tranny for drop

Dace · 03-09-2007, 08:18 PM

Just working on a trail up here in Summerland and I was wondering how much space betwen the drop and the start of the tranny and how steep should a tranny be for a drop, is there a formula for this at all?

brotay · 03-09-2007, 10:00 PM

How high is the drop and how fast are you going to be going off the drop? I'll give two examples of what I would do:

1. If the drop is ten feet high and your going to creep off of it, build the tranny steep and about half the height of the drop out from the take off. So ten foot high drop, slow speed, build tranny steep and about 5 feet from take off of drop.

2. If the drop is ten feet high and your gonna rip off of it, build the tranny not so steep and about the same length as the height of the drop. If your gonna go fast off a drop you don't want a super steep tranny because you run the risk of overshooting. So ten foot high drop, fast speed, build tranny long and semi sloped and about ten feet from drop take off.

Another thing when building trannies. Build them long. A bike length tranny can be dangerous if your guinea pigging a new drop. Two bike lengths is perfect.

Personally it's all feel when I build drops and jumps. If it looks wrong, it probably is wrong. Just skope the landing from the take off of the drop and take into consideration what speed you'll be going. Slow = close tranny, Fast = far tranny. Tossing a rock off the take off seems to be popular to finding where you should land

but that can be somewhat inaccurate.

To answer your question specifically the Physics Equation is:
x = vt where x is the horizontal distance in meters (distance of tranny from take off), v is the horizontal velocity in meters per second (your speed at take off), and t is time in the air in seconds.

Finding t is simple as well. t = square root(2y/g) where y is the vertical distance in meters (the drops height) and g is the constant gravity (9.8 m/s²).

Everything has to be in meters and seconds for these equations to work!

To put that to the test let's say your going 3 m/s off a 3 meter high drop. So we have the horizontal velocity and the height of the drop. We're trying to find x. We have v, v = 3 m/s, but we need t. So to solve for t we put in the height of the drop, 3 meters, into the equation above.

Square root of ((2*3)/9.8 = Square root of (6/9.8 = about 0.8 seconds. We now have t, t = 0.8 seconds. You'll be in the air for a little less than a second off a 3 meter drop.

So now substitute 0.8 for t and 3 for v.

x = 3*0.8 = 2.3 meters. Convert that into feet and you have your answer. So for a 3 meter (approx 10 feet) high drop you want to build the tranny about 2.3 (approx 7.5 feet) out from the drop going a speed of about 3 meters per second. 3 meters per second is somewhat fast so this would be the case of building a drop with a further out tranny.

Hope that answers your questions

Dace · 03-09-2007, 10:59 PM

Ha! That was an excellent answer really helps me out as I am new to this, the equation is great too! Sort of 2 questions here.......1. do most people prefer a drop that you can just nudge off of or one that you can fly off of? 2. I'm guessing mabye a little more than a bike length is on the part leading up to the drop itself is enough for a steep tranny, but would you say 3 bike lengths is a good distance for one you can fly off of or is two enough?

Thnx!

heckler · 03-09-2007, 11:11 PM

it all depends on the type of trail. If it's A-line, you want a fast drop. If it's a techy trail with slow corners, you want a slower drop

trail worker · 03-09-2007, 11:33 PM

just roll a rock off the end at riding speed, you can usually get a good idea where the tranny should be.

heckler · 03-10-2007, 12:11 AM

Quote:

Originally Posted by trail worker

just ghost ride your buddies bike off the end at riding speed, you can usually get a good idea where the tranny should be.

corrected.

henry11106 · 03-10-2007, 12:17 AM

what I do is just stand on the end of the take-off and look at where the tranny feels like it should be.

first I do some mock approaches on foot (or bike) to get a feel for how you will be hitting the gap/drop etc. a big aspect is how fast you will be moving after the section before the hit, and how much room there is after you land.

faster = longer gap.

as for angle, lay out some logs to get an idea of the shape of the tranny.
then stand on the end of the launch and look at where the top of the landing will be. adjust the logs so that you can just barely look down the top of the landing surface from the take-off.

build the tranny around the shape you end up with.

keep in mind:

steeper = lighter landing and more effective speed transfer, but easier (and nasty) to over-shoot.

flatter = heavier and less speed on the run-out.

this is what I consider to be ideal for jumps/drops with flat or slightly up-hill launches, but the angle of the lip plays a big part of this. steeper take-offs need steeper landings. down-hill drops need flatter-looking landings.

tossing a rock is a good way to get a rough estimate of the arc of the jump. just throw with the angle of take-off and watch how it lands.

and be sure to have a smooth transition to flat ground, or it will feel heavy.

ride and build enough and you will get a pretty good feel for this, then it's all easy.

