The Maxxis Ikon eXCeption Silkworm 29 x 2.2 is a performance cross-country mountain bike tire with a folding bead, 120 TPI casing, and 62a rubber compound. According to Maxxis, these two combined (120 TPI + 62a Compound) results in an "eXCeption" tire. On top of that it has "Silkworm Technology" which is an "exclusive material incorporated into the casing" to increase puncture and tear resistance. Together it should result in a long lasting, low rolling resistance tire. Let's find out how fast this tire really is.
The tire is made in Taiwan and seems well made. While unpacking the tire I immediately noticed it has a very stiff tread although the side walls are quite flexible, this probably is because of the Silkworm protection under the tread. I did have an issue with the packaging, which made it unclear which tire I received. The packaging showed specifications for a 60TPI tire and nowhere did it say anything about eXception or Silkworm except for a small sticker with a part number and "120 TPI". The tire itself does have the 120 TPI and Silkworm logos so I'm sure it's the right tire.
|Model||Ikon eXCeption Silkworm|
|Supplied By||Bought in store|
|New or Used||New|
|Specified Weight||560 grams|
29 x 2.20
26 x 2.20
Size and Weight Measurements
|Size and Weight Measurements (Bike Wheel: 622-17C, Pressure: 35 psi / 2.4 bar)|
|Specified Weight||560 grams|
|Measured Weight||583 grams|
|Measured Width Carcass||52 mm|
|Measured Width Tread||51 mm|
|Measured Height||53 mm|
|Measured Knob Height Center||2.5 mm|
|Measured Knob Height Edge||3.8 mm|
|Measured Total Thickness Sidewall|
|Measured Total Thickness Center (excluding knobs)|
The real measured weight is 583 grams, which is 23 grams more than specified. Volume wise it doesn't impress with a width of 52 mm and a height of 53 mm on a 17C rim which is slightly small for a 2.2 sized mountain bike tire. Knob height of the central knobs is 2.5 mm, knob height at the edge of the tire is 3.8mm. This is a typical knob height for a fast cross-country MTB tire.
Rolling Resistance Test Results
|Rolling Resistance Test Results (Speed: 29 kmh / 18 mph / 8 m/s, Load: 42.5 kg / 417 N)|
|Inner Tube||Conti MTB 29 (225 gr butyl)|
|Rolling Resistance 55 psi / 3,8 Bar||
|Rolling Resistance 45 psi / 3,1 Bar||
|Rolling Resistance 35 psi / 2,4 Bar||
|Rolling Resistance 25 psi / 1,7 Bar||
|Use the formula: RR (watts) = CRR * speed (m/s) * load (N) to calculate rolling resistance at a given speed and load|
Rolling resistance is very high, I totally did not expect this from a mountain bike tire with such a fast profile. At an air pressure of 25 psi, rolling resistance is 38.2 watts. When we compare this to, for example, a Racing Ralph or Race King, Rolling resistance per tire is 15 watts higher! That's pretty insane.
Puncture Resistance Test Results
|Puncture Resistance Test Result (higher is better)|
|Puncture Resistance Tread||7|
|Puncture Resistance Sidewall||4|
Also not expected is the average puncture resistance. The silkworm protection doesn't give any better puncture protection than other much faster mountain bike tires. Combined with the very high rolling resistance, I was expecting a puncture resistance score of at least 10 points.
This tire doesn't impress at all. The Silkworm puncture protection doesn't bring much to the table and rolling resistance is very high for a tire with a fast profile and medium knob height. Running a pair of these tires at 25 psi/1.7 bar will cost you about 30 watts when compared to a Race King or Racing Ralph mountain bike tire, that's 15% of the power of an average cyclist vaporized!
This tire costs way too much money, you're paying premium prices while "performance" line tires from other brands are better in all respects. Don't get fooled by low rolling resistance marketing!
VERDICT: Not Recommended