Oh Boy.....

DigUout · June 7, 2001

This is Part II of a reply started in Aftermarket.

I went pouting into Discount Tire after my topper/rack/light scheme didn't work out like I'd planned and drowned my sorrows in a new set of tires and wheels. I'd been running stock rims and some 245's but with the topper, the truck just didn't look good. So I bought 4 Eagle Alloy 589's and 4 Pathfinder (BFG) 285's. Oh my God the truck looks hot! And big!

I told the guy to crank the torsion bars no more than an inch if they needed, but if they wouldn't fit with that we'd go 265's on my stock rims. When they brought my truck out (the last of the day) I watched them drive around the lot and saw nor heard any rubbing. The guy told me he cranked the torsion bars almost to the max, 2 threads left, and said the front's a little bouncy. Why I didn't tell him to get back in there and bring it back down a little, I don't know. I must have felt bad for keeping them late....

Well 10 miles down the road (and 250 from the house) I am bouncing like I'm in the saddle. All I needed was stirrups. 200 miles through 2 lane Colorado roads for 4 hours! I couldn't go back because they were closing and following me out. I didn't want to stay the night in a hotel just to have them adjust it in the AM, so I drove home with a noticeable loss in acceleration and the front end bouncing like a years' worth of playmates. Even the Edelbrock's couldn't help the bounce.

So I'm going to try to bring the front end back down a little tomorrow, because it's not fun to drive and who knows what kind of damage I'm doing. But the drastic loss in power, is this normal? I expected a little less umph and MPG, but with the 4:10's I'm losing my acceleration? I don't want to spend any more money on HPP3's, intakes, exhausts, ignition systems, etc. It just seems to drag now like I'm towing a HUGE load. Maybe I should've just gotten the 265's?

Thoughts? Similar experiences?

Shaners · June 7, 2001

Going from 245's to 285's is a big step up. I would think you would notice a pretty good loss of power.

If you are in good with the chevy garage they can reprogram your computer for 265's. They cannot go to the 285 size because it isn't a stock size.

Your speedo is probably off 6-7 mph at cruising speed. (it reads sixty and your doing sixty plus!!!) Having the computer programmed for 265's should cut your misreading by about 1/2. You'll also notice a decrease in your fuel milage too (significant if you don't add in those extra miles that aren't shown on your odometer)

I'd drop that torsion bar down. If you don't offroad, then you shouldn't have problems with rubbing. If it rubs you may have to trim some of the plastic inner wheelwell. My biggest concern is that you could break one of your torsion bars with them cranked up so tight!!!

kaspar139 · June 7, 2001

I can totally relate. I went from 265's ( 31.6" ) stock on my Z to ( 33x12.5x9.75 ) 33" tires. And that is only an inch and a half!!! It has gutted me... I am running 3.73 gears, so a 4.10 swap is imminent. I feel the power loss, acceleration loss obviously, and mpg loss. Looks great, but I have to do something to fix the power.

WHICH by the way, I was at the dealer yesterday having my rear diff/driveshaft looked at (it is making a weird chirping/rubbing noise when I accelerate from a stop). Anyway, I asked them about the gear change, and they said I wouldn't even notice a difference! The mechanic said the gears for the front & back with NO labor would be over a ?!!! I told him, "Don't expect me to EVER have non-warranty work done here, because I KNOW it doesn't cost that much.". Sorry for the rambling, I am just pissed off, and know your pain. And, driving in Colorado no less, it is hardly as flat as it is here in Houston!

(Edited by kaspar139 at 7:55 am on June 7, 2001)

DigUout · June 7, 2001

Turned the bolts back 3 apiece this morning and 90% of the bounce is gone. No rubbing at full turn or turning on a bump. I also seem to have gotten most of my acceleration back. They had the bolts slap up to the backstops! I'll have the speedo redone when I have the alignment checked next week. I was wondering how off it'd be, thanks for the tip!

Now the truck is outfitted like I want, I need to take some money and buy a digital camera to post some pics. I'm not sure how scanned 35mm pics would look online, but I've taken a bunch as I've upgraded. I'll check into it....

MountaineerTom · June 7, 2001

Almost all of my pictures on my web site are scanned 35mm pics. There are a few (like the pics of my step rails) done with a digital camera, but it's an old camera, so the quality is not that good.

DigUout · June 7, 2001

Thanks Tom! We've been trying to guilt trip the new grandparents into a digital camera to e-mail pics of the baby, but so far no luck!

Shaners a question- When my dad first taught me to drive a stick, he taught me to watch the RPM gauge more so than the speedo. As I've always had sticks, I still drive more by the RPM's than the speedo. Has putting on larger tires affected my RPM gauge like it has my speedo and if so how much and what do I need to do to correct it?

Frank S · June 7, 2001

I'm not Sheaners but I'll give you my $.02.

The larger tires does not affect the tachometer rpm readings because it measures revolutions at the engine,not the tires therefore tire size would have nothing to do with the tachometer being off.

You may notice shifts at a higher rpm with an automatic transmission because the engine has to work a little harder to turn the larger tires but that should be the only differencs with the tach readings.

Shaners · June 8, 2001

yZR2K is right... The Rpm's are driven of the motor... however the corralation between the tach and the speedo are different now. The tach is always where it was because it is checking the exact revs of the motor. Your speedo is showing slower speeds than what you are actually traveling, and you are racking up fewer miles on the odometer than what you are going...

Next time you are on the highway on a flat section (if there is such a thing in Colorado, LOL!!!)you can do a simple test...

Set your cruise at exactly 60 mph, and hit your trip meter and your stop watch at the same time as a "mile" marker. Go for six miles if you can (by the mile markers), and then check your watch and trip odometer. Your trip meter will tell you how far off you are in mph's by a factor of 10. And it should take exactly ten minutes.

I'm going to guess that you will travel about 5.6 miles on your trip meter for the 6 miles on the mile markers. Times it by ten and you should set your speedo at 56 to show a true 60 to the cops radar.

Please remember that this is an exponential number and it keep growing the faster you go... for example your speedo may be off by three at 45, and four at 60, and five at 70 mph.

DigUout · June 8, 2001

Six miles of a flat section of the road???

HAHAHAHAHAHAHAHAHAHAHA!!!!

Shaners, you're killing me! :cheesy:

Next time you have your road atlas handy, look up Lake City, Co. The only thing flat around here is the lake, but I find you humorous as well as informative!

Seriously, thanks to both of you for the RPM info. My fishing buddy is a deputy and I thought he and I could sneak off with his radar gun and check how off the speedo is. Let you know what I find out.

Shaners · June 9, 2001

The radar gun would be the best bet!!!

mblrds · June 9, 2001

Six miles at 60 mph in 10 minutes?

I always thought at 60 mph, you're covering a mile a minute; 60 miles devided by 60 minutes equals 1 mile, but I could be wrong.

Is this some kind of new fuzzy math?

Shaners · June 9, 2001

Yes it is 1 mile per minute at 60 mph. Sorry about the fuzzy math... I knew what I wanted to say, but my fingers typed it wrong. I meant you should travel 10 miles in ten minutes @ 60 mph. With the bigger tires and the speedo being off... you will travel the ten miles on the "mile markers" in less than ten minutes, with the speedo at 60 because you are more than likely running close to 64 mph.

6 miles in ten minutes would equal out to 36 mph.

(Edited by Shaners at 11:41 pm on June 8, 2001)