Why are you spinning now? 60's inconsistant? if answer is no and no and all your doing is upping tire height/roll out and regearing to compensate for additional heigth/roll out, you essentially back in the same boat. Or are you planning to jump gear size dramatically with the additional foot print you'll have with the taller tires and thinking that is why you'll pick up a bit?

 

First, I'm not spinning off the line and my 60fts are very consistant with the 28" Goodyears, typically 1.48 to 1.50 from track-to-track.

Next, my 396 has a very broad power band, but it is somewhat maxed-out at 6500+ at the stripe with the 28" slicks. The 29" slicks will take me further down the track in each gear (in the broad power band) and could possible add some MPH at the stripe.

Additionally, it never hurts to try different combinations and evaluate the outcome. And, that is what I enjoy doing, testing different options.

WD

 

I see. It will be interesting to find out what happens, but am guessing you'll lose 60' and lost mph along with et...suspecting you'll drop approx .2-.3 in et and roughly 2-4mph and will be consistant 1.5? 60's

going up 1" in tire size sounds innocent enough, but the height is not the problem, it's the added roll out. Going from your 28" to 29" you will be increasing rollout by approx 4-6" depending on what your at already..with hoosier than i'm used to running it is an additional 6" of rollout when making this jump your proposing, and this is what kills performance.

I'm in the boat right now and am adding a 4.56 to compensate, buddy with his 454 chevelle is in the same boat and is jumping upto a 4.88. Dont forget too that with the additional rollout you will have, it's going to change the effeicency of the convertor too, so just going larger tire will cause more slippage since it's trying to work through less than adequate gearing.

Good luck and be sure to post what you find, but if it's like the rest of the results i've seen, you'll be regearing to end up at an overall final ratio that your at now with the shorter tire.

 

Josh
right now i'm running 28" tires and 4.11 in the 9". I'm supposed to drop to a 3.50 or slightly lower gear with the turbos, could I achieve the same thing by swapping to 30x9 tires or similar or is the regear my only choice?

 

you could change tires. I would not run that low of a gear

 

I'd be swapping tires to achieve the final gear ratio your looking for...taller the tire the better. dropping to that low of a gear is really gonna work that converter and build up alot of heat IMO. but you wont go wrong from a safety standpoint getting a bigger tire...just that much more contact area on the track so when she hits full boost you'll have a better chance of making it stick.

 

probably swapping converters to a lower one anyways with a nitrous sprag in there to take the extra torque, since I don't believe that converter in there now has one. I don't plan on spinning this motor much higher than 5200/5500 at the most so I think I'll run out of gear/tire rather quickly with 4.11s and 28s right now.

 

if you don't want to ruin the look just screw the inside. i've done it for years and i always mark my tire at the valve stem. never any movement and no, they don't twist.
i have 1.25 60's on a 3400# car.

 

[QUOTE]=IHI;5108821]going up 1" in tire size sounds innocent enough, but the height is not the problem, it's the added roll out. Going from your 28" to 29" you will be increasing rollout by approx 4-6" depending on what your at already..with hoosier than i'm used to running it is an additional 6" of rollout when making this jump your proposing, and this is what kills performance. [QUOTE]

Using Goodyear's data sheets and my math (circumference = 3.14 (π) x diameter) the difference in roll-out between a 26” and 28” slick is only 3”.

28” x 3.14 = 87.92"

29” x 3.14 = 91.06"

WD

 

[QUOTE=The Engineer;5145905][QUOTE]=IHI;5108821]going up 1" in tire size sounds innocent enough, but the height is not the problem, it's the added roll out. Going from your 28" to 29" you will be increasing rollout by approx 4-6" depending on what your at already..with hoosier than i'm used to running it is an additional 6" of rollout when making this jump your proposing, and this is what kills performance. my 28" to 29's was a 4" roll out increase...and it killed me...3" is'nt too far off and will really hurt performacnce is what i'm getting at unless you regear...summer is coming and proof in black and white will happen soon enough, but at least you'll know exactly what you have to do to get your ET/mph back.

 

You posted a range of 4" to 6", which 6" is "way off" from the actual 3" difference.

WD

 

You look at specs from different tire manufacturers and that 4-6" roll out is typical when comparing sizes. i'm a hoosier guy so i can tell you my old 28 QTP's had a 88" circumference, when i tried M/T 29.5's since Hoosier was out of the 29x9 at the time, they had a 94" circumference, the hoosier 29x9 i have installed now have a 92" circumference. so you be the judge about manufacturer listing's and actuals..m/t's .5" added an additonal 2" of circumference.


Point being going back to your inital post about wondering if your going to improve 60' with a taller slick...the bare facts, your going to slow down, no way around it since your reducing overall gear reduction by adding roll out, you will slow down your 60, not improve it.

 

Here is an update on the new 29" slicks (also Goodyears). Again, with the old 28" slicks my typical 60ft was 1.50 (at most tracks) with an occasional 1.48 at one track (Tulsa).

Last night at our local track there wasn't much heat in the track (night race), however, I had "very consistent" 1.50 60fts with the new 29" Goodyears! Additionally, it trapped over 122 MPH which is an improvement of slightly over one MPH.

So, the 29" slicks "did not" cause me to lose anything in the 60ft and considering the track conditions last night, I believe the potential is there to possibly improve on those occasional 1.48s I've had. Furthermore, the 29" appear to yield much more consistent 60fts. Definitely a win-win outcome with the new 29s!

The moral of this story is to make your own decisions related to your car’s setup and then do your own testing to determine the “actual” outcome. Cookie-cutter advice here on the forum doesn’t fit every situation.

Also, I don't use rim screws and I always mark the rim/slick. After the runs last night, both slicks slipped about one inch on the rim. Ouch! Hopefully, once the mounting slick-stuff dries-out they won't move any more.

WD

 

Well, you have 2 opportunities to go faster than normal...spring/fall...post your results back during "normal" air conditions we all see for the summer time and we both know your going to slow down...hence the spring/fall rush to get a good air time slip...but if your's gets faster yet during the heat of the summer, you da man.

 

I have been involved in NHRA drag racing (off and on) for the past 30 years. But I do appreciate you brining the issue of "air conditions" to my attention and how those conditions can affect performance at the track.

By the way, my weather station showed the D/A to be around 1700 last night. Not exceptionally great air, or good traction to work with during the cold track during the night race. However, I was very pleased with my new 29” slicks, both the 1.50s and the consistency round-to-round.

WD