The smaller the tire dia. the effective ratio will be heigher like 3.90 will act more like a 4.00 or so. But the larger dia. tire will have the opposite effect. And also if your lowered you might have to look at wheel well clearince
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07 REDFIRE GT 5 SPEED 3.55 gears
C&L Racer CAI XCAL2/Seq signals/GTAs/Steeda UDP/CHE K Member Brace W/Torq Links/J&M LCA/Spider DS/PRO.50 Shifter Hurst handle & "T"/Meziere EO2/ARH LT catted H /Prothane MM/Delet Plates/SLP BOSS 429 Scoop/Accel COP/PowerSlot/Hawk Pads/Tokico D-Spec/CHE Panhard Bar Brace/Steeda Adj. Panhard Bar/BMR F/R Sway Bars/Cervini ducktail spoiler/BMR UCA Mount/CHE UCA/GT\CS Rear Cover/AMChrome Bullets 18x9/10s/Nitto 255/45&295/45
Tillman Dyno Tune 307HP/322TQ
the 315 will give you a height of 25 11/16'' and the 295 will give you a height of 27 7/16'' a difference of about 1 3/4'' OAD. the 315 will take about 15% more revolutions to go the same distance. That will give you at least a 4+ rear ratio. What tire is currently on the car? Lets say it is something like a 265 which is 10.4'' wide. you move to 315 which is 12.4'' wide. That is a difference of 2''. If you add 25mm (1'')to your existing offset, (which can be done with a 1'' wheel spacer) you will be splitting the difference evenly. stay under an 1'' of additional offset and you should be golden even factoring lateral deflection when the car is cornering. there should be no tire-to-fender issues on the outside. The inside will have more than enough room. I typically add 2'' just to the inside. Thats the good news, the bad news is; I have never ever seen a 295 45/17. So go with the 315's they look cool and they are 7/8'' wider.
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97 Cobra-03 Cobra t56 and alum DS, SPEC111 clutch, FRPP 4:10,T&J Performance Forged 4v(8.9:1), Manley rods, Novi 2000 w/ Fast Track A/A I/C, Barry Grant Fuel syst., BBK longtubes and H-pipe, MSD ignition, Detroit True Track, Magnaflows, 315 NT01's on 17 x 11's, KB BAS, SCT tune and about a million other things. 575 RWHP. Going into the shop this winter, looking for 650 RWHP.
Right now it really doesnt matter what I have on now because they are 20's so the fact that my rotational weight is alot means that I couldnt even tell if the size is effective or not.
But they are 275/35/20
Yeah the 315's I think will look SICK but I am going for whats going to get me down the track the fastest. If its going to be a .1 second difference to me its worth it but if I wont see that then which ever tire fits better.
the 315 will get you down the track faster because it is smaller. the smaller the tire, the more torque. Also it is wider, so more contact patch. I love the guys who ask questions because they don't know, then get wise like they know it all.
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97 Cobra-03 Cobra t56 and alum DS, SPEC111 clutch, FRPP 4:10,T&J Performance Forged 4v(8.9:1), Manley rods, Novi 2000 w/ Fast Track A/A I/C, Barry Grant Fuel syst., BBK longtubes and H-pipe, MSD ignition, Detroit True Track, Magnaflows, 315 NT01's on 17 x 11's, KB BAS, SCT tune and about a million other things. 575 RWHP. Going into the shop this winter, looking for 650 RWHP.
the 315 will get you down the track faster because it is smaller. the smaller the tire, the more torque. Also it is wider, so more contact patch. I love the guys who ask questions because they don't know, then get wise like they know it all.
thats probably what I am going to look into then because I need all of the low end to get me off the line the fastest sense I am running Centrifugal. I have NO problem getting up to speed.
Also what does that last comment suppose to mean I really hope nothing negative towards myself
With the power you are making you could be looking at running out of gear when in 4th gear in the 1/4 mile. I'm sure you don't want to cross the line in 5th gear. I would go with the taller 295s. Worst case you may need to bring the rear up a little bit. Post some pics if you get a chance.
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DHG #01434 Bullitt - full JLT intake, MGW shifter, Accel coils (I wish I had 4.10s, o/r H, tune)
Black 89 LX(the drag car) best 8.75 at 80 mph in the 1/8
97 Mountaineer V8 AWD
I have 17s on mine. The rear tire is 315/35/17 take a look in my gallery. Im looking to do 20s. I personly think 315s are pretty wide on this body style. Just for daily driver though lol. hopefully that will help you out.
295/45R17 or 315/35R17 2005 Mustang GT 
