What would cause a lower speed per rpm on a taller tire?

[ggkthx]

2020 Supra on Ecutek
Stock Transmission
285/35/19 MP4S @ 36psi (26.9")

So based on the OEM gear and diff ratios and tire diameter (26.6"), at 7000rpm, 4th should hit 102mph and 5th should hit 133mph... however, all my data logs show me at a much lower speed, 98mph @ 7krpm in 4th. Each log has a small variance of a fraction of a mph at 7krpm, but all around 98mph. I have to hit about 7150rpm to reach 100mph during WOT according to logs. Seeing how my tire diameter is slightly taller than OEM, this seems really odd. I've also checked my draggy reports and they show similar mph and rpm relationship.

Other data logs I've seen posted here show everyone else's cars hitting 100mph well before 7,000rpm... What would cause my car to consistently hit a lower max speed at any given rpm than others?

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[PhantomPurple]

Your larger tires have a 1.1% increase in circumference over stock. The means that your speedometer will show about 99 mph when you're going 100. Speed, tire temp, and pressure will all increase your tire size slightly.

Also, the torque converter might be giving a little bit of slip.

 

[ggkthx]

So I was worried that it's just the car reporting the wrong speed, but my dragy shows shift points (dips in g-meter) at the same speeds as my Ecutek logs.

This happens at any tire temp, tested from 70 to 100.

 

[Awales74]

Are you the 1st owner of car?

 

[XtremeMaC]

Dragy also shows your vehicle speed. does that match ??

 

[ggkthx]

I'm the 2nd owner, but the 1st owner is my childhood best friend so I know everything he did and helped him with installs.

Dragy's speeds match my logs.

 

[Awales74]

Could the torque converter be giving up?

 

[ggkthx]

Is there anything I can log to see if the torque converter is having issues? Any symptoms I can observe?

I've almost always driven manuals so this is kinda new to me.

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