Ok, at work we had a little debate. The reason, I read somewhere today, that to increase speed, you needed to reduce tire size. I think the article said 15 tires were ideal for our Monte Carlos.

I thought this was nuts... Bigger tires cover more ground with each revolution.

A co-worker states yeah, The article is right because you lower the overall drive ratio.

Again, I was, WHAT... I know NASCAR runs 2.91 onlarger tracks and 3.71 forsmaller tracks or maybe it is the other way around, but we ran 4:56 rearends back in the day and took off our 14 tires and put on 15s

I think our drive chain is 2.9, and there is a 3.23 and 3.62 available.

Now I can see a circle track car running 2.91 and a strip car running 4.56. I can see a circle track car running 15s to keep them low to the ground for better handling and less drag. But street and basically street racing, bigger tires are better and bigger drive gear the better. Am I right or wrong? If I am wrong... then hell, there are a lot of cool 15 wheels out there.

 

a drasticly lower gear (numericly higher) wont increase your top speed, but sometimes a very slightly lower gear can.

on a number of cars with a 6spd manual trans. the top speed is achieved in 5th gear. running in 6th gear is a little too much load on the engine and it cant achive as high of rpm as it can with the lower gear ratio.

if you can rev out top gear a lower gear wont increase topspeed, but a higher gear may.

 

Ok... Brain fart... Stock tires on the Monte SS are 235/50/18 = 27.30" o.d., final drive 2.93:1, so if we went to 20" with 275/45/20=29.7" o.d.,

Ok... so, if I remeber right...
29.7*2.93/27.3=3.19 or new final drive ratio

so... if we could achieve 5500 RPMs in 4th gear, than:

5500 RPM * 29.7 / 336 / 3.19 = 152.40MPH vs
5500 RPM * 27.3 / 336 / 2.93 = 152.52 MPH

so... if ny math is correct, than the smaller tire, lower gear ratio is faster than the bigger tire, higher gear ratio.

Is my math correct boys?

 

It can't be because the stock tires are for 16" rims and the SS's have 17" rims. Not sure what the outside diameter is though to get you a good figure.

The higher gears (the ones that look lower) will give you more top end speed. I can't remeber the stock Monte but I "think" it's 2.93. The higher gear ratio's help out on acceleration and 1/4 mile times. I think the standard upgrades are 3.16 and 3.60 which will get you down the track about .2-.4 seconds faster, but they won't touch the stock topend speeds.

LAV74 would know much more about this as he has the upgraded transmission and racing gears.

Also thehigher gears will loose gas milage. You will go from like 29 on the highway to 27 or something like that.

 

Intimidator, the stock wheels on a 2006/2007 Monte Carlo SS are 18" with Goodyear RS-A 235-50-18. But I thinking now of putting on 16" with 205/50/16, lowering my Final Drive to 2.40 for an even faster topend. Then lower car and beefing the suspension. With the system I have in mind... My car will be a total of 4" lower between the smaller tires and spring height.

Resulting in a low, mean, road hugging machine. It will only be ok at the drag strip, but killer on the street.

 

Damn!!! I had no clue they jumped up to 18's!!

Well the 18's would still help out on the top end. The big keys with the accelleration would be rotational mass - the 18's probably weigh more - but the larger tires will offer the higher top end as well. 16's would just get you there sooner.

 

I'm sorry, but I disagree. Changing tire size has nothing to do with how many times your tires revolve per revolution of your driveline shaft. It does change how far your car moves on each engine revolution. Which is almost the same thing, I guess, just getting there differently. 27.3xpi=85.77". 29.7xpi= 93.3" or 8.8% faster. Final drive ratio is a factor of axle revolution to engine revolutions, basically. Smaller tires will spin up faster than the larger ones, they take less hp to turn (inertia). Taller tires will give you higher top end, but not necessarily in the 1/4 mi, just top end. More hp required to get there tho, because of the weight. Wheel weight is a real factor, also.
I have 2:93 drive in my Intimidator, but had 3:29 in my '01 SS LE. That car was about as quick off the line as this one. I have talked to my service tech about changing to a taller ratio, and that's what I would go with. 3:29. Very drivable.
Wayne
http://www.cardomain.com/ride/2319272

 

^^^ Totally on point...I'm sticking with 3.29 when i get my ZZP tranny...
But I need to get smaller wheels so I can see what the car can really do...

My 20' are not that heavy but the Rotors are...14' and 13' rear...Boo!!!!

 

Unless you can get lighter rims to help on that rotational mass. This is why Drag cars have the larger wheels in back and other 10 second sub cars. The larger tires will put more distance and will technically get better traction, but too heavy and you won't get up to speed in good time. It's a balancing act. You really need to test and see what works best at your hp/tq level.

 

Ok.. I was wrong!
A2006/2007 Monte SS has18"wheels with the stock tire being a Goodyear RS-A 235/50/18R which has an OD of 27.3How do I know this: 235 / 25.4 = 9.25. 50 /100 = .5 thus 9.25 * .5 = 4.63. We take 4.63*2 + trim size (18) = Tire OD or 27.25 or rounded up 27.3

So.. If you put on some 275/45/20 the OD would be 275 / 25.4 = 10.83. 45/100=4.5 thus 10.83 * .45 = 4.87 thus 4.87 * 2 + 20 = 29.74

Effective Drive Ratio:
Stock Tire / New Tire or 27.25 / 29.74 = 0.91627 This times our gear ratio of 2.93 or 0.91627 * 2.93 = 2.68 So the bigger tire lowers your drive ratio thus changing your cars performance.

Need Gear Ratio to bring your car back to Stock Performance level is:
New Tire / Old Tire x Current Gear Ratio or 29.74 / 27.25 * 2.93 = 3.197 or 3.20 would be the new Gear needed to maintain stock performance (THIS IS WHERE I MADE MY MISTAKE!)

The speedo changes too: So
20,800 / tire od = tire rev per mile or TRPM
Thus, old tire = 20800 / 27.25 = 763.30275
Thus new tire = 20800 / 29.74 = 699.39475
thus the variance factor is 763.30275/699.39475 = 1.09138

Now you can calculate speedo differences.
10MPH on Speedo = 10.91 MPH (Actual Speed)
20 MPH on Speedo = 21.83 MPH
30 MPH on Speedo = 32.74 MPH
40 MPH on speedo = 43.66 MPH
50 MPH on Speedo = 54.57 MPH
60 MPH on Speedo = 65.48 MPH
70 MPH on Speedo = 76.40 MPH
80 MPH on Speedo = 87.31 MPH, etc.