Dirt jumper bikes are used for jumping and whipping because of the lack of suspension, smaller-sized wheels, and vertical forks and handlebars, these bikes are specific for their own hard roller packs and jumpy tracks, but these are not used for downhills, because they speed of the bike tends to increases on DH trails and riders of the dirt jumpers would not be able to control them when these go out of control. disc brakes and rear and front suspensions on full suspension bikes would play a major role in stopping the bike and decreasing bike speed, but dirt jumper bikes do not have suspensions and disc brakes, these are simply made traditional bikes with a lack of modern features and modern bike parts.
The wheelsets and handlebars of dirt jumpers are exactly not manufactured for DH trails, and the steerer tube would handle these bikes at higher speeds on DH trails. you have to replace or exchange the rims of both front and rear tires with the DH bikes for making the wheelset of the dirt jumpers compatible with the down trails. most dirt jumper bikes are not tubeless, and these tubes are installed in their tires due to which there are more risks and chances of puncturing and flat the inner tubes, you have to carry all the tools and safety kits which include spare tubes, patches, and extra things for repairing punctures on DH trails, which is almost not a better idea to carry all these stuff with dirt jumpers.
Tubeless tires have the big advantage of maintaining and keeping the air pressure of tires at a recommended level, but tube tires at almost higher pressures on DH trails, so it is a big difference and issue for the dirt jumpers, if you are riding with the tube tires on jumpers, upgrade your tires to tubeless to maintain the gravity and gripping of tires on DH trails. also, you have to maintain the speed of your bike with dirt jumper bikes if you are using these bikes for DH trails. you have to p[ull the levers off your brakes after 2 to 3 feet, which is almost irritating, in the end, you will get tired too much by stopping your bike and squeezing of brake levers.
You have to change or replace the fork of the jumper with a DH fork, the height and angle of the DH forks are manufactured for DH bikes which will work much better on dirt jumpers but shorter dirt jumper forks are not recommended for DH trails.
Forks of dirt jumper bikes are smaller and shorter in size and their range is from 100mm to 110mm fork, but for DH trails long forks are mainly used which have 160mm, 170mm, or 175mm in length, and these long and raised forks would give much better grip when you pull the levers of the front brakes, with a shorter mm forks if you are riding at higher speed on DH trails you will jump and fly in the air above the handlebar of your bike and fall of on the ground, it is the reason that longer forks are recommended for downhill and technical trails.
Speed Of Dirt Jumpers On DH trails:
Dirt jumpers also have less speed than DH bikes, because of the lack of suspension and bad braking system, every time when you pull the brakes your bike will start skidding and slipping the front tire but DH bikes are more common in stopping of the bike by pulling the levers of the front brakes.
You have to install new comfortable grips in the handlebar tube for better gripping and handling of dirt jumpers on DH trails, their own grip is not used for the DH.
The frame of dirt jumpers is made in such a way that the bottom bracket is lower than the DH bikes, so a lower BB bike is not recommended for downhills, you have to raise the height of the bottom bracket by cutting the seat tube and the frame tube and again welding, it is not an easy step, you will spend a lot of bucks by doing this upgrade, but simply you can find another frame, if you have any spare frame of hardtail or full suspension bike, it is better to replace dirt jumper frame to increase to avoid big rocks and grown roots of the trails.
Lack Of Cassette And chainring:
Due to the lack f the rear cassette, derailleur, and crankset, the rotating force produced in the wheels by rotating the pedals and cranks of dirt jumpers is greater than the 7-speed and 10-speed bikes, it would also cause a big difference in boosting the speed of bike on DH trails, cassettes, and chainrings of the cranksets would play a big role in maintaining bike speed and for boosting and un-boosting purpose.
Replace the Front Tire Of the Dirt Jumper:
Dirt jumpers have different tires and tread patterns from the DH bikes, almost every time these tires would fail for different trails, and also the width of the front tires is different from the DH tires, so you have to select thicker and wider MTB tires for a dirt jumper, and also make sure the tire would never be skinny and slick in nature, thick combo ad knobby tires are installed in the front wheels of the dirt jumpers for DH trails.
Downhill Technical Trails:
Dirt jumpers are not used to train technical trails which include twisted trails, corner trails, zig-zag trails ad steep downhill trails where you are surrounded by long trees of the forests, almost 80% of the DH trails have long trees which are present o both left and right side of the trails, so the main thing is skills which you need to learn before going on DH trails, you have to master DH trails and learn each and every corner of the trail carefully, then you will be able to ride dirt jumper bikes on DH trails.