# Optimum distance of rollers?



## epic (Apr 16, 2005)

Hey guys, we're looking to build some cool rolling bridging and wondering what the correct distance is to make a set of rollers that will pump well. What is the optimum distance between crests, or how do you determine what it would be?


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## aero901 (Apr 11, 2012)

Spacing depends on how fast the rider is traveling and how big the roller is. 0.5-1.5 seconds between crests is a sensible starting point for pumpable rollers. To figure spacing, multiply the anticipated rider speed by the desired time between crests. Analyzing videos of people riding well built pumptracks will give a good idea of what pump frequency(s) work best.

Example: 
Rider Velocity * Pump Frequency = Roller Spacing

20 kph * 1 s * 0.2778 = 5.6 m

OR

10 mph * 1 s * 1.467 = 15 Feet

_1.467 & 0.2778 are conversion factors to make the units play nice._

The best method would be to find a set of local rollers that ride well and measure riding speed, the time or distance between crests, and the roller height (crest to trough). They can be reproduced in wood with this info. If there are no roller sections around, make a couple in dirt first to test and tweak the spacing/height before building the wooden version.


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## epic (Apr 16, 2005)

That sort of confirms everything I was thinking. I was hoping the answer would be something more like "sixteen feet" though.


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## The Sagebrush Slug (Jan 12, 2004)

epic said:


> That sort of confirms everything I was thinking. I was hoping the answer would be something more like "sixteen feet" though.


16' feet isn't wrong either. 

Actually, I'd argue that 11'-15' is optimal for trail pumps for Joe / Josette Average.

Shorter pumps are harder for beginners, especially at speed. In addition, the tops of short pumps are pronounced enough that they wear faster (e.g., from newbies' pedal strikes.)

Longer is certainly doable as Aero's calculations show, but how many of us really are going to pump something when going 30 KPH / 15 MPH? Or can actually sustain a pump for 1.5 seconds (that's a lot of lift time!)

So as with most things it depends on the audience, and Aero's suggestion to see what else around works is a great way to figure out what the existing audience wants.

All that said, if you're looking at slower speed then 10'-13' might be better, and of course wood won't have the wear issues of dirt. But you do want to avoid the risk of pedal strikes if there's any penalty for failure (e.g., alligators in the swamp!)

(I'm not convinced you want to build them in dirt first, though. That's a lot of work. Heck, I'm lazy enough that I'd call an indoor wood bike park, such as the Lumberyard, and see what they think.)


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## leeboh (Aug 5, 2011)

Rays' indoor bike bark might be helpful.


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## slapheadmofo (Jun 9, 2006)

cmc4130 in particular, as well as some others, has shared a ton of good info on this subject here:

http://forums.mtbr.com/urban-dj-park/dj-pump-track-plans-402237.html


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## Skelldify (May 10, 2013)

Just buy some of these, lol:
Progressive Bike Ramps -

That's what I was told by IMBA when I asked them about putting wooden features on trails.


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## cmc4130 (Jan 30, 2008)

slapheadmofo said:


> cmc4130 in particular, as well as some others, has shared a ton of good info on this subject here:
> 
> https://forums.mtbr.com/urban-dj-park/dj-pump-track-plans-402237.html


Yeah, thanks!

https://forums.mtbr.com/urban-dj-park/dj-pump-track-plans-402237-5.html#post8474399

As I said over in that thread, I paced these rollers at Whistler at 20'-22'-ish feet apart:










BMX race tracks can be a good place to get a sense of spacing. The faster you go, the more stretched out the rollers themselves should be. 









However, keep in mind that BMX race tracks evolved from MX tracks. And originally, rollers were called the "whoop de doos" or "whoops"--the goal was not necessarily pumping; in MX racing, they're more of a tough section to get through.

On BMX race tracks, sometimes rollers peakier than you would want on a "typical" pump track--because they're designed to be manualed. Or, it takes work to keep the front end down. They're not trying to make them in a full-bike-wheelbase wave pattern.... On the other hand, a lot of pump track competitions (like Sea Otter etc) also deliberately have peaky rollers for the same reason.


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