Welcome to the Australian Ford Forums forum.

You are currently viewing our boards as a guest which gives you limited access to view most discussions and inserts advertising. By joining our free community you will have access to post topics, communicate privately with other members, respond to polls, upload content and access many other special features without post based advertising banners. Registration is simple and absolutely free so please, join our community today!

If you have any problems with the registration process or your account login, please contact us.

Please Note: All new registrations go through a manual approval queue to keep spammers out. This is checked twice each day so there will be a delay before your registration is activated.

Go Back   Australian Ford Forums > MotorSport > Drag Racing

Drag Racing Discuss Drag Racing here be it dirt or tarmac. Sponsored by Sydney Dragway.

Reply
 
Thread Tools Display Modes
Old 04-05-2014, 10:26 PM   #1
XTJG33
1968 XTGT
 
XTJG33's Avatar
 
Join Date: Apr 2010
Posts: 745
Default Tyre Height Question

Hi Guys,
I have a 1968 XTGT Replica with 4.11's in the rear running a 255/60/15 tyre (27 inches high). Last weekend i took it down the quarter and crossed the traps at 13.63 @ 99.84 mph @ 5100rpm. i was changing at 6100 and had a 1.912 60ft.
If i fitted a 26 inch high tyre, say 235/60/15, would i get a better 60ft time and ultimately and better 1/4 time. what rpm would i be crossing the line at?

__________________
Project: 1968 XTGT Replica http://www.fordforums.com.au/showthread.php?t=11297583
Project: 1977 TD Cortina https://fordforums.com.au/showthread...89#post6008989

Life is like a grinding stone,
it either sharpens you up,
or grinds you down
XTJG33 is offline   Reply With Quote Multi-Quote with this Post
This user likes this post:
Old 05-05-2014, 01:37 AM   #2
GTB 351
FF.Com.Au Hardcore
 
GTB 351's Avatar
 
Join Date: Jan 2009
Location: Country SA
Posts: 722
Default Re: Tyre Height Question

I tried this many years ago and it was a backward step. Having said that, it may not be in your case; there are so many variables.
Buy yourself a Moroso Power Speed Calculator. Available at any speed shop for less than $20.
__________________
The Car -
http://www.fordforums.com.au/showthread.php?t=11358570
The Engine Rebuild-
http://www.fordforums.com.au/showthread.php?t=11361067
GTB 351 is offline   Reply With Quote Multi-Quote with this Post
3 users like this post:
Old 06-05-2014, 03:52 PM   #3
Giant
FF.Com.Au Hardcore
 
Giant's Avatar
 
Join Date: Jun 2010
Posts: 4,759
Valued Contributor: For members whose non technical contributions are worthy of recognition. - Issue reason: Organising Nulon to sponsor AFF. 
Default Re: Tyre Height Question

I have played with diff tyre sizes as it effectively reduces or increases your diff ratio it can help obtain the correct gearing. I think a shorter tyre would help you. Try the calculators to work out what's best
Giant is offline   Reply With Quote Multi-Quote with this Post
3 users like this post:
Old 06-05-2014, 06:53 PM   #4
mex351
FF.Com.Au Hardcore
 
mex351's Avatar
 
Join Date: Feb 2005
Location: Wagga
Posts: 1,910
Default Re: Tyre Height Question

Ant's LS powered XD wagon used 255x60x15 mt's to go 13.2 by swapping to my 255x50x16 tyres it went 12.8.No other changes just rims and tyres.ONBOC went faster with the taller 255x60x15 combo but slower with the 255x50x16.

Each combo is different and finding the right 1 for you is the hard part.
mex351 is offline   Reply With Quote Multi-Quote with this Post
3 users like this post:
Old 06-05-2014, 11:02 PM   #5
XTJG33
1968 XTGT
 
XTJG33's Avatar
 
Join Date: Apr 2010
Posts: 745
Default Re: Tyre Height Question

Thanks guys
I will try and get a Moroso Power Speed Calculator and see what it tells me. I have tried some online calculators but people say they are not accurate.

