Patrick fastest before rain ends Iowa test.

Danica Patrick set the pace as 26 drivers took to the track at Iowa Speedway for an IndyCar Series open test as preparations began for Sunday's Iowa Corn Indy 250 presented by Pioneer.

The Andretti Green Racing driver lapped the 7/8-mile oval in 17.4612secs to put herself ahead of Team Penske pair Helio Castroneves and Ryan Briscoe, but admitted that the merger between IndyCar and Champ Car would bring its own tactical elements to one of the shortest tracks of the season.

"It was a very productive day for the Motorola team," she noted, "We made a couple of changes throughout the day and were able to find some speed. My crew has worked hard and I think we're going to have a very good weekend.

"The more cars have made it more interesting. One of the things that's happened as a result of more cars is we've had a little bit more cautions, as well. So, there might be less lapped traffic to think about, [but] I'm not sure what to expect this year.

"The yellows have played into it but, if that doesn't happen, you have to stick your nose in, you have to go alongside them. I don't know what the line is going to be like. There's a lot of uncertainty in my mind right now about what it's going to be like, but lapped traffic makes it more exciting for the fans. From that angle, it's a good thing.

"I think that anybody watching [today] could see we were running a more traditional racing line around the track instead of [running] around the bottom. I was able to drive on the bottom for some of the track when I did a sticker [tyre] run at the end, but I couldn't do it the whole way around, [so] the racing is going to be a lot more exciting, with a lot more passing - just better, in general, than last year.

"I think it will be easier to pass cars that aren't very good. Last year, everyone was on the bottom, and the trick was that you had to go around the top to pass. It seems like it may be more like Richmond, where you have a more traditional line. Everyone still wants to go to the bottom, but you are running more against the wall on the straight. That gives you the opportunity to go more underneath. It will make that part a lot better, although it will still be difficult to pass, because you can't stick your nose underneath. It won't be like a mile-and-a-half, but it will be a lot easier than last year."

Castroneves was equally happy with second spot after a productive day, and was particularly pleased with the tyre choice made by Firestone for the weekend.

"We were working on the basics of setting the car up - fixing little problems here and problems there," the Brazilian revealed, "We were fixing little by little to keep the consistency, and we seemed to have that. Obviously, Ryan was working on different things, some race set-up, and we're very optimistic for both cars. It's so tight that we're looking for thousandths of a second, and everything you change in the car makes a difference. It shows on the lap time.

"I think we have more grip [this year] - Firestone seemed to do a good job with the tyres here. I have not tried new tyres after a few laps, but it seems to be holding pretty good, and hopefully the weather will co-operate as well and we won't have any cold tyre issues [as at the inaugural Iowa event in 2007] or anything like that."

Briscoe continued to ride the wave of improvement that has lifted him into the top five in points, finding his feet quickly at the quirky Iowa oval.

"Despite having only one session this afternoon, I think we were able to learn a lot," the Australian commented, "We made some solid progress with the race set-up and I think today was an encouraging start to the weekend. It's my first time running at Iowa Speedway, and so far I'm having a great time - but it's a challenging track."

Patrick's rookie team-mate, Hideki Mutoh, was fourth, while IndyCar Series points leader Scott Dixon, last year's polesitter at Iowa, rounded out the top five for Target Chip Ganassi Racing. The Kiwi, however, did not agree with Castroneves' assessment of track conditions.

"Since the last time we were here, there is definitely less grip and a few more bumps to negotiate," Dixon claimed, "But we didn't run as many laps as the others before the rain came and, in the amount of time we had, our focus was on balancing."

Track time was curtailed when a second two-hour session scheduled for late afternoon was cancelled due to a rain storm, but the 26 cars combined for 1380 laps in the two hours that were possible. Marco Andretti, Ryan Hunter-Reay, Dan Wheldon and Will Power rounded out the top ten, the Australian being the best of the Champ Car converts sampling the Iowa oval for the first time.

Tony Kanaan was among those to suffer when nthe rain arrived, the Brazilian having been confined to the pits for much of the one session to run.

"It was a really disappointing day for the Team 7-Eleven guys," he sighed, "Unfortunately, we had something break in the car during the first session and only got ten laps in. It's nice that they've added time tomorrow, but we missed out on some valuable track time today."

Milka Duno was uninjured in the only accident of the day, after the #23 Dreyer & Reinbold car spun in turn two and made moderate contact with the SAFER Barrier. The Venezuelan was forced to pull out the team's back-up car because of the incident, but she finished the day 24th fastest, ahead of both AJ Foyt IV and rookie Mario Moraes.

Further practice is scheduled ahead of Saturday's PEAK Motor Oil pole qualifying session.