Sandhills Open Road Challenge :: tech questions

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1 people online in the last 15 minutes - 0 members, 0 anon and 1 guests. (Most ever was 25 at 02:03:53 Tue Aug 21 2012)

RACER_X

21:40:33 Thu
Jun 18 2009
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tires

From the rules.....

1. LOAD CARRING CAPACITY: ALL TIRES MUST HAVE AN EQUAL OR GREATER
LOAD CARRYING CAPACITY THAN THE ORIGINAL TIRE. (i.e., The base tire for a 1999
Mustang is a P205/65R15 rated @ 1400 lbs. Any replacement tire must have a load rating of at least
1400 lbs. Regardless of the speed rating or what Division/Class the vehicle is competing.)

Why is this so important? This basically limits me to the OEM tire size. When the load rating finally climbs over the stock size the tire is to wide to fit.

---

Chris_Bischof

04:06:25 Fri
Jun 19 2009
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Re: tires

What size tire do you want to put on?

Bullet 245/45R17s were over 1500 lbs as are most replacement tires for this wheel

for 16" wheels 225/55R16 are over 1500 lbs.

For 15" wheels, 225/60's are over 1500 lbs.

With all of these tires, your speedo will read close.

---
Chris Bischof
Southlake, TX
UNGN.com

Yes, it is actually going 168 mph in this picture.

RED_G8_GT

16:51:47 Tue
Jun 23 2009
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Re: tires

Yeah, check out Tire Rack, and use the Plus 1 concept where it widens the tire, and lowers the aspect ratio.

wagonmaster

04:48:23 Wed
Nov 30 2011
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Re: tires

What about older cars, they only started factory load carrying ratings in 1989. my car is a 71?

cjhans

13:38:14 Tue
Jan 3 2012
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Re: tires

Quote: wagonmaster at 04:48:23 Wed Nov 30 2011

What about older cars, they only started factory load carrying ratings in 1989. my car is a 71?

Find the OEM tire size (and convert to radial size if bias ply), look up the load rating, then make sure your tire choice has a load rating that's greater than OEM. Low profile tires will often have a lower than expected load rating even though the width and diameter are the same or larger than OEM. 225/60R15 vs. 225/45R18 for example.

You should also look into how load ratings and pressure requirements change as you get closer to the max speed rating so you can be sure the actual weight on the tires doesn't exceed the rating (including some fudge factor for any downforce that may exist.

This link may help: http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=72

(that's how I figured out the tires for my 1973 anyhow. final judgement is of course up to the race officials)

:biggrin:

[2 edits; Last edit by cjhans at 14:12:02 Tue Jan 3 2012]

wagonmaster

06:17:47 Sat
Jan 7 2012
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Re: tires

Well the closest to factory is 215/70r14 but there is alot of load rating on tires not every tire has the same load rating. A goodyear tire may not have the same weight rating than the same tire in a dunlop.

I figure if I go with a tire with a rating at leadt in the mid 90s or higher I should be good. even better if I go with an XL ( extra load) tire. BTW: I am in the tire business

Tim

cjhans

00:28:48 Tue
Jan 10 2012
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Re: tires

Quote: wagonmaster at 06:17:47 Sat Jan 7 2012

Well the closest to factory is 215/70r14 but there is alot of load rating on tires not every tire has the same load rating. A goodyear tire may not have the same weight rating than the same tire in a dunlop.

I figure if I go with a tire with a rating at leadt in the mid 90s or higher I should be good. even better if I go with an XL ( extra load) tire. BTW: I am in the tire business

Tim

Seems all the tires on Tirerack.com in that size have a 96 load rating and a ~26" diameter.

26" is certainly a very common diameter, so finding something in a lower profile and higher speed rating shouldn't be difficult.

For example:
255/45r17 = 98W
285/40r17 = 100W
245/40R18 = 97Y

In the first example of the 255/45R17, the 98 load rating =1653 pounds, so your max load per tire at 168mph shouldn't exceed 1405 pounds due to the 85% capacity at the top end of the W speed rating. (this level of detail isn't actually in the rule book, but it's what I considered to maximize my own personal safety)

Quote: RACER_X at 21:40:33 Thu Jun 18 2009

Why is this so important? This basically limits me to the OEM tire size. When the load rating finally climbs over the stock size the tire is to wide to fit.

In regards to sizing....your stock tire is approx 26" (diameter) x 9" (section width). 225/50R17 is about the same size, but has a 98W rating. A 255/45R17 is 26x10 with a 98W rating, and I'd be willing to wager you could fit the extra width inside the wheelwell.

http://www.tirerack.com/tires/tires.jsp?tireMake=BFGoodrich&tireModel=Radial+T%2FA&partnum=17SR4RADTARWL2V2&vehicleSearch=false&fromCompare1=yes&tab=Specs

http://www.tirerack.com/tires/tires.jsp?tireMake=Kumho&tireModel=Ecsta+SPT&partnum=55WR7KU31&vehicleSearch=false&fromCompare1=yes&tab=Specs

Again, not a race tech, but that's how I've interpreted the rules. Hopefully somebody will correct me if I'm wrong.

:frankenstien:

[5 edits; Last edit by cjhans at 00:53:45 Tue Jan 10 2012]

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