Two 120 mm full-suspension cross-country bikes that blur the line between race and downcountry. The Spark RC has TwinLoc three-position suspension and an XC-race geometry; the Trek Top Fuel 9.8 is the Gen 4 refresh with longer reach and slacker angles for descending. Both run 29" wheels and accept 2.4" tires. Geometry and suspension feel decide which one fits your trails.
$3,500 - $12,000
Best for: XC racing and marathon events where climbing efficiency wins
$5,500 - $6,500
Best for: Downcountry riding and one-bike-quiver XC with descending priority
| Aspect | Scott Spark RC | Trek Top Fuel 9.8 |
|---|---|---|
| Reach (M) | 445 mm | 447 mm |
| Stack (M) | 610 mm | 608 mm |
| Head angle | 67.2° | 66° ✓ |
| Travel (rear/fork) | 120 / 120 mm | 120 / 120 mm |
| Bar-mounted lockout | TwinLoc (3-position) ✓ | None |
| Max tire | 2.4" | 2.4" |
| Complete bike weight (top build) | ~10.7 kg ✓ | ~12.0 kg |
| Size count | 4 (S-XL) | 5 (S-XL + M/L) ✓ |
| Measurement | Scott Spark RC | Trek Top Fuel 9.8 | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Size | S | M | L | XL | S | M | M/L | L | XL |
| Stack (mm) | 583 | 610 | 638 | 657 | 580 | 608 | 622 | 638 | 661 |
| Reach (mm) | 425 | 445 | 470 | 490 | 425 | 447 | 470 | 487 | 510 |
Both bikes share size labels (S / M / L / XL) and land within 5 mm of each other on stack and reach at every shared size - so a Spark M and a Top Fuel M put your hands and seat in nearly the same place. The Top Fuel adds an M/L between M and L that the Spark lacks, which matters most for riders between 5'10" and 6'0". Differences are in handling: Top Fuel runs slacker (66° vs 67.2°) for stability, while the Spark stays steeper for snappier XC turn-in.
Pick the Spark RC if you race XC, ride marathon events, or live on climbs where TwinLoc lockout actually pays back. Pick the Top Fuel 9.8 if you love XC efficiency but ride trails that descend faster than you climb. The 1.2° head-angle difference is small on paper but huge on a 30 mph descent.
Trek Top Fuel 9.8 - slacker head angle and the extra M/L size deliver a more relaxed cockpit on descents.
Scott Spark RC - sub-11 kg weight and TwinLoc lockout make it the obvious XC race winner.