ANALYSIS: How IMSA GTP cars race differently than DPi

Michael Levitt/Motorsport Images

ANALYSIS: How IMSA GTP cars race differently than DPi


ANALYSIS: How IMSA GTP cars race differently than DPi


With 36 hours of competition in the books, drivers are getting a pretty good handle on the new Grand Touring Prototype (GTP) cars in the top class of the IMSA WeatherTech SportsCar Championship. As the series heads into a couple of sprint races before the Le Mans break, everyone is gathering a pretty good picture of how the cars perform. Performance all alone, though, is one thing; how the cars actually race each other is quite another.

“I feel it’s hard to overtake,” says Renger van der Zande, driver of the No. 01 Cadillac Racing V-Series.R from Chip Ganassi Racing. “The speeds are higher but we have to brake a bit earlier and the weight is higher as well. The minimum speed [in the corner] is quite a lot lower so you cannot really rely on, ‘Let’s break super late and dive bomb someone.’ I think if you dive bomb someone you’re going straight — you’re going to miss the corner. I think with the DPi you could actually overtake someone on track because you had a bit more downforce, you had a bit more minimum speed and grip to get away with a mistake. With these cars, it seems like if you try to outbrake, you actually are going outbrake yourself and going off the track, so you have to be a bit more careful.”

Adds van der Zande’s teammate, Sebastien Bourdais: “I think it’s a little bit harder to follow really closely. These cars just seem to rely a lot on the little downforce that they have, which which kind of surprised me a bit. But we still have seen some passes and some good shows.”

While Acuras, Cadillacs and Porsches have demonstrated some close competition, the finer points of passing with the new cars are still being explored. Jake Galstad/Motorsport Images

Indeed, the Mobil 1 Twelve Hours of Sebring was a good show… until it wasn’t. There was close competition, drivers trying to use traffic to gain or keep an advantage, and a little bumping and banging. Sebring demonstrated that the gap between cars, and the clear advantage that some cars had on certain tracks, may be a thing of the past. For example, Sebring and Long Beach were expected to be Cadillac tracks in recent years, with the Acuras doing better on smoother circuits where ride height wasn’t as much of a factor. Drivers on both sides feel that difference is now either non-existent, or at least greatly reduced.

That could lead to closer racing, especially now that Porsche seems to have caught up with Acura and Cadillac, with BMW not far behind. And close racing on the streets of Long Beach usually means contact. Can the GTP cars take it as well as the DPi machines did?

“I think it’s pretty similar to what it used to be,” declares Bourdais. “Obviously, we don’t have much experience knowing what the car can withstand as far as side-to-side contact. But you take maybe less risk now with fewer little appendages to fly off the car, because they’re more clean, there’s less of them around the GTP. As far as suspension goes, I think it’s it’s at least as strong as the DPi.”

That was put to the test in the closing stages of Sebring, when the battle between the two Porsche Penske Motorsports 963s and the Wayne Taylor Racing Acura ARX-06 came to a head. Going off track as the GTP leaders tried to juke through GT traffic, Filipe Albuquerque slid across the Turn 3 apex in the No. 10 WTR Acura and collected Mathieu Jaminet’s No. 6 Porsche. The No. 7 Porsche, Felipe Nasr at the wheel, then hit them both.

“I can tell you one crazy thing: My car got wrecked twice,” says Albuquerque. “Front in first, and then second Porsche, heavily. They just changed the front uprights and the nose. It’s good to go. I think that shows how impressive those cars are.”

One thing that has brought in a new element isn’t necessarily the car’s themselves — although the way they get heat into new tires and wear the tires certainly plays a part — is the lower tire allocations. With teams having to double-stint tires more often, it brings an interesting dynamic between cars running a second stint on a set and cars on new rubber.

“As little fun as that might be for the driver, I think it does make the racing interesting,” explains Ricky Taylor, Albuquerque’s co-driver in the No. 10 WTR Acura. “At Sebring, a lot of people were off sequence with each other, double stinting when people were on their first stints. It made it very interesting, I think, at times. And when you have that little grip, it opens up some overtaking. I think for the show it was it was kind of entertaining.”

Due to the reduced downforce, when the GTP cars are on old tires, or cold tires, they can actually be slower than the GT cars. That can make traffic management on both sides a challenge, but with the GTPs having more power than their predecessors, the passes are usually quickly completed on the straights.

“They’ve lost a lot of performance in the slow-speed corners, and that’s quite noticeable, because that was already the type of corner where the DPI was massively different to us already,” says Ross Gunn, driver of the No. 23 Heart of Racing Aston Martin Vantage GT3 in GTD PRO. “And now they’re virtually the same minimum speed. So that definitely makes traffic management different — in some respects a bit more tricky. There are definitely ways, as a driver, you can drive around that and try and make sure that you’re making the most of every situation. But for sure, it’s a big learning process for us as much as as them.”

Downforce changes to have changed the dynamics of traffic management between the GTP and GT cars.  Richard Dole/Motorsport Images

Corvette Racing driver Jordan Taylor relates an instance when one of the BMW M Hybrid V8 GTP cars came around him, but then was so slow in the corner, Jordan went back around the BMW in the No. 3 Corvette. So, he says, it makes a GT driver think about going a little defensive to keep from losing time in the corner. But others note that, except in that instance of a GTP on old tires, it make the traffic equation a bit easier.

“The old cars used to corner like they were on rails,” explains Bill Auberlen, driver of the No. 96 Turner Motorsport BMW M4 GT3. “So they would go around you in the center of corners, and they’d always put you in a bad position. Now, they almost never pass you in the corner because they’ve got their hands full as it is. And on their second stint, they’re actually slower than us in the corner, so they hold you up. So what that does is it makes it really nice — they go blasting by you on a straightaway where you want them to pass; once you get past the brakes zone they sort of tuck in behind you, wait, and then go blasting down the next straightaway. It actually makes interacting with them a lot easier.”

The greater power of the GTPs does have a downside, though — greater closing speed means an earlier decision on where to put the car.

“It is nice to be able to clear everybody in the straight,” says Ricky Taylor. “Although the closing speed is so high that there becomes a level of commitment when you’re going down the straight and [the GT cars] are in their own battle. You have to pick a side to go, and especially when there are Ams in the car — do they see you, do they not … you’re trying to read body language from a much further distance and then commit to one side, because the penalty of picking the wrong side and having to lift and and move across is actually higher.”

The GTP and GT drivers have now had the chance to witness the dynamic on two rather different circuits, and now head to a third variety in the Acura Grand Prix of Long Beach next week. The street circuit has no really fast corners and only a couple of medium-speed turns, so it will be a completely new test for the drivers, but they’ll come away with more knowledge on how the new GTP cars race.