Inside view on effect of weight and rolling resistance on climbing

[Iwan Kemp]

Hans Heim, one of the head honcho's at Ibis posted this on a MTBR thread

http://forums.mtbr.com/ibis/do-you-have-both-sl-slr-hd-use-strava-825721.html

 

The HD 140 and 160 should be about the same climbing, all else being equal...

 

Here's some food for thought: Let's say you have a 175 lb guy with a 25 lb bike, for a total of 200 lbs (nice round number) who is going to climb a steep hill (slow, not much aerodynamic loss) that takes about 10 minutes putting out 300 watts.

 

In this case a 2 lb increase will be 1% of the total weight. Since most of your energy is going into lifting your weight up the hill when climbing at low speeds, it's probably roughly proportional to scale the climbing time to the weight. Very rough, but OK for a quick and dirty comparison.... So, a 10 minute climb (600 seconds) with an extra 2 lbs (1%) added might become about 6 seconds longer. (1% of 600)

 

Now another virtual test: Different tires

It's pretty easy to see 10-20 + watt differences in tire rolling resistance on mountain bike tires, so let's say you swap to some fast tires and save 15 watts. That is 5% of your power total saved and will get you up the same hill about 30 seconds faster. You're getting closer to that Strava KOM : )

 

If the suspension kinematics or shock tuning can save you 3 watts (1% of your power), they can equal out a 2 lb increase on the 200 lb bike / rider combination (1% of your weight).

 

OK, that's enough imprecision for one night, but you can see the point.

 

Saving weight off your bike is helpful for climbing but other factors can be more influential than people realize. It's easy to weigh a part or a bike, but not that easy to check other aspects like rolling resistance and suspension efficiency.

 

One test I used to do was a 3.5 hour 5000 ft of climbing ride and I'd time it with different tires. The fastest tires saved 30 minutes over the Nevegals I started with. They were sketchy and I had more fun on the Nevegals, but the speed was really noticeable. I bet there was a 30 watt difference or something like that.

 

G'night!

H

__________________

 

Hans

Ibis Cycles, Inc.

[davetapson]

Always said Nevegals are like riding in syrup. I've done SBR on them, and you can tell.

 

If anyone wants to know what a fast rolling tyre is, buy Nevegals, and you'll know what is not.

[Captain Fastbastard Mayhem]

Hans

Ibis Cycles, Inc.

 

 

 

FARK! 30 Minutes! And it's safe to say that his fitness over the period stayed static, 'cos as a bike tester you have to be fit!

Edited November 30, 2012 by cptmayhem

[Minion]

FARK! 30 Minutes! And it's safe to say that his fitness over the period stayed static, 'cos as a bike tester you have to be fit!

It's a nice figure for conversation, but I reckon a ride that long just introduces too many variables for accurate testing e.g. weather, surface condition, consistency of power etc. Fitness may be constant, but fatigue, rest etc. may be different.

 

I'd be more interested if he said he'd seen a consistent 30s improvement over a 4min ride done under controlled conditions e.g. same power, same time of day, minimal wind.

 

The overall point remains valid, though.

[Captain Fastbastard Mayhem]

It's a nice figure for conversation, but I reckon a ride that long just introduces too many variables for accurate testing e.g. weather, surface condition, consistency of power etc. Fitness may be constant, but fatigue, rest etc. may be different.

 

I'd be more interested if he said he'd seen a consistent 30s improvement over a 4min ride done under controlled conditions e.g. same power, same time of day, minimal wind.

 

The overall point remains valid, though.

 

That's just it - as a tester for Ibis he would have had to consider all of that anyway. So I reckon it's valid. Think of it in terms of road cycling. Stick a set of slicks on to an MTB and compare the resistance to that of an MTB with knobblies. Now change those same knobblies to Nevegals or similar. FAR more power being used to get the same time. If you expend the same amount of power as the oke on the slicks, you WILL be slower. Simple.

[Giant]

Next year, if its dry I'm doing sani on my road bike

[Minion]

That's just it - as a tester for Ibis he would have had to consider all of that anyway. So I reckon it's valid. Think of it in terms of road cycling. Stick a set of slicks on to an MTB and compare the resistance to that of an MTB with knobblies. Now change those same knobblies to Nevegals or similar. FAR more power being used to get the same time. If you expend the same amount of power as the oke on the slicks, you WILL be slower. Simple.

