cane89 wrote:

I'm not sure if that 23mm would fit

Why wouldn't you think the 23mm would fit? .......

Historically this would have been the thinking.
If you were to base your choice on data found at Sheldon Brown's website for example, you would see that the recommended tire width range for a 19mm interior width rim given as 28mm-44mm.
A 23mm tyre would be paired with a 13 or 15mm wide rim. So there is certainly guidance out there that doesn't tally with current norms. I think you'll find the same in relation to recommended tyre pressures, etc....

Re: 23mm GP5000 too narrow for 19mm inner rim? [Cane89] [ In reply to ]

Jul 18, 19 9:06

Post #12 of 17 (3769 views)

Not at 80psi you wont decrease Crr. In fact you will likely increase it at that low of a pressure and probably encounter pinch flats. A 23mm tire at your weight should be about 100psi for max Crr benefit as measure by Tom A and others.

A GP5k 23 will likely measure about 24+

Re: 23mm GP5000 too narrow for 19mm inner rim? [TPerkin2000] [ In reply to ]

Jul 18, 19 9:54

Post #13 of 17 (3746 views)

Ai_1 wrote:

RichardL wrote:

Cane89 wrote:

I'm not sure if that 23mm would fit

Why wouldn't you think the 23mm would fit? .......

Historically this would have been the thinking.
If you were to base your choice on data found at Sheldon Brown's website for example, you would see that the recommended tire width range for a 19mm interior width rim given as 28mm-44mm.
A 23mm tyre would be paired with a 13 or 15mm wide rim. So there is certainly guidance out there that doesn't tally with current norms. I think you'll find the same in relation to recommended tyre pressures, etc....

Yeah, that's kinda what I was reading. With those charts its not really recommenced, but people were saying those are outdated and running a 23mm on a 19+mm inner rim is fine.

TPerkin2000 wrote:

Not at 80psi you wont decrease Crr. In fact you will likely increase it at that low of a pressure and probably encounter pinch flats. A 23mm tire at your weight should be about 100psi for max Crr benefit as measure by Tom A and others.

A GP5k 23 will likely measure about 24+

Ok, I'll increase the pressure on the 23mm front. Any suggestions on what pressure I should have the rear 25mm GP5k at?

Re: 23mm GP5000 too narrow for 19mm inner rim? [Cane89] [ In reply to ]

Jul 18, 19 9:58

Post #14 of 17 (3743 views)

same plus 5psi or so. 98/103 is where I would start

Re: 23mm GP5000 too narrow for 19mm inner rim? [Cane89] [ In reply to ]

Jul 18, 19 10:13

Post #15 of 17 (3732 views)

I bit off topic, but I recently bought a new Conti 5000 tire - WOW! Did they ever change the dimensions!! I bought and mounted a 700 x 25, and it's only slightly "bigger" than the old 4000's on the same wheel!

Steve Fleck @stevefleck | Blog

Re: 23mm GP5000 too narrow for 19mm inner rim? [Ai_1] [ In reply to ]

Jul 18, 19 10:19

Post #16 of 17 (3725 views)

Campy recommends a minimum tire size of 25mm for its 17 internal width Boras, following ETRTO standards. I was told flat out by a Campy rep to go by the stated width of the tire and not the measured width, and that it was dangerous to run anything narrower. Disappointing since that system would not follow the rule of 105. I believe running lower pressure helps to mitigate the risk.

Re: 23mm GP5000 too narrow for 19mm inner rim? [Renault78law] [ In reply to ]

Jul 18, 19 11:14

Post #17 of 17 (3689 views)

Renault78law wrote:

Campy recommends a minimum tire size of 25mm for its 17 internal width Boras, following ETRTO standards. I was told flat out by a Campy rep to go by the stated width of the tire and not the measured width, and that it was dangerous to run anything narrower. Disappointing since that system would not follow the rule of 105. I believe running lower pressure helps to mitigate the risk.

Yeah, cause going by that chart based on ETRTO standards, it seems it would be difficult to follow the 105 rule most of the time, unless the outer width is significantly bigger than the inner width, like a 26mm outer and 15mm inner.

Also, if you look here: https://www.aero-coach.co.uk/gp-5000-data They didn't seem to have any issues mounting a 23mm to a 19.6mm inner rim and 24.7mm outer rim which is very similar to mine.

Last edited by: Cane89: Jul 18, 19 11:26

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