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I'm building up a Goldrush but with flat bars, mainly for commuting, and have fitted Vittoria randonneur 700x40. They should be reasonably smooth rolling, slick and fast enough, but big enough to take the edge off a small pot hole I hope.  Having fitted them they look tiny, or rather the Goldrush (particularly the frame) looks to have immense tyre clearance. Far more than the claimed 48mm. So I'm interested to know what fits as a cheap pair of fatter tyres with a little more tread to fit for a trip of road may be worth buying.
29er x2.1 kenda small blocks perhaps,
Specialized Fast Trak Sport 29 x 2.35 maybe. These are only a tenner.  What have people managed to fit OK?
Conti Race kings
I've got loads of room around the 45mm G-One Bites on mine... I'll be trying some 50's next.
No way a 2.35" MTB tyre would fit though... Especially not in the fork. I think you would be lucky to squeeze a 2.1 MTB tyre in there to be honest, even then it would be tight for clearance.
Fork is much tighter I agree. In the frame my forefinger is a snug fit either side of the 700x40....I ought to get the calipers on my finger I guess but must be 10+mm. 60mm would just rub, 55 or 2.2" would not but would with any wheel flex it would....2.1" tight but possibly OK. Of course one tyres 2.1" varies hugely though to the next.... confirmed fit of actually tested tyres would be ideal.
Race kings on Sports Pursuit cheap ATM.