Slow Z28

iTrader: (19)

Since i'm switching from my 6spd/4.30 setup to a Th400, i'm gonna need to do a gear swap too. My question is, at what point does the line cross in which you should go with less gear instead of a taller tire.

Now I know the obvious stuff, the taller tire will have an advantage in terms of more contact patch, but the disadvantage of needing more power to turn that tire. Is there even a real difference between two combos that give the same end result? Just as long as you have the ability to turn the tire, a larger tire will be the better setup?

Just as an example:

28" tire w/ 3.50's shifting at 6200 rpm = 148mph
29.5" tire w/ 3.70's shifting at same rpm = 147mph

I chose 6200 rpm just because with converter slippage that'd be closer to the desired 6600rpm i'd think, then again i might be off a bit.

What would be the better decision, and i don't mind cutting up the car at all if needed to fit a larger tire.

Chris

Nine Ball

iTrader: (38)

You should always try and use the smallest tire that will maintain traction with your setup. But, taller tires have more contact patch and can be more consistent than smaller tires.

Performance wise, you will probably run a bit quicker with the smaller tire IF the traction is the same.

Pro Stock John

iTrader: (34)

Chris are you going to be all motor or + power adder?

26's + 3.50 gear is nice for driving.

I'm T400 + 3.50 + 28x10.5 right now.

LTLHOMER

iTrader: (10)

Taller tires have more sidewall (and contact patch as mentioned before) and should theoretically hook better than a smaller tire w/ less gear.

TH400 + 4.10 + 30x12.5 et streets for me.

Slow Z28

iTrader: (19)

PSJ - power adder.

would one be more stable than the other at such high speeds? would the shorter tire be better since it has less of a sidewall so at the top end it has less "sway"?

BTL FED

iTrader: (9)

Yes the shorter tire will be more stable at the top end because there is less sidewall. But once you get used to the sway its not really a big deal. When I went to frank hawleys school I drove a supercomp and we were running a 34x17 or so slick with about 12 lbs of pressure in it. Talk about sway, at 150 mph it will make your butt pucker

Pro Stock John

iTrader: (34)

Chris if you are spraying those cubes, you will probably want to race on 28's to hook it.

I might get a set of 275-60-15 m/t dr's for the street. I don't like how wide the 325's are, and I'd rather run the taller 295's if I can fit them but the car starts to look ghetto on the street.

Slow Z28

iTrader: (19)

I just wanted to get it right since I have to do a gear swap. I guess going with the lower ratio and the smaller tire would allow me to do the cheaper thing and get a larger tire later on if i end up surpassing my goal and keep that lower ratio.

Pro Stock John

iTrader: (34)

Does gas mileage have any importance?

What kind of tires are you going to roll on most of the time?

Slow Z28

iTrader: (19)

gas mileage isn't too big of a deal since i have a daily driver.

street most of the time are gonna be some 28x11.5 QTP's. otherwise running on a full slick at the track of course. new tires will be needed soon so i wanted to get everything setup right so i didn't order something i didn't end up using

SilverGhost

iTrader: (53)

chris i agree with john in that if you are going to spray that motor off a T brake or what not then you should go for the larger tire.

the car will at least be more consistent in that manner, but I would expect it to sixty foot better as well.

Pro Stock John

iTrader: (34)

I doubt you'd want more than a 3.73 gear for your 388ci + nitrous. 4.10's would be limiting you in third gear. My my combo 3.65's calc'd out being ideal but I went with 3.50 since I'd rather be bit undergeared.

Slow Z28

iTrader: (19)

yeah, like i posted, i'm debating between the 3.50 and the 3.70 gearing. But spray off the t-brake that is why i was inquiring about the 29.5 tires and then sticking with a 3.70 gear ratio. Those calcs would get me to my ultimate goal, and i'll just "suffer" in the meantime if it's not enough gear.

Pro Stock John

iTrader: (34)

If you run a 29.5 you can go 3.70, 4.10 etc., but I don't personally plan to run more than the 28x10.5 I have now.