Originally Posted by
Sammyboy
Seriously, stability problems will get worse by switching to a front rack, not better. 20 lbs pulling the steering around is significant, and whilst it's manageable it is absolutely not going to be a better solution than a back rack. Try a better rear rack first. I'm also 250, and I can carry large loads on the back with no problems, but believe me, even with panniers on a lowrider rack, on a bike with slow geometry, 20lbs pulls me all over the place at the front.
I think that front load stability depends a lot on the geometry of the bike. For touring bikes, the general recommendation is to place 60% of your load over the front wheel, and 40% over the back. Dense items go in the front panniers, and bulky, light items go in the rear. Many complain of a front-end shimmy at speed with a heavy load on the rear and an unloaded front wheel. I haven't experienced this personally, but I do find rear-loaded bikes difficult to handle on climbs.
FYI - For point of comparison, I have two bikes with racks - an old centurion road bike with a rear rack, and a Surly LHT with front and rear racks. I regularly carry upwards of 50-lbs on the Surly. I prefer to place the heavy stuff up front. I can only carry about 20-lbs on the centurion before it starts feeling whippy and unstable. The bike does matter...