I'm currently training for the highland fling (half), so I mapped out a 60km ride that includes 1200m of climbing, single track, fire trails and a few roads to link it all up. For the first couple of weeks I rode it on my 29" carbon HT, and my times were consistently around 3:08 to 3:10. Rode it on my 26" dually today, and it took 3:22. Now the dually is 2kg heavier and has Kenda Nevegal tyres (the HT has Racing Ralphs), but I was surprised how much quicker I am on the HT.