Tire size vs. gear for drag racing

[sutyak]

I'm currently planning for my drag tire setup for the 04 Mach 1. It is a single turbo 5 speed.
My debate here is whether or not to stick with the 3.55's and a 26" tire, or go down to a 3.90 or 4.10 with a 28" tire. Given the dyno I expect a trap of around 135mph, but have zero track time to substantiate this so it's all bench racing for now.
The valvetrain is not built for higher RPM than stock.

My question is what are the pros and cons of a 26" tire vs. a 28" tire?
How about tube or no tube?

Assume a street suspension setup. All roll bars in place and less than ideal spring rates for drag. No weight reduction.

[1320goat]

I don't know what your transmission gearing looks like. In my GT500 with the 6060 trans, 3.73, and 28" tall drag radials..top of fourth takes me to high 130's at 6500 rpm.

[1320goat]

Here are my trans ratios 1st-4th. Hope this helps. 2.97, 1.78, 1.30,1.00

[sutyak]

Here are my trans ratios 1st-4th. Hope this helps. 2.97, 1.78, 1.30,1.00

Thanks, but I'm not trying to calculate my RPM across the line, rather asking the benefit of a taller or shorter tire for the same overall ratio.

[1320goat]

Ok. I just wanted to give you an example based on your expected 135 trap. I don't know if you would reach that with a 28" and 3.90s or 4.10s. Good luck, I'll move along

[sutyak]

Ok. I just wanted to give you an example based on your expected 135 trap. I don't know if you would reach that with a 28" and 3.90s or 4.10s. Good luck, I'll move along

Yep it would be close!

[Tom]

taller tire will grow more giving lower rpms up top (depending on the type of tire)

taller tire will weigh more / add rotating weight and possibly slow you down

taller tire lengthens the contact patch, putting more tire on the ground for better traction (if same width). That longer footprint means any single point on the tire is in contact with the ground for a longer period of time compared to a short tire. That point has a better chance of grabbing the ground and pushing you forward.


I just did this and decided to go with 28" tall tires and 3.71 gears instead of 26" tall tires and 3.11 gears.

[Martin0660]

I just went through this in depth ....

combo was 26" tire, 4.10 gear, hit peak RPM 30' before the stripe, but had to run the tires flat to hook.

changed to 28" tires, 4.30 gear, hit peak RPM right on the stripe (at same power level). Car 60' better with less dram a higher tire pressure ... Installed my tubes, car came ALIVE ... 60' better than I actually though possible, got stable, and worked great ....

"downside" is that because the car works better down low, I picked up ET and MPH so I run out of RPM 70' before the stripe .. I would need to go back to a 4.10 if I stay with this tuneup... I won't now as running 11-0 True Strret is the goal, and with the new front half I can tame it down to 125 mph or so.

28" no tube ...,



28" on a tube, 2 psi higher tire pressure and nearly 1/10th better 60'



and finally 28" tire, air pressure dialed in, a truckload of launch I couldn't put in it before, all in tubes ....



yes to 28" tires, tubes, then you need screws, but with my stick car, I won't go back tubeless

[sutyak]

I just went through this in depth ....

combo was 26" tire, 4.10 gear, hit peak RPM 30' before the stripe, but had to run the tires flat to hook.

changed to 28" tires, 4.30 gear, hit peak RPM right on the stripe (at same power level). Car 60' better with less dram a higher tire pressure ... Installed my tubes, car came ALIVE ... 60' better than I actually though possible, got stable, and worked great ....

"downside" is that because the car works better down low, I picked up ET and MPH so I run out of RPM 70' before the stripe .. I would need to go back to a 4.10 if I stay with this tuneup... I won't now as running 11-0 True Strret is the goal, and with the new front half I can tame it down to 125 mph or so.

28" no tube ...,

yes to 28" tires, tubes, then you need screws, but with my stick car, I won't go back tubeless

Thanks! I was hoping you'd reply. What exact tires so you use?

[Martin0660]

Current tires are 28-11.50-15 ET Street R ... They are DOT, and the R is only 9" wide .... My next tire will be back to the Hoosier Quick Time Pro as they are 10" wide.

[yeahloh95]

with your power level I would go 3,73 and a 28" tire , stick shift like bias ply

[George C]

28" 373gear 1:1 ratio 160mph @ 7500
28" 355 gear 1:1 ratio 164mph @ 7300

My experiences for reference

[Monkeygrits]

Subbed. I'm very interested in this conversation. I'd like to get the rear-end built on my Mach 1 this spring and I was thinking on going with 4.10s, 31 spring axles, and a trak loc. Not sure if I need the Trac loc or not. I'm N/A though. I wanted to get drag radials because I would be driving it to the track when I go occasionally. Looking at a 15" wheel I guess but I have no clue what tire or size to go with.

[Cam99]

I've been thinking of this same thing Mark. The TR3650 has an insane low first gear (3.37 or very close IIRC) so first will run out very quickly, especially on 26" tall tires. My car has 3.55's currently and I'm still thinking 28" might be a little better to live with on the track. Curious what you end up doing.

[Dickbag 5.h0]

Another vote for 3.73's and 28". I run a 26" and 4.10's in my supercharged 2000 GT, trapping 123mph at the very top end of 4th gear(6k rpm) crossing the line. At 135mph I would definitely be in 5th, you should still be able to run out 4th with that combo.