The weight may be noticable, especially during accelerations. Two other things to consider. First you went to a wider tire. Second I believe the Gatorskins are a stiffer feeling tire thant the GP4000. All of this might contribute to a sense of being slower.
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A conclusion is the place where you got tired of thinking. - S. Wright
Favorite rides in the stable: Indy Fab CJ Ti - Colnago MXL - S-Works Roubaix - Habanero Team Issue - Jamis Eclipse carbon/831