[Vtor_ZL1]

I like calling it stock and then oh it has catback and drag radials - just like stock.


Stomp n go !

[wnta1ss]

Originally Posted by s346k

depending on tire size the drag radials may be hurting more than helping

Considering that this car, being an LT1 model, came with 245 all-season tires, I find this theory highly unlikely. Agree though that his chosen size might not necessarily be optimal due to throwing off the shifts (auto with a locked tcm). My own car SS/A8 going from the stock 275/35-20 runflats to a 305/45-17 MT (taller) saw a pretty modest improvement. Stock=1.83 short and 12.06@114, MT=1.76 short and 11.97@113. Once I bought HPT and was able to log, I found that the tall tires were screwing up the shift points. When they figured out how to unlock the t87a tcm so we can tune it, I was then able to fix things.

[95 imp]

Originally Posted by Vtor_ZL1

I like calling it stock and then oh it has catback and drag radials - just like stock.


Stomp n go !

I'm thinking about putting a stock ported LT2 manifold on my ride and possibly a procharger after that. I'd use LT4 injectors and pumps so I can keep it all stock.

[s346k]

Originally Posted by wnta1ss

Considering that this car, being an LT1 model, came with 245 all-season tires, I find this theory highly unlikely. Agree though that his chosen size might not necessarily be optimal due to throwing off the shifts (auto with a locked tcm). My own car SS/A8 going from the stock 275/35-20 runflats to a 305/45-17 MT (taller) saw a pretty modest improvement. Stock=1.83 short and 12.06@114, MT=1.76 short and 11.97@113. Once I bought HPT and was able to log, I found that the tall tires were screwing up the shift points. When they figured out how to unlock the t87a tcm so we can tune it, I was then able to fix things.

so you took 75? lbs off the car with a drag wheel setup, used a taller tire that probably dead hooks and is quite lazy off the line, to go .09 quicker @ 1 mph slower? id call that a wash.

i was simply stating that i think the tall tire is slower than a short tire. if one is going to buy drag wheels, capitalize with the shortest and lightest tire you can get away with. n2o or power adder cars, sure. use a big tire. stock na car? no.

[stlwrx]

Originally Posted by Vtor_ZL1

I like calling it stock and then oh it has catback and drag radials - just like stock.


Stomp n go !

its an axel back not a catback, that is pretty much stock bud lol

[stlwrx]

Originally Posted by s346k

so you took 75? lbs off the car with a drag wheel setup, used a taller tire that probably dead hooks and is quite lazy off the line, to go .09 quicker @ 1 mph slower? id call that a wash.

i was simply stating that i think the tall tire is slower than a short tire. if one is going to buy drag wheels, capitalize with the shortest and lightest tire you can get away with. n2o or power adder cars, sure. use a big tire. stock na car? no.

I'm not too upset - I did not buy the wheels and tires - they are rear take-offs from my buddies z06. figure better than the 245 all seasons lol

[wnta1ss]

Originally Posted by s346k

so you took 75? lbs off the car with a drag wheel setup, used a taller tire that probably dead hooks and is quite lazy off the line, to go .09 quicker @ 1 mph slower? id call that a wash.

i was simply stating that i think the tall tire is slower than a short tire. if one is going to buy drag wheels, capitalize with the shortest and lightest tire you can get away with. n2o or power adder cars, sure. use a big tire. stock na car? no.

Wrong, changed only back tires, saved more like 20ish pounds. Car went a little quicker even though it was not that bad stock. You obviously missed the point, that op is starting out with worse tires than I did. Therefore he should gain more from going to a drag tire.

[s346k]

op: i get the 245 all season conundrum. id have done the same thing if it were available.

wnta1ss: all of the info was not available at the beginning. i've seen a lot of guys put 28" tires on their otherwise stock cars and barely go faster (your example). i was simply stating that a shorter tire is better for this particular setup. also, did you weigh the wheel/tire combo? hard to believe replacing a stock 20" wheel with a 17" drag wheel is only to drop 10 lb per side. maybe i'm using my wheels as comparison and they are heavier.

[wnta1ss]

Originally Posted by s346k

wnta1ss: all of the info was not available at the beginning. i've seen a lot of guys put 28" tires on their otherwise stock cars and barely go faster (your example). i was simply stating that a shorter tire is better for this particular setup. also, did you weigh the wheel/tire combo? hard to believe replacing a stock 20" wheel with a 17" drag wheel is only to drop 10 lb per side. maybe i'm using my wheels as comparison and they are heavier.

As far as weight, my old 17x10 Weld wheel that I was talking about with the MT tire was about ~52. Had not checked my stock SS 20x9.5 rears (split-spokes) with runflat 275s on, but had heard something like 62~64 for the 5-spoke wheels. That is why I said 20ish pounds, did not check mine stock so it's inexact. Have later checked my stock SS split-spoke 20x9.5 rear wheel with 275 PS4S tire and it was only ~58 like that. Obviously different wheels and different tires could change things, but I was talking about my specific change of stock split spoke/runflat to Weld 17/MT drag radial.

