After putting on a fair bit of weight I am using a mountain bike (Giant Boulder) for a while, but for road riding. As is often documented I find the 26x1.95 knobbly tyres a bit of a pain to roll along so am looking to fit slicks. I also want to fit mudguards and bought some last week. They are for maximum tyre size of 1.75. I bought them because I knew I was reducing the tyre size. My question is would I be OK using 26x1.5's which seem plentiful and OK for a tight budget. Would there be much difference in the rolling resistance.