Performance gap small if running directional tire backwards

JOHN MAHLER

SPECIAL TO THE STAR

Q: Thanks for all of your tips and info on tires over the years. I am a performance driving enthusiast and a tire fanatic; I look at tires all the time, whenever I can. If I notice someone’s tires unevenly worn, etc., I try to inform them to help ensure that their tires are safe.

My question: if unidirectional tires are on a vehicle in the wrong direction, can this be potentially dangerous? My assumption is that it could be, especially in the wet (presumably a tread pattern is designed to disperse water, and if pointing the wrong way, perhaps it could encourage hydroplaning, for example). Thanks again for continuing to share your tire knowledge with us.

A: Yes, you are a tire fanatic. Congratulations. Perhaps you’d like to take over the Tire Talk column when I retire?

All tire companies will tell you that it is unsafe to run directional tires backwards. It is the easy lawyer-correct answer.

In the dry, it really is not much of an issue as it is how much rubber contacts the ground rather than how the grooves are cut. You are correct, though, directional tires are meant to turn and grip in one direction.

Originally it was not just the tread pattern that mattered but also the belt package underneath. How the belts were joined in an overlapping fashion and stresses longitudinally could affect the join. With the advent of a continuous spiral (mummy-like wrapping) over the top of the belts, that concern is now gone.

Actual stats for loss of wet grip are not really available. The last ones I saw were from the late 1980s early ’90s on tires that had a v-shaped tread only. In that case, the grip loss was from 18 to 22 per cent when the tire was run backwards in the wet, depending on brand.

These days, the answer is less clear because most directional tires use two types of rain evacuation tread patterns.

It is popular to have circumferential grooves, which spit water out the back of the tire and combine that with angled or V-shaped grooves that channel the water out to the side or at least to the circumferential grooves.

Running one of these newer tires backwards would only affect the circumferential grooves a little bit since the feeder channels would not be working correctly. The angled V-channels would not work as well as they should.

Q: I just bought a 2000 Miata from a reputable new-car dealer but later noticed the tires, which have plenty of tread, but are cracked badly inside both shoulders of the tread portion, all the way around, all four tires.

My tire store people said they wouldn’t drive on these tires, so I took them to an independent mechanic who said they would pass the regular safety required for ownership transfers and that only cracking on the sidewalls would be cause for safety concerns.

I took the car back to the car dealer and his mechanics agreed. The sales manager, who also reads your column, said he would respect your opinion, as would I. The tires are Fuzion ZRi’s.

A: I’m afraid the tires really should be scrapped. They do technically pass a safety inspection, as the only requirement is tread depth and no sidewall bulges. The regulation is very old, very vague and loosely worded so most things can pass.

Not knocking your dealer, it is the government that is at fault for such loose standards.

Tire cracks are due to the tire drying out, due to abuse, excessive heat, old age, or in the case of a high-performance summer tire like the Fuzion, excessive cold. Once the cracking has started, it cannot be stopped. The loss of emollients has made the rubber stiff, and flexibility is what you need for grip.

So I would remove them, you just don’t know when the stress will make it go bang.

Q: We’re often counselled to eschew the pressure settings on gas station air supplies and check our tires with a good tire gauge. The problem is that we have no way to know if the tire gauge we picked up at the local hardware store (looks nifty but does it work?) is actually accurate.

I think it’d be fantastic if there was an accurate air source at the local tire store to compare my gauge to, but failing that (I’ve looked and looked and looked). Can you advise me on how to check the accuracy of my $15 tire gauge?

A: Very good question and a great idea for a testing station we could all use. Are you listening Canadian Tire?

I don’t know of a way to check gauges. My method is to have several. I use three and when one of the three does not agree with the other two, it hits the garbage can. I have never had all three disagree. If that occurs, I guess I’d have to go for a fourth opinion.

Next best method might be to fill a tire to a set amount at a service centre where the gauge is part of the inflating machine. Then check pressures with the hand gauge.

Email tire questions to John Mahler at thetireguy_1@hotmail.com. Please include vehicle's make, model and year, tire brand and size, as well as your name, address and phone number. Due to volume, personal replies cannot handled.

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