Difference in ET times with 4.10 gears?

[kooldawg6]

what do guys think will spin more stock 17 oem tires or rims or the 18s oem s ??????????with 4.10s

Given that the 17 and 18 are the same tire, it should be very close traction wise. In stock sizes, the 18 is about .1" taller than the 17. The 17 will have about 1" more sidewall to flex possibly helping straightline acceleration. The 17 wheel/tire combo also weighs less(I weighed mine when I did the swap, but I don't recall what either was )

 

[HIGH HEAT]

does anybody have 4:10s with a s/c? can you hook up at all?
what will 4:10 do to the rps' at hwy speeds with a manual

 

[stangdude2000]

what do guys think will spin more stock 17 oem tires or rims or the 18s oem s ??????????with 4.10s

The 17s most likely. Check my previous post in this thread for an explanation.

 

[DarkFireGT]

Why would the 17's spin more? You have more sidewall which means more surface area touching the pavement.

 

[ski]

In horrible weather @ one of the worst tracks in Florida...

Stock - 13.9+ @ 100
Pre 4.10s - CAI & Tune 13.8+ @ 102
Posst 4.10's - 13.1 @ 105

You also use drag radials, correct? If so, then it appears that gears, DR's, H-pipe, and pulleys reduced your ET by a total of 0.7 sec.
Did you install all of those mode simultaneously, or one at a time? If it was the latter, then how much of an ET improvement did you get from only the gears?
It also appears that your CAI and tune fell short of your ET reduction expectations.

 

[stangdude2000]

Why would the 17's spin more? You have more sidewall which means more surface area touching the pavement.

Well its more an educated guess, but could easliy be wrong. As long as the tire pressure is the same, you'll end up having the same contact patch area regardless of the sidewall or tire width. Pressure is force (weight) divided by area, so area is weight divided by tire pressure. 3500 lb car at 30psi would result in 4 contact patches about 29 square inches each if the weight was distributed evenly. Between tire widths, all that would change at the same psi is the length and width of contact patch. So theoretically, same friction.

With 17's, it would go back to the moment of inertia. Since it has a lower inertia, it needs less torque to get spinning. This is all theoretical, of course, and who knows how the real world would take its effect.

Can you tell I'm an engineer? Or enginerd as we lovingly say...

 

[DarkFireGT]

Well you should never run street tires at the track with 30 psi, for one. For two, at the same psi, a 18" tire with a side wall of 45 is going to have less contact with the road than a 17" tire with a sidewall of 55. Even if they're at 30psi, the 17" tire is going spread more because of the extra rubber. When you drop the psi down to 15-20, that multiplies the amount the 17" tire is able to spread out. While it does take less for for the engine to spin the wheel, you'll get more of a difference in contact surface area, than rolling inertia.

And that's just my take on it. I could be wrong as well. But if 18's were the best, drag racers would use those instead of 15's and 17's.

 

[anticubicle]

If you take drag racing seriously at all or just do it as an every other weekend hobby the best thing you can do for yourself (and the other racers even!) is buy some Mickey's and a set of cheap wheels.

 

[Five Oh Brian]

Given that the 17 and 18 are the same tire, it should be very close traction wise.

Actually, they are not the same tire - not even the same brand. Ford installs Pirelli PZero Nero All Season tires for the 17" wheels on new Mustangs, but uses BFG G-Force TA KDWS's for the 18" wheels. The Pirelli's are more of a long-life tire that offers less traction than the slightly softer BFG's.

Best 60' time I've ever run with the factory 18" BFG's was 1.865 with 26 psi. With 23 psi, best was 1.889. However, I really had to do big burnouts to warm them up enough to hook like that, and results were very, very inconsistent on the factory tires. Some runs were in the high 1.80's, many in the 1.90's, some over 2.00, so it was hard to dial in for bracket racing with any real accuracy.

Now, I only used drag radials at the track for consistency's sake. Short burnout to clean them off, then stage and go with perfect traction every time. Best 60' time with drag radials has been 1.833 and the worst 60' time with drag radials has been 1.899, so they're super consistent. Now I can dial in much easier with just the air quality (DA) to account for.

 

[kooldawg6]

Originally Posted by kooldawg6
Given that the 17 and 18 are the same tire, it should be very close traction wise.

