as another fact-gathering exercise, try using the forum's static IP instead of the URL by clicking this link:
http://69.27.101.36 if your speed returns than the DNS server that your browser is configured for, is having issues. I highly doubt that this is the issue, but if you do find success, continue using the static IP until some pimply-ass, high-school, summer intern is directed to reboot their server.
if after trying to use the static IP, the response is still slow, then unfortunately i can only offer consolation and condolences. there really isn't much you can do except bitch at your ISP; and this will more than likely end with their tech support dismissing it; because let's face it, even after you humor their instructions to repeat the clearing out of your browser cache, rebooting your computer and networking equipment, using the static IP address AND explain to them that you experience better performance by going through a proxy server; they aren't going to bring down their farm simply because one of their customers can't access one motorcycle forum. if you do manage to convince your ISP to reboot their racks, but in fact, it wasn't their routers that were embedding misinformation for the next hop, rather, the problematic router(s) lie(s) in (a) cluster(s) outside of your ISP's jurisdiction, your hope for a speedy recovery just ran into a brick wall.
don't misunderstand me as saying "don't bother". DO complain with your ISP and inform them that you are having problems interacting with the forum, but be prepared for their "whatever" response.
in the meantime, continue using that proxy link that i posted until some acne-faced geek trips over a power cord; or use another web proxy. the site will appear crippled because you won't be able to take advantage of some of the site's advanced coding such as java scripts, applets, or whatever is being used. there is an art in knowing what options to use--something that i never had the patience to learn.
like i said previously, a few of the Central Floridian members here who use Brighthouse Networks as an ISP experienced this very problem a few months ago. the issue disappeared after a week or three. I managed to pinpoint the eddy somewhere in the northeastern CONUS, but identifying which M/LAN is next to impossible with my meager toolset; and without the evidence allowing me to confront any ISP with "Hey, please reboot Rack X because there is a blade in there looping packets with so and so, here's the proof"; I had to access the forum through web proxies, periodically checking on sans-proxy access, until the problem cleared up.
Sorry to be the bearer of bad news.