Tuesday, December 11, 2007

More Arrowhead Training - Rolling Resistance Prediction

-picture of monday night 3 hour snowmobile training ride

This weekend I’ve tried a number of alternate cross training activities to integrate the family into my long training session… Cross country skiing with Josie in a backpack… hiking with Josie in a backpack… but by far the best cross training was 3 hours of sledding at the local golf course (pulling Josie up the hill with her on the sled). In addition, she got a huge kick out of this (not having to walk back up the hill). After this cross training session I attempted to go out for a short 2 hour ride during which I realized I had nothing left in the quads and hams. Note to self: “sledding is a good workout”, who whould have thought.

The last 2 weeks I’ve been experimenting with tires, tire pressure and other variables based on snow condition and temperature in an attempt to find a nice correlation of the results to help reduce rolling resistance during Arrowhead. Eureka! I believe I’ve been able to create a formula the will for each tire type that I’ve been riding suggest the optimal pressure to produce the minimal rolling resistance.

While some people always say higher the pressure the lower the rolling resistance… they are WRONG! Under numerous situations I’ve recorded a 20% decrease in rolling resistance with LOWER tire pressures. However too low and the numbers start going the opposite direction. Add to this formula the ability to predict which tire is the best selection and the reduction in rolling resistance goes up to nearly 50%!

I’ll be continuing to add ride data to the matrix to improve the regression formulas in addition to adding additional tire types (front and rear – loaded and unloaded). While there is still a lot of work to do with a couple of variables not taken into account (primarily weight distribution), I believe this may be one of the key factors to turning out a record course time at Arrowhead Ultra and possible TransIowa. However, the correlation matrix is currently based on snow conditions and would require substantial modification for gravel and pavement. In addition, I’d guess that the improvements of rolling resistance would be in the single digits (an hour vs. up to 15 hours for Arrowhead).

Note: Increasing the number of unknowns in a correlation matrix doesn’t add that much additional time for the predicted results… the difficult part is determining what factors are influences and which are not, in addition to collecting enough valid measurements.


Frank H said...

I would like to know how you measure rolling resistance and what are the factors you are considering.

I'm pretty much stuck with the equipment I've got: Snowcat rims and either Nokian Freddiez Revenge or WTB Weirwolf LT 2.55 tires. Obviously the Nokian are a bit too aggressive for this race, unless we're looking at sheet ice.

So my only factor to play with is tire pressure. Are you noticing that different tire pressure work differently on different snow conditions? Basically all I'm doing is lowering the pressure as much as I can without it being intolerably bouncy on the road and riding on that (10 F, 12 R).

Lance Andre said...

I have a flat stretch of trail that I ride over and over again... at a constant effort (HR). I then record time, gearing, temperature, and the 10 lbs penetration depth (1" square stick with 10 lbs tapped to it).

Question for you: How wide do the Weirwolf tires actually measure (and on what width rim)?

How did you come about the SnowCats? (I couldn't find them anywhere and settled on some Echo 45mm rims).