8Flat8_Ryder · 03-10-2007, 02:24 AM

My suggestion is read IMBA's trail solutions book and get the new book that will be out shortly and Talk to Jay Hoots.

brotay · 03-10-2007, 05:28 AM

Quote:

Originally Posted by Dace

Ha! That was an excellent answer really helps me out as I am new to this, the equation is great too! Sort of 2 questions here.......1. do most people prefer a drop that you can just nudge off of or one that you can fly off of? 2. I'm guessing mabye a little more than a bike length is on the part leading up to the drop itself is enough for a steep tranny, but would you say 3 bike lengths is a good distance for one you can fly off of or is two enough?

Thnx!

Your welcome man. This is a pretty winded explanation, I was bored haha. But listen to the other guys too, it's all about feel, I mean, the rock throwing (or bike tossing, thanks Heckler) technique works just as well as anything else. It doesn't have to be perfect but it has to work right. Good luck with your future trail building!

brotay · 03-10-2007, 05:29 AM

Quote:

Originally Posted by 8Flat8_Ryder

My suggestion is read IMBA's trail solutions book and get the new book that will be out shortly and Talk to Jay Hoots.

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Dace · 03-10-2007, 07:36 AM

Originally Posted by 8Flat8_Ryder
"My suggestion is read IMBA's trail solutions book and get the new book that will be out shortly and Talk to Jay Hoots."

Or, I could just post on nsmb and get like 4 experienced trail builder replies for free in like 6 hours.....leaves me time to build and have a nice brew in the forest...o.k., which leads me to my next noob question for a gap jump, any rules apply there on distance and speed?

Uncle Duke · 03-10-2007, 08:54 AM

Quote:

Originally Posted by heckler

corrected.

lol.

drummer_dil · 03-10-2007, 06:06 PM

just make a super fat and long tranny, like wayy wayy waaaay over kill and you will be fine. then the drop will be smooth and you wont have to worry about landing to flat

Uncle Duke · 03-10-2007, 06:16 PM

i like your style.

trail worker · 03-12-2007, 01:36 AM

Quote:

Originally Posted by 8Flat8_Ryder

My suggestion is read IMBA's trail solutions book and get the new book that will be out shortly and Talk to Jay Hoots.

While great for building "by the book" trails, IMBA's guide is far from a great source of trailbuilding info in my opinion. There is simply no substitute for getting out there and finding out what works and what doesn't in a given area. BC is a far cry from southern california for example, and the transition you will need on a drop with a gnarly tree and rock infested runout is different than building a transition big enough to land a jet fighter on at the whistler bike park.
The same goes for the trail cutting, benching and switchback guide they use, theres alot of talk, but not much about different applications in different areas.
Just my .02, but that book is somewhat of a pet peeve of mine after reading it and discussing it with a few other experienced builders. Lots of great information in there but theres alot of crap that doesn't actually apply to real world mountain biking.

03-09-2007, 08:18 PM	#1
Dace Deep6 Join Date: Nov 2006 Location: Ocean Grove Posts: 33 Rep Power: 0	tranny for drop Just working on a trail up here in Summerland and I was wondering how much space betwen the drop and the start of the tranny and how steep should a tranny be for a drop, is there a formula for this at all?

03-09-2007, 10:00 PM	#2
brotay Bustin' Tables! Join Date: Feb 2006 Location: Surrey Posts: 404 Rep Power: 320371	How high is the drop and how fast are you going to be going off the drop? I'll give two examples of what I would do: 1. If the drop is ten feet high and your going to creep off of it, build the tranny steep and about half the height of the drop out from the take off. So ten foot high drop, slow speed, build tranny steep and about 5 feet from take off of drop. 2. If the drop is ten feet high and your gonna rip off of it, build the tranny not so steep and about the same length as the height of the drop. If your gonna go fast off a drop you don't want a super steep tranny because you run the risk of overshooting. So ten foot high drop, fast speed, build tranny long and semi sloped and about ten feet from drop take off. Another thing when building trannies. Build them long. A bike length tranny can be dangerous if your guinea pigging a new drop. Two bike lengths is perfect. Personally it's all feel when I build drops and jumps. If it looks wrong, it probably is wrong. Just skope the landing from the take off of the drop and take into consideration what speed you'll be going. Slow = close tranny, Fast = far tranny. Tossing a rock off the take off seems to be popular to finding where you should land but that can be somewhat inaccurate. To answer your question specifically the Physics Equation is: x = vt where x is the horizontal distance in meters (distance of tranny from take off), v is the horizontal velocity in meters per second (your speed at take off), and t is time in the air in seconds. Finding t is simple as well. t = square root(2y/g) where y is the vertical distance in meters (the drops height) and g is the constant gravity (9.8 m/s²). Everything has to be in meters and seconds for these equations to work! To put that to the test let's say your going 3 m/s off a 3 meter high drop. So we have the horizontal velocity and the height of the drop. We're trying to find x. We have v, v = 3 m/s, but we need t. So to solve for t we put in the height of the drop, 3 meters, into the equation above. Square root of ((23)/9.8 = Square root of (6/9.8 = about 0.8 seconds. We now have t, t = 0.8 seconds. You'll be in the air for a little less than a second off a 3 meter drop. So now substitute 0.8 for t and 3 for v. x = 30.8 = 2.3 meters. Convert that into feet and you have your answer. So for a 3 meter (approx 10 feet) high drop you want to build the tranny about 2.3 (approx 7.5 feet) out from the drop going a speed of about 3 meters per second. 3 meters per second is somewhat fast so this would be the case of building a drop with a further out tranny. Hope that answers your questions __________________ If we hit that bullseye, the rest of the dominos will fall like a house of cards. Checkmate. Last edited by brotay; 03-09-2007 at 10:17 PM.

