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npdunn42 12-10-2012 02:38 PM

Selecting tire diameter
 
Looking for assistance with selecting the appropriate DR for my 1967 Chevy C10. I will have two sets of rear tires 1) For street use (which I already have) and 2) strictly for drag racing (to be put on @ the track).

I'am looking for help with selecting tire diameter. I took it to the track over the weekend. With 28 inch tires I crossed the trap at 5,100 rpms (the motor redlines @ 5,700). I smoked the tires and redlined the motor off the line easily with BFG Radial TA. I am not sure if need a 26, 27, or 28 inch tire. Also, not sure how much effect the loss of traction off the line effected RPM when I crossed the traps.


Specs: 67 SWB Chevy C10
3,920 weight
BBC 470 HP
Hughs 400TH
Hughes 2500 stall
3:73 posi
Front tires are BFG Radial TA

I appreciate the help.

Roger Gates 12-10-2012 04:46 PM

Quote:

Originally Posted by npdunn42 (Post 142983)
Looking for assistance with selecting the appropriate DR for my 1967 Chevy C10. I will have two sets of rear tires 1) For street use (which I already have) and 2) strictly for drag racing (to be put on @ the track).

I'am looking for help with selecting tire diameter. I took it to the track over the weekend. With 28 inch tires I crossed the trap at 5,100 rpms (the motor redlines @ 5,700). I smoked the tires and redlined the motor off the line easily with BFG Radial TA. I am not sure if need a 26, 27, or 28 inch tire. Also, not sure how much effect the loss of traction off the line effected RPM when I crossed the traps.


Specs: 67 SWB Chevy C10
3,920 weight
BBC 470 HP
Hughs 400TH
Hughes 2500 stall
3:73 posi
Front tires are BFG Radial TA

I appreciate the help.

Welcome - This seems like a "tech" question, but will try to give an answer from experience. There are several variables here. First - The smaller diameter, lighter tire you can use & still leave the starting line the more MPH you will run even though the RPM will be up. It can be compaired to someone running with track shoes on & wearing golishes. It takes more power to move a heaver tire & the weight is farther away from the center as the diameter increases. You also want to be 'done' coming into the first light if possible RPM wise. The weight & width of the rim also make a difference. Air pressure will change the contact patch on the ground & also have upper as well as lower limits for optimal bite. Your truck may have a lot more weight on the front than rear so it may require a wider tire. If you are going to use a "Drag" tire get one that is as wide as you can get under the wheel well on a somewhat narrower rim than the tire. Suspension will affect weight transfer & bite as will using a micro lock or transbrake. A suggestion is after you get the tires - make launches with the air pressure at the upper end of the range & look at the "patch", then go down 1 lb. at a time until you get a full pattern (same all the way across). Then go down 1/4 to 1/2 until you do not get an even mark. Measure the width of the patch. It is time consuming, but should pay off in the long run. Just be sure to launch the exact same way every time. After you get what you like with the tire try different launches. Remember - more than one change at a time may as well be like starting all over again from scratch. Get yourself a tablet & mark down everything so you can develop a base line to start from when conditions change. It AIN'T easy, but it is fun when you start to see results & consistancy.

twintownterror 12-11-2012 09:32 AM

Just going off an educated guess from my door car experience and the bit of info you gave. I would say 26".

TOP SECRET TRICK: A great deal if you have one in your area try a Pro Stock Bike racer for their slicks. They're barely used (darn near new when they get rid of them due to the light weight of their bikes and minimal runs put on them before changed) and they usually sell them relatively cheap.

15 X 8 rim works perfect, try starting around 15psi and go up or down from there like Roger said...

Also give the calculator a try at richmondgear.com

npdunn42 12-11-2012 11:26 AM

Thank you for this great information!

HEMI_guy 12-13-2012 01:21 PM

Quote:

Originally Posted by twintownterror (Post 143009)
TOP SECRET TRICK: A great deal if you have one in your area try a Pro Stock Bike racer for their slicks. They're barely used (darn near new when they get rid of them due to the light weight of their bikes and minimal runs put on them before changed) and they usually sell them relatively cheap.

Any issues in getting then pairs with matching circumfrances?

twintownterror 12-16-2012 10:25 AM

Quote:

Originally Posted by HEMI_guy (Post 143074)
Any issues in getting then pairs with matching circumfrances?

I never had any issues. Most times my 'supplier' sold them to me in pairs.


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