My car is a 88 CRX DX gutted in the rear. It has B16 first gen I/H/E and a 75 shot. My tires were 205/50/R15. I ran a 13.8 @ 104 MPH. My 60ft was a 2.3sec.

My second time out I changed the tires to 20" tall slicks, and opened the exhaust. I don't remember how wide the slicks were but I would guess around 7". They looked narrower than my street tires. This time I ran a 13.0 @ 100 MPH. 60tf was a 1.9sec.

My question is why did my mph drop even though I got to the end of the quarter faster. I see people running 110 mph with this ET all the time. From all the research I have done the biggest conclusion I see is low 60fts give you low MPH, it just doesn't make sence to me though.

Please give your experience and input. Thanks

 

bigger heavier slicks greatly improve your 60'ft and your overall time, but at the top end they tend to slow the car down because of the extra mass of rubber/wheels the motor has to turn.

 

And they are on the avg. lower psi of street tires

 

The 20" slicks are smaller than my street tires. My street tires are ~22" tall and the rims are about the same weight as the steel wheels the slicks were mounted on.

 

your not spinning as much off the line therefore lower trap.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by dunkd &raquo;</TD></TR><TR><TD CLASS="quote">your not spinning as much off the line therefore lower trap.</TD></TR></TABLE>I would agree with the fact that I'm spinning less off the line, but I don't understand how more traction/acceleration on the first 60 feet lowers my MPH at the quarter.

 

20 inch slicks tend to make the mph awfully low...

 

It's simple. Unless you're doing it wrong, you are running less air pressure in the slicks then in your street tires.

Doing a search would definately have helped. This topic has been covered hundreds of times in the FI and Drag forums.

 

A high 60ft. time will result in a slower ET, but a higher trap speed. And viseversa.

 

Doing a search would definately have helped. This topic has been covered hundreds of times in the FI and Drag forums. [/QUOTE]
I have searched this topic inside this forum and outside this forum. The threads don't answer my questions. Again, I realise a low 60 foot time will give you low MPH in the quarter. What I am having trouble understanding is why when you accelerate harder in the first 60 feet that your end MPH are low.

For example...you could say a person running a 16 second 1/4 mile will have a trap speed of about 80 MPH. If you take that same person and ran a 12 second quarter mile the end MPH would be higher. Now I would think a person running a 2.3 60 ft would have a lower MPH at the 60 ft mark then a person running a 1.9 60 ft. If you add the rest of the quarter mile to the 60 foot, why is the person with the 1.9 60 ft having an lower end MPH?

I need some help with the logic here, I am obviously missing something.

 

SLICKS

It's because most Hondas with good 60' times are most likely running slicks. Running slicks should mean that you are running lower tire pressure then street tires, which in turn helps you off the line, but hurts your acceleration the rest of the way down the track.

 

[QUOTE=slim9300]SLICKS

It's because most Hondas with good 60' times are most likely running slicks. Running slicks should mean that you are running lower tire pressure then street tires, which in turn helps you off the line, but hurts your acceleration the rest of the way down the track.

So your saying that the better gearing (going from 22" tall tires to 20" tall tires) and opening the exaust wasn't enough power to compinsate for the 4 psi tire pressure drop causing me to lose 4 MPH?

So that would mean that if I kept the same tire pressure and managed to get a lower 60 ft my end MPH would be higher, correct?

 

personally on my car i get lower traps with the street tires because i lose a lotta speed off the line but at one point in time when i was making less power i was getting the same traps with the slicks and street tires it didnt matter...what im saying is the general rule that better 60 ft = lower mph doesnt necessarily hold true all the times...but i have seen that 20 inch slicks seem to make ppl's mphs really low...and i know some ppl that went from 22 inch slicks to 26 inch (srt-4) and the mph went up a few...im betting if you ran some 22 inch slicks your mph would probably go back up some...

 

My co-worker has 24" tall street tires and ran a 12.12 @ 120 MPH with a 1.8 60 ft. He the added about 100 HP, dropped about 200 lbs, and changed to 26" tall slicks and ran a 10.88 @ 119 MPH with a 1.47 60 ft.

You say if I went up to 22" slicks from 20" I would gain a few MPH. With this example above it doesn't hold true. He also has pretty low MPH for his ET.

 

With better 60' times your mph is lower because you have closed more distance between your car and the line so there is less room to get up to a higher speed.. Make sense..

But a person with a shitty launch will have more room for high trap speeds but they didnt get the good launch so they are farther behind you hense slower ET but more room so higher traps..

Heres another good one.. If I started 100 feet in front of you and both our cars are exactly the same.. I have to go 1220' while you have to go 1320'.. I will get there faster than you will since I have less distance to go but you will be going faster since you have that extra 100' to accelerate..

