"Plus-sizing" Tires But Maintaining Original Width

[RidingOnRailz]

Does what I'm asking for make sense??

Traditionally, Plus-Sizing tires means a rim/tire combo that is both taller and wider than what came on it from the factory. Original height is maintained because only the rim(not the tire) increases in diameter, and thusly speedo is maintained. Well who and what army, LOL!, says plus-sizing HAS to go in both directions(taller and wider)??

What I'm looking to do is take a car with, say, 14" rims with 75-series tires, and go to 15s or 16s of the same width, and slap lower profile rubber(65-55 series) on them to firm up my ride and maintain speedometer. I'd love to do this with the mid-60s Buick I hope to acquire one day. After all a narrower tire/wheel assembly is more directionally prone than a wider package given the same aligment specs, right? The part I want to cut down on is all that floppy sidewall!

Is there such an animal?

[ricebike]

your initial definition is half-incorrect,

while the 2nd paragraph is the correct theory of "plus sizing" = to maintain the original factory height of the tire/wheel assembly

here's one of thousands of sites that can explain it to u:

http://www.tirerack.com/tires/tirete....jsp?techid=25

i like the interactive pic/ gif/ illustration on that site

it's important to maintain the same overall tire diameter whenever changing tires and wheel sizes to ensure sufficient ground clearance, appropriate driveline gearing and accurate speedometer readings.

i guess you were just interpreting it incorrectly

when you do finally take the plunge, measure the old tire/wheel combo as shown in the pic & compare it to the new tire-rim combo & you'll see 1st hand that it works!

(my 1st-hand experience was a former pepboys service writer who had done a few of these for customers)

edit: the only other thing you need to think about is wheel offset since your doing this to a RWD car. i mainly dealt with FWD newer vehicles & the only concern with them was to clear the strut assembly, control arms & brake caliper

i never got the overall diameters perfectly the same, but:

You will often find only +/- a few tenths of an inch difference in the overall diameter of the tires, as shown. This results in a negligible +/- four tenths of a mph speedometer variance.

the performance gains and "looks" of bigger rims/ shorter sidewall outweigh that small variance for those customers wanting to "upgrade" their ride's "shoes" :P

the newer vehicles with OBD II connectors have aftermarket "programmers" that will re-calibrate the speedometer or transmission gear to compensate for the tire/wheel changes; i'll let you google that because this is turning into an essay

[shorod]

Originally Posted by ricebike

the performance gains and "looks" of bigger rims/ shorter sidewall outweigh that small variance for those customers wanting to "upgrade" their ride's "shoes" :P

That depends on how you define "performance." So often I'm frightened to see huge wheels on cars with no attention paid to the brakes. In my mind, "performance" includes braking performance, and putting larger wheels on a car WILL impact braking performance in a detrimental way (unsprung weight).

I realize in this particular case we're not talking going from a 14" wheel to a 22" wheel, but it's still something to keep in mind for others who may be reading this and considering a more drastic wheel/tire combination for their whip.

-Rod

[ricebike]

true, but those are in the extreme cases where they went over "plus 3"



donk wheels with original brakes = stooooooooopppppppppppppiiiiiiiiiiiiiiiiiiiiiddddd dddddddd

truckers, though, know about the excess weight they're adding to their vehicles to gain "lift", and will upgrade suspension & brakes as well (it's a given)

but the OPs intent was to go plus 1 or 2 only... which will still be OK (weighing both old & new rim-tire combos if you want to go there as well)



plus 2 from 18 to 20" rim

vs.


plus 4 ~ now he has to worry about brakes/suspension

[shorod]

Originally Posted by ricebike

Holy Schnikes!

Originally Posted by ricebike

plus 4 ~ now he has to worry about brakes/suspension

And aesthetics. Those brakes just look dinky with the large wheels and large wheel openings!

-Rod

[RidingOnRailz]

Originally Posted by ricebike

your initial definition is half-incorrect,

while the 2nd paragraph is the correct theory of "plus sizing" = to maintain the original factory height of the tire/wheel assembly

here's one of thousands of sites that can explain it to u:

http://www.tirerack.com/tires/tirete....jsp?techid=25

i like the interactive pic/ gif/ illustration on that site



i guess you were just interpreting it incorrectly

when you do finally take the plunge, measure the old tire/wheel combo as shown in the pic & compare it to the new tire-rim combo & you'll see 1st hand that it works!

(my 1st-hand experience was a former pepboys service writer who had done a few of these for customers)

edit: the only other thing you need to think about is wheel offset since your doing this to a RWD car. i mainly dealt with FWD newer vehicles & the only concern with them was to clear the strut assembly, control arms & brake caliper

i never got the overall diameters perfectly the same, but:



the performance gains and "looks" of bigger rims/ shorter sidewall outweigh that small variance for those customers wanting to "upgrade" their ride's "shoes" :P

the newer vehicles with OBD II connectors have aftermarket "programmers" that will re-calibrate the speedometer or transmission gear to compensate for the tire/wheel changes; i'll let you google that because this is turning into an essay

Actually, I do understand plus-sizing very well. I just "Bushed" it up in my expression of it! I'll try it again:

Most plus-sizing cases I've seen involve a wider tire of the same height as factory with shorter sidewalls. Correspondingly the rim is wider and of a greater diameter to make up for aforementioned tire. Succinctly, most plus-sizing involves increasing dimensions of the rim in two directions.