I'm sure his testing goal as a tester was the overall response, performance and durability of the bike - something for which those factors and total time do not make much of a difference. On a ride that long, it would be extremely difficult to control all of the factors that would affect total time. If the goal was to test rolling resistance, it would be much easier and would give you better results to do back-to-back comparison on a short route with a power meter. Weather is roughly constant, the route condition won't change and power is the controlling factor for effort, eliminating feel, fatigue, rest etc. as influencing factors.

 

I do not dispute that rolling resistance makes a difference. I dispute that time change over a three hour+ ride is sufficient evidence of the magnitude of improvement. There are too many other influencing variable that are hard or impossible to control for.

 

I know there is a real difference between my Gatorskins and Open Corsa road tyres. I do not trust my time differences over a loop around Suikerbosrand (my fastest ever time was on a steel bike with Gatorskins), but I do base it on controlled, power-based testing that I have done on a short course (multiple <2min laps).

Edited November 30, 2012 by Minion

[Cycle Factory]

Hans Heim, one of the head honcho's at Ibis posted this on a MTBR thread

http://forums.mtbr.c...ava-825721.html

Post some of your own tests and results...

[RocknRolla]

bottom line he is getting to is:

 

ride a rigid with slicks?

 

Jokes aside, very informative read.

 

if youre doing a ride with lots of climbing, it will make sense to get the better rolli ng tyres, but for me it's all about the fun, and carving a corner with syrupy grip is a lot more fun than climbing more efficiently.

[Minion]

Post some of your own tests and results...

I need to dig out the results, but I'll post them if I can find them.

 

Testing was done based on the virtual elevation method. Measured power, speed and weight are used to back calculate an elevation profile. This can be compared to a measured elevation profile (not as accurate) or known points on a loop (e.g. start and end points on a loop will have the same elevation or multiple runs on the same loop must have the same profile) to determine CdA and Crr.

http://anonymous.cow...ndirect-cda.pdf

 

I chose a windless day and a loop between two traffic circles. This allowed turnarounds without using brakes (which messes up the VE profile).

Each test run consisted of 8 laps and took under 10min (allowing multiple runs during a single testing session).

All runs were completed within two hours (minimise temperature variation and resultant air density changes).

At the start of each run I measured the combined weight of me and the bike.

I rode all runs in the same positions (on the hoods).

I varied my speed throughout each run (gives more data points for VE analysis).

If I had to brake or change position during a run, the run was scrapped.

Speed and power were measured using my Powertap with a Garmin on 1s recording.

 

I performed a regression analysis to find CdA and Crr values for each run that gave the best match for the VE profiles of the individual laps in each run.

Edited November 30, 2012 by Minion

[M L]

Also interesting read: http://www.mtbonline.co.za/info/mtb-tyre-rolling-resistance.htm

[Iwan Kemp]

Post some of your own tests and results...

 

Still the property of Brand X...

[Hairy]

Stuff that.

• The bike must have awesome handling
  
• The bike must have awesome suspension and feel
  
• I want a bike that is lighter than the pro's racing XCO but as tough as a DH rig
  
• Bike must have 150mm travel
  
• come in a nice colour
  
• have super light wheels that are again tougher than a DH rig
  
• wheelsize ... well, I will have one of each please ... so then 3 x bikes please
  
• The tyres must grip like a MOFO and roll like lightning whilst being virtually indestructible
  
• It must be cheap ... i.e I can afford it.
  

That about sums it up for now

 

Edit on point two

Edited November 30, 2012 by Hairy

[Minion]

That about sums it up for now

You left off the integrated cappuccino maker.

Edited November 30, 2012 by Minion

[LazyTrailRider]

carving a corner with syrupy grip is a lot more fun than climbing more efficiently.

True, but it's at times also quite rewarding two-wheel-drifting through corners with low-resistance rubber.

[Hairy]

You left off the integrated cappuccino maker.

 

No the wife will wait for me at the end of the trail