LIFT VS. TYRE/RIM QUESTIONS

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Date: Mar 4, 2008

LIFT VS. TYRE/RIM QUESTIONS	Permalink

In my own understanding the main reason for lifting vehicles is to enable larger tyres to be used by the truck. otherwise it would make no sense to lift the vehicle yet the axle remains at the same height. The whole tyre question though is not very clear to me. Plz shed some light in respect of the following issues. 1. the stock xj usually has size 15 rims and tyres 225/75/15. of course i understand the 15 stands for the size of the rim. these measuments i guess are in inches. i see mention of 31 and such other figures when referring to tyre sizes. whats that unit of measure and what would 225/75/15 translate to? 2. what are the different tyre sizes that can be used with the stock rim - 15. and what would you recommend for the stock rim. 3. what size tyres are recommended for 3 or 4 inch lifts. Please give the answer in a layman's language. things like rim size, tyre thickness, height such........ i have read the tyre info in the tech page elsewehre in this site but i am unable to pursuade my mind to understand the info. __________________ 96 XJ COUNTRY (RHD)

89eliminator

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Date: Mar 4, 2008

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you gain more with a lift than just being able to fit larger tires. you gain added articulation (flex) as well as ground clearance (except for the axles)

well the 225/75/15 is in metric units. it translates to a 28in tall and 9in wide tire.

the width is what you have to worry about with a stock rim. a stock rim is 15x7, 15in diameter by 7in wide. you dont want to run a tire width bigger than 10.5in on it.

most will run a 31 to 33in tire with a 3-4in lift. it depends on how much cutting you want to do to the flares.

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LEAD_NOT_FOLLOW

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1. the stock xj usually has size 15 rims and tyres 225/75/15. of course i understand the 15 stands for the size of the rim. these measuments i guess are in inches. i see mention of 31 and such other figures when referring to tyre sizes. whats that unit of measure and what would 225/75/15 translate to?

You are correct, the 15 stands for the rim size and is measured in inches. The 225/75 is actually metric and is measured in millimeters. Just like we have standard and metric tools; we have standard and metric tires. Why? Who knows, but my assumption is it's easier to measure lower profile tires (car tires) via metric millimeters than it would be to say 3.25".

With your 225/75/15 the numbers themselves represent different aspects of the tire. The 225 is the width, the 75 is the height, and the 15 as stated prior is for the rim size.

To convert the metric to the standard is somewhat complicated to do, but if you follow the directions (or use an online tire size conversion calculator) it's not to difficult.

TO CONVERT TIRE SECTION WIDTH IN MILLIMETERS TO INCHES:
Section width in millimeters ÷ 25.4 = Section width in inches

EXAMPLE:
225 ÷ 25.4 = 8.86" nominal section width

TO CALCULATE TIRE SECTION HEIGHT:
Section width x aspect ratio percentage=section height

EXAMPLE:
8.86 x 75% = 6.65" nominal section height

TO CALCULATE NOMINAL OVERALL TIRE DIAMETER:
(section height x 2) + wheel diameter = overall tire diameter

EXAMPLE:

(6.65 x 2)

+

15

=

28.3" nominal overall diameter

So your 225/75 equates to a 28.3 x 8.86 tire, or 28 x 9 if you don't want to be technical about it.

2. what are the different tyre sizes that can be used with the stock rim - 15. and what would you recommend for the stock rim.

A stock rim is typically 15x7. You can go as tall as you want; however it's the width that you need to be concerned about. On a 7" wide rim I would not go wider than a 10.5" tire; espeically if you ever plan on hitting any trails. Going wider will be more likely you'll pop a bead. Yes it can be done, but the tires will "balloon" out and the first time you hit them on a rock (or pothole for that matter) you'll blow your bead out.

Ask Rebecca how fun blowing beads are...

3. what size tyres are recommended for 3 or 4 inch lifts.

This is one of those questions your going to get about 30 different answers on.

I ran 31's on 4.5" for a year and a half, now I run 35's on 5" of lift. Rebecca (my wife) ran 31's on 3.5" of lift for awhile and now she's running 33's on the same lift.

I'm one who prefers a larger tire on a smaller lift. This helps keep the COG (center of gravity) down and your much more stable on the road and trails. Some will argue to the death with me that uptravel (how far your tires go up in your suspension cycle) is everything in the world and we need to run larger lifts with smaller tires or cut the heck out of our fenders to get max uptravel. I dissagree for the most part on that statement. If you bumpstop (an object put on your axle to limit the amount of uptravel) correctly it will force the oposite end of the axle to be pushed down (downtravel) on the other side since it's a solid axle and you'll gain just as much flex (slang for articulation) in your suspension.

It also depends on the width of the tires/backspacing of the rims and if your willing to trim at all/remove your flares. I REALLY like how Rebecca's XJ rides and performs offroad with 3.5" (it's really probally 4" since it's a Rubicon Express lift and they sit a tad higher than advertised) with the 33x12.5 tires. I also REALLY like how my XJ performs with 5" of lift and 35" tires. I've trimmed (and removed my flares) to fit the 35's just a bit, she's not trimmed at all and still has her flares. Key in my opinion is to keep it as low as you can to fit the size tires you want.

So to answer your question I would run 33" tires at 4" of lift with very minimal trimming and bumpstop it correctly. You also need to take into consideration if your doing to be daily driving it what gears you have in your axles. A stock 3.55 gear ratio with 33's tends to suck the petrol down a lot faster than 3.55 with 31's.

I hope I've left it understandable enough for you. If you have any other questions just ask and we'll get it so you understand.

-- Edited by LEAD_NOT_FOLLOW at 11:00, 2008-03-04

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