Am I asking for trouble with this tire size combo?

gus6464 wrote:WTB Resolute 650x42 on the rear
Schwalbe Thunder Burt 650x2.1 front

Will the size difference be too much? This is on a Slate.

I did that with 700c.  Its awesome.  No problem at all.  That large TB makes the bike handle totally different – it feels like a drop bar mountain bike.  The large knobs and more squared off shoulder make it feel a little different (i.e. more like a mountain bike).  Over all, it slowed down the steering response a little – making the bike more stable – which is what I want when conditions warrant a 2.1 tire. 

That TB should have pretty low rolling resistance, but it feels a slower.  Maybe its just the weight, but it doesn’t feel alive on hardpack.  But on rough gravel or single track I’m blasting through with no hesitation, nor do I have to be carful picking my line like I would with 40mm front tire.

I don’t know if you have spare wheels, but put that 42mm rear on a 700c and the 2.1 on a 650b and you’ll have basically same rolling diameter front/rear.

Personally, I think the furious fred (700c only) makes a better all around gravel tire – it certainly feels a lot faster and its rounded profile makes it corner better on pavement or hardpack.