Different offsets and front and rear

[bark]

I'd like to get your opinions/knowledge on pros and cons of different front/rear offsets in regards to handling. Reason for asking is that there are a set of rims for sale 15x7 with +33 fronts and +15 rears. Any advice?

I've currently got 17x7 +40 and want to downsize but fill the guards a bit more. I'm not fussed if I have to roll guards a bit to accommodate.

[sliq]

not sure about handling. but who cares. they would look HOT.

[Steampunk]

not sure about handling. but who cares.

*sigh*

[sliq]

not sure about handling. but who cares.

*sigh*

all sarcasm is lost on the internet

[Steampunk]

not sure about handling. but who cares.

*sigh*

all sarcasm is lost on the internet

lol it does actually, as I was agreeing with you sliqmeister. You need new batteries in your sarcasm detector.

here's something from someone who may or may not know what he is talking about from both the good ol' trial and error process and the fact he may or may not be studying engineering:

I used a set of wheels for a trackday which were 15 x 7, +24 with 195/55R15 tyres and these JUST missed the stock guards without rolling and about 2 deg neg camber. The only rubbage they had was on the guard liners and the highest mounting tab for the guard liner on the front guard, I just bent that one out of the way. I think that was mainly cos they had too higher profile tyres on them.

If all else fails you could always just roll the guards, a bit of street sign pole can get this done pretty quick

Tim

sorry for the cut'n'paste Tim, but what you stated was pretty much ignored last time, so we shall try again shall we?

[rascal]

I'd like to get your opinions/knowledge on pros and cons of different front/rear offsets in regards to handling. Reason for asking is that there are a set of rims for sale 15x7 with +33 fronts and +15 rears. Any advice?

I've currently got 17x7 +40 and want to downsize but fill the guards a bit more. I'm not fussed if I have to roll guards a bit to accommodate.

I doubt there would be too many issues with the staggered setup. I'd imagine that it would ever so slightly move the balance of the car towards understeer. Would marginally soften the rear wheel rate due to extra leverage.

I ran +13 front and +38 rear on my prev race car (25mm bolt on spacers in the front only) and it added just the tiniest bit of oversteer, (but not enough to justify softening the rear bar one notch)

Not sure what model you have, but my NB has 15x7 +17 on the back with -3neg and they dont rub. (Well not on the street!! Havent had it trackside yet..)

[wun911]

I have always wondered about this myself.
I know lotus do this big wide at the back and small skinny at the front.

1 How does it effect how I set up my alignment?

2 With different offset wheels front and back. I cant line up the wheels with a piece of string anymore seeming the rear wheels with physically stick out more, how do I go about creating toe in on the rear wheels? Do you guys bolt on the stock wheels then go off to do your alignment???

3 Does it induce over stear or under stear?

[rascal]

Wun.

You can still use the string method, just allow an extra X mm between the tyre edge and the string to cater for the extra X mm of offset.

Big wide tyres at the back would induce understeer. (more grip at rear relative to front.)

[bark]

Thanks for the replies guys, my car is a NA6. Sounds like this could be a goer!

[Charlie Brown]

Before you jump in with the 30 offset for the front you should do a Google search and read up on “Scrub Radius” and “Bump Steer”. It may change your mind.

I do know that you will need to increase your toe-in to compensate for the wider track.

Maybe do a search in Miata.net for some more answers or fire an e-mail off to Fat Cat Motorsports for expert advice.

On a completely separate matter, I’d expect that although they may ‘look good’ they will be illegal due to the track width increasing by more than 25mm. This will then void your insurance as the car wouldn’t be classified as roadworthy.

[manga_blue]

I've tried all sorts of combinations of from +13 to +25 front and rear. I found they all felt a little bit different but I couldn't say that there were any real problems with any of the setups. The bump steer and scrub radius effects are there but they were much less of a worry in practice than I expected. Best handling seems to be at around +20F/+15R on 15x6.5 for my setup but I'd say this wouldn't be the same for everyone.

I really only do those wide setups on the track. The tyres do stick out a fair bit. On the street they would just be horribly obvious cop magnets, as well as throwing spray everywhere anytime you visit somewhere that rains, like NSW or QLD.

[AB7]

I tried many different offset on my car. I can tell you from my own experience, I wouldn't worry much about scrub radius, bump steer issue unless you are getting close to 0 offset.

Regarding insurance, oh well they can void your insurance for whatever reason if it's not standard! Wether if your car is lowered, with intake, rims, ect...

If you worried about that, than keep it bog standard.

[ebola]

Regarding insurance, oh well they can void your insurance for whatever reason if it's not standard!

Get your car engineered and you will be fine.

You will find that to pass engineering you can only increase the rim width 1.5 inches on an MX5 and the track by 20mm. This means that to pass engineering a max of 7 inches. Take into account that the increased width will increase your track (assuming the same offset) so you will not be able to lower your offset much at all and expect to pass.

Also be aware that the speed/load rating on the tires must be the same or greater than the originals. You can find what it is on your drivers door. Going a lower profile lowers this rating and you will not pass engineering. You can get R type tires that have a higher rating to cover any discrepancies.

Chances are that your 17s wouldn't get passed for all those reasons...

I do recommend you engineer your car. Both because its the official way things should be done, but mostly because you can wave an engineers certificate in front of the cops nose and direct him to your new modified vehicle compliance plate with all the mod details listed, then tell him to faaaarrrrkkkkk off! That's if you want to be polite anyway.

[StanTheMan]

I do recommend you engineer your car. Both because its the official way things should be done, but mostly because you can wave an engineers certificate in front of the cops nose and direct him to your new modified vehicle compliance plate with all the mod details listed, then tell him to faaaarrrrkkkkk off! That's if you want to be polite anyway.

As far as I know Police are still within their right to defect a vehicle even if its engineered. Most cops are reasonable and will not.
they can defect anything they deem not right. Engineered or not. I don't know if you have to still pay the fine or not but just because its engineered, does not guarrantee not to get defects , under no circumstanced tell the cop to F*&ck off. Because that will almost guarantee a defect of some sort.

[rascal]

You will find that to pass engineering you can only increase the rim width 1.5 inches on an MX5 and the track by 20mm. This means that to pass engineering a max of 7 inches. Take into account that the increased width will increase your track (assuming the same offset) so you will not be able to lower your offset much at all and expect to pass.

If the wheel has the same offset then the track width will be exactly the same for the wider rim as for the narrow rim.
The track width is the distance between the centrepoints of the rims.