Fitting a Race Seat with Schroth iNDi Seat

“I think I’ve cracked a rib!”

As I came off sideways into the gravel at Coppice at Donington Park I knew I was going to experience a big stop.

I hadn’t put enough temperature in my rear tyres (that lesson is now learned!) and, as I stamped on the brakes, the whole chassis snapped left faster than I could catch it. I skimmed sideways across the gravel at something in the ballpark of 100 mph.

As the car’s skirt dug into the gravel, the car stopped with enough force to wind me. It hurt.

Though the car and I were seemingly undamaged, the next morning I had chest pains that lasted for two months.

The culprit, a cracked rib caused by a bucket seat with no lining.

This should be every driver’s conclusion from my experience:

Always Get a Proper Race Seat Fitted

I’d been running all year in my Radical SR1 with a proper seat installed, but now I’d graduated to the Radical SR3 I wasn’t sure that I needed an insert as urgently. I was, after all in a single seater style “bucket” seat with much more support around the sides.



The bucket seat in this Radical SR3 rsx without seat insert

Can you see how square it is at the back? Well, my back isn’t square, so it’s not a perfect fit!

Any big lateral shock and my round rib cage is going to be forced into a square hole. If I’m not connected to the race seat perfectly, I’m not able to feel the car as well, either,

This, in my inexperience is a mistake and now I’m nursing an injury as proof.

Seat Fitting: Radical SR3 Shell with Schroth iNDi Seat Kit

Today, I’m going to get a race seat professionally fitted with Andrew Bentley, one of our recommended coaches and official Schroth iNDi Seat consultant.

Here’s Andrew:

Schroth Racing is everywhere in Motorsport; especially in safety gear. If there’s an opportunity to improve the safety in my cockpit, I’m going to take it.

How to fit a Schroth iNDi Race Seat Insert

Here’s the seat fitting process we’re going to follow today. I’d say from the outset that while you could use the kit yourself, it’s much more sensible to have it fitted with someone with lots of experience!

To take us through the step by step, I’m going to hand over to Andrew who’ll talk us through his approach to making a perfect seat insert.

Why do I need an insert?

Andrew explains.

“I’m often surprised when experienced drivers ask me this question. To me, it makes perfect sense to be completely connected to the car through the seat. With a properly fitted seat, you’ll feel much more of what the car is doing, you’ll feel more comfortable in the car so more confident and you’ll be much safer if you have a bump as the loads are spread out. I’ve even had a number of drivers come back to me to tell me they’ve found time by being sat correctly and much more comfortably. This system allows you to take more time to get the driver in the correct position and work through various options to find the best solution.”



A Recent Seat Fit with Team Parker Racing.

The Kit

The kit is fairly simple in terms of the contents:

A strong, stretchy bag filled with little white beads. A bottle of resin and a measuring jug along with a hose which fits onto the valve on the bag. Like all things that look simple, the kit is in fact very clever.

The beads are a specific size and material for very good reasons, the resin is unique in the industry and has many attributes which make it easy and safe to work with.

The only additional kit you’ll need is a vacuum pump which is available separately, or you can use an electric pump (an airbed pump is perfect).

Preparing for a Seat Fit

Anyone who’s worked on race cars will know that preparation is hugely important. This is obviously no different. I measure the seat to make sure the bag is the correct size and it is suitable for the application.

There are many variables with seat fitting, but once you know what they all are, you can get a pretty good idea of where the driver will need to be, what you’ll need to do to make that happen and also what problems you might run into.

You’ll also need to prepare the area, taping sharp edges, belt holes or, in the case of a tube frame chassis, potentially boxing off areas so the bag doesn’t ingress into hollows which mean it will be hard to get the seat out.

The driver should be in his full kit, boots and all. This means you’ll be building a seat exactly as they will be driving the car.

Taking a few measurements allows me to transfer that information onto the bag to give me a guide to the seat shape.

The Two Stages to a Seat Fitting: Dry Fit and Wet Fit

The seat fit is a two stage process. We do a dry fit, with no resin. Once you’ve got the beads where you want them and the driver is comfortable, the driver gets out, you remove the bag from the shell, add the resin, mix and the re-run what you’ve just done to get the seat how the driver wanted it.

