Correct tyre size and psi?

robbiepapenfus
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Correct tyre size and psi?

Postby robbiepapenfus » Thu Jan 18, 2018 2:08 pm

Hi All,

I want to make sure that I’m using the correct tyre size and pressure on my road bike..

I have a full carbon fibre road bike, which I use only for my daily commute (about 40kms per day). My weight is about 74kgs and I currently have 700 x 23 (Gatorskins), which I put up to about 110psi each morning before my ride.

These are the only tyres and pressure I have used on the bike, so its difficult for me to compare with anything else (i.e. wider tyres etc).

Do you think the 23’s would be best suited or should I look at trying 25’s?

Cheers,
Robie

defy1
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Re: Correct tyre size and psi?

Postby defy1 » Thu Jan 18, 2018 2:34 pm

im 70kgs, I did ride 23s at 110psi, 25s at 100
and now 28s at 80-90psi
28s are the best by far

robbiepapenfus
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Re: Correct tyre size and psi?

Postby robbiepapenfus » Thu Jan 18, 2018 2:37 pm

defy1 wrote:im 70kgs, I did ride 23s at 110psi, 25s at 100
and now 28s at 80-90psi
28s are the best by far


Best in what respect? Puncture resistance and softer ride?

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Tim
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Re: Correct tyre size and psi?

Postby Tim » Thu Jan 18, 2018 2:41 pm

You could safely drop the pressure by about 20 PSI and roll just as fast and a whole lot more comfortably.

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Re: Correct tyre size and psi?

Postby g-boaf » Thu Jan 18, 2018 3:19 pm

robbiepapenfus wrote:Hi All,

I want to make sure that I’m using the correct tyre size and pressure on my road bike..

I have a full carbon fibre road bike, which I use only for my daily commute (about 40kms per day). My weight is about 74kgs and I currently have 700 x 23 (Gatorskins), which I put up to about 110psi each morning before my ride.

These are the only tyres and pressure I have used on the bike, so its difficult for me to compare with anything else (i.e. wider tyres etc).

Do you think the 23’s would be best suited or should I look at trying 25’s?

Cheers,
Robie


23mm is okay - that's what I run at the moment. I'm 60kg and use 90-95psi in them, unless I don't check them regularly and they go down a bit. My bikes won't fit 28mm. 25 works fairly well, is more comfortable. Don't think they roll any better.

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Re: Correct tyre size and psi?

Postby uart » Thu Jan 18, 2018 3:26 pm

What's best depends on what type of surface you are riding on, but at 74kg then what you're currently running would best suit very smooth pavement.

If you're riding a lot of rougher "chip seal" type roads then lower pressure will be more comfortable and just as fast. The problem with lowering the pressure for rougher roads however, is that you then become more vulnerable to "bottoming out" and pinch punctures.

That's why a lot of people go to slightly larger tyres when they want to drop the pressure, but at 74kg I think there is still scope for you to drop your PSI on the existing tyres. I'd try dropping by about 10 psi on the back and 15 on the front and see how that feels.

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Re: Correct tyre size and psi?

Postby march83 » Thu Jan 18, 2018 3:28 pm

Tim wrote:You could safely drop the pressure by about 20 PSI and roll just as fast and a whole lot more comfortably.


This. I'm 82kg:

23s at 80psi
25s at 70psi

I cannot understand running more pressure unless you only ever ride flawless surfaces.
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Derny Driver
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Re: Correct tyre size and psi?

Postby Derny Driver » Thu Jan 18, 2018 4:26 pm

Just to p1$$ everyone else off, Im saying
Stick with 23s. 2mm makes FA difference
95-100 front
100 to 110psi back

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Duck!
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Re: Correct tyre size and psi?

Postby Duck! » Thu Jan 18, 2018 5:24 pm

Optimal pressure for any tyre is most closely related to your weight, but the construction of the tyre will play a part too, so what's best for one model of tyre will not necessarily hold true for a different tyre under the same rider.

A generally accepted standard is that the optimum pressure for any tyre & rider is that at which the tyre will compress or sag by 15% of its profile height when weighted. Start by measuring from the ground to the edge of the rim sidewall at its lowest point, with no weight on the bike. Then sit on the bike, and get an assistant to take the same measurement. Adust pressure until the measurement is 15% less than the unweighted one. Due to the weight distribution, the front tyte pressute will be lower than the rear.
I had a thought, but it got run over as it crossed my mind.

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Derny Driver
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Re: Correct tyre size and psi?

Postby Derny Driver » Thu Jan 18, 2018 5:27 pm

Duck! wrote:Optimal pressure for any tyre is most closely related to your weight, but the construction of the tyre will play a part too, so what's best for one model of tyre will not necessarily hold true for a different tyre under the same rider.

A generally accepted standard is that the optimum pressure for any tyre & rider is that at which the tyre will compress or sag by 15% of its profile height when weighted. Start by measuring from the ground to the edge of the rim sidewall at its lowest point, with no weight on the bike. Then sit on the bike, and get an assistant to take the same measurement. Adust pressure until the measurement is 15% less than the unweighted one. Due to the weight distribution, the front tyte pressute will be lower than the rear.

15% is not much !!
Looks like some of these big boys running 28s at 60psi will need to pump up their tyres!!

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bychosis
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Re: Correct tyre size and psi?

Postby bychosis » Thu Jan 18, 2018 5:51 pm

I’m similar weight and run 23s at 80-90 on front and 90-100 on back. I don’t inflate daily and use the squeeze test to work out when to pump them up, by which time they are often down to 70 or so.
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madmacca
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Re: Correct tyre size and psi?

