Need some advice...

[GT500Steve]

You have DR's or slicks?

DRs.

 

[VTXFrank]

Don't worry so much about final gear ratio. You want to calculate what rpm you'll be turning when you cross the stripe.

Can ya help me out with how to do that? Seriously, my head is killing me today and it's just not making sense for some reason.

 

[joedls]

Can ya help me out with how to do that? Seriously, my head is killing me today and it's just not making sense for some reason.

Sure. I have a calculator on my computer. When I get home I'll plug it in. What is your trap speed? 1/8th or 1/4?

 

[VTXFrank]

Sure. I have a calculator on my computer. When I get home I'll plug it in. What is your trap speed? 1/8th or 1/4?

It's in my sig. That's on street tires though, not any kind of racing tire. I expect that will go up quite a bit with DR's.

Thanks!

 

[joedls]

It's in my sig. That's on street tires though, not any kind of racing tire. I expect that will go up quite a bit with DR's.

Thanks!

OK. I also will need your transmission gearing. I'm not familiar with your newer cars. Don't be surprised if your trap speed goes down as your ET gets quicker though.

 

[joedls]

OK. I got the info I need.

In the 1/4 mile, in 4th gear, with a 26" tire and 3.55 rear gears, if you cross the line at 116 MPH, you'd be turning 7025 RPM. That would be perfect for you car, IMHO, for the 1/4 mile.

In the 1/8th mile, in 3rd gear, you'd be turning 7055 RPM at 91 MPH.

I'm assuming you can bump your redline up to 7200 or so? I'd go with a 26" tire if I were you.

 

[stkjock]

I can tell you with my MT ET Street 265/40/18's in the rear the car doesn't launch worth a damn. It's almost like my car is in a reverse rake when I run those tires. There is no sweet launch rpm. They either spin or wheel hop. I'd go with max sidewall that you can.

Then your suspension. I had those and pulled 1.60 60s

The 275/50-15 is 26.1" diameter. That would be better with me being N/A and 3.55 gears?

I'm worried that using full on slicks would cause damage to the rear end or the stock clutch. Is this a valid concern using slicks?

Go 26" out back

That 28" tire is too tall with his gearing.

+1

Isn't there some kind of online calculator for figuring out the final gear ratio with different tires? My head hurts too much to research it.

Yes just google it, I don't have the link on my iPad

 

[TheKurgan]

Then your suspension. I had those and pulled 1.60 60s



Go 26" out back



+1

Yes just google it, I don't have the link on my iPad

Yeah I know the suspension sucks for drag racing, but the tires are going to happen first next year. I'll go with the same tire, a 26" 50 series Hoosier. I'm betting I can gain at least 4/10's in my 60 foot time just from switching tires/wheels.

 

[ILW84U]

Isn't there some kind of online calculator for figuring out the final gear ratio with different tires? My head hurts too much to research it.

This may help you out. It's an Excel file not an online calculator though.

 

[VTXFrank]

OK. I got the info I need.

In the 1/4 mile, in 4th gear, with a 26" tire and 3.55 rear gears, if you cross the line at 116 MPH, you'd be turning 7025 RPM. That would be perfect for you car, IMHO, for the 1/4 mile.

In the 1/8th mile, in 3rd gear, you'd be turning 7055 RPM at 91 MPH.

I'm assuming you can bump your redline up to 7200 or so? I'd go with a 26" tire if I were you.

Yeah, my RPM is set to 7300. I was crossing the line at 7100rpm from the tach in the 1/8th at 91.56mph.

So a 26" tire it is. I was thinking this is what I would need, but with this headache I have today, I had to make sure I was thinking correctly.

This may help you out. It's an Excel file not an online calculator though.

Thank you for that. I'll have to look at it when my brain stops cramping.

 

[joedls]

This may help you out. It's an Excel file not an online calculator though.

That spreadsheet is set up for a 5 speed. I'm pretty sure Tom has a 6 speed. Or the calculations I gave him are all wrong.

 

[VTXFrank]

I have a six speed manual. Thanks for looking that over!

 

[ILW84U]

Sorry about that. I didn't even consider that fact.

 

[06vistabluegt]

Mickey Thompson recommends bias ply for stick/trans brake cars and radials for footbraked autos. I ran radials when my car had a stick. They are either dead hook or spin like crazy. A bias tire is supposedly more forgiving. If they spin, chances are better they'll spin a little the grab instead of spinning in one place.

 

[VTXFrank]

Mickey Thompson recommends bias ply for stick/trans brake cars and radials for footbraked autos. I ran radials when my car had a stick. They are either dead hook or spin like crazy. A bias tire is supposedly more forgiving. If they spin, chances are better they'll spin a little the grab instead of spinning in one place.

I noticed that while reading up on the 2011+ GT's on various sites. A LOT of folks say the same thing. Their experiences on the track show the bias-ply doing better and being less "damaging" to the drive train because they will spin a bit, then grab.