Any benefit to a shorter tire???

[2016GTJake]

I realize almost everyone is trying to keep their tire height similar to stock... is there a benefit to purposely going down in tire height. Nothing extremely drastic. Looking at maybe 3/4 to 1 inch shorter. In theory Im thinking ill see a little better times on my 60 foot.

Ive had my 2016 Gt (automatic transmission) for less than a month. Was very committed to finding a manual 3v s197 until I came across a smoking deal on this car. Long story short, i'm new to the s550 and trying to find the best setup.

This is mostly used as a weekend car, with 10ish drag strip days a year. Possibly some road course days in a year or two.

In the last month ive gotten an axle back, sct tuner, and c&l intake. Working on wheels and tires now. Im also debating between Going shorter tire or swap to 3.73 gears when the one piece driveshaft shows up.

goal is 12.5 1/4 mile n/a

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[BmacIL]

goal is 12.5 1/4 mile n/a

This can be done with none of that. If you really want to improve your 60 foot, get a pair of 17x9.5 or 17x10.5 wheels and MT Street S/S tires, either 275/45R17 or 305/45R17 respectively, along BMR's CB005 cradle lockout. You'll run low 12s without the tune/intake if you know how to launch and shift.

 

[Hack]

Yes there can be benefits to a shorter tire. Favorable gearing for launch and possibly lighter weight. In theory.

In practice I'm sure Big Mac is correct.

 

[Idaho2018GTPremium]

Keep in mind a smaller diameter tire reduces the contact patch area, thus reducing available traction. A larger diameter tire is "flatter", less arched. It's one of the reason top fuel drag cars' tires expand. They get narrower which seems counter intuitive, but flatter, thus increasing the contact patch for traction in a straight line.

 

[Hack]

Keep in mind a smaller diameter tire reduces the contact patch area, thus reducing available traction. A larger diameter tire is "flatter", less arched. It's one of the reason top fuel drag cars' tires expand. They get narrower which seems counter intuitive, but flatter, thus increasing the contact patch for traction in a straight line.

Like the GT350R tires have less traction than the GT350s? At the limit, in theory you are right, but a 1/2 inch diameter change on a 28 inch tall tire isn't going to do much.

 

[CrashOverride]

The shorter effective gearing is helpful, but I think the problem is that there is so little sidewall, then they can't grab like a smaller-rim wrinklewall tire. I think you will get better performance with getting the stickiest tire you can find for drag racing.

For road courses, I think you would need to know the track and where your shift points are. If you spend a lot of time out of the power zone, then it might help a little, but if it's going to cause you an extra shift, then it won't be worth it. Technically though, with the decreased diameter, you would also get lower inertia, so your brakes would be more responsive (And due to the gyroscope effects of the spinning mass, your steering would be a little easier).

But for the cost of it, I would spend the money on something else - go with the 3.73's if you really want the shorter gear. I have it in my PP car, and I like it, but I will say that if you drive around town and like to keep it around 2000 RPM, you are going to shift a lot. I am in 5th at 45-50, so I run through the gears every time I need to stop. I could easily do 1-3-5 but I don't like to do that because it's harder on the synchros.

Also, if you ever think you will supercharge it, you might want to keep the stock gearing to aid in traction.

 

[Shifting_Gears]

Thinner sidewalls are counteractive for drag racing.

The gearing effect is the selling point but stepping down a size essentially won’t produce a major benefit and any benefit could be countered by increased traction or hop issues of a shorter sidewall.

A real drag tire has a soft and tall sidewall to allow the tire to flex and dig into the pavement.

Lighter driving driveshaft and 3:73 swap will provide real, consistent gains.

 

[2016GTJake]

I greatly appreciate the experience. A lot to consider. Hadn’t even considered the contact patch being affected by a shorter tire. This being a new set up... I’m thinking I’ll run as close to stock as I can.

BmacIL brings up a good point tho. Might not be a bad idea to get a set of drag tires purely for drag strip days.

thank you all for the input!

 

[Roadway 5.0]

If you drop from a 45 series to a 40, 35, or so on (with width constant), you’ll also lower the car a bit closer to the ground. Good for handling, not so good for clearance.

 

[Dana Pants]

Autocrossing people adjust tire height to get the right top speed in second gear.

My autocross rear tire is 285 30 r18. Definitely makes the car more spunky compared to 275 40 r19.

 

[Cory S]

I'm going slightly shorter myself.(3/4") My 16' 6R80 with 3.15's is just a titch tall in gearing. Going to 315/35/17 555R rears, and skinny fronts. I'll save 65-66lbs of weight as well over the stock 255/40/19's.

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