Center Lock vs Four Bolt Wheels

[MBillings]

What is the difference between center lock and four bolt wheels? (I'm shopping for wheels and I can't find center locks.)

thanks,
Mike

[RussMcB]

I converted some 4-bolt wheels to center lock by fabricating adapters but it wasn't worth the effort. It was a pain and the final result wasn't great. Buying a set of new Panasport wheels from Keith Averill was much easier and smarter. I think the price was near $900, which isn't much more than than the cost of used wheels.

To answer your question, though: The center hole diameter may not be right, the drive pin holes aren't there and the offset may not be right for your car/upright.

[Neil_Roberts]

What is the difference between center lock and four bolt wheels?

Center lock wheels are retained with one big nut in the center, sometimes with a big machined aluminum washer between the nut and the wheel. Drive and braking torque is transferred through some number of smooth OD drive pins in the hubs that engage matching holes in the wheel. Four bolt wheels are what you see in any parking lot.

I've studied the math behind aerospace failure modes and effects analyses, and I've done a few of them myself. If a joint is modified to have two fasteners instead of one, you don't get half the probability of failure: you get 1/10th the probability. Knowing that, and having seen a lot of center lock wheels come loose, I have converted my DB-6 to 4 lug wheels. Centerlocks are only tolerable if quick pit stops during a race are in the plan.

[kea]

The other plus of a four bolt wheel over that of a center lock, is with the same pin or bolt circle, the clamping force is over a larger area on a four bolt (lets say 3-3/4", not counting the size of the inserts that Panasport uses), compared to that of a common 3" center cap.

[Dick R.]

Mike,

If your application is still autocrossing the disadvantages noted for centerlocks (which my 85 VD has) are probably not a big deal compared to road racing. I don't know what it would take to convert my car to 4 lug but it would probably obsolete 12 centerlock wheels.

FYI I did learn the hard way in an autocross to frequently check the torque of the big single nut and to NOT continue using an AN grade nyloc nut that spun on/off with no resistance. Fortunately when the wheel passed me I was almost finished braking for a 20 mph or so tight 180.

Dick
CM 85
85 VD

[DanW]

Center lock wheels are retained with one big nut in the center, sometimes with a big machined aluminum washer between the nut and the wheel. Drive and braking torque is transferred through some number of smooth OD drive pins in the hubs that engage matching holes in the wheel. Four bolt wheels are what you see in any parking lot.

I've studied the math behind aerospace failure modes and effects analyses, and I've done a few of them myself. If a joint is modified to have two fasteners instead of one, you don't get half the probability of failure: you get 1/10th the probability. Knowing that, and having seen a lot of center lock wheels come loose, I have converted my DB-6 to 4 lug wheels. Centerlocks are only tolerable if quick pit stops during a race are in the plan.

Neil,

I agree with your FMEA of single nut vs, 4 bolt probability of failure. However, maintenance induced failure Pf is exactly the same. If the mechanic or driver forgets to torque one big single nut, he is just as likely to forget to torque four nuts.

Regards,
Dan Wise

[Roux]

I on the other hand have always collected up a mish mash of wheels (normally chosen by optimizing on cost and low mass simultaneously) so I had different lugnuts for the dry tires than for the rains. By some luck they all seemed to have the same inside hole diameter so I changed over to center lock so that I can have oddball wheels and not have to have a bucket full of lugnuts and a mess during changeover. Now if I had just spent the money up front to buy 3 sets (now 4 sets) of identical wheels, I could have avoided the issue but I could not justify the one time cost.

I have had two failures. One with galling of the threads (now I use zink coated threadrod and nuts) and once when I must have torqued up the left rear twice and not the right rear. Both times resulted in some lost track time, but now I have a system that solves both issues. Pins stay on the windsheild until a wheel is tighten properly, and dry lube on clean threads.

FWIW I have never had a nut that was torqued tight come loose, nylock or not.