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tgreaves &raquo;</TD></TR><TR><TD CLASS="quote">With better 60' times your mph is lower because you have closed more distance between your car and the line so there is less room to get up to a higher speed.. Make sense..

But a person with a shitty launch will have more room for high trap speeds but they didnt get the good launch so they are farther behind you hense slower ET but more room so higher traps..

Heres another good one.. If I started 100 feet in front of you and both our cars are exactly the same.. I have to go 1220' while you have to go 1320'.. I will get there faster than you will since I have less distance to go but you will be going faster since you have that extra 100' to accelerate.. </TD></TR></TABLE>

Ohh, good response. Essentially, if you have lower trap speeds than other people at similar times, just consider yourself a good driver.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">So your saying that the better gearing (going from 22" tall tires to 20" tall tires) and opening the exaust wasn't enough power to compinsate for the 4 psi tire pressure drop causing me to lose 4 MPH?

So that would mean that if I kept the same tire pressure and managed to get a lower 60 ft my end MPH would be higher, correct?</TD></TR></TABLE>

What tire pressure are you running in your slicks? How about your street tires?

I would say yes to the second question. But the fact of the matter is that no human has the consistancy to accurately be the judge.

 

Less air in your tires leads to more rolling resistance(more traction) but more resistance can make your car feel like a snail on the highway, ever notice how your car pulls to whichever said has a tire low on air pressure? Lower your air pressure to 15psi and go do a 4th gear pull on the highway and notice how long it takes to top it out, now put 35psi of air in them and do it again, i gaurantee you notice a HUGE difference, you'll also notice you get alot better gas mileage too

 

Good to get a little support on this one, as simple as it may be. And It seems obvious to me that this is what's going on for him.

 

The reason slicks produce lower MPH's is because of more rolling resistance. They hook more why? A: because the grade of rubber used has a higher coefficient of friction than other tires, and B: their sidewalls are softer so they dull the effect of immediate torque transfer and change it into sidewall wrap.

As a result, the same things that give you more traction at low speed is the same thing that works against you at high speed. The tires like to be stuck to the asphault, so they'll give you traction down low. The tires like to be stuck to the asphault, so they'll fight you up high.

BTW, cars also dyno at less power with the more driveline slack there is (which sidewwall wrap could definitely be considered as) because more work is being done and less force transmitted.


&lt;----just read "Devine's" response. My fault.

 

In addition, it is generally true that with less wheelspin off the line, you will trap slower. It happens all the time at the track.

I get crazt sideways out of the hole and only pull 1.9, and my car traps fast. If I come out less sideways and harder to a 1.7 or so, then I will have a quicker ET and a slower trap (generally speaking).

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kpt4321 &raquo;</TD></TR><TR><TD CLASS="quote">In addition, it is generally true that with less wheelspin off the line, you will trap slower. It happens all the time at the track.

I get crazt sideways out of the hole and only pull 1.9, and my car traps fast. If I come out less sideways and harder to a 1.7 or so, then I will have a quicker ET and a slower trap (generally speaking).
</TD></TR></TABLE>

Presuming all of the inputs remained constant, all of this is probably a result of:

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 1316130057 &raquo;</TD></TR><TR><TD CLASS="quote"> the same things that give you more traction at low speed is the same thing that works against you at high speed. The tires like to be stuck to the asphault, so they'll give you traction down low. The tires like to be stuck to the asphault, so they'll fight you up high.</TD></TR></TABLE>

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tgreaves &raquo;</TD></TR><TR><TD CLASS="quote">With better 60' times your mph is lower because you have closed more distance between your car and the line so there is less room to get up to a higher speed.. Make sense..

But a person with a shitty launch will have more room for high trap speeds but they didnt get the good launch so they are farther behind you hense slower ET but more room so higher traps..

Heres another good one.. If I started 100 feet in front of you and both our cars are exactly the same.. I have to go 1220' while you have to go 1320'.. I will get there faster than you will since I have less distance to go but you will be going faster since you have that extra 100' to accelerate.. </TD></TR></TABLE>

The distance of the quarter mile doesn't change. The only thing that has changed is the rate at which you accelerate through the first 60 feet. Weather you accelerate fast or slow through the first 60 feet, you still 1260 feet left to accelerate. So if you went fast through the first 60 feet you would think it would be a good head start on MPH for the 1260 feet you have remainder.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Jockobo &raquo;</TD></TR><TR><TD CLASS="quote">20 inch slicks tend to make the mph awfully low...</TD></TR></TABLE>

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by slim9300 &raquo;</TD></TR><TR><TD CLASS="quote">

What tire pressure are you running in your slicks? How about your street tires?

I would say yes to the second question. But the fact of the matter is that no human has the consistancy to accurately be the judge. </TD></TR></TABLE>

I was running 16 psi on the street tires and 12 psi on the slicks.