Fitting Borbet B 9J's (speedo adjustment?)

[kman82]

I was chatting to a mate in the pub about my speedo being miles out after fitting the 215/40 R16 tyres. 80 mph seems to be reading as 90 and it revs much higher too, The tyre's make more of a difference than i though they would.

Anyway my mate said back in the day they use to fit an electronic device on the speed sensor wire going to the diff. You can preset what percentage your tyres are out and it adjusts the signal for you. Does anyone know if there is anything similar suitable for the E30?

[Rav335uk]

Take a look at the link below.
I have worked out how far your speedo is out.

http://www.willtheyfit.com/index.php?wi ... mit=Submit

[kman82]

yeah 4.86%

I doesn't sound like a lot but when compared to the sat nav its miles out.

30 = 35
80 = 90

seems to be more than 4.86% out, maybe theres another issue and the tyres have made it worse?

[kman82]

Am i right in thinking a different ratio diff wouldn't affect the speedo, just the revs??

[Rav335uk]

Am i right in thinking a different ratio diff wouldn't affect the speedo, just the revs??

Sounds right

[huish]

Ah man!! this tyre size business is doing my head now....

I've got Eibach pro kit 35mm drop all round and 205/55 R15 BBS on the rears and they look the perfect size for my wheel arches.
On the front I have 195/55 R15 BBS and they look too small. The last thing i want to do is to put a smaller rolling radius on and the wheels get lost in the arches.
Have you lot got yours dropped more than 35mm at the front?

I went to my local tyre garage today to see if they had any 225/40 lying around I could test fit but they said they dont come across them that often. Would it rub the arches all the time or just if I had a couple of fat mates in the back?

A good size that would work well is 215/45 but the selection of tyres is pretty naff

get 215/35/16 their dear but a better look than 205/40 an the 215/40

[Jhonno]

225/40 is the best size imo..

Roll the arches if you need to.

[kman82]

215/35/16 would just be daft IMO

The 40's are tiny on the wheels and cause speedo / high rev problems as it is

My car isn't all that low and I reckon I will be fitting 225/40 next time round

Anyone got any thoughts on the speedo issue?

[Rav335uk]

8j Alpinas run 225/45/16's, so running what your suggesting shouldn't put the speedo out too much.