How To Tilt A Reclining Seat By Raising Only The Rear Mounting Points
A customer with a 2017 BMW M240i asked how to change the rake of a Recaro Sportster CS. The seat fits on its base and sliders, but it sits too low and leans back too far, so he wanted the rear raised by 30 to 40 mm with the front left alone. No frame on the market does that, and the spacers we sell lift the whole seat. The route is your own spacers under the rear mounting points with longer bolts, and because the slider then sits tilted, flat spacers do not sit square.
- The 290 mm fixing span and the rear lift are drawn to scale
- The angle worked out for 10, 20, 30 and 40 mm lifts
Your own spacers under the rear mounting points, with longer bolts
No manufacturer's frame or component sets a different height at the front and the back, and we don't sell a part that lifts only the rear. To change the rake you make or source 10, 20, 30 or 40 mm spacers for the rear fixings and use longer bolts.
- Spacers go under the rear mounting points only, the same height under each
- A flat spacer under a tilted slider leaves the faces out of parallel, by the same angle as the tilt
- A 30 to 40 mm lift over a 290 mm span is about 6 to 8 degrees, so wedge shaped spacers sit better than flat ones
- Prop the rear on blocks and sit in the seat before you make anything
What the customer asked
The seat is a Recaro Sportster CS, the aftermarket base mount recliner, on an SWM base with Sparco sliders, in a 2017 BMW M240i (F22). It fits. Two things bother him. It sits too low, and the cushion has a heavy rake, so it leans back more than he likes. He asked for the rear to come up 30 to 40 mm with the front unchanged, and wanted ideas for bases, heights and spacers to do it.
Garreth went through the makers one by one: Recaro, Planted, SWM, OMP, Sparco, Corbeau and the rest. Every direct fit frame is a fixed piece, with the front and rear mounting heights set by the frame, and none of them changes the angle.
The spacers we sell run from front to back, so they lift the whole seat and leave the rake alone. They suit a seat that sits too low, and our seat spacer guide lists them. To change the rake you need spacers under the rear mounting points only, made or sourced yourself, with longer bolts to suit, adjusted until the angle feels right.
If you are fitting the same seat to the same car, our F22 Sportster fitting guide covers the frames and runners, and the BMW M240i bucket seat guide lists the seats for the car.
Three drawings of what he is after
We have drawn these side on, with the front of the car on the right. The 290 mm between the fixings and the rear lift are to scale. The heights of the frame and the slider are schematic, because they change from seat to seat and car to car.
Drawing 1: the stack
Drawing 2: the standard front and rear heights
Drawing 3: the rear raised on spacers
Work out the angle before you make anything
The seat pivots about the front fixing, so the angle comes from two numbers: the lift at the rear and the distance between the front and rear fixings you are spacing. Divide the lift by that distance and the answer is the tangent of the angle. Over the 290 mm Recaro pattern, a 30 mm lift gives 5.9 degrees, 35 mm gives 6.9 and 40 mm gives 7.9. Measure the span on your own setup, because a different slider or frame will have a different one.
A point further back than the rear fixing rises by more than the spacer does. The rise at any point is its distance behind the front fixing multiplied by lift divided by span. A point 350 mm behind the front fixing rises about 42 mm when the rear fixings go up 35 mm, which is where a seat that sat too low gains its height.
| Rear spacer | Seat tilt, and how far the faces are out of parallel | Rise of a point 350 mm behind the front fixing |
|---|---|---|
| 10 mm | 2.0 degrees | 12 mm |
| 20 mm | 3.9 degrees | 24 mm |
| 30 mm | 5.9 degrees | 36 mm |
| 40 mm | 7.9 degrees | 48 mm |
Your own spacers, longer bolts, and the catch
Put the same height under both rear fixings so the seat tilts straight forward without twisting to one side. Spacers of 10, 20, 30 or 40 mm are easy to find, and you can build a height in between by adding a thin one to a thick one, although one spacer of the right height beats a stack because every layer adds bending load on the bolts. The bolts stay the same size, thread and strength as the originals, longer by the thickness of the spacer, so the thread goes in as far as it did before.
