How Do You Fit A 4 Point Harness In A Mini Coupé R58 With No Rear Seats?
A customer with a Mini Coupé R58, the JCW two-seater hard top, wants a 4 point harness and asked what he needs behind the seats. The R58 has no rear seats, so there is nothing behind the seats to anchor the shoulder straps to. Garreth's answer is a half cage, with a 4 point harness whose wrap-around shoulder straps loop round a bar on the cage. We supply the cage and the harness, and a garage or the owner fits them.
- Strap angles and the loop method come from our harness fitting guide
- Harness details read from each listing, one by one
Fit a half cage, then a 4 point harness with wrap-around shoulder straps
The R58 has no rear seats, so the cage supplies the bar the shoulder straps need. The straps loop round it. We supply the parts and do not fit them.
- SW Motorsports list a half cage kit for the R58 Coupé, bolt-in or weld-in
- Choose the harness bar option so the strap has a bar to run down to
- Wrap-around straps pass three times through the slide, with 100mm of tail
- The straps anchor to the car, never to the seat
What the customer asked
The owner has a Mini Coupé R58, the JCW two-seater with a hard top. He wants a 4 point harness and asked us what he needs behind the seats to fit it.
Garreth’s answer is short. With no rear seats, the shoulder straps need a bar of their own to reach, and a half cage gives you one.
Why a cage is the answer
Our harness fitting guide is clear about where a harness anchors. The straps mount to the bodyshell, to proper chassis anchorage points or to a harness bar that forms part of the roll cage, and never to the seat, its frame, its runners or its subframe. In the R58 the cage supplies the bar.
SW Motorsports list a Mini R58 Coupé half cage kit. It is a DIY half cage kit made from 45mm x 2.5mm CDS tube to the E355+N specification, and it arrives unassembled with the tubes notched and bent. It can be bolted in or welded in, and the listing says it suits anyone with welding and fabrication abilities. The options include a hoop cross, gussets, a rear cross and a hoop cross harness bar. The shoulder straps are going to loop round a bar, so it is the harness bar option you want, and it comes together with the hoop cross.
We supply the cage and the harness and do not fit them. A garage or the owner does the fitting, and our guide to installing a bolt-in roll cage covers the order of the job. For what a harness bar is on other cages, our E36 Compact harness bar guide has an example.
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Three drawings of the strap path
These are drawn to show the idea and are not to scale. The angles and the loop method are the ones in our harness guide, which takes them from Motorsport UK’s installation guidance and FIA Appendix J Article 253.
Drawing 1: the strap from the shoulder to the bar
Without a HANS or other head and neck restraint, the shoulder strap may drop no more than 45 degrees below horizontal. With one, the figure is no more than 20 degrees, and the strap must never angle upwards. A bar that sits above the shoulder is the arrangement to design out, because the strap would then rise from your shoulder to reach it. Measure with the driver sat in the car and the device on, not with an empty seat and a tape.
Drawing 2: the straps seen from above
Seen from above, the angle between the two shoulder straps must sit within 10 to 25 degrees, and 20 to 25 degrees is recommended. Keep the anchorages symmetrical about the centreline of the seat.
Drawing 3: looping the harness bar
For the wrap-around method, Motorsport UK give the specification as three passes through the 3 bar slide, with at least 100mm of strap protruding and the slide as close as possible to the bar. When the strap loops a cross member the pivot for measuring the angle is the centre of the tube. If you bolt the straps to the bar instead, an insert must be welded into the bar for each mounting point, and the tube cannot simply be drilled.
A range of 4 point harnesses for the cage bar
A shoulder strap can reach the bar in two ways. It can loop round the tube, which is the wrap-around method in drawing 3. Or it can bolt or clip to an insert welded into the bar, as our harness guide describes. Wrap-around is the cleanest, so Garreth starts there. The other belts work with an insert fitted to the bar, and we confirm the fixing before you order. The table shows how each listing describes its fixing.
