Any way to help my braking in the snow? - Page 2

gtsr515 · 01-31-2002, 12:58 PM

The rating on the sidewall of a tire is NOT just it's MAXIMUM pressure rating, if that was the case there would be only one number, not a range of say 32-44psi.

As I said before, when performance driving is the issue, you want the tire at it's maximum or a little more, to keep the contact patch square to the road and the sidewall at a 90 degree angle to the road or track (in a perfect world), 32psi in a tire pushed on a race track will perform like crap, rolling over the rim inducing massive understeer. We have proven this time and time again at Skip Barber.

The compression braking thing will work, but you need to match rev's on the downshift with the precision of Michael Andretti or the rears WILL lock up in the snow, use your brakes, THAT is what is meant to stop the car, compression braking in the snow is too risky, unless your Mr. Andretti. Bottom line is be carefull when doing that. And Peckerwud, you HAVE locked up the rears before, you just can't see it, NOBODY's that good.

I have a Sand Dune Racer (Hot V dub motor in a tube frame), and that only weighs 910 pounds, 1250 with me in it and I get the best performance with the tire at or near maximum psi, weight of the vehicle does not determine inflation pressure, it is a factor, but not the main factor. When asking 100% from your tires, be it racing or hauling dirt or bricks, you must inflate to max or near maximum to receive the 100% your asking for.

A tire doesn't know if it has a CRX sitting on it or a Dodge Ram?, all it knows is if you start to push me, I need air to respond. Lowering air pressure in a radial is rarely needed.

And a brake proportioning valve is equally risky, but not if used properly, if your's locks up by looking at the brake pedal, something is wrong with the unit, or you have to much bias to the rear, it has helped me for 20 years in those lovely Chicago winters.

Hey! i just thought of what would help your winter braking the best........move to Florida like I did!

Good luck to all!!!!!!!!!

RED92LX50 · 01-31-2002, 01:15 PM

gtsr515 - I can understand that when driving at or near the limits of a car (and tires) like on a race track, it make sense to have more psi in your tire than usual (but not necessarily for Daily Driving).

I guess my question is: Why do VEHICLE manufacturers put Front and Rear inflation specifications if (as you say) you should pump up the tires to the TIRE Manufacturers Specs. My Ford Explorer has a recommended (from Ford) Front & Rear pressure of 32psi - I can't think of any tire that I could buy that says recommended pressure 32psi on the side of it.

I guess we are just going in cirlces (so to speak!). An intersting discussion noetheless.

95mustanggt · 01-31-2002, 03:20 PM

All right lets look at the tire pressure issue with a little bit of science

Tire pressure is dependant on 2 things not just one. First you have the wieght of the car and second you have the contact area of the tire.

Pressure is defined as a load over a given area (P = F/A). So if 2 cars that have the same tires but weigh 2 different amounts, those 2 cars should have different tire pressures. Like wise 2 cars with the same weight (say 2 95 GT's

), but one has fat tires one has skinny tires, the tire pressures will have to be different. To preserve P = F/A.

If you have a stock sized tire I would follow the manufacturer's pressure recommendations. BUT you have to also check with your tire manufacturer to make sure that your tire operates in that pressure range.

If I took the 245's off my back rims and put on 275's the tire pressure would have to drop. The force ( = P X A) would be the same (the weight does not change), but the area increases so the pressure has to decreace. Make sense? Beening a engineer means that you normally can't communicate your thoughts all that clearly

.

Having said that, some tires are designed to different specifications and operate to different design applications and therefore this analysis may not be correct.

PKRWUD · 01-31-2002, 11:58 PM

Hehe, when we race, our left rear tire usually has 3.5 psi. Yes, that's three and a half psi. Our right rear has no more than 8 psi, and the fronts are 12 (right) and 10 (left). Of course, the right rear is 16" wide, and we are running on dirt/clay. That's Sprint cars for you though.

