- Joined
- Aug 1, 2003
- Messages
- 9,610
yes this is an old thread , id guess twister doesnt need any advice as this was almost 2 1/2 years ago since he posted
26" to a 28" is 7% diference in size
mph is a function of hp so you may not see a mph gain
if you were still making power at 5800 and dropping rpm by 7% (about 400 rpm) doesnt change your hp than you should trap the same but the 28 will add 7% to your load (same as dropping rear axle ratio) and the tires are heavier so mph could even go down
now if your 5800 trap rpm puts you past your combo(cam) and hp was dropping off before raching the traps and the 7% drop puts you back in where your car is making more hp than trap speed may go up
28s will need more to get off the line (youve droped your effictive rear ratio by 7% ) so your previous launch on 3.42s with 26 tire will seem like you have 3.18s with the 28 , but the 28 should grp allittle better allowing you to push the launch rpm a little higher without spinning out of the hole
another thing to consider when or before going to a 28 is the offset and width of your rim may cause interfernce with the tire and your wheellips or the frame and you may need to run air bags with a lot of air to keep the tire from geting ripped up or spacers to keep tire off the frame
and as shawn (tta343) pointed out if you still have overdrive thats always an option , i went 10.52 127 on a 26" 255/50 -16 on gtas ,with 1.50s for 60' on a 3750rpm launch (6-7 psi) using OD early in the run shifting to 4th anywhere from 55-5800, and trapping at 5400
im on a 400 trans now (no OD
) so running with a 28 inch tire puts me through traps at about 6,000 and to acheive the same ets as the 26" tire i have to launch harder and run more boost
mickey has a 27" 255/60-15 that i just tried on my 87 , 118.5 trap speed at only 5550 never got into OD , no fitment issues fits stock 7" but i have them on an 8.5" rim , and it sonly 3.5% change from the 26" tire
26" to a 28" is 7% diference in size
mph is a function of hp so you may not see a mph gain
if you were still making power at 5800 and dropping rpm by 7% (about 400 rpm) doesnt change your hp than you should trap the same but the 28 will add 7% to your load (same as dropping rear axle ratio) and the tires are heavier so mph could even go down
now if your 5800 trap rpm puts you past your combo(cam) and hp was dropping off before raching the traps and the 7% drop puts you back in where your car is making more hp than trap speed may go up
28s will need more to get off the line (youve droped your effictive rear ratio by 7% ) so your previous launch on 3.42s with 26 tire will seem like you have 3.18s with the 28 , but the 28 should grp allittle better allowing you to push the launch rpm a little higher without spinning out of the hole
another thing to consider when or before going to a 28 is the offset and width of your rim may cause interfernce with the tire and your wheellips or the frame and you may need to run air bags with a lot of air to keep the tire from geting ripped up or spacers to keep tire off the frame
and as shawn (tta343) pointed out if you still have overdrive thats always an option , i went 10.52 127 on a 26" 255/50 -16 on gtas ,with 1.50s for 60' on a 3750rpm launch (6-7 psi) using OD early in the run shifting to 4th anywhere from 55-5800, and trapping at 5400
im on a 400 trans now (no OD
) so running with a 28 inch tire puts me through traps at about 6,000 and to acheive the same ets as the 26" tire i have to launch harder and run more boost mickey has a 27" 255/60-15 that i just tried on my 87 , 118.5 trap speed at only 5550 never got into OD , no fitment issues fits stock 7" but i have them on an 8.5" rim , and it sonly 3.5% change from the 26" tire