[R. Pare]

NEVER try converting a 4-lug wheel to use as a center lock unless you already have experience with that particular design wheel - the stress loads are entirely different between a wheel designed as a centerlock and one designed strictly for 4-lug. The wheel designed as a 4-lugger is quite often a lot thinner at the center than a wheel designed for centerlock, and can break from the increased loads at the center. SOME wheels you can get away with that practice, but not too many.

Failure/loosening of a center lock, while greater than for a 4-lug, is still very remote IF you have everything correct - quality stud, quality nut, quality clamp washer, no interference between the wheel and the radius at the base of the centering snout, etc.

[Roux]

Good advice. I only used wheels that were already being used by others as center lock. Sets of Compmotives, Technos and Kodiak.

[rickb99]

What is the difference between center lock and four bolt wheels? (I'm shopping for wheels and I can't find center locks.).... Mike

Up above you've heard the mechanical differences between the two.

Basically, from a practical stand point, Center Locks make NO SENSE on a 'sprint' type race car (such as SCCA racing and 85% of sports car racing). Stick with 4/5 lug nut wheels.

If on the other hand, you're going serious Endurance racing or any form of racing where pit stops/tire changes are required, then there's an advantage to Center Locks (quicker tire changes/shorter pit stops).

But, given that, center locks are 'really cool looking'

Yes IMPORTANT to check the wheel nut TIGHTNESS before EVERY trip on to the track... fer sher.

Center Locks are sorta 'un-American' which is why NASCAR doesn't use them.. LOL

[problemchild]

Basically, from a practical stand point, Center Locks make NO SENSE on a 'sprint' type race car (such as SCCA racing and 85% of sports car racing).

It rains in the Northeast, sometimes without warning. Sometimes, just before a session, we are not sure whether the track will be wet or dry. During the VIR F2K race, many cars changed tires during the race ..... yes, pit stops under FC caution.
I certainly would prefer centerlocks given the choice. Considering how many modern cars have them, I expect most would agree.

[starkejt]

I have had to do last minute tire changes many times, for rain or occasionally because you aren't sure until the last minute which compound you are going to run. Not to mention in a runoffs week(s) setting, when you are changing tires frequently, centerlocks are nice. I remember one runoffs going through 11 sets of tires, with some sets being mounted on the car more than once, meaning a lot of changes. Having only one nut per wheel is nice in a situation like that.

The one problem I have had with centerlock wheels was when I installed the wheel with the face on top of the drive pins, aka the pins were not in their respective holes. Somehow I didn't notice what I had done, and in the first braking zone, the (front) wheel came off. He managed to make the corner without even touching the brake rotor to the ground.

[KevinFirlein]

. He managed to make the corner without even touching the brake rotor to the ground.[/quote]


Cole would say that just proved he was going to slowly to start with. I loved testing with Steve but he was merciless. "why did you get loose in t10 ?" .."wind blew the cut grass onto the line"..." then you shoulda crashed, quit wasting my time"

back on topic , pro center lock for the reasons stated above, quick tire changes are much easier and Ive only ever had one stub axle failure on my old RT4 at the 97 Runoffs and that could easily be blamed on me as I couldnt tell you how old the thing was.

[starkejt]

Cole would say that just proved he was going to slowly to start with. I loved testing with Steve but he was merciless. "why did you get loose in t10 ?" .."wind blew the cut grass onto the line"..." then you shoulda crashed, quit wasting my time"

Troof, but it WAS the outlap in a new car.

[rickb99]

It rains in the Northeast, sometimes without warning.

LOL we race in the Northwest! Where as everybody who lives anywhere else will tell you, it rains EVERY DAY!!! Well that's not true but it does rain a lot

We had center locks on the Reynard FC. Jeff's FIRST EVERY NOVICE race I changed wheels/tires with him sitting in the car ready to go to pre grid. Yes, under 2 minutes and he made it.

YOU HAVE A POINT THERE.

On the other hand, in 2.5 years of racing that was indeed the LAST TIME we had to run rain tires.. go figure. Yes it rained again but never for his sessions.