Take care,
-Chris

01-31-2002, 12:58 PM	#21
gtsr515 Registered Member Join Date: Nov 2001 Location: Sunny, Hot, Sebring, Florida Posts: 725	The rating on the sidewall of a tire is NOT just it's MAXIMUM pressure rating, if that was the case there would be only one number, not a range of say 32-44psi. As I said before, when performance driving is the issue, you want the tire at it's maximum or a little more, to keep the contact patch square to the road and the sidewall at a 90 degree angle to the road or track (in a perfect world), 32psi in a tire pushed on a race track will perform like crap, rolling over the rim inducing massive understeer. We have proven this time and time again at Skip Barber. The compression braking thing will work, but you need to match rev's on the downshift with the precision of Michael Andretti or the rears WILL lock up in the snow, use your brakes, THAT is what is meant to stop the car, compression braking in the snow is too risky, unless your Mr. Andretti. Bottom line is be carefull when doing that. And Peckerwud, you HAVE locked up the rears before, you just can't see it, NOBODY's that good. I have a Sand Dune Racer (Hot V dub motor in a tube frame), and that only weighs 910 pounds, 1250 with me in it and I get the best performance with the tire at or near maximum psi, weight of the vehicle does not determine inflation pressure, it is a factor, but not the main factor. When asking 100% from your tires, be it racing or hauling dirt or bricks, you must inflate to max or near maximum to receive the 100% your asking for. A tire doesn't know if it has a CRX sitting on it or a Dodge Ram?, all it knows is if you start to push me, I need air to respond. Lowering air pressure in a radial is rarely needed. And a brake proportioning valve is equally risky, but not if used properly, if your's locks up by looking at the brake pedal, something is wrong with the unit, or you have to much bias to the rear, it has helped me for 20 years in those lovely Chicago winters. Hey! i just thought of what would help your winter braking the best........move to Florida like I did! Good luck to all!!!!!!!!! __________________ Remember...2nd place is 1st place for losers!

01-31-2002, 01:15 PM	#22
RED92LX50 Registered Member Join Date: Aug 1999 Location: Fairfax, VA Posts: 220	gtsr515 - I can understand that when driving at or near the limits of a car (and tires) like on a race track, it make sense to have more psi in your tire than usual (but not necessarily for Daily Driving). I guess my question is: Why do VEHICLE manufacturers put Front and Rear inflation specifications if (as you say) you should pump up the tires to the TIRE Manufacturers Specs. My Ford Explorer has a recommended (from Ford) Front & Rear pressure of 32psi - I can't think of any tire that I could buy that says recommended pressure 32psi on the side of it. I guess we are just going in cirlces (so to speak!). An intersting discussion noetheless. __________________ 1992 LX 5.0 Convertible Red/Blk Gears, Exhaust, bolt-ons... R.H.C. #51

01-31-2002, 03:20 PM	#23
95mustanggt Registered Member Join Date: May 2000 Location: Kamloops, BC Posts: 2,875	All right lets look at the tire pressure issue with a little bit of science Tire pressure is dependant on 2 things not just one. First you have the wieght of the car and second you have the contact area of the tire. Pressure is defined as a load over a given area (P = F/A). So if 2 cars that have the same tires but weigh 2 different amounts, those 2 cars should have different tire pressures. Like wise 2 cars with the same weight (say 2 95 GT's ), but one has fat tires one has skinny tires, the tire pressures will have to be different. To preserve P = F/A. If you have a stock sized tire I would follow the manufacturer's pressure recommendations. BUT you have to also check with your tire manufacturer to make sure that your tire operates in that pressure range. If I took the 245's off my back rims and put on 275's the tire pressure would have to drop. The force ( = P X A) would be the same (the weight does not change), but the area increases so the pressure has to decreace. Make sense? Beening a engineer means that you normally can't communicate your thoughts all that clearly . Having said that, some tires are designed to different specifications and operate to different design applications and therefore this analysis may not be correct. __________________ 1995 Mustang GT 20016 F150 Lariat Super Crew

01-31-2002, 11:58 PM	#24
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	Hehe, when we race, our left rear tire usually has 3.5 psi. Yes, that's three and a half psi. Our right rear has no more than 8 psi, and the fronts are 12 (right) and 10 (left). Of course, the right rear is 16" wide, and we are running on dirt/clay. That's Sprint cars for you though. Take care, -Chris __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

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