gp4000s 28mm on 21mm internal widht rims + 70kg rider ==> tyre pressure?

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Delorre
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Joined: Sat May 24, 2014 12:09 pm

by Delorre

Hi guys, until now, I've always used gp4000s 23mm tyres. On my roval 32 wheels, they are around 26mm wide and with my weight and normal use (mostly bad Belgian roads), I put around 90psi in it. On such wide rims, I know I should use 25mm conti's for optimum confort, but I prefer the 23's for regular use all year around.

Now, as my Endurace came with 28mm conti's (that I never used) and I will ride the tourist version of E3 Harelbeke (something like RVV) this weekend, I put the 28's back on the wheels to give it a try, given there are several cobblestone sections, flat and uphill, but also extended periods of just normal roads.

I was thinking to use 65psi at the back and 60psi at the front. Does this seem OK for a 70kg rider?

by Weenie


NovemberDave
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by NovemberDave

That should be plenty. The 28s will likely be comfortably wider than 30mm, so it's even possible you'll find that firm at your weight, but it's not a bad starting point.

Enjoy the ride!

Marin
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Location: Vienna Austria

by Marin

Agreed, you could go even lower. The 28 Contis were 31mm on my 18c rims, so they'll be enormous on your Rovals.

I'm riding 28mm tires at 4.5 bars at 77kgs, so going lower would probably be ok for you.

However... Conti GP 4000s II are among the least comfortable tires around, no matter the size.
A 25 Corsa G+ will be *much* smoother than a 28 Conti.

Delorre
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by Delorre

OK, will do a few tests this evening on a (not to bad, unfortunately) cobble section not far away from my home, starting with my intended 60F/65R. As there are also lots of normal roads, it's not PR after all, I don't want to go too low.

Delorre
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by Delorre

Marin wrote:Agreed, you could go even lower. The 28 Contis were 31mm on my 18c rims, so they'll be enormous on your Rovals.

I'm riding 28mm tires at 4.5 bars at 77kgs, so going lower would probably be ok for you.

However... Conti GP 4000s II are among the least comfortable tires around, no matter the size.
A 25 Corsa G+ will be *much* smoother than a 28 Conti.


They are really HUGE on the Rovals, will measure them when I have a caliper at hand. But really no clearance problems with the Endurace. Could still go up a few tyre sizes without problem.

Delorre
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by Delorre

Back home from a short ride over carefully choosed bad roads and 2 cobblestone sections (in worse condition than I remembered from years ago). Conclusion:

-60F/65R is spot on for a mixed use. Could have gone lower for the cobbles, but the 'normal' ride would suffer from it.
-Real peace of mind, you don't have to look were you put your wheels, you don't have to look for the best patches of road, no, you go straigh on and roll over everything.
-first time in my life that cobbles are (more than) bearable
-you definitively feel the +130gr rotational weight every time you have to accelarate and when you go uphill
-On higher speed (35 km/h and more), you feel the bike is a little slower than with 23mm tyres (26mm in relality)
-avg Stages power of the ride went up again vs the 23mm tyres for a comparable avg speed. Conditions are off course never the same, but 205w avg for a little more than 30km/h avg is high in my book. I already noticed the thing when I swith between the Addict and the Endurace (10 à 15w difference between both bikes with the same Stage crank I switch over from bike to bike) with almost the same tyres (Force Attack on the Scott, 4000s on the Endurace), but the difference has never been that big between both bikes.

Delorre
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Joined: Sat May 24, 2014 12:09 pm

by Delorre

Small update after today's ride, with lots of cobbles. Everything went very well and it was a confirmation of yesterday's testing. Pressure was spot on for everything but the badest cobbles (especially uphill, were I sometimes wished I had a little less pressure), but otherwise, I 've never been so comfortable on those small, bumpy farm roads covered with debris, stones, sand, you name it. Only nickpick : the handling of the bike has become 'endurance' slow with the big tyres. It's a + on those bad roads, but you have to keep that in mind on twisty, fast descends. And although the bike feels slower and heavier, I endend with 32 km/h avg on 120km with lots of RVV climbs and sections. Given the roads used, not sure I would have been faster with my hardcore racer.

For those interested : tyres are 31,6mm wide and 29mm high @60psi. Once stretched a little, that will be something like 32mm wide :o

russianbear
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by russianbear

Thanks for posting about how wide the 23mm tires are on those wheels. Cements my choice. Can't believe I'm going back to 23mm tires hah.

Delorre
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by Delorre

My conti gp4000s 23 tyres are 26,5 mm wide on the Rovals, and wider than my dad's 25mm on older Campa Zonda wheels. Don't have the height in mind anymore, sorry, but dad's 25 mm are taller. Unless you ride very bad roads, those 23mm are a really good match for the Rovals, with a smooth transition between tyre and rim.

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mpulsiv
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by mpulsiv

Delorre wrote:My conti gp4000s 23 tyres are 26,5 mm wide on the Rovals, and wider than my dad's 25mm on older Campa Zonda wheels. Don't have the height in mind anymore, sorry, but dad's 25 mm are taller. Unless you ride very bad roads, those 23mm are a really good match for the Rovals, with a smooth transition between tyre and rim.


Don't worry about smooth transition from tire to rim too much. Per wind tunnel data, its ~ 0.9 watt to go from 23mm to 25mm. Instead, focus on comfort, grip and rolling resistance on wider tires. Every time you pick a water bottle from cage and take a sip, it cost you ~ 20 watts.

I run 28mm GP4000S on my endurance bike and 25mm on my race bike. You could not pay me enough to go back to 23mm tires! Industry is moving at full speed to increase tire clearance on all road bikes. Needless to say the wave of modern rim profile. In 2-3 years, 23mm will be at scarcity.
Racing is a three-dimensional high-speed chess game, involving hundreds of pieces on the board.

:arrow: CBA = Chronic Bike Addiction
:arrow: OCD = Obsessive Cycling Disorder

by Weenie


Delorre
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Joined: Sat May 24, 2014 12:09 pm

by Delorre

mpulsiv wrote:
Delorre wrote:My conti gp4000s 23 tyres are 26,5 mm wide on the Rovals, and wider than my dad's 25mm on older Campa Zonda wheels. Don't have the height in mind anymore, sorry, but dad's 25 mm are taller. Unless you ride very bad roads, those 23mm are a really good match for the Rovals, with a smooth transition between tyre and rim.


Don't worry about smooth transition from tire to rim too much. Per wind tunnel data, its ~ 0.9 watt to go from 23mm to 25mm. Instead, focus on comfort, grip and rolling resistance on wider tires. Every time you pick a water bottle from cage and take a sip, it cost you ~ 20 watts.

I run 28mm GP4000S on my endurance bike and 25mm on my race bike. You could not pay me enough to go back to 23mm tires! Industry is moving at full speed to increase tire clearance on all road bikes. Needless to say the wave of modern rim profile. In 2-3 years, 23mm will be at scarcity.


My 23mm tyres are well worn, next set will be 25mm ones, we will see how I like them. Thing is, for the moment, the Endurace is sitting in the living room most of the time, my Scott being the 'good' bike I use now for general riding. And that one still rolls on a Force/Attack combo :lol: , wrapped around 24mm Bora's. Will also try the 25mm ones on the Scott for 1 or 2 ridesnas soon as I get the 25mm for the Endurance.

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