Road Bike Tire Test: Bontrager R4 320

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  • Bontrager R4 320
Performance compared to all other road bike tires
(100% is best)
Pro Members get 11-point radar charts

Bontrager R4 320 road bike tire on a rolling resistance test machine

The Bontrager R4 320 is a hand-built cotton clincher tire which is used by a lot of road teams that are sponsored by Trek/Bontrager. When used by road teams, rolling resistance is one of the most important criteria and when looking purely at the specifications, this should be their fastest tire. Bontrager further claims the R4 320 to have amazing road feel thanks to its supple cotton casing yet is also extremely durable and puncture resistant thanks to the "Hard Case Lite" protection that is applied under the tread.


After inspecting the R4 320 a bit closer, it looks a lot like a Vittoria Corsa with a different tread glue on. I'm pretty sure at least the casing is made by Vittoria in their factory in Thailand. It's interesting to see if the Bontrager engineers have been able to improve the compound and puncture resistance compared to the Vittoria original that appears to be the gold-standard in cotton tires.

Manufacturer Specifications


Manufacturer Specifications
Brand Bontrager
Model R4 320
Year 2016
Tire Type Tubetype (clincher)
Supplied By Bought in store
New or Used New
Mileage 0 km
Price Range Very High
Buy At
Manufacturer part number
TPI 320
Compound
Bead Folding
ETRTO 25-622
Size Inch 28"
Specified Width (mm) 25
Specified Weight 230 grams
Max Air Pressure (psi) 140
Made In Members Only
Available Sizes 25-622 (700x25C)

Bontrager R4 320 Test Results

Bontrager R4 320 road bike tire on a rolling resistance test machine

Size, Weight, and Thickness Measurements


Size, Weight and Thickness Measurements
Specified Weight 230 grams
Measured Weight 226 grams
System Adjusted Weight
(tire + inner tube (100 gr)
326 grams
Measured Width 25 mm (un-round)
Measured Height 22 mm (un-round)
Total Tire Thickness Center 2.2 mm
Total Tire Thickness Sidewall Members Only
Unmounted Casing Width No Data
Unmounted Tread Width No Data
Tread Cover (Tread / Casing Ratio) No Data
All size measurements are taken at an air pressure of 100 psi / 6.9 bars on a 17.8 mm inner width rim.

The R4 320 is only available in the bigger 25-622 size. Real measured width on a 17C rim, at an air pressure of 100 psi is 25 mm. Although the measured size is very close to the rated size, keep in mind the Vittoria 25-622 tires actually measure closer to 27 mm on a 17C rim. Weight is a bit lower than the specified weight (230 gr) at 226 grams.


The total measured thickness of the tread is 2.2 mm which is slightly less than the Vittoria Corsa G+ (2.4 mm), but thicker than the Specialized Turbo Cotton (2.1 mm) The sidewalls have an average thickness of 0.8 mm which is also in-line with the cotton competition.

Rolling Resistance Test Results


Rolling Resistance Test Results
Inner Tube Conti Race28 (100gr butyl)
Measured Width 25 mm (un-round)
Rolling Resistance
Real tire width in mm:
22-24 = 132 psi/9.1 bar
25-27 = 120 psi/8.3 bar
28-29 = 108 psi/7.4 bar
Ultra High Air Pressure

(120 psi / 8.3 bar)
11.5 Watts
CRR: 0.00345
Rolling Resistance
Real tire width in mm:
22-24 = 110 psi/7.6bar
25-27 = 100 psi/6.9 bar
28-29 = 90 psi/6.2 bar
Extra High Air Pressure

(100 psi / 6.9 bar)
12.2 Watts
CRR: 0.00366
Rolling Resistance
Real tire width in mm:
22-24 = 88 psi/6.1 bar
25-27 = 80 psi/5.5 bar
28-29 = 72 psi/5.0 bar
High Air Pressure

(80 psi / 5.5 bar)
Members Only
Rolling Resistance
Real tire width in mm:
22-24 = 66 psi/4.6 bar
25-27 = 60 psi/4.1 bar
28-29 = 54 psi/3.7 bar
Medium Air Pressure

(60 psi / 4.1 bar)
Members Only
The Road Bike section is a multi tire size section, air pressures have been adjusted to the measured casing width.

All numbers are for a single tire at a speed of 29 km/h / 18 mph and a load of 42.5 kg / 94 lbs.

Use the formula: RR (Watts) = CRR * speed (m/s) * load (N) to calculate rolling resistance at a given speed and load.

In the rolling resistance test, the R4 320 performs very strong and outperforms important competitors like the Vittoria Corsa G+ (read review), Conti GP4000S II (read review) and Schwalbe One V-Guard (read review) by a small margin. Unfortunately, it does get outperformed by the Specialized Turbo Cotton (read review) which is still the fastest (non-tubeless) cotton tire on the market.

Puncture Resistance Test Results

Bontrager R4 320 road bike tire on a rolling resistance test machine
Puncture Resistance Test Results (higher is better)
Total Puncture Score Tread 44 Points
Total Puncture Score Sidewall Members Only
Tread Puncture Force Sharp Needle 10 Points
Tread Puncture Force Blunt Needle No Data
Tread Total Tire Thickness 2.2 mm
Sidewall Puncture Force Sharp Needle Members Only
Sidewall Puncture Force Blunt Needle No Data
Sidewall Total Tire Thickness Members Only

In the tread puncture resistance test, the R4 320 scores 10 points which isn't all that exciting. I do find it interesting to see the Vittoria Corsa G+, Specialized Turbo Cotton and R4 320 to all score very close to each other in the puncture tests. To be exact, the Turbo Cotton scores slightly worse on puncture resistance but has a lower rolling resistance. The Corsa G+ scores slightly better in the puncture resistance tests but has a higher rolling resistance.

Static Grip Test Results


NOTE: Grip test data is only available on tires tested after November 2018. You can find more information about our grip test here: Introducing Grip Testing

Static Grip Test Results
Wet Grip Average No Data
Wet Grip Center No Data
Wet Grip Edge No Data
Grip in points = coefficient of friction * 100

Conclusion


  • Bontrager R4 320
Performance compared to all other road bike tires
(100% is best)

Pro Members get 11-point radar charts

Of the cotton tires, the Bontrager R4 320 seems to slot in right between the Specialized Turbo Cotton (read review) and Vittoria Corsa G+ (read review) in both the rolling resistance, puncture resistance, and tread thickness tests. If you want the fastest (non-tubeless) cotton tire out there, the Specialized definitely is the tire to have. The Vittoria Corsa G+ seems to be a bit stronger and comes with a thicker tread, but has a slightly higher rolling resistance than the R4 320.


If you have to use the R4 320 because you're sponsored by Trek/Bontrager and get these for free, you're probably not leaving much on the table. If I needed some cotton tires and had to pay for them myself, I would probably go for the low rolling resistance Turbo Cotton, or grab the Corsa G+ for the better puncture resistance and lower price.

RATING: 4.0 / 5
TEST VERDICT:
Recommended


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