Actually, they are not the same tire - not even the same brand. Ford installs Pirelli PZero Nero All Season tires for the 17" wheels on new Mustangs, but uses BFG G-Force TA KDWS's for the 18" wheels. The Pirelli's are more of a long-life tire that offers less traction than the slightly softer BFG's.

Obviously, I wasn't clear on that statement at all
I do know the factory tires are different brands for the 17 and 18 wheel. I was meaning if you had a 17 and 18 tire of the same brand. Very easy to see the confusion in my original statement

 

[stangdude2000]

Well you should never run street tires at the track with 30 psi, for one. For two, at the same psi, a 18" tire with a side wall of 45 is going to have less contact with the road than a 17" tire with a sidewall of 55. Even if they're at 30psi, the 17" tire is going spread more because of the extra rubber. When you drop the psi down to 15-20, that multiplies the amount the 17" tire is able to spread out. While it does take less for for the engine to spin the wheel, you'll get more of a difference in contact surface area, than rolling inertia.

And that's just my take on it. I could be wrong as well. But if 18's were the best, drag racers would use those instead of 15's and 17's.

Thats actually not true. Against the law of physics. As long as the tire pressure is constant - doesn't matter if its 15 psi or 30 psi - the total contact patch between ANY two tires supporting the same amount of weight will be the same. Switching tire profiles will merely change the shape of the contact patches. At 15 psi, evenly distributed weight on all 4 tires, our cars would have 4 patches each a ballpark 58 square inches. Increase tire width from 8 to 10 inches, for example, and you would decrease the length of that contact patch from 7.25 to 5.8 inches.

I agree contact patch would effect more than the inertia, especially with vehicles this size that aren't close to optimized, but it is not something that should be overlooked either. Inertia is one huge reason why people use lightweight flywheels, small rims, and even aluminum (or lighter) driveshafts. You'll never see a serious drag racer merely drop rim size (on drive wheels) without doing something to improve traction.

 

[ragged86]

i ran 8.67 in the eight mile with the factory 3.31 gears on the pirelli factory 17's, c@l cold air, and a tune. with the 4.10 gears i ran a best of 8.31 in the eighth with drag radials. my best 60' on the pirelli tire was 1.97, and with the drag radials and gears it was a 1.92. i need a converter really bad.

 

[billy_tripper]

Why would the 17's spin more? You have more sidewall which means more surface area touching the pavement.

The 17's do NOT have more surface area touching the pavement. I can see why it would be easy to think that when both of the tires are 235 width, but the width is referring to section width (the farthest outer edge of the sidewall when it's blown up on a standard rim). With the 18, you have less sidewall and so it doesn't curve back inward as far when you get out towards the tread of the tire. Therefore, the tread is wider on a 235/50 compared to a 235/55 by a substantial margin. I just learned this from looking at a lot of new tires and comparing sizes and section widths, etc.

edit: I have a 235/55r17 here and a 245/40r18 to compare. I know that's a different size, but I'm just using it to prove a point. The 245 is only 10mm wider and being a low pro 40 series you would baredly have any sidewall flex. I did some measuring and on the 235/55r17 and I think you should be able to get 8 inches across of contact if the air is REALLY low. About 7 with normal air pressure. On the 245/40r18 you would get about 9.5" of contact with regular air pressure. 10mm is less than half an inch and you're gaining over 1.5" with the 40 series 18".

 

[chubhunter]

I was running 3.31 gears. I've tried launching at different rpms but I've found about 1500-1800 to be the best. After I got the gears it seems like I can't go over about 1800 and the tires try to break loose. It's an auto so I don't have to worry about powershifting, and shift rpm and I didn't get a timeslip either time. Thanks for the help guys and any more input is appreciated. I may try the factory 17's to get my time down a little, but I still am boggled by the small gain from the 4.10's when they feel so much stronger. The only thing I can figure out is the really cold temps from the first run helped me.
Also, without the gears I ran an 8.9 first, then an 8.8, then a 8.74, then an 8.8 something. With the gears I ran 7 runs and even when I got a horrible start I still ran a worst run of 8.76.

I changed from the factory 3.55's to 4.10's in my 05 and my times didn't improve either. I believe some of the problem was very hot track temps with the 4.10's. And I'm still running the stock tires. Wheels spin was a huge problem. Even when I would get a real good 60 ft time I would blow it by completely losing it when I hit second gear. Wheel spin is a big problem. However on the street it feels so much stronger and I would never go back to the 3.55's.