03-10-2007, 12:17 AM	#7
henry11106 chainsaw-wielding zealot Join Date: May 2005 Location: Coquitlam Posts: 698 Rep Power: 1131	what I do is just stand on the end of the take-off and look at where the tranny feels like it should be. first I do some mock approaches on foot (or bike) to get a feel for how you will be hitting the gap/drop etc. a big aspect is how fast you will be moving after the section before the hit, and how much room there is after you land. faster = longer gap. as for angle, lay out some logs to get an idea of the shape of the tranny. then stand on the end of the launch and look at where the top of the landing will be. adjust the logs so that you can just barely look down the top of the landing surface from the take-off. build the tranny around the shape you end up with. keep in mind: steeper = lighter landing and more effective speed transfer, but easier (and nasty) to over-shoot. flatter = heavier and less speed on the run-out. this is what I consider to be ideal for jumps/drops with flat or slightly up-hill launches, but the angle of the lip plays a big part of this. steeper take-offs need steeper landings. down-hill drops need flatter-looking landings. tossing a rock is a good way to get a rough estimate of the arc of the jump. just throw with the angle of take-off and watch how it lands. and be sure to have a smooth transition to flat ground, or it will feel heavy. ride and build enough and you will get a pretty good feel for this, then it's all easy. __________________ Disclaimer: the above text is in no way or form intended to harm you. if by any chance you are offended by it, please take a moment to Harden the F* Up. thank you. "Trust that little voice in your head that says, 'wouldn't it be interesting if...'; and then do it." -Duane Michals FOR SALE: NEW Small/med KBC Moto/ATV/MTB Helmets - $70!!! WANTED: Argon cylinder! 55-125cf also WANTED:** SRAM Rear Derailleur. AND 2.35" 60a hard rubber MTB tire.

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03-09-2007, 10:59 PM	#3
Dace Deep6 Join Date: Nov 2006 Location: Ocean Grove Posts: 33 Rep Power: 0	Ha! That was an excellent answer really helps me out as I am new to this, the equation is great too! Sort of 2 questions here.......1. do most people prefer a drop that you can just nudge off of or one that you can fly off of? 2. I'm guessing mabye a little more than a bike length is on the part leading up to the drop itself is enough for a steep tranny, but would you say 3 bike lengths is a good distance for one you can fly off of or is two enough? Thnx!

03-09-2007, 11:11 PM	#4
heckler skookum Join Date: Oct 2003 Location: The Darkside Posts: 14,542 Rep Power: 13158808	it all depends on the type of trail. If it's A-line, you want a fast drop. If it's a techy trail with slow corners, you want a slower drop

03-09-2007, 11:33 PM	#5
trail worker bikes on the brain Join Date: Nov 2002 Location: West Kootenays Posts: 5,771 Rep Power: 8773456	just roll a rock off the end at riding speed, you can usually get a good idea where the tranny should be.

03-10-2007, 02:24 AM	#8
8Flat8_Ryder Student of Freetardness Join Date: Jan 2006 Location: On my bike Posts: 893 Rep Power: 0	My suggestion is read IMBA's trail solutions book and get the new book that will be out shortly and Talk to Jay Hoots.

03-10-2007, 07:36 AM	#11
Dace Deep6 Join Date: Nov 2006 Location: Ocean Grove Posts: 33 Rep Power: 0	Originally Posted by 8Flat8_Ryder "My suggestion is read IMBA's trail solutions book and get the new book that will be out shortly and Talk to Jay Hoots." Or, I could just post on nsmb and get like 4 experienced trail builder replies for free in like 6 hours.....leaves me time to build and have a nice brew in the forest...o.k., which leads me to my next noob question for a gap jump, any rules apply there on distance and speed?

03-10-2007, 06:16 PM	#14
Uncle Duke goes around comes around Join Date: Dec 2003 Location: ziration nation Posts: 7,378 Rep Power: 16669757	i like your style.