Zipp RollingRoad shows why 303 Firecrest recommended tire pressures are so low

Written by Zach Overholt Jul 06, 2020 1:48 p.m. ET

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Recently, the Zipp 303 Firecrest wheels got a big upgrade. The newest version is faster, lighter, and wider than before and with that comes a new recommended tire pressure chart. Compared to what most riders are used to running, the recommended pressures are low. Really low. With wider rims meant for wider tires, even the heaviest riders are recommended to stay well under 100 psi.

Zipp RollingRoad Tire pressure recommendations — Note that these pressures are only recommended if you’re using the new wider 303 Fire Crest wheels. Otherwise, use Zipp’s tire pressure calculator here.

Why So Low?

Tyler went into great detail on the original post, but one of the biggest changes to the rim design was a much wider profile with a 25mm internal width with a hookless bead. That allows a wider tire to better fill in the gap between the edge of the rim and the tire allowing for smoother airflow and better aerodynamics.

But more importantly, the wider rim and wider tire results in a wider and shorter tire contact patch. That results in reduced tire sag, which has been tested to improve the rolling resistance since the tire is deforming less. Note that the contact patch is still the same size, but the shape has changed. With less efficiency lost to the tire deformation, the thought is that you can get away with lower pressures which have a big advantage…

Zipp RollingRoad

… as proven by the Zipp RollingRoad. Essentially a cobblestone treadmill, the RollingRoad helped Zipp to visualize what effect tire pressures have on whole-body vibration. Based on their data from the RollingRoad tests, Zipp found that the difference between ultra-low and high pressure can be as much as 50 watts. That’s 50 watts that you stand to gain by moving to a wider tire on a wider rim while riding at 20mph over various surfaces. Compared to the usual wattage savings touted by aerodynamic components, that’s huge.

For more on Zipp’s Total System Efficiency, check out the link below.

sram.com

Zach Overholt

5,633 articles

Zach Overholt is the Editor in Chief of Bikerumor. He has been writing about what’s new in the bicycle world for 12+ years. Prior to that, Zach spent many years in the back of a bicycle shop building and repairing nearly every type of bike, while figuring out how to (occasionally) ride them.

Based in Ohio, Zach is now slowly introducing a new generation to cycling and still trying to figure out how to fit the most rides into a busy schedule as a new dad.

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3 years ago

It’s all cute and shit, but what’s an lsb and a psy?

Michael

3 years ago

“but what’s an lsb and a psy?”
Isn’t he the guy from South Korea that got a lot of press after he released the song Gangnum style.?

Chris

3 years ago

Cool. But can we talk about how many watts it really saves on a typical paved road that doesn’t have rectangular plastic speed bumps every foot? Send it to bicyclerollingresistance for a real test.

Greg

3 years ago

Reply to Chris

Bicyclerollingresistance isn’t a real test. If anything, this is much more realistic. Bicycle Rolling Resistance and just about every other tire test place use a roller against the tire. Unless you’re only riding over logs, it doesnt translate exactly to the real world. If the roller was as big as the tire (it’s not), then the tire deflection would be equivalent to a wheel half its diameter. That’s one reason why, even with a diamond plate surface, BRR tests show lower and lower resistance numbers as the pressures go up. In the “real world” with a surface as rough as asphalt, the resistance numbers would flatten out and then go back up. The test is still useful, but as always you have to be aware of the test limits.

blahnblahblah

3 years ago

Reply to Greg

but this is not really a test either, is more likely marketing bs to justify designing a cheap to manufacture rim were the the tire will blow of a pressures above 70 or so psi

Jon D

3 years ago

I foresee people taking these claims about performance on a very bumpy surface and arguing they mean something on relatively normal tarmac.

Brad Comis (@BradComis)

3 years ago

Reply to Jon D

Tom Anhalt has already done some testing on this. Check out his blog for the results. I believe Silca has some info on this too as does Bicycle Quarterly

Lyford

3 years ago

Reply to Brad Comis (@BradComis)

https://blog.silca.cc/part-4b-rolling-resistance-and-impedance

Pressures on rough pavement

Shafty

3 years ago

Reply to Brad Comis (@BradComis)

It’s great they made a chart, but no way am I getting away with 56psi without wearing out my sidewalls or getting pinch flags at the first real pothole. I call BS on this as anything more than MINIMUM pressures. Fine, the tire is retained at that low pressure, but you’ll never ride any distance with that setup without issues.

john

3 years ago

Reply to Shafty

Remember the pressure can be lower when the rim is wider to support it. > running the same low pressure with a 4mm narrower rim will not yield the same results.

