Wheel Size Question...

[texasz]

Ok, now I've been hanging out listening to people talk about going from the stock 14" up to 15", 16", 17" and even 18" wheels. What I want to know is how does this change the way the car drives? I have heard that changing the wheel size changes your gear ratio. How? Does this provide greater high end speed or what?

Can someone please explain the effects of going to a larger wheel to me?

[JEFF]

If you want to keep your speedometer reading correctly ....

the larger the wheel the lower the profile on the tire,trying to keep the total diameter the same as the stock combination. This works up to a point .... then you need to replace the speedo gear in the transmition ( thats easy to do ).

The larger tire over all diameter the smoother the ride over bumps/pot holes. Example: Roll a penny (small dia. tire) down the road into a pot hole about the size of your fist (sat 1/2" deep) The penny falls in the hole (hard clunk on small tire) Now roll a large frizbee over the same hole ... see what i mean?

Remember: the lower the profile on your tire the less cusion there is for the bumps.(harder on suspention parts). But the trade off is that you get less sidewall flex --- improving your handling.

- Hope that helps.

- Jeff

[Brett240]

first off when changing up wheel sizes in most cases the aim is to keep your overall wheel tyre diameter combo the same to keep your gearing the same.

by increasing the diameter the cars theoretical top speed will increase and acceleration will decrease, vice versa for decreasing tyre diameter.

if you change from a 14 inch wheel to a 15 inch wheel, to keep the overall diameter the same you now need a 15 inch tyre with a lower aspect ratio (distance from outside of wheel rim to the start of your tread ). this has 2 effects, with a smaller aspect ratio there is less rubber to flex, effectivly stiffening your ride and improving handling. the lower the ratio the better you grip and braking... to a point. if you put heavy 20 inch wheels on your car it will increase unsprung weight to a point where you will stuff your cars handling characteristics.

generally a 17 inch wheel is considered the best compomise.

hope this helps

[Mudge]

http://www.geocities.com/z_design_studio/transmission.html

[Brett240]

mudge, thats a pretty useful tool. only thing is it doesnt have the 240 five speed the came into Aus and the UK. is there a box on that graph that uses the same ratios?

[Mudge]

Actually the early US 5 speed should match the 240Z 5 speed, I believe this is correct according to the Haynes I have, this would be a .864 5th gear.

I would personally shoot for a 15-17" wheel and no more, I have 15x7" and they are pretty nice overall, but would eventually like a 16x8-10" or possibly a 17x10" if I could get one at a reasonable price point (insert laughter here).

Take into consideration going this big requires fender flares and coil overs, not exactly cheap, but for road racing I want the ultimate in grip. Right now with 195/60 15" I dont have nearly enough tire to hold the brakes, otherwise the car handles very very nice.

[texasz]

So how big can you go before you have to do other mods (coil-overs, flares, etc.) 15", 16", 17", etc.? Also what is the offset?

[Victor Laury]

I have a excell spreadsheet, called TransCalc with your aussie/euro/jdm market 5 speed ratios as "std. Roadster trans"

Plug your tire size and rear ratio in and it charts speed/RPM in each ratio.

If Mike will instruct me, I'll Upload it to our Downloads section. I don't want to email to each person that asks for it, last time, it was too much work to keep up with the requests.

[zed240au]

its not the diameter that will really bring in new costs its the width that will make the need for flares or coil overs

its not till you go over 7" wide that you need to look at flares or coil overs

I actually used the jag that run idea and raise rear spring perches to get my 15 x 8 under the back instead of coil overs

I am running 15 x 7 all round on my car with 225 50 tyres orginally was running 15 x 8 on back with 245 50 tyres but cant get the 245 50 tyres anymore

Mick

[That Ozzy Guy]

Originally posted by texasz

So how big can you go before you have to do other mods (coil-overs, flares, etc.) 15", 16", 17", etc.? Also what is the offset?

Like Mick said it's the width that requires mods. I remember asking one of the local tyre specialists what is the widest he could fit on my bog stock 240. He quoted me a comfortable 215 which is about 8.5in.

[escapedan]

I am still only 2 weeks into z ownership....pls forgive my early ignorance!!

Is it safe to assume that 16x8 rims will fit nicely under stock wheelwells at all corners without requiring fender flares? If so, what tire size would be recommended for this rim?

I have just purchased a 73 240z with the intent of autocrossing it. Any suggestions for shock/spring and rim/tire setup would be greatly and sincerely appreciated!

