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About tire stretching.. is half an inch (0.5 in.) OK? 175/65R15 on a 15X6.5 wheel

Maintenance/Repairs
#1

I’m on a mission to reduce unsprung weight, and what could be more unsprung than… tires?

Still, tires need to be made of ‘stuff,’ of ‘materials,’ so tires need to weight something.

So Vredestein makes a GOOD tire (based on Tirerack reviews) called the Quatrac 5. In the 175/65R15 size, the weight is only 14.X lbs. (versus the average of 17 lbs.)

Since I’m pairing these with a set of Konig Helium lightweight alloys (11.2 lbs.) this makes for a pretty drastic weight reduction.

The Konig Heliums are 15X6.5

175/65R15 are spec’d for a wheel width of 5 inches to 6inches. Mounting these tires on a 6.5 wheel puts it out of spec by half an inch…

I’m thinking that since there’s so much sidewall, this should be OK (maybe even beneficial since this stiffens up the sidewall a little–I’m told these tires have soft sidewalls!)

What do you think?

#2

If you install different size wheels/tires on the vehicle, what are you going to run the pressure(s) at?

Because the pressure(s) spec’d on the door jamb no longer apply?

Tester

#3

1/2 should be OK. It will stabilize the tread a bit better. But you would be worlds better getting rid of the 1.5 inches of aluminum ring on those wheels if you want to reduce unsprung weight.

I would not be choosing tires by their weight, myself, but I don’t know what you are trying to acheive by reducing unsprung weight.

#4

I intend to experiment with the tire pressure a bit-----starting with 30 to 32 and working my way up or down, but I bet 30 to 32 is exactly right.

Reducing unsprung weight brings only benefits, that’s been my understanding: I expect better handling, better braking, better acceleration, and less chassis disturbance when hitting potholes.

I got lucky that the Konig Heliums fit my car, they’re only 11 lbs and cost only 90 dollars! The classic Enkey RPF1 weight 2 lbs. less but cost 230 dollars (they weight 9 lbs. and are 15X7 which is wider than I would like.)

I actually like the looks of the Konig Heliums more than the coveted (and thus theft magnet) RPF1’s.

#5

image

Tester

6 Likes
#6

Why, oh why, do people feel compelled to spend so much time and money to “Google improve” the cars designed by professional engineers?

Guess we’ll never know.

1 Like
#7

What is the stock tire size?

#8

All the benefits you listed are correct in theory but incorrect with the path you have chosen.They will be worse. Why? Narrower tires will lose handling, and braking. Acceleration will depend on how much power the car has and if it breaks traction.

As for potholes… The heavier wheel and tire force the tire to absorb more of the pothole. The lighter wheel and tire force the dampers to absorb more. The initial impact will be worse.

You chose the Vredsteins for weight alone, they may suffer in all those areas you want to improve compared to an equal width tire and will perform more poorly in a narrower size.

#9

If this is the 2007 Toyota Corolla then why does anyone think they will gain anything noticeable by a few pounds ?

I certainly would not put anything but the correct tires on my vehicle .

2 Likes
#10

This is a 2012 Honda Fit (base model)

It comes with steel wheels in the size 15x5.5 with 175/65R15 tires, the wheel offset is 53mm.
The wheels are 18 lbs, the tires Sumitomo P02 tires are 18 lbs. for a total of 36 lbs.

It is being replaced with 15x6.5 Konig Heliums with a +40mm offset, these wheels weigh 11 lbs. with lighter weight (but still quality tires,) I can save about 10 to 11 lbs. per corner of unsprung weight.

I’m guess people are voting no on this, an alternative size for these new wheels are 185/60R15. Maybe that’s a better size.

#11

Whose thread is this , Queue or mareakin ? Or are they the same person ?

#12

On a base Honda Fit? It’s a waste of time and effort.

2 Likes
#13

I am struggling to understand what you are hoping to accomplish by reducing the weight of your car by a whopping 40 to 44 LBs. The best wheels for any car are the steel wheels provided by the manufacturer, and the best tires are a quality set in the original size. The steering and suspension are designed to work best with the original wheel and tire size. Using anything else can cause more harm than good.

#14

Chart shows that a 6.5 wide wheel rim should have a minimum 185 tire and ideally a 195 or 205. Last thing you want is a tire losing a bead while cornering or while going through a massive pothole.

I don’t have an issue with mods as I’ve twisted a few things beyond recognition over the years myself. However, you need to be safe about it and as far as the mods you mentioned it won’t even be noticeable while driving.

2 Likes
#15

Reducing the rotating mass by 40 lbs is equal to shedding 80 lbs from the body, great for drag racing but this car isn’t going to the track. There might be a .1 to .2 MPG fuel economy improvement.

#16

First, let’s get some terms correct:

The specified rim width for a 175/65R15 is 5.5". The allowable rim width range is 5" to 6".

So a 6.5" rim width is 1" wider than spec and OUTSIDE the allowable range.

Within the allowable range, there is not much tire performance differences. But outside that range they start to be significant. In the case of wider, the tread will dearch and tend to ride on the shoulders. That produces wear and handling issues (the vehicle will be more sensitive to hydroplaning, dry traction will be reduced, the ride is going to be harsher, but responsiveness will be better.)

Oh, and the tire warranty would be void.

5 Likes
#17

Well now hang on folks. Yeah, Honda engineers designed the car, but they designed the car primarily for economy, not performance. This is a Fit, not an S2000. There’s nothing wrong with modifying a car to better suit your desires, provided you do it safely.

But speaking of safely, I’m not a fan of tire stretching. I know some people think it looks cool, but it’s also dangerous.

1 Like
#18

I’m also having a problem with why you’d want to go to the time and expense of doing this mod, especially since it’s outside spec and of questionable practical benefit?

Appearance, sure and we’ve all seen plenty of pointless wings on fwd cars and coffee can mufflers on stock cars but instead of focusing on just one technical parameter, unsprung weight, it seems like your best bet would be to remain within the design parameters and put your money into a really good tire that best fits your intended use.

#19

image
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What/why is rationale for manufacturers using this tire size?
Why such a narrow tire on a 19” rim?

#20

Maybe on a BMW’s i3 EV? Trying to minimize rolling resistance? Where’s you get this photo?