So I have both. Last time out started on the 15's. 60 foots were 1.6's no matter what I did. Bigger burn outs, used 2 step, free rev, lower tire psi. I simply swapped back to my 16's and picked up .15
So before I sell these 15's anybody have an idea why they won't hook? They were new fresh, nice and soft rubber. My 16's are 4 years old and stick! I really expected to brake some axles with the adde sidewall the 15's offer. I am stunned.

 

Personally im looking to get away from the etstreets, and head into a etdrag. The sidewalls are softier.
Now to your issue
Were you spinning the tires off the line, what tire pressure, rpm, any video of the launch?

Need data!!

 

They need few good extra long burnouts before they start hooking usualy

 

Here is the video. Runs in order you can see me swap to the black wheels (16's).

I was also out a few weekends before and had 4 passes on them.

I always start at 14psi and drop from there. I even tried going up to 15 on these. Tire spin off the line.

 

Yeah, I have thought about getting some et drags but just for fun. All the classes I run in require dot tires. I still want to have bragging rights that's it's a street car!

 

I like the stability of a radial too....I get uncomfortable when the rear starts wiggling around @ 100+ MPH.
I start with 13 PSI and usually leave it there.
my best is a 1.6 also.

 

But I have gone 1.36 on the 16's

 

I start at 10.5psi an usallu end up @9.5psi cut high 1.4-1.5s all day

Lower your tire pressure!!!!

 

Trust me I have run lower psi. This is my 4th set of et streets on my rx7, have also run nitto dr and bfg drag radials. I found that on my 16's I cut the best on 13-14psi. Best 1.36! Have you ever tried to run higher? You might be surprised.

My real question wasn't really what tire pressure, rpm, length of burn out but was more of could there be an issue with theses tires? Could 15's come with a harder material?

 

The video isn't there..

That is weird the 15s don't hook as good as the 16s I assume with same air psi, Maybe they do need more burnouts/passes.

14psi is too much, mine don't hook unless they are down around 10 psi (14-16 psi and mine would spin too much), that's where you get the 1.3s and 1.4s

 

Compound is the same and specs are close enough to the same Mickey Thompson Performance Tires & Wheels

 

I used to believe 10 psi was the best. I read somewhere that this was too low. Said thus would cause them to not be flat tread wise but buckle. I tried upping the psi each pass until I got worse and 13-14 depending on the conditions is what yielded the best. Can't deny the results.

 

Funny b/c my results complete oposite, at 13-14 they spin and would cut 170's-80, drop drop drop and now i still wonder how they would be at 9 psi

 

Maybe power is the difference or did you have the same results on your old set up?

Also what springs and struts are u running?

I am considering a set of et streets in 27's. Really want to run my new wheels.

 

Well majority of the data was from the old setup, still leavin on the 2 step @7k...
New setup still leaving at 7k but started back at 13 psi and found my sweet spot at 10psi... Now that i have data logs i leave at about 12psi of boost.
I run a oldschool setup
Tociko iluminas ( setting2) , eibach prokit, ubotanium bushings, rotary extreme trail and toelinks, factory sway. When i get home ill make a excell sheet on all my60's new and old so im not speaking from memory.

What rpm is your 2 step set for?

 

I leave at higher rpm's. My 2 step is set for 7800. But my better 60 foots have come from free revs and that was closer to rev limiter. I too always datalog every pass. I have also found that stock touring model spring/ struts in the rear have worked the best for me. Have tried 4 different struts and springs. Now I feel this set up could be just a tad harder as it looks like it bounces from bottoming out.

So it sounds to me that there are different combos that will work just depends on your setup.

 

Oops. Here is side view.

 

that is correct but thats for street tires and does not pertain to slicks/drag radials

every car will have a different sweet spot
under laod/accelleration the tire will grow and psi will jump up so take that into consideration.
plus the compound will play a huge factor along with the manufacture

 

SO old setup 13PSi tires, 7k 2 step, 22 Passes average 1.740 60' (I removed anything over 2 sec as its not gonna give a relative avarage when it all went wrong)

New setup, 10-10.5 psi tire pressure 14 slips average 1.510 with a low of 1.369!!!
Theres a few more passes but i cant find the slips

 

Len, what kind of boost is it making on the 2-step?

 

data logs showing 12-13bls when i dump the clutch, I'll look at it in more detail just to be sure

 

Double checked, since I dont have a speed sensor (yet) I cant see first movment but can see rpm going above 7k, so
13 psi then .05 later 7600 rpm and 20 psi
The Dis-2 just holds the rpm, we do all the fuel and timing kung fu in the microtech when on the step

 

Here is a log of one of my better launches. First row is time, duty, leading, trailing, rpm, speed then boost in bars. 1.31 before first read the 1.45 after. This was from a few years back 6.44 1/8th @108mph

 

and 1.39 sixty foot.

 

I can see the new tires getting lower 60ft. There not spinning like the old ones. I don't look at the launch rpms and boost off the line. I look at how far the rpms/boost fall after the launch.

just a thought