THSCC Forums

Gurus,

I recently had to replace a hub on the Radical, and it turns out that Radical has changed the type of hubs it uses to ones with smaller wheel stud holes. The holes in the new hub are about .505" whereas the knurl diameter on the studs I have been using is .563"

My question: can I simply drill out the newer hub and press in the .563" studs, letting the knurl on the stud do the work, or do I need to have the inside of the stud hole knurled (or splined, I suppose) as well?

Thanks,
Matt

Matt,

I don't recall seeing any internal splines or knurling in the hubs when I've replaced studs in the past. However, I wasn't looking for them. I have 2 reservations towards drilling out your current hubs to match your studs.

One is wrt strength. It is possible you could critically weaken the hub with such material removal. In fact, that may have something to do with why Radical has gone to smaller diameter studs. Typically, a mechanical designer or engineer will allow 1 to 1.5 hole diameters worth of material from the edge of the hole to the edge of the part. I've got a spare Miata hub or 3 out in the shed and for reference can take a look at them tomorrow evening. I definitely wouldn't go less than 1 hole diameter(new hole) of material thickness though.

Second is the required hole size and drilling it. I'm not sure what diameter you would drill to accomodate the .563" dia knurling. No doubt it's less than .563". I'll check my Machinery's Handbook tomorrow and see what is recommended. It may be a special size that you won't easily be able to obtain a drill for. Also you need to exercise caution when drilling the hole to ensure you don't "waller it out" and make the hole too big so that the stud won't be held in place. Additionally make sure the new hole is square to the hub surface so that the stud will install square and you'll A) be able to get the wheel on and B) not shear the stud(s) when tightened because they're not receiving a true tensile load.

A third issue that just comes to mind is wrt to the diameter of the bolt circle. Is it the same as your older hubs? If not, don't waste your time any further. Check with the manufacturer to ensure they sent you the correct part (they're not always right). It wouldn't hurt to double check with them any way.

Just things that I would give consideration to. YMMV.

_________________
“I feel safer on a racetrack than I do on Houston's freeways.” - A.J. Foyt

Kevin Butler
Mobetta Autosport Spec E30 #612
2003 C5 Z06 Corvette
AFR Miata, SM2 61, '93 w/200 SC'd RWHP - soon to be resurrected
Waaaay too many other projects....

Good points, Kevin.

I don't think strength is an issue, since it's only about .050" difference in total diameter.

That being said, it would be crucial to choose the correct drill size and ensure the cut was square.

The bolt pattern is identical, already checked that.

I believe that Radical is using the same modified automotive hub they were before (from a Fiat, or a VW or something), they're just moodifying it slightly differently now. For all I know it could be due to a change in wheel vendor.

-Matt

Matt, do you have a large supply of the existing studs? It would seem to me to be questionable to modify the hub to accomodate a different stud as the studs are, in most cases, replaced more frequently. If the new hubs are .505, I would imagine that there should be matching studs available. If this is so and you bore out your hubs, you have locked yourself into using the previous design stud which could soon be NLA. So, if you have a huge number of the old studs, then that might be OK, otherwise, I would make very sure that there isn't a matching stud with the correct knurl. It is much harder to make a hole smaller than bigger.

If the hub is general automotive, and the studs follow suit, I am sure that there are number of people here with access to the Dorman master catalog that has lists of all studs by length, shoulder, knurl, thread etc. If you are looking for a specific configuration in a stud, I imagine that it can be found.

_________________
Rich
http://www.v8mongrel.com/

I upsized studs (12mm to 14mm). on the rally car a year ago and have not had any problems so far even under the abuse of rally. I ended up using a machine shop in Garner. It was cheaper than a quality drill bit. Seems like they charged $10 per hub for drill and install. The cautions I read above are all valid and that is a big part of why I went to the machine shop. I can dig up the name of the shop if you want.

Go into a Napa and ask to see their Big Book 'o Wheel Studs, they should have it in there. Additionally, you can go to http://www.motormitedormancatalog.com and search around there.

Or do what I would do, and call up Radical and get their part number for that wheel stud.

