MFJ

iTrader: (4)

My T/A is pretty much bone stock. I went from a 245/50r16 to a 255/50r16. I know that changes the gearing a little being a taller tire. How much ET loss is that. I thought what I would lose in ET I would gain in less tire spin.

BlackScreaminMachine

iTrader: (17)

I am no expert, but I am willing to wager the difference should be unnoticeable.

MFJ

iTrader: (4)

I haven't noticed any real loss of ET, I haven't gained any either, but a little loss in MPH on the big end. It seems like it takes a little longer to rev up but I guess longer rev with a taller tire must be balancing out.

redtan

iTrader: (5)

Whatever differences you noticed in ET and trap were because of variances in how you drove, weather etc. There's no way 10mm worth of extra width and 5mm taller tire would cause any distinguishable differences unless you went to a different type of tire (from a/s to summer+, from summer to drag radial+ etc.)

My ETs and traps vary by a few tenths and mph on the same day with the same exact mods all from how I drive and launch it. If you noticed a difference, it wasn't from your tire but from how you drove it or the conditions.

BlackScreaminMachine

iTrader: (17)

122.5mm Old tire

127.5mm New tire

** Remeber the Aspect ratio is the 2nd number which is a percentage of the first... and thats the side wall which is your Overall Diameter or O/D

5MM difference equals... 0.20" or 3.15/16

You added 0.20" of meterial and OD increased by that much but I don't see that being of signifgance.

IMO.

*edit Redtan got there before me, the diff is not that much.

COOKIE MONSTER

iTrader: (5)

Why not go find out?

MFJ

iTrader: (4)

My 255/50 is a DR. My 245's were street tires. Maybe that's the difference I'm feeling.

redtan

iTrader: (5)

Ok that's a pretty big jump, and should very well affect your ETs and trap speed as you will be able to launch harder and get down the track quicker.

If your ETs haven't improved with the DRs vs street tires, then you either 1) didn't use them correctly thus did not benefit from having stickier tires or 2) you don't make enough power for stickier tires to make a difference.

I very much doubt #2 because even on a bone stock LS1 you still can roast the tires, so it must be #1. You just need more practice and launching skills to be able to put the much stickier tire to benefit at which point you should see a few tenths drop in ET and maybe lose 1-2mph in trap speed.

One more thing, as mentioned before, all these variances would be due to the compound of the tire and its benefits in launching ability. No gains or losses would be because of the slightly wider or slightly taller tires whatsover.

MFJ

iTrader: (4)

My 60' is quicker but my trap speed is down a couple of MPH. ET is about the same still. Getting ready to put in a new clutch and that should help with the launch too. I was just wondering why my 60' time was quicker but MPH was lower. Figured it had to be the tires.

BlackScreaminMachine

iTrader: (17)

You need to post timeslips and day/time so we can get an idea on weather.

My feeling is that IF Your HP to Weight Ratio is the same and all you did was go from Zero feet to 60 feet a little quicker, your still trying to move the same amount of mass with the same amount of power. I often seen my 60 foot improvements showing on the ET rather then MPH.

MPH is though effected by tire pressure and that if your running too little, and if you upped it and still cut the same 60 foot, your MPH WILL IMPROVE.

So depends on how much info you give us. What was the....

Time Slips before and after
Date and times of runs
Tire Pressure
Technique

MFJ

iTrader: (4)

I have them at home. When I get there I'll post some examples.

MFJ

iTrader: (4)

These were from a week ago. I'm launching as hard as the clutch will allow. Which right now is 2600 rpm. Any more than that it slips and takes forever to get the clutch smell out of the car. These runs were both from 2200 rpm launch.

Weather conditions. Best as I can remember.
84 degrees
DA 1730
Humidity 82-85%

Left lane Right lane
60' 1.965 2.019 1.986
330' 5.617 5.667 5.635
1/8th 8.514 8.534 8.518
MPH 84.11 83.54 84.00
1/4 13.181 13.182 13.103
mph 100.25 105.60 106.75

Does that make any sense? I have more runs from that night but they are just as weird as this. Could the beam not be catching my wheels? A week earlier i ran a 13.002 @ 108 with a 1.96 60' & 8.47 1/8th mile with a 1500-1600 da.

redtan

iTrader: (5)

Which one of those times was you?

It doesn't make sense that a lower 60' gets the same ET. Lower trap yes maybe by 1-2mph, but if you're hitting the same ET but with better 60' then you must be losing power up top.

MFJ

iTrader: (4)

All 3 runs are mine. 1 run in the left lane and 2 runs in the right lane. The lower my 60' gets the slower my MPH is on the big end. I also had a 2.10 60' with a 106.8 mph but it was a 13.29 run.

Before the DR's I was only getting 2.0 60' times but was consistantly in the 107.5 mph and was running the same low 13's even had a 13.006 on a 1.98 60'

BlackScreaminMachine

iTrader: (17)

Left lane Right lane
60' 2.019 1.986
330' 5.667 5.635
1/8th 8.534 8.518
MPH 83.54 84.00
1/4 13.182 13.103
mph 105.60 106.75

These ones show an improvement (driver). I never really bought into the 1 tenth in the 60' = 2 tenth for ET as that cannot be true at all speeds. BUT you also have to factor in driving as it is the driver that has a direct effect in shifting the car which will always be a variable even if your perfect, the trans can have an issue.

If your smelling clutch your most likely riding the **** out of it and it's days are numbered, at this point you should start saving for a new one and line lock.

I need to know the actual track you raced at and the day, IF you can the time of day. Also do you recall the tire PSI?

MFJ

iTrader: (4)

Jackson, SC drag strip. March 29th. 1st run was around 7:30 left lane, 2nd run was around 8:45 and the 3rd run was around 9:30. Estimating the times.
Tire pressure 1st run was 25 psi cold, 2nd run was at 35 psi hot 3rd was the same.

BlackScreaminMachine

iTrader: (17)

Carolina Dragway as of 04/02/12

7:53 AM 66.9 F 79 % 29.82 in Density Altitude: 1464 feet
8:53 AM 70.0 F 73 % 29.82 in Density Altitude: 1669 feet
9:53 AM 77.0 F 60 % 29.82 in Density Altitude: 2121 feet

Track 490 ft above Sea Level

The MPH shows that your in the high 12 range but I think its a issue with driver consistancy from start to stop and your clutch is probably not liking what your doing. The "Feels like it takes longer to Rev" is most likely slippage.

Taking the car to the dyno would show this in most cases.

What clutch is in there, milage, and what slave/master you running? Last time you bled it?

MFJ

iTrader: (4)

It was in the afternoon "pm". I bought the car with a "Zoom" clutch in it. Sucks!. Slave /master ??? Never bled it. It is low on clutch fluid though.

BlackScreaminMachine

iTrader: (17)

Bleeding the clutch is a requirement, master is most likely stock, and slave "should" have been replaced upon putting the Zoom in.

Search this section on "Gravity Bleed" I posted the proceedures a few times, follow this and you will give yourself the best shot possible.

MFJ

iTrader: (4)

It's Dot 3 brake fluid right?