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Apologies in advance if this belongs in another forum. I know the issue of rolling resistance has been beat to death over the years with not a whole lot of consensus emerging...but I'm still willing to risk a question.

I've been riding a weekly dirt double track training ride (well nearly a race) with friends for a couple of years. We ride the same 4 mile rolling loop and our times are very consistent. The terrain is sandy/grassy with some fast turns and a little gravel every now and then. It tends to be a bit wet and soft through the winter. A couple of months ago I switched to Crows and my times are a little slower and it just feels sluggish -- like I'm pushing one higher gear. My previous tires have been Karmas . I recently took the Crow off and tried a Small Block Eight. The Eight feels more lively and improved my time.

Here's where I'm confused.....the Crow, Karma and 1.9 "Eight" all weigh about the same. Shouldn't the Crow have the least RR with it near absence of tread? FWIW, it's not a matter of hooking up -- they all work well on this course, just as mentioned the Crow just seems to bog down. Any thoughts on whether it's my imagination or could a tire with a more aggressive tread roll faster?
Thanks
 

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chips & bier
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It could be your imagination, but rolling resistance depends quite a bit on tire pressure, cross-section, durometer, the type of rubber (silica-based tires tend to have a relatively low RR), the tread pattern (which affects elastic deformation and hence RR...), and so on. It could very well be that the Eights roll better.

(I'll leave it to Nino to show us graphs of the old Michelin XLS.... another knobby with relatively low RR for the soft rubber and large knobs it uses...) :-D
 
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