Techbench Tuesday: Detroit to Belle Isle
The streets of Belle Isle just outside Detroit are host to the upcoming NTT IndyCar Series Double Race Weekend and the bumps of the concrete surface are ready to greet the pitch just two weeks after the 105th Indianapolis 500.
Belle Isle has been hosting the Indy car race since 1992 with two breaks between 2002-2006 and 2009-2011. The street circuit has been a double event since 2013, but only one rider has swept the double and that is Graham Rahal, whose father Bobby won the first Belle Isle race.
Rahal’s race engineer Allen McDonald joined Rahal Letterman Lanigan Racing after the 2018 season. He never won in Detroit but the # 15 Honda is fifth in the standings and a good result can propel the team into the top three of the ranking.
But getting a good result means taming the bumps and surface transitions at Belle Isle. The track is mostly concrete, but the transitions between concrete and asphalt can be quite bumpy and concrete has its own characteristics.
âThe concrete track adds a few things, first of all it’s much less sensitive to temperature than an asphalt track,â said McDonald. âSecond, it absorbs rubber in a different way. It will be interesting to share the track this week with IMSA, but often things move a lot. This trail really changes a lot over the weekend so you have to keep it up.
“You have to balance the need for compliance, having a car that’s very good on bumps with a car that’s also reasonably good for aero, and that adds some configuration challenges.”
Starting the lap around the 2.35 mile 14-turn circuit is a quick right-left sequence that goes over a small hill. This is the same sequence of turns where in 2018 GM executive vice president Mark Reuss crashed the Corvette C7 race car ahead of this year’s second race in the doubles program.
âThere’s some elevation change and it’s bumpy, so we’re coming back to full aerodynamic compromise compliance,â said McDonald. âWe tend to use soft springs obviously on a street course and that kind of gets you into the third use area. [springs] for ride height control and places like turn 2 with elevation change where the car is in compression, it is very difficult to properly control third engagement. You can imagine that in a turn like this, where the car is heavily loaded, suddenly going to a third spring or a third spring or back and forth can be very unsettling for the car, so turns like these add a particular engineering challenge.
The second turn leads into a long straight that gives the riders a great passing opportunity before turn 3. However, going wrong on Turn 3 can be disastrous as James Hinchcliffe, Alexander Rossi and Josef Newgarden proved in 2019 with their collision in the second race.
Further into the lap, turn 6 leads to a long straight and another passing opportunity for turn 7. After slower turns 8-11, the lap ends with three quick right turns.
The race weekend has limited track time between IMSA and Indy Lights. IMSA has two full practice sessions on Friday, Indy Lights has 40 minutes of practice while there is one 75 minute session for IndyCar drivers.
That would be a big deal, but McDonald’s has a third car to pull data from this coming weekend. RLL will have Santino Ferrucci in the # 45 Honda alongside Rahal and Takuma Sato. Having a third car means the team can go in a third direction for the base setup.
“This is more information, given the lack of track time we have and because we have this extra week we have come up with a whole bunch of different ideas that we would like to test, so that gives us three riders that we can split up those tests and move on and I think the communication at Indy has been fantastic with all three drivers and there is no reason that it should not continue in Detroit.
Practice is Friday (June 11) at 5:00 p.m. ET with races Saturday at 2:00 p.m. and Sunday at noon.