--- On Wed, 9/9/09, Jeff Palmer <jpalmer@MTS.NET> wrote:
> It's getting to be time to replace the 14 inch tires on my
> 85
> Westfalia.  So I'm thinking about an upgrade to 15
> inch wheels.  I
> know on my hybrid bicycle the tires are much narrower than
> on my
> mountain bike, and the rolling resistance is much lower
> (empirical
> testing from an arts student!).  

This has also been thoroughly tested by bike racers. Compared to a small, say 16 or 20" biker wheel gain from the lower rolling resistance using a 700 or 27" wheel outweigh the weight penalty of the larger wheel.

> So I'm wondering how
> moving to larger/
> wider wheels and tires would affect my fuel economy.
> 
> Thanks in advance
> Jeff in Winnipeg (hey summer just arrived!)

On the van I don't think the diameter change of an inch will have a dramatic effect on rolling resistance. Tire type can though. The wife's Vibe/Matrix came with "Continental EcoPlus" tires, and with those our average fuel economy (measured by recording every fillup for several months) was 7l/100km. We changed them for studded Gislaved Frost and fuel economy worsened to 9-10l/100km. All of this is primarily highway driving, so engine warm up or stop-and-go has little effect. Weather and temp might have a small impact, but I'm pretty sure tires were the main change. (Used Continental and until Christmas and Gislaved Jan-Apr. Yes, I'm lazy with my tire changes. This year winters will go on in Dec, and off in Mar.)

Will a 20-30% fuel economy improvement be possible for a Westy? Well maybe if changing from an extremely aggressive all terrain or winter tire to a smooth road tire, and driving is mostly country highways at 90-100km/h (55-65mph)

Gain will be less pronounced at at higher speeds (air resistance dominates) and in city driving (losses due to stop and go dominate).

Martin and '82 Westy "Poppie" 1.9TD, 8.8l/100km

 

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