New tyres 205/40/17
 

I'm FINALLY taking delivery of my car on Monday. Even though it arrived on Thursday, apparently it takes more than two days to do a groom. Even more annoying was driving past the dealership last night and seeing the car just sitting in the showroom!

So I went and ordered my tyres, 205/40/17's. Why did I go with this size?
They have the lowest circumference of any feasible option. 195/45/16 would've been even smaller, but that would've been taking the point too far. Also, I wouldn't be able to fit the brakes I want under a 16" rim, and I'd already bought 17s anyway.

Why am I focused on a small circumference wheel? Well it has numerous benefits. For a start, less unsprung weight = better handling. Secondly, smaller circumference tyre = effectively shorter gearing = better acceleration & braking. Thirdly, lower COG.
Regarding COG, a lot of people confuse COG with wheel arch gap. If you put a bigger radius wheel and tyre on from stock you are RAISING the COG.
Putting my wheel/tyre on lowers my COG 18mm over a stock setup. Straight away, my COG with stock suspension is probably lower than another setup with massive rims and tyres and coilovers.
Running my setup with stock suspension will look a bit rude though, as the down side to all this is that I end up with more wheel arch gap. But, of course I can add coilovers with will lower my COG further and reduce this arch gap. Also, because my wheel/tyre is smaller, I'll be able to going lower before I have any form of rubbing/fouling; should I feel the need to go that low.

Related to above, I realise I most this will seem like the tyre is going to be to skinny, but I disagree. I've owned 4 silvia, that all at one time or another were putting down 300rwhp (the level were I see myself taking the new 86) and at no time did I feel that a 205 tyre was too skinny. Sure, you couldn't give it the full beans in 1st, or around a corner in 2nd or 3rd, but that was the fun of the setup!

Interesting, im running 205/55/16 n thinking of goin 215 45/17 for more grip instead...

Any pictures or experiences with this setup?

Yup. It's good. Drifts easier

Falkin tires make the 452 in a 215 35 17. FYI

FWIW, my 205/50/17 snows are wider than the stock 215/45/17 primacy tires.

As for the COG, does the lower COG from smaller tires actually help? It would interesting to see how smaller diameter tires affect the RC and COG, and more importantly how the COG moves compared to the RC.

If it is enough grip really depends on what type of driving you are doing. Not ideal for autoX or track events, but I am sure they are fun to go drifting in.

If you are getting that in detail with its benefits, another benefit is a thinner sidewall so there would be less flex if you are comparing direct compounds.

^^ Width isn't everything on a track, CSG found 225's are faster than 245's because they hold heat better. A stockish power level (not FI) FRS/BRZ just won't heat up 245's enough for optimal grip.

AutoX is a different beast since you can't warm up your tires, so how much heat they're holding lap after lap doesn't really come into play.

So just wondering, does anyone have any pics of a setup with 205/40-17s? OP apparently was banned before being able to post up (not sure why though, checked out the post history and didn't see anything too weird). The only pics I could find of that size tire are here

http://www.ft86club.com/forums/showp...53&postcount=2

but that's on a heavily lowered vehicle.

what brand of tire did the op get i wonder?

@Manji thanks for the pics. Looks like you could benefit from some wheel hub spacers?
@troek - no idea, been looking at the General G-Max AS-03 myself, they're 4 lbs. lighter than stock and have very positive reviews in the kind of weather we experience here in Southern Maryland.

my friend ran the snot out of those tires on his r32 gt-r and loved them. not terribly high grip but they were extremely predictable and had progressive breaking traction. lots of tire talk. made for some fun times up in the mountains.