going from 27" to 28" tires?

Need new tires; was in the ET Street Radial 255/60 (listed at 27.1" dia). Thinking of going either the ET Street R 255 (listed at 27.5) or the ProBracket Radial 28x9 (listed at 28" tall).

These would be strip only.

with my old 12 second 340 combo going from a 26 to 27" tire was only worth about .05, not a lot.

depends mainly on your convertor. if it is a custom convertor built for your combo, you won't slow down at all, most likely. you may even go faster. btdt.

Also what gear do you run and whats the trap rpm and the shift rpm ? Ron

X 2; if you're close to running out of RPM w/ the shorter tire, you could pick up MPH & lower ET w/ a taller tire.

I used to switch between 28" DOT tires and 29.5" slicks: the car was .2 and 2 MPH faster w/ the slicks simply because the car stopped pulling on the top end when using the shorter tires.

It is a custom converter; 9-1/2" Lupo - Dynamic built specifically for this combo. Currently running a 3.91 gear. Shift point is 6400, and it traps around 6200 I think... apparently I'm not good at looking down at the dash at 115 MPH. Doesn't feel like its running out of pull at the top, but I don't have much to compare to, as this is the only car I've raced in years.

On your deal the car may end up being faster with the taller tires, if so it won't be the first time a BB car goes faster with taller rear tires
Basically if you shift at the same RPM as before the car will be down the track further on each shft so it will spend less time in high gear which may mean it pulls harder in high gear
My old Duster went quicker faster with a set of M/T 10.5x31x15 W slicks (101 inch circumference)compared to a smaller set of 13x30x15ET Street Radials with 96.4 circumference. The motor crossed the finish line at 7000 RPM with the ET Streets, 6500 RPM with the taler slicks. I shifted it between 7000 to 7300 RPM in 1st and 2nd gear on all those runs back then. Let us know the results when you do the swap

I agree as thats just what I was thinking. I run 30" tall tires with 4.30's and I would like to try a 31" tall tire as I feel it may go faster with a taller tire. Many times if your combo is maxed out you will pick up mph and some et. But the only real way to know is to give it a try as on some combo's it could slow down some. Good luck , Ron

I went from a Hoosier 14/32w circumference was 102 to a Goodyear 14/31 with 98 circumference and saw no change it even RPM the same.

Good info, everyone. I tend to be analytical and think in terms of numbers, so it just made sense to me that bigger tires would effectively reduce gearing, and thus slow the ET. But in light of everyone elses experiences, Perhaps I'm oversimplifying....

Thanks!

The only time i have back to backed to back different height tyres car changed from 10.93's to 10.88's similar mph
That was both radial slicks , 9x30R15 Hoosier (29.9" tall) then Hoosier 275/60R15 (27.7? tall)
I went 10.96 for 2 passes on the 275 swapped to the 9x30 for 2 passes then back to the 275
I was stunned when it went 10.88 then 10.89

My 2 cents you wont know till you try on your car

Tex

Speed will often pick up. ET could go in ether direction depending on if you are running out of motor now - or not.