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Re: Vittoria CS 25mm CRR test [rruff] [ In reply to ]
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rruff wrote:
25mm and 23mm will both have the same spring rate at 80-85psi. Thank you Josh Poertner! And I think I've seen Damon Rinard mention this as well.

Correct: Spring rate depends strongly on inflation pressure, and not very strongly at all with width or volume.

Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)
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Re: Vittoria CS 25mm CRR test [damon_rinard] [ In reply to ]
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Even though the spring rate at ride height is the same, the curve is different as you compress into the tyre.
This will show up on sharp edge features like joins in the pavement.
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Re: Vittoria CS 25mm CRR test [lanierb] [ In reply to ]
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Would you happen to have the values of comparable tire in the same width, say the conti TT or SS, at hand? Had a quick look but couldn't find the numbers here to compare
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Re: Vittoria CS 25mm CRR test [Ben6] [ In reply to ]
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Ive been running Challenge Latex tubes for years, really good luck with them. Also have removable core, if I ride in flat prone areas I use about 20ml of stans in them, works ALMOST as good as tubeless, so far two holes sealed with maybe 10 psi loss, made it home no problem(using GP Force tires)
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Re: Vittoria CS 25mm CRR test [lyrrad] [ In reply to ]
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lyrrad wrote:
Even though the spring rate at ride height is the same, the curve is different as you compress into the tyre.
This will show up on sharp edge features like joins in the pavement.

Here are the measurements I made:



Looking first at the force-deflection response against a flat surface (upper data series):
The non-linear part of the curve is in the lower left, with body weight around 40-50 kgf on each wheel, or roughly 1g (no bump). If I had the original data (not just this photo) I'd be able to zoom in.

Then as the wheel gets more heavily loaded (moving up and to the right), the curves basically straighten out. In the upper right you can see hand notes indicating where tires of different widths have roughly the same slope (stiffness) when inflated to the same pressure.

This is why I mentioned the spring rate depends more on inflation pressure than tire dimensions.

Then at the far right, you can see where each data series bends sharply upwards: force increases and deflection barely changes. This is the flat surface bottoming the tire against the rim. Here the "travel" depends mainly on tire height, not inflation pressure. This is one reason bigger tires are usually nice when your riding surface calls for lower inflation pressures.


Looking next at the force-deflection response against an 8 mm radius edge:
Not much relation, they all bottom out pretty easily!

Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)
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Re: Vittoria CS 25mm CRR test [lanierb] [ In reply to ]
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lanierb wrote:
I just tested one of these new tires and here's what I got (with 2017 CS 23mm for comparison):

Width / Height / CRR
2017 CS 23mm / Latex tube / Jet 6+ rim / 100 psi: 25.8mm / 23.8mm / 0.00311
2018 CS 25mm / Latex tube / Jet 6+ rim / 100 psi: 28.0mm / 25.7mm / 0.00288

Thanks for sharing this, helps clarify the final variable in the BRR data (you wouldn't happen to have data for a GPTT by any chance?)

If I take a GPTT 25mm (27), butyl tube, no sealant as:
- 10.5W, 100 psi
- 11.8W, 80 psi

Switching that for a latex tube, would put it at ~8.5W/9.8W, so pretty close to the CS23:

Corsa Speed 23mm (25), no tube, 20ml sealant
- 8.3W, 100 psi
- 9.2W, 80 psi

But if your 93% 23/25 holds the CS25 would be 7.7W/8.5W (tubeless)

Tricky bit is the latex vs tubeless, no idea if that would put the GPTT & CS back in line.
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Re: Vittoria CS 25mm CRR test [SteveM] [ In reply to ]
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SteveM wrote:
lanierb wrote:
I just tested one of these new tires and here's what I got (with 2017 CS 23mm for comparison):

Width / Height / CRR
2017 CS 23mm / Latex tube / Jet 6+ rim / 100 psi: 25.8mm / 23.8mm / 0.00311
2018 CS 25mm / Latex tube / Jet 6+ rim / 100 psi: 28.0mm / 25.7mm / 0.00288


Thanks for sharing this, helps clarify the final variable in the BRR data (you wouldn't happen to have data for a GPTT by any chance?)

