Need some advice to wheel and tire set up

[Bluemustang]

Could do what I planned. Pickup a set of 19x11 in ET24 and ET50. Then it should fit up front with no spacers or extended studs. But obviously lose ability to rotate. MRR M600 or APEX SM-10 have offsets that will fit the front in an 11" wide wheel.

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[MajHazrd]

Looks like everyone is good with the the smaller diameter of the 275 (1.3") or of the 285 (1"). With stock diameter 275/40ZR19s (27.8") I'm getting about 132 - 135 mph in 5th at 6500 rpm.
Anybody have any idea what top speed is in 5th with 275/35/19s?

I want to square up for track day and 9.5" rims from American Muscle. Looks like I have 3/4" clearance from rim to the strut.

 

[bnightstar]

I'm getting about 132 - 135 mph in 5th at 6500 rpm.
Anybody have any idea what top speed is in 5th with 275/35/19s?

I want to square up for track day and 9.5" rims from American Muscle. Looks like I have 3/4" clearance from rim to the strut.

I got 275/35 square for the season on the PP wheels but you need to consider that 275/35 square lowers the back to much and changes how the car sits. I good advice is 275/35 with 285/35 on the back. Don't know regarding MPH but it's my worry as well.

 

[Norm Peterson]

I'm getting 138 mph @ 6500 with 275/40-19's, MT-82 original gearing, and 3.73's in the axle. This considers tire compliance effects but not any possible tachometer error, lag, or parallax error in reading it.

With 275/35-19 that goes down to 133 mph. 285/35-19's give 134 mph.

There could be slight variations from those numbers, depending on whose tires and their actual dimensions and revolutions per mile.


Norm

 

[MajHazrd]

I got 275/35 square for the season on the PP wheels but you need to consider that 275/35 square lowers the back to much and changes how the car sits. I good advice is 275/35 with 285/35 on the back. Don't know regarding MPH but it's my worry as well.

I have BMR springs that lower it about .75 to 1" in the front and .5" in the rear. So there is still a .5" difference, but appears to be what everyone is running on the track.

 

[MajHazrd]

I'm getting 138 mph @ 6500 with 275/40-19's, MT-82 original gearing, and 3.73's in the axle. This considers tire compliance effects but not any possible tachometer error, lag, or parallax error in reading it.

With 275/35-19 that goes down to 133 mph. 285/35-19's give 134 mph.

There could be slight variations from those numbers, depending on whose tires and their actual dimensions and revolutions per mile.


Norm

Thanks Norm. I can create some formulas knowing the speed at 6500. At 7,000 with the smaller tires I should still be able to get just over 140 mph in 5th.

 

[bnightstar]

I have BMR springs that lower it about .75 to 1" in the front and .5" in the rear. So there is still a .5" difference, but appears to be what everyone is running on the track.

With 275/35 square you have 1.1" drop at the front and 0.4" at the back which makes the front of the car sit higher than the back.

 

[Norm Peterson]

Thanks Norm. I can create some formulas knowing the speed at 6500. At 7,000 with the smaller tires I should still be able to get just over 140 mph in 5th.

When one or two mph might matter, you should be including about a 3% drop in actual speed from what working directly from tire diameter or nominal tire size would indicate. IOW, if calculating from a 27" tall tire gives you 140 mph at some rpm "X", your true road speed at X rpm with the same tire and gearing will be closer to 136. Most times this 3% approach ends up being very close to what working with published tire revs/mile gives.


Norm

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