varying impreza tyre sizes (profiles)? bad idea?

[rb5230]

i need to get some new tyres soon for my RB5, and i have decided i want toyo t1r`s.

Now i know that from factory the are a 205/45/17 sized tyre but i also know that many people swap them and use a 215/40/17 tyre, but then also there is the option of using a 205/40/17 which is about £88 cheaper for a full set.

i know it may mess very slightly with the calibration of the speedo although the difference is so minimal i really would expect hardly any difference at all, and also the ride quality might be slightly worse, but then its not like the difference between having 18 inch alloys and 17s, it is just a very small difference in the profile of the tyre if anything surely it should make for less sidewall flex.

I used to be a tyre fitter for mercedes and personally i think it would be fine but i was wondering if anyone else had any 1st hand experience of this sort of thing.

These are camskills prices:

http://camskill.co.uk/products.php?plid=m54b0s457p... £78.60
http://camskill.co.uk/products.php?plid=m54b0s103p... £71.60
http://camskill.co.uk/products.php?plid=m54b0s13p1... £56.70

So quite a difference in price. Thanks

[NorthDownsScooby]

As long as you're on the same size & profile all round then I'm sure it'll be fine.

Have you checked the specific differences it'll make on a tyre calculator type site...?

[rb5230]

NorthDownsScooby said:

As long as you're on the same size & profile all round then I'm sure it'll be fine.

Have you checked the specific differences it'll make on a tyre calculator type site...?

i am pretty sure it is fine just wondering what other people thought.

any links for this tyre calculator?

by my calculations it would be just over 10mm of difference in total, so 5mm on each side of the tyre if you get my meaning, so rolling radius would basically the same as wearing tyres with not much tread left, although they would in fact have full tread.

[NorthDownsScooby]

http://www.google.co.uk/search?q=tyre+calculator&a...

google is your friend ;-)

[rb5230]

i looked at another calculator and it said at 70mph i would actually be travelling 67.67mph, so at least i would be safe when it comes to scameras.

[NorthDownsScooby]

Oh yeah your real speed will always be under what the speedo is reading. I think it HAS to be actually.

[paulmoonraker]

NorthDownsScooby said:

Oh yeah your real speed will always be under what the speedo is reading. I think it HAS to be actually.

My sat nav always says i am going slower that the speedo - thats on all 4 cars I have used it in.

[Toltec]

I think the load rating on the 205/40s is too low for an Impreza.

I run 215/45 17 on mine, mainly because I wanted to get a set of Bridgestone RE050A for it. Has the added side benefit of making the speedo a bit more accurate. The later cars seem to run this size too.

Toyos in that size not a bad price either http://camskill.co.uk/products.php?plid=m54b0s15p1... £73.80

[GravelBen]

Toltec said:

I run 215/45 17 on mine, mainly because I wanted to get a set of Bridgestone RE050A for it. Has the added side benefit of making the speedo a bit more accurate. The later cars seem to run this size too.

Its also the standard 17" tyre size for Legacies if thats in any way relevant.

[rb5230]

Toltec said:

I think the load rating on the 205/40s is too low for an Impreza.

I run 215/45 17 on mine, mainly because I wanted to get a set of Bridgestone RE050A for it. Has the added side benefit of making the speedo a bit more accurate. The later cars seem to run this size too.

Toyos in that size not a bad price either http://camskill.co.uk/products.php?plid=m54b0s15p1... £73.80

The load rating is sufficient for a 2000kg car as far as i can see.

A 215/45/17 tyre i think would look a bit odd as the profile would be a fair bit higher due to the extra width and would also knock the speedo out the wrong way.

Thanks for the input though, it seems Bridgestones are quite highly regarded these days.

[Toltec]

rb5230 said:

Toltec said:

I think the load rating on the 205/40s is too low for an Impreza.

I run 215/45 17 on mine, mainly because I wanted to get a set of Bridgestone RE050A for it. Has the added side benefit of making the speedo a bit more accurate. The later cars seem to run this size too.

Toyos in that size not a bad price either http://camskill.co.uk/products.php?plid=m54b0s15p1... £73.80

The load rating is sufficient for a 2000kg car as far as i can see.

A 215/45/17 tyre i think would look a bit odd as the profile would be a fair bit higher due to the extra width and would also knock the speedo out the wrong way.

Thanks for the input though, it seems Bridgestones are quite highly regarded these days.

I just looked it up, original tyre load rating for a classic is 87v. Don't forget the cornering on a performance car is going to put much higher loads on the tyres.

The slightly larger tyre fills the wheel arch a bit more and imho looks better, my speedo still over reads, though only by 5% now.

I really like the Bridgestones, a little less outright grip than GSD3s, but far more feel so you can actually push them harder. You get what you pay for though as they are closer to £100.

Edited by Toltec on Saturday 11th December 17:55

[rb5230]

Toltec said:

I just looked it up, original tyre load rating for a classic is 87v. Don't forget the cornering on a performance car is going to put much higher loads on the tyres.

an 87V rated tyre is only good up to 149mph and 2180kgs though which is basically the top speed of the vehicle which seems a little dodgy to me, the 84 W rated toyos i am looking at are rated to 167mph and 2000kgs, so surely this is just the difference of having a couple of passengers but gives a little more leeway in the top speed stakes?

all this talk is now making me think i should overspec the tyres when it comes to speed and load ratings now.

Edited by rb5230 on Saturday 11th December 18:06