[zed240au]

my experience my car is 70 model but you wont get 16 X 8 under a 240 with out modifing struts or flares i would say 16 x 7 with 225 wide tyres probaly even 235 if they make them in 16 i know my 245 on 15 just rubbed with the inner rear lips cut off

Mick

[Brett240]

when i had standard suspension i could get 16 by 7's under each corner with 225 50 series tyres no problem, though it was a snug fit, but no rubbing anywhere

[escapedan]

Thanks so much for the info. I have just started using this forum and what a huge help! Its great to be a Z owner and I am looking forward to being able to eventually answer questions instead of just asking them!!

[That Ozzy Guy]

Originally posted by escapedan

...I am looking forward to being able to eventually answer questions instead of just asking them!!

he he. That's what I thought too but here I am still asking the questions. Guess I'm still an aprentice. These guys are a fantastic bunch so don't feel bad asking any question.

[Tourniqet]

How does changing to coilovers effect the width of tire you can fit? I can see maybe minor changes because of lowering and making the a-arms a little more parralell to the ground but it seems that It would not be that much?!?!

[Brett240]

generally aftermarket coil over setups use narrower srpings and seatss, so there is a greater gap in between the wheel and spring allowing for a wider rim.

[Tourniqet]

Hmm.

That makes sense but I though the space between the wheel and the inside of the fenderwell would be a bigger issue. At least in the front where the wheels turn...

[240ZX]

Tourniqet,

I have coilovers on all four corners, 10" free length springs up front and 8" free length springs in the rear. My wheels are 17 x 8 up front and 17 x 9 in the rear. Tires are 215-40 x 17 front and 235-40 x 17 rear. I can assure you they do not rub any where! I've seen guys with the same wheel setup as mine with even bigger tires......generally, 225-45 x 17 front and 245-45 x 17 rear. If you visit my gallery you can view my setup on my 240. The lowest part of my 240 is at 3 3/4" above the road surface. Mind you, I don't drive through shopping centers with speed bumps!!! Anyway, this setup has been successfully done by many z owners. Good luck with your adventure. Hope this helps you out a little.

[Tourniqet]

240zx

That is a GORGEOUS car!!! What type of fuel pressure gauge is that? Are those custom fule rail/tubing. What kind of electric radiator is that? Enough with the questions tell me EVERYTHING!

[240ZX]

Well,

The fuel pressure gauge is a Mallory 3 port (one return line to the tank). The fuel lines I made up myself from SS tubing. The electric fan was purchased from Motorsport Auto (see their cataloge). It was really fun redoing my Z, but it's much much more fun to drive!!! I never knew a Z could corner so well...and its only a street car. Can you believe the paint job, it's the only thing I didn't address. It's the same paint that was on it when I got the car, over 20 years ago. Of course it has always lived in a garage too! If you ever need advice on your project, feel free to inquire and I will assist you if I can. Thanks for the kudo's

[Tourniqet]

Those wheels look to fit the car well, I thought 9 inch rear wheels would stick out like a sore thumb! how did you do it without fender flares!?!?!

[240ZX]

Tourniqet,

To get the wheels to fit within the stock wheelhouse you will first have to use a coilover setup with a 8" free-length spring. The rear wheels I purchased ( I got them used ) have an offset of 35mm, so I had to fabricate custom spacers to aquire the correct position. Mind you, I have about 1/8" clearance between the inside edge of the rear wheel and the strut. It took some calculating to get it right the first time. But, as you can see it turned out well with no rubs anywhere. I forgot to mention that all my struts have been shortened 1 1/2". This is not required but by doing so you will have better usable shock travel with a lowered car. The rear tire size is 235-40 x 17 however, I've seen this setup using 245-45 x 17 with no problems. Clearances on this setup are very close. Hope this answers your inquirey.

Respectfully,

240ZX

[SuDZ]

Originally posted by 240ZX

Tourniqet,

To get the wheels to fit within the stock wheelhouse you will first have to use a coilover setup with a 8" free-length spring. The rear wheels I purchased ( I got them used ) have an offset of 35mm, so I had to fabricate custom spacers to aquire the correct position. Mind you, I have about 1/8" clearance between the inside edge of the rear wheel and the strut. It took some calculating to get it right the first time. But, as you can see it turned out well with no rubs anywhere. I forgot to mention that all my struts have been shortened 1 1/2". This is not required but by doing so you will have better usable shock travel with a lowered car. The rear tire size is 235-40 x 17 however, I've seen this setup using 245-45 x 17 with no problems. Clearances on this setup are very close. Hope this answers your inquirey.

Respectfully,

240ZX

What kind of rims are those? Are they still available from places?

SuDZ