_________________
Has no responsibility whatsoever.

Matt, I think drill a BIG hole and weld the stud in! Or, JB weld. Or, just use 3 studs. After all, how much does the damned thing weigh, 300 pounds? The designers of the Radical probably used 4 studs so they could fill all the holes in the wheels!

PS. I'd like to drive it BEFORE you follow my advise.

Ron

OK,

Information on stuff like wheel studs is not in my Machinery's Handbook, so you'll need to check with a stud manufacturer for the appropriate hole size for the studs you want to fit. I saw something when I took a quick look on the internet that makes me think those holes may need to be reamed for the appropriate size/finish.

Another question that comes to mind is with respect to secure mounting of the wheelsl. With the smaller studs, you'll have smaller nuts (I'm sorry ). Your wheels have the holes sized for the larger stud. So now, you'll wind up with oversized wheel holes. The smaller nuts will result in a reduced surface area footprint. That, plus the now oversized hole could possibly leave you with inadequate surface area for safe and secure mounting of the wheels. This could result in the wheels pulling over the nuts.

This is a worse case scenario of course, but I'd go to the manufacturer and point out these issues to them. I'd be interested in what their viewpoint/recommendation would be. Again, YMMV. Sorry for not having any black and white answers.

_________________
“I feel safer on a racetrack than I do on Houston's freeways.” - A.J. Foyt

Kevin Butler
Mobetta Autosport Spec E30 #612
2003 C5 Z06 Corvette
AFR Miata, SM2 61, '93 w/200 SC'd RWHP - soon to be resurrected
Waaaay too many other projects....

A change in knurl diameter is not automatically translated into a change in stud diameter. A .505" and .563" knurl would both be in the rang of common sizes for a 12mm thread stud. It is possible that there is no change in wheel nut used.

_________________
Rich
http://www.v8mongrel.com/

A little more information:

The stud I need is a 1/2-20 3" long with a 0.505" knurl diameter. Good luck trying to find that.

It seems that Radical has gone to a shorter stud (1.5") due to going with a different wheel vendor, slightly different brake package, etc. etc. I'm not upgrading wheels and brakes because I need new wheel studs.

As for studs being no longer available, I'm fairly confident that Moroso, Summit, etc. will continue to manufacture 1/2-20 x 3" with a .563" knurl for a while (since they've been doing it for about 30 years now).

I can't find a 3" with 1/2-20 thread that will fit the .505 hole. In fact I can't find a stud of ANY thread that is 3" in length to fit the .505 hole.

Kevin, mfg suggests .554 to .561 sized hole for the .563 knurl diameter studs.

Thanks for all of the responses so far.

And Wes, you don't EVER call Radical for parts. Ever. Not unless it's a Radical specific part, which I KNOW this isn't. They don't manufacture their own wheel studs. That shipping from the UK just KILLS you.

This is what I get for owning a real race car, I guess.

-Matt

Have you checked these guys out? http://www.trackstore.co.uk

This is where the MR2 guys get our wheel studs. I have had real good experiences with this company.

_________________
Jim Pastorius
2008 Silverado VortecMax
1992 Camaro CMC#92
2002 BMW R1150R

2009 3rd Place CMC Mid-Atlantic Championship
2009 CMC Hyperfest Winner

I meant to call them for a cross reference part number. I'm pretty sure that it would not be Radical specific.

Mosler at Summit

Are you willing to use a metric lugnut?

_________________
Has no responsibility whatsoever.

Probably Loop Road in Garner. They've never let me or anyone I know down yet.

_________________
“I feel safer on a racetrack than I do on Houston's freeways.” - A.J. Foyt

Kevin Butler
Mobetta Autosport Spec E30 #612
2003 C5 Z06 Corvette
AFR Miata, SM2 61, '93 w/200 SC'd RWHP - soon to be resurrected
Waaaay too many other projects....

I love that place...

Wes,

Saw that one at Summit. I'm not sure that 2.5" is enough maybe. I'd prefer not to have different lugs per different wheels. I suppose there are worse fates than having to change the lugs on all the wheels (although then I'd have to find a 2.5" metric stud with a .563 knurl diameter).

-Matt