Postby madmacca » Thu Jan 18, 2018 8:13 pm

Derny Driver wrote:Just to p1$$ everyone else off, Im saying
Stick with 23s. 2mm makes FA difference
95-100 front
100 to 110psi back


Going from 23 to 25 mm is only a 8.6% difference in width, but it makes about an 18% difference in tyre volume.

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Derny Driver
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Re: Correct tyre size and psi?

Postby Derny Driver » Thu Jan 18, 2018 8:17 pm

madmacca wrote:
Going from 23 to 25 mm is only a 8.6% difference in width, but it makes about an 18% difference in tyre volume.

Did you measure that yourself, or did a tyre manufacturer tell you?

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Re: Correct tyre size and psi?

Postby Thoglette » Thu Jan 18, 2018 10:33 pm

Derny Driver wrote:
madmacca wrote:Going from 23 to 25 mm is only a 8.6% difference in width, but it makes about an 18% difference in tyre volume.

Did you measure that yourself, or did a tyre manufacturer tell you?

That'd be basic math :-) And 32 to 23 is almost double. Now whether the tyres are the width printed on the sidewalls is another matter all together.
At 74kg you don't need 110psi. Somewhere there's some charts comparing weight-on-wheel to pressure for the "magic" 15%.
Derny Driver wrote:Looks like some of these big boys running 28s at 60psi will need to pump up their tyres!!

As DD points out you could run a whole lot less than the 15% figure but it increases the risk of pinch flats. The limit is when you start to get squirm => tyre roll off. I'm about the same weight and can get down to 60psi on 23mm before it gets ugly.

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RobertL
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Re: Correct tyre size and psi?

Postby RobertL » Fri Jan 19, 2018 10:23 am

Gatorskins will give a fairly firm ride too, because they have a pretty tough sidewall construction. I changed from 25mm Gatorskins to 25mm GP4000s and the ride is much more comfortable - almost to the point of being a bit bouncy in comparison.

If I was you, I would keep those tyres until they wear out and then think of changing size. Personally, I would cope with them and not spend the extra $$ now replacing perfectly serviceable tyres.

Also, you probably don't need to pump them up every single day. Once or twice a week should be fine.
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robbiepapenfus
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Re: Correct tyre size and psi?

Postby robbiepapenfus » Fri Jan 19, 2018 10:29 am

Thanks for the advice!

I will definitely keep the the current 23's on my bike. This morning i put 95psi in the front and 105 in the back.. it was a much softer ride.

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foo on patrol
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Re: Correct tyre size and psi?

Postby foo on patrol » Fri Jan 19, 2018 11:25 am

madmacca wrote:
Derny Driver wrote:Just to p1$$ everyone else off, Im saying
Stick with 23s. 2mm makes FA difference
95-100 front
100 to 110psi back


Going from 23 to 25 mm is only a 8.6% difference in width, but it makes about an 18% difference in tyre volume.


That's not correct, because not all brands measure the same size. :wink:

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defy1
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Re: Correct tyre size and psi?

Postby defy1 » Fri Jan 19, 2018 12:03 pm

robbiepapenfus wrote:
defy1 wrote:im 70kgs, I did ride 23s at 110psi, 25s at 100
and now 28s at 80-90psi
28s are the best by far


Best in what respect? Puncture resistance and softer ride?


Comfort and grip. The harshness of imperfect asphalt is smoothed out. Grip around corners is amazing.

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rodneycc
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Re: Correct tyre size and psi?

Postby rodneycc » Fri Jan 19, 2018 1:54 pm

I tend to go with the below:
13mm rim - 23mm (or less I don't think I've ridden 13mm or maybe a long time ago)
15mm rim - 23/25mm (23mm is more aero according to the science)
17mm rim - 25/28mm (25mm pref)
19mm rim - 25/28mm (not much in it more likely a frame clearance issue which makes the decision).
Also can depend on your tyre manufacturer of choice.
Pressures are subject to weight and riding conditions I find.
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singlespeedscott
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Re: Correct tyre size and psi?

Postby singlespeedscott » Sat Jan 20, 2018 4:16 pm

Toss the tatterskins, worlds worst tyre.

Get some good quality 25mm, or 28mm if they will fit your frame, tyres from Conti, Vittoria, Veloflex, Challenge, Schwalbe, Compass, or Panaracer. They will roll a lot better on both smooth and rough surfaces.

Get some Orange Seal in your tubes to deal with flats.

At 78 kg I run 80 psi in the back and 60 psi in the front with my old 25mm Vittoria SC tyres. Never had a pinch flat and I ride some pretty ordinary roads as well as some dirt. On high speed descents I have no issue with tyre roll either just plenty of braking and cornering grip.
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g-boaf
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Re: Correct tyre size and psi?

Postby g-boaf » Sat Jan 20, 2018 5:47 pm

singlespeedscott wrote:Toss the tatterskins, worlds worst tyre.

Get some good quality 25mm, or 28mm if they will fit your frame, tyres from Conti, Vittoria, Veloflex, Challenge, Schwalbe, Compass, or Panaracer. They will roll a lot better on both smooth and rough surfaces.

Get some Orange Seal in your tubes to deal with flats.

At 78 kg I run 80 psi in the back and 60 psi in the front with my old 25mm Vittoria SC tyres. Never had a pinch flat and I ride some pretty ordinary roads as well as some dirt. On high speed descents I have no issue with tyre roll either just plenty of braking and cornering grip.


Bingo, Gatorskins are rubbish. But, they do seem to work out as a trainer tyre if you have one of those old school tyre on roller type trainers. Amazingly, they last longer than those special trainer tyres.

If someone does a lot of riding on rough bike paths/shared paths or very bad roads, then 25mm makes sense.

But I used them overseas in the mountains and they worked out fine as well. Didn't have a puncture at all the whole time.

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