Diff Speed Sensor (changing wheel size)

[winstontj]

I'm looking to put more wheel on the car - meaning probably go up to 16" rims (still undecided) as well as increase the overall tire size. With cars in the past I have increased rim size and gone down to lower profile tires maintaining the same rolling distance and keeping the speedo accurate.

On the e30 there is a hall type speed sensor on the wheel side of the diff correct? Is there a way to tune or adjust this so the speedo will accurately reflect vehicle speed if I install larger tires?

Thanks for any help. My biggest concern is that by going larger the speedo will understate which in my book is a real good way to start getting speeding tickets at highway speeds.

[MR 325]

The speedo reads at the diff.

If you run correctly sized tires you will have no issue. 205/50/16 or 225/45/16 would be perfect.

[AndrewBird]

All a hall effect sensor is is a magnetic trigger. There is a spot on the diff that is magnetic and when this spot passes the sensor, it sends a pulse to the speedo. These pulses are what make it work. In order to change it, you would have to change where the magnetic spot is. I.E. Not possible without EXTREME modification/fabrication.

Just run lower profile tires.

This is a great calculator to help find what size you want:

http://www.miata.net/garage/tirecalc.html

[winstontj]

45 series seems really low profile. Is there a good tire selection in the 205/50/16 size? I'll go look on tirerack right now but figured since you are answering I might as well ask!

[MrK]

1. BMW speedos are a little optimistic, so getting a slightly larger overall diameter would probably make your speedo more accurate, if anything.
2. WHY do you want to increase your overall wheel diameter? e30s don't like to accomodate larger wheels. Rubbing is much more likely then.

[FredK]

There aren't that many tires in 16" these days. 205s are more plentiful than 225/45 R16. But, they do make Hankook Ventus RS2s in 225/45 R16.

[winstontj]

When I look at the wheel well it looks like I could use more tire under the car. The current 14" basketweaves just look too small. I'd like at a minimum 15" but ideally what I would like is to keep the car and speedo accurate.

[FredK]

IMHO the car will look great once you get a nice, correctly sized tire on a properly lowered car.

[Garageaholic]

This is a great calculator to help find what size you want:

http://www.miata.net/garage/tirecalc.html

Great link. Thanks!

[winstontj]

I wish I had photos available to post. The car sits nicely on 14" basket weaves now. It's lowered (properly) and still looks to me like it needs more. I'll post up some pics tonight when I get home. The wheels JUST tuck up under the fender in the back and in the front are about even or a slight tuck. It's the space between the front and back of the wheel wells that I don't like. I'm a HUGE fan of BMW engineers. I believe they knew (and still know) what they are doing and there is no reason to undermine their intentions. The car was built in such a way that it needs very little IMO. Maybe it's just a jump up to 15" basket weaves and proper tires?

[FredK]

Just drink a few beers. Everything looks better with a few beers. :mrgreen:

Ah, a thought just occurred to me. Maybe the PO of your car put undersized tires on the baskets. There's a better selection of tires in 195/60 R14, and it's possible the PO put these on instead of the stock 195/65 R14 that BMW specifies.

[winstontj]

Just drink a few beers. Everything looks better with a few beers. :mrgreen:

Ah, a thought just occurred to me. Maybe the PO of your car put undersized tires on the baskets. There's a better selection of tires in 195/60 R14, and it's possible the PO put these on instead of the stock 195/65 R14 that BMW specifies.

Don't mean to come off sounding homo or anything but where do you live? I just posted up in the gatherings that I want to get together with any boston area owners for a drive sometime - you seem to know alot about these cars. Also I'll be drinking a few beers & chopping up my old 2002 sometime soon. You are more than welcome to join and kick some tires or take out some agression if you feel so inclined!

I'll look - I think they are 60 series tires. They are Hakkapil..... (Hakk-1's) winter studless snows with very little tread. I'll be replacing them sometime soon and it never occured to me that they may not be the correct size BMW called for. I'll look into that and keep my eyes open for a set of 15" basketweaves. The 14"ers would look great on a 2002 IMO.

[e30_325es]

FYI, stock diameter tires are right around 24 inches or just a hair smaller, so keep it around there and your speedo shouldn't be off by much.

[FredK]

Don't mean to come off sounding homo or anything but where do you live?

HAHAHAHA. That's an awesome way to ask a question.

I live in Southeast MA, an hour or so south of Boston.

Also I'll be drinking a few beers & chopping up my old 2002 sometime soon. You are more than welcome to join and kick some tires or take out some agression if you feel so inclined!

Hahaha sweet! You should graft a $500 '02 to your car and save it! Though chassis work is probably easier said than done.

Yeah when the weather gets warmer I'll probably see you at some meets.

[winstontj]

Most of the car work/chopping, etc I do is actually at a buddy's place in Carver. He's a Triumph guy but owns a gt3 2002 track car, a triumph track car & others. I'm sure as soon as the weather is warm we'll bump into each other sooner or later.