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How the IMSA TR8 went faster


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I had a TR4 for 24 years and the first glimps I had on the wedges I had from a TR book which had a colored center with a few photos of the Group 44 IMSA TR8.

I was impressed by the shape (of the things to come), the wide fenders and these super wide wheels on the rear axle.

The last pages of the book showed the standard TR7/8 cars, means I saw the Group 44 first and the standard version later but was already in love.


In year 2012 I've got an invitation to go to the Kastner Cup in USA  - Road America. I said - "I come, but I need a race car"

So they asked who might be willing to share his car with me. I suddenly got a call in German language from Canada.

"Hi, I'm Peter and you can drive my car all weekend long. I send you photos"

 

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Surprise surprise, a bing banger TR I was offered.

So I ran that #42 car at Road America and some month later I bought it.

When I drove the car in Europe, it sure was fast but it struggled on cornering and braking. Everything was great designed but didn't seem to work well together to make the car handle.

Then at Spa 2018 I lost the roof spoiler at Blanchimont corner and the car went wild. The laptimes went 10 seconds slower!

On this photo you see the roof spoiler short before getting ripped off.

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The weird behavior of the car was the first clear sign that something on the car was setup wrong.

So I started testing without the roof spoiler to make the car handle and came up with new spring rates, damper settings and tire compounds.

And look at that - suddenly the car can follow a BMW M1 and leaving TVRs behind.

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From that point I refined the setup more and more, camber, castor, brake biase, tire width and some little other things to tweak.

This made the car faster than most of the Porsches, except the Group 5 versions.

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At Brands hatch I demoralized the Porsches but the car developed a problem on the front shocks. They were functionless and the ride was bumpy and bouncy with almost no control.

But even that problem didn't stop the car to get on the Podium, right behind of the Group 5 Ford Escord and a Cobra 7L Cobra with wings and carbon body.

Here the start order.

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Last race in 2019 was at the Nurburgring and the car did a pole position with a 2 second gap to the 2nd place.

Seems the car is now doing what Bob Tullius promised, best race car he ever drove. And I agree....these IMSA TR8 GTO cars are hard to beat race cars.

Edited by MadMarx
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Congratulations Christian, you’ve come a long way and added a lot of sophistication to a car which it should have had it before. Many kudos to your application and expertise, when we talked at Brands you said you would make your changes count and your results back that up. 
I watch your further results with interest.

best regards Mick Richards

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13 hours ago, kiwican said:

That is a stunning looking car, backed up  by a great sound.

If you re-install the roof spoiler will that add anything on top of what you have already achieved?

Simon

hi simon,

after the car did handle without the the roof spoiler I did some further adjustments to make it handle with the roof spoiler.

First I noticed that the back end was sticking to much compared to the front end.....inducing understeer.

I added a rubber lip to the front spoiler to close the gap between road and car. That rose the overall downforce but more biased to the front because the car has no skirts on the side. With the roof spoiler and the rubber lip I have now balance between front and rear. The adjustable sway bar did the rest.

The roof spoiler doesn't change the top speed of the car. It is not noticeable.....maybe 1mph at 160mph lowering the top speed to 159mph. This is not much compared to the gain on cornering. Means, I leave the roof spoiler always on.

 

I think Bob Tullius said, with the whale tail spoiler they get the 400 pounds of lift down to zero and with roof spoiler it's creating downforce. I don't know the value....maybe 100 pounds of downforce?

 

And yes....the sound is not too bad.
On this video I was running in the next problem.....from the high cornering forces the 3-piece wheels started leaking.

I went backwards from pole to 11 I guess.

 

 

On the last video you can see some differences between the first races in Europe and some later races. The car is less sideways in the recent times. And it sideways, than with good control.

 

 

 

Edited by MadMarx
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