[lt4camaro]

Originally Posted by wnta1ss

Considering that this car, being an LT1 model, came with 245 all-season tires, I find this theory highly unlikely. Agree though that his chosen size might not necessarily be optimal due to throwing off the shifts (auto with a locked tcm). My own car SS/A8 going from the stock 275/35-20 runflats to a 305/45-17 MT (taller) saw a pretty modest improvement. Stock=1.83 short and 12.06@114, MT=1.76 short and 11.97@113. Once I bought HPT and was able to log, I found that the tall tires were screwing up the shift points. When they figured out how to unlock the t87a tcm so we can tune it, I was then able to fix things.

Can you explain ?I recently read the A10 shifts by MPH when at WOT, does the taller tire tend to reduce the shift RPM , would a shorter tire show a shift at WOT at a higher RPM? how does the computer get wheel speed, front or rear? a taller tire in the rear would in simple terms show a lower RPM at a given speed. I have been toying with the Idea of a inch shorter rear tire to gain some gear ratio and maybe make the trans shift closer to redline in auto mode at WOT especially in the lower gears. You touched on tall tires screwing up your shift points, you have my interest and would love to hear what you have to say.. I will be driving a A10 LT1

[wnta1ss]

Originally Posted by lt4camaro

Can you explain ?I recently read the A10 shifts by MPH when at WOT, does the taller tire tend to reduce the shift RPM , would a shorter tire show a shift at WOT at a higher RPM? how does the computer get wheel speed, front or rear? a taller tire in the rear would in simple terms show a lower RPM at a given speed. I have been toying with the Idea of a inch shorter rear tire to gain some gear ratio and maybe make the trans shift closer to redline in auto mode at WOT especially in the lower gears. You touched on tall tires screwing up your shift points, you have my interest and would love to hear what you have to say.. I will be driving a A10 LT1

Yes the autos shift on mph. Think that the computer uses the speedometer, but the car also has speed sensors on all 4 wheels for stabilitrack/abs. I only tried the 28" DRs when the trans was locked, so I don't know for sure what a 26" would do to it. Will mention that putting 26" tires on back makes stabilitrack get mad. Based on my past experience with the locked trans, I think that it might be a good idea to get stock diameter, or as close as possible, for a 2020. Not a very common diameter in DRs, but Nitto does make the 555R2 in 275/35-20, which was the stock rear size on my SS for example. Of course, only testing and logging would tell what the sizes actually do to the shifting.

[lt4camaro]

Originally Posted by wnta1ss

Yes the autos shift on mph. Think that the computer uses the speedometer, but the car also has speed sensors on all 4 wheels for stabilitrack/abs. I only tried the 28" DRs when the trans was locked, so I don't know for sure what a 26" would do to it. Will mention that putting 26" tires on back makes stabilitrack get mad. Based on my past experience with the locked trans, I think that it might be a good idea to get stock diameter, or as close as possible, for a 2020. Not a very common diameter in DRs, but Nitto does make the 555R2 in 275/35-20, which was the stock rear size on my SS for example. Of course, only testing and logging would tell what the sizes actually do to the shifting.

I was thinking of a 26.7 to a 27.0 inch tall tire. The OE diameter is 27.6 to 27.7, I do not think those diameters would bother anything and give me a little gear advantage . The 2.77 rear would be nice if it was a 2.85 ratio.

[KingLT1]

Taller tires reduces shift extension meaning you will fall back to a lower rpm on shift. You will go faster on a shorter tire if you can hook. I believe the top bolt-on A8 cars run a 26" tire for better gearing at the track, then move to a 28" with more power like H/C because the 26" will no longer hook. I ran a 305/35/20 555r even when bolt-on NA and it was 5-6 tenths quicker over the stock run flats but lost a little trap speed. Hard street tires put more power to the ground over drag radials. On a dyno you will see 15whp difference. So if all you care about is mph or roll racing then run a shorter harder street tire. If you want to hook then taller softer compound with a side wall that will flex is what you want. Sticking with something like a 275/35/20 555r2 is probably a good middle ground.

[lt4camaro]

Originally Posted by KingLT1

Taller tires reduces shift extension meaning you will fall back to a lower rpm on shift. You will go faster on a shorter tire if you can hook. I believe the top bolt-on A8 cars run a 26" tire for better gearing at the track, then move to a 28" with more power like H/C because the 26" will no longer hook. I ran a 305/35/20 555r even when bolt-on NA and it was 5-6 tenths quicker over the stock run flats but lost a little trap speed. Hard street tires put more power to the ground over drag radials. On a dyno you will see 15whp difference. So if all you care about is mph or roll racing then run a shorter harder street tire. If you want to hook then taller softer compound with a side wall that will flex is what you want. Sticking with something like a 275/35/20 555r2 is probably a good middle ground.

Great info for sure KingLT1, thank you. I will be only 30-40 RWhp over stock, with a 10 speed auto. I air down on a hot OE tire to 25PSI and do a good clean burnout and would be looking to do a high 1.80 60ft. So a little shorter gear works for me to 1/4 mile the car on a track and even fool around on the street. I do no high speed roll racing at all and only care about ET at the strip. Thats why I am leaning toward a 27 tall tire which is .7 shorter than OE, and maybe 1 inch shorter max. My 2015 manual trans base stingray with Z51 sized michelin pilot SS tires , very minor bolt on tricks and setup, does 11.78 in the 1/4 with a 1.97 60ft. I concentrate on one thing with a manual, get out of the hole with no spin as fast as i can.