What I want to do, as best as my pea brain can express it, is to install tires of the same height(diameter) and width as factory but with shorter sidewalls. That will require a taller rim of the same width. Succinctly, I would like to increase the dimension, of the rim, in only one direction.

Do I make more sense this time?

[ricebike]

that'll cost way more $$$

CNC machine, custom specs cut from billet aluminum block is currently the only way to go with your idea for now

[RidingOnRailz]

Originally Posted by ricebike

that'll cost way more $$$

CNC machine, custom specs cut from billet aluminum block is currently the only way to go with your idea for now

I don't believe that. What I'm looking for must exist readily out there. Does anyone here understand visually what I'm trying to accomplish verbally? And this is not for looks or anything, I just want a subtle handling improvement by shortening the sidewalls of the tires. I'll probably also max out the caster - something that can easily be done on a '64 Buick or similar.

[ricebike]

that's the only other option i can think of...

i mean, does a 1" difference in rim width really impact that much?

[curtis73]

This isn't that difficult. Let's say you have 185/75-14s on 14x6" wheels.

Just buy some 16x6" wheels and put 185/60-16 (or whatever aspect ratio actually keeps the same diameter). Just be careful you don't back yourself into a corner. Make sure there are plenty of tire choices in the size you need. I did that once. I went from 235/xx-14 up to 225/60-16 and now nobody makes that size anymore so I have to do some re-engineering.

The only other thing I should mention... taller sidewalls have more options of rim widths they'll fit on. Tire manufacturers list acceptable rim widths. As you go to a shorter sidewall, you might find that your tire width is no longer acceptable on the same width rim.

Edit: and Kudos to you for not conforming to the "wider is better" theory.

[fredjacksonsan]

Here's a really good tire size calculator:

http://www.1010tires.com/TireSizeCalculator.asp


Agree with Curtis; since it's your intent to keep the treadwidth the same size, simply compare different wheel sizes until you get one that's close to original.

[ricebike]

there are some rims on the market that has the same width as your original rim, but they're a bit much as well...

i think the original 14" rim has a 5.5" width... so if you bump up to a 16" diameter, and staying "thin", it's going to cost more, but i see them starting to make it for a few customers that want to keep the same width...

http://www.performanceplustire.com/p...urerID%5B%5D=1

and as curtis said, the tire choice & cost will also go up

[RidingOnRailz]

Originally Posted by ricebike

there are some rims on the market that has the same width as your original rim, but they're a bit much as well...

i think the original 14" rim has a 5.5" width... so if you bump up to a 16" diameter, and staying "thin", it's going to cost more, but i see them starting to make it for a few customers that want to keep the same width...

http://www.performanceplustire.com/p...urerID%5B%5D=1

and as curtis said, the tire choice & cost will also go up

The above should be the RULE, not the exception! And it should cost less than going taller and "fatter". A relatively taller tire/wheel package will resist turning better than a tire/wheel package of the same height(diameter) but wider, given the same caster & sai settings and allowance for scrub.

It will also concentrate more weight beneath itself, something to consider in winter weather.

[RidingOnRailz]

According to the link in post#11 my ideal solution is:
(STOCK)205/60-R16 = (PLUS)205/55-R16.5 But that tire/rim combo is not available, at least not on this planet.


My ideal available solution is:
(STOCK)205/60-R16 = (PLUS)205/55-R17

Two downsides: I will have to give up Mastercraft Avenger tires, aaaand, if I'm reading the tire calculator's information right, it will increase my indicated speed(MPH) even more than it already is!

Which leads me to my next question: How easy is it to calibrate my speedometer?

I checked it against both my GPS and already irate drivers, and I've determined I'm doing only 57mph at an indication of 60 on the speedo. If I put these tires & rims on I'll be doing only 55-56 at that indication! The error drops to 2mph at 30 indicated and increases to 4mph over 80 indicated(meaning I'm actually going only 76). Hey, at least it's hard for me to get speeding tickets. LMAO!!!

So I think I want to fix my speedometer first before shopping for tires/wheels.

[ricebike]

thanks for the update... admire your tenacity to try to stay within those limits

dunno if someone will make a custom speedometer gear set up to your specs... most of the speedometer gears I took out on electronic speed sensors are mostly made with plastic... but with a 60's engine and probably cable-operated trans speed sender, you'll probably have to dig further into the depths of teh internetz to find another enthusiast striving for the perfect speedometer calibration :P

if you had an electronically hooked-up engine/trans, it's as easy as plugging into the OBDII port and changing it...