During my epic Lao ride in Nov, I noticed that some touring bikes wore different sized tires. The front being a bit fatter than the rear. In my former life as a car enthusiast, economy rally driver and a half-baked auto mechanic, I fully understand the need for the driving wheel to have better traction especially high powered RWD cars. Many of these hi performance cars wear fatter rear than the front like a dragster.
In the latest Lexus IS-F, the wheel size is - 225/40YR19 front – 255/35YR19 rear.
BMW's M3 share a similar story - 245/40 ZR18 - 265/40 ZR18
But for the case of bicycles, its interesting to note the reverse. I did not understand the rationale for this until I was flying down the mountains of Laos at 50km/h and suddenly, the road disintegrated into stones and pebbles. Any motorcyclist or mountain biker will tell you that if you loose your rear end, there is still hope. But once your front wheel slips, it is next to impossible to recover. And hi-speed crashes fully loaded can be a very painful experience.
Thus, I have just fitted a Schwalbe Big Apple in the front of my yellow Speed Pro and the latest Marathon Supreme on the rear. They look rather odd but the reason for my little experiment is to enjoy the cushy, grippy character that the 2.0 BAs are famous for.
The narrower rear 1.6 Supreme should transfer the power better and its touted to be "touring tire that can do everything". The Chief Designer claims it is impossible to incorporate any more innovative features into the Supreme - thus the US$69 retail price for one rubber donut.
Stay tune to see if the case for being unequally yoked turns out to be a happy one...
*My buddy Chris Wee usually sets up his bike this way for serious touring.
Big Apples 2.0 vs stock Marathon (tikit) 35-349 vs Marathon Supreme 1.6
Update 8 Dec 2010 - I have posted my latest thoughts on this set-up here.