ABOUT: Getting new rims? All the info you need here
 

The series is only part of the rolling diameter. it combined with the width determines the rolling diameter. series is how tall the sidewall is in percentage compaired to the width.

Tyres are labeled www/hh/rr lls

Where www is the overall width of the tyre in mm

hh is the height of the side wall from the rim to the outermost point and is expressed as a ratio of the width (see twilightproteges post)

rr the total diamater of the rim in inches (some BMW use mm but they are rare and obvious), multipy by 25.4 to convert to mm

ll is the load rating, the higher the number the higher the load rating

s is the speed rating, a letter, the closer to 'Z' the higher the speed rating

So the diamater of the standard BA 1.8 185/65/14 is 65% of 185 = 120.25mm top and bottom of the rim = 240.5mm plus the 14" rim (355.6mm).
Total 596.1mm
BA alloy option 195/55/15 is 55% of 195 = 107.25mm top and bottom of the rim = 214.5mm plus the 15" rim (381mm).
Total 595.5mm

Use this to calculate your original diamater then you can make variations to plan

http://www.miata.net/garage/tirecalc.html

and calculate the offset you need here

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


Or this one which does both:

http://www.rims-n-tires.com/rt_specs.jsp

Stage two, I've taken this from an American book about 20 years old but the information is sound (all be it in inches and MPH)

Tires Are “Gears” Too!
Having the latest hot-tip racing tire is nice — but not if its diameter fouls up your gear ratio. Can’t happen, huh? OK try this. You’ve been running the 5.50-9.20—14 tires on your 510 with a 4.11 rear gear. These have about 24.12- inch diameter at 24 PSI inflation. Get a gear/tire size computer wheel. This little circular slide rule calculator puts the whole thing in your pocket so you can impress your team mates and fellow racers with your knowledge of what’s happening. Set the tire diameter next to the gear ratio, then find 7,000 driveline RPM (same as engine RPM because this is measured in 4th gear, which is 1:1). Read the top speed (4th gear) of about 121 MPH.
Your ex-wife loses grasp of things one afternoon and write you an alimony check. You squander this new found fortune on a set of 10.45—14 tires with a shorter diameter (only 22.4 inches) than you had been running. Play the computer wheel game again and you’ll see that 7,000 RPM now gives 111 MPH. This might help you on a short track where you didn’t use much 4th gear — but if the next race features two long straightaways, you’ve got to figure out what to do. Change rear gears, twist the engine tighter, go back to a taller tire or just be content to finish somewhere in the pack with what you already have in the tire and gear departments? You might be better of leaving your new tires in their wrappers!

A 510 is the old Datsun 1600 '68-'73

okay i didn't understand that, but thats why your supose to keep the same rolling diameter!!!!! thanks for the sites tho, i need to see pricing for tyres too they are expensive

Tyres are what you pay for them, you can get cheap tyres that last a long time but they won't offer much in the way of grip, or you can buy Yokohama semi slicks (just road legal) which stick like you wouldn't believe but last 5000km if your lucky. Best people to quote you on tyre prices would be your local tyre shop, give 'em a call

hahahaha! LMAO luv'd that explination! Nice work! U get to understand the same thing in grand turismo3 when setting all the gear ratio's! One race u luv it, the next u just keep watching the pack pull away!

Its mainly to keep your speedo reasonably accurate by fittng tyres of the same rolling diameter.

Wheel offset calculator
Wheel offset explained
Hope this helps

And a guide to Markings, Speed Ratings and Load Ratings

http://www.blackcircles.com/general/sidewall

Important when you've got a bloody BA with a ridiculously high load rating!

hey its not that bad. integras and civics are 87

When the sidewall height is indicated, ie 35, does it include the tyre bead in it's height? I ask this because my tyres are 215/35/18 and by the calculation I should have a sidewall height of 75mm, but my sidewalls are no where near that big. I think they would be lucky to be 50mm from the edge of the rim to the tread.

Offsets and Stud Patterns:

BA Astina Hatch + Hardtop

I4 - 4x100 stud pattern, +45 offset
V6 - 5x114.3 stud pattern, +45 offset

Feel free to add BG and BJ, peoples

BJ Astina (non SP20)

4x100 +45 offset

Updated with an online offset calculator in the first post.

will 18 x 8 wheels fit a hardtop if they're only 42 offset?
I know this is probably explained somewhere above but I'm not really mechanicly minded at all.
Cheers Couchy

thats what the offset calculater above is for, use it.