| Harness | Webbing and buckle | Fixing in the listing | Approval |
|---|---|---|---|
| TRS Clubman 4 Point | 50mm webbing, steel adjusters, push-click buckle | Bolt-in, with a clip-in version | ECE road, not FIA |
| Sparco 4 Point Club Racer | 3 inch shoulder, 2 inch lap, aircraft cam-lock buckle | Not stated in the listing, so we confirm it | FIA 8854-1998 |
| TRS Magnum 4 Point FIA | 75mm shoulder and lap, steel adjusters, rotary buckle | Clip-in or wrap-around | FIA 8854-1998 |
| Schroth Profi II ASM | 3 inch shoulder, 2 inch lap, alloy adjusters, rotary release buckle | Clip-in, for harness bar and cage use | FIA 8854-1998 |
| Takata Race 4 Snap-On | 3 inch shoulder, 2 inch lap, cam-lock buckle | Shoulder brackets removable for wrap-around on a harness bar or cage | FIA 8854-1998 |
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The TRS Magnum also comes as the Superlite and the Ultralite, and the Willans Club 4×4 Saloon lists clip-in or wrap-around too. The Schroth Profi II-FE has shoulder clip fittings that come off for direct roll bar attachment. For two seats, we list the TRS Magnum 4 Point as a pair. FIA 8854-1998 is the older four point standard, so check your class regulations if you plan to compete, and our guide to FIA harness belts and road belts explains the difference.
Fitting it
Fit the cage first, and sit in the seat before it is fixed for good. Check where the harness bar falls against your shoulders, because the strap has to run down to it and not up. Then fit the straps with the driver strapped in, with the device on if you wear one.
A few points from our harness guide apply to the R58. Mounting bolts are a minimum of 7/16in UNF or M12 grade 8.8. Where the harness is FIA homologated, the manufacturer’s own mounting specification can govern, so read what came in the box. Do not shorten or alter the straps to make them fit, because that invalidates the homologation. Keep the 3 bar slide clear of the seat and out of the shoulder slots. Afterwards, check the webbing and the brackets regularly.
If you are partway through, take a picture from the side and one from above and send it over, and Cameron will say where the straps want to land.
Common questions
What do I mount the shoulder straps to in a Mini Coupé R58?
To a harness bar on a roll cage. A half cage gives you the bar the R58 lacks behind the seats.
Can I anchor the harness to the seat or its frame?
No. The FIA prohibit anchoring the harness to the seats or their supports, and that includes the runners and the subframe. The straps anchor to the car.
Which of your 4 point harnesses have wrap-around shoulder straps?
The TRS Magnum 4 Point, Superlite and Ultralite, the Willans Club 4×4 Saloon CB432 and CB433, and the Takata Race 4 Snap-On, whose shoulder brackets are removable for wrap-around mounting.
Do you fit the cage or the harness?
No. We supply the parts, and a garage or the owner fits them. The cage kit is a DIY kit that arrives unassembled and suits someone with welding and fabrication skills.
Does the R58 cage kit include a harness bar?
The kit lists a hoop cross harness bar as an option, and the harness bar comes with the hoop cross. Choose it when you order, because the straps loop round that bar.
How many times does the strap go through the slide?
Three, with at least 100mm of strap protruding, and the 3 bar slide as close as possible to the bar.
What angle should the shoulder straps be?
No more than 45 degrees below horizontal without a HANS, and no more than 20 degrees with one, never angled upwards. Measure from the top of your shoulder, or from the top of the device, with you sat in the car.
Can I bolt the straps to the bar instead of looping them?
Yes, if an insert is welded into the bar for each mounting point. The tube cannot simply be drilled and a bolt passed through it.
What we would do
Garreth
Garreth's top tip
Fit the half cage first and choose the harness bar option, then pick a 4 point harness from the range above. The TRS Magnum and the Takata loop straight round the bar, and the rest need an insert in it, so tell us which belt you like and we will say how it fixes.
Remember that we supply and do not fit, so line up a garage or your own welding before the kit arrives.
Cameron
Cameron's fitting view
Sit in the seat before the cage is fixed for good and see where the bar falls against your shoulders. I measure the strap angle from the centre of the tube with you strapped in, and keep both anchorages mirrored about the seat.
Send me a photo from the side and one from above and I will say whether the strap path works.
Planning a harness for your R58?
Tell us the car, the seats and whether you wear a head and neck restraint. Cally, our digital receptionist, takes your details, and Cameron comes back with the cage option and the harness to match.
