1997 Mazda MX-5 Miata: Momo Wheel Gory Details
January 26, 2011
Perhaps you're perplexed as to why one -- namely, us -- would want to replace the steering wheel in a car like Project Miata, our longterm 1997 Mazda Miata project car.
Well, I'll tell you why.
Mainly, the size and position of the stock Miata's wheel sucks. The non-telescoping, non-tilting, smashed-against-the-dash tiller forces you to move the seat forward into a somewhat more knees-bent driving position than you'd find in other cars. It's got a large-ish overall diameter (and has a pencil-thin rim) to boot.
As a result, tall guys tend to bang their right knee against the steering wheel and/or have difficulty executing heel-toe downshifts.
It appears the driving position was arranged around the proportions of a Japanese guy instead of an American dude (don't laugh, it happens; see first-gen Honda Fit). Or it could be that the US airbag requirement drove the engineers to put some real estate between the wheel and the driver's torso to minimize collateral damage during an airbag deployment. Note that Canada-spec (non-airbag) Miata steering columns of this era located the wheel closer to the driver.
Whatever the reason, the last straw in our case was that the leather on our stock 128k-mile wheel was delaminating and pockmarked like Edward James Olmos' face, and the two probably felt similar. It had to go. Yes, the airbag goes with it, and I'm okay with that, as airbags of this era were designed for unbelted occupants and so deployed with considerably more force than today's bags. I'll stay belted, remove the bomb and save myself the broken arm, thanks. But with what to replace the stock wheel?
First thing is to settle on the desired overall diameter. The stock wheel is 365 mm. The selection of 350 mm aftermarket wheels is huge. This size will also provide more knee clearance and slightly quicker steering with a touch more effort. Fine by me.
Then you need to decide how much closer you want the new steering wheel to you. In this case, the target was an inch or so, as this is enough to make a noticeable difference (more than you might think) while still leaving the stalks within easy reach. Since the stock wheel is about 120 mm in overall height (from rim face to the back of the splines), the target dimension (this is known as offset) for the new wheel is roughly 145 mm. The installation of an aftermarket wheel always includes an adapter of some length which must be added to the wheel's offset. Learning the adapter's length prior to purchase is easier said than done.
As for the rim, wood is just out. No silly flat-bottom nonsense, either. Suede provides great grip when used with racing gloves, but can be slippy with bare hands (until your palms sweat), plus suede dirties very quickly and gets crusty due to UV exposure.
Leather wrap and round rim it is. Easy decision.
It turns out the Momo Mod 08 ($180 online) fits the bill, as the offset is 90 mm while the Momo adapter is 55mm in length, giving us 145 mm overall stack height. Clearly, the Mod 08 is a deep dish wheel, so it looks bitchin, too. I wanted to avoid adding spacers if possible, since more stuff stacked atop the adapter is, well, more stuff. Less is better.
Ah, the Momo adapter. This piece of metal is simultaneously indispensible and infuriating. It turns out Momo didn't develop an adapter specifically for the Miata, instead simply reusing one they developed for another Mazda. Go figure. Best-selling sports car in the world, and Momo couldn't be bothered with developing a plug and play adapter. But I digress.
The Momo adapter makes the installation a pain, but the fact that it is engineered to collapse in an impact means you really, really want it. There are other aftermarket adapters that allow for easy installation, but none of them appear to have been designed to be crashworthy.
Looky here. The Momo adapter has a face and struts made of steel, around which an aluminum base has been cast. Each strut has the built-in mechanical fuse shown here which makes for controlled deformation in an impact.
When you attempt to actually install the Momo adapter onto the steering shaft, you quickly realize that the adapter runs right into the clockspring connector. This doohickey houses a long ribbon of wire wound in the shape of a loose circle, and its function is simply to allow the wiring for the horn and airbag to make the leap from the steering wheel, which moves, to the dash, which doesn't. Horns are important, even in race cars, so the clockspring (below left) needs to stay.
In short, you need to clip off the connector for the horn and airbag (don't bother de-pinning it; there's not enough space in the adapter to package the stock connector shell), modify both the clockspring connector (center) and the adapter, and when you've hacked them both away to the extremes of your comfort level, they'll just barely coexist peacefully. It takes a die grinder, a Dremel and many cuts-and-tries to get it right. Above right is the adapter midway through hacking it up.
The rest of the installation is straightforward stuff -- wire up the horn, click in the airbag resistor purchased from a friendly member of clubroadster.net, tuck the wires inside the adapter and bolt on the wheel.
With all that said, the Momo wheel is truly a nice bit of kit. There's no flex to speak of and the leather looks and feels great. Its thicker rim just feels more substantial, and the wheel placement is much more agreeable and, yes, there's now more knee room. The new wheel makes a surprising difference. I'm a fan.
As a bonus, the horn button is now in the location to which your brain automatically guides your palm when that douchebag in the bro-dozer changes lanes on top of you.
Jason Kavanagh, Engineering Editor @ 128,458 miles.