Theoretical watts lost due to too wide a tire

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spartacus
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Joined: Mon Apr 04, 2011 6:53 pm

by spartacus

Sorry but I can't seem to find data on this. Say you have a 25mm wide rim then go from a true 25c tire to a true 28c tire, approx how many watts difference in drag might there be? I know there will be a difference in cross wind feel.

PeytonM
Posts: 196
Joined: Wed Apr 24, 2019 10:59 am

by PeytonM

2 watts or less.

I've seen data in white papers over the years from Dt Swiss, Swiss side, vision, Merida and it's all been consistently 1-2 watt penalty going to 28mm.

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warthog101
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by warthog101

That is far call. 25f 28r.

spartacus
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by spartacus

PeytonM wrote:
Sat Aug 20, 2022 10:12 am
2 watts or less.

I've seen data in white papers over the years from Dt Swiss, Swiss side, vision, Merida and it's all been consistently 1-2 watt penalty going to 28mm.
Thanks, I'll have to see if I can find some of these. I'm surprised the difference is so small.

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C36
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by C36

It depends what your rim width is. If your rim is 25-26mm and you go from 25 to 28mm tire you will loose in the 4-5W if your rim is wider you will be in the 1-2W range (data for reasonable speed around 30 or 40kph).

That’s one of the reasons Canyon send their bikes to Tour with 23 front 25 rear tires (and now with wider rims, with 25-28 combo).

spartacus
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by spartacus

C36 wrote:
Sat Aug 20, 2022 4:45 pm
It depends what your rim width is. If your rim is 25-26mm and you go from 25 to 28mm tire you will loose in the 4-5W if your rim is wider you will be in the 1-2W range (data for reasonable speed around 30 or 40kph).

That’s one of the reasons Canyon send their bikes to Tour with 23 front 25 rear tires (and now with wider rims, with 25-28 combo).
Let's say the wheel is 50 deep and 25mm wide, you put on a 28c tire that measures 28-29c.

Wondering if there are tests with data and graphs? Where is the 4-5w number coming from?

I know it makes a difference I'm just curious how much.

Singular
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Joined: Mon Jul 27, 2020 8:59 am

by Singular

Not nothing, at least according to the below:

https://www.hambini.com/testing-to-find ... le-wheels/

(but that's 23 to 25, but still...)

spartacus
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Joined: Mon Apr 04, 2011 6:53 pm

by spartacus

Singular wrote:
Sat Aug 20, 2022 5:13 pm
Not nothing, at least according to the below:

https://www.hambini.com/testing-to-find ... le-wheels/

(but that's 23 to 25, but still...)
18w at 50kph if I'm reading that right? I think the old c60 was 24-25mm wide and the gp4000 ran a size large...

Singular
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by Singular

spartacus wrote:
Sat Aug 20, 2022 5:23 pm
Singular wrote:
Sat Aug 20, 2022 5:13 pm
Not nothing, at least according to the below:

https://www.hambini.com/testing-to-find ... le-wheels/

(but that's 23 to 25, but still...)
18w at 50kph if I'm reading that right? I think the old c60 was 24-25mm wide and the gp4000 ran a size large...
Correct - if anything, the negative effect of a lightbuld-shape tyre is apparent in this test. The wider Enves fare significantly better in this instance.

PeytonM
Posts: 196
Joined: Wed Apr 24, 2019 10:59 am

by PeytonM

Hunt limitless white paper has some good info comparing wheels with Pro One 25mm and 28mm @45kph

Rapide 0.04w
Hunt 60 0.12w
Roval 64 0.4w

However all are wide rims. Looks to be front wheel only.

Singular
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by Singular

Yep, for those wheels the tires are still within the established effectice range.

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C36
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by C36

spartacus wrote: Wondering if there are tests with data and graphs? Where is the 4-5w number coming from?
That was from a road test done by a continental team on a open velodrome 2 or 3 years ago. They also tested at higher speed but I lost trace of the results.


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xav
Posts: 269
Joined: Tue Dec 05, 2006 9:59 pm
Location: UK

by xav

It really depends on the wheel you're putting it on. And that doesn't just mean simple width/depth measurements, as the location of maximum width on the rim is really important - just having a number which says how wide a wheel is at either the brake track or an indeterminant point further down doesn't give you the whole answer as the location of this maximum width.

You should also consider the speeds that you're travelling - if you're being quoted 1w at 45kph then this is very little (difference in speed of 0.045kph), whereas 1w at 30kph is double this from a speed perspective (0.1kph).

It's one of those unfortunate things where there is no blanket answer, and you have to do the testing on the exact wheel and tyre model you're comparing to understand the impact. Some wheels are specifically designed to accommodate a range of tyre sizes, others less so.

spartacus
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Joined: Mon Apr 04, 2011 6:53 pm

by spartacus

xav wrote:
Mon Aug 22, 2022 11:36 am
It really depends on the wheel you're putting it on. And that doesn't just mean simple width/depth measurements, as the location of maximum width on the rim is really important - just having a number which says how wide a wheel is at either the brake track or an indeterminant point further down doesn't give you the whole answer as the location of this maximum width.

You should also consider the speeds that you're travelling - if you're being quoted 1w at 45kph then this is very little (difference in speed of 0.045kph), whereas 1w at 30kph is double this from a speed perspective (0.1kph).

It's one of those unfortunate things where there is no blanket answer, and you have to do the testing on the exact wheel and tyre model you're comparing to understand the impact. Some wheels are specifically designed to accommodate a range of tyre sizes, others less so.
Thanks, this makes sense, I was just hoping there were tests done where someone intentionally tested tires that are wider than recommended (3-4mm wider than the wheel) on various rims but so far the hambini one is the only one I've seen, and that was kind of accidental due to the gp4000 running large and being inflated to high psi.

Lakal
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Joined: Thu Apr 23, 2020 12:20 pm

by Lakal

In this blog Josh from Silca is sharing some data from an old Zipp 404 with a 23mm GP4000 and a 25mm GP4000 at different pressure levels (widths).
https://silca.cc/blogs/silca/part-5-tir ... rodynamics

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