The angle is the catch. The frame stays flat on the floor, but the slider above it now leans forward, so a flat spacer between the two touches only along one edge. At 35 mm that is 6.9 degrees out of parallel. The bolt then pulls the slider foot down onto a sloping face, and the thread is no longer square to the frame, which can bend the bolt or leave the foot rocking on the spacer. That is why this is a workshop job.
Wedge shaped spacers, cut to the angle you settle on, sit flat on both faces and let the bolt pull straight. A fabricator or machine shop can make a pair from your measurements. Cameron will work out the angle and the bolt length with you, and we are happy to look at what you plan to make before you spend anything.
Try the angle with blocks first
Testing costs nothing. Put blocks of wood of the height you want under both rear fixings, or under the rear of the slider, and sit in the seat. You will know within a minute whether 30 mm is enough or whether 40 mm feels better.
While you are sitting there, check four things: where your hips and view have moved to, the gap between your knees and the steering wheel, the clearance to the roof, and the reach to the pedals with the slider run fully forward. If the seat has a recline adjuster, set the backrest again as well, because the tilt has leant it forward by the same angle as the cushion.
Any change in seat height or angle also moves your shoulder line, so check the harness anchor points afterwards. Our harness fitting guide shows the angles. When the blocks feel right, measure the lift and the angle and have the spacers made to match.
Common questions
Is there a frame or bracket that sets a different front and rear height?
No. Garreth has been through every maker, and every direct fit frame has fixed mounting heights at the front and the rear. The angle changes only when you lift one end of the setup you have.
Can I use your seat spacers to raise just the rear?
No. Ours run from front to back, so they lift the whole seat by the same amount and the rake stays as it was. They suit a seat that sits too low, and the seat spacer guide lists them.
How much will a 35 mm rear lift tilt the seat?
About 6.9 degrees over a 290 mm span. A 30 mm lift gives 5.9 degrees and 40 mm gives 7.9. Measure the distance between your own front and rear fixings, because the angle depends on it.
Why do the spacers need to be wedge shaped?
The slider tilts once the rear is lifted, so a flat spacer meets it at an angle and touches along one edge. A wedge cut to the same angle sits flat on both faces, and the bolt pulls straight down through it.
Will the backrest angle change as well?
Yes, by the same amount, because the seat tilts as one piece. A recliner can be set back again with its adjuster once the new angle is in.
Do I need longer bolts?
Yes. Use the same size, thread and strength as the originals, longer by the thickness of the spacer, so the thread engages as far as before. Tell us the bolt size and we will say what length to order.
What happens if I put the spacer under the front instead?
It does the opposite. The front rises, the seat tilts back and the cushion leans back further.
Will the slider still work normally?
It tilts with the seat, so the seat rises and falls slightly as it runs. Check the full travel and that it locks at each position before you rely on it.
What we would do
Garreth
Garreth's top tip
Don't go looking for a frame that tilts the seat, because there isn't one, and we don't sell anything that lifts only the rear. Keep the base and sliders you have, and use your own 10, 20, 30 or 40 mm spacers with longer bolts.
Settle the height with blocks of wood first, then have the spacers made to suit.
Cameron
Cameron's fitting view
Measure the span between the fixings first, then work the angle from the lift. The faces will be out of parallel by that angle, so I'd have wedge shaped spacers made, keep both rear spacers the same, and check the slider runs freely before the seat goes back in for good.
Send me the seat, the base and the slider and I'll work out the angle and the bolt length with you.
Want the rake changed on your seat?
Tell us the seat, the frame or base, the sliders and the lift you want. Cally, our digital receptionist, takes your details, and Cameron comes back with the angle and the bolt length.