James

3 years ago

What happens when you stand up and sprint though

Tom

3 years ago

Reply to James

Well, you wobble a bit!

jednobiegowiec

3 years ago

I’m about 67kg, that goes 148lb. I don’t have fancy-shmancy rims, but I still use 55/60 on tubeless 28c tyres.
No rolling, no burping, no flats, no issues, long distances.
Can’t smell any BS in here, according to my experience.
Cheers!
I.

csr

3 years ago

Delighted to see these numbers – with wide rims and tubed 28c Conti 4000/5000s, my 150lb self is very happy at 55/65 psi on our shitty roads. Smooth ride, no squirm. Pinch flats only if you hit something stupid (like usual). Get a digital gauge and try it for yourself, it’s a dramatic. Might put a few more pounds in when riding hard in a pack, as sometimes the potholes are a surprise.

Mike

3 years ago

Reply to csr

With these new hookless rims you’ll be able to lower those pressures

Aaron

3 years ago

I’d just find a better road to ride on.

SomeGuy

3 years ago

So they proved that riding over a road littered with 1×4 lumber is faster if you have lower tire pressure? That doesn’t say much for standard road conditions.

Dinger

3 years ago

Reply to SomeGuy

Depends where you ride, I guess. The best scenic roads where I ride and race are rarely perfectly smooth. Whenever bumps or road texture can be felt, they’re slowing you down.

These video tests were designed to visually demonstrate the difference between the last gen product and its recommended tire setup and the new one and they do that well.

Yourt

3 years ago

right on! Lbs…. euh…. who cares: i put 83 kg on the scale. And I live in Belgium, Yeah right… the country where you can really test those things. Bicycle Rolling Resistance is synthetic maybe, but with the same parameters (they put a 40 kg load on the wheel, right?) it enables comparing things. We know about MTB 29’ers and passing obstacles, road tyres of 25 at lower pressure,… but this still looks like commercial BS. What’s the reference? How much weight did they put on? How about rolling resistance?

Dave E

3 years ago

They’re for tubeless use only. Not worrying about pinch flats is one of the biggest advantages of tubeless tires/wheels. My wheels aren’t as wide as these (21mm internal, 28mm external), but I’m still running pretty low pressure (60/70) on 28c tires. I weigh 155lbs.

Michael

3 years ago

I think their pressure recommendations are a bit high. I generally run in the 40s on 28mm tires and I weigh 70kg/155lbs. But then again I race CX…and there we run can 17psi in 33mm tires.

Rodrigo Diaz

3 years ago

That is a real concern. I can run very low pressures in some of my wheels but I don’t like how they feel when sprinting or cornering. A good example is CX – I have ended riding around the 27 psi mark because the start and the corners on paved areas (most of our races include at least a bit of a parking lot/packed dirt) were unsatisfactory for my not-very-smooth style.

Same with road wheels, though. I can probably ride my road tires around 60 psi but they feel vague in hard corners. Probably just one of those things you get used to – but I haven’t!

Erik

3 years ago

Actually the chart recommends about 5 psi more than I am comfortably and durably riding right now with 28c GP5000 tires. You have to keep in mind that this chart is for rims with an internal width of 25 mm, so a 28c tire will measure around 31 mm, which is a lot of volume increase (about 25% compared to 28c on 18 mm internal rims).

Scott Yarosh

3 years ago

I ride 60/65psi on 25c GP5000TL on 21mm ID rims. I weight 175 pounds. They feel completely fine during all types of riding.

Richard

1 year ago

I have these rims with 28c pro one on them. Low tire pressure does feel smooth on country side road. But it’s super laggy on smooth pavement. 20mph on flats you’re looking for around 220-230watts I’m 6feet 170lbs.