+45 offset? Is offset tire wall. Ive been trying to work out the terminology, ive assumed things in the past but never been sure. If the BHA run a 45mm tirewall then ive F***ed up when getting new tires. But the ive always kind of known that.

Offset is disatnce from the centre of the rim to the point where the hub bolts to the rim. Check out the link at the top for a diagram.

As for 8" wide rims and +42, you'd have to test fit them...but i reckon they'll rub on the struts!

7" wide is as far you can go with the 45+ offset mine nearly hit the struts with this configuration

would definitely rub i think after looking at the clearance i have on the 7" 17's i have now.
I did check the calculator above,,, and these wheels would be 11 mms closer to the strut and there isn't that much room now.
Would aftermarket struts or coilovers give more clearance?

Depends how low you're running the coilovers - as the adjusting collars are level with the rim lip on mine, and i have about 8mm clearance with +37 rims.

Added a new offset/wheel width/tyre size calculator i found - very cool!

http://www.rims-n-tires.com/rt_specs.jsp

i know this has been asked before but what is the offset for 03 sp20 thanks guys

http://www.astinagt.com/forums/showt...ht=sp20+offset

read that..

I'm not real goot with offset tyre sizes etc. and can't really work out the calculator.

But i was thinking of putting 18"x8" Rims on my mrs '95 BA Astina Hatch. Is this possible? or do i have 2 have 18"x7.5"?

What tyre/rim/offset sizes do you guys reccomend?

I reckon u should stick to 18x7.5 if you have strut type shocks. I've got 18x7.5 with 215/35/18 tyres and theres barely any space between the wheel and the strut. Not sure what my offset is but i think its around 40mm.

To make the tyre calc work we really need to know the rim widths too.
Does anyone know standard BA V6 rim widths?
Even better does anyone know the distance from the mounting surface to the standard strut?
Or what other wheels fit? Skyline, etc etc

I4 - 14x5.5, 15x6
V6 - 16x6 (maybe 6.5)

or if you are unsure, go to your garage and have a look yourself

and the measurements you just asked for, dont be lazy, your car is in the garage, get the measuring tape out.

V6 = 16x6.5 IIRC.

:) Not at home ATM I'm interstate, just bored looking for wheels while I wait for a plane. Did I see somewhere that you had an LSD?? If so what did you get/how much etc? (me being lazy again, I could search but ... well ... I'm lazy)

Thanks Rupewrecht

hey guys. i just stumbled across this. thought it might be a little handy ;)

http://soarercentral.com/sc-forum/me.../283/1565.html

Hello, I'm sorry for being one of those morons who can't figure anything out regarding offset and all that stufff. Is it uncool to just follow the directions on the plate on my car that says what tyres can fit on a 14 inch rim and on a 15 inch rim? Or can you guys help me to get a wider tyre than a 195 60 R15? (Or is it 195/55/r15)

re ask the question, and think about it before typing it first.

Legally you can increase wheel diameter by up to 1" and width by 0.5"
The V6 has factory 16"x6.5" so 17"x7" is about as big as you can legally go without an engineers report. Practically though 205 tires are what will fit between the guards if you don't want to do a lot of number crunching and chasing rims with perfect offsets.
BTW, it doesn't matter if you have an I4 or V6 the chassis is the same.

actually in victoria - it is +15mm/-15mm overall diameter and +25mm max width.

so running 215/35R18 on a 18x7.5 rim would be biggest on a I4 Astina. +42mm to +45mm offset is the way to go.

sorrry but i have no idea how to use those calculator thingos..:(

could someone tell me what the specs would be for a BJ 98 model?

im wanting to get 18's but im worrried about scrubbing of the guards.

what would be the specs for 18's and 17's?

cheers guys

you could probably do 8 inch wide with an offset of about 45.. the tires will be more of an issue though. maybe someone else can help with those

17"x7.5" rim, with 42-45 offset would be best...

If you an 8" wide rim, expect to have to lip the rear guards as they'll scrub ;)

Cheers
Marc

sweet, thanks mate.

so 18's are a no no im guessing?

you can, but you might have problems with legalities...

you should be right 18s are sort of legal as you chassis comes with 16s standard for the sp20 am i not correct? or is it 15s.. eithr way 18 is max, well for me anyway, the ba v6 comes with 15s and the bloke at blowjobTmart said going from 15 stock 18 is largest or some thing.. if you do get 18s, 7.5 is a good width ;)