Can you post up a problem shot? That would help in figuring out your problem.
Higher ISO in a DSLR is literally digital "gain" so unless you're shooting in lower light levels your ISO should be at 100. However high ISO settings do not necessarily cause over exposed shots, that's generally a metering issue.
Those aren't overexposed at all, you can tell because you haven't blown any of your white areas. If anything a bit more exposure would define the rider better - notice how the blacks are crushed a bit in the rider's chest area, but those are pretty good overall I'd say from an exposure standpoint.
You're losing a little sharpness by having the lens way to stopped down. The lens is almost closed (f18 / f22) because you've got the ISO set too high for daylight shooting. Try again with your ISO set to 100 and I think you'll see more detail and better contrast. Notice how everything including the background is in focus in the first shot, that's because you've got almost unlimited depth of field at f22.
Stark midday lighting is never going to give you that rich saturated color I think you think you're not getting due to exposure.
Rich is right. When possible, I try to keep the ISO as low as possible. For fast moving action I start low with my ISO to see if I can get what I want as far as shutter speed. I adjust my settings and then if I find it's not enough, then i bump my ISO up to the next level and repeat. Now, I kind of know what general settings works for my camera and start closer to that range. I try to keep away from 800 and higher but do use them for certain reasons, such as low-light action. I love shooting 100 ISO when opportunity allows me to. Long exposures at night on 100 ISO are lots of fun. For the most part. I find a lot of the time I fall right around 400 for my ISO settings when shooting wakeboarding. However, I've been shooting less photos and more video with my EX1. I need another set of eyes and another set of hands so I can do both at the same time. LOL!
Definitely open up that aperture too. I usually have around an f11 in the middle of the day but depending I may try and get a really good close shot that draws all my focus to the rider and keeps the background out of focus more. Depending on the situation but generally speaking opening that aperture will allow me to do that.