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Spitfire Lock-Ins 99 Duro

When it comes to skate wheels, Spitfire has held it down since day one. As one of the most dominant wheel brands in the market, Spitfire has seasoned experience in developing the best wheel formulas that can handle heavy shredding. Not to mention, they also have a stacked team (Andrew Reynolds, Kyle Walker, Ishod Wair, AVE, Luan Oliveria to name a few) who can put these wheels to the ultimate weartest, and give constructive feedback on how to make the wheels even better.

When it comes to developing the perfect set of wheels for skating, there are a couple factors that need to be considered. Material is of the utmost importance, and currently the industry standard is the use of a plastic called polyurethane. The advantage of using polyurethane is the ability to control the variation of hardness; this means with different blends, the wheels can be fine-tuned to achieve different skateboarding performance properties like slide ability, response, and durability. The wheel size also has a lot of influence on the physics of skateboarding. The wheels, in combination with the trucks, define the total height of the board from the ground. Similar to what we mentioned with high trucks, thicker wheels also contribute to the large distance your tail has to travel to hit the ground to pop a trick. Although it’s a small difference in millimeters, thicker wheels mean the tail has a longer time to smack the ground, which also means the nose is at a steeper angle in the air; in theory, this makes for a higher pop as long as you have the physical strength in your legs to blast a quick and high pop. The hardness of wheels are measured on a durometer scale. Softer wheels are perfect for rough grounds because they absorb and dampen the impact from uneven surfaces or cracks in the ground. Softer wheels also offer a lot of grip but do not have a comparable response and quickness compared to harder wheels. Hard wheels (99A – 101A), on the other hand, are perfect for slides and speed. They do not adapt well to uneven surfaces but do offer excellent slide properties, which makes them perfect for technical skating. The last and perhaps most important factor to consider in making skateboard wheels is the susceptibility to flatspotting. There’s always a big discussion about flat spots. Flatspots are dependent on the type of skating, and currently in the industry, there is no 100% flatspot safe wheel option. Companies always try to develop polyurethane based recipes that try to prevent flat spot and although some work well, there is no 100% guarantee.


We tried out the Spitfire Wheels Formula Four 53mm 99Duro set. At 99Duro, the wheels were made out of a softer urethane blend. The differences between 101Duro hardness blends are minimal, but the 99 Duro does offer more control on different surfaces since the softer material compound has better grip for similar speed properties. Our wheels were 53mm, which is a good medium thickness for high trucks; this combination ensures that wheel bite isn’t a problem. Formula Four is a special polyurethane blend developed by Spitfire to combat against flatspotting, but the real highlight of this wheel is the new special shape termed “Lock-Ins”. The concept stems from slipping out on round ledges when grinding because the inside surface of the wheels are also symmetrically round. When the round wheel touches with the round ledge, the control behind holding the grind is much harder. Spitfire’s Lock-In wheels are designed asymmetrically; while the outside of the wheel is round, the inner is shaped with a straight line. This was noticeable when we put the wheels to the test by skating round ledges; we could not only feel better control in grinding from the lock-in but could also hear the difference in sound as well when the wheel and ledge made contact.

Other than the lock-in design, we tested out the susceptibility to flatspotting. From power slides, to lipslides, and blunts, our test showed that the Formula Four blend had really good resistance for flatspots compared to the other Spitfire wheels we’ve tried. After shredding them up for a while with a bunch of power slides, one wheel eventually got a small flat spot. As we said, no wheel is 100 percent safe from flatspotting, but Spitfire’s Formula Four Lock Ins are damn close.

1 Comment
  • Cornelia Ulrich
    September 6, 2021

    Ich benötige für meinen Enkel unbedingt Lock ins in 99-101 A 51- 52 mm.(blau) .Wie komme ich daran und woher?

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