End of the day i will know the true answer if i make the change and give it a run down the quarter. but my gut feel tells me i have to get a better 60ft and ultimately a better ET
__________________
Project: 1968 XTGT Replica http://www.fordforums.com.au/showthread.php?t=11297583
Project: 1977 TD Cortina https://fordforums.com.au/showthread...89#post6008989

Life is like a grinding stone,
it either sharpens you up,
or grinds you down
XTJG33 is offline   Reply With Quote Multi-Quote with this Post
This user likes this post:
Old 09-05-2014, 09:21 PM   #6
Woodykustoms
FF.Com.Au Hardcore
 
Join Date: Nov 2009
Posts: 976
Default Re: Tyre Height Question

Be interested what you find what works for you, I think you are on the right track with the shorter tyre....
Woodykustoms is offline   Reply With Quote Multi-Quote with this Post
This user likes this post:
Old 11-05-2014, 03:15 PM   #7
XTJG33
1968 XTGT
 
XTJG33's Avatar
 
Join Date: Apr 2010
Posts: 745
Default Re: Tyre Height Question

I will let you know Woody when I do it
__________________
Project: 1968 XTGT Replica http://www.fordforums.com.au/showthread.php?t=11297583
Project: 1977 TD Cortina https://fordforums.com.au/showthread...89#post6008989

Life is like a grinding stone,
it either sharpens you up,
or grinds you down
XTJG33 is offline   Reply With Quote Multi-Quote with this Post
This user likes this post:
Old 30-06-2014, 10:44 PM   #8
sweet na
Regular Member
 
Join Date: Jun 2014
Posts: 169
Default Re: Tyre Height Question

I'm assuming it's a Toploader and that you're crossing the line in 3rd gear. With the 235/60-15 you'll pick up about another 300 rpm across the line and will definitely accelerate better but may not launch any better unless it's a drag radial. I'm sure you'll have fun trying and that's what it's all about at the end of the day!
sweet na is offline   Reply With Quote Multi-Quote with this Post
Old 01-07-2014, 12:08 AM   #9
XTJG33
1968 XTGT
 
XTJG33's Avatar
 
Join Date: Apr 2010
Posts: 745
Default Re: Tyre Height Question

Quote:
Originally Posted by sweet na View Post
I'm assuming it's a Toploader and that you're crossing the line in 3rd gear. With the 235/60-15 you'll pick up about another 300 rpm across the line and will definitely accelerate better but may not launch any better unless it's a drag radial. I'm sure you'll have fun trying and that's what it's all about at the end of the day!
Cheers, I have a C4, and I want to try a drag radial. I would hate to go out there and get wheel spin. I have tried to find some used 235/60/15 ET streets with some tread so I can get 2-3 passes out of them but no luck yet.
And yes it is fun trying
__________________
Project: 1968 XTGT Replica http://www.fordforums.com.au/showthread.php?t=11297583
Project: 1977 TD Cortina https://fordforums.com.au/showthread...89#post6008989

Life is like a grinding stone,
it either sharpens you up,
or grinds you down
XTJG33 is offline   Reply With Quote Multi-Quote with this Post
Old 01-07-2014, 10:10 AM   #10
sweet na
Regular Member
 
Join Date: Jun 2014
Posts: 169
Default Re: Tyre Height Question

That's good that you're running an auto, makes launching a lot easier. Just keep an eye out at the strip for guys running the smaller tyres and talk to them about selling them to you before they're worn out.
sweet na is offline   Reply With Quote Multi-Quote with this Post
2 users like this post:
Old 01-07-2014, 11:41 AM   #11
XTJG33
1968 XTGT
 
XTJG33's Avatar
 
Join Date: Apr 2010
Posts: 745
Default Re: Tyre Height Question

Good thinking 99
__________________
Project: 1968 XTGT Replica http://www.fordforums.com.au/showthread.php?t=11297583
Project: 1977 TD Cortina https://fordforums.com.au/showthread...89#post6008989

Life is like a grinding stone,
it either sharpens you up,
or grinds you down
XTJG33 is offline   Reply With Quote Multi-Quote with this Post
This user likes this post:
Old 03-07-2014, 07:15 PM   #12
99er
Regular Member
 
