transammiller

iTrader: (21)

just curious who here runs 4.30s with a six speed? i am considering a Moser 9" and i am curious about the 4.30s. i hear great things about the 4.11s.

jmm98LS1

iTrader: (28)

Had 4.56's originally and have 4.30's now, what do you want to know?

transammiller

iTrader: (21)

well i am driving the car from Dallas to Jacksonville, Florida and need to keep the revs down while i'm cruising. i know the 4.11s will keep me below 2000 rpm at 70 mph so i was just curious how much rpm you are running at 70 or so? i was considering 4.56s as well.

BlackScreaminMachine

iTrader: (17)

Run the gear calculator.

I would but it is blocked at work, for some odd reason.

I got a good friend who just became a moderator here in the Drag section always hounding me to go 4.30's but that is because I intend on racing on a 28" tall tire, I do not want to drive 28" on the street all the time, I have a tolerence but thats pushing it.

Now he has me driving around town in 4th..... to get used to a Th400..... UUUGGGGGGHHHHH!!!

SIC LSX

iTrader: (10)

based on a stock 275/40r17 = 25.6 inch tire

3.42's + 2000rmp's=89mph
4.10's + 2000rpm's=74mph
4.30's + 2000rpm's=70mph

based on 275/60r15 = 27.99 inch

3.42's + 2000rmp's=97mph
4.10's + 2000rpm's=81mph
4.30's + 2000rpm's=77mph

BlackScreaminMachine

iTrader: (17)

Thanks for posting that, also to note if racing and you run on a Bias-Ply like a ET Drag, it does grow approx 1" so you will get some more out of the gear before shifting.

airforcemanss

iTrader: (23)

i was not aware of this. so, running a smaller rim bigger tire is more beneficial for mph? so i guess for street racing a 15" (street lites) rim with some mt streets would be better than 17" rim with 315 nittos on the rear? i plan on doing 4.11's down the road but it seems like it would be a no brainer to run 4.30's it your still only at 2000rpm at 77mph!

i thought with a taller tire you would loose speed because of more rotational mass. and like the OP said above you would also get about a 1" flex on top of that for even more of a benefit.

good info not hijacking here but adding more depth to the OP's question.

BlackScreaminMachine

iTrader: (17)

Smaller rims means less meterial and the weight of the rim is more then the rubber of the side wall of the tire. The MPH comes in when the overall diameter of the tire increases. Its a cheap way of making a car have a higher or lower top speed.

I have seen some magazines like GMHTP when they had their Project Alero put a smaller O/D tire on to effectivly increase the Final Drive ratio in the transmission, the side effect is often the side wall decreases and even with a stickier compound the tire gets shocked too easily and spinning occurs.

An engine makes "X" amount of HP and TQ at a given RPM range (lets say idle to 7,000). A transmission gear and a final drive gear will determine the tq multiplication and at what mph is the car can do given the gear selection of the operator.

When you upshift or down shift, the motor is not making any less or more power, the ratios of the trans and rear end is effecting what is being put to the pavement.

Here is a great example of TQ Multiplcation, it is a Acura site but the explaination is sound.

http://www.team-integra.net/sections...?ArticleID=707

Going back to the MPH vs O/D tire size, the larger diameter you have given all the ratios not changing will allow the driver to stay in a selected gear long and gain more mph in that gear before being forced to upshift.

With working with Land Speed cars, one soon learns about what it means to have a properly geared car and that the "wall" exsist.

In 1/4 Applications where weight is an important factor and that most 4th gens tend to be on the heavier side like to have sidewall to cushion the shock and that with the mph it may run by the 1/4 marker, having a tire O/D higher then stock is a benefit since shifting into 5th will make the car nose dive just before the finish line.

Having more gears is better then less, the new 6 speed autos are showing that now. I am amazed when driving a new G8 and how the power feels seemless and unlimited, since there is not as large of gaps between the gear shifts.

**Edit**

There is one part that I forgot, when talking about MPH in relation to a Bias ply vs a Radial tire, Radial tires are stiffer and ultimately promote mph over a same sized bias-ply (same rim, same O/D), the benefit of the Bias-ply is to get that wrinkle wall and contact patch that for the most part Radials have an issue with.

Now the diff/gap between the 2 tires decreases if the bias ply uses a 15" rim vs a 17" rim and a radial given the O/D remains the same even with tire grow. The larger the rim, often is considered heavier, most times large diam. rims are not made with light weight metal either since strength is a big consideration in construction.