One of the hardest parts is turning something that is two dimensional (the flat bag of beads) into something three dimensional (the bag of beads in the seat shell).

You can take a bit of time here to work out where you will need the various thicknesses of beads, for example, positioning some beads ready for lumbar support or around the legs.

I make markings on the bag of the outer measurements of the seat shell, the width and length, allowing for consistency of placing the bag in the shell. I get the driver to sit in the car with no bag in.

This means I can see where there are gaps around their body, or if they need additional height. With no resin in, the dry fit allows you to spend as much time as is needed getting the positioning right.

Fitting the Bag

Make sure the bag is properly into the shell with no gaps.

With no resin in and the beads roughly where I think the driver will need them, everything is ready for them to sit in and give it a first try with the bag.

Dry Fit

Time to get your driver into the seat.

The bag material is strong enough to stand on, but the driver shouldn’t twist their foot on it, be gentle when getting in so as not to put a hole in the bag or you’ll have to tape it up so it can still hold a vacuum. Make sure the driver doesn’t drag the bag down when getting into the seat.

Let the driver take some time to get where they feel comfortable. Also, make sure they are central as possible.

Positioning

You can’t take too much time on this part, this is when the driver can understand all the options open to them for the positioning, changing a number of things until you strike the best balance. One of the main things I focus on here is getting the driver to the correct height.

When doing this, you must consider safety, driver comfort and to a lesser degree, centre of gravity. The most important thing is to make sure you’re bellow the roll line of the car.

Each car is different and some international series have different requirements, so I won’t give any figures here, but, you should spend as much time as is needed to get the height of this correct.

When the safety element is covered, it’s then down to driver preference as to where they sit.

There’s no real right or wrong. Some drivers might want to be higher to see the corners of the car, others might want to be lower, out of the turbulence in an open cockpit car or just hunkered down into the seat.

A lot of engineers want drivers to sit as low as possible, which is of course based on well established principles of physics. That’s all good and well, but if a driver can’t see an apex curb, the gain in lowering the centre of gravity by 10mm will be lost in not being able to see where they’re going.

I would say you should always do the fit with the wheel in place so the arms are in the correct position. Also, try to build the insert as far back into the seat shell as possible. Don’t use it to push the driver forward to reach the wheel and pedals if those can all be moved back to meet the driver. Only exception here is if the insert is for a multi driver car where driver changes are required in a seat which does not move.

Mixing It Up

Once you have got the driver exactly where they want to be and all the heights are good, it’s time to mix the resin with the beads.

The resin is a two part mix and with just the first part in the bag, you can spend as much time as you like getting all the beads covered. Once you’re happy you’ve got good coverage, add the second element to the mix and start your stopwatch because you now have 30 minutes before the seat mix goes off and is hard.

All the preparation at the start will help now you’re working against the clock.

Put the beads back where they were at the end of the dry fit.

Get the driver in and check heights again. This is the time to move beads around if required. There will always be some adjustment.

Curing

All the way through the curing stage, you’ll need to keep pulling a vacuum to make sure the beads stay where you want them.

After about 25 minutes of the driver sitting still, start to check the resistance of the beads in the bag. If they feel firm and push back to their original form it’s done. If they are still squishy and you can leave a finger imprint, leave it another 5 minutes.

Don’t worry about all the excess, under there somewhere is a perfect mould of your drivers backside.

I use a hot knife to trim away the unwanted material.

A hacksaw blade or long, sharp blade will work too. Just be careful of fingers, cables and wires. I like to take some time to make the insert fit the shell neatly.

A Finished Seat Insert Ready to Be Covered!

It is now ready to be tested on track and if all is good, the insert can be covered in race seat fabric and even embroidered with drivers name and sponsors.

Safer is Faster

Thanks to Andrew for helping to put this article together. In a decent seat, you’re safer but you’re also better connected to the chassis of the car. That means you can feel what the car’s doing more effectively, which means you’re faster.

About the author

Richard Baxter is an amateur driver having run in Radicals, Funcup cars, Mazda MX5’s and Classic Formula Ford

Read his personal blog, Purplemonkeydishwasher here, Follow him on Twitter here or follow his sim racing action at simracingcockpit.com.