Join Date: May 2014
Posts: 162
Default Re: Tyre Height Question

you should try to set it up to cross the finish line in top gear close as possible to redline.the bigger the tyre the more mile an hour considering you have the power to turn them quickly.generally speaking one tenth in the first half track converts to two tenths at the line.lots of variables.set it up for your max revs to when your camshaft stops pulling,in 1st gear take it to redline,the other gears to when your cam stops pulling.where is your max torque at rpm.all that said i think you need a smaller tyre to reach higher rpm at the line.or launch harder.how are you launching

Last edited by 99er; 03-07-2014 at 07:20 PM.
99er is offline   Reply With Quote Multi-Quote with this Post
Old 03-07-2014, 08:16 PM   #13
XTJG33
1968 XTGT
 
XTJG33's Avatar
 
Join Date: Apr 2010
Posts: 745
Default Re: Tyre Height Question

Thanks, i change shift points from 5500 by 200 rpm leaving the line at 2500 with not wheel spin and good hookup. Best time was when I changed at 6100. Crossed the line at 5100rpm at 100 mph. I want to cross the line at say 5700-5900.
__________________
Project: 1968 XTGT Replica http://www.fordforums.com.au/showthread.php?t=11297583
Project: 1977 TD Cortina https://fordforums.com.au/showthread...89#post6008989

Life is like a grinding stone,
it either sharpens you up,
or grinds you down
XTJG33 is offline   Reply With Quote Multi-Quote with this Post
Old 06-07-2014, 01:37 PM   #14
99er
Regular Member
 
Join Date: May 2014
Posts: 162
Default Re: Tyre Height Question

thats sounds like a good launch.looks like you need smaller tyres.but how much smaller.there will be a ratio as per inch in tyres as to affecting rpm at the line.i dont know what it is.for example if 1 inch down gives you 200 rpm, at the line you need to go down 3 inches to pick up 600 rpm.have you got any 14inch rims and tyres you could try
99er is offline   Reply With Quote Multi-Quote with this Post
Old 06-07-2014, 02:52 PM   #15
XTJG33
1968 XTGT
 
XTJG33's Avatar
 
Join Date: Apr 2010
Posts: 745
Default Re: Tyre Height Question

Cheers, yeah would be good to know by how much the smaller tyre will affect the rpm. 14 inch rim with a 235/60/14 might be a good idea. Never thought of that one. Will look into it. Or even better, just build a faster engine....hahaha
__________________
Project: 1968 XTGT Replica http://www.fordforums.com.au/showthread.php?t=11297583
Project: 1977 TD Cortina https://fordforums.com.au/showthread...89#post6008989

Life is like a grinding stone,
it either sharpens you up,
or grinds you down
XTJG33 is offline   Reply With Quote Multi-Quote with this Post
Old 06-07-2014, 03:16 PM   #16
sweet na
Regular Member
 
Join Date: Jun 2014
Posts: 169
Default Re: Tyre Height Question

It's a shame you're in Adelaide, I've got some Toyo Proxes Ra1 225/50-14 which are 22.5" high and 8" tread width. Used them on my XY when I wanted to lower the gearing without changing diff ratios.
sweet na is offline   Reply With Quote Multi-Quote with this Post
This user likes this post:
Old 09-12-2014, 03:02 PM   #17
crappy408
Starter Motor
 
Join Date: Dec 2014
Posts: 1
Default Re: Tyre Height Question

Quote:
Originally Posted by sweet na View Post
It's a shame you're in Adelaide, I've got some Toyo Proxes Ra1 225/50-14 which are 22.5" high and 8" tread width. Used them on my XY when I wanted to lower the gearing without changing diff ratios.
If you think you could launch at a drag strip on those tyres you are tripping.
crappy408 is offline   Reply With Quote Multi-Quote with this Post
Reply

Thread Tools
Display Modes

Forum Jump


All times are GMT +11. The time now is 07:51 PM.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Other than what is legally copyrighted by the respective owners, this site is copyright www.fordforums.com.au
Positive SSL