If I take a GPTT 25mm (27), butyl tube, no sealant as:
- 10.5W, 100 psi
- 11.8W, 80 psi

Switching that for a latex tube, would put it at ~8.5W/9.8W, so pretty close to the CS23:

Corsa Speed 23mm (25), no tube, 20ml sealant
- 8.3W, 100 psi
- 9.2W, 80 psi

But if your 93% 23/25 holds the CS25 would be 7.7W/8.5W (tubeless)

Tricky bit is the latex vs tubeless, no idea if that would put the GPTT & CS back in line.

My own $0.02: the GP TT is durable enough that the minor speed penalty is worth it to me to run it over the Corsa Speed. Not to mention installation/removal is worlds easier...
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Re: Vittoria CS 25mm CRR test [SteveM] [ In reply to ]
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Tom tests with latex:
https://docs.google.com/spreadsheets/d/1vTm2AQYKeDuabP8Qiv5_AjatJVNYSY_DRBOeFmO3-_8/edit#gid=2047093726


Presuming you are trying to go from his measured 23 TT to the unknown 25 GPTT.




The 23CC GP TT = 26w (per pair)


The 23 GP4000S2 =32w (per pair)
the 25 GP4000S2 =31w (per pair)
---
Given both a black chili, probably safe to assume the 25cc GPTT is around 25w per pair.


Corsa speed is 24w per pair so , maybe a little further off, but yeah, pretty close


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Re: Vittoria CS 25mm CRR test [damon_rinard] [ In reply to ]
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damon_rinard wrote:
lyrrad wrote:
Even though the spring rate at ride height is the same, the curve is different as you compress into the tyre.
This will show up on sharp edge features like joins in the pavement.


Here are the measurements I made:



Looking first at the force-deflection response against a flat surface (upper data series):
The non-linear part of the curve is in the lower left, with body weight around 40-50 kgf on each wheel, or roughly 1g (no bump). If I had the original data (not just this photo) I'd be able to zoom in.

Then as the wheel gets more heavily loaded (moving up and to the right), the curves basically straighten out. In the upper right you can see hand notes indicating where tires of different widths have roughly the same slope (stiffness) when inflated to the same pressure.

This is why I mentioned the spring rate depends more on inflation pressure than tire dimensions.

Then at the far right, you can see where each data series bends sharply upwards: force increases and deflection barely changes. This is the flat surface bottoming the tire against the rim. Here the "travel" depends mainly on tire height, not inflation pressure. This is one reason bigger tires are usually nice when your riding surface calls for lower inflation pressures.


Looking next at the force-deflection response against an 8 mm radius edge:
Not much relation, they all bottom out pretty easily!

So from your graph I get that at 1G, which is normal ride height, that you are operating in or near the edge of the non linear region of the curve so it is the lower force impacts that we as riders are sensitive to.
I am thinking that there is still not much extra force in a pavement step or road profile to bring it up into the linear zone.
I cannot tell from that low quality graphic if a wider tyre extends the non linear zone higher in the force curve or not.
Any hope of getting the original data? Or maybe being able to post just the wider of those rims tested with various width tyres to clear the clutter?
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Re: Vittoria CS 25mm CRR test [lyrrad] [ In reply to ]
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lyrrad wrote:
So from your graph I get that at 1G, which is normal ride height, that you are operating in or near the edge of the non linear region of the curve so it is the lower force impacts that we as riders are sensitive to.
I am thinking that there is still not much extra force in a pavement step or road profile to bring it up into the linear zone.
I cannot tell from that low quality graphic if a wider tyre extends the non linear zone higher in the force curve or not.
Any hope of getting the original data? Or maybe being able to post just the wider of those rims tested with various width tyres to clear the clutter?

Hi lyrrad,

Thanks for your comments.

Yes, around 1g we're just near the edge of the non-linear/linear part. Would be nice to zoom in there. I wish I still had the original data but unfortunately the photo is all I've got.

Maybe someone with the machinery and time could measure newer rims and tires?

Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)
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Re: Vittoria CS 25mm CRR test [damon_rinard] [ In reply to ]
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I am more curious now so I think I may strap a phone on the frame and go measure vertical G loads riding up my street.
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