Question about slick size

What I have are a set of MT 29.5-9 on a 3000lb car with 4:30 gear, aprox 400 hp. Its time to replace the tires. My question is, If I went to a 28" tire, what would the 60ft change and how would it affect the mph at the stripe. Its not really alot of difference in height so I was hopeing that it would not really hurt the top end and help the car leave. The 60' on the car with the 29.5's are 1.55. What do you guys think? Thanks.

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My question is, If I went to a 28" tire, what would the 60ft change and how would it affect the mph at the stripe.

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Here is an example, put your rpm in and recalculate. This assumes that your mph doesn't change.

RPM2 = RPM1 x 29.5/28
6321 = 6000 x 29.5/28

If your combo likes the change, it might improve mph maybe 0.5. If it runs out of breath, it could reduce mph by more than 2.0
If everything works, I think it should improve the sixty foot by maybe 0.03